Power plants – Motive fluid energized by externally applied heat – Noncommunicating heat transferring motive fluid system
Patent
1992-01-22
1993-09-07
Lazarus, Ira S.
Power plants
Motive fluid energized by externally applied heat
Noncommunicating heat transferring motive fluid system
10 39182, F01K 2304
Patent
active
052418251
DESCRIPTION:
BRIEF SUMMARY
The presently most environment-friendly process for generating electric power based on the combustion of solid fossile fuels, such as coal, comprises burning the fuel in a finely divided form in a steam generator of the type ACFBC (atmospheric circulating fluid bed combustion) with the addition of finely divided lime stone and/or dolomite. Since it is possible to carry out ACFBC with >99% of fuel efficiency at such a low temperature as 850.degree. C. the NOx formation is very low and simultaneously >90% of the content of sulphur in the fuel can be bonded to the lime formed by the combustion.
By operating the steam generator at a high pressure, such as 145 bars, and a steam temperature of 535.degree. C. electric power can be generated in a condensor steam turbine with a net efficiency of about 38%.
In order to achieve a higher efficiency, concepts have been developed based on combinations of gas and steam turbines with combustion in a steam generator under pressure, so-called PFBC (pressurized fluid bed combustion). The flue gases from the pressurized fluid bed are after multi step cyclone cleaning used directly in a gas turbine, and the exhaust gases from said turbine are used for generating a certain quantity of steam. The main steam generation is, however, performed in tube panels arranged in the fluid bed and its walls. With a PFBC concept it is possible to reach with condensation an actual net efficiency of about 42%, whereby about 20% of the electric power is generated in the gas turbine.
The drawbacks of a PFBC concept are partly a comparatively higher bed temperature (880.degree. C.) which means a higher NOx production, and partly a risk for blade failure in the gas turbine in case the cyclone cleaning fails, and a substantial complication of the operation because of the unavailability for inspection and repair caused by enclosing the fluid bed and cyclones in the pressure chamber.
The instant invention constitutes an environment-friendly method for producing electric power with a net efficiency of about 46% based on combustion of solid fossile fuels in a steam generator of the type ACFBC in combination with two gas turbines and a condensor steam turbine. The concept according to this invention thus gives a substantially higher net efficiency than the PFBC concept although it is less complicated from a mechanical as well as an operational point of view.
The method according to this invention is characterized in that the fossile fuel, which suitably comprise >20% and preferably >30% of volatiles, is first pyrolyzed in a finely comminuted form in contact with hot bed material in a fluid bed through which flows a controlled partial flow of the circulating bed material flow f an ACFBC steam generator, which partial flow combined with formed char is recirculated to the combustion chamber of the steam generator where the char is used as fuel, whereas the produced pyro gas, after per se known cleaning, is used in a gas turbine unit, and the exhaust gas from said unit is used, suitably after reheating, for generating steam, preferably high pressure steam, whereas the other gas turbine unit is operated with compressed air from the high pressure compressor of the unit, which air is heated indirectly in a heat exchanger submerged in a classical type fluid bed through which flows a controlled partial flow of the circulating bed material flow of the ACFBC steam generator, the final heating of said compressed air being performed by burning directly therein a gaseous and/or liquid fuel, suitably internally produced such a fuel, especially pyro gas, and wherein said gas turbine unit is operated with back pressure by using the exhaust gas from the power turbine part thereof, which has a comparatively high temperature, as fluidizing gas (primary air) and secondary combustion air in the ACFBC steam generator when producing there superheated high pressure steam for the condensor steam turbine unit.
The invention is also characterized by performing the separation of the bed material from the hot flue gas sus
REFERENCES:
patent: 4896498 (1990-01-01), Knizia
patent: 4996836 (1991-03-01), Reh et al.
Collin Mans
Collin Per
Heyman L.
Lazarus Ira S.
Meller Michael N.
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