FCC Bagasse White Paper for MACT Subcategory.doc 

Bagasse-Fired Boilers Should Be Regulated in a Separate Subcategory 

Under the Boiler MACT Rules 

Submitted by 

Golder Associates Inc. 

and 

C. David Cooper, PhD, PE, QEP, 

Professor of Environmental Engineering 

University of Central Florida 

On behalf of the 

Florida Sugar Industry1

March 30, 2009 

I. Introduction

The U.S. Environmental Protection Agency (EPA) is currently developing new Boiler Maximum 

Achievable Control Technology (MACT) rules, which will regulate the bagasse-fired boilers operated by 

the Florida Sugar Industry. Accordingly, the Florida Sugar Industry is providing this white paper to EPA 

to explain why bagasse-fired boilers should be placed in a separate subcategory under the new Boiler 

MACT rules promulgated pursuant to Section 112 of the Clean Air Act (CAA). Bagasse is a unique 

biomass fuel, with unique chemical and combustion characteristics, which is burned in unique boilers. 

Since the very beginning of its operations in the United States, the sugar producing industry has used 

bagasse as the primary fuel for its boilers. Bagasse is burned in these boilers to generate the steam and 

electricity that power the operation of the sugar mills. Bagasse is created as a co-product of the sugar 

manufacturing process, when sugarcane undergoes grinding to extract the sugar in the cane. The 

bagasse-fired boilers are specifically designed to process (burn) bagasse and they are wholly integrated 

into the operations of the sugar mills. 

EPA has the statutory authority to create a subcategory for bagasse-fired boilers pursuant to 

Section 112 of the CAA. EPA already has created various subcategories in EPA’s MACT rules 

because EPA has recognized that a facility’s emissions can be significantly affected by the facility’s 

fuel, design, size, age, and use. EPA should create a subcategory for bagasse-fired boilers because 

 

1

 The Florida Sugar Industry is comprised of sugarcane processors located in south Florida. These processors 

harvest sugarcane to produce raw and/or refined sugar. The Florida Sugar Industry operates industrial boilers 

fired primarily by bagasse, which is a co-product of the sugarcane processing operations. Wood and other 

agricultural materials, as well as very limited amounts of fossil fuel, may also be burned in the Florida Sugar 

Industry’s boilers. The Florida Sugar Industry also is coordinating the submittal of this paper with a sugarcane 

processor located in Hawaii. 
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bagasse is a unique fuel, bagasse-fired boilers are unique in their design, and these unique 

characteristics significantly affect the boilers’ operations and emissions. 

Creating a subcategory will help ensure that the MACT emissions standards for bagasse-fired boilers 

are based on the performance of “similar sources,” as required by the CAA. Conversely, EPA will 

not be able to establish an appropriate MACT floor for bagasse-fired boilers if bagasse-fired boilers 

are regulated in a MACT category that includes other types of solid fuel-fired or biomass-fired 

boilers. 

II. Background Information on Sugarcane and Sugarcane Processing

The following discussion summarizes some basic information about sugarcane, sugarcane processing, 

and bagasse. Sugarcane is a member of the grass family, and is grown in numerous countries around 

the world, including the United States, China, India, Cuba, Venezuela, Indonesia, Australia, and many 

more. The cane grows year round, but typically the harvesting and milling operations occur over just 

a few months. In the U.S., the sugar mills typically run 24 hours per day during the milling season. 

The milling operations usually are completed in 3 to 4 months in Louisiana, 4 to 6 months in Florida, 

and 9 months in Hawaii. 

The tops of the sugarcane plants and most of the leaves are removed in the field and then the cane is 

brought to the mills in large trailers by truck or railcar. The typical composition of the sugarcane is 

presented in Table 1, below. 

