MEMORANDUM

From: The Office of Air Qu ality 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 partic le 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 product s. Filterable PM consists of incombustible inert matter (ash), and condensable PM consists of gases that will condense into a liqui d or solid upon reaching ambient temperature. For coal-fir ed boilers, condensable PM may cont ain sulfuric and nitric acids, high molecular weight organics, and other co mpounds. Total suspended particulate (TSP) encompasses all sizes of filterable PM. Partic ulate matter that is less than 10 microns in aerodynamic diameter is generally referred to as PM 10 . 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 PM 2.5 . 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 PM 2.5 and condensable PM are considered direct PM 2.5 emissions. In
addition to direct PM 2.5 emissions, indirect PM 2.5 , or secondary PM 2.5 , is formed when precursors
such as SO 2 , NO X , VOCs, and ammonia form PM 2.5 through reactions in the atmosphere.

The present subpart Da filt erable PM emissions standard for owne rs/operators of new facilities is 0.14 lb/MWh gross energy output or 0.015 lb/MMBtu h eat 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 facili ties is 0.055 lb/MWh.

PM Control Technologies

The following is a brief summary of some of th e 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 provi ded by the technology provider in publically available sources. Incl usion of a technology in this summa ry is not intended to be an endorsement of that technology by the US EPA the US Government

Mechanical/Inertial Collector s (Cyclones/Multicyclones) . A cyclone is a cylin drical vessel, usually with a conical bottom. The flue gas enters th e vessel tangentially and sets up a rotary motion whirling in a circular or conical path. The particles are 'throw n' against the walls by the centrifugal force of the flue gas motion where they impinge and eventually settle into hoppers. The removalefficiency 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 desi gned 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 effi ciency of any wet scrubbing system. In a venturi scrubber, water is injected into the flue gas stream at the ventur i throat to form fine dr oplets. 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 SO 2 and particulates by utilizing the alkaline fly ash as sorbent. Lime or some other sorbent is fre quently used to boost SO 2 removal efficiencies. In general, venturi scrubbers in combination with a mechanical collector are not expected to reduce PM emissions to the level requ ired by the NSPS. In addition, venturi scrubbers tend to have relatively high energy cons umption and do not control filterable PM 2.5 as well as a comparable ESP or fabric filter.

Flue Gas Desulfurization (FGD) . FGD technologies designed for SO 2 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 t echnology that utilizes electrical charges to attract particulate ma tter 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 pa rticulate matter is then attracted to the ESP’s positively charged collection plate. Particulate ma tter 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-e ntrained in the flue gas stream during rapping. Some emissions dur ing rapping of the last field ar e 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 inten tionally 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 (NH 3 ), and sulphur trioxide (SO 3 ) into the flue gas prior to the ESP. The removal effici ency 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 pr ocess 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 pa rticles become obsolete. A WESP is a feasible control technology for reducing fine filterable and condensable PM em issions. However, WESPs require saturation of the flue gas stream with water and generate wa ste water and sludge. The power required collectingparticulate matter in the WESP and the pressure loss across the WESP are the main operating costs of the WESP system. A WESP system may incr ease 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 mechanis m, and a hopper to collect the accumulated PM. As the flue gas enters the fabric filter enclosure, PM accumulate s 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 spec ified pressure drop has b een 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 (R GFF), reverse air with mechanical shakers, and pulse jet fabric filter (PJFF). Each of the above cleaning me thods 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 incr ease the condensation and theoretically increases control of condensable PM. A FF has a higher pr essure 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 pollu tion control technologies. The ve rified fabric filter products
indicate the fabric can achieve PM 2.5 emission levels as low as 0.0001 lb/MMBtu. The list of fabric filter products include felted bags and high efficien cy 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 ti mes 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 part iculate matter control. Intrinsically coated filters are made from fibers that are coated, usually with a fluoro-polymer, such as Te flon®. These filters are highly durable and have a smaller pore size betw een fibers, which improves filterable PM 2.5 control. Membrane filters have a polytetra fluoroethylene (PTFE) coating, su ch as Teflon®, on the fabric, as opposed to the individual fibers. This also provides enhanced control for filterable PM 2.5

. However, the use of either intrinsically coated or membrane bags tends to inhibit the filter cake
formation. The filter cake formation can increase s the effectiveness of the FF for controlling PM 2.5 precursors and condensable PM 2.5

.

Reactant/Sorbent Injection . Injection technologies to control condensable PM emissions utilize injection of a sorbent or reacta nt. The most common injection ch emicals include sodium bisulfite (NaHSO 3 ), sodium carbonate (Na 2 CO 3 ) or trona, and hydrated lime (Ca(OH) 2 ). Ammonia (NH 3 ) and magnesium hydroxide (Mg(OH) 2 ) have also been used. The sorb ents or reactants utilize their physical and chemical properties to react with or adsorb condensable PM (e.g., H 2 SO 4 ) to produce asolid byproduct that can be collected in the particulate c ontrol system. Sorbent injection is typically
installed between the SCR and a fabric filter or ESP.

COHPACTM . The COHPAC TM 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 fi elds of collecting plat es with FF modules (COHPAC II). The technology is based on the fact th at a FF collects higher levels of particulateand finer particulate-than an E SP of equivalent size. The FF acts as a "polishing device".

Advanced Hybrid Particulate Collector . The Advanced Hybrid Pa rticulate Collector (AHPC)
utilizes both electrostatic collection and filtration in a unique geometric configuration that achieves
PM control with much less collec tion area than conventi onal 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 plat es. The collection plates are perforated (45% open area) to allow dust to reach the bags. Howe ver, since the particles become charged before they pass through the plates, over 90% of the PM ma ss is collected on the plates before it reaches the bags. When pulses of air are used to clean the filter bag surfaces, th e dislodged particles are thrown back into the ESP fields where they have a nother 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 competit ive with or lower than existing technologies.

Max-9TM . The Max-9TM technology is an electrostatic precipitator /pulse-jet baghouse hybrid, employing high voltage discharge elect rodes to charge the PM, but w ith fabric filters instead of collecting plates in the casing. Du st particles in the gas are charge d 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 surf ace, resulting in a highly porous filter cake. The Max-9TM ESFF technology is reported to provide hi gh collection efficiency while ope rating 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 f acilities below the existing NSPS filterable PM standard (0.015 lb/MMBtu), that have some type of SO 2 , 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 0.052J 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 COGENERATI ON 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 Co mpany, 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 0.814Ninety four percent of the 54 f acilities 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 mo dified 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 pr ovides 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 co ated or membrane filter media bags and FGD in combination with
both DSI and a WESP. 48 of the f acilities listed in figure 1 reporte d gross electrical output during the performance test. Because no owners/operators of EGUs are presently specifically attempting to control condensable PM, beyond eliminating the vi sible 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. Th e top 20 percentile of th ese performance tests is
0.055 lb/MWh.