Method and System for Heating of Water Based on Hot Gases

Abstract

Heat can be recovered from hot gas produced in a thermal reactor ( 1 ), by injecting water into the gas at one or more injection zones ( 4 ) in such an amount and in such a way that the gas temperature due to water evaporation is reduced to below 400° C., preferably below 300° C., possibly below 150-200° C., and the gas dew point becomes at least 60° C., preferably at least 70° C., possibly 80 or 85° C. The gas can then be led through a condensing heat exchanger unit ( 8 ), where at least some of the gas contents of water vapour are condensed, and the condensing heat can be utilized for heating of a stream of fluid, mainly water. Hereby, a method for production of hot water is obtained, which is cheap and simple and has low maintenance costs, and which moreover has a high efficiency degree and good environmental qualities The method can be used for a broad spectrum of fuels and conversion technologies.

1 - 18 . (canceled) 
     
     
         19 . A method for recovering heat from hot flue gas produced in a thermal reactor fuelled with solid fuel, said method comprising the steps of:
 injecting water into in the gas at one or more injection zones in such an amount and such a way that due to evaporation of injected water the flue gas temperature is reduced to below 400° C., and the gas dew point becomes at least 60° C.,   subsequently passing the gas through a condensing heat exchanger, where at least some of the water vapor in the gas is condensed and condensing heat is released, and   utilizing the condensing heat for heating a stream of fluid, such as water, in the heat exchanger.   
     
     
         20 . A method according to  claim 19 , wherein the gas dew point becomes at least 70° C., preferably 80° C. or 85° C. 
     
     
         21 . A method according to  claim 19 , wherein the flue gas temperature is reduced to below 300° C., preferably to 150-200° C. 
     
     
         22 . A method according to  claim 19 , wherein the injection zones are located in one or more of the thermal reactor, zones downstream of the thermal reactor in a gas flow direction, the fuel in the thermal reactor and the heat exchanger. 
     
     
         23 . A method according to  claim 19 , wherein impurities are removed from the gas by means of a bag filter, a cyclone, an electro filter, a scrubber or the like. 
     
     
         24 . A method according to  claim 19 , wherein impurities are removed from the condensed water. 
     
     
         25 . A method according to  claim 19 , wherein pH of the condensed water is adjusted. 
     
     
         26 . A method according to  claim 19 , wherein at least some of the water injected in to the flue gas is vaporized using a nozzle. 
     
     
         27 . A method according to  claim 19 , wherein part of the injected water is injected at a speed above 20 m/s in a gas flow direction. 
     
     
         28 . A method according to  claim 19 , wherein the fluid heated in the heat exchanger is further heated, e.g. by means of a fluid cooled feeder, a fluid cooled grate, fluid cooled surfaces in the reactor or other cooled surfaces around the thermal reactor. 
     
     
         29 . A method according to  claim 19 , wherein water vapor and heat are transferred to combustion air, which is led to the thermal reactor. 
     
     
         30 . A method according to  claim 19 , wherein the thermal reactor is of the fluid bed type, and injection of water into the bed is used to regulate temperature and flow conditions in the bed. 
     
     
         31 . A method according to  claim 19 , wherein condensed water from the heat exchanger is injected in the one or more injection zones. 
     
     
         32 . A system for decomposition of solid fuel and for production of hot fluid, said system comprising
 a thermal reactor for decomposing the fuel and producing hot flue gas from the fuel,   an evaporative cooler with water injection devices, e.g. in the form of nozzles, for injection of water into the flue gas so that the injected water evaporates,   a control system for controlling the water injection into the gas so that, as a result of evaporation of injected water, the gas temperature is reduced to below 400° C. and the gas dew point becomes at least 60° C., and   a condensing heat exchanger for condensing at least some of the water vapor in the gas and utilizing condensing heat for heating a stream of fluid, such as water.   
     
     
         33 . A system according to  claim 32  further comprising one or more nozzles for injecting water into one or more of the fuel in the thermal reactor, the thermal reactor and the flue gas in connection with the heat exchanger. 
     
     
         34 . A system according to  claim 32 , further comprising a gas cleaning unit in the form of a bag filter, electro filter, scrubber or the like. 
     
     
         35 . A system according to  claim 32  including means for leading at least some of the fluid from the heat exchanger to another unit for further heating. 
     
     
         36 . A system according to  claim 32 , further comprising an enthalpy exchanger, where water vapor and heat are transferred to combustion air to be added to the reactor. 
     
     
         37 . A system according to  claim 32  including a fluid bed reactor with means for injection of water into the bed in order to adjust temperature, emissions (NOx) and flow conditions.