TABLE 1 

TYPICAL SUGARCANE COMPOSITION (FROM VARIOUS LITERATURE SOURCES) 

Constituent Percentage 

Water 75 

Sugars (mostly sucrose, with some glucose and fructose) 12 

Fiber/Pith (mostly cellulose, with some lignins) 12 

Other (mostly salts and soil minerals, with some organic compounds) 1–2 

In the sugar mill, the cane is first cut into smaller pieces.2

 Next the sugarcane is subjected to grinding 

and washing, which may occur 4 to 8 times in a sugar mill “tandem”. This process extracts as much 

as possible of the sugarcane juices (primarily sucrose) from the cane. This process also removes 

some, but not all, of the soil that may be carried with the sugarcane from the fields. The sugarcane 

juices are then clarified and evaporated to produce raw sugar crystals. 

Bagasse is the traditional name given to the cellulosic fiber and pith that remain after the sucrose juice 

has been extracted from a sugarcane stalk during the milling process. The composition of the 

biomass is changed in this process of producing bagasse from sugarcane. The typical moisture 

content in bagasse is about 50 percent, sugars are about 1 to 2 percent, and fiber content is about 

50 percent. 

The heat needed to operate the evaporators in the sugar production process, and the power needed to 

operate the mill equipment, are obtained by burning the bagasse in boilers that are specifically 

designed for the simultaneous drying and combustion of bagasse. The design of a sugar mill always 

includes the complete integration of the bagasse-burning boilers with the rest of the mill. The bagasse 

generated in the mill is normally sent directly to the boilers as fuel. The boilers produce steam, which 

 

2

 In Hawaii, but not Florida, the cane is washed in a cane “cleaner” prior to cutting. The cleaner is used to 

remove some of the extraneous soil that adheres to the cane when it is brought in from the fields. 
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in turn is used in the mill. The steam also is used in steam turbine generators to produce electricity 

for the mill’s internal consumption. In many locations, excess electricity is fed back into the local 

power grid. 

This process of producing bagasse as a co-product of the sugar production process is unique and 

differs from the process used to produce other biomass fuels. For example, most woody biomass is 

normally only cut or chopped into smaller pieces; it is almost never crushed, ground, or washed. The 

heating value of woody biomass is typically 4,500 to 5,000 British thermal units per pound (Btu/lb) 

as-fired. The moisture content of woody biomass ranges between 20 percent and 50 percent. 

Rice is first dried to about 12 percent to 14 percent moisture, then passed through cleaners that 

remove the impurities from the fields. The rice is then de-hulled, and these hulls can be burned as 

fuel. However, neither the rice nor the hulls are ground or washed. Consequently, the hulls do not 

undergo a change in composition and their moisture content is very low. The heating value of rice 

hulls is about 6,000 Btu/lb as fired, which is much higher than that of bagasse. For these reasons, 

burning rice hulls in a boiler produces a much hotter flame and therefore much different emissions 

compared to bagasse, particularly for particulate matter (PM), carbon monoxide (CO), and organics. 

Peanut processing is similar to rice processing, and produces peanut shells that can be burned. 

However, the shells are not washed, they have not undergone a change in composition, and the 

moisture content of the peanut shells is very low. 

Normally, bagasse generated in the mill is sent directly to the boilers as fuel, without intermediate 

storage. Thus no blending or further processing of the bagasse takes place prior to combustion in the 

boilers. This characteristic of bagasse boilers differs from other biomass-fired boilers. 

III. EPA’s Statutory Authority to Create Subcategories

Section 112 of the CAA contains the statutory requirements for establishing emission standards based 

on the use of MACT. Section 112(d)(1) of the CAA expressly authorizes EPA to establish 

subcategories: 

The [EPA] Administrator shall promulgate regulations establishing emission 

standards for each category or subcategory of major sources... The Administrator 

may distinguish among classes, types, and sizes of sources within a category or 

subcategory in establishing such standards... 

