Renewable Energy Technology Assessments - Kauai Island Utility ...
Renewable Energy Technology Assessments - Kauai Island Utility ... Renewable Energy Technology Assessments - Kauai Island Utility ...
Kaua’i Island Utility Cooperative Renewable Energy Technology Assessments 3.0 Renewable Energy Technology Options The prospects for power generation from biogas produced at local wastewater treatment plants are also minimal. Kauai has four public wastewater treatment plants, all relatively small (the highest average flow is at Lihue, 1.2 million gallons per day). According to Mel Matsumura of the County, there is little potential for biogas utilization. For example, biogas production at the Lihue treatment plant is flared with a small “candle-like” flame. Apparently the County had been approached by a biogas developer in the past, but after visiting the site, the developer did not make contact with the County again. Most new housing and resort developments on the island are served by private water and wastewater systems, reducing the possibility that there will be a significant developable resource in the future. 10 3.2.2 Landfill Gas Landfill gas (LFG) is produced by the decomposition of the organic portion of waste stored in landfills. Landfill gas typically has a methane content between 45 and 55 percent and is considered to be an environmental risk. Political and public pressure is rising to reduce air and groundwater pollution and the risk of explosion associated with LFG. From an energy generation perspective, LFG is a valuable resource that can be burned as fuel by reciprocating engines, small gas turbines or other devices. LFG was first used as a fuel in the late 1970s. Since then, LFG collection and utilization technology has steadily improved. LFG energy recovery is now regarded as one of the more mature and successful of the waste to energy technologies. There are more than 600 LFG energy recovery systems in 20 countries. Applications LFG can be used to generate electricity and process heat or may be upgraded for pipeline sales. The major constituents released from landfill wells are carbon dioxide and methane. LFG contains trace contaminants such as hydrogen sulfide and siloxanes that should be removed prior to combustion. Power production from LFG facilities is typically less than 10 MW. As discussed earlier, several types of conversion devices can be employed to generate electricity from LFG. Typically the equipment requires only minor modification so long as the gas is properly cleaned and prepared. Internal combustion engines are by far the most common generating technology choice. About 75 percent of landfills that generate electricity use engines. 11 10 Mel Matsumura (Chief Engineer Kauai County Wastewater Division), personal communication, June 16, 2004. 11 EPA Landfill Methane Outreach Program. 21 March 2005 3-18 Black & Veatch
Kaua’i Island Utility Cooperative Renewable Energy Technology Assessments 3.0 Renewable Energy Technology Options Depending on the scale of the gas collection facility, it may be feasible to generate power via a combustion turbine and/or a steam turbine. Testing with microturbines and fuel cells is also underway, although these technologies do not appear to be economically competitive for current applications (see Section 3.10). Resource Availability Gas production in a landfill is primarily dependent upon the depth of waste in place, age of waste in place, and amount of precipitation received by the landfill. Each landfill is unique because each has a different volume, receives a different amount of water, and has a different material composition. This variability makes it important to measure the quantity and quality of LFG before installing a power generation system. In general, LFG recovery may be economically feasible at sites that have more than one million tons of waste in place, more than 30 acres available for gas recovery, a waste depth greater than 40 feet, and the equivalent of 25+ inches of annual precipitation. There are methods of changing both the quantity and quality of the LFG, if required, but doing so will affect the long term gas production. It is particularly important to understand that every landfill will reach a point after closure at which time the LFG production will decrease and eventually diminish below economically viable levels. Figure 3-5. LFG Well Drilling. Many existing larger landfills have collection systems to remove leachate and LFG from the landfill to prevent it from infiltrating ground water supplies and causing other nuisance problems. These systems are usually connected to a flare system if there is not a power generation system installed. The flares combust the methane in the LFG. 21 March 2005 3-19 Black & Veatch
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Kaua’i <strong>Island</strong> <strong>Utility</strong> Cooperative<br />
<strong>Renewable</strong> <strong>Energy</strong> <strong>Technology</strong> <strong>Assessments</strong><br />
3.0 <strong>Renewable</strong> <strong>Energy</strong> <strong>Technology</strong><br />
Options<br />
Depending on the scale of the gas collection facility, it may be feasible to<br />
generate power via a combustion turbine and/or a steam turbine. Testing with<br />
microturbines and fuel cells is also underway, although these technologies do not appear<br />
to be economically competitive for current applications (see Section 3.10).<br />
Resource Availability<br />
Gas production in a landfill is primarily dependent upon the depth of waste in<br />
place, age of waste in place, and amount of precipitation received by the landfill. Each<br />
landfill is unique because each has a different volume, receives a different amount of<br />
water, and has a different material composition. This variability makes it important to<br />
measure the quantity and quality of LFG before installing a power generation system.<br />
In general, LFG recovery may be economically feasible at sites that have more<br />
than one million tons of waste in place, more than 30 acres available for gas recovery, a<br />
waste depth greater than 40 feet, and the equivalent of 25+ inches of annual precipitation.<br />
There are methods of changing both the quantity and quality of the LFG, if required, but<br />
doing so will affect the long term gas production. It is particularly important to<br />
understand that every landfill will reach a point after closure at which time the LFG<br />
production will decrease and eventually diminish below economically viable levels.<br />
Figure 3-5. LFG Well Drilling.<br />
Many existing larger landfills have collection systems to remove leachate and<br />
LFG from the landfill to prevent it from infiltrating ground water supplies and causing<br />
other nuisance problems. These systems are usually connected to a flare system if there<br />
is not a power generation system installed. The flares combust the methane in the LFG.<br />
21 March 2005 3-19 Black & Veatch
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