Utilizing landfill gas to fuel a gas-to-energy plant producing waste heat to fuel a liquid waste evaporator

Abstract

Landfill gas is a renewable energy resource produced from decomposition of organic waste in municipal solid waste landfills. The gas is generated in significant quantities for IO to 20 years after waste is disposed of in a landfill. Utilization of landfill gas presents many challenges in filtering contaminants from the gas and monitoring pollution emitted from the combustion process. Being a waste product, landfill gas has cost advantages as compared to natural gas fuel. Landfill gas has been used to fuel reciprocating engines sets in local distributed electrical generating plants and various industrial processes for many years. Electricity generated from the power plants cannot compete with the base load price of coal and gas-fired plants. The government has enacted legislation to assist renewable energy resource developers in obtaining capital, and to provide tax incentives and credits to lower electricity generation cost of these "gas-to-energy" plants. Upon expiration of Section 29 credits, the number of new landfill gas-to-energy facilities constructed in the United States fell to only 22 by the year 2002. Reinstallation of incentives through Section 45 credits within the Energy Policy Act of2005 resulted in renewed interest in gas-to-energy plants. Higher electricity prices from conventional coal and gas-fired generating plants have narrowed the gap in production cost as compared to renewable energy resources. Higher energy prices have also sparked a renewed interest in combined heat and power (CHP) systems. CHP systems provide fuel for secondary processes by utilizing waste heat from a power source such as reciprocating engines used in distributed electrical energy plants. CHP systems can increase overall efficiencies of engines from the thirty percent range to over ninety percent. Most CHP systems easily double the efficiency of engine output, resulting in significant savings in energy cost for facilities. There are numerous obstacles to overcome, in which many facilities find they cannot utilize CHP systems. The must be an adequate demand for the electricity generated, and a corresponding demand for the secondary process desired. If electricity is to be sold on the power grid, satisfactory agreements must be reached between the CHP power producer, the utility purchasing the power, and the government. In 2005, a gas-to-energy electrical generating plant has been constructed at Waste Management's Liberty Landfill near Monticello, Indiana. A proposal to utilize waste heat from the engine exhaust is being considered for fueling an industrial liquid waste evaporator. The addition of a waste heat-fueled evaporator would significantly increase the energy efficiency of the distributed power plant. Savings in fuel cost of the evaporation facility is believed to result in lowering overall cost of the liquid waste disposal processes. In this project, there are three separate entities involved in the components of the CHP system. Waste Management supplies the landfill gas and operates the power plant; Wabash Valley Power owns the plant and markets electricity produced; and Liquid Solutions LLC owns an existing onsite landfill gas-fueled evaporator and proposes to construct a second evaporator that is fueled by waste heat from the plant's engine exhaust. Even though the evaporator existed prior to construction of the plant, it was initially desired to relocate the evaporator to another landfill, which allowed construction of the gas-to-energy plant. Once the gas-to-energy plant was placed online, it was found there is not enough landfill gas to fuel the existing evaporator. The landfill gas field must be expanded and the existing evaporator be retrofitted to operate on a reduced quantity of landfill gas. The perplexing problem of inadequate gas supplies resulted in a realization to utilize waste heat from the engines to fuel an expansion of the evaporation system. This paper examines several aspects of power generation from landfill gas and the use of exhaust heat. Discussions relate to the following key primary subject areas: (I) the landfill gas fuel as compared to conventional fuel sources, (2) use of reciprocating engines used to generate electricity, (3) combined heat and power systems to fuel secondary processes, particularly liquid waste evaporation and, (4) the financial feasibility of incorporating the combined heat and power system with the existing gas-to energy plant and landfill gas-fueled evaporator. This paper should not to be used as a financial evaluation by any parties and is intended to be used as a general feasibility study only. Additional analysis must be performed to determine the feasibility for the specific project to be implemented and any specific considerations applicable.