Calcinacion

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* *
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ISSN 1018-5593
Commission of the European Communities
energy
Calcination of limestone in a
circulating fluidized bed with coal
residues as fuel

Commission of the European Communities
energy
Calcination of limestone in a
circulating fluidized bed with coal
residues as fuel
(This project was originally supported under the Demonstration programme.
This programme ended in 1989 but all existing projects continue to be promoted
under the new Thermie initiative which commenced in 1990)
Kaldin BV
SaeffelderstraaHO
6104 RA Koningsbosch
The Netherlands
Contract No CS 008/89 NL
Final report
Directorate-General
* Energy
1993
PARI EUROF. BlWWk
N Q EUR 14828 EI
it IM . ///i?/?yr f I f M

Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General XIII
Telecommunications, Information Market and Exploitation of Research
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of the Commission is responsible for the use which might be made of
the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1993
ISBN 92-826-6304-3
© ECSC-EEC-EAEC, Brussels • Luxembourg, 1993
Printed in Belgium

CONTENTS
CONTENTS Ill
SUMMARY V-IX
LIST OF TABLES AND FIGURES XI
PROJECT DETAILS 1
1. INTRODUCTION 3
2. DESCRIPTION OF THE PLANT 5
2.1 General 5
2.2 Conditions for the design 5
2.2.1 General 5
2.2.2 Calcining humid limestone with fine-
grained coal as a fuel 6
2.2.3 Calcining humid limestone with coal
residues as fuel 6
2.2.4 Process-conditions of the drying unit. . 6
2.2.5 Emissions 7
2.2.6 Mass- and energy balance 7
2.3 Description of the design 8
2.3.1 General 8
2.3.2 Storage and dosage of raw materials and
fuel 9
2.3.3 The circulating fluidized bed (CFB) . . . 10
2.3.4 The pre-heating system. 12
2.3.5 The fluidized bed cooler. , . 12
2.3.6 The sifter-milling section 12
2.3.7 The product storage 13
2.3.8 The flue gas treatment unit 13
2.3.9 The measuring and controlling system . . 14
2.3.10 The drying unit 14
3. CALCINING LIMESTONE WITH COAL AS FUEL 16
3.1 Global description of the progress 16
3.2 Process-parameters 16
3.3 Disturbances and modifications 17
3.4 The warranty test 17
3.5 Emissions 19
3.6 Raw materials 19
3.6.1 Limestone 19
3.6.2 Fine-grained coal 20
3.7 Product-quality 20
3.8 Application of the product in sand-lime bricks . 22
3.8.1 General 22
3.8.2 Description of the sand-lime brick
production process of factory De Hazelaar 23
3.8.3 Composition of the mixture 23
3.8.4 Properties of sand-lime mortar and
-bricks 23
3.9 Mass- and energy-balance 25

4. CALCINING LIMESTONE WITH COAL RESIDUES 26
4.1 Introduction 26
4.2 Operation time 27
4.3 Global description of the progress 27
4.4 Process parameters 2 9
4.4.1 General 29
4.4.2 The CFB temperature 29
4.4.3 Sifter/milling section 29
4.4.4 The drying unit 3 0
4.5 Process - experiences, disturbances and
modifications 30
4.6 Emissions 31
4.6.1 NOx -emission 31
4.6.2 Noise emission 32
4.7.1 Limestone 33
4.7.2 fine-grained coal 33
4.7.3 Coal residues 33
4.7.4 Other raw materials 34
4.8 Products-quality 34
4.8.1 General 34
4.8.2 Flyash-lime 35
4.8.3 Kaldin lime and Filter lime 3 6
4.9 Application of the product in sand-lime bricks. 38
4.9.1 Introduction 3 8
4.9.2 Use of lime at De Hazelaar 38
4.9.3 Composition of the sand-lime mortar. . . 38
4.9.4 Laboratory tests 39
4.9.5 Experiences in practice 40
4.10 Mass- and energy-balance 41
5. OTHER APPLICATIONS 43
5.1 Introduction 43
5.2 Slaking of the lime 43
5.3 Asphalt filler 43
5.4 Sewage skudge stabilization 43
5.5 Masonery mortars 44
6. ECONOMICAL ASPECTS 45
6.1 General 45
6.3 The product 45
6.4 Outlook 46
7 . PUBLICITY AND COMMERCIALIZATION 48
8. CONCLUSIONS 49
REFERENCES 51
IV

SUMMARY
Introduction
In a cooperation between NOVEM and Kaldin BV, in Koningsbosch
(in the province of Limburg, The Netherlands), a plant has
been erected in which a fine-grained limestone is calcined in
a fluidized bed with coal residues as fuel. It is expected
that in this unit 14 tons of limestone can be calcined
together with 12.5 tons of coal residues.
The starting up of the plant and the introduction of the
product on the market have been supervised in a measuring and
monitoring program (no. 2534). All the activities which
Kaldin has developed within this program are described in the
following report.
Description of the plant
The calcination unit as designed by Lurgi is composed of the
following parts:
1. Storage of raw materials and fuel, such as limestone,
coal, coal residues and oil.
2. The circulating fluidized bed (CFB) where the transition
of limestone into lime and carbondioxyde takes place.
3. Parts where drying and pre-heating of the limestone take
place with the use of hot flue-gasses leaving the CFB. Two
cyclones take care of the feed-back of the material to the
CFB.
4. The circulating fluidized bed cooler, in which the product
leaving the CFB is cooled in a direct (air) and indirect
(water) way.
5. The sifter and milling section, in which the product is
classified and milled to the desired fineness.
6. Product storage.
7. Flue gas treatment, where the flue gasses are successively
cooled, undusted and emitted. The non-contaminated gasses
can be used as drying-air in the drying-unit.
8. The measuring and controlling system with which the
process can be controlled and directed.
Burning lime with fine-grained coal
Progress
In April 1989 the plant has been started up followed by a
period of about 9 months in which limestone has been calcined
with only fine-grained coal as fuel. This phase is considered
as phase 2 of the project. Especially during the first few
months after starting up the plant disturbances occurred

mainly as a result of the generated amount of dust and the
"sticky" character of this material. Some components of the
unit blocked up regularly. After modifications have been made
to several of these components, this kind of disturbances was
partly reduced.
The use of only coal as a fuel is disadvantagous, because of
the occurence of caking in several components of the plant,
thus reducing the total yearly production hours.
In a warranty test it has been shown that the unit can operate
without any disturbances while producing a product which can
be used as a raw material for the production of sand-lime
bricks. During this test, the NOx-emission has been measured by
Kaldin at 940 mg/Nm3
, which is above the limit mentioned in the
nuisance act. After modifications have been made to the CFB,
after the end of the measuring and monitoring program, the NO,,-
emission has been reduced.
The product
The product which is produced in phase 2 is a mixture of
mainly free CaO (about 62 % ) , Si02 and CaC03.
Application in sand-lime bricks
The main part of the product has been used as a raw material
for the production of sand-lime bricks in the sand-lime brick
factory De Hazelaar which is situated beside the Kaldin plant.
In practice, an increase of product-loss has been found due to
the relatively large variation in free CaO content of the
Kaldin product during a large part of the program.
Mass- and energy-balance
During the warranty test an average energy efficiency for the
calcination of CaC03 of about 48 % (related to the
theoretically needed calcination energy) has been realized.
During the entire phase 2 this was about 44 %.
The burning of lime with coal residues
Progress
On 30 January 1990, the first coal residues have been
processed in the plant. This marked the beginning of phase 3
of the measuring and monitoring program. The original set-up
of the program included a gradual increase of the coal
residues input up to 12.5 tons per hour. In practice the coal
residues input has been increased from about 2 tons in
February to about 6 tons during the months July through
September. Due to problems with the quality of the sand-lime
bricks, the coal residues input has again been decreased to
about 2 to 4 tons per hour until the end of phase 3. After the
end of phase 3 the measuring and monitoring program has been
VI

concluded, which implies that no experience has been gained
concerning the maximum anticipated input of coal residues.
Only during short periods more than 6 tons of coal residues
have been used (8 tons of coal residues and 16 tons of
limestone per hour during a test). The average coal residues
input has been 2.5 tons per hour at a limestone input of about
15 tons per hour. Besides coal residues also 1.2 tons of
several types of coal per production hour have been used as
fuel .
Process-technological experiences and disturbances
As a result of the use of coal residues as fuel some
disturbances which occurred during phase 2 of the program did
occur less during phase 3. These disturbances are mainly:
- Caking in various components of the plant. The use of coal
residues has an abrasive effect on the cakes.
- The incomplete fluidization of limestone due to the
relatively coarse grains in the limestone. The input of coal
residues reduces the average grain size of the bed-material
which makes it easier to fluidize the bed.
Beside the reduction of several disturbances due to the use of
coal residues, some other disturbances appeared as a result of
the use of coal residues. These are the following:
- as a result of afterburning, mainly of FBC coal residues, in
the product-cooler sometimes sintering of the product does
occur and in the flue gas pipes the temperature increased.
Emissions
During the period when coal residues were used, the N0X-
emission was higher than during the time when only coal was
used. It exceeded the limit which is mentioned in the nuisance
act (500 mg/Nm3
). The NOx-emission varied between about 900 and
2100 mg/Nm3
. No clear relation is visible between the NOx-
emission and the type and quantity of coal residues which have
been used. Modifications to the CFB have been made after the
conclusion of the measuring and monitoring program and these
have lead to a decrease of the NOx-emission. Tests have shown
that when additional measures are taken, the N0X emission can
be kept below 500 mg/Nm3
, when using more than 2 tons of coal
residues per hour.
However, a reduction of the NOx-emission below the limit
mentioned in the nuisance act often implies a decrease of
product quality concerning the outburn of coal particles and
the calcination ratio.
The emission of noise of Kaldin lies above the maximum level
which is mentioned in the private nuisance act. Modifications
have and will be made to the main sources of noise, which lead
to a decrease of the noise emission. However, at the end of
the program, the maximum level was still exeeded.
VII

