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.

1 . A coal-fired power generating system, comprising:
 an indirect-heating dryer comprising a heating medium passage inside a casing thereof, the dryer being configured to dry a coal fed into the casing by performing indirect heating with steam fed to the heating medium passage;   a coal-fired boiler for combusting a dried coal to generate steam; and   a steam turbine for generating power with the steam from the boiler,   the coal-fired power generating system being configured to heat boiler supply water for the coal-fired boiler with extracted steam extracted from the steam turbine,   wherein the coal-fired power generating system comprises:   a line for using part of the extracted steam as heated steam for the indirect-heating dryer;   a steam condenser for the steam turbine;   a heat recovery unit provided on a path of a dry exhaust gas from the indirect-heating dryer,   the heat recovery unit being configured to transfer heat of the dry exhaust gas to condensate of the steam condenser, the heat recovery unit having a heat recovery quantity adjusting unit for adjusting a quantity of heat recovery of the heat recovery unit; and   a line for using the condensate having the heat recovered from the dry exhaust gas by the heat recovery unit for heating the boiler supply water.   
     
     
         2 . The coal-fired power generating system according to  claim 1 , wherein the heat recovery unit comprises a wet scrubber provided at the path of the dry exhaust gas from the indirect-heating dryer and a heat recovery heat exchanger for performing heat exchanging between circulating water of the wet scrubber and the condensate of the steam condenser, and the heat recovery quantity adjusting unit is configured to adjust the quantity of heat recovery by controlling an amount of the circulating water of the wet scrubber. 
     
     
         3 . The coal-fired power generating system according to  claim 1 , wherein the heat recovery unit comprises a heat pump unit. 
     
     
         4 . The coal-fired power generating system according to  claim 2 ,
 wherein the wet scrubber is a two-stage type, and   a first heat recovery heat exchanger corresponding to circulating water of a first-stage scrubber heats the boiler supply water, a second heat recovery heat exchanger corresponding to circulating water of a second-stage scrubber receives the boiler supply water and heats the boiler supply water to a higher temperature, and the second heat recovery heat exchanger is a heat pump.   
     
     
         5 . The coal-fired power generating system according to  claim 1 , wherein a boiler combustion exhaust gas is fed as a carrier gas into the casing of the indirect-heating dryer. 
     
     
         6 . A coal-fired power generating method for a coal-fired power generating system, the system comprising:
 an indirect-heating dryer comprising a heating medium passage inside a casing thereof, the dryer being configured to dry a coal fed into the casing by performing indirect heating with steam fed to the heating medium passage;   a coal-fired boiler for combusting a dried coal to generate steam; and   a steam turbine for generating power with the steam from the boiler,   the system being configured to heat boiler supply water for the coal-fired boiler with extracted steam extracted from the steam turbine,   the method comprising the steps of:   using part of the extracted steam as heated steam for the indirect-heating dryer and condensing exhaust of the steam turbine by a steam condenser;   providing a heat recovery unit at a path of a dry exhaust gas from the indirect-heating dryer, the heat recovery unit being configured to transfer heat of the dry exhaust gas to condensate of the steam condenser, the heat recovery unit having a heat recovery quantity adjusting unit for adjusting a quantity of heat recovery of the heat recovery unit; and   using the condensate having the heat recovered from the dry exhaust gas by the heat recovery unit for heating the boiler supply water.   
     
     
         7 . The coal-fired power generating method according to  claim 6 , wherein a boiler combustion exhaust gas is fed as a carrier gas into the casing of the indirect-heating dryer, and the dry exhaust gas has a dew point in a range from 80° C. to 95° C.