Control Technology for Coal-fired Boilers:
Applications to China
Charles B. Sedman, Hcng Ban", and John P. Gooch*
National Risk Management Research Laboratory, United States Environmental Protection Agency
Research Triangle Park, North Carolina, USA
^Southern Research Institute, Birmingham, Alabama, USA
Abstract: Air pollution regulations in Europe, Japan, and the United States have driven the development of
technologies to control fine particles, acid gases and toxic metals emissions. Due to higher capital costs,
retrofitting of older and smaller facilities has been avoided by either ceasing operations or switching to more
expensive, but cleaner, fuels. New regulations in the United States for fine particles and toxic air pollutants are
causing a rethinking of traditional control strategies which have addressed each pollutant somewhat separately
and relied on the lowest sulfur coals. This paper examines new multi-pollutant technologies and improvements
to old technologies that may allow China and other rapidly developing nations to mitigate the high cost of
retrofits and still achieve cleaner air. A program is outlined to jointly investigate some of these technologies for
application to China.
Keywords: Control technology, acid gases
1. Background
The earliest emission regulations focused on reducing acute exposures of man and material to the dust and soot
particles from industrialization and, to a lesser extent, acid vapors. As the mechanisms of smog formation and
chronic effects of air pollution exposure became better understood, the invisible components of combustion - sulfur
oxides (SOX), nitrogen oxides (NOX), and carbon monoxide (CO) were regulated. Technologies were developed to
address solid particles (PM), SOX and NOX, somewhat independent of each other, and the succession of regulations,
controls for compliance, and new regulations for acid rain (in the 1980s for Europe and 1990s for the U.S.) resulted
in two entirely different scenarios. The TA Luft fuel combustion regulations essentially forced the use of wet sulfur
dioxide (SO2) scrubbers and catalytic NOK reduction units on all major fuel burning installations in Germany, with
older and less efficient plants being phased out; these regulations have generally been adopted by the European
community and are gradually being implemented (Ellison, 1988). In the U.S., Acid Rain legislation and resulting
regulations encouraged a market-based approach of SOi emissions trading, which resulted in the use of lower-sulfur
fuels, less capital intensive than the installation of new technology. Consequently, new technologies have been
largely ignored, and the modest increase in technology use has been more wet limestone SOj scrubbers and
combustion NOX controls (EIA, 1997). [Japan had earlier adopted local and regional emissions policies that
similarly encouraged the rapid implementation of wet SO2 scrubbers and catalytic NOX controls (Ando, 1985);
Japanese vendors have influenced the choice of control systems in the Far East based on this experience].
2. Current Technologies
2.1 Add Gases
An excellent review of acid gas emissions control was recently published in Chemical Engineering Progress,
October 1998 (Brown, 1998). The reader is referred to this article for technical details on each system. The article
does not completely address the shortcomings of each technology, nor speculate on the impact of potential future
regulations on its use, as will be attempted here:
Wet Limestone Scrubbing is the technology of choice in the U.S., Europe and Asia for coal-fired power plants. In
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this process, limestone is slurried with water and contacts flue gas, absorbing the SO2 as follows:
CaCO3 + SO2+l/2O2->CaSO<+ CO2 (forced oxidation) (1)
CaCO3 + SO2 -> CaSO3 + CO2 (inhibited oxidation) (2)
The advantages include an inexpensive reagent, >95% absorption of SO2 and halogenated acid gases, single-module
operation, and 30 years of development in fuel burning applications. The waste solids are recoverable as salable
gypsum, with forced oxidation of the circulating liquor. Energy penalties to the host power plant vary from 1 to 2
percent of plant gross generating capacity. The absorber module is typically downstream of all other emission
control systems, and catches any byproduct emissions of upstream technologies. Another advantage to upstream
dust collection and downstream flue gas desulfurization (FGD) product collection is the availability of salable fly ash
to concrete and paving aggregate markets. Since it is operated as a gas absorber with minimal gas pressure losses, it
is somewhat ineffective on hydrophobic pollutants, such as elemental mercury vapor, and fine condensables such as
sulfuric acid mist (Jones and Ellision, 1998). As the concentration of halogen acid gases increase, limestone and
lime scrubbers have increasing difficulty in maintaining optimum chemistry for simultaneous absorption of SO2,
generation of sulfite/sulfate crystals, and separation of solids from recirculating liquor.
Lime Spray Drying is an established technology competing with limestone wet scrubbing. The reactions are similar
to the above for wet FGD, except for the elimination of CO2, since lime enters the reaction as Ca(OH)2 rather than
CaCCb, wherein about one-third of the solids product is CaSO« and two-thirds CaSOs. It is installed upstream of
the dust collector, and uses the dust collector as an integral part of the solids handling and recycle solids circuit.
The advantages of spray drying are reduced water usage, no water-solids separation, and lower capital cost. Whereas
halogenated acids such as hydrochloric acid (HC1) adversely affect wet scrubber operations in mass transfer, solids
separation, and materials, the presence of chlorides in spray dryers enhances mass transfer and collection of fine
particles (Barton et al, 1991). Sulfuric acid mist is also more readily collected in the spray dryer-dust collector
system (Gooch and Sedman, 1997). Disadvantages are a dry waste of fly ash and spent sorbent which is difficult to
market, usually ending up in a landfill; and the economic limitations to (1) low-to-moderate sulfur fuels because of
mass transfer limitations inherent in the technology (95% SO2 removal on <2% sulfur fuel is the upper limit for
most applications), and (2) smaller facilities requiring only one module. Energy requirements are somewhat less
(<1% derate) than for wet limestone scrubbing, especially if solids recycle is not required for mass transfer.
