Heated-die Screw-press Biomass Briquetting Machine Manual

Heated-die Screw-press
Biomass Briquetting Machine:
Design, Construction and Operation Manual
Prepared under
Renewable Energy Technologies in Asia:
A Regional Research and Dissemination Programme
(RETs in Asia)
Funded by
Swedish International Development and Cooperation Agency
(Sida)
Energy Field of Study
School of Environment, Resources, and Development
Asian Institute of Technology
Thailand
1

Heated-die Screw-press
Biomass Briquetting Machine:
Renewable Energy Technologies in Asia:
(RETs in Asia)
School of Environment, Resources, and Development
Thailand
3

RENEWABLE ENERGY TECHNOLOGIES IN ASIA
Heated-die Screw-press Biomass Briquetting Machine:
PUBLISHED BY
Regional Energy Resources Information Center (RERIC)
P.O. Box 4, Klong Luang
Pathumthani 12120
Thailand
E-mail: enreric@ait.ac.th
Website: http://www.serd.ait.ac.th/reric/
Copyright © 2003. Regional Energy Resources Information Center (RERIC),
Asian Institute of Technology. All rights reserved.
No part of this book may be reproduced by any means, stored in a retrieval
system, or transmitted in any form or by any means, electronic, mechanical,
photocopying, recording, or otherwise, without the written permission of the
publisher.
Printed in Thailand
Neither the Swedish International Development Cooperation Agency (Sida) nor
the Asian Institute of Technology (AIT) makes any warranty, expressed or
implied, or assumes any legal liability for the accuracy or completeness of any
information herein provided. References herein to any apparatus, product,
trademark or manufacturer do not constitute or imply its endorsement,
recommendation or favouring by Sida or AIT.
4

Preface
This work is a result of adaptive research and development activities carried out
within a regional programme entitled “Renewable Energy Technologies in Asia: A
Regional Research and Dissemination Programme (RETs in Asia)”. The
programme was sponsored by the Swedish International Development
Cooperation Agency (Sida), and was coordinated by the Asian Institute of
Technology (AIT). Thirteen national research institutes from six Asian countries:
Bangladesh, Cambodia, Lao PDR, Nepal, Philippines and Vietnam were involved
in the programme. It promoted three technologies: solar photovoltaics, solar
drying and biomass briquetting.
This booklet contains the design, construction and operation details of an
improved heated-die screw-press type biomass briquetting system developed
within the biomass briquetting project. The major improvements achieved in the
present design compared to existing briquetting systems of similar type are (i)
reduction in electrical energy consumption, (ii) enhanced screw life, and (iii)
smoke reduction. With these improvements, the system is expected to produce
cheaper briquettes, which can effectively replace fuelwood, which are currently
the dominant cooking fuel in rural households. With lesser smoke released during
the improved briquetting process, it is also less harmful to the operator.
Prof. S.C. Bhattacharya
December 2003 RETs in Asia Coordinator
5

Table of Contents
Page
No.
1. Introduction 5
2. Design and Construction Details 6
2.1 Briquetting Machine 6
2.2 Biomass Pre-heater 6
2.3 Biomass Die-heating Stove 6
2.4 Smoke Removal System 7
3. Design Drawings 9
4. Operational Details 25
3.1 Effects of Biomass Pre-heating and Screw
Speed on Briquetting Energy Consumption
25
3.1.1 Introduction 25
3.1.2 Testing with Wide-pitch Screw 25
3.1.3 Testing with the Close-pitch Screw 26
3.1.4 Performance of the Biomass Stove Die
Heater
27
3.1.5 Conclusions 27
3.2 Effects of Raw Material Type on Briquetting
Energy Consumption and Screw Life
29
3.2.1 Introduction 29
3.2.2 Rice husk as raw material 29
3.2.3 Mixed Raw Materials of rice husk and
saw dust
32
3.2.4 Conclusions 33
7