EPA has exercised this statutory authority in many prior rulemaking proceedings. For example, EPA 

previously created subcategories when EPA set the MACT emissions standards for industrial boilers 

and electric utility steam generating units. EPA created these subcategories because EPA wanted to 

account for the differences between source types, the types of fuel used, the size of the regulated 

units, and other factors. In EPA’s “Notice of Regulatory Finding on the Emissions of Hazardous Air 

Pollutants from Electric Utility Steam Generating Units” [Federal Register (FR), December 20, 

2000], EPA stated: 

In developing standards under Section 112(d) to date, the EPA has based subcategorization 

on considerations such as: the size of the facility, the type of fuel used at the facility, and the 

plant type. The EPA may also consider other relevant factors such as geographic conditions 

in establishing subcategories. 
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In EPA’s 2004 MACT proposal for electric utility steam generating units (Utility MACT) 

(FR, January 30, 2004), EPA stated that it has broad discretion to create subcategories based on these 

same criteria (i.e., size of the facility, type of fuel used, and plant type) [p. 4664]. In addition, “EPA 

also is free to consider other relevant factors, such as geographic factors, process design or operation, 

variations in emission profiles, or differences in the feasibility of application of control.” [p. 4664]. 

In the Utility MACT, EPA exercised its discretion by proposing to create five separate subcategories 

for coal-fired electric utility boilers [p. 4666]. Four of the proposed subcategories were based on the 

type of coal burned (i.e., bituminous/anthracite, sub-bituminous, lignite, and coal refuse). The fifth 

subcategory was based on the type of process used by the utility to convert coal into electricity (i.e., 

integrated gasification combined cycle technology). 

Section 112(d)(3) of the CAA indicates that the MACT floor for new sources shall be established by 

determining “the maximum degree of reduction in emissions that is deemed achievable for new 

sources in a category or subcategory”. The MACT floor for new sources must be based on the 

emissions achieved by “the best controlled similar source, as determined by the Administrator.” 

[Section 112(d)(3)]. The EPA’s regulations define the term “similar sources” to mean: 

“a stationary source or process that has comparable emissions and is structurally similar in 

design and capacity to a constructed or reconstructed major source such that the source 

could be controlled using the same control technology.” [40 CFR 63.41] 

When the definition of “similar source” is read in conjunction with the mandate in Section 112(d)(3), 

which requires EPA to evaluate similar sources when setting MACT standards, it is clear that EPA 

has the discretion to establish MACT standards and MACT categories that account for the differences 

in design and capacity between sources. Indeed, the use of subcategories is necessary to ensure that 

EPA’s MACT standards are only applied to groups or classes of sources that have similar design, 

operational, and performance characteristics for controlling HAP emissions. 

Therefore, when setting MACT standards for industrial boilers, it appears that EPA is authorized to 

distinguish between: 

 (a) general classes or types of fuels (e.g., solid, liquid, and gaseous fuel); 

 (b) specific classes or types of solid fuels (e.g., coal, wood, bagasse, and other biomass); 

 (c) types of boilers (e.g., spreader stoker, fuel cell, and fluidized bed); 

 (d) sizes of boilers; and 

 (e) geographical locations of the boilers. 

Determining the appropriate source categories and subcategories is a critical first step when EPA sets 

the MACT floor for biomass-fired boilers, because there are a wide range of combustion processes, 

control technologies, unit sizes, and fuels consumed by biomass-fired boilers. These factors can have 

major impacts on a boiler’s performance and emissions profile. 