Coal residues
The aim of the project has always been the use of Dutch coal
residues as a raw material and fuel in the calcination of
limestone. The Dutch types of coal residues, which have been
supplied by Vliegasunie, AKZO and by DSM, have a relatively
low heat of combustion compared to the used types of German
coal residues which arise at fluidized bed combustion (in
average 2.2 vs. 7.7 MJ/kg). Also the negative prices of the
Dutch coal residues are lower than the negative prices of
German coal residues. In view of the economic viability of the
plant, it has therefor been decided to use German coal
residues beside the Dutch coal residues.
The product
During the first part of phase 3 only one product, the so-
called flyash-lime, has been produced. Depending on the coal
residues input, the free CaO content of this product varies
from 35 to 60 %.
Since the end of September 1990 the dust from the cloth filter
and the heat-exchanger are lead to a product-silo, this dust
is considered as a separate product, the so-called "Filter
lime". This product makes up about 25 % of the total product.
The other 75 % of the product is since then called "Kaldin
lime". Beside a relatively low free CaO content (about 34 % ) ,
the Filter lime consists mainly of CaC03 (about 25 %) and
silicates (about 40 % ) . Kaldin lime mainly consists of free
CaO (about 64 %) and of silicates (about 33 % ) . The variations
in the Kaldin lime are smaller than the variations in the
previously produced flyash-lime and the Filter lime.
Application in sand-lime bricks
During the measuring and monitoring program the application of
fly-ash lime, Filter lime or Kaldin lime has almost completely
been realized as a binding agent for the production of sand-
lime bricks. Almost the entire product has been sold to sand-
lime brick factory De Hazelaar.
The assumed advantage of the use of coal residues in sand-lime
brick production concerning a higher green strength of the
product, could not be demonstrated in practice.
Based on experiences in practice concerning the quality of the
sand-lime bricks and elements, the quantity of free CaO which
is dosed in a sand-lime mortar has not been decreased, which
means that, compared to the previously used type of lime, much
more Kaldin product had to be used in order to reach a similar
quality of the sand-lime bricks and elements.
Mass- and energy-balance
During phase 3 in average 13.0 tons of CaC03 have been
processed per production hour. The total quantity of used
- VIII

fossil energy amounts to 49.7 GJ/hr. This results in an energy
efficiency during phase 3 of 46 %. About 40 % of the energy
leaves the plant with the heated flue gasses.
The average quantity of fossil energy which is needed for the
production of 1 ton of free CaO is 8.3 GJ. During periods when
the Kaldin plant has been operated at optimum conditions, this
use of fossil energy is reduced to about 7.5 GJ per ton free
CaO.
The use of electric energy during an average period in which
the plant is operated without interruptions, without the use
of the drying-unit, is about 1100 kWh per hour (157 kWh per
ton of free CaO, at 7 tons of free CaO per hour).
Other applications
Beside the application in C.S. bricks, other applications for
the product have been studied, but have so far only reached an
experimental stage. The most promising applications are the
following:
- as a filler in asphalt
- in masonry mortars
- in sludge stabilization
Economical aspects
The economic viability of the plant depends largely on 2
factors:
1. The price of the product, which is mainly influenced by
the free CaO content.
2. The price and carbon content of the coal residues.
The use of coal residues with a high carbon content (and a
high negative price) results in a good profitability of the
plant.
The sale of the Kaldin product has mainly been limited to
sand-lime brick factory De Hazelaar. As a result of this
restricted sale, together with the occurrence of disturbances
in the plant, the production level (about 30,000 tons/yr in
stead of the anticipated 90,000 tons/yr), and therefor also
the proceeds, of the Kaldin plant reached a far lower level
than which was anticipated.
IX

LIST OF TABLES AND FIGURES
TABLES
Table 1 -
Table 2 -
Table 3 -
Table 4 -
Table 5 -
Table 6 -
Table 7 -
Table 8 -
Table 9 -
Table 10 -
Table 11 -
Table 12 -
Start-case calculations concerning mass- and energy-
balance for the calcination of limestone with coal
and with coal residues, 8
Average raw material input and product output during
phase 2, compared to the data of the warranty-
test, 17
Specifications of raw material input and product
during the warranty test ( 4 - 7 December 1989), 18
Chemical composition (main components) of the fine-
grained limestone which is processed during
phase 2, 20
Average properties of the product which is produced
during phase 2, compared to the properties of the
product which is produced during the warranty
test, 21
Calculated average mineralogical composition of the
product of phase 2 and the warranty period, 22
Properties of sand-lime mortar and -brick with
different types of lime and 6.5 % water during phase
2 (at laboratory scale), 24
Use of raw materials and production per production
hour during phase 3, 28
Average properties of flyash-lime (February -
September 1990), 35
Average global mineralogical composition (in %) of
Kaldin and Filter lime, 37
Average properties of Kaldin lime and Filter lime
(October 1990 - April 1991), 37
Properties of sand-lime mortars with Dornap lime and
with flyash-lime, based on laboratory tests, 40
FIGURES
Figure 1 - Schematic flow sheet of the calcination unit, 9
Figure 2 - Main properties of the product generated during
phase 2, 21
Figure 3 - Average raw material input and production per hour
per month during phase 3, 28
Figure 4 - Average properties of flyash-lime and a combination
of Kaldin lime and Filter lime per month, 36
XI -

PROJECT DETAILS
CALCINATION OF LIMESTONE IN A CIRCULATING FLUIDIZED BED
WITH COAL RESIDUES AS FUEL
Project number
Contractor
Contactpersons
Co-contractor
CS 008/89 NL
KALDIN B.V.
SaeffeIderstraat 10
6104 RA Koningsbosch
The Nederlands
Mr. M.P.G. Stassen
Mr. R.H.W.W.M. Hermans
(Phone no. 04743 - 2341)
LURGI NEDERLAND B.V.
Backershagen 97
1082 GT AMSTERDAM
Author : Drs. H.M.L. Schuur
Projectbureau voor
Industrie en Milieu B.V.
Koningsbosch, March 1992
1 -

Kaldin calcination plant in Koningsbosch, The Netherlands

1. INTRODUCTION
Since about 1980 the energy policy of the Dutch government has
for an important part been focused at the re-introduction of
coal as a fuel. The activities which have been carried out in
this policy, are placed in the National Clean Coal Program,
N.O.K.). Because of the fact that with the burning of coal
also residues arise, the attention of the N.O.K. has also been
put to a useful re-use of these residues, in order to minimize
their effect on the environment.
In the same period the Holding De Hazelaar was investigating
the technical possibilities to calcine a fine-grained
limestone into lime and to use this lime as a raw material for
the production of sand-lime bricks.
In a cooperation between the Netherlands Agency for Energy and
the Environment (NOVEM) and the Holding De Hazelaar the
possibilities have been studied to calcine the fine-grained
limestone with the energy which can be derived from coal
residues with a high coal content (> 5 % ) . However,
conventional technologies which are used to calcine limestone
such as shaft and rotary kilns are not suitable for the
processing of fine-grained materials.
After the execution of desk-studies and pilot-plant tests it
has been decided to calcine the fine-grained material with a
circulating fluidized bed system which was developed by Lurgi
GmbH in Frankfurt.
Based on the results of these studies and tests, Kaldin b.v.
has been founded. Thereupon, on the site of sand-lime brick
company De Hazelaar in Koningsbosch, a demonstration plant has
been built, which is in operation since april 1989. The
construction of the plant and the introduction of the product
on the market is covered by a measuring and monitoring program
(no. 2534) which is financed by the NOVEM and the European
Community. For the course of this program a monitoring panel
has been installed. This panel was given all the information
concerning the progress and acquired knowledge within the
program and had the possibility to make changes in the program
if necessary. The members of the panel are representatives of
NOVEM, Kaldin, Lurgi and the Vliegasunie.
The aim of the measuring and monitoring program project is to
produce a type of lime in a technical and economic justifiable
way based on:
1. Limestone which comes available as a side-product in
limestone quarries and
2. Coal residues with a relatively high coal content,
with a minimum effect on the environment.
- 3

The product, a fly ash-lime mixture, has to be at least
applicable as a raw material in the sand-lime brick industry.
This re-use of coal residues corresponds with the Dutch policy
concerning energy and environment and will lead to a reduction
of other sources of energy in the production process of
Kaldin. In addition it contributes to a solution for the coal
residue problem.
Data have been collected concerning the technical, economical
and environmental aspects of the process, about the quantity
and quality of the product and about the application of this
product as a raw material in sand-lime brick production. These
data have to be collected in phases 2 and 3 of the following
described phases of the project:
Phase 1: Design and erection of the plant (Until April
1989) .
Phase 2: Starting up the plant, test runs and warranty test
based on limestone and coal (period until July
1989) .
Phase 3: Demonstration of the use of coal residues in
different mixtures up till 6.25 tons per hour
(period until April 1991)
Phase 4: Continuation of the demonstration up till a maximum
of 12.5 tons coal residues per hour (period until
April 1992).
Phase 5: Optimizing the process and the production based on
the information which is gained during the
preceding phases (period until October 1992).
During the course of the project the deadlines for some phases
have been changed. Phase 2 for example covers a longer period
than which has been anticipated and only at the end of January
1990 the first amount of coal residues has been processed.
An intervention in the pursued length of time of the program
took place at the end of April 1991 when the entire program
was brought to an end. Because of not anticipated costs, the
realized project costs at the beginning of 1991 reached a
level which had been planned for the end of the measuring and
monitoring program (October 1992).

2. DESCRIPTION OF THE PLANT
2.1. General.
Calcining limestone is based on the following equation:
CaC03 + energy > CaO + C02
limestone lime carbondioxyde
Depending on the calcination process, this reaction takes
place at temperatures between 800 to 900 °C. The optimum
temperature for the reaction to take place in a circulating
fluidized bed lies between 900 and 1050 °C. The energy which
is needed for this reaction, is provided by coal residues
(with a carbon content higher than 5 %) by fine-grained coal
and by oil. Beside a substantial saving in energy costs, the
use of coal residues as a fuel leads to a product which
contains burned-out coal residues. This treated coal residues
can, in some applications, have a positive effect on the
properties of the endproduct.
Because of the use of fine-grained materials, the conventional
lime production technologies, such as shaft and rotary kilns,
can not be applied. In cooperation with NOVEM, pilot-plant
tests have been carried out by Lurgi which indicated that the
circulating fluidized bed technology was the best way to treat
the fine-grained raw materials. Based on the results of these
tests, Kaldin b.v. was founded and a plant has been developed
and constructed. In the following paragraphs successively the
conditions on which the design has been based and the final
design of the plant will be described.
2.2. Conditions for the design.
2.2.1. General
The unit has been developed to operate with the use of two
different combinations of raw materials:
1. Calcining humid limestone with fine-grained, dry coal as a
fuel.
2. Calcining humid limestone with dry coal residues.
Lurgi has warranted the operation of the unit for the first
combination of raw materials. Although the unit has been
designed for an operation with the use of coal residues, a
warranty for this way of operation has not been given. This is
the reason that for the use of coal residues as a fuel for the
calcination of limestone a measuring and monitoring program
has been started.