The newest entry is circulating bed scrubbing using hydrated lime. At present only two commercial systems operate
in the U.S., but the advantages for retrofitting existing facilities are noteworthy. The system operates upstream of an
existing dust collector, much like the spray dryer, but is essentially a vertical pipe with internals that encourage
solids-gas mixing and flash drying of moisture, within a fraction of the gas residence time of its competitors. With
no lime slurrying or spray nozzles, many of the operating problems of dry scrubbers are avoided. At least five
vendors offer this class of scrubber (Lavely et al., 1997; Braf andHuckriede, 1995, Burnett et al., 1995; Ahamn and
Buschmann, 1997; Sedman, 1998). With high solids recirculation, 98% removal of SO2 has been achieved in
European applications, and the system has been applied to higher-sulfur (4%S) fuels. The disadvantages of this
system are dry solids disposal, upper size limits on single-module operation, and larger solids loadings on the dust
collector. Energy penalties are similar to that of spray drying with solids recycle.
Other systems which may have a local advantage due to cheap reagents, water/solids disposal options, or unique site
limitations, include clear liquor (sodium) scrubbing, dry sodium injection, duct lime injection, and furnace
limestone injection [the last two processes are not discussed in Brown's paper (Brown, 1998)]. Also regenerable
scrubbing systems that use ammonia as a scrubbing agent may have an economic advantage where there is a strong
market for ammonium sulfate fertilizer (Brown et al., 1995). Other processes which produce dilute sulfuric acid or
elemental sulfur as a solids byproduct are also available, but have not made an impact on the existing market.
The penetration of acid gas controls into industrial market sectors illustrates the operational and economic
advantages of each system. The U.S. utility market uses wet lime and limestone scrubbing on about 25% of the
total coal-fired boiler capacity (Brown et al., 1998). Only a handful of utility boilers use other systems. Industrial
process steam generators prefer clear liquor scrubbing; a smaller number of spray drying systems have been installed
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(Dickerman and Johnson, 1979). Coal-based cogeneration plants and waste-to-energy plants prefer spray dryer
technology with fabric filter solids collection. Waste-to-energy plants are more concerned with HC1 control than
SO2. The scrubbing systems for HC1 are identical to that for SO2) but operating conditions differ, e.g., the pH for
HC1 wet scrubbers is lower and the flue gas temperature is higher for HC1 spray dry and circulating bed units (EPA,
1987).
2.2 Fine Particles
Fine particulate matter (PM) emissions from combustion consist of entrained ash, condensed vapors, and secondary
particles from the reaction of acid gases and hydrocarbon vapors with atmospheric gases downwind of the exhaust
stack. Particle control technology currently focuses on sequestration of the primary fine particles and condensed
vapors at flue gas temperatures greater than 50-55 °C (the dew point range of most flue gases from fuel combustion),
more typically 150°C, the temperature at which most particle controls operate. Primary mechanical collectors have
long been inadequate to meet emission standards and, as standards have become increasingly stringent, medium-
and high-energy wet scrubbers have largely disappeared for new applications.
The two dominant particle collectors are fabric filters and electrostatic precipitators (ESPs). ESPs are used by nearly
90% of the coal-fired utility boiler capacity, while industrial steam generators and cogeneration plants prefer fabric
filtration. ESPs operate on the principle of charged particles migrating toward grounded collection surfaces.
Incoming particles are charged by a series of wires and migrate toward flat metal plates parallel to the wires and gas
flow path. Particle collection is influenced by the ability of a particle to be charged (resistivity), the strength of the
charge and collecting field, and the time for the particle to migrate to the collector plate. Flue gas temperature,
composition, and humidity are also important factors in ESP performance. The particles not collected by ESP
include particles that, by their resistivity and size, do not migrate to the collecting plates within the residence time
in the ESP, or those particles that are re-entrained into the gas stream after being collected. In some cases,
mechanical misalignment will allow some particle-laden gas to "sneak" through the system without being exposed
to a charging or collecting field (Szabo et al., 1984).
Fabric filters (Hovis, 1986) are in widespread use throughout industry for dust control; however, the application to
combustion gases lagged that of the ESP because of the corrosive nature of flue gases and fears of baghouse fires due
to carryover of hot particles from combustors (EPA, 1982). Fabric filters operate on the principles of interception and
impaction, wherein particles are filtered out of moving gases by the fabric and/or the filter cake of previously
collected particles. While some larger particles may penetrate the fabric and eventually work through the matrix into
the exhaust stream, most particle emissions are attributable to holes or pores in the fabric or filter cake. Fabric filter
performance is relatively unaffected by particle size, shape, or electrical resistivity, and is therefore more versatile
than electrostatic precipitation. A weakness of fabric filtration is the tendency of bags to plug or develop leaks, and
the need for constant inspection and maintenance for optimum performance. The gas pressure loss for large gas
volumes through a baghouse can be a substantial energy penalty for electric power generators, and is a factor in their
preference for ESPs.
Wet scrubbers were once used extensively for particle emission control, but have diminished in popularity in favor
of ESPs and fabric filters. For applications on wood waste and multiple waste boilers, where combustible and/or
very sticky particles are likely, wet scrubbers are used (EPA, 1982). The ability of wet scrubbers to collect finer
particles is directly proportional to the energy input, through gas-side pressure drop and water nozzle pressure.