As noted above, the Florida Sugar Industry believes the MACT standards for industrial boilers should 

include a category for biomass-fired boilers, and a subcategory for bagasse-fired boilers. This 

category and subcategory are necessary to ensure that EPA only compares the performance of 

“similar sources” when EPA sets the emissions standards for bagasse-fired boilers. Boilers that burn 

bagasse should be in a separate category than boilers that burn wood or other types of biomass, as 

explained below. 
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IV. Characteristics of Bagasse and Bagasse Boilers

A. Key Characteristics of Bagasse Fuel 

Bagasse has the following key characteristics, which collectively make bagasse unique and much 

different than other types of biomass fuel: 

 Bagasse is a co-product of an industrial process, wherein sugarcane is 

crushed and washed, and water displaces sucrose within the sugarcane fiber; 

 The industrial process alters the configuration and composition of the 

biomass; 

 The bagasse goes directly from the process (mill) to the boilers for fuel; 

 The geographic area in which sugarcane is grown, and the variety of 

sugarcane that is grown, affect the composition of the bagasse; 

 Bagasse boilers must be designed specifically and uniquely to burn this 

unique fuel; 

 Bagasse absorbs moisture while stored; 

 Harvesting conditions and harvesting methods affect the composition, 

including the moisture content, of the bagasse; 

 Bagasse as produced and burned has a high moisture content; 

 It is very low in heavy metals; 

 It is typically only 2 percent ash; 

 The heating value (Btu/lb) as fired is ample, but it is relatively low by 

comparison to the heating value of wood and other types of biomass; 

 Its use eliminates the need to import and use millions of gallons of fuel oil or 

other types of fossil fuel each year in Florida and Hawaii, and thus its use 

greatly reduces the emissions of greenhouse gases in Florida and Hawaii; 

 It is a renewable resource, which is produced annually without disturbing 

new land. 

Bagasse consistently contains from 48 percent to about 55 percent moisture as produced, and about 

2 percent ash. The solids portion is composed mostly of cellulose fiber and pith, but it also contains 

some minerals, ash, and a small amount of sugars. It is the high moisture content of bagasse that 

renders it unique compared to many other forms of biomass, such as wood. This high moisture 

content has a direct effect upon its combustion characteristics. 

Bagasse is also unique in that it is “spongy,” like peat moss. Consequently, the bagasse absorbs 

moisture more easily than woody biomass. Moisture is absorbed and contained throughout the 

bagasse material, as opposed to woody biomass, where the moisture is primarily surface moisture. 

This difference affects the combustion characteristics of bagasse and emissions of organics (CO). 

Both the high moisture content and the low ash content of bagasse is a result of the thorough washing 

of the sugarcane during the processing to extract the sugars. In this process, water displaces sucrose 

within the fiber of the sugarcane. The washing removes some, but not all, of the soil material that 

comes into the mill with the sugarcane. 

As noted above, the mill-run bagasse has a moisture content ranging from 48 percent to 55 percent, 

but it also has a heat content of about 3,600 to 4,200 Btu/lb as-fired. Consequently, bagasse can be 

readily used as a valuable fuel. Indeed, bagasse has been the main fuel of the sugar industry for the 

past 200 years. When bagasse is burned, small amounts of ash remain, most of which either falls out 
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as bottom ash or is collected by air pollution control devices. Most of the sugar industry uses wet 

scrubbers and/or multi-clones. Two bagasse boilers at one sugar mill in Florida have an electrostatic 

precipitator (ESP) control device. 

Bagasse furnace ash and fly ash contain some unburned carbon and some of the non-combustible 

minerals that entered the mill (some from the soil clinging to the cane, but also some minerals in the 

cane itself). Some of the soluble minerals are extracted during the washing of the bagasse and are 

later precipitated from the sugarcane juices. These “clarifier muds” are not combusted, but are 

returned to farm fields to reduce the need to add fertilizers or other necessary soil amendments. 

As noted earlier, bagasse is a very clean fuel with respect to heavy metals and, as a result, the ash 

particles emitted from bagasse-fired boilers contain extremely low concentrations of such metals. 

Bagasse boilers are equipped with either wet scrubbers or ESPs and emit relatively small amounts of 

PM and thus even smaller amounts of metal hazardous air pollutants (HAPs). 

