This document summarizes air pollution control technologies for the sugar cane industry. It discusses increasing emission standards that require technologies like wet scrubbers and electrostatic precipitators. It analyzes bagasse fly ash composition and compares control devices. Technologies like multicyclones and spray towers can achieve emissions below 120 mg/Nm3, while scrubbers and precipitators can achieve lower emissions. Larger boiler capacities decrease the annual cost of precipitators.

1. AIR POLLUTION CONTROL IN THE SUGAR CANE INDUSTRY
Electo Silva ~ o r a '
Istvan Hervas ~ i t i v a ~
' Escola Federal de Engenharia de Itajubi DMEIIEM
Av. BPS 1303, CP 50, Itajubi-MG 37500-000 Brazil
ABSTRACT
A review about air pollution control technologies for the cane sugar industry, including final
emissions and efficiencies is presented. The tendency of the emission standards to beconze more
rigorous, forcing the use o f wet scrubbers and electrostatic precipitators is mentioned. An analysis
of the bagasse fly ash granulometric conzposition is presented, highlighting the existence of a fine
and a coarse fly ash component. Finally, the results of a techno-economical analysis of different
contvol technologies a/*epresented.
Keywords :Air pollution, bagasse boileras, sugar cane industry.
INTRODUCTION
A radical solution to global environmental problems could be the intensive use of renewable
energy and related systems that can emerge as fossil fuels substitutes. With the use of advanced
technologies biomass becomes one of the most notable renewable fuels, because it will be possible
in the near future to produce bio-fuels and to generate electric power on a commercial scale at
competitive costs.
/
However, biomass is not free of environmental impacts and the determination of its impacts is $he
subject of various research projects around the world. Cane bagasse is a lignocellulosic by-product
of the sugar industry and one of the most plentiful biomass residues available in the world. Cane
bagasse can be considered a relatively clean fuel with its major environmental impact being
particulate emission. However NO, and PAH - polycyclic aromatic hydrocarbons must be
considered as well. With the aim to increase electricity cogeneration in the sugar industry, a strong
investment process is under way in Brazil and other sugar producer countries. With this, measures
must be implemented to avoid considerable environmental damages.
The purpose of the paper is to discuss the state-of-the-art of air pollution control technologies in
the cane sugar industb. Recent publications (Silva and Olivares 1995, Silva 1997) were reviewed
and completed yith' data about the techno-economical analysis of different bagasse boilers
particulate collection systems. Information about air pollution control measures in recent large
cogeneration 'was included.
,'
EMISSION STANDARDS
In 1991 Australian and South African established particulate emission standards for bagasse boilers
that allowed maximum concentrations of 450 mg/Nm3, while in other sugar cane regions such as
Hawaii allowed emission limits were higher - 870 m g / ~ m 3
(Echavarria and Whalen, 1991).
Presently in South Africa for new boilers, the emission limit is 120 mg/Nm3 (Magisiner 1996). In
1992, the Environment and Forest Ministry of India approved the following emission standards :

2. for inclined grate boilers - 250 mglNm3, for spreader-stockers boilers - 800 mgINm3 (Cordovez
1997). Alternatively, in Mauritius and Malaysia the particulate emission standard is 400 mglNm3.
For considerations about project funding in the sugar cane industry the World Bank recommends
the particulate emission to be lower than 100 mglNm3, in some cases for small boilers the allowed
value is 150 ~ng/Nm"~orld Bank 1997).
In Brazil the Environmental Agency of the Sao Paulo State - CETESB (CETESB 1986) carried
out a study about the value to be included in bagasse boilers particulate emission standards, and
finally proposed 120 r n g l ~ m ~ .
According to CETESB studies a clear plume corresponds to
particulate concentrations of about 85 mg/Nm3. A final version of these emission standards must
be approved shortly. Table 1 presents the emission standard proposal presented by CETESB for the
State of Sao Paulo (Pestelli 1997). As observed the tendency for the emission standards is to be
each time more rigorous. For example, in large-scale cogeneration projects the final emission being
considered is 50 mg/~m3.
Table 1 : Particulate emission standards proposal for bagasse boilers in Brazil.
Sugar Mill Location Standard
Reserved Area New installations not permitted.
Old Boilers. 701ng/Nm3
Urban Area or in process
of urbanization New Boilers
Old Boilers
Rural Area New Boilers 100mg/N~n3
Old Boilers 120mglNm3
Emission factors mean the quantity of pollutants emitted by each product unit or by each energy1
fuel consumed unit. So, knowing the total amount of products and/or the total fuel consumption it
is possible to calculate the total emissions of the analyzed plant or equipment., The EPA has
published a set of bagasse boiler emission factors (Table 2) expressed as g of pollutant 1 kg of
generated steam or in grams of pollutant1 kg of burned bagasse (EPA 1995).