Wetted-plate or pipe ESPs have been developed for use in applications where particles are likely to adhere too
strongly to collecting surfaces, or are likely to lose charge and re-entrain into the gas stream (Monroe et al., 1997).
A more recent application is the use of wet ESPs downstream of wet acid gas scrubbers to control condensed sulfuric
acid mist (Henningsgard et al., 1997).
2.3 NO, Control
Fuel combustors typically emit NO* primarily as nitric oxide (NO) from the reaction of oxygen in combustion air
with fuel-bound nitrogen (fuel NO*), as well as nitrogen in the air (thermal NOK). NO has proven to be one of the
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more difficult pollutants to control, because of its weak acidity and solubility in water. Attempts to oxidize NO to
nitrogen dioxide (NO2) to be absorbed as a nitrate in alkaline acid gas scrubbers have been less than satisfactory.
Problems resulting from this oxidation approach include: complications with the SO2 absorption chemistry, adverse
impacts on solids separation and the ability to generate a salable byproduct gypsum, and plume opacity increases at
the stack exit due to the presence of any unabsorbed NC>2. Some vendors have incorporated multiple absorbers to
avoid these interferences (Lani et al., 1997), The prevention of NO (and any NO2) formation by combustion
modifications and post-combustion reduction by injection of a reducing agent such as ammonia are the NO* control
methods of choice.
Combustion controls have proven the easiest to implement for NOX control. Minimizing oxygen in the combustor
yields fuel efficiency benefits, as well as NOK reductions. Reducing the peak flame temperature also lowers the
thermal NO* component. Staging the combustion is especially beneficial in the reduction of NO* from fuel nitrogen,
wherein the fuel nitrogen is released in a lean oxygen zone, then additional air added to complete combustion after
the fuel nitrogen has largely recombined as molecular nitrogen (N2). So-called Low-NOx burners combine air
staging, gas recirculation, and oxygen trim, to lower combustor NO* emissions up to 50% (Campbell et al., 1991).
Add-on NOX controls have been developed for use with combustion controls where NOX reductions greater than 50%
are desired. Selective Non-Catalytic Reduction (SNCR) injects a reducing agent into the combustion zone, usually
ammonia or urea, which reduces NO to N2 and O2. The reduction of NO, typically 20-50% above combustion
modifications alone, depends on injection into the proper temperature zone, good mixing of gas and reducing agent
in that zone, and the stoichiometric ratio of reductant to NO. As the ratio of reducing agent to NO is increased, the
amount of unreacted reagent (ammonia slip) increases and adversely affects the use and sale of collected fly ash. Most
SNCR systems are designed to limit ammonia slip to less than 20 ppmv. Where SOs is present, an unwanted
reaction of ammonia and SO3 to produce ammonium bisulfate may occur, resulting in fouling of heat exchanger and
dust collector surfaces downstream (Campbell et al., 1991).
Selective Catalytic Reduction (SCR) uses a reduction catalyst, usually vanadium pentoxide, and a reducing agent,
again ammonia or urea preferred, to reduce NO and NO2 to nitrogen. The flue gas temperature is critical, with
optimum performance occurring at approximately 370-400 °C (700-750 °F); therefore, the SCR module is usually
located between the feedwater heater (economizer) and air preheater on a boiler. Further downstream from the boiler,
flue gas reheat is required to boost temperatures for SCR, adding significantly to the operating cost. Operating
penalties for ammonia slip are similar for SCR and SNCR, but SCR can maintain ammonia slip below 5 ppmv.
Other adverse side reactions include oxidation of SO2 to sulfur trioxide (SO3), which is also managed by careful
temperature control. Gas pressure drop of conventional honeycomb catalyst beds may be avoided somewhat by using
plate catalysts. SCR is capable of 90% NOX control, but at less than optimum operating conditions for SO3 and
ammonia slip. Better SCR operation is observed at 50-80% NOX control levels (Campbell et al., 1991).
The post-combustion reduction reactions include:
2NO+4NH3+2O2->3N2+6H2O(SNCR and SCR) (3)
6NO+4NH3->5N2+6H2O(SCR) (4)
With urea or other amine (NH2) functional chemical additives, the reaction is
NH2+NO->N2+H2O(SNCR and SCR) (5)
2.4 Toxic Metals and Gases
United States regulations for combustion sources include mercury and dioxin/furan limits for waste incinerators
(Licata et al., 1997). Fossil fuel combustors in the U.S. do not currently control metal or organic vapors, although
deliberations are ongoing for mercury emissions from fuel combustion.
The acid gas scrubbers used for HC1 and SO2 control on waste incinerators also remove a substantial portion of
dioxins and mercury (Sankey and Licata, 1997). This is thought to be because the mercury is primarily in the form
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of mercuric chloride (HgCl2), which is water-soluble and reacts readily with an alkaline reagent, such as lime. The
dioxins are semivolatile, readily adsorb onto fly ash particles, and are collected as a fine particle. Activated carbon
may be used as an absorbent for both mercury and dioxins, by injecting as a powder with lime in spray dry or
circulating bed systems, or as a fixed bed in series with a wet scrubber (Waffenschmidt and Goff, 1997), This
practice is more common in Europe than in the U.S.