PM is a good surrogate for metals emissions from bagasse-fired boilers, but given the low metals 

content of bagasse ash, an appropriate PM emissions limit for bagasse-fired boilers could likely be 

higher than the PM emissions limit for other solid fuel boilers. Additionally, the wet scrubbers used 

at most sugar mills will remove almost all of the small amounts of hydrogen chloride that might be 

formed in the boilers from the combustion of bagasse. 

B. Key Combustion Characteristics of Bagasse 

Bagasse has the following key combustion characteristics, which collectively make bagasse unique 

and much different than other types of biomass fuel: 

 It has a low combustion temperature because it has a high moisture content; 

 It is burned in boilers with relatively high heat release rates; 

 It has relatively low NOx emissions and very low SO2 emissions; 

 It is carbon neutral; 

 It is burned for combined heat and power production (i.e., steam and 

electricity); 

 It combusted on a seasonal basis. 

If EPA contemplates setting emission limits for organic HAPs, or for CO as a surrogate for organic 

HAPs, EPA should recognize that the unique nature of bagasse and the unique design of bagasse 

boilers strongly influence emissions. The high moisture content (48 to 55 percent) of bagasse (and 

especially the moisture absorbed in the fiber) results in a relatively low combustion temperature in 

bagasse-fired boilers. This is because a significant amount of heat is consumed in the furnace by the 

process of evaporating the water from the bagasse, and the amount of moisture released suppresses 

the combustion temperatures. 

This factor, combined with the furnace design, and in particular the amount of heat input per unit of 

furnace volume [British thermal units per hour per cubic foot (Btu/hr-ft3

)], causes significant effects 

on the combustion process and the subsequent emissions of PM and CO. Higher heat release rates 

produce lower residence times for combustion gases within the furnace, allowing less time to 

completely burn out the CO in the gases. Typical existing Florida and Hawaii bagasse boilers have 

furnace heat release rates ranging from 23,000 to 72,000 Btu/hr-ft3

. By comparison, the newest, most 

modern bagasse boilers (constructed in 1997 and 2004) have heat release rates of 18,000 and 

23,500 Btu/hr-ft3

, respectively. These lower heat release rates are coupled with more modern 
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combustion controls, which allow these boilers to achieve much lower CO emissions than a typical 

bagasse boiler. 

For all the reasons discussed above, we are convinced that the emissions data from other solid-fuel 

boilers are not representative of bagasse boilers. Including bagasse boilers with other solid-fuel or 

biomass boilers will result in an inappropriate MACT floor for bagasse boilers. Therefore, the 

Florida Sugar Industry believes that it is appropriate for bagasse boilers to be placed in a separate 

subcategory (containing only bagasse boilers) under Section 112 of the CAA when EPA establishes 

MACT standards for industrial boilers. 

Additionally, it must be emphasized that sugarcane processing is a seasonal operation; in some cases, 

the season is only a few months. Given similar emission factors, seasonal operations produce lower 

total annual emissions than year-round operations. It also means that many of these boilers are older 

compared to non-seasonal industries because (being used only part of a year each year) they are 

typically operated for more years to achieve the same total operating life. This seasonality is another 

factor in requesting a separate sub-category for bagasse boilers. 

Bagasse has always been the primary fuel used in sugar mills, except where a cheaper fuel has been 

available (e.g., coal in China, heavy oil in Venezuela, and natural gas in Louisiana in the 1960s). 

In those cases where a cheaper fuel was available, the bagasse was sold as a feedstock for paper 

production or other uses, because the bagasse was too valuable to be discarded. Other fuels 

(e.g., natural gas, oil, or occasionally wood) may be used in a sugar mill during start-up operations or 

during times when bagasse moisture is abnormally high, but once the boilers achieve normal 

operating conditions, the boilers typically burn 100 percent bagasse.3

 Bagasse has been categorized 

by the sugar industry and government regulators as a co-product of cane sugar production. 