2.2.2. Calcining humid limestone with fine-grained coal as
a fuel.
The conditions for the design are based on a limestone with d50
= 500 jum and pre-dried fine-grained coal with less than 8 %
water and which can be transported pneumatically. The
limestone input can be 21 tons per hour.
Based on these parameters Lurgi has given the following
warranties:
product output : > 10.4 tons/hour
degree of calcination : > 97 %
- carbon outburn : > 98 %
product fineness : d97 < 90 /xm
Beside these warranties, Lurgi has guaranteed that the unit
will meet all the governmental requirements which are
applicable for the operation of the plant. This means for
example that the emission of different components and the
production of noise has to meet the limits which are mentioned
in Kaldin's private nuisance act (see section 2.2.4.).
2.2.3. Calcining humid limestone with coal residues as
fuel.
The conditions for this design are also based on a limestone
with dso = 500 jim but with dry coal residues as fuel. The lime-
stone input can be 14 and the coal residues input 12.5 tons
per hour.
Although in the design of the calcination plant the use of
coal residues, has been taken into account, Lurgi has not
given any warranties concerning the product output or the
quality of the product when using coal residues as a fuel.
2.2.4. Process-conditions of the drying unit.
In order to re-use the flue-gasses from the calcination unit a
drying unit has been designed. This unit has initially been
designed for the drying of very fine-grained limestone which
originates from chemical processes and has an average water
content of about 25 % (m/m). Lurgi has warranted the water
content of the endproduct at a maximum of 3 %. Other process-
parameters on which the drying unit has been designed are the
following (when operating the calcination unit with coal
residues as fuel):
input wet limestone : > 25.0 tons per hour
product output : > 19.1 tons per hour.
6 -

2.2.5. Emissions.
Requirements for the environmental aspects of the Kaldin plant
which are described in Kaldin's private nuisance act concern
mainly the compartments air and noise.
Concerning the compartment air, it is expected that the
emissions of N0X and dust will probably be the most critical
emissions. It is expected that requirements for other
components which are mentioned in this nuisance act do not
exceed the requirements. The requirements for all the
different emissions are mentioned below.
Dust
NO,
S02
HF
Pb
Zn
Cd
Hg
As
Sb
<
<
<
<
<
<
<
<
<
<
50 mg/Nm3
500 mg/Nm3
700 mg/Nm3
1 mg/Nm3
1 mg/Nm3
1 mg/Nm3
0,1 mg/Nm3
0,1 mg/Nm3
0,1 mg/Nm3
0,1 mg/Nm3
The noise rate level contour at the limit of the parcel as
required in the nuisance act is 50 dB(a) during day time and
40 dB(a) when the unit is operated during the night.
2.2.6. Mass- and energy balance.
Lurgi has carried out start-case calculations concerning the
operation of the plant with fine-grained coal and with coal
residues as fuel.
These calculations are based on a limestone with a CaC03
content between 85 and 92 % and a water content between 4 and
8 %. The heat of combustion of the coal is set at 26 MJ/kg and
the coal content of the coal residues is 15 %. The output of
free CaO has in both scenario's been set at 7.0 tons per hour.
It is furthermore assumed that the production takes place
continuously, except during weekends and holiday periods. The
possible amount of production hours is therefore: 24 (hours) x
5 (days) x 48 (weeks) = 5780. Assuming that 80 % of these
hours will be realized, the total amount of production hours
per year will be 4608.
7 -

Table 1 - Start-case calculations concerning mass- and energy- balance
for the calcination of limestone with coal and with coal
residues
Scenario 1 2
Coal coal residues
15.75
0
0
12.50
55.0
19.2
88,470
7.0
32,260
36.5
Limestone
Coal
coal residues
Product
Free CaO
Free CaO in
product
t/h
t/h
GJ/h
t/h
GJ/h
t/h
t/j
t/h
t/j
%
42,
32,
15.75
1.694
44.1
0
0
9.2
r390
7.0
r260
76.3
2.3. Description of the design,
2.3.1. General.
The calcination unit as designed by Lurgi is composed of the
following parts:
1. Storage of raw materials and fuel, such as limestone, coal,
coal residues and oil. These parts take care of the
storage, buffering of these materials and of the dosage to
the furnace.
2. The circulating fluidized bed (CFB) where the transition of
limestone into lime and carbondioxyde takes place.
3. Parts where drying and pre-heating of the limestone take
place.
4. The circulating fluidized bed cooler, in which the product
leaving the furnace is cooled in a direct (air) and
indirect (water) way.
5. The sifter and milling section, in which the product is
classified and milled to the desired fineness.
6. Product storage.
7. Flue gas treatment, where the flue gasses are successively
cooled undusted and emitted. The non-contaminated gasses
can be used as drying air in the drying unit.
8. The measuring and controlling system with which the process
can be controlled and directed.
Based on this division of the calcination unit in the
following sections a description of every part will be given.

A schematic flow sheet of the calcination unit is given in
figure 1.
Storage and dosage of raw materials and fuel.
The main raw material which is used in the calcination unit is
limestone, coal residues are used both as a raw material and
as a fuel and fine-grained coal and oil are two types of fuel
that are used. Air is needed as a source for the combustion of
the fuels and as a transport medium.
Limestone
The storage of limestone takes place in open air on the
terrain close to the plant. From this outdoor storage the
limestone is tipped into a bunker by means of a shovel. The
dosage of the limestone is performed by means of a centrex, a
rotating arm which scrapes the bottom of the bunker and which
moves the limestone to a central opening on the lower side of
the bunker. By controlling the amount of revolutions per
minute, the amount of limestone, which falls on a conveyor-
belt can be dosed. From this conveyor-belt the limestone
arrives at the transportation screw of the venturi dryer.
Figure 1 - Schematic flow sheet of the calcination unit

Coal
The storage of fine-grained coal takes place in an explosion
safe silo with a content of 120 m3
, which has a de-aeration
system and a cloth filter. The level to which the silo is
filled can be monitored by a feeling weight. The dosage of the
coal to the CFB is controlled by means of a rotary valve. By
changing the amount of revolutions per minute, more or less
material can be dosed. The amount of coal which is dosed
depends also on the bulk density and on the fossil energy
content of the fine-grained coal.
coal residues 1
The coal residues 1 silo is suited for the storage of dry coal
residues, which can be dosed to the fluidized bed without any
pre-treatment. The silo has a content of 120 m3
, and has a de-
aeration system and a dust filter. The level to which the silo
is filled can, like with the coal silo, be monitored by a
feeling weight. The dosage and transport of the coal residues
to the CFB is performed by means of a rotary valve and a pump.
coal residues 2
The storage and dosing system of the coal residues 2 silo is
identical to that of the coal residues 1 silo. To the coal
residues 2 silo provisions have been made which make it
possible to store materials that have been dried in the drying
unit. This means that not only coal residues can be stored in
this silo, but also for example dried sewage sludge or fine-
grained limestone.
Heavy oil
The storage of heavy oil takes place in a tank with a content
of 50 m3
, which is provided with a level detection.
Air
Air is needed as an oxygen supplier for the combustion of the
different kinds of fossil fuel. Beside this function, air is
needed for the pneumatic transport of several materials. The
two main current which lead to the CFB, the primary and the
secondary air, are pre-heated by the fluidized bed cooler,
before they are injected into the CFB. Both the primary and
the secondary air supply are generated by two blowers with a
pressure of 500 mBar at a flow rate of maximum 9000 Nm3
per
hour.
2.3.3. The circulating fluidized bed (CFB)
The circulating fluidized bed is the heart of the plant. This
is where the actual calcination of limestone takes place at an
optimum residence time and steady and even temperatures,
within a range of 875 to 1050 "c. Both the residence time and
the temperatures can be separately varied, which is an
10

important condition to reach the desired quality of the
product.
The CFB has been designed for the treatment of solid raw
materials with an input capacity of about 25 tons per hour.
When the calcination of limestone is carried out only with the
use of coal, then about 21 tons of limestone and about 2.0
tons of coal can be processed. When only coal residues are
used as a fuel, according to the engineering of the plant,
12.5 tons of coal residues can be used with an input of 14
tons of limestone.
The circulating fluidized bed system is composed of different
components which all contribute to an optimum process. These
are:
- The circulating fluidized bed
The recycling cyclone
The syphon
The circulating fluidized bed
The circulating fluidized bed (the furnace) is in theory a
cylinder which consists of a refractory masonry, surrounded by
an insulating layer with a steel lining on the outside. The
circulation of the bed is obtained by the injection of air.
The primary air is pre-heated in the fluidized bed cooler and
then blown into the fluidized bed at the lower end of the
furnace via multiple injection points. The secondary air is
also pre-heated in the fluidized bed cooler, but is injected
at a higher level of the CFB.
The combustion in the CFB takes place in two phases. As a
result of a oxygen-deficit, the combustion in the lower part
of the CFB is under-stoichiometric. From the input of
secondary air a surplus of oxygen does exist which leads to a
complete combustion of the fuels, combined with an optimum
calcination of the limestone. In the lower part of the CFB a
high concentration of solid material does exist, which
stimulates the combustion of the fuel. The residence time on
the CFB can be controlled using the differential pressure over
the CFB in combination with the amount of input and output of
the materials.
The recycling cyclone and syphon
The recycling cyclone is attached to the CFB and is also
covered with a fire-proof lining. The cyclone separates the
major part of the product from the flue-gasses. After
separation this material arrives in the syphon which is
connected at the lower side of the cyclone. When the syphon is
sufficiently filled with solid material, a part of the
material is recirculated back to the CFB and at the same time
another part is tapped from the syphon into the fluidized bed
cooler.
11

2.3.4. The pre-heating system
In the pre-heating system the hot flue gasses from the CFB are
brought in contact with the cold humid limestone. As a result
of water evaporation and pre-heating of the limestone,
temperatures in this part of the system reach values between
500 and 700 *C. Thereafter the gasses are separated from the
solid material in the first and second cyclone and the solid
material is transported back to the CFB. The pre-heating
system consists of 3 main parts:
a venturi;
the primary cyclone;
the secondary cyclone.
The venturi
The aim of the venturi is to bring the humid limestone in
contact with the hot flue gasses from the CFB. The venturi
consists of a especially constructed narrowing in which the
loss of pressure is limited together with an optimal mixing of
the solid material with the flue gasses. The flue gasses are
thereafter dedusted in the two cyclones which are placed after
the venturi.
Primary and secondary cyclone
The primary and secondary cyclones are two identical cyclones
which are connected in series and are meant to dedust the flue
gasses. The solid material is thereafter transported back to
the CFB. The flue gasses follow their way to the heat-
exchanger and cloth filter where they are further cooled and
dedusted.
2.3.5. The fluidized bed cooler
The fluidized bed cooler has a double purpose; partly it will
cool the calcined product from the CFB and partly the needed
primary and secondary air supplies are pre-heated. In this way
an optimum energy transmission takes place. The product which
arises from the CFB is cooled from a temperature of 900 - 1000
°C down to less than 100 'c. From this cooler the product is
transported to the intermediate bunker of the sifter-milling
section. The cooling is performed with air (direct and
indirect) and with water.
The cooler is based on the principle of fluidized bed cooling
and consists of 6 chambers. The transport of the product from
one chamber to another is performed by air which is injected
into the bottom part of each chamber.
2.3.6. The sifter-milling section
The sifter-milling section can be considered a system in a
system. In this section the product which arises from the
12

