### 1 MEMORANDUM

From: The Office of Air Qu ality Planning and Standards U.S. Environmental Protection Agency

To: Combustion Turbine NSPS Docket (EPA-HQ-OAR-2004-0490)

Date: June, 2012

Subject: Relevant Analysis from Docket No. EPA-HQ-OAR-2008-0748 – “Standards of Performance for Stationary Combustion Turbines”

Relevant Analysis

On March 20, 2009, the Federal Register published th e direct final amendments to the stationary
combustion turbine NSPS SO 2 

### standard for biogas-fired turbin es (74 FR 11858). On February 6, 2011, Air Products submitted a request that subpart KKKK be amended in a similar manner for blast furnace gas-fired turbines since the issues would be simila r to those faced by owners /operators of landfill gasfired turbines. The EPA has concluded it is appr opriate to proposed expa nding the current biogas SO 2 

### standard to all low-But gases. This would accoun t for the development of technologies capable of using these gases and the environmental benefits that result from the use of these gases.MEMORANDUM

From: Christian Fellner, Office of Air Quality and Planning Standards

To: Stationary Combustion Turbine NSPS Di rect Final Docket (EPA-HQ-OAR-2008-0748)

Date: March 2009

Subject: SO 2 Control Costs for Owners/Operators of Stationary Combustion Turbines Burning Biogas

Background

As discussed in the preamble to this rulemaking, we ha ve concluded that it is envi ronmentally beneficial to
amend the SO 2 limit for owners/operators of stationary combustion turbines burning biogas from 0.060 lb
SO 2 /MMBtu to 0.15 lb SO 2 /MMBtu. The stationary combustion turbine NSPS does not cover hazardous air pollutants and presently only establishes emission limits for NO X and SO 2 and the direct final rule focuses on those pollutants. The NSPS is a technology specific standard and does not analyze and compare the life cycle environmental impacts of waste reduction, com posting, recycling, composting, and incineration to
landfills.

SO 2 Control Data

The cost effectiveness of removing H 2 S from biogas varies significantly with both the flow rate of the landfill gas and the quantity of H 2 S in the landfill gas. For large landfills with high levels of H 2 S emissions, controls are generally cost effective. Technologies usi ng catalysts that are regenerated are only available for systems that are recovering over 200 kg of sulfur per da y. At the revised emissions rate of 0.15 lb/MMBtu, this would equate to a landfill ge nerating 3,500 scfm of landfill gas. Solid and liquid scavenging systems are the primary technologies for removing H 2 S when the daily load of sulfur is less than 200 kg/day. While the initial costs of these systems are genera lly low, the operating costs can be high and the cost effectiveness of
SO 2 control is approximately $10,000 per ton.

Emission Comparisons

Information on the emissions from landfills is available from EPA’s AP 42 emission factors (http://www.epa.gov/ttn/chief/ap42/ch02/index.html), a nd general information and estimations of the environmental benefit of recovery landfill gas for useful purposes is available from EPA’s Landfill Methane Gas Outreach Program (http://www.epa.gov/lmop/). Th e environmental benefits on recovering landfill gas for a useful purpose is substantial, both from a health and climate persp ective, when compared to allowing that gas to be released dire ctly to the atmosphere.

Subparts Cc and WWW require that larger landfills coll ect and treat portions the landfill gas to minimize emissions. The simplest approach is to flare the landfill gas without any useful energy recovery. The following emission comparison is strictly illustrative, but demonstrates the environmental benefits of recovery landfill gas for a useful purpose instead of flaring it. Since turbines burning landfill gas operate continuously, the displaced utility emissions are assu med to be from a new coal-fired boiler meeting the limits in subpart Da, the utility NSPS.Table 1: Comparison of Landfill Flare Plus Utility to Turbine Emissions

Flare Utility Turbine Difference
NO X (tons) 18 19 37 0
SO 2 (tons) 39 27 39 (27)
CO 2 (tons) 30,000 38,000 30,000 (38,000)

Key Assumptions

• Recovered landfill gas = 2,000 standard cubic feet per minute

• Heating value of the landfill gas = 500 Btu/scf

• Turbine efficiency = 25% (HHV)

• NO X emissions rate from flare = 0.068 lb/MMBtu

• NO X emissions rate from turbine = 0.14 lb/MMBtu (~ 35 ppm)

• NO X emissions rate from utility = 1.0 lb/MWh (coal utility NSPS limit)

• SO 2 emissions rate from landfill gas = 0.15 lb/MMBtu

• SO 2 emissions rate from utility = 1.4 lb/MWh (coal utility NSPS limit)



### For the pollutant on interest in the direct final amendments, SO 2 

### , onsite emissions are unchanged, but overall emissions are decreased by 27 tons. In addition, overall CO 2 

### emissions are reduced by 38,000 tons. While onsite NO X 

### emissions increase by 19 tons, when the displaced utility emissions
are accounted for the overall NO X 

### emissions are equivalent. Furt hermore, in the absence of the direct final amendments to the turbine NSPS, deve lopers might elect to use reciprocating internal combustion engines to recover the landfill gas inst ead of treating the gas and using a turbine. Reciprocating internal combustion engines tend to have much high NO X 

### and CO emissions than
turbines and the local emissions woul d be increased under that scenario.