1. Introduction
Biomass briquetting research within the RETs in Asia programme has been
conducted with two main objectives: (i) to improve the biomass briquetting
system by reducing the electrical energy consumption, enhancing the screw
life, and by incorporating a smoke removal system, and (ii) to develop
domestic as well as institutional type biomass stoves which can burn
briquettes. Towards achieving these objectives, several prototype designs
were developed and tested at AIT. Based on the experimental results, final
designs of a biomass pre-heater, biomass die-heating stove and a smoke
removal system were developed. Additional experiments were carried out to
investigate their performance and to find the optimum operating parameters.
This report presents the details of the design and the results experiments
thus carried out.
2. Design and Construction Details
The improved briquetting system developed at AIT consists of the following:
a briquetting machine, a biomass pre-heater, biomass die-heating stove and
a smoke removal system.
2.1 Briquetting Machine:
The briquetting machine used in this study was a Bangladeshi design, the
major components of which were imported by AIT from BIT. All planned
improvements were implemented on this machine, and tests were conducted.
Table 1 presents the technical specifications of the machine. Figure 1 shows
the improved briquetting system configuration; while drawings of the
machine, screw and die are given in figures 2, 3 and 4 respectively.
Table 1. Technical specifications of the basic biomass briquetting machine
S. No. Item Description Quantity
1. Induction motor 20 HP at 1450 rpm, 380 volts/ 3 phase 1 unit
2. V-Belts B-90 2 pcs
3. Pulleys (Cast iron)
12.5 cm dia.
47.0 cm dia.
1 no.
1 no.
4 Bearings
N 6312
N 6311
1 no.
1 no.
5
Main power transmission
shaft (Bright steel)
3" dia. 1 no.
7 Die (Cast iron) 9.7 cm dia., 30 cm long 1 no.
6 Screws (Mild steel) 2 1/4" dia., 45 cm long 1 no.
8 Bush (Cast iron)
Dia: 73 mm outside x 59 mm inside
Length: 32 mm
1 no.
9

2.2 Biomass Pre-heater:
The biomass pre-heater is essentially a shell and tube heat exchanger.
Biomass is passed through the ‘tube’ by a motor-driven screw feeder, while
hot flue gases from a biomass gasifier passes through the ‘shell’.
Temperature of the flue gases could be controlled by mixing cold air with the
hot gases. The preheater was 1.2 m long and 42 cm wide and consisted of a
feeder drum placed on a rectangular chamber. The raw material was
preheated while being conveyed through the feeder drum by means of a
screw. The preheater screw was rotated by a variable speed motor. The hot
flue gas from the combustion chamber was passed through the space
between the feeder drum and the rectangular chamber and discharged to the
atmosphere. Thus, the feeder drum was heated by the flue gas at the bottom.
The rectangular chamber was insulated by a 2.5 cm thick layer of rockwool
insulation to reduce heat loss to the surroundings. Pre-heated raw material
from the preheater exit was fed directly to the briquetting machine.
The speed of the preheater screw feeder could be selected based on the
required biomass flow rate into the briquetting machine. Electrical energy
consumption by briquetting machine, die heaters and preheater motor may
be recorded from energy meters installed for the purpose. Figures 5-8
present the detailed design of the pre-heater assembly developed at AIT.
2.3 Biomass Die-heating Stove:
After conducting extensive studies with a biomass gasifier stove and a
combustion stove, the later was found to perform better, by offering steady
die temperature and better temperature control. The stove was of mild steel
(1.5 mm sheet) construction, with a furnace of 20 cm x 35 cm x 40 cm (w x b
x h) volume and 2 m long chimney attached to it at the top. The die of the
briquetting machine passes through the furnace, exposing its outer surface to
the flames inside the furnace. The furnace was insulated with a 30 mm
refractory lining at its inner surface. Doors were provided for loading the fuel
as well as to remove the ash. An ash scraper was fixed below the grate to
remove excess ash from the furnace, which will fall through the grate.
Two steel baffles were fixed just above the die, to converge the flames
towards the die surface. They were insulated at both sides using refractory
cement. The baffles were found to improve the heat transfer from the flames
to the die considerably.The design details of the stove has been given in
Figure 9.
Fuel (briquette pieces of size 40 x 40 mm size) is loaded through the side
doors upto the bottom level of the die and ignited using some wood chips and
kerosene. When the die temperature reached 350°C, the briquetting machine
is started. During production, the temperature drops to 320-330°C, and this
10

