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Production of electrical energy and heat from gas microturbines using biogas : Waukesha Wastewater Treatment Plant / Brian L. Tierney.

by Tierney, Brian L.

Cogeneration of electric power and heat

Biogas -- Environmental aspects

Gas-turbine power-plants

Waste products as fuel

185 leaves : ill. ; 29 cm.

Thesis advisor: Steve Arant

Committee members: Dr. Michael Swedish, Dr. Deborah Jackman

Project significance -- Project objective -- Case study: Sheboygan WWTP microturbine cogeneration project -- Case study: Essex Junction WWTP microturbine cogeneration project -- Waukesha Wastewater Treatment Plant overview -- Literature review -- Anaerobic digestion process -- Gas microturbine background -- Alternative distributed generation technology -- Gas microturbine operation on anaerobic digestion -- Materials and methods -- General -- Funding sources -- Data analysis and results -- Gas microturbine design and specifications -- Integrated UV disinfection/algal rapid growth-harvesting system (IUVDARGHS) design and specifications -- Electrical and thermal production -- Potential energy savings -- Anaerobic digester gas usage and projected natural gas costs -- Emissions reduction -- Gas microturbine cost estimate -- Alternative distributed energy solutions -- Conclusions and recommendations -- A: 2008 Waukesha WWTP digester operating data -- B: Biogas analysis report -- C: Waukesha WWTP partial site plan -- D: Alternative 1 - proposed design and location -- E: Alternative 2 - proposed design and location -- F: Alternative 3 - proposed design and location -- G: Energy calculations and cost analysis -- H: Distributed generation interconnection guidelines -- I: Distributed generation application form -- J: Distributed interconnection agreement -- K: WE Energies customer biogas generating systems -- L: Vendor information -- M: Permissions.

The Waukesha Wastewater Treatment Plant (WWTP) serves approximately 65,000 residents with an average daily flow of 11.0 million gallons per day. Wastewater is generated by residential, industrial, and commerical customers. The City also accepts wastes by truck through the Hauled Waste Program. Currently the Waukesha WWTP flares all of the biogas produced in the WWTP's anaerobic digester except for the biogas produced during the winter months. In the winter, the plant utilizes a small portion of the biogas to directly power the plant's boilers and produce heat. This biogas can be used to produce electricity and reduce pollution from an energy consumption standpoint. The WWTP could use its biogas either to power the wastewater treatment plant or to return electricity to the grid, and thus benefit from incentives offered for renewable power or to meet a state Renewable Portfolio Standard.

In this report, a Capstone CR65-ICHP Micro Turbine cogeneration system will be compared to the current, traditional process of flaring biogas. Biogas must be flared to meet the plant's air permit, which is regulated by the Wisconsin Department of Natural Resources because of the biogas' high methane content. Methane is a greenhouse gas that has an impact 21 times greater than an equivalent amount of carbon dioxide. Flaring the biogas converts the methane primarily into heat, light, and carbon dioxide. To further reduce greenhouse gas emissions, the biogas can be utilized to create energy when ignited. The energy produced from the previously wasted biogas will prevent pollution produced from the local utility, WE Energies, by lowering the energy demand of the community and reduce approximately 3.63 million pounds of emissions from their coal fired plants. The WWTP will produce electricity instead of continuing to be a customer that solely consumes energy.

Three microturbine cogeneration system alternatives were evaluated in this report. Alternative 1 utilizes a four microturbine system to operate 24 hours a day on the WWTP's average of 142,000 ft3/day of biogas with a lower heating value of 579.9 BTU/ft3 from four anaerobic digesters. Alternative 2 consists of a larger, eight microturbine cogeneration system, operated only during on-peak hours to take full advantage of WE Energies buyback rate. This alternative would involve the installation of a 120,000 cubic foot membrane biogas storage system. Alternative 3 consists of a zero carbon, five microturbine system, which sequesters the microturbine exhaust with an algae growth-harvesting system. The algae biomass would be harvested several times a day and increase the amount of biogas produced in the digesters.

The most feasible option for the Waukesha WWTP was determined to be Alternative 1. This option costs approximately $1.3 million with a simple payback period of 14 years. When considering a 20 year facility plan, Alternatives 2 and 3 also generated a viable payback period of 17.3 and 14.5 years, respectively.

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