fluidized bed cooler is milled to a specific fineness (97 %
smaller than 90 microns). To reach this fineness a closed
milling section has been chosen. This means that the material
is recycled until the desired fineness is obtained. The wind
sifter and ball mill are the two main components of this
section. From an intermediate bunker which provides a constant
product input, the product is lead to the wind sifter via an
elevator and a conveyor screw. The wind sifter separates the
product into a fine-grained and a coarse-grained part. The
fine-grained part is transported from the wind sifter to one
of the productsilo's. The coarse-grained part is dosed to the
ball mill. In the ball mill this coarse-grained material is
milled to the desired fineness. The milled product is
transported back to the wind sifter together with new material
from the intermediate bunker.
2.3.7. The product storage
For the storage of the endproduct two identical silo's have
been constructed. Each silo has a content of 400 m3
. On each
silo a cloth filter has been installed in order to separate
the solid particles from the pneumatic transport air. The
possibility has been created to transport the dust from the
heat exchanger and cloth filter directly to one of the silo's.
The transport to the clients is carried out by silo-wagons.
2.3.8. The flue gas treatment unit
The flue gas treatment unit has a double purpose. On the one
side the flue gasses are dedusted before they can be emitted,
on the other hand on economical basis, the energy which is
present in the flue gasses has to be re-used as much as
possible. The flue gas treatment unit is composed of the
following components:
The heat exchanger
- The cloth filter
- The flue gas fan and chimney.
The heat exchanger
The heat exchanger is composed of two chambers which each have
a vertically positioned bundle of pipes. In this process an
indirect heat transfer to the open air takes place. This
cooling air is heated and can be used as a drying-air in the
drying unit. On the tube-side of the heat-exchanger a cleaning
system is installed in order to remove the cakes of dust from
the inside of the pipes. The dust which is removed from the
inside of these pipes can be transported to the CFB or to one
productsilo via two rotary valves, a conveyor screw and a
pneumatic pump.
13

The cloth filter
In the cloth filter the flue gasses are furthermore separated
from the dust. The amount of dust in the flue gasses will
finally reach a quantity smaller than 50 mg per Nm3
which means
that it meets the requirements of Kaldin's private nuisance
act. The cloth filter is composed of a cloth with an active
specific surface of about 1000 m2
. The amount of dust which has
to be separated from the flue gasses is estimated at about 5 %
(m/m) of the raw material input into the CFB. Just like the
dust which is separated from the flue gasses in the heat-
exchanger, this dust can be transported to one of the
productsilo's or to the CFB.
The flue gas fan and chimney
The flue gas fan and the chimney are the last two parts of the
plant which the flue gasses have to pass before they are
emitted. The flue gas fan is provided with a regulator with
which the amount of flue gasses per time period can be
controlled and which as such can compensate a loss of pressure
in the system which can be caused in the heat exchanger, the
conduit-pipes, the cloth filter or the chimney.
The chimney has a height of 41 m and provides as such in an
effective dispersion of the flue gasses.
2.3.9. The measuring and controlling system
Beside the already mentioned measuring and controlling
equipment for the dosage of different materials, measuring and
controlling points have been placed on several locations in
the plant. Pressure and temperature sensors have been placed
on critical locations and several flow rate sensors for
nitrogen and oxygen have been placed in the flue gas channels
of the plant. In the control centre all the signals can be
monitored, controlled and saved.
2.3.10 The drying unit
The drying unit has been designed to re-use the energy which
is present in the flue gasses in an economically useful way.
As described in section 2.3.8., via an indirect way the open
air is heated to a temperature of maximum 250 *C. This air is
free of contaminations and can therefore be used for the
direct drying of several types of materials, without the
possibility that they might become contaminated. Initially the
unit was designed for the drying of a fine-grained limestone
which arises from a chemical process with a water content of
about 25 % (m/m).
The drying unit bears a resemblance to the venturi pre-heating
system of the calcination unit. The drying unit is composed
of:
- 14

a bunker
a transport system, divided in a conveyor belt, an elevator
and an input unit
a venturi dryer
a cyclone
a cloth filter and
- a productsilo
The storage of the materials which have to be dried takes
place in open air on the terrain close to the plant. From this
outdoor storage the material is dumped into a bunker by means
of a shovel.
The dosage of the material to the drying unit is performed by
means of a centrex, which is comparable to the limestone
dosage to the CFB. From the centrex this material is
transported to the venturi-dryer via conveyor belts and an
elevator. As a result of the intensive contact between the
warm gasses and the humid material, the water will evaporate
rapidly. In a cyclone and a cloth filter which are placed
behind this venturi dryer, the gasses are separated from the
solid material (mainly dust). The gasses are thereafter
emitted via the central chimney. Depending on its application,
the dried material can be stored in a productsilo with a
content of 120 m3
or in the coal residues 2 silo of the
calcination unit.
- 15 -

3. CALCINING LIMESTONE WITH COAL AS FUEL
3.1. Global description of the progress
After the calcination unit had been built, according to the
planning, in april 1989 it was started up with the use of coal
as a fuel to calcine the limestone. This took place during a
period of about 9 months. This period corresponds with phase
no. 2 of the measuring and monitoring program.
In the original project-planning the concluding date for phase
no. 2 was 1 July 1989, but unlike this planned concluding
date, only on 30 January 1990 the first coal residues has been
processed and phase no. 3 was started. The reason for this
delay can be found in a number of unforeseen disturbances
which prevented a good progress of the operation. During the
first 4 months after starting up the unit relatively short
periods of production were alternated with long periods in
which actions had to be taken to deal with the disturbances.
In total during this phase of the project about 1600
production hours were realized. This involves an effectiveness
of the available operation hours of 46 %.
In September 1989 the first long run with fine-grained coal as
fuel took place, and during the first week of December, in
stead of in July, Lurgi has carried out a warranty test for
the plant. On 30 January 1990 the first coal residues has been
used and phase 3 of the measuring and monitoring program was
started.
3.2. Process-parameters
The first detailed process data were registered during the
warranty test which was carried out by Lurgi during a period
of 72 hours, between 4 and 7 December 1989 (see § 3.5). These
data can be considered as representative for periods of phase
2 in which a relative high production level has been obtained.
During the entire phase 2, the plant has been mainly operated
at a part of the maximum attainable production capacity. This
explains the difference between the average production figures
of the entire phase 2 and of the period during which the
warranty test took place (table 2).
The raw material input during the warranty test can be
considered as an ideal situation, which can be attained when
the plant is operated at (almost) its maximum capacity with no
16 -

disturbances in the process and only small variations in the
composition of raw materials.
Table 2 - Average raw material input and product output during phase 2,
compared to the data of the warranty test
Phase 2
total per hr
Warranty-
period
per hr
Limestone (tons)
CaC03 (%)
water (%)
CaC03 (tons)
Coal (tons)
Product (tons)
free CaO (%)
free CaO (tons)
24,000
19,160
2,400
13,200
8,140
14.8
85.7
6.9
11.8
1.4
8.1
61.7
5.0
3.3. Disturbances and modifications
Beside some small disturbances which were relatively easy to
manage, during the first months after starting up the plant,
main disturbances took place. The disturbances resulted often
in adjustments of parts of the plant and adjustments in the
way the plant was processed.
From the time that the plant was started up, problems occurred
as a result of an overdoses of dust and the nature of this
material. This often resulted in obstructions and caking in
several parts of the plant. In order to solve this problem
adjustments have been made to several parts of the plant. This
resulted in a decrease of the problems which occurred due to
the generation of dust and the character of this material.
The presence of coarse grains lead to an accumulation of
coarse material on the bottom of the CFB. As a result thereof,
the CFB had to be tapped off more often. After the
installation of a sieve, the problem with accumulations of
coarse material at the bottom of the CFB have been decreased.
3.4. The warranty test
During a period from 4 until 7 December 1989 Lurgi has carried
out a warranty test in order to demonstrate that the plant can
be operated under the given conditions and with the given
- 17

product specifications. The warranted specifications (table 3)
are all given for the calcination of limestone with only coal
as fuel and not with the use of coal residues.
During the warranty period no complications occurred and this
period may therefore be considered as representative for a
period during which the plant is operated almost at the
maximum capacity with coal as a fuel and without any appearing
disturbances.
The specifications of the production process and of the
product are given in tables 2 and 3. From these data can be
concluded that the warranted specifications concerning product
quantity, carbon outburn and the amount of product passing a
sieve of 90 microns have been met.
Table 3 - Specifications of raw material input and product during the
warranty test ( 4 - 7 December 1989)
Warranty Realized
19,
1,
11.
99,
95,
2,
.7
.84
.7
.2
.6
.5
limestone (tons/hr)
coal (tons/hr)
product (tons/hr)
carbon outburn (%)
calcination ratio (%)
> 90 /xm (%)
10.4
> 98.0
97.0
< 3.0
Concerning the calcination ratio it has to be stated that more
than one definition can be applied. In this case the
calcination ratio is defined as 100 x (CaC03 input - CaC03
output)/CaC03 input. When the calcination ratio is considered a
measure for the efficiency of the plant to turn CaC03 into free
(or active) CaO, the following equation can be applied:
Calcination ratio =
free CaO in product
total CaO in product
x 100 (%)
Independant of the way the calcination ratio is defined, the
product which was generated during the warranty test did not
meet the warranted calcination ratio.
Because of the more constant process-conditions during the
warranty test compared to those of the entire phase 2, the
quality of the product which is generated during the warranty
test is more constant than the average quality of the product
which is generated during phase 2. The product generated
during the warranty test has also a higher CaO content (both
free and total).
18