can be maintained by adding fuel periodically (every 5 minutes) to the stove.
Primary air for combustion is taken through the ash pit door, which is kept
open during operation. Secondary air is taken through the fuel doors, which
also are kept open partially. Figures 10 and 11 show the stove during
operation.
2.4 Smoke Removal System:
The system has three main components: (i) a smoke collection box, (ii) a
suction line connecting the primary air supply port of the biomass stove to the
smoke collection box at the top, and (iii) another suction line which connects
the exhaust of the die-heating stove to the biomass pre-heater. The metal
box traps the smoke during the briquetting process, the deflector mechanism
breaks the briquette into certain lengths, and the smoke is sucked through
the biomass stove, whose exhaust is connected to a chimney through the
biomass pre-heater. The schematic diagram of the system is given in Fig 12.
The exhaust from the stove is used for pre-heating the biomass raw material.
Smoke produced from briquettes is collected in the box and burnt up in the
stove. Unburned gases, along with the exhaust flue gas of the stove, are
sucked through the biomass pre-heater using a suction blower, and
exhausted through a chimney; Figure 13 presents the system configuration.
The smoke collection box is constructed of mild steel sheet of 1.5mm
thickness. A circular conduit is fixed at one end of the box, where briquette
from the die of the briquetting machine enters the box. The edge of the
conduit welded to the metal box serves to snap the briquette which comes
out of the die, assisted by the deftector plate as shown in Figure 14. The
deflector plate is rigidly fixed to the body of the metal box. A strip of MS sheet
is fixed below the path of briquette, and another perforated sheet above, to
‘guide’ the briquette straight. A slider plate is provided below the path of the
briquette so that the broken piece of briquette slide through the plate and
exits the box at the bottom. A conical cover (hood) is fixed to the box using a
water-seal, which prevents smoke from escaping the joint.
The exhaust from the smoke collection box is connected to a flexible
aluminum duct (commonly used in air condition ducting), the other end of
which is connected below the grate of the die-heating stove. The smoke thus
enters the stove along with its primary air supply, and is burnt up in the stove.
It was found that occasionally, the briquette entering the smoke collection
box tends to bend sideways, thus affecting normal operation. Two guide
plates, one below and the other above the briquette, fixed along the path of
the briquette, eliminate this problem. The top plate is perforated so as not to
11

obstruct the flow of smoke upwards. Handles are provided to the metal box
for easy handling.
Figure 14 presents the detailed drawing of the smoke collection box. The
isometric view of the box is given in Figure 15. Figures 16-19 illustrate the
design and operation of the system in detail. A suction blower of 150W, fixed
at the pre-heater exit provides the required suction to overcome the
resistance for the flow of flue gas inside the pre-heater. The capacity of the
blower was selected such that the airflow provided the required pre-heat
temperature (110-120°C), while maintaining the die temperature at 300-
320°C. (It has been found, from experimental results, that a pre-heat
temperature of 110-120°C for a screw speed of 370 rpm is the optimum in
terms of less briquetting energy consumption for the particular briquetting
machine).
During operation, the die temperature is maintained at 300-320°C by
adjusting the fuel feeding to the stove. The pre-heat temperature, however,
fluctuates more (in the range of 90-130°C), as there is no provision in the set-
up to control it independently. It is felt that the benefit from such a system to
independently control pre-heat temperature will not be economically
justifiable. It may also add to operational difficulties and require fairly skilled
technicians to operate the briquetting system.
Care should be taken while operating the machine using raw material with
moisture content in excess of 7%. Briquettes tend to ‘shoot’ through the die
as the steam trapped inside the die tries to escape. Raw material should
therefore be dried sufficiently before using, so that moisture levels are below
7%. Sufficient protection should be provided to avoid damage that may be
caused by flying pieces of briquettes through the mouth of the die in case of
‘shooting’.
12

3. Design Drawings
1. Biomass Pre-heater
2. Screw feeder
3. Biomass stove for die heating
4. Smoke collection box
5. Main bearing for screw
6. Motor of briquetting machine
7. Flexible pipe
8. Flue gas suction blower
9. Raw material hopper
10. Motor for feeder screw
11. Conduit pipe
Figure 1: Schematic Diagram of the Improved Briquetting System incorporating the
Biomass Pre-heater, Biomass Die-heating Stove and the Smoke Removal System
All dimensions are in centimeters
160
15
67
100
12
5
Figure 2. Design details of the briquetting machine
13

