Wastewater or other organic wastes are not subject to the same law. Landfill sites that have a use for the waste heat from the microturbines are also more attractive - yet most sites don't have a use for the heat. ONE creative example is a landfill site nearAntioch, lllinois, which is piping landfill gas overto 12 Capstone microturbines at a high school (about 1 km away). Recovered heat is used forthe school's sports complex and swimming pool. This illustrates another point: using the biogas to supply on-site or nearby loads, rather than exporting all the electricity to the grid, means that price can be compared to retail electricity prices rather than wholesale prices. WASTEWATERTREATMENT PLANTS Wastewater treatment plants are an excellent application for microturbines because they can feed the microturbines' waste heat back into the digesterto maintain the process temperature. Typically, these plants will use the microturbine waste heat to preheat water for their boiler, thus saving on natural gas costs - see Figure 2. Ron Meyer at the Sanla Margarita Water District, which has two 30 kW Capstone microturbines with heat recovery, commented that the planı operators are really excited about the projeci - the efficiencies, the heat production, and the savings. They're actually more interested in the heat than in the electrical production. Becausethey use it day-today. And they have a couple of ideas for even more ways they can use the heat.' Even though nearly every region of the US has a wastewater treatment plan!, only plants that use anaerobic digestion as part on their treatment process produce biogas. Most of the plants that do have anaerobic digestion, though, often just flare off the biogas. Because plan! operators are focused on meeting water quality and disposal standards rather than energy production. Consequently, On-site generation with heat recovery ARTICLE / MAKALE these plants represent a largely untapped market - see Figure 3. The size ofwastewater treatment plants varies. Some plants barely produce enough digester gas to power a single small microturbine. For example, the Jeannette wastewater treatment plan!, east of Pittsburgh, only has enough biogas to operate its 30 kW-rated Capstone microturbines at 18 kW. The largest wastewater treatment plants produce enough biogas for 20-25 MW. As with landfill sites, microturbines are really more suitable at smaller plants than larger ones. The Town of Lewiston Water Pollution Control Center, for instance, has two Capstone microturbines. Timethy Lockhart, Chief Operater, says, 'We're a 2.75 million gallon (per day) piant. lfyou're in that neighbourhood, it's a pretty good application for microturbines. lf you're a larger facility, you're probably betler off running one large reciprocating engine rather than 1 5 or 20 microturbines. But for a smaller niche, 1 think it's a good fit.' lngersoll Rand's new 250 kW EcoWorks microturbine will expand the range of landfill and digester sites appropriate for microturbines. in total, about 100 microturbines currently run on biogas from wastewater treatment plants in the US. Most plants use all the electricity output from the microturbines and don't export to the grid. Besides having a good use for the waste heat, wastewater treatment plants have some ether specific advantages for microturbine applicatiens. Compared to ether market secters, municipal-owned wastewater treatment plants have access le capital, can telerate a lenger payback period, and are already semewhat familiar with distributed generation, since many have back-up generaters. On the ether hand, seme installers anecdotally repert that water agencies can be bureaucratic te werk with (so the sales cycle is lenger), and that, as a sector, wastewater treatment plants are generally reluctant te try new er unfamiliar technelegies. Two views of the microturbine installation at the San E/ijo Water Rec/amation Faci/ty. ENERJi & KOJENERASYON DÜNYASI 55
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