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Abstract Stable natural gas prices and increasing power costs are making gas fired cogeneration systems economically attractive to hospitals. This paper presents analytical methods for preliminary evaluation of the economic feasibility of a proposed cogeneration plant. Equations are developed which permit rapid estimation of: generator size, cogenerated power cost, economic payback, additional hospital gas consumption due to cogeneration, and cogeneration cycle efficiency. Introduction Cogeneration consists of two (2) simultaneous processes: on-site power generation, and utilization of heat from the engine which drives the generator. The recovered engine heat can provide domestic hot water, space heating, absorption chilling, and other thermal loads. Cogeneration cycles produce more useful energy output (electrical and thermal) per unit of fuel energy input than a base loaded central power plant. The efficiency of a cogeneration cycle is maximized when all recoverable heat is utilized. Heat from a reciprocating engine is recovered from the jacket coolant, oil cooler, and exhaust gas. Recoverable heat is fully utilized when the cogeneration plant is sized to supply the base, or minimum, thermal load of the facility. The analytical methods presented in this paper focus on the lowest monthly thermal load as the basis for selecting the KW rating of the generator. A cogeneration plant selected on this basis will operate constantly at full Kilowatt (Kw) rating to provide the base thermal load. The equations developed are used to calculate the following parameters:Generator Size (KW): proper sizing of the generator permits full utilization of recoverable heat, and maximizes cycle efficiency.Cogenerated Power Cost ($/KWH): this parameter permits economic evaluation of the cost of cogenerated power which can be sold back to the electric utility.Simple Payback Period (years): enables feasibility analysis of various cogeneration plants, based on generator power, availability, purchased power cost, maintenance coat, fuel cost, engine fuel rate, recovered heat, and efficiency of existing boilers.Additional Gas Consumption With Cogeneration (MCF/yr): this parameter enables the natural gas supplier to estimate additional revenues which result from the operation of the cogeneration system.Cogeneration Cycle Efficiency (%1): permits rapid comparison of several proposed cogeneration systems, based on engine fuel rates and recoverable heat rates. P. 7^ |
