| It's a main issue in the field of environmental chemical engineering to find effective and cheap absorption medium for the wet flue gas desulfurization(FGD) process. At the same time, much attention have been paid on finding more effective and economy methods on ammonia stripping as pre-process for landfill leachtae bio-treatment. The study in this paper put forward and developed a system of integrating SO2 absorption into flue gas with landfill leachate coupled with ammonia stripping for the first time, in which SO2 in the flue gas could be absorbed by the alkaline and S(IV) oxidation catalyzed by metal ions in landfill leachate while the heat needed for stripping some ammonia from landfill leachate at high temperature can be provided partially or totally by the higher temperature flue gas. The reaction mechanism, macro kinetic control factors, operating parameters in normal packed column, and rate-based model of the process were systematically investigated in the present paper.Due to the complexity of landfill leachate composition, the reaction mechanism of SO2 absorption into flue gas with landfill leachate coupled with ammonia desorption was studied using a stirring vessel. The orthogonal experimental results indicated that the influence degree sequence of effect on SO2 absorption efficiency with landfill leachate form large to small was pH value, the catalysis of Fe2+ and Mn2+, the catalysis of Cl~ and the concentration of toluene and ethanol. The quantitative experiments showed that the pH value of landfill leachate was the key factor bothfor SO2 absorption and ammonia stripping. Under the condition of initial pH vajue being 8.5, terminal pH value being 6.0 and L/G ratio being 3L/m3, experiment results showed that average absorption efficiency of SO2 was 85% and average desorption efficiency of ammonia was 44%. The catalysis of Fe2+ and Mn2+ was important for SO2 absorption when pH value was below 7.0. Catalysis activity of Mn2+ was better than that of Fe2+ although their react steps were very similar. The catalysis of Cl" could only be effective if companied by the catalysis of Fe2+and Mn2+. Ethanol could inhibit S(IV) oxidation. S(IV) oxidation could improve the solubility of organics such as toluene in landfill leachtae, and the products were water-soluble and belonged to biodegradable surfactants which could be used as substrates for microbiology in the post bio-process. However, positive effect of catalysis of Cl", Fe2+ and Mn2+ on S(IV) oxidation has superiority over the negative effect of ethanol inhibition on S(IV) oxidation. Macro kinetic experiment results indicated that gas phase diffusion resistance could be the control step of the process when pH value was above 8.5, and liquid phase diffuse resistance could be the control step of the process when pH value was between 4 to 6.5 due to S(IV) oxidation, and the gas phase and liquid phase diffusion resistance might both have effects on the control step of the process when pH value was between 6.5 to 8.5.Operating parameters, including liquid retention time, temperature, ratio of liquid /gas flow rate, liquid spraying density, SO2 concentration in flue gas, and NH/-N concentration in landfill leachate, were studied experimentally in a normal packed column. Based on experimental results, numerical simulation equations of SO2 absorption efficiency and ammonia desorption efficiency corresponding to the operating parameters were developed. The experimental results indicated that ammonia desorption efficiency increased when liquid retention time was below 20 min and SO2 absorption efficiency decreased when liquid retention time became long. High temperature was benefit to ammonia stripping and disbenifit to SO2 absorption. SO2 absorption efficiency and ammonia desorption efficiency both improved with increasing the ratio of liquid /gas flow rate and the liquid spraying density. High concentration of SO2 in flue gas had negative effect on SO2 absorptionand ammonia stripping, while high concentration of NH4+-N in landfill leachate had positive effect. Unde...
|
PDF Full Text Request