3
Grooving: R7
All dimensions are in
Figure 3. Briquetting Die (Bangladeshi Design)
6
37
All dimensions are in
Figure 4. Briquetting Screw (Bangladeshi Design)
14

FEEDING HOPPER
OUTER PIPE INNER PIPE
SCREW
Preheated
biomass
From
Gasifi
er
740
43
Raw
material
Note: All dimensions are in millimeter
Figure 5. Biomass Preheating System: General View
15

BAFFLE
II
3
φ 160
500 500 500
D1=210 D2 =350
FLUE GAS EXIT
(L100 GI PIPE)
φ 60
500
I
Figure 6. Biomass Preheating System: Outer Pipe
16

WELDING
LINE
D2 =
R:170
R:10
BAFFLE
WELDING
LINE
SECTION I SECTION II
Note:
- Material: Mild Steel Sheet, δ = 3 mm
- Welding of two end flanges will be done after fixing the inner pipe inside the outside tube
- All dimensions are in millimeters
Figure 7. Outer Pipe: Details of sections I and II
17

φ 100 3
φ 24
D 210
FLANGE
φ 250,
8 HOLES
BEARING
φ 30
φ 250
Note: All dimensions are in millimeterφ 80
φ
BEARING
φ 30
A
A
2,300
2.4
A - A
Figure 8. Biomass Preheating System: Inner Pipe
18

66 66 66 66 66 66
φ 23
φ 30
20
2,400
R = 35
R = 100
BAFFLE
40
A - A
Figure 9. Biomass Preheating System: Feed Screw
19

Note: All dimensions are in millimeter
Refractory
insulation
3 thick
Die dia. + 0.2
10
12
10
12
2
Chimne
15
35
15
Rods for
grate
Ash pit door
20 x 13
22
1
15
Figure 10. Die Heating Stove for Briquetting Machine
20

Figure 11. Biomass Die Heating Stove in Operation
Figure 12. Combustion inside the stove
21

Smoke
Collection
Box
Biomass
Die-heater
Stove
Suction Blower
Chimney
Smoke Exhaust
Biomass Pre-
heater
Figure 13. Schematic diagram of the Smoke Removal System
Die of
Briquetting
Machine
Die-
heating
Stove
Conical Hood
Smoke
Collection
Exit for
briquette
To
Preheating
System
Conduit Grate
Flexible
Aluminium Duct
Chimney
Figure 14. Schematic diagram of the Smoke Removal System
22

Circular opening,
9 cm dia.
R12
8
B
AA
Section A-A
B
View B-B
Briquette
Die of Briquetting
Machine
Briquette
Sheet Metal Box (59x45x52
59
52
Slider
Deflector
Plate
Briquette Exit
14
8
Smoke
Collection
Box
Top View
Handles
Conduit, 9∅
45
Perforated
guide plate
Figure 15. Final Design of the Smoke Collection Box
23

Conduit 9 cm Ø
Water seal
(2 cm wide x 2cm deep)
Deflector Plate
Connection to stove
primary air inlet
8
Hood
52
45
59
Figure 16. Isometric view of the smoke collection box
Figure 17. Smoke collection box - inner details
24

Figure 18. Smoke collection box - assembled view
Figure 19: Smoke Removal System in Operation
25