3.5. Emissions
During the warranty test in December 1989 detailed
measurements of flue gas components or of noise rate level
have not been carried out. Only the regular 02 and NO,,
measurements have been carried out with the standard equipment
of Kaldin. In a mutual agreement between Lurgi and Kaldin
additional emission measurements have been carried out in a
later stage.
The NOx-emission which was measured by Kaldin during the
Warranty test is about 940 mg/Nm3
at 7 % 02, which is higher
than the requirements which are mentioned in Kaldin's nuisance
act (500 mg/Nm3
). After gaining more experiences concerning the
use of coal residues, and the corresponding level of the NOx-
emission, effective modifications to the CFB have been made in
order to decrease the NOx-emission. After the end of the
program, with the use of only coal as a fuel the NOx-emission
could be decreased to a level below 500 mg/Nm3
, when using a
limited quantity of combustion air. In this case the quality
of the product, concerning the carbon outburn, could not
always be guaranteed.
Other randomly measured components such as C02, CO and S02 and
components measured at dust samples such as the quantity of
dust, Cd, Pb, Zn, Sb, Hg and fluorides, stay far below the
requirements mentioned in the private nuisance act [1].
3.6. Raw materials
3.6.1. Limestone
During the entire phase 2 a fine-grained limestone has been
processed. This limestone arises as a side-product after
crushing and sieving of limestone, which is used for lime
production in conventional lime calcining kilns.
The composition of the fine-grained limestone is shown in
table 4. Most of the data have been provided by the supplier,
only the CaC03 and water content are averages from the analyses
which have been carried out by the Kaldin laboratory.
The grain size of the limestone is between 0 and 3 mm, and in
average (d50) 0.7 to 0.8 mm.
The limestone is not a pure limestone but consists partly of
sand and clay (about 10 to 15 % m/m). The presence of these
components has a positive effect on the transportability of
the limestone in the plant. On the other hand, the free CaO
19

content of the product is lower than it would be with the use
of a pure limestone.
During phase 2 in total about 24,000 tons of limestone have
been processed.
Table 4 - Chemical composition (main components) of the fine-grained
limestone which is processed during phase 2
Component
CaCO-j
water
Si02
A1203
Fe203
MgO
Average
85.7
6.9
9.3
1.0
1.0
0.3
Standard
deviation
3.2
0.9
3.6
0.5
0.5
0.4
3.6.2. Fine-grained coal
During phase 2 a total amount of 2400 tons of high quality
fine-grained coal has been used. This fine-grained coal has
such a quality that an almost complete combustion of the coal
was attained and no process-technological problems of the
plant can be attributed to the use of this coal.
3.7. Product-quality
The product which is generated with only coal as fuel is
mainly a mixture of free lime (CaO) and silicates (mainly Si02/
coming from the limestone). Subsidiary components are CaC03/
Ca(0H)2, CaS04 and coal residues (coming from the coal). The
colour of the product is off-white.
During phase 2 about 14,000 tons of product have been
generated. The average composition and properties of this
product are shown in table 5. As a reference, the properties
of the product which is produced during the warranty test are
also shown.
During the first months after the plant was started up large
fluctuations occurred in the properties of the product (figure
2). This is caused by the regular interruptions in the
production process (disturbances and modifications). After the
plant started to generate the product in higher quantities and
in a more regular way, the quality of the product improved and
became more constant.
- 20 -

Table Average properties of the product which is produced during
phase 2, compared to the properties of the product which is
produced during the warranty test
Phase 2 Warranty test
Property Unit Avg. Avg.
t80*
Total CaO
Free CaO
fr CaO/tot CaO
rain
%
%
%
4.2
68.9
61.7
89.6
4.8
74.2
65.8
88.7
the reactivity of the lime
apr may jun Jul aug sep oct nov dec jan
_^_ CaO tot _^_ CaO free _^_ CaOtfCaOtot
Figure 2 - Main p r o p e r t i e s of t h e p r o d u c t g e n e r a t e d d u r i n g
phase 2
21 -

The standard deviation of the free CaO content of the product
which is generated during the warranty test corresponds to the
standard deviation of types of lime which are sold by other
lime-producing companies (about 1 % ) . This implies that a
product which is produced in a continuous process, at almost
the maximum capacity of the plant and with coal as fuel, has a
composition which is sufficiently constant.
The reactivity of the product was generally too high to be
used as a raw material for the production of sand-lime bricks
in the factory of De Hazelaar. This is mainly the result of
the relatively low temperature (960 "C) at which the CFB was
processed. Therefore in the milling section of the Kaldin
plant a retarder has been added to the lime.
Based on data such as the chemical properties of the product,
the content of silicates of the limestone and the ash content
of the coal, a global mineralogical composition of the product
can be calculated. The results of these calculations are shown
in table 6.
The difference between the mineralogical composition of the
two products is a lower free CaO content and a higher content
of silicates of the average product which is generated during
the entire phase 2 compared to the product generated during
the warranty test.
Table Calculated average mineralogical composition of the product
of phase 2 and the warranty period
Component (%) Phase 2 Warranty t e s t
CaO
MgO
Ca(0H)2
CaC03
Coal ash
org. carbon
silicates
57.8
0.5
4.5
8.0
1.3
0.1
27.8
62.5
0.5
3.7
7.0
1.1
0 . 1
2 5 . 1
3.8. Application of the product in sand-lime bricks
3.8.1. General
About 86 % of the product of phase 2 (11,400 tons in total)
has been used as a raw material for the production of sand-
lime bricks in sand-lime brick factory De Hazelaar. Beside
this application smaller amounts of this product have been
- 22 -

sold to another sand-lime brick factory and have been used as
a raw material in cement-production.
3.8.2. Description of the sand-lime brick production
process of factory De Hazelaar
The production of sand-lime bricks is performed with a fine-
grained sand which is extracted from the quarry situated near
the factory. This sand is mixed with lime and water and
thereafter stored in a reactor, in order to allow the lime to
slake. Then the sand-lime mixture is remixed and pressed into
moulds of specific sizes. The moulded products are steam-cured
during 12 to 16 hours at about 200 "c and 16 Bar steam-
pressure. Under these conditions the Si02 of the sand goes into
solution and reacts with the free CaO to form calcium-
silicates, which will harden the sand-lime bricks.
3.8.3. Composition of the mixture
The composition of the sand-lime mixture is calculated based
on the minimum amount of free lime which has to be available
in this mixture. This implies that in a sand-lime mixture with
Kaldin lime (which has a lower free CaO content than the type
of lime which has formerly been used by De Hazelaar: Dornap
lime) more Kaldin lime has to be dosed. This means that a
higher amount of fine-grained particles is dosed to the
mixture as was the case before Kaldin lime was used. The
possible positive effect of the addition of this extra amount
of fine-grained particles to the properties of the sand-lime
bricks has not been taken into account in this calculation.
3.8.4. Properties of sand-lime mortar and -bricks
Laboratory experiments
On laboratory scale several experiments have been carried out
with Kaldin lime compared to Dornap lime. In table 7 the
results of a test with mixtures of Dornap lime and with the
product which has been generated during the warranty test are
shown.
The increase of the free CaO content leads with all samples to
an increase of both the apparent density, the green strength
and the compressive strength. In order to realize a certain
percentage of free lime in the mortar, more Kaldin lime had to
be added than when Dornap lime is used, which makes it
difficult to compare the two mixtures. The increase in fine-
grained particles in the mixture can have a slightly positive
effect on the green strength and on the compressive strength.
However, it has to be stated that in practice no relation
could be found between the measured green strength and a
decrease of product-quality caused by fracturing. As a result
thereof the data in table 7 are not easily to interpret.
23

At the end of phase 3 of the measuring and monitoring program
the method for the determination of the green strength has
been changed in such a way that a relation between the above
mentioned parameters could be distinguished.
Table 7 - Properties of sand-lime mortar and -brick with different
types of lime and 6.5 % water during phase 2 (at laboratory
scale)
Type of lime Green Apparent Compressive
and free lime strength density strength
(* d.m.) (kPa) (kg/m3
) (MPa)
Dornap
5.5
6.5
7.5
Kaldin
5.5
6.5
7.5
lime
lime
3.2
4.2
5.6
3.0
4.6
6.3
1780
1800
1820
1770
1790
1800
25.1
30.5
36.2
28.2
31.7
38.4
Experiences in practice
Only after August 1989 when the production of the Kaldin plant
reached a satisfactory level, the quality of the Kaldin lime
became sufficiently constant to justify a 100 % replacement of
Dornap lime by Kaldin lime.
However, the variations in the quality of the limestone and of
process-conditions of the Kaldin plant, still lead to
variations in the reactivity and in the free CaO content of
the Kaldin lime. In the sand-lime brick factory this caused
difficulties with the production of sand-lime bricks and
elements.
As a result of the variations in the free CaO content of the
Kaldin lime compared to the Dornap lime, mixtures of sand with
Kaldin lime showed a variable need for water. As a result
thereof several charges of sand-lime mortar were too dry or
too wet. This has lead to a higher product-loss, because of
fracturing and pressure-cracks.
- 24

3.9'. Mass- and energy-balance
During the warranty period, when the plant has been processed
at optimum conditions (no stops, no disturbances, almost
maximum capacity) a total of 59 GJ of fossil energy (fine-
grained coal) had to be used to calcine 16.0 tons of CaC03 per
hour. This implies that an energy-efficiency of the Kaldin
plant of about 48 % can be realized (related to the
theoretically needed energy).
During the warranty test the amount of fossil energy which is
needed per ton of free CaO is 7.6 GJ. Considering the fact
that Kaldin generates a product with a certain positive value
of the inert fraction, the amount of energy needed for the
production of 1 ton of product (5.0 GJ) has also to be taken
into consideration.
At a constant production, without any stops or disturbances
and without the use of the drying unit, the electricity use is
about 1100 kWh ( = 4.0 GJ) per production hour.
25

4. CALCINING LIMESTONE WITH COAL RESIDUES
4.1. Introduction
On a laboratory scale, several investigators (Wittneben [2]
and Bloem [3]) have found indications that the use of coal
residues as a raw material in sand-lime bricks can have a
positive effect on the green strength of the moulded product
and on the compressive strength of the cured product (taking
into account the only limited amount of parameters studied).
The greatest disadvantage of the use of coal residues in this
application is the discolouration of the sand-lime bricks. In
stead of white this becomes grey, depending on the carbon
content and the amount of coal residues which is used.
In tests on a pilot-plant scale performed by Lurgi in 1985, it
has been shown that the carbon in coal residues could be
sufficiently burned out in a fluidized bed. After burning out
the carbon, the coal residues could be used as a raw material
for the production of sand-lime bricks, because the
discolouration of the product is acceptable.
A study carried out by Ingenieursbureau Dekker in 1985 [4]
showed that the product (a coal residues-lime mixture) is
suitable for the use in sand-lime brick production and it can
result in a higher green strength of the moulded product, a
higher compressive strength of the cured product and a saving
of the amount of free lime which has to be dosed.
During phase no. 3 of the measuring and monitoring program the
above mentioned conclusions have been checked for the product
which was generated by Kaldin and for the sand-lime bricks
which have been produced by De Hazelaar with the use of Kaldin
lime.
In practice it appeared that several technological
disturbances occurred during phase 2 which resulted in a delay
of the time that the first coal residues could be processed.
In stead of 1 July 1989, only on 30 January 1990 the first
coal residues could be used.
The measuring and monitoring program has been prematurely
concluded after the end of phase 3. As a result thereof no
experiences have been gained with the production of lime with
a maximum coal residues input of 12.5 tons per hour. However
during some short periods, for example during a test which was
monitored by TNO in January 1991, the input of coal residues
has been increased to a reach level which was as high as
possible for that time.
26 -

