MEMORANDUM 

From: The Office of Air Quality Planning and Standards 

 U.S. Environmental Protection Agency 

To: EGU NSPS Docket (EPA-HQ-OAR-2011-0044) 

Date: March, 2011 

Subject: Control of Total PM Emissions 

Introduction 

Particulate matter (PM) may be classified by particle size and as either filterable or condensable 

PM. Filterable PM originates from ash in the fuel, incomplete combustion products, and flue gas 

desulfurization (FGD) reaction products. Filterable PM consists of incombustible inert matter (ash), 

and condensable PM consists of gases that will condense into a liquid or solid upon reaching 

ambient temperature. For coal-fired boilers, condensable PM may contain sulfuric and nitric acids, 

high molecular weight organics, and other compounds. Total suspended particulate (TSP) 

encompasses all sizes of filterable PM. Particulate matter that is less than 10 microns in 

aerodynamic diameter is generally referred to as PM10. All particulate matter emitted from a 

controlled EGU stack is expected to be less than 10 microns in size. Particulate matter that is less 

than 2.5 microns in aerodynamic diameter is referred to as PM2.5. Condensable PM is included in 

this category because it is expected that all condensable PM is less than 2.5 microns in the 

atmosphere. Filterable PM2.5 and condensable PM are considered direct PM2.5 emissions. In 

addition to direct PM2.5 emissions, indirect PM2.5, or secondary PM2.5, is formed when precursors 

such as SO2, NOX, VOCs, and ammonia form PM2.5 through reactions in the atmosphere. 

The present subpart Da filterable PM emissions standard for owners/operators of new facilities is 

0.14 lb/MWh gross energy output or 0.015 lb/MMBtu heat input. An owner/operator may also elect 

to comply with an emission limit of 0.030 lb/MMBtu heat input and a 99.9% reduction in potential 

PM emissions. This filterable PM standard is approximately equivalent to a total PM standard 

(filterable + condensable) of 0.30 lb/MWh. The proposed total PM standard for new and 

reconstructed facilities is 0.055 lb/MWh. 

PM Control Technologies 

The following is a brief summary of some of the PM control technologies, including propriety 

technologies. This summary is not intended to be a comprehensive list of available technologies. 

The performance values given here are those that have been provided by the technology provider in 

publically available sources. Inclusion of a technology in this summary is not intended to be an 

endorsement of that technology by the US EPA the US Government 

Mechanical/Inertial Collectors (Cyclones/Multicyclones). A cyclone is a cylindrical vessel, usually 

with a conical bottom. The flue gas enters the vessel tangentially and sets up a rotary motion 

whirling in a circular or conical path. The particles are 'thrown' against the walls by the centrifugal 

force of the flue gas motion where they impinge and eventually settle into hoppers. The removal 
efficiency is between 75 and 99% for particle sizes between 1.0 and 100 μm. Cyclones are robust 

technologies that can deal with the cyclic operation and load changes. However, their efficiency is 

moderate when compared with an ESP or fabric filter. 

Wet Scrubber. The basic principle of wet scrubbers designed for PM control is to provide sufficient 

contact between the flue gas and scrubbing liquid to facilitate removal of the PM. Venturi 

scrubbers are the most commonly used scrubber for particle collection and are capable of achieving 

the highest particle collection efficiency of any wet scrubbing system. In a venturi scrubber, water 

is injected into the flue gas stream at the venturi throat to form fine droplets. Fly ash particles 

impact with the droplets forming a wet by-product which then generally requires disposal. Many of 

the wet particulate scrubbers are designed to control both SO2 and particulates by utilizing the 

alkaline fly ash as sorbent. Lime or some other sorbent is frequently used to boost SO2 removal 

efficiencies. In general, venturi scrubbers in combination with a mechanical collector are not 

expected to reduce PM emissions to the level required by the NSPS. In addition, venturi scrubbers 

tend to have relatively high energy consumption and do not control filterable PM2.5 as well as a 

comparable ESP or fabric filter. 