3. Table 2- Emission factors for bagasse boilers (EPA, 1995)
Pollutant gkg of steam g/kg of bagasse
Particulate matter
(TPS)
- Without coiltrol
- Controlled
Cyclones
Wet scrubbers
PM-10
- Controlled
Wet scrubbers
COz
- Not controlled
NO,
- Not controlled
PAH - Polycyclic
aromatic hydrocarbons
- Not controlled 2,5 5,0
FLY-ASH GRANULOMETRIC COMPOSITION
The fly-ash granulometric composition is one of the input data used for particulate control
equipment design calculations. Bagasse ash granulometric composition published data differ
considerably by authors, probably caused by dependence on cane preparationfsystem, combustion
technology (pile or suspension burning) and bagasse characteristics. So available data shown in
figure 1 can be reduced to two granulometric composition curves, one corresponding to fine
volatile ash (higher heavy line) and the other to coarse volatile ash (lower heavy line). Another
important parameter to be considered is the particulate load in exhaust gases. For most
applications 5000 mg/Nm3 is considered an average value.
Partlcle s i r e (rn icrons)
+
1979 CSlR SOUTH AFRICA 1972 AUSTRALIA
-+-1979 CSlR SOUTH AFRICA -
&
1972 AUSTRALIA
-FINE -COARSE
Fig.1 : Granulometric composition of bagasse fly-ash according to different sources.

4. PARTICULATE CONTROL DEVICES FOR BAGASSE BOILERS
Configurations used in the sugar industry for particulate control devices are presented in figure 2.
Final emission values are the mean ones for different sugar mills. As shown it is not possible to
reach emissions lower than 120 m g / ~ m 3
without tlie utilization of scrubbers, electrostatic
precipitators or combined particulate control technologies. Table 3 shows a qualitative comparison
of the main particulate control devices.
Table 3 - Qualitative comparison of particulate separators
Separator Advantages Disadvantages
Cyclones - Low cost - Low efficiency, mainly for
- High temperature operation small particles (5 to 10 pm)
- Low maintenance cost
(lack of moving parts)
/
Wet scrubbers Can be used for inflammable - Corrosion
and explosive particulates.
Particulate removal and - Secondary pollution
absorption at tlie same time.
Variable removal efficiency. (Produce a liquid effluent
that require treatment)
Gas cooling.
Electrostatic precipitators High efficiency.
Can treat great gas volumes
with a small pressure drop.
Dry and wet separation.
Wide range of operational
temperature.
High investment cost.
Low flexibility.
Great space needs for
installation
Low operation costs.

5. a) Multicyclone
b) Spray Tower
c) Electrostatic Precipitator
d) Multicyclone +ElectrostaticPrecipitator
Fig.2 : Particulate emission control configurations for bagasse boilers