4. Operational Details
4.1 Effects of Biomass Pre-heating and Screw Speed on Briquetting
Energy Consumption
4.1.1 Introduction
A detailed analysis was done on the improved briquetting system to study the
effects of biomass pre-heating and screw speed on the energy consumption
of the briquetting process. The electrical coil heaters were used for die
heating since measurement of energy consumption is easier and more
accurate than if a biomass stove die-heater is used.
Two designs of briquetting screws were developed by BIT, for higher and
lower screw speeds. The design variation was only on the pitch of the screw,
which was wider in one design than the other. Experiments were conducted
on both the designs, to analyse their technical performance. This report
presents the experimental data, results and analysis.
4.1.2 Testing with the Wide-pitch Screw
First, the briquetting experiments were performed using the wider pitch screw
with and without biomass preheating. Ricehusk was used as raw material.
Tables 2 and 3 present the summary results of the experiments. Average
total electrical energy consumption by the briquetting machine without
biomass pre-heating was 0.20 kWh/kg at an average production rate of 85.4
kg/hr (Table 2) whereas, briquetting with biomass preheating consumed an
average of 0.178 kWh of electrical energy for each kg of briquettes produced
(Table 3).
Table 2. Briquetting with wider pitch screw, without biomass pre-heating
Run
Average
die
Production Electricity consumption (kWh/kg)
No. Temp. (°C) rate (kg/hr) Heater Motor Total
1 440 84.6 0.077 0.128 0.206
2 430 84.0 0.074 0.126 0.200
3 440 81.4 0.070 0.140 0.210
4 410 85.0 0.071 0.123 0.194
5 410 92.0 0.065 0.126 0.191
Average 85.4 0.0714 0.1286 0.2002
26

Table 3. Briquetting with wider pitch screw, with biomass pre-heating
Run
No.
Average
die
temp,
Avg.
biomass
temp,
Production
rate
Electricity consumption
kWh/kg
°C °C kg/hr Heater Motor Total
1 420 110 87.7 0.068 0.106 0.179
2 410 120 81.0 0.059 0.115 0.178
3 410 125 78.5 0.064 0.104 0.176
4 410 130 80.6 0.061 0.112 0.179
5 410 150 83.9 0.061 0.109 0.177
Average 82.34 0.0626 0.1092 0.1778
Average savings in the electrical energy consumption due to pre-heating
were 12.3% at heater and 15.1% at motor respectively. The average total
energy saving (electrical heater and motor) was about 11.2%.
For briquetting with preheating, the highest and lowest electrical energy input
to the system were found to be 0.18 kWh/kg and 0.17 kWh/kg of briquettes
produced, respectively. The highest and lowest electrical energy
consumption for briquetting without biomass preheating was found to be 0.21
kWh/kg and 0.19 kWh/kg of briquettes produced, respectively.
Production capacity was in the range of 80 - 90 kg/hour and good quality
briquettes could be produced at a die temperature of around 410-440°C.
Nevertheless, electrical energy was saved at the heater, motor and overall
system. When the die temperature was below 400°C, the quality of briquettes
produced was poor, as indicated by many cracks on the briquette surface.
4.1.3 Testing with the Close-pitch Screw
Briquetting experiments were also carried out with the screw having closer
pitch. The results of the experiments are presented in Table 4 and 5.
Table 4. Briquetting with close-pitch screw, without biomass pre-heating
Run Average die Production Electricity consumption (kWh/kg)
No. temp. (°C) rate (kg/hr) Heater Motor Total
1 390 91.6 0.060 0.112 0.172
2 390 87.7 0.071 0.113 0.184
3 365 85.9 0.071 0.110 0.181
4 380 88.3 0.070 0.110 0.180
Average 88.38 0.068 0.111 0.179
27

Table 5. Briquetting with close-pitch screw, with biomass pre-heating
Run
No.
Average
die
temp:
Average
biomass
temp:
Production
rate
Electricity consumption
kWh/kg
°C °C kg/hr Heater Motor Total
1 390 100 82.2 0.058 0.094 0.168
2 370 115 81.2 0.053 0.105 0.165
3 390 130 80.0 0.045 0.097 0.150
4 390 140 84.5 0.052 0.101 0.161
Average 82.0 0.052 0.099 0.161
In the case of closer pitch screw, average electrical energy savings at the
heater, motor, and overall system were 23.5%, 10.8%, and 10.2%
respectively. The production capacity was also slightly higher than that for the
wider pitch screw.
4.1.4 Performance of the Biomass Stove Die Heater
The briquetting machine was tested with a biomass stove die-heater as well,
the fuel for the stove being ricehusk briquette chips. The briquette quality was
very good at a temperature of around 320°C, in the beginning of the
operation. With the passage of time, the temperature gradually came down to
250°C and briquettes could still be produced only with a change of color of
briquette surface from black (at higher temperature) to gray (at lower
temperature). It takes around 35 minutes to bring the die temperature to
320°C, when briquetting could be started. The die temperature was noted to
often go out of control, irrespective of primary air supply control. It was found
that this was due to fuel blockade inside the pyrolysing chamber. An ash
scraper was then introduced, which could be operated at regular intervals
(once in 15-20 minutes) to clear the accumulated ash. The stove performed
remarkably well after this modification.
4.1.5 Conclusions
Experiments were conducted to investigate the effect of raw material pre-
heating, screw speed and screw pitch on the overall energy consumption.
Two screws - a wide-pitch screw and a close-pitch screw - were used in the
experimentation. It was observed that the close-pitch screw design performed
better than the wide-pitch screw. It consumed lower electrical energy for both
with and without biomass pre-heating compared to the other. Moreover, in
the case of close-pitch screw, the briquetting could be accomplished at
comparatively lower temperature. The following observations were made
while using ricehusk as briquetting raw material:
28