4.2. Operation time
During phase 3, except for some periods, a continuous
production has not been realized. In total, during phase 3
3960 hours production has been realized. This implies an
efficiency of the use of the available operation time of 60 %,
Compared to phase 2 this is an improvement of 12 %.
During almost the entire phase 3 the plant has been operated
in a continuous shift system (3 shifts, 5 days a week).
4.3. Global description of the progress
Originally the aim of the measuring and monitoring program was
to increase the coal residues input gradually from 0 to 12.5
tons per hour. During this increase the effect on the process-
conditions, the quality of the product and the quality of the
sand-lime bricks have been monitored.
During the first two months of phase 3 (February and March
1990) an input of about 2 tons coal residues per hour has been
realized during the periods in which the coal residues has
actually been processed. The limestone input during this
period varied between 13 and 17 tons per hour. No disturbances
were directly a result of the use of coal residues. In April
1990 the coal residues input has been increased to 3 - 4 tons
per hour, interchanged with periods during which this input
was less. Also with the use of this quantity of coal residues
no disturbances occurred which could be related to use of coal
residues. During large parts of the months July, August and
September 1990 the coal residues input has been increased to
about 6 tons per hour. Due to problems with the quality of the
sand-lime bricks, at the end of September it has been decided
to decrease the coal residues input back to 3 - 4 tons per
hour. During the last couple of months in 1990 this has been
reduced to about 3 tons per hour. During the entire phase 3 an
average of 2.53 tons of coal residues per production hour has
been processed.
During a short period in January 1991 (several hours), under
the supervision of TNO [5], a test has been carried out with
an input of 8 tons of coal residues per hour and 16 tons of
limestone per hour. This resulted in a product output of 15 to
16 tons per hour, depending on the carbon content of the coal
residues). During this test, stable process-conditions have
been realized. From this test can be concluded that a further
increase of the coal residues input was technologically
- 27

possible. Also the quality of sand-lime elements with the
product which was generated during this test was satisfactory.
In a few tests, beside coal and coal residues, also heavy oil
has been used as a fuel.
feb mar apr may jun Jul aug sep oct nov dec jan feb mar apr
. Limestone . Coal ± PFA . Product
Figure 3 - Average raw material input and production per hour per month
during phase 3
Table 8 - Use of raw materials and production per production hour
during phase 3
limestone
coal residues
coal
heavy oil
product
(CaOf = 54.7 %)
CaOf
total input
and production
(tons)
59,200
10,000
4,640
92
43,500
23,800
input and production
per production hour
(tons/hr)
15.0
2.53
1.17
0.02
11.0
6.0
28 -

The limestone input per hour varied generally between 13 and
16 tons per production hour. The average limestone input
during phase 3 was 15.0 tons per hour. Because of the use of
coal residues the use of coal has been decreased compared to
phase 2. Moreover, the limestone which is used in phase 3 has
in average a higher CaC03 content than in phase 2. This implies
that even more energy was needed to calcine the total amount
of available CaC03.
During phase 3 beside coal residues several other industrial
side-products have been processed in the Kaldin plant. These
were mainly limestone granules and smaller quantities of
petrocokes, SKW and marble powder. Some of those products
have been processed successfully, others were not. These
products are all discussed in section 4.7.
Until the end of September 1990 the dust which accumulates in
the cloth filter and the heat-exchanger has been transported
to the intermediate bunker, after which it passes the sifter.
Since then this dust has been transported to a productsilo and
it is considered as a separate product, named "Filter lime".
This product implies 25 % of the total production. The other
75 % of the total production is the main product of the Kaldin
plant and is named "Kaldin lime".
4.4. Process parameters
4.4.1. General
The process parameters during phase 3 do not deviate much from
those during phase 2. Small differences are mainly present in
the temperature of the CFB and the temperature of the primary
and secondary air.
4.4.2. The CFB temperature
- top CFB = 960 - 1010 "C
- bottom CFB = 950 - 1000 °C
The temperature of the CFB has mostly varied in the above
mentioned ranges. Until September 1990 the temperatures
corresponded mainly to the lowest figures. After September the
temperature of the CFB has been increased in order to produce
a less reactive lime.
4.4.3. Sifter/milling section
Since September the dust from the heat-exchanger and the cloth
filter has not any more been transported to the intermediate
- 29 -

bunker (as mentioned in § 4.3), but to a separate productsilo.
As a result thereof, the ball mill and elevator have been
partly unloaded. Hence, the sifter/milling section can now be
used periodically in a cycle of for example 3 hours on and 2
hours off, in stead of being used continuously.
4.4.4. The drying unit
During phase 3 in the drying unit a total of 1056 tons of wet
material has been dried. This quantity is mainly composed of
SKW and coal residues.
The drying of relatively coarse-grained materials such as sand
and limestone was realized without any difficulty. The drying
of the fine-grained materials such as SKW and coal residues
caused some problems relating to the transportability of the
products, which have limited the drying of these materials
during the course of the project.
The water content of the dried material was always smaller
than 1 %. This corresponds to the warranted limit which was
given by Lurgi.
4.5. Process-experiences, disturbances and modifications
Many problems which occurred during the time that limestone
has been calcined with only coal also occurred during the time
that coal residues was used. However some differences in the
behaviour of the disturbances can be noticed.
Problems which mainly occurred when only coal was used as a
fuel and which decreased when also coal residues was processed
are the following:
- Caking in several components of the plant, especially in
the recycling cyclone, venturi, first cyclone and the
product cooler has been decreased. The use of coal residues
has an abrasive effect on the cakes.
- As a result of the use of coal residues the average grain
size of the bed material decreased, which made it possible
to fluidize a slightly coarser limestone.
Beside the decrease of some disturbances, others did appear as
a result of the use of coal residues:
- As a result of after-burning of the coal residues, the
product temperature of the fluidized bed cooler increased
which resulted sometimes in sintering and obstructions in
the cooler chambers.
30 -

The increase of the flue gas temperature, also as a result
of after-burning of the coal residues, lead to a
deformation of the valves in the return pipe between the
first cyclone and the CFB.
Other problems cannot directly be related to the use of only
coal or coal + coal residues as fuel. These problems are
mostly a result of the generation of a large volume of dust
and the nature of this material.
Depending on the type of coal residues, mostly a small amount
of coal is allways needed in order to keep the the process
conditions at a constant level.
4.6. Emissions
4.6.1. NO^-emission
The components which are continuously analyzed in the flue
gasses of Kaldin are N0X and 02. The N0X content is measured
before the chimney at the same spot as the 02 measurement is
performed.
From these data (in ppm) the NOx-emission can be calculated in
mg/Nm3
, according to the unit in which this parameter is
defined in the private nuisance act, with the aid of the
following formulae:
N0X (mg/Nm3
) = N0X (ppm) x 2.05 x
20.94 - 7 % 02
20.94 - % O,
When coal residues are used, a higher N0X content of the flue
gasses is measured than with the use of only fine-grained
coal. The NO^-emissions with coal residues varied between 900
and 2100 mg/Nm3
, compared to 940 mg/Nm3 which was measured
during the warranty test with only coal (see § 3.5).
During a test period in phase 3, continuous measurements have
been made by DHV of the following components: C02, CO, 02, N0X
and S02 [l]. Samples of the dust have been taken every hour.
These samples have been analyzed on the following components:
Cd, Pb, Zn, Hg, Sb and fluorides.
Also the analyses of DHV show a higher NO*-emission (1000 -
1300 mg/Nm3
as an average per hour) than which is allowed
according to the private nuisance act.
Of the 3 samples of dust which have been measured, the amount
of dust of one sample exceeds the limit mentioned in the
31

nuisance act. This is mainly caused by a damage of the cloth
filter at the time the dust samples have been taken. In a
later stage, the bags of the cloth filter have been replaced.
The S02-emission stays largely below the limit of 700 mg/Nm3
.
Also the above mentioned components which have been measured
on the dust samples stay largely below the limits mentioned in
the nuisance act.
After the end of phase 3, several tests have been carried out
regarding possible measures which could be taken to reduce the
N0X emission. From these test results it became clear that the
NO* level depended largely on both the total amount of nitrogen
present in the fuel and on the amount of air which is used for
the combustion of the fuel. Following these results,
modifications have been made to the CFB, which have resulted
in a decrease of the NOx-emission.
With the use of only coal as a fuel the NOx-emission can be
decreased to a level below the limit mentioned in the private
nuisance act (N0X < 500 mg/Nm3
), when using a limited quantity
of combustion air and a reduction of the quality of the
product. When more than about 2 tons of coal residues are
processed, additional measures have to be taken to further
reduce the N0X emission to a level below 500 mg/Nm3
. Tests have
shown that this can be achieved up till a coal residue input
of at least 8 tons per hour. The quality of the product
concerning the carbon outburn and calcination ratio can
however not be guaranteed.
4.6.2. Noise emission
In April 1990 acoustic measurements have been carried out by
Cauberg-Huygen concerning the noise emission of Kaldin and of
De Hazelaar and the nuisance that this noise caused to the
near environment of these factories [6]. When these results
are compared with the limits mentioned in the private nuisance
act, it appears that on some locations the noise level exceeds
the limit which is set for the nighttime (40 dB(A) between
11.00 pm and 7.00 am).
Based on these results, at the end of phase 3 modifications
have been made to some components of the installation and
vehicles which have led to a reduction of the noise level,
although new acoustic measurements have not yet been carried
out in order to quantify this reduction of noise rate level.
32

4.7. Raw materials
4.7.1. Limestone
During phase 3 a total of about 59,200 tons of limestone has
been calcined. The limestone is supplied in a fine-grained
fraction (0/2 or 0/3). This material arises as a side-product
from the crushing process in limestone quarries.
Before September 1990 mainly limestone with a CaC03 content of
about 86 % and a water content of 6.5 % has been processed.
After September 1990 mainly a limestone with a CaC03 content of
about 96 % and a water content of 3 % has been processed. The
advantage of the use of this latter limestone is a higher free
CaO content of the Kaldin product.
Beside the fine-grained limestone from Belgian quarries, about
1600 tons of drinking water granules have been processed.
These granules have a CaC03 content of about 95 %. During the
time the drinking water granules could be supplied, they have
been processed with a ratio of 1 part of granules to 5 parts
of other types of limestone. A good fluidization of the bed
was always maintained.
4.7.2. Fine-grained coal
During phase 3 a total of 4640 tons of fine-grained coal have
been used as a fuel. This coal has been furnished by different
suppliers. The grain size of the coal was between 0 and 1 mm.
4.7.3. Coal residues
The basic idea behind the Kaldin process has been the
calcination of limestone with Dutch coal residues. Especially
coal residues with a high carbon content (> 5 %) will be
suitable. Therefor contracts with 3 Dutch companies (AKZO, DSM
and Vliegasunie) have been signed concerning a regular supply
of coal residues which arises from coal combustion processes
at these companies.
During the first part of phase 3 of the measuring and
monitoring program the highest quantity of Dutch coal residues
has been processed, but gradually these types of coal residues
have been substituted by German FBC coal residues. At the end
of phase 3 about 7,745 tons of German coal residues and only
2,309 tons of Dutch coal residues has been processed. The
decision for this substitution is based on two reasons:
1. Better prices can be obtained for the German coal residues
33