3. New Technologies and Technology Drivers
In the United States, compliance with Acid Rain Amendments to the 1990 Clean Air Act is still in progress. Many
fossil fuel boilers that have switched to lower sulfur fuels have struggled to upgrade and adapt ESPs designed for flue
gases from higher sulfur fuel. A number of flue gas additives to improve ESP performance have been commercially
employed, including SCXj injection, sodium addition to the furnace, and water injection/humidifieation, all designed
to improve the charging and migration of particles in the ESP field (Marchant et al, 1996). Recent revisions of the
National Ambient Air Quality Standards for Paniculate Matter and Ozone foreshadow more reductions of acid gases
and NOX beyond Acid Rain targets, as well as a new definition of fine particle that may include those condensable
particles excused by previous standards (EPA, 1997a). Possible mercury emission limits further confuse the choice
of an optimum control strategy. Visible emissions regulations at the exhaust stack and emerging regional haze
policies add further to the dilemma.
3.1 Multipollutant Approach
One strategy proposed to address the specter of frequent adjustments to emissions regulations, as well as the periodic
ratcheting down of allowable individual pollutant emissions, is EPA's Clean Air Power Initiative (CAPI). Under
this strategy, a comprehensive set of environmental regulations would be developed specifically for utility power
plants to meet long-term environmental goals (EPA, 1997b). Even if this approach is never implemented, all owners
and vendors of combustion pollution control equipment can use similar considerations to those proposed under
CAPI, to minimize the impact of continual upgrades and retrofits to meet future codes. For example, since 65% of
the U.S. capacity has only ESP post-combustion emission controls, the limitations of ESPs for metal vapor and
acid gas controls need to be addressed. A number of options to add-on acid gas/metals absorption exist (Gooch and
Sedman, 1997), including:
a. add-on wet FGD after ESP
b. add-on spray dry or circulating bed FGD upstream of ESP
c. add-on small pulse-jet baghouse with sorbent injection downstream of ESP
d. add SCR/SNCR upstream of ESP to a, b, or c
Options a and c allow the operator to sell fly ash instead of incurring additional solid waste disposal cost. Option d
may force the operator to landfill fly ash. Option a may not adequately address SO3/H2SO4 emissions, while none of
the options may adequately address mercury emissions without better sorbents. Each option may have a role
depending on the plant's size, fuel, economic lifetime, and space for retrofit installation.
Some newer and emerging technologies may provide more retrofit options for the operator. The following is a brief
summary of these with references for more detailed descriptions.
3.2 Primary Fine PM Technologies
Many "tweaks" are available which offer incremental improvement to existing technologies, including chemical
additives and unproved ESP charging hardware, but three hybrid systems may reduce fine PM emissions by
providing collection mechanisms that substantially increase the probability of capture. These are the Compact
Hybrid Paniculate Collector (COHPAC), developed by the Electric Power Research Institute; the Advanced Hybrid
Particulate Collector (AHPC), developed by the Energy and Environmental Research Center of North Dakota under
U.S. DOE sponsorship; and the Electrostatically Stimulated Fabric Filter (ESFF) being developed by Southern
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Research Institute under U.S. EPA sponsorship. The COHPAC concept adds a small pulse-jet fabric filter baghouse
immediately downstream of an ESP (COHPAC I), or replaces the latter ESP stages within the ESP structure
(COHPAC II). Residual particle charge is reported to improve the fabric filter performance, so that very low
emissions have been experienced (Miller et al., 1996).
The AHPC system (Miller et al., 1997b) combines reduced-size ESP and fabric filter compartments within a single
vessel and introduces proprietary synergistic principles to achieve:
- reduction of re-entrainrnent and re-collection of dust caused by close bag spacing
- reduction of chemical attack on bagfilters
- ultra-high collection efficiencies
The ESFF system consists of dust precharging at the baghouse inlet and vertical charging wires placed at the
centerline of each four-bag array which induce an electrostatic field between the wire and the grounded cage
supporting each bagfilter. Modeling based on small-scale research indicates up to an order of magnitude reduction of
submicron particles and two orders of magnitude supermicron particle reduction at a pressure loss of only 20-30%
compared to that of conventional fabric filtration (Plaks and Daniel, 1989). COHPAC I units are in commercial
operation (Miller et al., 1997b), while COHPAC II is still in pilot evaluation, AHPC and ESFF are similarly
undergoing pilot evaluation.
3.3 Gas Absorption
The class of Circulating Bed Absorbers offers opportunities for multiple pollutant control. Special sorbents for toxic
metals and organics such as activated carbon, zeolites, or calcium silicates may be easily added to the lime or
sodium stream, and the long solids residence time allows for good utilization of sorbent. Oxidants, which would
cause potential wet chemistry problems in wet scrubbers, would not present such problems in dry solids absorption;
hence, simultaneous removal of SO* / NOX by an oxidant/alkaline solid combination would be more practicable. At
least two oxidants, ozone and chloric acid, are being investigated for application to multipollutant scrubbing
(Anderson et al., 1998; Mendelsohn and Livengood, 1998). Pilot tests of these concepts are being planned for mid-
to-late 1999 on two circulating bed systems (Sedman, 1998).
3.4 New Sorbents
Several classes of sorbents have been developed for use in dry absorption processes, such as the Circulating Bed
Absorber, which may further enhance applications to coal combustion facilities. These include combination activated
carbon-lime sorbents, lime-impregnated vermiculite, zeolites, and calcium silicates, SorbalitTM is one example of
an activated carbon-lime sorbent targeted for combined SOX and toxic metals/organics control (Licata and Goetz,
1997), Sorbtech, Inc. has developed a sorbent that claims mercury control capability (Nelson and Miller, 1997), PSI
Inc., under a U.S. Department of Energy grant, is developing a zeolite sorbent for mercury vapor sorption; since
zeolites also are used in many catalytic applications, multiple-use zeolite sorbents offer intriguing possibilities for
use in circulating bed absorbers (Morency et al., 1998). Calcium silicate sorbents are the subject of several U.S.
patents (U.S. Patent, 1995), and offer potential for multiple pollutant control in combustion flue gas (Ghorishi and
Sedman, 1998).
