Development of large scale DME diesel power generation plant, NO_x reduction technology by large amount of EGR and DME use SCR

摘要

Recent sudden rise of crude oil price affect industrial activity and large amount of energy consumption will lead environmental pollution. From this point of view groping for the alternative fuel is pressing need. Among alternative fuels, DEM is expected as clean new fuel. DME does not exhaust soot, PM and according to this, NO_x can be drastically reduced by EGR. It has higher cetane number, and is suitable for diesel engine. JFE and Daihatsu have jointly developed 1250kWe world largest DME diesel power generation system. On this paper, main contents are focusing on special feature of DME power plant system and de-NO_x technology especially EGR and SCR that uses DME as reducing agent. Characteristic of DME for diesel fuel: Chemical formula of DME is CH30CH3 and most simple ether compound. Boiling point is -25.1℃ at 0.1 Mpa and vapor pressure is 0.61 Mpa at 25℃ It has the characteristic that can be easily liquefied. Its exhaust gas contains no SO_x because there is no sulfur in DME and no soot and PM because there is no carbon bond in molecular structure of DME. As cetane number is 55-60, it is suitable for diesel engine. Large rate of EGR is possible compared with heavy fuel oil because its exhaust have no soot. According to this drastic de-NO_x is possible. As about 10% of the amount of CO_2 exhaust can be decreased for the same thermal efficiency compared with the oil fuel, and it contributes global warming control. On the other hand, there is a disadvantage such as causing the wear out of pump plunger, and needle of fuel injection nozzle because of low lubricant. And it becomes the causing of fuel pump low charge efficiency because of low viscosity. These disadvantages are the development items. Development items and test resit: Test equipments are mainly composed of DME fuel system, 260mm Bore DME diesel engine, and de-NO_x system. Running test started from 2004, and by using this test plant, some elementary technology, matching, verification, and endurance test were done. Peculiar test items and results are follows. Fuel system: To inject DME from fuel injection nozzle on liquid form, temperature and pressure control system was tested. And after stop engine, to prevent vaporization of residual DME in fuel line, special purge system was tested. Respective system functioned finely and performance was verified. De-NO_x system: EGR system and SCR that uses DME as reducing agent were tested. Thanks to large amount of EGR such as over 40% EGR ratio, below 30ppm(O_2=13%) could be realized on engine itself. And combination of EGR and SCR, below 15ppm could be realized and this value was about 1% of original engine outlet. As the conclusion, DME have the potential for alternative fuel for diesel engine, and will contribute energy security and environment protection.