6. a) Wet scrubbers.
Figure3 shows the most frequently used constructions for wet scrubbers: perforated tray,
spray towers and Ventury scrubbers. Its main design and operation parameters are presented
in table '4. The "cut diameter" parameter shows the particle diameter for which the
separator operates with a 50 % eff~ciency.
I PERFORATED TRAY
SCRUBBER
I CLEAN GAS
SPRAY TOWER
CLEAN GAS
-
WATER
*/IN*
DIRTY GAS I
WATER I
EXIT t CLEAN GAS I
Fig.3 : Particulate emission control configurations for bagasse boilers
Table 4 - Wet scrubbers design and operation parameters.
Parameter Perforated trays Spray tower Ventury scrubber
scrubber
Cut diameter (pm) 1.0 > 1.0 0.1 - 0.4
Gas velocity (rnls) 1.0 1.0 - 1.8 40 - 150
Pressure drop (kPa) 2 - 3 0.2 - 2 3 - 20
Water gas ratio (l/m3) 0.26 - 0.39 0.05 - 10 0.5 - 5
Power consumption 52 - 130 14 - 52 78 - 312
(kWh/1000 m3)
A spray tower type wet scrubber for a 80-120 t h steam capacity boiler ha8 a cost in the
range $US 0.3-0.6 million. A multicyclone system for the same steam capacity boiler costs
about $US 100-1.50 thousand.
b) Electrostatic precipitators.
Presently for large cogeneration projects in the sugar industry, it is common to use
electrostatic precipitators as particulate control device. In the Okeelanta Sugar mill near
South Bay, in Florida, a 70 MW cogeneration plant was built, and began its commercial
operation in 1995. Particulate control is achieved by electrostatic precipitators, with a three
fields construction, designed for a final emission of 46 mgkWh. The precipitator has spiral
type discharge electrodes and an efficiency of 99.21 % (ABB 1994). In biomass burning
boilers, the carbon ash content is high, increasing the fire risk and the possibility of the
precipitator damage.

7. Usually an electrostatic precipitator for an 80 tlh steam capacity boiler has an installed cost
in the range $US 1.0-1.6 million, depending on local taxes, the availability of devices for
elevated works and the local personnel experience.
Another example of electrostatic precipitator is the Bois-Rouge sugar mill in Reunion Island
that has a 60 MW cogeneration plant (two 30 MW units). A ~nulticyclonesystem is
installed as a pre-cleaning device before the precipitator. For a 3000 m g l ~ m 3particulate
concentration in exhaust gases, the separator reduces final emission to 100 m g / ~ m ~ ,
when
the plant operates with bagasse, and tn 5
1
1 xg,'?;m3 when operating with mineral coal. In
this plant the electrostatic precipitator has only two fields, which, according to Magasiner
(1996), is enough to reach the emission limits. Field quantity defines t h e separation
efficiency, so for 1 pm particles with one field the efficiency is of about 90%, with two
97%, and with three approximately 99 %.
The core separator.
Core separator is a new technology for particulate separation, based on centrifugal effect.
Core separator efficiency is higher than the multicyclone one, due to the fact that separation
and collection processes occurs in various elements (figure 4), thus avoiding the particulate
carry-over usually happening at the cyclone exit section. The core separator cost is
approximately three times higher than the same capacity in a multicyclone. However, for 10
pm particles, the core separator and multicyclone efficiencies are 94 % and 20 %
respectively (Wysk et al. 1996). As seen, core separator efficiency is as high as a ventury
scrubber. An assessment carried out by the core separator manufacturer, considering bagasse
volatile ash granulometry, density and other characteristics resulted in a final estimated
emission of 100 mg/Nm3. Measurements in a demonstration plant are necessary to confirm
this prediction.
DlR
N GAS I
e SEPARATOR
CLEAN
1- GAS
SOLIDS 0
Figi4 : Operating principle of the core separator (Wysk et al. 1996)
TECHNOECONOMICAL ANALYSIS OF DIFFERENT PARTICULATE CONTROL OPTIONS
A te~hnoeconomicalanalysis was carried out to compare different options for bagasse boilers
particulate separators. The specific annual cost of particulate separation measured in $/(t/h) or $1
~ m ~ ,
and also the specific investment and the specific operational cost were calculated and used
as a tool in the analysis. Three boiler capacities were considered for the calculations : 40, 80 and

