1998-05-20
2000-11-07
Kamen, Noah P.
60 39464, F02G 300
Patent
active
061417963
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The problems associated with the use of coals as a gas turbine fuel for high efficiency power generation are well known. This invention is directed to the provision of an improved process and apparatus whereby such problems are overcome or, at the least, considerably alleviated.
BACKGROUND
(i) Current conventional wisdom is that direct firing of coal or the use of hot, substantially uncooled gas from a coal gasifier is probably the best means to achieve high generation efficiencies with coal-fired gas turbine systems. However, it is known that ash particles, vaporised salts, and sulphur compounds which result from direct coal firing or from the use of hot gases from coal gasifiers, are difficult to eliminate without substantial cooling of the gases.
(ii) It is known that cooling and washing of gas leaving coal gasifiers can substantially remove all the compounds which give rise to problems with high temperature components in gas turbines. However it is accepted that such a cooling and washing produces a very dilute fuel gas heavily contaminated with water vapour which is generally regarded as being unsuitable for combustion in conventional gasifiers. In some currently proposed schemes for Integrated Gasification Combined Cycle processes (known in the art as IGCC processes), fuel gas produced by simple total or partial adiabatic cooling of gasifier product gas also lowers the flame temperature of the diluted fuel gas to the point where stable combustion and the high combustion temperatures required by high efficiency IGCC system designs are not attainable with the highly water vapour-diluted coal-based fuel gases.
(iii) It is generally accepted that, notwithstanding the known problems of added complexity caused by the introduction of additional equipment, efficient coal firing of gas turbines can only be achieved with the use of combined cycles, ie. the incorporation of a waste heat boiler in the turbine exhaust and the use of a steam turbine cycle.
(iv) It is also conventional wisdom to consider that higher compression ratio turbines are the optimum means to achieve high efficiency with coal-fired gas turbine systems even though such turbines present known problems associated with the use of high compression ratios. The problems of drying and gasification of carbonaceous fuels and particularly high water content carbonaceous fuels such as lignite, when used as a power generation fuel or feedstock for synthesis gas production, are also well known.
(v) Prior Art Proposal
The foregoing problems are outlined in a recent prior art development which proposes a means and process whereby solid moisture-containing coal can be utilised to generate power. According to this proposal, the process cannot however readily deal with a solid lignite having a significant moisture content if it is converted into a water-lignite slurry typically containing 25% or possibly less solids (wet basis). Even though the higher water content lignite could be more readily handled, it was apparently considered that loss of efficiency of the overall process and also the known problems in combusting water vapour laden, very low heating value fuel gas in gas turbines would be too disadvantageous. Consequently, the use of such a coal slurry was apparently considered to be not technically feasible and to be likely to result in major combustion problems, and inability to achieve a high combustion temperature with consequent low power generation efficiency. with the gasification process is to be further adiabatically cooled by the injection of water and the saturated gas is then washed or treated by known means to remove particulates, and is then further cooled to reduce the water content of the gas such that it is increased in calorific value and can be used in known combustion systems. Gas treatment at water saturation temperature can remove particulates and may also enable the removal of sulphur compounds by known means following that stage. This final cooling has the inherent disadvantage of removing water vapour
REFERENCES:
patent: 4866928 (1989-09-01), Raiko
Isentropic Systems Ltd.
Kamen Noah P.
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