2. The average net heat value of the German coal residues is
higher (7.7 MJ/kg) than of the Dutch coal residues (2.2
MJ/kg).
The average net heat value of all the coal residues which was
used during phase 3 is 6.4 MJ/kg and the average loss on
ignition (which is a measure for the organic carbon content)
is 21.3 %.
The German FBC coal residues all originate from small static
fluidized beds which are used for city-heating and for the
generation of electricity.
4.7.4. Other raw materials
Petrocokes
During the months September and October 1990 a total of 88
tons of petrocokes has been used as fuel. This is a side-
product of oil refinery. It has a fairly sticky nature and
does consist mainly of cokes and for a smaller part of oil.
The cokes has a higher temperature of ignition than the fine-
grained coal. The residence time in the CFB is too short to
obtain a complete combustion and therefor the not completely
combusted material becomes a part of the product or leads to
afterburning which causes a sintering in the fluidized bed
cooler as mentioned in section 4.5.4.
SKW
SKW is a fine-grained calcium-carbonate which arises as a
side-product with the production of fertilizers. This material
consists mainly of CaC03, about 7 % of organic carbon and about
25 % water. The fossil energy content, represented as the heat
of combustion, is 1.8 MJ/kg. Before being introduced into the
CFB the SKW has to be dried in the drying unit.
4.8. Product-quality
4.8.1. General
The product which is generated as a result of the calcination
of limestone with coal residues is a mixture of free CaO,
burned out coal residues and the inert fraction of limestone.
The free CaO is a raw material for the production of several
building materials such as sand-lime bricks. The burned out
coal residues can serve as a filler or as a pozzolanic binder.
During the first part of phase 3 (until the end of September
1990) one product was generated (the so-called "flyash-lime").
This product left the plant completely via the sifter-milling
section. After September 1990, the dust which collected in the
- 34

cloth filter and the heat-exchanger has been separately
transported to one productsilo. This is a very fine-grained
and relatively CaO-poor lime. It is since then called "Filter
lime". The relatively coarse-grained and CaO-rich lime which
still leaves the sifter-milling section is then called the
"Kaldin lime" (see § 4.3).
4.8.2. Flyash-lime
The flyash-lime has been produced during a period of 8 months
since the beginning of phase 3. The increase of the coal
residues input from 0 to 6 tons per hour has lead to a
decrease of the free CaO content in this product from about 60
to 35 % (figure 4). The rest of the product consists mainly of
burned out coal residues and of the inert part of the lime-
stone. The average free CaO content during this part of phase
3 is 52.7 %. In table 9 the average properties of this product
are given.
Due to the relatively large variations in the coal residues
input and the variations in the composition of the coal
residues, the quality of the flyash-lime also shows large
variations.
The reactivity of the flyash-lime (tso) has mostly been 3 to 4
minutes. In September 1990 it has been decided to increase the
temperature of the CFB in order to produce a lime with a lower
reactivity. As a result thereof in the sand-lime brick factory
less retarder had to be dosed.
Table 9 - Average properties of flyash-lime (February - September 1990)
unit average
Total CaO % 62.0
Free CaO % 52.7
tao min 4.3
- 35 -

feb mrt apr may jun jul aug sep okt nov dec jan feb mrt apr
_*_freeCaO ___ tot CaO _^_ ealc. ratio
Figure 4 - Average p r o p e r t i e s of f l y a s h - l i m e and a combination of Kaldin
lime and F i l t e r lime per month
The average flyash-lime c o n s i s t s of the following mineralo-
gical components:
Free CaO
Ca(0H)2
CaC03
S i l i c a t e s , e t c .
50,
2,
7,
38.
4.8.3. Kaldin lime and Filter lime
As mentioned in § 4.8.1, since the beginning of September 1990
the product has been separated into Kaldin lime and Filter
lime. The largest volume of this product is Kaldin lime (about
75 % of the total product). This product reaches the
productsilo via the sifter-milling section. The smaller
product volume (25 %) is Filter lime which originates from the
cloth filter and the heat-exchanger.
Together with the separation of the product into Kaldin lime
and Filter lime, another type of limestone (with a higher CaC03
content) started to be used. This resulted in an increase of
both the free and total CaO content of the product. An
- 36

overview of the properties of Kaldin lime and Filter lime are
given in table 11.
Kaldin lime
Especially because of smaller variations in the coal residues
input during the time that the endproduct has been generated
in two separate volumes, the quality of the Kaldin lime is
more constant than the quality of the flyash-lime. During
periods, in which the coal residues input has been relatively
constant, the standard deviation in the CaO content reached a
level (1 - 2 %) comparable to other types of lime which are
currently sold on the market.
The average grain size (dso) of this product is about 27 ;im and
the specific surface is about 1900 cm2
/g (measured with Silas
method). This is comparable to other types of lime which are
currently on the market.
Table 10 - Average global mineralogical composition (in %) of Kaldin and
Filter lime
Free CaO
CaC03
Ca(0H)2
CaS04
Org. Carbon
Silicates, etc.*
Kaldin lime
60.1
2.0
4.1
1.2
0.0
32.6
Filter lime
32.2
25.0
2.8
0.4
0.6
39.0
Including the components MgO, NaO, Ka0, A1203 and Fe203
Table 11 - Average properties of Kaldin lime and Filter lime (October
1990 - April 1991)
unit Kaldin Filter
lime lime
Total CaO % 71.8 60.3
Free CaO % 63.2 34.3
t80 min 6.6 47
Filter lime
The average free CaO content of Filter lime is far less than
the free CaO content of Kaldin lime (34.3 % versus 63.2 % ) ,
while the difference in the average total CaO content is much
smaller (see table 11). This is mainly caused by the higher
amount of CaC03 (25 %) in the Filter lime and partly by the
37

higher amount of silicates (see table 10). The average grain
size (d50) is about 5 /iin and the specific surface area is about
6700 cm2
/g^ This is far less than the average grain size of
types of lime which are currently on the market.
4.9. Application of the product in sand-lime bricks
4.9.1. Introduction
As indicated in the introduction of chapter 4, the use of coal
residues can have a positive effect on the quality of sand-
lime bricks. The quality of sand-lime bricks with flyash-lime
or a combination of Kaldin lime and Filter lime has been
studied both in the laboratory and at production scale.
4.9.2. Use of lime at De Hazelaar
During the time that the flyash-lime was produced almost the
total quantity of this product has been sold to De Hazelaar.
After the product was separated into Kaldin lime and Filter
lime, especially a part of the Filter lime has been supplied
to other sand-lime brick factories, but even during this
period the main part of the product has been supplied to De
Hazelaar. During phase 3 of the project, in total 41,500 tons
of the Kaldin product has been processed at De Hazelaar and
1900 tons of (mainly) Filter lime has been sold to third
parties.
4.9.3. Composition of the sand-lime mortar
In order to obtain a sufficient green strength of the moulded
product and compressive strength of the cured product, a
minimum amount of CaO is necessary. This amount of CaO has
always been the base for the calculation of the composition of
the sand-lime mortar. The expectation was that, with the use
of the Kaldin product in about the same quantity as the
previously used Dornap lime, a comparable green strength and
compressive strength could be obtained (with the use of less
free CaO). The burned-out coal residues particles which
replace a part of the fine-grained sand could help to keep the
green strength at a sufficiently high level.
In the beginning the Kaldin product (flyash-lime by that time)
has been used in quantities which were based on an equal free
CaO content in the sand-lime mortar as before. Due to the
lower CaO content of the flyash-lime a larger amount of fine-
grained particles was dosed to the sand-lime mortar. Based on
the experiences in practice concerning the quality of the
sand-lime brick elements, in a later stage the free CaO
content in the sand-lime mortar has not been decreased. This
38

means that the fine-grained particles have always acted mainly
as a filler in addition to the fine-grained sand particles.
In practice during a longer period of time a mixture of Dornap
lime and flyash-lime has been used for the production of sand-
lime bricks and elements.
4.9.4. Laboratory tests
With the flyash-lime several laboratory experiments have been
carried out in which the properties of the sand-lime mortars
and sand-lime bricks have been compared with the mortars and
bricks which were produced using Dornap lime [8]. Following,
the most important results will be discussed. For more detail
the reader is referred to [8].
The samples have been produced by mixing the raw materials in
a laboratory mixer and moulding the mortar into cylinder-
shaped samples. Thereafter they are steam-cured in the plant.
The green strength is determined after the moulding of the
samples and the compressive strength after steam-curing. In
table 12 the results of a comparative study between sand-lime
bricks with a flyash-lime (free CaO = 37 %) and with Dornap
lime are shown. From these results it can be concluded that a
larger amount of fine-grained particles (the samples with fly-
ash lime) result in an increase of the apparent density of the
product, together with an increase of green strength and
compressive strength. The water absorption and expansion of
these samples are lower. In order to reach a similar free CaO
content in the mortar, compared to Dornap lime, more than
twice the amount of flyash-lime has to be dosed.
It has however to be noted that question marks have to be
placed with these tests. The apparent density of the samples
is about 150 kg/m3
higher than the apparent density of the
products which are produced in practice by De Hazelaar.
As a result thereof all the data mentioned in table 12 deviate
from the data of products generated in practice. This applies
mainly to the green strength. In practice hardly ever can be
seen that the green strength of a moulded sand-flyash-lime
mortar is higher than of a moulded sand-Dornap lime mortar
(based on an equal free CaO content). Therefor, at the end of
phase 3 the moulding pressure for the preparation of the
samples has been decreased. The result thereof was, in
contradistinction with former times, that a clearer relation
could be seen between the green strength and the product-loss
as a result of fracturing (see section 4.9.5).
39

