Structure and main technical principles of flue gas recovers and flue gas economizers

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This post was last edited by gn_1984 on 2015-9-21 at 15:50. The structure of the waste heat recovery unit is that of a shell-and-tube waste heat boiler; its function is to reduce the high-temperature process gases generated by the sulfur production furnace to the temperature required by the condensation cooler through heat exchange, while simultaneously producing low-pressure saturated steam to recover heat. Half a year after the device was put into use in 2005, leaks were detected at the joints between some of the heat exchange tubes and the tube sheet, as well as perforations in those heat exchange tubes. Installing a waste heat recovery unit in the boiler’s rear flue can reduce the exhaust gas temperature, thereby lowering the coal consumption rate. Taking a 670 t/h boiler as an example, through heat transfer calculations for 10 different heating area configurations of the waste heat recovery unit, system thermodynamic calculations, and technical-economic index calculations, and with maximizing the net present value of investment as the optimization goal, the functional relationships between the optimal heating area of the waste heat recovery unit (the optimized design) and the steel-to-coal ratio, operational life, and annual power generation capacity of the unit were determined. http://www.gzqingli.com/upfile/2015/07/20150714135518_667.jpg As the demand for energy conservation becomes increasingly urgent, the use of heat exchangers for the recovery and reuse of thermal energy has become a trend; by optimizing heat exchange networks, significant energy savings and economic benefits can be achieved. In terms of heat energy conservation, it is necessary to maximize the amount of waste heat recovered, as well as minimize the temperature difference for heat transfer in the heat exchangers; in other words, energy should be recovered as much as possible both in terms of quantity and quality. In waste heat recovery system technology, the heat loss due to flue gas accounts for 60%–80% of the total heat losses, making it the largest component among all such losses. It is also an important factor that affects the thermal efficiency of gas-fired heating water heaters. How to reduce the flue gas temperature, minimize heat losses from flue gases, and improve thermal efficiency is an extremely important task in design and renovation; it represents an effective way to achieve low carbon emissions as well as energy savings and reduced consumption. The principle of flue gas waste heat recovery technology is to use a flue gas waste heat recovery unit to transfer the waste heat and phase change latent heat present in the flue gas to the return water side of the boiler, thereby raising the temperature of the return water and **increasing the thermal efficiency of the heating water boiler. In the primary heat exchanger, the flue gas primarily releases its sensible heat; after the temperature of the flue gas reaches around 130–150°C, it enters the flue gas waste heat recovery unit. There, the flue gas cools further, and at temperatures below the dew point of the water present in the flue gas, the water vapor in the flue gas condenses, releasing latent heat. As a result, the temperature at the outlet of the flue gas can drop to around 50°C. The condensate is discharged outside through the condensate collector at the bottom; after treatment, it can be sent to the waste heat recovery unit. Composition principle: Main components include the suction unit (jet-type entrainment heater), the vapor-liquid separation unit (vapor-liquid separation tank), the electrical control and level control unit (electrical control box and level display/adjustment mechanism), and the pressure restoration and return unit (pressure booster pump). The system uses working water (desalted water, make-up water, etc.) as the medium; through the suction action of the jet-type mixing heater, the exhaust steam is drawn in and heat exchange is instantaneously completed with the working water. The mixture is then concentrated in a vapor-liquid separation tank, and non-condensable gases are removed from it. After adjustment via precise level control and intelligent electrical control, the mixture is sent back to the original system using a booster pump. The heat energy of the exhaust steam and the working fluid are fully captured by the pipes.