| In China,thermal power generation is still the main source of electricity for domestic and industrial use,and accounts for about 70% of the total installed capacity and total power generation.The flue gas emitted by these thermal power plants carries a lot of heat and moisture.Directly discharging the flue gas into the atmosphere will not only waste the scarce water resources.It is also easy to cause adverse effects on the ecological environment in which we live.At the same time,these low-temperature flue gases with a large amount of heat and moisture will cause low-temperature corrosion on the heating surface of the tail of the thermal power unit.Increasing operating costs and equipment maintenance costs of thermal power plants.Therefore,recycling the large amount of water and heat carried in the exhaust flue gas is an important research content and research direction to realize the deep energy saving and emission reduction of thermal power units.The use of gas-liquid membrane separation technology to recover the moisture and heat in the flue gas emitted by thermal power plants has gradually attracted the attention of researchers in the industry.Porous ceramic membrane has many advantages such as high strength,corrosion resistance,high thermal stability and good heat and mass transfer performance.It is a high-quality utilization material for recovering moisture and heat from the flue gas emitted by thermal power plants.The use of porous ceramic membranes to recover the moisture and heat in the flue gas is expected to become an effective way to save energy and water in thermal power plants.However,there are many controversies in many studies on whether there is capillary condensation in porous ceramic membranes with pore diameters in the range of 2-50 nm.In order to explore the performance of the inorganic porous ceramic membrane to recover water and heat and the presence or absence of capillary condensation.This paper studies the mass and heat transfer mechanism of the simulated thermal power plant’s low-temperature and saturated steam-containing flue gas after limestone wet desulfurization in the externally coated hydrophilic inorganic porous ceramic membrane.The main research contents are as follows:(1)Propose a test plan for the moisture and heat recovery performance of the flue gas in the outer-coated hydrophilic single-channel ceramic membrane module,Build an experimental platform for testing the heat and mass transfer performance of single-channel ceramic membrane modules,Analyze whether the instruments and equipment used in the research institute meet the accuracy requirements,and develop a data acquisition system based on T-type thermocouples.In order to reduce the experimental measurement error,each group of experiments runs for 30 minutes,and 3 sets of thermocouples are installed at the inlet and outlet of the flue gas and cooling water of the membrane module.The data is measured every ten seconds,and each set of data is the average of over 500 sets of data for each test point during the entire experiment.(2)The theoretical analysis of capillary condensation based on the Kelvin equation.Found that under the precondition of not being affected by external conditions,Saturated water vapor does theoretically have capillary condensation on porous ceramic membranes with pore diameters in the range of 2-50 nm.However,this analysis does not combine reality.When the inorganic porous ceramic membrane actually recovers the heat and moisture in the flue gas,in order to prevent the cooling water from overflowing to the intake side,water pumping is often used.That is,the pressure range on the cooling water side is mostly a negative pressure state with a relative pressure of minus 0.01 MPa to minus 0.03 MPa,while the flue gas side is mostly a state close to atmospheric pressure with a relative pressure of 0to minus 1kpa.The pressure in the hole is much greater than the plane pressure,which is the opposite state of the theoretical situation.At the same time,the water recovery performance of the single-channel ceramic membrane module was analyzed and tested.The key parameters such as simulated flue gas flow rate,cooling water flow rate,simulated flue gas temperature and cooling water temperature were compared with different pore diameters of porous ceramic membranes The water recovery rate is the ratio of the water flux passing through the ceramic membrane tube per unit area and the water recovered per unit operating time to the total water entering the membrane module during the operating time.The final parameters are optimized.The hot water temperature range is 35℃-55℃,the cooling water temperature is 10℃-35℃,the air flow rate is 9L/min-19L/min,and the cooling water flow rate is in the range of 0.9L/min-1.4L/min.The parameter independence analysis was carried out internally to verify the influence of various experimental parameters on the performance of the externally coated hydrophilic porous ceramic membrane to recover the moisture of the flue gas.(3)After studying the influence of various external conditions such as cooling water temperature,cooling water flow rate,flue gas temperature and flue gas flow rate on the recovery of moisture in the flue gas of the hydrophilic outer-coated inorganic porous ceramic membrane,The analysis method of the single-channel inorganic porous ceramic membrane to recover the heat in the flue gas and the influence of various parameters on the heat recovery of the ceramic membrane module are studied.Relevant tests and data analysis were performed on single-channel ceramic membranes of 20 nm,50nm,100 nm,and 3μm,respectively.The comparison and analysis of four kinds of inorganic porous ceramic membranes with different pore diameters under the same working condition is the size of the heat passing through the unit area per unit time,that is,the size of the heat flux.At the same time,it also analyzes the ratio of the total heat recovered during the running time to the total heat entering the ceramic membrane module during the running time,that is,the heat recovery rate.Experiments have proved that under the experimental conditions,the temperature difference between the two sides of the ceramic membrane,that is,the temperature difference between the cooling water and the flue gas,is the main influencing factor that affects the heat recovery of the ceramic membrane module. |
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