4. EPA-SRI Cooperative Program with China
4.1 Background
Air quality and health have become major concerns of China, and the growth of energy production by coal-fired
electricity and steam generation has greatly exacerbated existing problems. With the high ash and sulfur content of
coal in China, the emissions of SOX and other acid rain chemicals have become the major air pollution problem.
Fine particles from coal-fired power plants are also likely to be an environmental issue.
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Major pollutants generated by coal combustion include SOX, NOX, and PM, Most electric power generating boilers
in China are controlled only by ESPs, which capture most of the fly ash particles. Fabric filters are not generally
used in China because of lack of a supporting fabric and bag manufacturing industry. Boilers supplied by joint
Chinese, U.S., and Japanese firms are amenable to conventional NOX combustion control. Therefore the two major
problem areas are reduction of SOX and fine PM emissions. SOX emissions are largely uncontrolled, and control of
fine PM emissions has not been emphasized. SO* emission is the most prominent issue in areas where high sulfur
coal is used for power generation.
Communication and discussions with Chinese research and government organizations have helped to identify the
pressing need to control emissions from smaller (<100 MWe) coal burning installations, which constitute about
one-third of the generation capacity in China. These smaller, older plants are poorly controlled, have short exhaust
stacks, and have a significant impact on local health and air quality. In the long term, replacement by newer, larger
boilers, or by more advanced technologies such as fluidized bed combustion seems inevitable . But the best near-
term solution for PM emission control or SOX control is to use low-cost, multipollutant control technologies for the
remaining economic life of these boilers. Southern Research Institute has entered into a Cooperative Agreement with
the U.S. EPA to assist in transfer of emission control technology to China that can be readily applied to the existing
boiler population and integrated into plans for future expansions and new facilities. The proposed program is to
simply (1) select the most cost-effective and easily retroiittable technologies, (2) evaluate these technologies on
Chinese coals, and (3) make arrangements with U.S. and China suppliers to initiate and support demonstrations of
these technologies. These technologies include simple upgrades to ESPs, small-scale fabric filter evaluations, and
hybrid ESP-fabric filter technology; low-cost multiple pollutant gas absorbers; and combustion fuel staging for NOX
reductions,
Southern Research and EPA are actively supporting two projects in Russia and Ukraine to upgrade ESPs and add
low-cost acid gas control within the ESP, called E-SO*. Each ESP is optimized using mathematical models and
low-cost upgrades such as the use of sodium injection and cold-pipe precharging. The E-SOX technology (Figure 1)
can simply add water fogging to further improve particle collection efficiency, or also add lime or sodium reagents to
the water sprays for acid gas control (Redinger et al., 1991).
Southern Research and EPA have partnered with Southern Company, the largest U.S. coal-firing utility, and the
Institute of Clean Air Companies to evaluate the ESFF technology (Figure 2) described earlier, as a stand-alone
particle control, in conjunction with fluid bed absorption, or as a retrofit last ESP stage. The partnership is currently
operating pilot ESFF facilities and is prepared to assist in the development of similar facilities in China.
With assistance from the Tennessee Valley Authority, the partnership, above, is also constructing a circulating bed
absorber with separate stages for acid gas removal and NOX oxidation-absorption. The technology will also address
mercury emissions and serve to agglomerate fine particles into more easily collected larger particles upstream of the
ESP or baghouse. The technology is especially suited for retrofits and readily accommodates fuel variability.
Commercial partners are eager to apply this technology to Chinese coal and waste combustors.
Other vendors have recent experience in sorbent-based technologies for SO* control and fuel staging (rebuming) for
NO* control. Further, EPA has developed a number of advanced sorbents made from lime and silica to apply with
the circulating bed technology and other dry-sorbent-based technologies. It is intended that these technologies be
included in future discussions under this program,
4.2 Relevance to Environmental Concerns in China
This project is designed to provide unbiased technical assessment and evaluation of available low-cost
desulfurization technologies that are suited for Chinese coal and sorbent. Because each technology has its advantages
and disadvantages, the development effort will also look into combining the best features of the reactor, sorbent, and
particle removal method to match the specific needs in China and Southeast Asia. Focus will be upon the
differences between U.S. and China coals and sorbents and their impact upon control technology applications. The
result and information obtained by the project will be helpful to Chinese regulatory organizations and electric power
industry. The former can use the information for decision making in terms of achievable emission target,
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technological availability, and economics; the latter will benefit directly from this project in selecting emission
control technology.
In addition to mitigation of local and regional air quality problems, the initiation of emission controls increases the
need for emissions monitoring to assess performance and optimize the control process. Emissions' monitoring is
essential in any development of a global control strategy that involves emissions trading. This project will directly
target emissions of SOX, NO*, HC1, mercury, and fine PM, and should help promote a better accounting of
emissions of these pollutants at the stack.
While COz is not directly addressed, the installation and use of less- intensive energy technologies (e.g. dry vs. wet
FGD, multipollutant absorbers vs. single absorbers for each pollutant, and electrostatic fabric filtration vs. fabric
filtration) translate into less CO2 emitted per megawatt of electricity produced, when compared to technologies being
offered commercially. As the database for each technology is generated, the energy (and C02) savings over
commercially available technologies will be assessed and included in technical reports.