As part of EPA’s Industrial Combustion Coordinated Rulemaking (ICCR) process and the 

development of the Boiler MACT rule, three sugar producing companies in Florida collected a large 

number of samples of bagasse during the period 2002-2006, and conducted proximate and ultimate 

analyses as well as analyses for various metals. The results of the Florida ultimate analyses are 

shown in Table 2. 

TABLE 2 

TYPICAL ULTIMATE ANALYSIS OF FLORIDA BAGASSE (DRY BASIS) 

Component Typical Range 

Carbon 50% 45 – 53% 

Hydrogen 6% 4.7 – 6.7% 

Oxygen 40% 37 – 44% 

Nitrogen 0.4% 0.25 – 0.55% 

Sulfur 0.06% 0.03 – 0.09% 

Ash 3% 1 – 11% * 

Chlorine 0.035% 0.013 – 0.092% 

High heating value 8,100 Btu/lb 7,400 – 8,500 Btu/lb 

(Original moisture) 52% 48 – 55% 

* Depending on harvesting and processing techniques and soil type, the amount 

of soil or sand clinging to the cane can vary from < 1.0 percent to 11 percent. 

 

3

 One mill in Hawaii uses somewhat less bagasse (i.e., about 70 to 80 percent of its annual heat input), which 

the mill supplements with fossil fuels when necessary to maintain stable combustion or meet power demands 

during the off-season. 
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Very low levels of some heavy metals may be found in bagasse ash. However, the metals content of 

the bagasse is so low that the metals content of the ash also is very low. Table 3 presents some data 

concerning the mineral content of bagasse ash, based on various sources in the literature. Table 4 

provides some specific data on the metals content in bagasse ash from one mill in Florida. 

TABLE 3 

TYPICAL MINERAL CONTENT OF BAGASSE ASH (FROM THE LITERATURE) 

Component 

Typical Content 

(% by weight, dry basis) 

Silica (SiO2) 71 

Alumina (Al2O3) 5 

Calcium oxide (CaO) 4 

Magnesium oxide (MgO) 2 

Iron oxide (Fe2O3) 6 

Phosphates (P2O5) 2 

Potash (K2O) 5 

Manganese oxide (MnO) 4 

Sodium oxide (Na2O) 1 

TABLE 4 

ELEMENTAL ANALYSIS OF ASH SAMPLE FROM BAGASSE BOILER IN FLORIDA 

Element 

Boiler ash 

(ppmw, dry) 

Al (Aluminum) 1,940 

Ag (Silver) < 1.1 

Sb (Antimony) <6.5 

As (Arsenic) 2.6 

Be (Beryllium) <0.43 

Cd (Cadmium) < 1.1 

Cr (Chromium) 7.5 

Cu (Copper) 56.4 

Hg (Mercury) <0.4 

Mn (Manganese) 377 

Ni (Nickel) <3.3 

Pb (Lead) < 2.2 

Se (Selenium) 1.5 

Tl (Thallium) <5.4 

Zn (Zinc) 62.5 

As stated previously, testing was performed on a large number of samples of bagasse from three 

Florida sugar mills during 2002-2006. The samples were tested for heavy metals as well as for 

ultimate analysis. These results contributed to the ICCR and Boiler MACT efforts to characterize the 

metals content of various fuels. Table 5 presents the results of the metals testing on the whole 

bagasse samples obtained from these three facilities. Note that for several of the metals, the result is 

below the detection limit, thus confirming again that the metals content of bagasse is extremely low. 
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TABLE 5 

BAGASSE METALS CONTENT, FROM EXTENSIVE SAMPLING (2002-2006) 

AT THREE FLORIDA MILLS 

 Concentrations, ppm* 

(dry basis) 

Element Average Range 

As 0.5 0.15 – 0.90 

Be <0.2 <0.1 – <0.2 

Cd <0.4 <0.1 – <0.4 

Cr 0.4 <0.1 – 1.0 

Hg <0.03 <0.01 – 0.11 

Mn 11 5 – 20 

Ni 0.3 0.1 – 1.7 

Pb 0.26 0.1 – 0.9 

Se 0.8 0.15 – 1.2 

* Non-detects are shown as less than (<) the 

detection limits. For those elements with a 

mixture of detects and non-detects, a value of 

one-half the detection limit for each occurrence 

was used in calculating the average. 