♦ Average savings in the electrical energy consumption due to
pre-heating were 23.5% at heater and 10.8% at motor
respectively, with close-pitch screw. The average total energy
saving was about 10.2%.
♦ The lowest electrical energy consumption for rice-husk was
0.172 and 0.150 kWh/kg of briquettes produced, without and
with preheating respectively.
The above results do not take into account the electrical energy consumed by
the motor, which feeds the raw material through the biomass pre-heater. If
that is taken into account, the net energy saving due to pre-heating ricehusk
may not be significant.
It was found that the moisture content of ricehusk should not be more than 7-
8% for smooth operation of the machine. At higher moisture levels, shooting
occurs from the die outlet while the briquetting operation was on, and
briquettes could not be produced both with and without biomass preheating.
4.2 Effects of Raw Material Type on Briquetting Energy Consumption
and Screw Life
4.2.1 Introduction
Experiments were conducted on the final design of the improved briquetting
system, integrating the biomass pre-heater, die-heating stove and smoke
removal system, to investigate the effect of raw material type on the
performance of the integrated system. This section presents the test results
and operating parameters of the improved briquetting system based on the
experiments conducted.
A set of experiments were carried out without pre-heating the biomass, and
another set with pre-heated biomass, to measure the energy savings due to
pre-heating as well. Other parameters such as screw speed and die
temperature were maintained constant in both cases, to the possible extent,
for a consistent comparison. Biomass stove was used in both the cases for
die heating.
Two sets of experiments were conducted: (1) with ricehusk, and (2) with
mixed raw materials, of ricehusk and sawdust, at 1:1 ratio, to investigate the
energy consumption of the briquetting process as well as the life of
briquetting screws.
29

4.2.2 Ricehusk as raw material
The briquetting machine was run at three different screw speeds, 370 rpm,
465 rpm, and 560 rpm, and its performance evaluated. Tables 6 and 7
present the experimental results at a screw speed of 370 rpm, with and
without pre-heating.
Table 6. Briquetting without preheating. Screw speed: 370 rpm
Expt. No. Production
rate (kg/hr)
Total energy
consumption
(kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 68.5 0.107 9.6 260
2 64.8 0.103 9.3 237
3 68.0 0.103 9.1 248
Average 67.1 0.104 248
Table 7. Briquetting with preheating. Screw speed: 370 rpm
rate (kg/hr)
Total energy
consumption
(kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 63.0 0.121 9.3 266
2 66.0 0.088 9.3 273
3 68.9 0.137 9.7 226
Average 66.0 0.115 255
It may be noted that the total electrical energy consumption of the briquetting
process actually increased with pre-heating the ricehusk, indicating a
possible mis-match between the screw speed and optimum loading of the
electrical motor. The screw speed was therefore increased to 465 rpm, and
the experiments were continued. Tables 8 and 9 present the results of the
experiments.
rate (kg/hr)
Total energy
consumption
(kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 66 0.152 9 224
2 70 0.133 9 251
3 84.5 0.116 11 253
Average 73.5 0.133 243
30

