Study On The CaCO₃-CaSO₄ Wet FGD Flue Gas Exhaust Heat Recovery System

Recently,most of the coal-fired boilers,flue gas has a high temperature,which creating serious waste of energy,even more than 120℃.Moreover,heating surface of the tail coal-fired boilers with high-sulfur have more higher flue gas temperature.The temperature of the flue gas passed the CaCO_3-CaSO₄ wet FGD is45-50℃.Therefore,there has urgent need to carry out boiler flue gas heat recovery and utilization,improve efficiency and reduce energy waste.By exhaust heat recovery system,the temperature of gas may be reduced to 30℃⁴0℃,and save the latent heat to improve the efficiency of coal.The latent heat which was saved by the recovery system will help to conserve resources,reduce emissions,environmentally friendly.This article describes the temperature distribution features o f supply and backwater in coal-fired boilers.In fact,the temperature of backwater during the heating season is often far less than the design return temperature can be recycled CaCO₃-CaSO₄ wet FGD flue gas waste heat,and transfer into the net backwater.CaCO₃-CaSO₄ wet FGD flue gas,and designed a new CaCO_3-CaSO₄ wet FGD flue gas exhaust heat recovery system.It uses water leaching and heat transferring to recovery two kinds of heat which was hidden in the high temperature flue gas.After heat exchanging with flue gas in the spray tower,recycled water extracting heat from the circulating water pump system,and then the backwater was heated by extracted heat in the heat supply network.After the above processing,the same amount of heat produced in the recovery system requires much less coal,which improves fuel efficiency and the system energy efficient.First of all,the waste heat recovery program is introduced.The form of waste heat recovery is "flue gas spray heat exchanger" + "heat pump" which is use d in the Flue gas waste heat recovery system.The high temperature flue gas is in direct contact with the low temperature internal circulation water returned from the heat pump In the spray bath of the spray heat exchanger.The temperature of the flue gas is down after the heat released,and the heat of the circulating water absorbs the heat.The internal circulation of water with high temperature from the internal circulation pump to the heat pump,the internal circulating water heat is extracted by heat pump to heating the hot water back from the heat network.The circulating water with low temperature leave the heat pump go into the spray tower again for next cycle.The dosing system,sludge treatment system,anti-corrosion materials and equipment which were used to solve the problem of circulating water p H control,sludge treatment,corrosion are analyzed.This paper selected coal-fired boiler as the study project,and then calculated the parameters about thermal and hydraulic,and finally estimated of the new flu e gas heat recovery system can recover heat.No flue gas reheating device is set up in the scheme.In order to meet the requirements of the exhaust gas temperature for future,it is necessary to reserve the flue gas reheating unit.The flue gas is heated and the temperature rise from 40℃to 50℃in the heat exchanger.Finally,based on static payback period,IRR and dynamic payback time,we give the economic assess of two kind of proposal.Economic evaluation of the results can be concluded:Three dynamic evaluation of the first absorption heat pump solutions are better than the vapor compression heat pump program,so that the first absorption heat pump program is superior vapor compression heat pump program.,the heat recovery device can recover more than 17 MW by the analysis of the actual operation data of the waste heat recovery system,and the system is operated continuous and stable.The syetem can make better economic benefits.