Da Teng's research while affiliated with North China Electric Power University and other places

The saturated flue gas is difficult to recover and use as low-grade waste heat in a coal-fired power plant. The absorption heat pump is important equipment for recovering low-grade waste heat. In this article, the saturated flue gas waste heat is recovered to reduce the turbine extraction steam of low-pressure heaters. The simulation system is built, and the operational characteristics are analyzed. The feasibility of saturated flue gas waste heat recovered is verified by the absorption heat pump to heat the boiler feedwater. The results show that generator pressure and throttle pressure have significant influence on the operational performance of the absorption heat pump. There is the risk of solution crystallization with the high-concentration dehumidification solution. The equivalent enthalpy drop of the extraction steam is lower in the higher number of heater stages, representing the weaker electricity generation capacity. The waste heat temperature of saturated flue gas can be raised by 30–40 °C, which is used as the low-grade heat source for the absorption heat pump. The feedwater of low-pressure heaters is heated by the absorption heat pump, and its temperature ranges from 59.2 to 83.8 °C. The simulation system can efficiently recover the waste heat of saturated flue gas up to 9.99 MW and achieve additional electricity generation up to 0.56 MW in the coal-fired power plant.

Acoustic reinforced heat transfer is an active reinforced heat transfer method that has the advantages of having no contacts and being high energy and adjustable. To explore the convective heat transfer characteristics under the audible acoustic field, a convective heat exchange experimental platform was built; the platform was a double-pipe heat exchanger. Comparative experimental research on heat transfer of hot flue gas both with acoustic field and without acoustic field was carried out. The results verified that the heat exchanger with an acoustic field had better heat transfer effect. The effects that parameters (such as sound pressure level, acoustic frequency, and the inlet temperature of the hot flue gas) had on the enhanced heat exchange effect were systematically studied. The influence law of the acoustic field on the convective heat transfer capacity of heat exchanger was obtained. The results show that, with an acoustic field, the temperature of the hot flue gas at the outlet of the heat exchanger decreases significantly, whereas the heat transfer power, convective heat transfer coefficient, and the Nusselt number increased significantly. Within the selected range of experimental parameters, 0.6 kHz is the optimal acoustic frequency for enhanced heat transfer. With an increase in the sound pressure level, the reinforcement efficiency increased. At the same time, increasing the inlet temperature of the hot flue gas helped to enhance the capacity of the sound wave to strengthen the heat transfer. When the temperature of the inlet hot flue gas was 59 °C, the sound pressure level was 145 dB, the acoustic frequency was 0.6 kHz, and the maximum reinforcement efficiency was 76.22%.

The typical flue gas exhaust temperature of coal-fired boilers is up to 150 °C. There is a considerable amount of waste heat that cannot be efficiently recovered. This study describes a zero-energy consumption absorption heat pump system that can improve the thermal efficiency and recover moisture. In the proposed system, lithium bromide solution serves as the recyclable heat-transfer medium, which absorbs sensible heat at the outlet of the air preheater by a generator. The latent heat of the flue gas is absorbed by an evaporator, and the condensate water appears. Theoretical investigation and mathematical models are built. Meanwhile, the operating parameters of the system are displayed. The results showed that the acid dew point of flue gas is related to the water content. The sorption heat pump efficiency (coefficient of performance) increased to 1.64. Compared with the two-stage heat exchanger system, 24.4 t/h condensate water and 47.21 MW waste heat were recovered. The flue gas temperature at the chimney entrance was reduced by 4.18 °C.

The direct discharge of flue gas from the coal fired boiler can result in significant water loss. Membrane separation technology is an effective means to solve the flue gas dehydration problem. Based on the permeation characteristics of porous membrane materials, ceramic membrane method flue gas dehydration is a complex mass transfer process. In this paper, the ceramic membrane transport condensers were built with circulating water, positive pressure purge gas and negative pressure purge gas as the cooling medium, respectively. Changing flue gas parameters and cooling medium parameters, the correlation coefficients of water vapor pressure difference, transmembrane pressure difference and Reynolds number with permeate flux were investigated. The results showed that the key factors that determine the permeate flux were slightly different with the different experimental conditions. Changing the flue gas temperature or the cooling medium temperature has an obvious effect on the water vapor pressure difference. There is a significant correlation between the water vapor pressure difference and the permeate flux. Changing the flue gas flow or the cooling medium flow, the water vapor pressure difference is less variable, and the transmembrane pressure difference is not the key factor affecting the permeate flux, and the Reynolds number is the key factor affecting the permeate flux. Meanwhile, the experimental process revealed that an excessive transmembrane pressure difference can cause non-condensable gases in the flue gas to enter the cooling water tank.

The wet saturated flue gas discharged by coal-fired utility boilers leads to a large amount of low-temperature wasteheat loss. Inorganic ceramic membrane is acid-base resistant and has strong chemical stability. It is an ideal material forrecovering low-temperature waste heat from flue gas. The experiment of waste heat recovery of flue gas was carried outwith inorganic ceramic membrane as the core, and the characteristic parameters of low-temperature flue gas at the tailof the boiler were analyzed; taking 316 L stainless steel as the comparative object, the strengthening effect of inorganicceramic film on improving heat recovery power and composite heat transfer coefficient was discussed. The results showthat the waste heat recovery of flue gas is mainly the evaporation latent heat recovery of water, accounting for about90%; circulating water is used as cooling medium, and the waste heat recovery capacity of flue gas is stronger;compared with circulating water, when air is used as the cooling medium, the effect of inorganic ceramic membraneflue gas waste heat recovery is more significant, and the enhancement coefficient is as high as 9; increasing the flue gasflow is helpful to improve the heat recovery power and composite heat transfer coefficient; at the same time, inorganicceramic membrane can also recover condensate with high water quality. The results of this paper can provide areference for the application of inorganic ceramic membrane in flue gas waste heat recovery.