Bagasse from Hawaii is very similar to bagasse from Florida with respect to metals content, except 

for manganese (Mn) and chromium (Cr). The Mn in Hawaiian bagasse is significantly higher than 

Florida samples, and the Cr in Hawaiian bagasse is somewhat higher than Florida. Most likely, this is 

due to a higher percentage of those elements in the Hawaiian (volcanic) soils. 

Mercury emission factors for bagasse boilers in Florida were established separately, based on a series 

of 27 stack tests that were conducted as part of a mercury study in 1993. These test results were 

submitted to and accepted by the Florida Department of Environmental Protection. Additional 

mercury testing was conducted in 2001-2003. The results of the Florida testing were mostly below 

detection limits. The results from the Florida and Hawaiian bagasse testing correspond to emissions 

factors (assuming no controls) for mercury of approximately 1.2×10−6

 and 2.6×10−6 lb/MMBtu, 

respectively. 

C. Key Characteristics of Bagasse Boilers and Operation 

Bagasse fuel is a light-weight, fibrous, high-moisture content fuel, and is combusted differently than 

wood/wood chips, which are heavier, lower moisture, and have a higher heating value. If EPA 

contemplates setting emission limits for organic HAPs, or for CO as a surrogate for organic HAPs, 

EPA should recognize that the unique nature of bagasse and the unique design of bagasse boilers 

strongly influence emissions. 

As described previously, moisture in bagasse is both surface moisture and moisture contained 

throughout the fiber. As a result, this moisture is more difficult to remove compared to surface 

moisture such as that present with wood. The combustion of bagasse in a bagasse boiler is carried out 

in a two-step process within the furnace. The first step is drying of the bagasse, which occurs mainly 

in suspension but also on the stoker grate or fuel pile. The second step is combustion of the bagasse. 

The high moisture content (48 to 55 percent) of bagasse coupled with the unique moisture properties 

results in a relatively low combustion temperature in bagasse-fired boilers. This factor, combined 

with the furnace design, and in particular the heat release rate (amount of heat input per unit of 

furnace volume), causes significant effects on the combustion process and the subsequent emissions 

of CO compared with fossil fuels or woody biomass. Existing bagasse boilers were designed with 
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smaller furnace volumes and higher heat release rates than the newest bagasse boilers. Nonetheless, 

even the newest bagasse boilers with low heat release rates experience variable and transient CO 

emissions due to their integration with mill operations, as described below. 

Using bagasse as a fuel also produces lower emissions of nitrogen oxides (NOx) and sulfur dioxide 

(SO2) compared with fossil fuels. Bagasse, like most biomass, has a significant oxygen content 

within its molecular structure. Bagasse also has a significant moisture content. The internal oxygen 

and internal moisture content of bagasse contribute to bagasse burning at a lower temperature than 

fossil fuels. In turn, the lower combustion temperature reduces the formation of combustion-related 

NOx [mostly nitric oxide (NO) and nitrogen dioxide (NO2)], in comparison to the levels associated 

with the combustion of fossil fuel. This reduction is important because NOx is one of the main 

pollutants responsible for urban smog and ozone, and SO2 and NOx are the largest contributors to acid 

rain. 

