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MEMORANDUM 

From: The Office of Air Quality 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 the direct final amendments to the stationary 

combustion turbine NSPS SO2 standard for biogas-fired turbines (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 similar to those faced by owners/operators of landfill gasfired turbines. The EPA has concluded it is appropriate to proposed expanding the current biogas SO2

standard to all low-But gases. This would account 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 Direct Final Docket (EPA-HQ-OAR-2008-0748) 

Date: March 2009 

Subject: SO2 Control Costs for Owners/Operators of Stationary Combustion Turbines Burning 

Biogas 

Background

As discussed in the preamble to this rulemaking, we have concluded that it is environmentally beneficial to 

amend the SO2 limit for owners/operators of stationary combustion turbines burning biogas from 0.060 lb 

SO2/MMBtu to 0.15 lb SO2/MMBtu. The stationary combustion turbine NSPS does not cover hazardous air 

pollutants and presently only establishes emission limits for NOX and SO2 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, composting, recycling, composting, and incineration to 

landfills. 

SO2 Control Data

The cost effectiveness of removing H2S from biogas varies significantly with both the flow rate of the 

landfill gas and the quantity of H2S in the landfill gas. For large landfills with high levels of H2S emissions, 

controls are generally cost effective. Technologies using catalysts that are regenerated are only available for 

systems that are recovering over 200 kg of sulfur per day. At the revised emissions rate of 0.15 lb/MMBtu, 

this would equate to a landfill generating 3,500 scfm of landfill gas. Solid and liquid scavenging systems are 

the primary technologies for removing H2S when the daily load of sulfur is less than 200 kg/day. While the 

initial costs of these systems are generally low, the operating costs can be high and the cost effectiveness of 

SO2 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), and 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/). The environmental benefits on recovering landfill gas 

for a useful purpose is substantial, both from a health and climate perspective, when compared to allowing 

that gas to be released directly to the atmosphere. 

Subparts Cc and WWW require that larger landfills collect 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 assumed 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 

NOX (tons) 18 19 37 0 

SO2 (tons) 39 27 39 (27) 

CO2 (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) 

• NOX emissions rate from flare = 0.068 lb/MMBtu 

• NOX emissions rate from turbine = 0.14 lb/MMBtu (~ 35 ppm) 

• NOX emissions rate from utility = 1.0 lb/MWh (coal utility NSPS limit) 

• SO2 emissions rate from landfill gas = 0.15 lb/MMBtu 

• SO2 emissions rate from utility = 1.4 lb/MWh (coal utility NSPS limit) 

For the pollutant on interest in the direct final amendments, SO2, onsite emissions are unchanged, 

but overall emissions are decreased by 27 tons. In addition, overall CO2 emissions are reduced by 

38,000 tons. While onsite NOX emissions increase by 19 tons, when the displaced utility emissions 

are accounted for the overall NOX emissions are equivalent. Furthermore, in the absence of the 

direct final amendments to the turbine NSPS, developers might elect to use reciprocating internal 

combustion engines to recover the landfill gas instead of treating the gas and using a turbine. 

Reciprocating internal combustion engines tend to have much high NOX and CO emissions than 

turbines and the local emissions would be increased under that scenario.