The Effect Of Sulfur And Chlorine On The Release And Transformation Of Potassium From Biomass During Co-combustion Of Coal And Biomass

Energy is the driving force behind the development of human society.At present,fossil energy still occupies a major position in the global energy consumption structure.Due to the limitation and pollution of fossil energy,biomass energy,as one of clean and renewable energy,has broad application prospects.However,alkali-metal vapor with low melting point will be released during biomass combustion,resulting in slagging,high temperature corrosion,ash deposition and other problems,which limits the large-scale utilization of biomass.It is generally believed that alkali-metal K,which is easy to volatilize,will be retained in the solid phase by sulfur in coal during co-combustion of coal and biomass,and the release of SO₂ during coal combustion can also be reduced;chlorine in coal can promote alkali metal release;there may be some reaction and competition mechanism between the two.Based on the background of co-combustion of coal and biomass,this paper added various forms of sulfur and chlorine in coal to biomass to simulate the effect of sulfur and chlorine on the release and conversion of potassium from biomass during co-combustion.In this paper,experiments were carried out from three aspects:study on comprehensive combustion characteristics in the single-particle furnace,chemical analysis of effects of sulfur and chlorine in coal on migration/conversion of biomass potassium,and on-line measurement of dynamic release characteristics of biomass potassium.In this paper,three typical biomass and two different rank coals were selected to study the comprehensive combustion characteristics of typical biomass/coal,the effects of different temperatures as well as effects of sulfur and chlorine in coal on biomass combustion.Experiment results show that under the condition of high heating rate,different combustion stages overlap in parallel.The addition of biomass can obviously improve the combustion characteristics of the mixed fuel of coal and biomass,increase the weight loss rate and accelerate the combustion process.The promotion effect of furnace temperature rise on biomass combustion is mainly concentrated in the initial stage of particle combustion.During co-combustion of different fuels,volatile matter mainly affects the weight loss rate,and fixed carbon content mainly affects the burnout time.At 1000K?727??,sulfur and chlorine in coal have little effect on biomass combustion.In the aspect of off-line chemical analysis,different forms of sulfur and chlorine in coal were added to rice straw and corncob,the effect of combustion temperature on the sulfation and release of potassium as well as the effect of sulfur and chlorine on the migration and conversion of potassium were studied by means of fractional extraction combined with ICP-AES,XRD analysis and simulation of Factsage.The results show that the potassium in biomass mainly exists in the form of water-soluble,and the potassium released in the combustion process mainly comes from the water-soluble type,besides part of water-soluble potassium is converted to insoluble potassium.Fixation by sulfur is related to temperature and can be divided into potassium sulfate fixation below 900?and aluminosilicate fixation of potassium above 950¹000?.At815?,the principle of fixation by sulfur is to promote K to be retained in the form of K₂SO₄ and to inhibit the formation of some insoluble mineral potassium.Ammonium chloride?inorganic chlorine?promotes the conversion of K into easy-released KCl.The competitive effect of sulfur and chlorine is related to fuel;for rice straw at S/Cl=1,the effect of chlorine on potassium release is stronger than that of sulfur on potassium fixation,which is opposite during corncob combustion.Ferrous sulfide promots the gas phase release of potassium due to its catalytic effect on rice straw combustion;ammonium sulfate?inorganic sulfur?is difficult to decompose into sulfur dioxide,while dimethyl sulfone and thiophene alkane sulfone?organic sulfur?and PVC?organic chlorine?have little effect on potassium migration/conversion due to the characteristics of rapid volatilization or decomposition under heat.Factsage was used to simulate the effect of sulfur and chlorine in coal on the release and transformation of potassium from rice straw.The obtained law is similar to that of experiments,sulfur promots the retention of potassium in ash in the form of stable sulfate,while chlorine promots the release of potassium to the gas phase in the form of KCl.In the aspect of on-line experiments,the multi-point LIBS system was used to measure the dynamic release of potassium from rice straw at multiple points,and the influence law of sulfur and chlorine in coal on dynamic release of K during rice straw combustion was studied,the obtained results are in good agreement with offline laws.K release during rice straw combustion can be divided into volatile combustion stage,residual coke burnout and ash reaction stage,of which the latter is the main interval for K release.As the radius of the measuring point increases,the potassium release curve decreases,the release time shortens,and the release peak gradually delays.The slight increase of K total release in on-line measurement is related to further decomposition of potassium aluminosilicate at higher temperature.Sulfur effectively inhibits the dynamic release of K;dimethylsulfone?organic sulfur?has no obvious effect on the dynamic release of K due to its volatile nature when heated;a small amount of SO₂decomposed by ammonium sulfate?inorganic sulfur?under strong heating environment slightly inhibits the dynamic release of K;the catalytic effect of FeS on combustion promotes the release of K.Ammonium chloride?inorganic chlorine?has a little effect on promoting release,and PVC?organic chlorine?has little effect on the dynamic release of K due to its rapid decomposition and release.