The integrated operation of sugar mills and sugar mill boilers is unique and unlike any other industry, and 

this can have a direct impact on emissions from the boilers. The bagasse for the boilers comes directly 

from the mill. When the quality of cane coming into the mill changes (e.g., due to wet, muddy field 

conditions), the performance of the mills can be adversely affected. Any change in the output of the 

mills will have an immediate impact on the quality of bagasse being fed to the boilers. Bagasse moisture, 

for example, can swing wildly in a very short period of time. These fluctuations in the quality of the 

bagasse necessitate constant adjustments by boiler operators (e.g., adjustments to combustion air) to 

optimize combustion as the fuel quality varies, and may also require the use of supplemental fuels 

(e.g., fossil fuels) to stabilize combustion. 

All of these adjustments contribute to transients in CO emissions, and therefore higher average CO 

emissions than a boiler operating on fuel of consistent quality. Even the burning of supplemental fossil 

fuels cannot always resolve these transient CO conditions. As a result, even newer bagasse boilers can 

experience higher CO emissions than wood or other biomass-fired boilers. 

By comparison, wood-fired boilers will typically be firing fuel from storage piles, which will result in a 

much more consistent fuel quality being provided to their boilers. Thus, wood-fired boilers may be less 

likely to experience these fuel-related transients than bagasse-fired boilers. 

Fluctuating steam loads are typical of sugar mill operations and they contribute to emissions transients. 

This phenomenon can be witnessed in the control room of any sugar mill and it is documented by the 

steam charts for the boilers. Unlike utility boilers and many industrial boilers which operate at a 

relatively steady load, steam loads at a sugar mill can vary widely over short periods of time. Field 

conditions or a lack of cane can result in the sudden starting and stopping of the mills, which are a major 

steam load for the boilers. The rapid change in steam load has a dual impact on the boilers because it 

causes emissions transients and it also adversely impacts the bagasse moisture when the mill restarts 

because the hydraulic pressure exerted by the mills is dependent on adequate steam load. 

Similarly, conditions in the boiling house can cause increases and decreases in steam demand. For units 

that supply power to electric utilities, fluctuations on the transmission line grid can result in a sudden 

increase in electricity demand, which again results in an increase in steam demand. These operational 

considerations significantly affect the emissions from bagasse-fired boilers and thus they are important 

factors to consider when determining the emissions standards that are achievable for sugar mill boilers. 
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D. Geographical Characteristics of Bagasse Fuel and Bagasse Boilers

Bagasse and bagasse boilers are unique because of the geographic area in which sugarcane is grown 

and bagasse is produced. Different varieties of sugarcane have been developed over the years to 

enhance the yield of the sugarcane when processed (i.e., higher sucrose content and/or extraction), 

and to also grow during differing times of the year (i.e., early or late sugarcane). These differing 

varieties of sugarcane produce differences in bagasse composition. The different varieties of 

sugarcane affect how the bagasse boilers must be operated (e.g., excess air), and they affect the 

boilers’ emissions. 

Another geographic factor that affects the burning of bagasse in the boilers are the heavy rains which 

can occur in southeast Florida and Hawaii. During the harvesting season, the sugar mills are rarely 

shutdown, but sometimes, after very heavy rains, they must be because the sugarcane harvesting 

equipment cannot access the sugarcane fields. At these times, when the mills do start back up, the 

sugarcane comes in from the fields wetter than normal, and with higher quantities of muck and sand. 

These impurities can affect the quality of the bagasse produced, and the burning conditions in the 

boilers, producing higher emissions than is normally the case. Other biomass fuels do not experience 

these unique conditions. 

V. Summary and Conclusions

In summary, bagasse is a valuable fuel that is unique to the sugar industry. Bagasse is a result of the 

cane sugar production process, which alters the characteristics of the biomass. Bagasse-fired boilers 

are uniquely designed to dry and burn bagasse in an integrated process that results in unique 

emissions. Given the nature of bagasse, as well as the design and operation of sugar mill boilers, 

EPA should establish a separate subcategory for bagasse boilers under Section 112 of the CAA. 

A separate category is necessary to ensure that the MACT standards for bagasse-fired boilers are 

based on “similar sources,” as required by Section 112 of the CAA.