Research On Basic Aluminum Sulfate Regenerative Wet Flue Gas Desulfurization Technology

Basic aluminum sulfate(BAS)regenerative wet flue gas desulfurization(FGD)technology is an effective and promising method to control SO2 emissions from coal-fired flue gas,in which SO2 could be recovered as sulfur source.Based on the concept of efficient,economical and resourceful development,this paper systematically researched BAS regenerative wet FGD process,mainly including three key processes,namely SO2 absorption?byproduct oxidation inhibition and absorbents regeneration.Especially,as an environment-friendly compound,ethylene glycol(EG)was first applied to inhibit desulfurization byproduct oxidation,which exhibited excellent inhibition effects.Furthermore,we proposed a novel vacuum regeneration method for desorption process related to BAS rich solution,and researched the topics of regeneration performance and energy comsuption.This study will benefit for the design and industrial applications of BAS regenerative wet FGD technology.The main contents are as follows:Using the bubbling reactor,the effects of various operating parameters on the SO2 absorption performance relevant to BAS solution have been investigated.The results indicated that larger the amount of aluminum and basicity could improve the desulfurization performance;increasing the flue gas flow rate had little effect on the desulfurization efficiency,while could increase the oxidation efficiency;flue gas with high SO2 concentration could also be well suited for the desulfurization process;higher temperature could lower the desulfurization efficiency,and weaken the inhibitory action of EG;compared with no inhibitor,the adding of EG could cause lower desulfurization efficiency,while with adding EG 1%(v/v)above,the oxidation efficiency could keep 10% below in 120 min.According to the established mass transfer model,SO2 absorption process in BAS solution with bubbling was commonly controlled by a combination of gas-film resistance and liquid-film resistance.Through the laboratory small scale apparatus,the impact of various operating conditions on the regeneration performance for BAS rich solution has been studied,and a novel vacuum regeneration model was established.The results show that SO2 desorption rate is close related to the water evaporation rate,meanwhile both decreasing regeneration pressure and increasing temperature would significantly improve the SO2 desorption performance.In the vacuum regeneration process,water vapor energy consumption accounted for more than 85% of total energy consumption.Furthermore,compared with the traditional direct heating method,vacuum regeneration would greatly improve the SO2 desorption rate,and the energy consumption was lower under the regeneration pressure 23 kPa below.The results for SO2 absorption-desorption repeated experiments demonstrated that the desulfurization efficiency and pH value would slightly decrease with cycles,while the SO2 desorption efficiency could always keep at around 98%.In addition,the samples of basic aluminum sulfate solution before and after the cycle were analyzed by infrared spectroscopy,indicating that BAS has a stable chemical structure.Using the aeration stirred reactor,the influences of various operating conditions on the S S(IV)oxidation rate have been investigated,and the macro-kinetics of S(IV)oxidation was determined.The results confirmed that increasing the basicity?gas flow rate and stirring rate could improve the S(IV)oxidation rate,while high amount of aluminum would hamper the S(IV)oxidation rate.Furthermore,the general reaction rate was found to be 0.21 order in sulfite and first-order in oxygen,respectively,and the apparent activation energy was calculated to be 24.5 kJ/mol.Combined with the mechanism of S(IV)oxidation proposed,the corresponding kinetic model was established,indicating the general oxidation rate of S(IV)in BAS solution was controlled by the mass transfer of oxygen.As a result,the intrinsic kinetics was speculated,indicating the reaction orders with respect to sulfite and oxygen to be 0.42 and 1.0,respectively.Using the aeration stirred reactor,the impact of various operating parameters on S(IV)oxidation process under oxidation inhibition condition has been studiesr,and the inhibitory mechanism of EG was analyzed.Through the screening of several inhibitors,it indicated that EG is optimal inhibito.The results show that high amount of aluminum could reduce the inhibitory action of EG,and air flow rate had little effect on S(IV)oxidation rate.Furthermore,the general oxidation rate was found to be 0.96 order in S(IV),1.04 order in oxygen,and – 2.4 order in EG,respectively.The apparent activation energy was calculated to be 52.0 kJ/mol.In addition,the first hydroxy in EG plays a decisive role concerning S(IV)oxidation inhibition reaction,while the inhibitory action of another hydroxyl is relatively weaker.According to the experimental data,the corresponding kinetic equation was obtained.Finally,based on above experimental results,the impact of various operating parameters on BAS regenerative wet FGD process under oxidation inhibition condition has been studied through the packed tower.The experimental results confirmed the optimal conditions as follows: amount of aluminum as 30 g/L,basicity as 25~30%,liquid-gas ratio as 3 L/m~3,and EG concentration as 2%(v/v).