| Municipal Solid Waste (MSW) combustion is the one way of waste disposal. MSW is always rich in organic chlorine and inorganic chlorine. The concentration of HCl can reach as high as several hundreds to several thousands ppm when combusted. HCl can cause the high temperature corrosion of the heating surface corrosion, which restricts the main stream parameters of MSW incineration power generation, resulting in low efficiency. Especially at 250-450 ℃, high concentration of HCl enhances the toxicity of PCDD/Fs. So there is an urgent need to carry out in-depth study on the high efficiency removal of HCl at medium-high temperature.Compared with the removal efficiencies of adsorbents under the middle-high temperature, for the characteristics of HTLs, such as interlayer ion exchange, acid base, thermal stability and so on, the HTLs is chosen to remove HCl under middle-high temperature as the adsorbent. By changing the composition of the material, a novel HTLs, which called Ca-Mg-Al HTLs is developed. Then the TG, FTIR, XRD, BET and SEM-EDS are applied to characterize the physical and chemical properties of obtained samples, to obtain the influence of properties of Ca-Mg-Al HTLs adsorbent on the removal efficiency. The results show that Ca-Mg-Al HTLs have obvious characteristics of layered structure.A fixed bed experimental system was built to test the property of adsorbent. The effects of different operating conditions on the adsorption of adsorbent, such as reaction temperature, gas flow rate, initial concentration of HCl, particle size and so on and different prepared conditions, such as Ca/Mg molar ratio, pH of the solution and aging temperature were investigated. When the reaction temperature at 250-650 ℃, at the initial stage, the adsorption rates of all samples were more than 0.6 mg/g·min. After 680 min, the higher the temperature, the earlier the end of the adsorption. While the gas flow rate was 0.5-1.3L/min, the average removal efficiency was 95%, and the deep removal efficiency could reach more than 99%. And the performance of the adsorbent decreased when the particle size was less than 0.15mm or more than 2mm. When Ca/Mg was 4, pH value was 11～12 and aging temperature was 90 ℃, the HTLs had better characteristics of removing HCl.The removal efficiency of optimal adsorbent prepared was compared with traditional sorbents such as CaO, NaHCO3 under the same quality and operation conditions. The removal efficiency of Ca-Mg-Al HTLs is much higher than CaO, NaHCO3, more than 95%. In order to further study the adsorption process of HCl on Ca-Mg-Al HTLs, the adsorption kinetics, adsorption equilibrium and adsorption thermodynamics analysis of the dynamic adsorption process of HCl were investigated. The results show that the adsorption process contains diffusion, physical adsorption and chemical adsorption, and the Bangham adsorption kinetics model can be used to predict the adsorption process of HCl on the adsorbent. The first stage is controlled by chemical adsorption, and activation energy is 193.498 KJ/mol; Both the Freumdlich and Langmuir adsorption isotherm model can well predict the adsorption process. The value of n in the Freundlich adsorption isotherm model is greater than 1, which means HCl is easily removed by the prepared HTLs. The adsorption thermodynamics research indicated that the free energy of adsorption, adsorption enthalpy and entropy change of adsorption were negative, this means that the adsorption of HCi is a spontaneous, exothermic process.In order to remove HCl deeply at medium-high temperature, the reactor is also needed to be matched with the adsorbent. The cross-flow moving bed was proposed to be reactor. The system of cross-flow moving bed was built. The effect of different gas temperature on the temperature distribution in the moving bed was studied. When the gas flow rate increased from 3 m3/h to 5 m3/h, the higher the temperature in the bed can be reached. But when the gas flow is too large, up to 6 m3/h, the residence time of gas in the bed is too short, the quantity of heat transfer is reduced and the temperature increase rate is reduced. When the particle velocity increased from12mm/s to 18mm/s, the residence time of gas is increased, so the temperature increase rate is increased. However, the temperature reduced with increasing particle velocity, which reach up to 23mm/s. In order to remove HCl deeply at medium-high temperature, the gas needs enough residence time in the reactor to react with the adsorbent. The integrated heat transfer coefficient and mass transfer coefficient are obtained.Based on the results obtained, Eulerian-Eulerian models were established to simulate the removal of HCl in cross-flow moving bed. Three kinds of internals:herringbone, triangle and splayed were used to ensure the same bed layer can maintain the same residence time. Then the complicated flow, heat transfer and HCl removal data analysis were carried out. Chemical reaction model was introduced into the species transport model. The effect of operating parameters on HCl removal including reaction temperature, gas flow velocity and so on were investigated. The results show that the Ca-Mg-Al HTLs can remove HCl at medium-high temperature. A certain gas flow rate can improve the removal efficiency of adsorbent. In order to ensure the utilization of adsorbent, the appropriate velocity of adsorbent is selected. |
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