Water Spray Heat Exchanging For Coal-fired Boiler Flue Gas Heat Recovery

Today’s coal-fired boiler exhaust gas te mperature is120℃or higher. Highsulfur coal boiler exhaust gas temperature may be higher. Using a specia l heatrecovery syste m to reduce the flue gas temperature to60℃~70℃and thendischarge can recover a lot of sens ible heat and latent heat.This part of the heatto be used not only can achie ve energy conservation,but also conducive toenvironmenta l protection.This paper analyzes the return water temperaturedistrib ution of the coal-fired bo ilers in the way of qua lity adjustment. The actualreturn water temperature are far lower than the design return water temperaturein most of the time of heating season. F lue gas waste heat can be recyc led intothe heating network backwater.In this paper, for the characteristics of coal-fired boiler flue gas, a coal-fired boiler exha ust flue gas heat recovery system is raised, whic h ischaracterized by water and smoke into direct contact heat tranfer. The system isdivided into two heat trans fer process: the first is the use of p late heat excha nger,and the second is the use of heat pump syste m, The recovery of was te heat iseventua lly sent to the heat supply network backwater. Through this way boilerfuel usa ge can be reduced.Next are the system therma l and hydraulic calculations. Calc ulate therecyc le heat of the new flue gas heat recovery syste m for different types of coal-fired boilers. Determine the structure and size of the heat exchanger roomsaccording to the flue gas vo lume and flue gas flow rate. According to thecirculating water to determine the number of nozzles and it sarrange ments.Calculate the area of the plate heat exchanger according to the heat.After hydraulic calc ulation of the heat recovery system, determine circulationpumps head and the pipeline s diameter. Write a Matlab computation programfor thermodynamic calculation o f the heat pump system.Fina lly, this paper gives a economic eva luation o f different types of boilerheat recovery syste m. Use three kinds of dyna mic evaluation: annua l cost, lifecycle cost and dynamic investme nt recovery period. The econo mic eva luationshows, the first absorption heat pump scheme is better than a vapor compression heat pump sche me. The annua l cost of the first absorptio n heat pump programand life cyc le costs are all lower than the vapor compression heat pump scheme.Its dynamic investment recovery period is also far less than the vaporcompression heat pump scheme.The result of this paper provides a reference for improving coal-fired boilerexhaust syste m and improving bo iler therma l efficie ncy.This topic from the "12th Five-Year" National Science and TechnologySupport Program of China "cold district heating system energy saving keytechnology and engineering demonstration"(2011BAJ05B04) and “the urbandistrict heating energy effic ient planning and key technology research anddemonstration”(2012BAJ04B01).