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U �l Mr. Frank DeMaris October 18, 2010 Page 3 of 7 i As provided in the original application, the sulfur oxide (SOx) emissions based on 150 ppmv inlet ` concentration will remain. The BACT analysis provided indicated that treatment options are considered technologically feasible but are not cost effective at 150 ppmv or lower. The BACT analysis for SOx is provided in Appendix C. The site has generally low sulfur in the LFG (less than 50 ppmv); however, this parameter is outside of Ameresco's control, and the 150 ppmv limit ^ will provide a needed margin of safety for changing conditions. Siloxane Pretreatment Process Description SJVAPCD requested that additional information be provided for the gas pre-treatment system. First ,T there is a pretreatment skid, with gas compression and mechanical refrigeration/ dehydration, which G reduces water vapor moisture, dissolved contaminants, and particulate matter from the LFG. A siloxane removal system (SRS) follows the pretreatment. Siloxanes in the LFG are removed using a regenerative Temperature Swing Adsorption (TSA) process with a proprietary solid media blend. The TSA system consists of two parallel vessels, which stand about 11 feet high and have a six foot e M diameter. When the LFGTE facility is operating, there will be one vessel in adsorption operation while the other media vessel will be going through its regeneration cycle or idle. During the adsorption cycle, the media will adsorb siloxane compounds, and some of the other compounds typically present in LFG. The resulting "clean" LFG will provide fuel for the reciprocating IC engines. After adsorbing contaminants for a period of 24-36 hours, the media in the vessel will become saturated, and gas will be sent to the other vessel. Then regeneration of the first vessel will begin. The maximum regeneration cycle (including warm up and cool down cycle) does not exceed half of the time of the adsorption cycle. The media regeneration system includes electric heater units, air compressors, and associated piping and system controls. During the regeneration cycle, ambient air (about 1,300 scfm at 4 psig) will be heated with an electric heater to approximately 450 degrees Fahrenheit (°F) and will be used to purge the media bed of siloxanes and other collected contaminants. This purge air will first contain higher concentrations of organic constituents at the beginning of the regeneration cycle, the siloxanes and mostly air at the end of the cycle, and all purge air will be directed to the small enclosed flare for destruction. This variability in the purge air, as the media bed goes through its regeneration cycle, is problematic for source testing since the constituents in the purge air will vary throughout the regeneration cycle. Likewise, the waste gas flare must be designed differently than normal enclosed landfill gas flares where this type of variability is not encountered. Because extremely low concentration levels of siloxane degrade the reduction efficiency of the back end control equipment, Ameresco will include a second stage siloxane cleaning system called the Fixed Bed Polisher. This system includes two non -regenerative vessels containing activated carbon to remove any remaining organic contaminants before fueling the reciprocating engines. The flare for the SRS regeneration off -gas is an enclosed 30 foot high ground flare firing approximately 100- 200 scfin of LFG at approximately 50% methane to maintain the required .i destruction temperatures. The flare has a minimum combustion temperature of 1,500 °F (1,500 to r