rate (kg/hr)
Total energy
consumpn.
(kWh/ kg)
Moisture
content
(%)
Average Die
Temp. (°C)
1 73.0 0.131 8.5 253
2 76.3 0.133 6.1 248
3 69.6 0.115 9.1 271
Average 73.0 0.126 257
At a screw speed of 465 rpm, the total electrical energy consumption slightly
decreased with pre-heating the ricehusk. The decrease was however not
significant. Also, there was a general increase in energy consumption at this
screw speed, both with and without pre-heating, when compared to screw
speed of 370 rpm. No significant difference was noted in the production rate.
The screw speed was further increased to 560 rpm and the results analysed.
Tables 10 and 11 present the results of the experiments at 560 rpm.
rate (kg/hr)
Total energy
consumption
(kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 78.0 0.131 11.0 237
2 80.6 0.150 9.0 238
3 87.4 0.130 9.5 230
Average 82.0 0.137 235
Expt.
No.
Production
rate (kg/hr)
Total energy
consumption
(kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 79.6 0.113 8.7 230
2 73.7 0.135 9.2 225
3 61.0 0.163 8.6 246
Average 71.4 0.137 234
Figure 20 illustrates the relationship between the screw speed, production
rate and energy consumption, with ricehusk as raw material.
31

Screw Speed Vs Production Rate and Power
Consumption(100% rice husk)
40
50
60
70
80
90
100
370 465 560
Screw speed (rpm)
Productionrate(kg/hr)
0.000
0.020
0.040
0.060
0.080
0.100
0.120
0.140
0.160
Powerconsumption
(kWh/kg)
Production rate Power consumption
(a) Without pre-heating
Screw Speed Vs Production Rate and Power
Consumption (100%Rice husk)
40
50
60
70
80
90
100
370 465 560
Screw speed (rpm)
0.100
0.105
0.110
0.115
0.120
0.125
0.130
0.135
0.140
Powerconsumption
(kWh/Kg)
(b) With preheating
Figure 20. Screw speed Vs. Production Rate and Specific Energy Consumption,
with ricehusk as raw material
Energy Consumption:
With ricehusk as raw material, the energy consumption figures with and
without pre-heating show inconsistent results, with no direct correlation
between energy consumption, production rate and screw speed.
While pre-heating results in a slight reduction in energy consumption by the
electrical motor driving the screw, the saving, in most cases, is more than
offset by the energy consumed by the motor driving the conveyor screw in
the biomass pre-heater. Thus, the experimental results so far indicate that
pre-heating ricehusk does not seem to offer definite energy saving
advantages.
Briquetting Screw Life:
It has been noted that a higher briquetting screw speed reduces the screw
life and therefore is not a preferred option to increase production rates. Screw
life was found to be highest at a screw speed of 370 rpm while it was lowest
at 560 rpm. Pre-heating the ricehusk seems to decrease the screw life by
about 25% for screws made of mild steel, and tempered in oil.
Briquette Quality:
Briquette quality is inspected visually, and judged in terms of the
smoothness, cracks, and colour of the briquette surface. Without pre-heating,
the quality of ricehusk briquettes is generally better than that with pre-
heating. This may be due to drying of the ricehusk during the pre-heating
process to below a minimum level of moisture, which is required for good
binding of the ricehusk particles.
32

It was found that fresh ricehusk is a better raw material than that which is
kept in storage for prolonged periods, in terms of briquette quality, production
rate and energy consumption. The ‘old’ ricehusk releases a powdery dust
around the machine during the briquetting process, which may be harmful if
inhaled. Also, ‘old’ ricehusk produces low quality briquettes, with cracked
surfaces and small pieces of briquettes.
4.2.3 Mixed raw materials, of ricehusk and sawdust, at 1:1 ratio by
volume.
Ricehusk and sawdust were mixed at 1:1 ratio by volume, and the briquetting
experiments were continued. Tables 12 and 13 present the results for a
screw speed of 370 rpm while Tables 14 and 15 furnish the test results at a
screw speed of 465 rpm.
rate (kg/hr)
Total energy
consumpn. (kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 89.5 0.0849 10.5 225
2 98.2 0.0678 6.85 241
3 93 0.0785 8.8 229
Average 93.6 0.0771 232
rate (kg/hr)
Total energy
consumpn. (kWh/ kg)
Moisture
content (%)
Average Die
Temp.(°C)
1 81.1 0.0877 5.9 282
2 74.33 0.0867 6.6 264
3 72 0.095 5.6 258
Average 75.81 0.0898 268
rate (kg/hr)
Total energy
consumpn. (kWh/ kg)
Moisture
content (%)
Average Die
Temp. (°C)
1 66.4 0.0864 8.6 258
2 87.69 0.0877 9 211
3 96 0.0778 10 225
Average 83.36 0.0839 231
33