4.3 Objective and Approach
The objective of this project is to assess and evaluate current low-cost desulfiirization technologies applicable to
smaller coal-burning units in China and Southeast Asia. The pilot-scale (3.7 MBtu/hr) testing and development
effort at Southern Research Institute (SRI) will use U.S. and Chinese coals and alkaline sorbent for technical
assessment and comparison. Issues such as how to improve ESPs for added sorbent particles, Chinese coal and
sorbent characteristics, S03 emissions, and other concerns such as mercury will be considered in the technology
assessment and development. The project will be implemented in close cooperation with U.S. industrial partners
and Chinese researchers in the National Engineering Centers, State Key Laboratories, and the energy/environmental
industry in China.
Potential U.S. industrial partners were selected for discussions concerning teaming arrangements based on the
requirements for low capital costs, potential applicability to small-to medium-sized combustion sources in China,
and compatibility with existing development programs at SRI. Table 1 lists the technologies and partners
identified to date.
Table 1, Potential Partners and Technologies
Potential Partner
Alanco (AZ)
EERC (CA)
Beaumont Env. Systems (PA)
BOC Gases (NJ)
ICAC Members
ICAC Members
Technology
Charged diy sorbent
injection
High efficiency dry sorbent
Circulating fluid bed absorber
LoTOx oxidation system
for NO* reduction
Fabric filter and electrostatic
precipitator upgrades
Mercury control methods
Agreement Method
Subcontract or purchase order— EPA
Coop Agreement
Subcontract or purchase order—EPA
Coop Agreement
Subcontract or purchase order—EPA
Coop Agreement
To be determined
To be determined
To be determined
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Major Chinese research and development organizations, as well as regulatory organizations responsible for coal
power generation and emissions control, were contacted to establish communication and cooperation. These
organizations include Tsinghua University in Beijing, Thermal Power Research Institute in Xian, Zhejiang
University in Hangzhou, China Environmental & Development International Committee, and Environmental &
Resource Protection Committee of the National People's Congress. Issues such as the specifics and the current
status of coal use and environment including coal properties, power plants, and emission control technologies and
regulations were discussed. The communication paved the way for establishing cooperation and collaboration
partners in the future.
The technical assessment and evaluation of low cost desulfurization technologies at SRI are in progress and expected
to finish in two years. Three Chinese coals and three sorbents are being shipped to SRI. Furnace tests will start later
this year and continue through the year 2000. In addition to publications and regular reporting to EPA, a workshop
in China is planned for the later part of the project to present the results of the project. The technologies developed
at SRI can be transferred to China for demonstration. The partners such as National Engineering Centers, State Key
Laboratories, or any other environmental firms in China, may provide further evaluation and serve as technical
support within the country.
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References
Ahman, S., Buschmaon, J.:
NID - A New Dry Flue Gas Desulfurization System, in EPRI-DOE-EPA Combined Utility Air Pollutant
Control Symposium, SO2 Control Technologies, EPRI TR-108683, V2, August 1997.
Anderson, M., Skelley, A., Goren, E., Cavello, J.:
A Low Temperature Oxidation System for the Control of NOX Emissions Using Ozone Injection, presented
at Forum 98 - Cutting NO, Emissions, Institute of Clean Air Companies, Durham, NC, March 18-20,
1998.
Ando, J.:
Recent Developments in SO2 and NOX Abatement Technology for Stationary Sources in Japan; EPA-
600/7-85-040 (NTIS PB 86-110186): Air and Energy Engineering Research Laboratory, Research
Triangle Park, NC, September 1985.
Barton, R., Dawson, C., Burnett, T.s Hollinden, G., Wertz, K,, Blythe, G,, Rhudy, R.:
SO2 Removal Performance Improvements with Chloride Addition at the TVA 10MW Spray Dryer/ESP
Pilot Plant, in Proceedings: 1990 SO2 Control Symposium V2, EPA- 600/9-91 -015b (NTIS PB 91-
197228), pp 4C3-24, May 1991.
Brown, C.:
Pick the Best Acid-Gas Emission Controls for Your Plant, Chemical Engineering Progress, pp 63-70,
October 1998.
Brown, G.N., Janssen, K.E., Ireland, P.A.:
Substantial Cost reduction Realized for the First Ammonia Scrubbing System, in 1995 SO2 Control
Symposium, Book 2, Session 5B - Emerging Processes, Electric Power Research Institute, Palo Alto, CA,
March 1995.
Brown, T., O'Dowd, W., Reurher, R., Smith, D.:
Control Of Mercury Emissions from Coal-Fired Power Plants: A Preliminary Cost Assessment, in
Proceedings: Conference on Air Quality: Mercury, Trace Metals and Paniculate Matter, Energy and
Environmental Research Center, Grand Forks, ND, December 1998.
Burnett, T.A., Puschaver, E.J., Little, T.M., Lepovitz,L.R., Airman, R.F.:
Results from the Phase II Testing of the Gas Suspension Absorber Flue Gas Desulfurization Technology at
the Center for Emissions Research, in 1995 SO2 Control Symposium, Book 2, Session 4B - Dry FGD,
Electric Power Research Institute, Palo Alto, CA, March 1995.
Campbell, L., Stone, D., Shareef, G.:
Sourcebook: NOX Control Technology Data, EPA-600/2-91-029 (NTIS PB 91-217364): Air and Energy
Engineering Research Laboratory, Research Triangle Park, NC, July 1991.
Dickerman, J., Johnson, K.:
Technology Assessment Report for Industrial Boiler Applications: Flue Gas Desulfurization, EPA- 600/7-
79-178J (NTIS PB 80-150873): Industrial Environmental Research Laboratory, Research Triangle Park,
NC, November 1979.
