MEMORANDUM 

From: The Office of Air Quality 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 reaching 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 PM10. All particulate matter emitted 

from an 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, SO2 and NOX are precursor and form PM2.5 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 heat 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 collection device with a venturi constriction that 

utilizes a scrubbing liquid. The venturi causes the gas velocity to increase which helps the 

atomization of the scrubbing liquid and improves liquid-gas contact. In general, venturi 

scrubbers in combination with a mechanical collector 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 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. 

A dry ESP can be located either upstream of the air preheater (hot-side ESP) or downstream of 

the air preheater (cold-side ESP). 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 collection device that utilizes fabric filters or 

“bags” to collect particulate matter. 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 

particulate matter. As the flue gas enters the 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 across 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 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 

particulate matter that has accumulated on the fabric filter. Once removed, the particulate matter 

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. 

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

utilized to reduce SO2. However, the FGD technologies 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 

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 

(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. 

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 typical location of a WESP would be 

downstream of an FGD. A WESP is a feasible control technology for reducing total PM 
emissions. A WESP system will produce a waste water stream that will require treatment. The 

power required to collect 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 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 regulatory baseline and the proposed regulatory 

amendment. We defined two separate baselines for the comparisons. The first baseline 

considers the existing NSPS requirements in the absence of other regulatory requirements. The 

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

Toxics Rule. The alternate baseline is lower than the NSPS, since these regulations require 

additional reductions beyond what the NSPS requires. 

To estimate impacts of the proposed NSPS amendments, we estimated the incremental costs for 

two 500 MW model plants. One of the model plants burns Illinois bituminous coal and the other 

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

a fabric filter and the baseline total PM emissions 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 sorbent injection would enable an owner/operator of 

a new affected facility to reduce 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 total PM standard is equivalent to the proposed 

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