rate (kg/hr)
Total Energy
consumpn. (kWh/kg)
Moisture
content (%)
Average Die
Temp.(°C)
1 100.5 0.0955 8.5 263
2 99.8 0.0804 7.6 247
3 98 0.1008 8.4 235
Average 99.43 0.0922 248
Figure 21 illustrates the relationship between the screw speed, production
rate and energy consumption, with mixed raw material, of ricehusk and
sawdust, at a ratio of 1:1 by volume.
Screw speed Vs Production Rate and Power Consumption
(50% rice husk-50% sawdust)
40
50
60
70
80
90
100
370 465 560
Screw speed (rpm)
0.072
0.074
0.076
0.078
0.080
0.082
0.084
0.086
Powerconsumption
(kWh/kg)
(a) Without pre-heating
Screw speed Vs Production Rate and Power
Consumption (50%rice husk-50%sawdust)
40
50
60
70
80
90
100
370 465 560
Screw speed (rpm)
0.088
0.088
0.089
0.089
0.089
0.089
0.089
0.090
0.090
0.090
Powerconsumption(kWh/kg)
(b) With preheating
Figure 21. Screw speed Vs. Production Rate and Specific Energy
Consumption, with mixed raw material, of ricehusk and sawdust.
Energy Consumption:
Mixing sawdust with ricehusk has resulted in an overall reduction in energy
consumption by the briquetting process, when compared to pure ricehusk as
raw material. While the specific energy consumption without pre-heating
dropped by about 25%, energy consumption with pre-heating also came
down by about 22%, for a screw speed of 370 rpm. Similar trend was also
noted for the screw speed of 465 rpm.
Briquetting Screw Life:
In general, the screw life with the mixed raw materials was significantly
higher compared to that with pure ricehusk. A 25% increase in screw life was
34

realised for a screw speed of 370 rpm, while the increase was 60% for a
screw speed of 465 rpm.
Briquette Quality:
Unlike in the case of pure ricehusk, pre-heating offers better quality
briquettes with the mixed raw materials. The production rate is lower at 370
rpm, while it is higher at 465rpm.
4.2.4 Conclusions
Several experiments were carried out to evaluate the effect of raw material
type on the performance of the integrated biomass briquetting system,
consisting of the biomass pre-heater, die-heating stove and smoke removal
system. Results indicate considerably less energy consumption when mixed
raw materials (ricehusk and sawdust, at 1:1 ratio by volume) are used in
comparison with pure ricehusk as raw material. Significant reductions in
electrical energy consumption have been realised with the introduction of the
die-heating stove to replace the electrical coil heaters. The smoke recycling
system has also improved the working environment at the briquetting plant,
by significantly reducing smoke in the vicinity.
35

40
About RETs in Asia …
The project ‘Renewable Energy
Technologies in Asia: A Regional Research
and Dissemination Programme’ (RETs in Asia)
was initiated in 1997 with the broad aim of
contributing to sustainable development of
the Asian region through promoting the
utilization of renewable energy resources for
meeting indigenous energy needs of the
countries in Asia. The project promoted the
diffusion of selected renewable energy
technologies in a group of six Asian countries
through a regional research and
dissemination program. Regional approach
and institutional co-operation remained in
the forefront of strategies adopted by the
project. Photovoltaics, solar and biomass-
based drying, and biomass briquetting are
the technologies selected for promotion. The
project is supported by the Swedish
International Development Cooperation
Agency (Sida) and coordinated by the
Asian Institute of technology (AIT).
For further information, please contact:
mme
ology
nd
c.th
Prof. S.C. Bhattacharya
Coordinator, RETs in Asia Progra
Asian Institute of Techn
P.O. Box 4, Klong Luang
Pathumthani 12120, Thaila
Tel: +66-2-524 5403
Fax: +66-2-524 5439
E-mail: bhatta@ait.a
A publication of RETs in Asia
http://www.retsasia.ait.ac.th/

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