8. 120 t/h, the typical commercial range for bagasse boilers. A flue gas temperature of 250°C and an
excess of air of 45% were assumed. In the calculations, tlie fine volatile ash granulometric
composition from figure 1 was considered.
In figure 5, the relationship between tlie specific annual cost, expressed as US$/(t/h) year, and the
boiler capacity are presented. It is shown that electrostatic precipitator and venturi scrubbers Iiave
the greater annual specific cost, whicli decreases with the increase in the boiler capacity. It is
observed also that electrostatic precipitator specific annual cost has the tendency to reach that of
ventury scrubber values for steam capacities of about 120 tlh. On the other hand, ~nulticycloneand
spray tower specific annual cost remains approximately constant.
/+
Spray Tow er
I
J*ventury Scrubber 1
20 40 60 80 100 120 140
Boiler Capacity tlh
Source date for fig.5 specific annual cost expressed as $/(t/li). year vs. Boiler capacity
Tlh Multicyclone Spray Tower Ventury Electrostatic
Scrubber Precipitator
Fig.5 : Influence of the boiler steam capacity on the particulate control equipment
specific annual cost expressed as $(t/h) year.
CONCLUSIONS
The observed tendency is for the bagasse boiler particulate emission standards to be more rigorous
with time, whicli forces the introduction of new technologies in the emission control practice.
Based on available bibliographic data on bagasse volatile ash granulometric composition, it is
possible to define two typical compositions: a fine and a coarse one.
Electrostatic precipitators Iiave the higher annual specific costs compared with other particulate
separation technologies: this decreases for large boiler capacities, making them more suitable for
utilization.

9. Spray tower wet scrubbers are the most widespread technology for particulate separation in bagasse
boilers. Further improvement must be considered for the reduction in water consumption and
greater operational efficiency.
The construction of a core separator demonstrative unit can be considered to confirm expected
final emissions lower than 100 mg/Nm3.
REFERENCES
ABB. (1994). Proposal for electrostatic precipitator - Okeelanta Cogeneration Project. ABB
Environmental Systems Division.
CETESB.(1986). ElnissIo de material particulado proveniente da combust30 de bagaqo de eana ern
caldeiras (proposta para o estabelecimento de padrao).
Echavarria, M. and Whalen, S. (1991). Air quality and processing sugarcane. Proceedings of the
International Conference on Energy from Sugarcane: Progress and Pvospects, Milo, Hawaii,
pp. 283-314.
EPA. (1995). Compilation of air pollutant factors AP-45.
Cordovez, M . (1997). Personal communication.
Magasiner, N . (1996). Personal communication.
I Pestelli, A. (1997). Personal communication.
I
Silva, E. (1997). Control de la contamination del aire en la industria azucarera. Document
prepared for the LAICA International Seminac Costa Rica.
Silva, E. and Olivares: E. (1995). Bagasse suspension burning and air pollution", International
Sugar Journal, ,Vol. 94, p. 683-684.
Wysk, R.S. Easom, B.H. and Litke, M. (1996). New particulate control technology for energy
production systems. Paper: 96-RA105A.02, Air and Waste Management Association, 89th
Annual Meeting and Exhibitions.
World Bank. (1997) P~llutionPrevention and abatement. Part 111.
1

10. CONTROL DE CONTAMINACI~NDEL AIRE EN LA INDUSTRIA AZUCARERA
Electro Silva Lora
Istvan Hervas Jativa
Escuela Federal de Ingenieria de Itajuba
DMEIIEM
Av.BPS 1303, CP 50, Itajuba-MG 37500-000, Brasil
RESUMEN.
Se present6 una revision acerca de la tecnologia de control en contaminaci6o del aire por la
industria azucarera, emision final y eficiencia. La tendencia de las normas de emisiones a
convertirse en normas mas rigmosas, forzando el uso de torres humedas para el lavado de gases
y precipitadores electrotaticos, es comentado. Se realizo analisis de la co~qposicjongranulometrica
del materia1:volatil de la ceniza del bagazo, y se detennino que este posee ceniza volatil de tipo
fina y gruesa. Finalnlente, se present6 el resultado de un analisis tecno-economico de diferentes
tecnologias de control.
Palabras claves : Contamination del aire, calderas de bagazo, industria de caiia de azucar
ES Eora
RESUME
On presente une revue du contrble de la pollution de l'air, des emissions et des efficiences dans
l'industrie sucriere. En generale les norlnes deviennent plus rigoureuses et on doit se servir de
plus en plus de depoussiereures et de precipitateurs electrostatiques on a analys6 la bagasse pour
les cendres volatiles et on commente sm ces resultats. Finalement on commente sur des points
concernant le coOt du contrble.