Coal-fired power generating system and coal-fired power generating method

Abstract

There is provided a coal-fired power generating system that, in addition to recovering latent heat of condensation and the like from a dry exhaust gas of a drying device, which is for predrying coal, precludes a large variation, from a design value, of the amount of steam flowing at a final stage of a steam turbine.The coal-fired power generating system includes an indirect-heating dryer 1 including a heating medium passage inside its casing, a coal-fired boiler 3 for combusting coal to generate steam, and a steam turbine 6 for generating power with the steam from the boiler 3. The dryer dries the coal fed into the casing by performing indirect heating with steam fed to the heating medium passage. The coal-fired power generating system heats boiler supply water for the coal-fired boiler 3 with extracted steam extracted from the steam turbine 6. The coal-fired power generating system also includes a line for using part of the extracted steam as heated steam for the indirect-heating dryer 1, a steam condenser 5 for the steam turbine 6, a wet scrubber 11 provided on a path of the dry exhaust gas from the indirect-heating dryer 1, heat recovery heat exchangers 22 and 24 for performing heat exchanging between circulating water of the wet scrubber 11 and condensate of the steam condenser 5. The coal-fired power generating system is configured to heat boiler supply water by using the condensate having heat recovered from dry exhaust gas by the heat recovery heat exchangers 22 and 24.

Description

TECHNICAL FIELD[0001]The present invention relates to a coal-fired power generating system and a coal-fired power generating method for predrying and pulverizing coal and feeding the coal to a coal-fired boiler to drive a steam turbine for power generation.[0002]In particular, the present invention relates to a coal-fired power generating system and a coal-fired power generating method that are designed to, in addition to recovering latent heat of condensation and the like from a dry exhaust gas of a drying device, which is for predrying the coal, preclude a large variation, from a design value, of the amount of steam flowing at a final stage of a steam turbine.[0003]More specifically, the present invention is suitable to suppress a reduction in efficiency of power generation performed using a low rank coal, such as brown coal, lignite and sub bituminous coal, for combustion.BACKGROUND ART[0004]In recent years, approaches have been devised for new coal-fired power generating systems...

AI Technical Summary

Benefits of technology

The present invention can recover energy from the exhaust gas of a drying device and prevent changes in the amount of steam flow at the final stage of a steam turbine, which can reduce power generation efficiency.

Problems solved by technology

This may reduce the amount of steam generated by a boiler commensurately, resulting in a deterioration of the efficiency of power generation (the amount of power generation / the quantity of heat of the coal).

Releasing the dry exhaust gas without processing may lead to a loss of effective heat.

Furthermore, extracting part of the medium-pressure or low-pressure steam from the steam turbine may reduce the amount of steam flowing at a final stage of the steam turbine, resulting in an increase in exhaust loss and a reduction in turbine efficiency.

Such a significant reduction in the amount of steam may lead to a reduction in turbine efficiency, serving as an impediment to a sufficient improvement in efficiency of the power generation expected through the predrying of the coal.

This may result in vibration and the like, which leads to another disadvantage of a reduced range of a low load operation in comparison with traditional techniques.

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