Impact of Negative Factors on Performance of Cryogenic Unit of LNG Gas-Turbine Engine Fuel System
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IMPACT OF NEGATIVE FACTORS ON PERFORMANCE OF CRYOGENIC UNIT OF LNG GAS-TURBINE ENGINE FUEL SYSTEM I. A. Arkharov, E. S. Navasardyan, A. S. Krotov, and Ya. V. Samokhvalov UDC 629.063.6; 662.758.3 LNG gas-turbine engines have several advantages over diesel engines: capacity to develop higher power with smaller weight and size, lower fuel price, environment friendliness, etc. At the same time, this type of engines is characterized by low efficiency at insufficient load and high idle-run fuel consumption. A part of the energy losses under these conditions occurs in the cryogenic unit of the LNG gas-turbine engine fuel system. Schematic diagrams and characteristic features of the cryogenic unit of the LNG gas-turbine engine are presented. Schemes of LNG delivery with vapor-pressurization, sparging of the tank with an external noncondensing gas, and use of pumps are described. The impact on the fuel system performance of such factors as fuel delivery mode, LNG flow return, restraining temperature of the delivered LNG, variation of LNG composition, etc. are investigated. The criteria of efficiency of the system in start, main, and idle modes are calculated by mathematical modeling method. Keywords: LNG, gas-turbine engine, fuel system, pressurization system.
In conformity with the changes in the MARPOL Protocol, Annex VI adopted in 1997 for prevention of marine environment pollution, considerable limitations are imposed on sulfur and nitrogen oxides emissions by ships. Emissions are reduced in three stages (Fig. 1). At the last stage (in 2020 or in 2025 if deferred), the permissible emission limit will be lowered 9 times. The upper sulfur oxides content limits in the emission control areas (ECA) will be markedly lower (35 times) than in other maritime areas [1]. The ground for imposition of limits is adverse effect of emissions on the environment of coastal areas. Fuel combustion products (nitrogen and sulfur oxides) are one of the major causes of acid rains and smog that adversely affect human health [2]. Ships with engines running on heavy diesel oil must be provided with selective catalyzers (to reduce emission of nitrogen oxides) and scrubbers (to catch particles of sulfur oxides) for adherence to environmental standards. When marine gas oil is used as the fuel, only nitrogen oxide catalyzers are needed for cleaning the exhaust gases. For ships, installation of catalyzers (because of low capital costs) is the only way to adhere to emission standards. When natural gas obtained by vaporization of liquefied natural gas (LNG) is used as the fuel, cleaning systems are not needed because the oxides emission level is lower in the case of natural gas combustion compared to marine gas oil combustion. According to the data in [3], when natural gas burns, sulfur oxides emissions are negligible and nitrogen oxides and carbon dioxide emissions are far less than when heavy diesel oil or marine gas oil burns (reduction of emission of carbon dioxide is up to 20% and of nitrogen oxides, up to 85%). LNG as a fuel with a high thermal eff
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