Experimental Study On The Simultaneously Removal Of SO₂ And NO From Biomass Combustion Using Organic Calcium Compounds

China is rich in biomass resources.Directly combustion is one of the major technologies for lar-scale,efficient,and clean utilization of biomass.However,with the increasing strictest of environmental regulations,SO₂ and NOx emissions from combustion of biomass including sewage sludge,and peanut shell should not be neglected in the large-scale biomass combustion process.The development of flue gas purification process from single pollutant control to multiple pollutants removal is a major challenge and a hot topic of research.To develop the technology for simultaneously remove the SO₂ and NO emissions from the direct combustion of biomass,the thermochemical transformation law of biomass under the effect of the organic calcium compounds?OCC?adding in different combustion regions and the control mechanism of pollutant emissions were investigated by using thermogravimetric analyzer,fixed bed,drop tube furnace,and a fluidized bed combustion system.The systematic study including five parts has been carried out by means of experimental and theoretical analysis.They are the studies on combustion characteristics and reaction kinetics of biomass blended with OCC,pore characteristics and fractal mechanism of solid samples during thermal treatment process,sulfur release and sulfur migration mechanism of biochar,biomass reburning characteristics and nitrogen migration mechanism in biochar,and experimental study on synergistic desulfurization and denitrification characteristics in a laboratory scale fluidized bed combustor.Experiments were conducted in a thermogravimetric analyzer to assess the enhancement of combustion characteristics of different biomass blended with OCC.The characteristic temperatures and combustion performance indexes were defined.Effect of reaction atmosphere,and mole ratios of calcium to sulfur?Ca/S ratio?on the combustion characteristics were also investigated.The Coats-Redfern method was firstly used to calculate the kinetic parameters of the biomass blended with OCC.Results indicated that combustion performance for most biomass impregnated by OCC were improved,however,an inverse trend was found for sewage sludge.A stochastic nucleation model?G???=[-ln?1-??]²?for accurately describing the kinetic characteristics of biomass blended with OCC has been obtained.The pore characteristics and fractal mechanism of the blended fuel of OCC and biomass were studied in the process of combustion or pyrolysis,and the pore structural evolution and interaction law of the OCC and biomass was clarified in this study.The results showed that the addition of OCC increased the coarseness of the surface in the biomass thermal process,and maked it tend to present a three-dimensional network structure and increased the volume roughness of the pore structure of the products,which was beneficial to the biochar combustion and the improvement of the desulfurization efficiency.The effects of the main operating parameters on the pore characteristics can be described accurately by the fractal dimensions calculated according to the fractal theory.The sulfur retention rate of biochar decreased significantly with the increases of pyrolysis temperature.The OCC addition significantly reduced the sulfur precipitation rate of biomass and its biochar and improved the sulfur fixation ratio.The sulfur functional groups of biochar included thiol?S1?,sulfide?S2?,thiophene?S3?,sulfoxide?S4?,sulfone?S5?and sulfate?S6?.In the blended treatment process,the S5content was the largest when the Ca/S ratio was lower,indicating that the SO₂ was captured by self-desulphurization via cyclization reactions under this condition.With the increases of Ca/S ratio,the S6content increased significantly,implying that the more stable calcium sulfide and calcium sulphate were formed to achieve sulfur retention at this stage.The reburning experiments were conducted in a drop tube furnace.Results showed that the denitrification rate of biomass with high volatile content was relatively high,and the denitrification rate of dry sludge could still reach 44.1%.This proved the feasibility of reburning technology using dry sludge to removal NOx.After adding different OCCs,the denitrification rate of biomass reburning significantly increased.The porous CaO formed during the release of organic gases from OCC catalyzed the pyrolysis of protein nitrogen?P-N?with active side chain in biomass,resulting in the formation of many H radicals that change the migration pathway of the main nitrogen functional groups in biochar.A new ruburning method for the simultaneously removal of SO₂ and NO emissions using the OCC blended with the biomass was proposed.A laboratory scale fluidized bed combustor was used in this employed to investigate the effect of the OCC addition on the biomass staged combustion and the cooperative control mechanism of the key pollutant emissions.The biomass with high sulfur and nitrogen contents were used.The synergistic control mechanism of pollutant emissions by OCC adding in different combustion regions was comprehensively revealed.Results showed that the fuel staged combustion significantly decreased the NO emission from the direct combustion of peanut shell and sewage sludge.Based on fuel staged combustion,the addition of OCC in the reburning zone can effectively reduce the SO₂and NO simultaneously.Both pollutant emissions data obtained in this study were within the acceptable range of Chinese regulations.Results indicated that the design of the system for simultaneously removal the SO₂ and NO from biomass combustion is basically reasonable and the whole system can operate in a coordinated and stable manner.