10
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EIA:
The Effects of the Clean Air Act Amendments of 1990 on Electric Utilities: An Update, U.S. Department of
Energy, Energy Information Administration, March 1997.
Ellison.W.:
Assessment of SO2and NO* Emission Control Technology in Europe, EPA-600/2-88-013 (NTIS PB 88-
168992): Air and Energy Engineering Research Laboratory, Research Triangle Park, NC, February 1988.
EPA :
Nonfossil Fuel Fired Industrial Boilers - Background Information, EPA-450/3-82-007 (NTIS PB 82-
203209): Office of Air Quality Planning and Standards, Research Triangle Park, NC, p4-24, March 1982.
EPA :
Municipal Waste Combustion Study; Flue Gas Cleaning Technology, 530-SW-87-021d (NTIS PB 87-
206108): Air and Energy Engineering Research Laboratory, Research Triangle Park, NC, June 1987.
EPA:
National Ambient Air Standard for Particulate Matter; Final Rule; Federal Register, Vol. 62, No. 138, July
18, 1997a.
EPA:
EPA's Clean Air Power Initiative (Revision 2), Office of Air and Radiation, U.S. Environmental
Protection Agency, Washington, DC, June 1997b.
Ghorishi, B., Sedman, C.:
Low Concentration Mercury Sorption Mechanisms and Control by Calcium-Based Sorbents: Application
in Coal-Fired Processes, JAWMA 48:1191-1198, December 1998.
Gooch, J.P., Sedman, C.:
Advanced Fine Particulate Control and Implications Toward Solving Multiple Pollutant Control Problems
in Coal-Fired Boilers, in EPRI-DOE-EPA Combined Utility Air Pollutant Control Symposium,
Particulates and Air Toxics, EPRI TR-108683, V3, August 1997.
Graf, R.E., Huckriede, B.W.:
10,000 Hours Commercial Operating Experience with Advanced-Design, Reflux Circulating Fluid Bed
Scrubbing Employing Slaked Lime Reagent, in 1995 SO2 Control Symposium, Book 2, Session 4B - Dry
FGD, Electric Power Research Institute, Palo Alto, CA, March 1995.
Henningsgard, R.M., Lynch, S.D., Altaian, R.A.:
Summary of Wet ESP Operation at NSP's Sherco Station, in EPRI-DOE-EPA Combined Air Pollutant
Control Symposium, Particulates and Air Toxics, EPRI TR-108683-V3, Electric Power Research
Institute, Palo Alto, CA, August 1997.
Hovis, L.:
Operation and Maintenance Manual for Fabric Filters, EPA-625/1-86-020 (NTIS PB 88-180120): Air and
Energy Engineering Research Laboratory, Research Triangle Park, NC, June 1986.
11
-------
Jones, C., Ellison, W.;
SO3 Tinges Stack gas from Scrubbed Coal-Fired Units, Power, pp 73-75. July/August 1998.
Lani, B., Babu, M., Breault, R.:
High Velocity Scrubbing of SO2 and NO*, in EPRI-DOE-EPA Combined Utility Air Pollutant Control
Symposium, SO2 Control Technologies, EPRI TR-108683, V2, August 1997.
Lavely, L.L., Schild, V., and Toher, J.:
First North American Circulating Dry Scrubber and Precipitator Removes High Levels of SO2 and
Particulates, in EPRI-DOE-EPA Combined Air Pollutant Control Symposium, Particulates and Air
Toxics, EPRI TR-108683-V3, Electric Power Research Institute, Palo Alto, CA, August 1997.
Licata, A., Goetz, E.:
Lime Enhances Moving Bed Filters for Mercury and Dioxin Control, in: Proceedings of Fifth Annual
North American Waste-to-Energy Conference, Research Triangle Park, NC, pp 587-602, April 1997.
Licata, A., Hartenstein, H., Terracciano, L.:
Comparison of U.S. EPA and European Emission Standards for Combustion and Incineration
Technologies, in: Proceedings of Fifth Annual North American Waste-to-Energy Conference, Research
Triangle Park, NC, pp 701-722, April 1997.
Marchant, G., et al.:
Advances in Fine Particle Control Technology, presented at the Ukraine-United States Technology
Meeting, Kiev, Ukraine, September 10-11, 1996.
Mendelsohn, M., Livengood, D.:
Control of Gaseous Elemental Mercury Using Oxidizing Solution Sprays, in Proceedings: Conference on
Air Quality: Mercury, Trace Metals and Particulate Matter, Energy and Environmental Research Center,
Grand Forks, ND, December 1998.
Miller, R., Harrison, W., Prater, D., Chang, R.:
Recent Compact Hybrid Particulate Collector (COHPAC) Data for Fine Particulate Matter and Air Toxics
Removal from Coal-Fired Power Plants, ICAC Forum >96, Baltimore, MD, March 1996.
Miller, R., Harrison, W., Prater, D., Chang, R.:
Alabama Power Company E.G. Gaston 272 MW Electric Steam Plant- Unit No. 3 Enhanced COHPAC I
Installation, in: Proceedings EPRI-DOE-EPA Combined Air Pollutant Control Symposium, Particulates
and Air Toxics, EPRI TR-108683-V3, Electric Power Research Institute, Palo Alto, CA, August 1997a.
