Biogas-fuel/ed microturbines a/ready occupy a profitab/e niche for distributed generation in the US, particularly at sma/1 /andfi/1 sites and wastewater treatment plants. Here Christine Hur/ey looks at technology considerations, operating experience, and at market and site conditions, predicting continued growth for the technology. poaltlva outlook far growth in tha US ı Microturbines are demonstrating some unique attributes for running on biogas that enable them to compete against reciprocating engines - particularly at smaller sites. in fact, biogas applications are among the most promising early applications for microturbines. Biogas is available from landfill sites, wastewater treatment plants, agricultural and livestock operations, food processing plants, gasified woody biomass, or other sources oforganic waste. The combustible portion ofthe gas is methane (CH4). Most of the rest is CO2, with small amounts of nitrogen, oxygen, hydrogen, water (the biggest source of problems in biogas applications), hydrogen sulphide and trace elements. Microturbine manufacturers have laken note of the market opportunities available from biogas and have modified their systems to better handle the unique qualities of biogas and the impurities it contains - see Table 1. LESSONS LEARNED FROM END-USERS We have interviewed planı operators at nine wastewater treatment plants and two landfill sites operating a combined total of 60 microturbines, and found the following results in common: O Site operators are generally happy with the microturbines and would recommend them to other landfill sites and wastewater treatment plants - particularly for smaller sites. O Early landfill and digester installations had some start-up problems, including gas compressor failures, but those problems have been resolved for existing and new sites. End-users now reportfew problems with the operation of biogas-fuelled microturbines. O New Capstone installations have a standardized gas-processing system that is simpler, more compact, and more reliable than previous installations. O Compared with their previous electricity and heating bills, operators of landfill and digester sites are reporting quite significant cost savings as a resul! of using microturbines - particularly where state, loca!, and utility grants are available to help coverthe capital costs ofthe equipment. O Operators ofseveral wastewater treatment plants and landfill sites said they specifically bought microturbines because the units run cleaner than engines. On the last point, Capstone certifies that NOx emissions will be less than 9 parts per million (ppm), but its landfill and digester applications often only have 1-3 ppm. in contrast, emissions from uncontrolled reciprocating engines running on biogas can be in the range of 50-200 ppm.
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