MEMORANDUM

From: The Office of Air Qu ality Planning and Standards

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

Date: March, 2011

Subject: Control of Total PM Emissions

Introduction

Particulate matter (PM) may also 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. Condensable PM consists of gases that will condense into a liquid or solid upon reach ing ambient temperature. 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 PM 10 . All particulate matter emitted from an EGU stack is expected to be less than 10 microns in size. Partic ulate 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 a ll 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, SO 2 and NO X are precursor and form PM 2.5 through reactions in the atmosphere.

The present subpart Da PM emissions standard for owners/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 99.9 percent emission

reduction.

PM Control Technologies

Venturi Scrubber . A venturi scrubber is a PM collecti on device with a ventur i constriction that utilizes a scrubbing liquid. The venturi causes the gas velocity to increase which helps the atomization of the scrubbing liquid and improve s liquid-gas contact. In general, venturi

scrubbers in combination with a mechanical coll ector are not expected to reduce PM emissions to the level required by the NSPS.

Dry Electrostatic Precipitator (ESP) . A dry ESP is a PM control technology that utilizes electrical charges to at tract particulate matter present in the gas stream. An ESP consists of negatively charged discharge electrodes and positiv ely charged collection plates. The negatively charged electrodes create a corona of electrical charges transm itting a negative charge to the particulate matter in the gas stream. The negativ ely 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 mechanica lly “rapped” causing the PM to fall into hoppers. The PM thatcollects 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 duri ng rapping of the last field are unavoidable. A dry ESP can be located either upstream of the air preheater (hot-side ESP) or downstream of the air preheater (cold-side E SP). Either location selected for the dry ESP operates at a temperature above the dew point of condensable particulate matter. Dry ESPs are intentionally operated at high temperatures to prevent corrosion problems that can result from condensable acid gases

Fabric Filter (FF) . A fabric filter baghouse is a PM collectio n device that utilizes fabric filters or “bags” to collect particulate matter. The design fo r 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 re pair of one compartment (or group of bags) at a time. A compartment within the fabric filter in cludes the bags as the filter media, a tube sheet that supports the bags, a PM dislodging mechan ism, and a hopper to collect the accumulated particulate matter. As the flue gas enters th e fabric filter enclosure, particulate matter accumulates on the bags and a “filter cake” is formed. The “filter cake” will continue to accumulate on the bags until the pressure drop acro ss a compartment has increased to a specified limit. Once the specified pressure drop has been attained the particulate matter is removed by placing the compartment in clea ning mode. Several methods fo r 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 methods is capable of removing the particulate matter that has accumulated on the fabr ic filter. Once removed, the particulate matter is collected by the ash hoppers. In a dry FGD application, the ba ghouse operates at lower temperatures due to the cooling in the dry FGD. This lower operating temperature may increase

the condensation and theoretica lly increases control of conde nsable PM. A FF has a higher pressure drop and greater ener gy penalty than an ESP.

Flue Gas Desulfurization (FGD) . Both dry and wet flue gas desulfurization technologies are

utilized to reduce SO 2 . However, the FGD technologies are also capable of reducing acid gases that are considered condensable particulate ma tter. An FGD is not a primary PM control technology; however FGD technolog y is a feasible control tec hnology for reducing condensable

PM emissions

Reactant/Sorbent Injection . Injection technologies to control condensable PM emissions utilize injection of a sorbent or reactant. The mo st common injection chem icals 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 sorbents or reactants utilize their physical and chemical properties to react with or adsorb condensable PM (H 2 SO 4 ) to produce a solid byproduct that can be colle cted in the particulate control system. Sorbent injection is typically installed betw een the SCR and a fabric filter or ESP.

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 wa ter. The typical location of a WESP would be

downstream of an FGD. A WE SP is a feasible control tec hnology for reducing total PMemissions. A WESP system will produce a waste wa ter stream that will re quire treatment. The power required to collect partic ulate 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 will increase auxiliary power consumption approximately 0.5 percent primarily due to additional power requirements for

collection.

PM Control Costs

Cost estimates were prepared for the regul atory baseline and th e proposed regulatory amendment. We defined two separate baselin es for the comparisons. The first baseline considers the existing NSPS requirements in the ab sence of other regulatory requirements. The

alternate baseline takes into acc ount the requirements of New Source Review and the proposed

Toxics Rule. The alternate baseline is lower than the NSPS, since th ese regulations require additional reductions beyond wh at the NSPS requires.

To estimate impacts of the proposed NSPS amendm ents, we estimated the incremental costs for two 500 MW model plants. One of the model plan ts burns Illinois bituminous coal and the other

burns subbituminous coal from Montana. The regulatory baseline alread y includes an FGD and

a fabric filter and the baseline total PM emissi ons rate is 0.31 lb/MWh. The proposed standard

of 0.055 lb/MWh would result in a reduction of 480 tons annually. We have concluded that the use of a WESP system in combination with sorben t injection would enable an owner/operator of a new affected facility to redu ce total pollutant to the proposed standard. The total annual costs would be an additional $8 million dollar. The incremental cost $17,000 ton is considered cost
effective. However, since the toxics rule to tal PM standard is equi valent to the proposed

standard the actual costs and benefits of the proposed amen dments would be negligible.