Table 12 - Properties of sand-lime mortars with Dornap lime and with
flyash-lime, based on laboratory tests
Dornap lime (free CaO = 85 %)
Free CaO % 5.5
Green strength kPa 1.0
Compr. strength MPa 25.3
App. density kg/m3
1825
Water absorption % 13.2
Expansion mm/m 0.7
Flyash-lime (free CaO = 37 %)
Free CaO %
Green strength kPa
Compr. strength MPa
App. density kg/m3
Water absorption %
Expansion mm/m
5.5
1.7
31.9
1870
12.8
0.3
6.5
1.8
33.5
1825
13.1
0.7
6.5
2.2
35.8
1880
12.3
0.6
7.5
2.3
37.3
1840
13.0
0.9
7.5
3.9
42.3
1900
12.3
0.4
8.5
3.7
1860
13.2
1.4
8.5
5.0
43.6
1930
11.6
0.8
9.5
4.9
43.6
1860
13.7
1.4
9.5
6.8
46.7
1925
11.9
0.4
4.9.5. Experiences in practice
During the main part of phase 3 the product-loss of both
bricks and elements was about the same as during phase 2.
A good quality of sand-lime bricks and elements has been
obtained with the use of a flyash-lime or a combination of
Kaldin lime and Filter lime.
However, during some periods with a higher coal residues input
in the Kaldin plant, an increase of product-loss has occurred,
mainly in production of the large elements. Especially the
larger elements are very sensitive for fracturing just after
the moulding of the element and for pressure cracks during
steam-curing. It has to be noted that the increase of product-
loss is probably not only caused by the increase of the coal
residues input in the Kaldin plant. In a latter stage, after
the end of the measuring and monitoring program, with an input
of more than 4 tons of coal residues per hour also a good
quality of the sand-lime elements could be obtained. The above
mentioned increase of the product-loss will therefor, beside
the coal residues content in the product, have been generated
by a complex of causes, such as the quality of the sand and
variations in the quality of the lime and their interactions
[9]. Moreover the personnel of the sand-lime brick plant
gained more experience in the production of bricks and
elements with the use of Kaldin lime and Filter lime. It can
therefor be expected that the product-loss can be further
decreased in the near future, also with a relatively high
input of coal residues.
40 -

During phase 3, the supposed advantage of the use of coal
residues in sand-lime bricks concerning a better green
strength of the moulded product could not been proven. In
practice, a mortar with a combination of Kaldin lime and
Filter lime sometimes showed a slight increase, but sometimes
also a slight decrease of the green strength compared to a
mortar with Dornap lime (with an equal free CaO content of the
mortar). The decrease of the green strength can probably be
attributed to a higher need of water because of the higher
content of fine-grained particles in the mortar.
4.10. Mass- and energy-balance
In average during phase 3 13.0 tons of CaC03 per hour have
been processed in the CFB. This means that 13.0 times the
theoretically needed energy for the calcination of 1 ton of
CaC03 (= 1.77 MJ/kg) =23.0 GJ/hr is needed for the calcination
of all the CaC03. The real amount of energy which is needed is
naturally higher because of energy needed for the warming up
of all the components, heat transmission to the walls, to the
flue gasses, etc. By addition of all the sources of energy of
the used types of fuel, and comparing this total amount with
the theoretically needed amount of energy, the efficiency of
energy for the calcination of CaC03 can be calculated.
During the calcination of CaC03 with coal residues as fuel also
fine-grained coal has been used. The average coal residues
input during phase 3 (2.53 tons per hour) has replaced 600 kg
of coal per hour (of an average composition). The total amount
of processed fossil energy during phase 3 (mainly provided by
coal and by coal residues) mounts up to about 50 GJ/hr.
The efficiency of the fossil energy for the calcination of
CaC03 during phase 3 therefor reaches 46 %. Compared to phase 2
this implies an improvement with 2 %. A direct relation
between the efficiency and the coal residues input is not
clear. About 40 % of the used energy is leaving the process
with the flue gasses. When this energy is used in the drying
unit, the overall energy efficiency of the plant is higher.
The total amount of fossil energy which is needed for the
production of 1 ton of free CaO is 8.3 GJ. This is high
compared to energy which his needed for the production of 1
ton of free CaO in shaft kilns and rotary kilns. In shaft
kilns this amount of energy is about 5 GJ and in rotary kilns
about 6 GJ. During periods that the plant is operated under
optimum conditions, and in a continuous shift system, the
fossil energy use can be reduced to figures between 7.5 and
8.0 GJ per ton CaO.
41

Because in the Kaldin plant a product is generated which can,
beside the value of the free CaO, also have a certain value as
a (reactive) filler, the needed amount of fossil energy for
the production of 1 ton of product has also to be taken into
account. During phase 3 this is in average 4.5 GJ.
During an average period in which the plant has been operated
continuously and the drying unit has not been switched on, an
average of 1100 kWh (=4.0 GJ) of electric energy per hour is
used.
This is higher than which was originally expected (800 kWh =
2.9 GJ/hr).
42

5. OTHER APPLICATIONS
5.1. Introduction
As mentioned in section 4.9. almost the total amount of the
product has been applied as a binding agent in calcium-silica-
te production. In this application it was however not possible
to notice an advantage of the use of this lime over the use of
another type of lime.
Beside the application in C.S. production, different applica-
tions of the product have been studied. The most promising
applications are the following:
a filler in asphalt
sludge stabilization
masonry mortars
5.2. Slaking of the lime
Before the calcinated product can be used in some of the above
mentioned appications, the free CaO of the product has to be
slaked into Ca(0H)2. Because the slaking process of the product
can sometimes be rather long and irregular (especially concer-
ning the filter lime), tests have been carried out with a
three-stage slaking installation. Both Kaldin lime and filter
lime which were slaked with this installation are completely
expansion-free with a water content < 1 %. With the slaked
product generated in these tests, the possibilities of
application in asphalt and masonry mortar have been studied.
5.3. Asphalt filler
Fly-ashes, pulverized limestone and hydrated lime are materi-
als which are often used as a filler in asphalt. In contradis-
tinction to normal asphalt, in very open asphalt a filler with
a Ca(0H)2 content of about 50 % is applied. Laboratory tests
have indicated that the slaked product of the calcination
process, especially the slaked filter lime is a good filler in
very open asphalt. The potential market is estimated at
100.000 - 120.000 tons of Kaldin lime per year [7].
5.4. Sewage sludge stabilization
The degree of stabilization of sewage sludges depends on the
amount of waterreduction and on the hardening of the sludge
which can be achieved. These properties are influenced by the
amount of free CaO which can be dosed to the sludge and by the
43

amount of inert fine-grained particles which are used for the
stabilization.
Because of its higher free CaO content, Kaldin lime is more
suitable for sludge stabilization and because of the higher
quantity of fines the filter lime can be suitable. Tests on
laboratory scale and in practice which were carried out after
the end of phase 3 of the program, have shown promissing
results. The potential market is estimated at 10.000 - 15.000
tons of lime per year.
5.5. Masonry mortars
By using lime in a masonry mortar the workability and the
waterretention of the mortar are positively influenced.
It also decreases the elasticity modul of the hardened mortar,
Laboratory tests have shown that both products, Kaldin lime
and filter lime can replace a lime which is normally used in
this application, especially in dry prefab masonry mortars.
The potential market is estimated at 10.000 - 12.000 tons per
year [7],
44

ECONOMICAL ASPECTS
6.1. General
In 1991 an interim evaluation of the economic aspects of the
Kaldin plant has been carried out by DHV. The aim of this
study was to determine the value of the project for the
National Coal Investigation Program (NOK). The bureau A+
calculated the economic viability of the Kaldin plant when
products with a different free CaO content are produced.
The main conclusions of these studies, together with an
exploitation overview will be discussed in the following
sections. For more detail the reader is referred to [7] and
[10].
6.2. Raw materials
The economic viability depends for a large part on the input
of coal residues with a high carbon content.
The coal residues which come available at electric power
stations mainly have a relatively low carbon content.
Moreover, these types of coal residue are currently used in
other applications. The coal residues which come available
with fluidized bed combustion have a much higher carbon con-
tent. Although this type of coal residue arises at a smaller
scale, in Germany a sufficiently high supply of these ashes is
available at higher negative prices. Economically this type of
coal residue is therefor more attractive than the Dutch types
of coal residue arising from coal-fired electric power stati-
ons.
Mainly due to transportation costs, the limestone price in The
Netherlands is relatively high compared to the effective cost
of limestone at the quarry. The ideal situation is when a
calcination plant is situated close to a limestone quarry, or
when industrial side-product, such as drinking water granules
can be used.
6.3. The product
As indicated in section 4.6., the product consists partly of
free CaO and partly of an inert fraction. To both parts a
certain value can be attributed, but the price of the product
depends mainly on the free CaO level in the product.
An indication of the price of the product can be obtained by a
calculation based on a price for the binder (free CaO) and a
price for the filler (the inert fraction) with the following
formulae, which is based on the current price level:
price of the product = f 140,- x free CaO + f 40,- x inert.
45

One ton of a product with a free CaO content of 55 % (average
of phase 3) would therefor achieve a price of f 95,- (without
transportation costs). However, the value of the filler (in
combination with free CaO) has so far not been demonstrated in
C.S. brick production, but can become relevant in applications
such as a filler in asphalt.
It has been calculated [7] that the plant has the highest
economical efficiency when a product with a free CaO content
between 50 and 60 % is produced, although this optimum depends
also on the possible applications of the product.
Another aspect is that currently the main part of the Kaldin
product is sold to sand-lime brick factory De Hazelaar. Other
possible applications such as in masonry mortars, sludge
stabilization, or as a filler in asphalt have only reached an
experimental stage, but seem promising (chapter 5).
Therefor, during the measuring and monitoring program less
product could be produced than which was originally
anticipated (about 32.000 in stead of 90.000 tons/yr). The
proceeds of the Kaldin plant have therefore been lower than
expected.
6.4. Outlook
There are two ways in which the plant can be operated:
1. Burning limestone with coal
2. Burning limestone with coal residues and small amounts of
coal.
For the process with limestone and coal it must be mentioned
that due to problems with caking in several components of the
plant, a production time of 8000 hours per year cannot be
expected. Together with the high investment of the plant, this
leads to a high cost price of the product. On the other hand
the product will have a low price because of the low CaC03
content of the limestone, resulting in a low CaO content of
the product. The use of a limestone with a high CaC03 content
in this plant is only possible in combination with coal
residues.
These considerations lead to the conclusion that the
production of lime with only limestone and coal will not
result in an positive economic viability of the plant.
When using coal residues a higher amount of production hours
can be achieved, because the internal part of the components
are "cleaned" by the coal residues. This will lead to lower
costs of the product. Although Kaldin is still in the middle
- 46

of product development, new products can be produced with the
use of a high coal residue input, which could have advantages
over some traditionally used products. This means that,
although at this moment a production at full capacity is not
possible due to the limited market, in the future, some larger
new markets could be opened with new products (see chapter 5).
- 47

7. PUBLICITY AND COMMERCIALIZATION
At the official opening of the Kaldin plant, in cooperation
with NOVEM, a week of different activities was organised.
These activities involve an opening ceremony and a number of
lectures which have been given on the treatment of waste
materials. The opening of the plant has been broadcasted on
some television stations and several articles have been
published in local and national papers.
During the course of the measuring and monitoring program,
representatives of companies from all over the world and
representatives of the EC have visited the plant.
On a request of the board of the province of Limburg, a paper
was presented for the EUREKA representatives in Maastricht. A
lecture on the Kaldin project has also been given on a
symposium organized by "Haus der Technik" in 1991.
48

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