Miller, S., Schelkoph, G., Dunham, G., Walker, K., Krigmont, H.:
Advanced Hybrid Particulate Collector, A New Concept for Air Toxics and Fine Particle Control, in:
Proceedings EPRI-DOE-EPA Combined Air Pollutant Control Symposium, Particulates and Air Toxics,
EPRI TR-108683-V3, Electric Power Research Institute, Palo Alto, CA, August 1997b.
Monroe, L., Cushing, K., Harrison, W., Altman, R.:
Testing of a Combined Dry and Wet Electrostatic Precipitator for Control of Fine Particle Emissions from
a Coal-Fired Boiler, in EPRI-DOE-EPA Combined Air Pollutant Control Symposium, Particulates and
Air Toxics, EPRI TR-108683-V3, Electric Power Research Institute, Palo Alto, CA, August 1997.
12
-------
Morency, J,, Panagiotou, T., Senior, C.:
The Use of a Novel Sorbent to Reduce Mercury Emissions from Fossil Fuel-Fired Power Plants, presented
at the AWMA 91st Annual Meeting & Exhibition, San Diego, CA, June 1998.
Nelson, S., Miller, J,:
New Mercury Control technology for the Fort Dix Waste-to- Energy Plant, in: Proceedings of Fifth Annual
North American Waste-to Energy Conference, Research Triangle Park, NC, pp 587-602, April 1997.
Plaks, N, Daniel, B.E.:
Advances in Electrostatically Stimulated Fabric Filtration, in Proceedings: Seventh Symposium on the
Transfer and Utilization of Paniculate Control Technology, Vol.1, EPA-600/9-89-046a (NTIS PB89-
194039), May 1989.
Redinger, K., Hovis, L., Owens, F., Chang, J., Wilkinson, J.:
Results From the E- SO, 5 MW Pilot Demonstration, in: Proceedings 1990 SO2 Control Symposium,
Volume 4, EPA-600/9-91-015d (NTIS PB91-197244), Air and Energy Engineering Research Laboratory,
Research Triangle Park, NC, May 1991.
Sankey, M., Licata, A.:
Air Pollution Control for Waste-to-Energy Plants - What Do We Do Now?, in: Proceedings of Fifth
Annual North American Waste-to-Energy Conference, Research Triangle Park, NC, pp 151-170, April
1997.
Sedman, C.:
Development of Multipollutant Emission Control Technology for Stoker Boilers, presented at the Stoker
Boiler Workshop, Dayton, OH, August 1998.
Szabo, M., Hawks, R., Sanders, G., Hall, F.:
Operation and Maintenance Manual for Electrostatic Precipitators, EPA-625/I-85-017 (NTIS PB 86-
216785): Air and Energy Engineering Research Laboratory, Research Triangle Park, NC, September
1984.
U.S. Patent 5,401,481, March 1995.
Waffenschmidt, J., Goff, S.:
Mercury Emissions - Trends and Control Effectiveness, in: Proceedings of Fifth Annual North American
Waste-to-Energy Conference, Research Triangle Park, NC, pp 587-602, April 1997.
13
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Lime
Water
Lime Preparation
Boiler
illfllunlBH8iin
-------
Outlet
Jf
High Voltage
Power Supply
Insulator
Cell Plate
4_
Corona Discharge
Electrode
Grounded
Wire Cage
- Intel
Grounded
Wire Cage
Filter
o e
ooo
Top View
•Cell Plate
Figure 2. Electrostatically Stimulated
Fabric Filtration (ESFF)
15
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NRMRL- RTF- P-433
TECHNICAL REPORT DATA
(flease readlastMctiom on the reverse before camplef _
1, REPORT NO.
EPA 600/A-00/003
2.
4. TITLE AND SUBTITLE
Control Technology for Coal-fired Boilers:
Applications to China
S, REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
C. B. Sedman (EPA); and H. Ban and J. Gooch (SRI)
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Southern Research Institute
2000 Ninth Avenue, South
Birmingham, Alabama 35205
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Cooperative Agreement
CS 824904 and ETI-642
12. SPONSORING AGENCY NAME AND ADDRESS
EPA, Office of Research and Development
Air Pollution Prevention and Control Division
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Published paper; 10/98-7/99
14. SPONSORING AGENCY CODE
EPA/600/13
is.SUPPLEMENTARY NOTES ^PPCD project officer is Charles B. Sedman, Mail Drop 04, 9197
541-7700. Presented at 4th Int. Coal Conference, Beijing, China, 8/16-20/99.
. ABSTRACT
paper examines new multipollutant technologies and improvements to
old technologies that may allow China and other rapidly developing nations to miti-
gate the high cost of retrofits and still achieve cleaner air. A program is oulined
to jointly investigate some of these technologies for application to China. (NOTE:
Air pollution regulations in Europe, Japan, and the U.S. have driven the develop-
ment of technologies to control fine particles, acid gases, and toxic metals emis-
sions. Due to the high costs of retrofits, smaller and older facilities have been
closed or switched to more expensive, but cleaner, fuels. New regulations in the
U. S. for fine particles and toxic air pollutants are causing a rethinking of traditional
control strategies that have addressed each pollutant somewhat separately and re-
lied on the lowest sulfur coals.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
bJOENTIFIERS/OPEN ENDED TERMS
COSAT1 Field/Group
Pollution
Boilers
Coal
Combustion
Emission
Particles
Metals
Toxicity
Pollution Control
Stationary Sources
China
Acid Gases
13 B
13 A
21D
2 IB
14G
11F.07B
06T
18. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (ThisReport}
Unclassified
21. NO. OF PAGES
15
20. SECURITY CLASS (This pagej
Unclassified
22. PRICE
EPA Form 2220-1 (9-73)
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