Survey of modern power plants driven by diesel and gas engines

This paper surveys the latest technology of power plants driven by reciprocating internal combustion (IC) engines, from information collected from publications made mainly during the 1990 s. Diesel and gas engines are considered competitive prime movers in power production due mainly to their high full- and part-load brake thermal efficiency, ability to burn different fuels, short construction time and fast start-ups. The market for engine power plants has grown rapidly, with estimated total orders for reciprocating engines of 1 MW output and more reaching the 5000 unit level, (10 GW), between June 1995 and May 1996. Industrialized countries much prefer combined heat and power (CHP) production. Intense interest has been shown in recent years in alternative gas fuels; natural gas appears to be the most promising, but liquid petroleum gas, gas from sewage disposal plants, landfill gas and other biogases, as well as wood gas have also been recognized as other alternatives. Liquid alternatives such as fusel and pyrolysis oil have also been mentioned, in addition to information on coal burning engines. The percentage of gas engines used has increased and different ones are being developed, based on either the traditional spark ignition (SI), dual-fuel technology or the more recent high pressure gas injection system. In cold climates, energy production is largely based on CHP plants. Waste heat is utilized for local, regional or district heating or for industrial uses like drying, heating, cooling etc. Even radiative and convective heat from gen-set surfaces are employed, and boilers are used with exhaust outlet temperatures of below dew point. Combined cycle schemes, including turbo compound systems and steam turbines, are also incorporated into engine power plants in order to increase output and efficiency. Two-stroke, low-speed diesel engine plants show the highest electric efficiencies, with combined cycle plants reaching up to 54%, while gas engine plants achieved between 35% and 47%. The total efficiency of a CHP plant depends on its heat recovery system, recording at its highest rating 98% efficiency. Exhaust emissions of IC engine power plants must be reduced both by internal and post-combustion methods. The lean-burn SI gas engines seem better with regard to engine-out emissions, while other gas and oil-driven engines with higher oxides of nitrogen emissions are worse. The paper deals only with post-combustion exhaust cleaning systems, reporting on the development of selective catalytic processes (SCR) and three-way catalysts. Data was also collected on combined oxi-cat and SCR reactors and NO reduction concepts that utilize other media than ammonia or urea, as well as more advanced post-combustion methods.