Theory And Application For Gas-fired Boiler Waste Heat Recovery

Natural gas is an environmental benign fossil fuel. Nowadays, Gas-fired boiler used in life and industry has been boosted in our country, which causes that the boiler becomes one of the main natural gas consuming equipments. However, in our country, utilization coefficient of gas-fired boiler is not as high as Occident. Due to higher temperature of flue gas, the waste heat of flue gas is not reclaimed and utilized availably. Aiming at the problem reclaiming waste heat of gas-fired boiler, this paper does systemic research work on theory and practical application.In reference to the analysis of heat transfer coefficient of Nusselt in the process of pure steam condensing, a boundary layer of noncondensable gas is defined in order to set up a mathematical model about a heat transfer process that the stationary vapor and noncondensable gas mixture condenses on a vertical wall, and the heat transfer coefficient in the condensation is worked out, which accords with some assumed conditions. The prediction about the thickness of condensate film adapt to the length of vertical wall is given. The conclusions show the difference in the condensing process under a same condition between vapor and noncondensable gas mixture and pure steam, and indicate the influence of the wall temperature in the condensing heat transfer. The conclusions accord with the results in the open literature.The paper makes optimization among heat-transfer performance, anticorrosion and costs for production as for the separated condensing gas-fired boiler, designs a condensing heat exchanger able to equip on the conventional gas-fired boiler, and finally carries out experimental study on it. The results of calculation and experiment show that the conventional gas-fired boiler equipped with a condensing heat exchanger can effectively recover the waste heat of flue gas, thus, the thermal efficiency of the boiler is enhanced by about 10%.As for the problem that heat-supplying efficiency drops as result of surplus capability of a single high-power boiler of the heat supplying during the whole year, the paper designs and studies the module copper pipes gas-fired boiler supplying hot water.The paper has also analyzed the economic efficiency of the gas-fired boiler equipped with separated condensing heat exchanger that is used in life and industry hot water boiler. Through analysis of static investment return, when the conventional gas-fired boiler with 6T/h capacity equipped with the condensing heat exchanger...