Flue Gas Desulfurization (FGD). FGD technologies designed for SO2 control are also capable of 

reducing acid gases that are considered condensable particulate matter. An FGD is not a primary 

PM control technology; however FGD technology is a feasible control technology for reducing 

condensable PM emissions. 

Dry Electrostatic Precipitator (ESP). An ESP is a PM control technology that utilizes electrical 

charges to attract particulate matter present in the gas stream. An ESP consists of negatively 

charged discharge electrodes and positively charged collection plates. The negatively charged 

electrodes create a corona of electrical charges transmitting a negative charge to the particulate 

matter in the gas stream. The negatively charged particulate matter is then attracted to the ESP’s 

positively charged collection plate. Particulate matter accumulates on the collection plate until the 

plate is mechanically “rapped” causing the PM to fall into hoppers. The PM that collects in the 

hoppers is then removed by the ash handling system. An ESP consists of a series of the electrical 

fields described above in order to capture any PM that may be re-entrained in the flue gas stream 

during rapping. Some emissions during rapping of the last field are unavoidable. An ESP can be 

located either upstream of the air pre-heater (hot-side ESP) or downstream of the air pre-heater 

(cold-side ESP). Either location selected for the ESP operates at a temperature above the dew point 

of condensable particulate matter. ESPs are intentionally operated at high temperatures to prevent 

corrosion problems that can result from condensable acid gases. Particulate removal efficiencies in 

ESPs can be improved by flue gas conditioning. Flue gas conditioning involves injecting 

conditioning agents such as elemental sulphur, ammonia (NH3), and sulphur trioxide (SO3) into the 

flue gas prior to the ESP. The removal efficiency is between 99.00 and 99.99% for particle sizes 

between 0.01 and 100 μm. 

Wet Electrostatic Precipitator (WESP). A WESP operates in saturated flue gas conditions, where 

the flue gas is below the dew point of many acid gases and other condensable PM. The collector 

plates of a WESP are washed with water. The process eliminates the need for rapping as the liquid 

film removes any deposited fly ash particles. Thus, problems with re-entrainment, fly ash 

resistivity, and capture of fine particles become obsolete. A WESP is a feasible control technology 

for reducing fine filterable and condensable PM emissions. However, WESPs require saturation of 

the flue gas stream with water and generate waste water and sludge. The power required collecting 
particulate matter in the WESP and the pressure loss across the WESP are the main operating costs 

of the WESP system. A WESP system may increase the amount of waste water that requires 

treatment and the WESP system auxiliary power will consume approximately 0.5% of the gross 

output primarily due to additional power requirements for collection. 

Fabric Filter Baghouse (FF). A fabric filter baghouse is a PM collection device that utilizes fabric 

filters or “bags” to collect PM. The design for a fabric filter is fairly simple. The flue gas enters an 

enclosure that contains compartmentalized groups of bags. The bags are operated in a manner to 

allow for cleaning, maintenance, and repair of one compartment (or group of bags) at a time. A 

compartment within the fabric filter includes the bags as the filter media, a tube sheet that supports 

the bags, a PM dislodging mechanism, and a hopper to collect the accumulated PM. As the flue gas 

enters the fabric filter enclosure, PM accumulates on the bags and a “filter cake” is formed. The 

“filter cake” will continue to accumulate on the bags until the pressure drop across a compartment 

has increased to a specified limit. Once the specified pressure drop has been attained the PM is 

removed by placing the compartment in cleaning mode. Several methods for cleaning a fabric filter 

compartment include reverse gas fabric filters (RGFF), reverse air with mechanical shakers, and 

pulse jet fabric filter (PJFF). Each of the above cleaning methods is capable of removing the PM 

that has accumulated on the fabric filter. Once removed, the PM is collected by the ash hoppers. In 

a dry FGD application, the baghouse operates at lower temperatures due to the cooling in the dry 

FGD. This lower operating temperature may increase the condensation and theoretically increases 

control of condensable PM. A FF has a higher pressure drop and greater energy penalty than an 

ESP. 

