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All of which result in a net power output of 21.58 MWe and net heat rate of 9,834 Btu/kW-hr (LHV).
Plant economics
For the project, the gas treatment and compression system proved to be the most expensive plant subsystem. However, the self regenerating system, despite its high capital cost, turned out to be the most economical long-term choice for LFG treatment since it minimizes or eliminates frequent scrubbing media change out. The capital cost difference between the renewable H2S scrubber and the similarly sized iron-sponge will be amortized through a 15-month period. Similarly, the O&M costs would be reduced significantly by employing a regenerable siloxane system, so that the pay back period would only be 3.5 months more than a throw-away carbon media system.
The net present value of the gas treatment and compression system accounting both for capital cost and O&M costs during a 5-year period were calculated for the project and used in the decision to purchase the above described LFG treatment system. The pay back
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The owner will sell all the power generated to the grid at market rate while purchasing the required auxiliary power from the grid through an existing favorable power contract.
Using the ratio of the power sales price to the power purchase price, a weight factor was devised and an effective heat rate of 9,260 Btu/kW-hr (LHV) was determined for the plant, which will result in a profitable operation for the owner.
At ISO conditions, both the power output and the heat rate would be better.
Summary
This case study presents the critical design features of a 26 MWe combined-cycle power plant, which will run solely on LFG. LFG is a renewable energy source and is a cost effective alternative to natural gas, provided that it is pretreated to gas turbine or engine manufacturer’s specifications.
A state-of-the-art regenerable gas treatment system will be installed to ensure reliable long-term operation of the power plant by minimizing or eliminating outages that otherwise would occur due to the contaminants found in the untreated LFG. Despite its higher initial capital cost, the regenerable system is proven to be more economical than classical gas treatment systems that use disposable scrubbing media.
Economic analysis also indicates that treated LFG will yield a better IRR than natural gas through the life span of the plant.
Since there is no alternative fuel for the plant, it is paramount that the LFG treatment system be inspected and maintained on a continuing basis as changing LFG conditions might adversely affect the short- and long-term performance of the system.
This case study can be useful as a template for future landfill power projects, where large quantities of LFG (4,000 scfm or larger) are available for power generation.
However, it is recommended that the economic viability for individual landfill projects be evaluated against site specific parameters, such as the LFG purchase and/or treatment cost, revenues from byproduct sulfur sales, additional value obtained from heat recovery and the power sales price.
Editor’s note: This paper, PWR2009-81086, was printed with permission from ASME and was edited from its original format. To purchase this paper in its original format or find more information, visit the ASME Digital Store at www.asme.org.
Walter I. Serbetci holds master’s and Ph.D. degrees in Mechanical Engineering from Rensselaer Polytechnic Institute in Troy, N.Y. He has more than 22 years of engineering experience in thermo-mechanical systems and power plant design. As the engineering manager at WorleyParsons-Chicago he was involved in the design and betterment of 35 fossil fuel plants and three nuclear power plants. Serbetci has extensive EPC experience, especially on gas turbine and combined-cycle plants, and in multi-discipline engineering team management. As the managing director of EnerconAmerica, a boutique energy consulting firm based in Chicago, Ill., he is providing engineering and management services to the power industry, A/E firms and plant owner’s. He has authored 21 publications in the areas of thermal systems and power plant design.
Gregory Kindt has a bachelor’s degree in Chemical Engineering from South Dakota School of Mines and Technology in Rapid City, S.D. He has more than 25 years of engineering and project management experience in power generation and air pollution control systems. Kindt has been employed by WorleyParsons-Billings (formerly UniField Engineering Inc.) since 1992. He has significant experience in project engineering and project management for power generation projects including gas turbine and combined cycle, solid fossil fuels, biomass and combined heat and power (CHP) facilities. Current project responsibilities include project management of the landfill gas (LFG) fueled 28 MWe combined-cycle power plant to be constructed at the Roosevelt Regional Landfill in southcentral Washington.
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