The specific fabric for an FF is selected based on the operating parameters, pollutant characteristics, 

and mechanical operation. The EPA has an Environmental Technology Verification (ETV) 

program to verify innovative pollution control technologies. The verified fabric filter products 

indicate the fabric can achieve PM2.5 emission levels as low as 0.0001 lb/MMBtu. The list of fabric 

filter products include felted bags and high efficiency microfiber felts, intrinsically coated (IC) 

bags, and membrane bags. 

Felted filters are often used on PJFF and do not require an initial filter cake to collect fine 

particulates. Felted filters are generally 2 to 3 times thicker than woven filters, which improves fine 

particle collection. High efficiency microfiber felts are similar to felted fibers, but they use ultrafine fibers to enhance fine particulate matter control. Intrinsically coated filters are made from 

fibers that are coated, usually with a fluoro-polymer, such as Teflon®. These filters are highly 

durable and have a smaller pore size between fibers, which improves filterable PM2.5 control. 

Membrane filters have a polytetrafluoroethylene (PTFE) coating, such as Teflon®, on the fabric, as 

opposed to the individual fibers. This also provides enhanced control for filterable PM2.5. 

However, the use of either intrinsically coated or membrane bags tends to inhibit the filter cake 

formation. The filter cake formation can increases the effectiveness of the FF for controlling PM2.5

precursors and condensable PM2.5. 

Reactant/Sorbent Injection. Injection technologies to control condensable PM emissions utilize 

injection of a sorbent or reactant. The most common injection chemicals include sodium bisulfite 

(NaHSO3), sodium carbonate (Na2CO3) or trona, and hydrated lime (Ca(OH)2). Ammonia (NH3) 

and magnesium hydroxide (Mg(OH)2) have also been used. The sorbents or reactants utilize their 

physical and chemical properties to react with or adsorb condensable PM (e.g., H2SO4) to produce a 
solid byproduct that can be collected in the particulate control system. Sorbent injection is typically 

installed between the SCR and a fabric filter or ESP. 

COHPACTM. The COHPACTM technology combines an ESP with a high air to cloth ratio FF. The 

FF is placed in a separate casing downstream of the ESP (known as COHPAC I) or within the 

existing ESP's casing by replacing one or more fields of collecting plates with FF modules 

(COHPAC II). The technology is based on the fact that a FF collects higher levels of particulateand finer particulate-than an ESP of equivalent size. The FF acts as a "polishing device". 

Advanced Hybrid Particulate Collector. The Advanced Hybrid Particulate Collector (AHPC) 

utilizes both electrostatic collection and filtration in a unique geometric configuration that achieves 

PM control with much less collection area than conventional PM devices. The design configuration 

of AHPC is unique because, instead of placing the ESP and FFB sections in series, the filter bags 

are placed directly between the ESP collection plates. The collection plates are perforated (45% 

open area) to allow dust to reach the bags. However, since the particles become charged before 

they pass through the plates, over 90% of the PM mass is collected on the plates before it reaches 

the bags. When pulses of air are used to clean the filter bag surfaces, the dislodged particles are 

thrown back into the ESP fields where they have another opportunity to be collected on the plates. 

Tests to date show that the AHPC provides over 99.99% particulate collection efficiency for all 

particle sizes, at a cost that is competitive with or lower than existing technologies. 

Max-9TM. The Max-9TM technology is an electrostatic precipitator/pulse-jet baghouse hybrid, 

employing high voltage discharge electrodes to charge the PM, but with fabric filters instead of 

collecting plates in the casing. Dust particles in the gas are charged by the discharge electrodes, and 

are attracted to the grounded metal cage inside the filter element. The negatively charged particles 

repel each other on the filter surface, resulting in a highly porous filter cake. The Max-9TM ESFF 

technology is reported to provide high collection efficiency while operating at significantly lower 

system pressure drop than a comparable FF. 

PM Control Performance 

Figure 1 shows the total PM emissions reported to EPA as part of the EGU NESHAP information 

collection request (ICR) for facilities below the existing NSPS filterable PM standard (0.015 

lb/MMBtu), that have some type of SO2, control that and use a fabric filter. 

Figure 1: Total PM Performance Test Data 

Plant Name Boiler ID 

Total PM 

(lb/MMBtu) 

Total PM 

(lb/MWh) 

Manitowoc 9 0.0036 0.042 

Springerville 4 0.0037 0.033 

Reid Gardner 1 0.0043 0.042 

San Juan 3 0.0044 0.045 

Northside Generating Station 1A 0.0045 0.041 

Northside Generating Station 2A 0.0046 0.042 

Walter Scott Jr. Energy Center 4 0.0051 0.042 

Clover 2 0.0053 0.052 
J K Spruce **1 0.0054 0.057 

AES Hawaii BLRA 0.0057 0.041 

Chambers Cogeneration LP 1,001 0.0059 0.121 

Sunnyside Cogen Associates 1 0.0062 0.066 

San Juan 4 0.0063 0.064 

Weston 4 0.0068 0.056 

Craig C2 0.0070 0.074 

AES Hawaii BLRB 0.0073 0.056 

Brandon Shores 2 0.0074 

Cholla 4 0.0074 0.073 

INDIANTOWN COGENERATION L.P. 1 0.0081 0.077 

San Juan 1 0.0082 0.083 

San Juan 2 0.0088 0.086 

Hawthorn 5A 0.0088 0.083 

Cholla 3 0.0089 0.096 

Chambers Cogeneration LP 1,002 0.0089 0.124 

Craig C1 0.0092 0.095 

PANTHER CREEK ENERGY FACILITY 1 0.0093 0.099 

PANTHER CREEK ENERGY FACILITY 2 0.0093 

Piney Creek Project 31 0.0102 

Spruance Genco, LLC BLR02A 0.0105 0.148 

Logan Generating Plant 1,001 0.0118 0.112 

Southampton Power Station 1 0.0124 0.167 

Louisa 101 0.0135 0.111 

H L Spurlock Station 3 0.0140 0.128 

Sandow Station 5B 0.0140 0.055 

Oak Grove 1 0.0160 0.170 

Rawhide 101 0.0165 0.143 

Seward 1 0.0178 0.156 

Seward 2 0.0178 

Wygen 1 1 0.0205 0.231 

H L Spurlock Station 4 0.0227 0.198 

Birchwood Power Facility 1 0.0230 0.204 

Morgantown Energy Facility CFB1 0.0240 0.255 

AES Warrior Run Cogeneration Facility 1 0.0244 0.246 

Northampton Generating Company, L.P. NGC01 0.0244 0.239 

Nebraska City 2 0.0246 0.218 

Sandow Station 5A 0.0247 0.110 

Springerville 3 0.0278 0.246 

Cambria Cogen 1 0.0313 

Cope COP1 0.0320 0.272 

Twin Oaks Power One U2 0.0323 0.283 

Clover 1 0.0350 0.318 

Cambria Cogen 2 0.0424 

Hanford CB1302 0.0584 0.601 

Hardin Generator Project U1 0.0820 0.814 
Ninety four percent of the 54 facilities performance tests in lb/MMBtu are achieving an emissions 

rate of 0.034 lb/MMBtu for total PM, and we have concluded that this value is an achievable 

standard for owners/operators of modified facilities. The rate is also approximately equivalent in 

stringency to the existing filterable PM standard, because no specific condensable PM controls 

would necessarily be required. This standard provides amply compliance margin since eighty eight 

percent of the facilities are achieving an emissions rate of 0.030 lb/MMBtu and seventy five percent 

are achieving an emissions rate of 0.023 lb/MMBtu. 

We have concluded that new EGUs will factor in condensable PM controls. BDT for new EGUs 

would be a fabric filter with coated or membrane filter media bags and FGD in combination with 

both DSI and a WESP. 48 of the facilities listed in figure 1 reported gross electrical output during 

the performance test. Because no owners/operators of EGUs are presently specifically attempting 

to control condensable PM, beyond eliminating the visible blue plume that can occur from sulfuric 

acid mist emissions, we concluded it was appropriate to use the top 20 percentile of the performance 

test data for the proposed total PM standard. The top 20 percentile of these performance tests is 

0.055 lb/MWh.