| The steel industry is an important basic industry of the national economy,and it is a technology,resource and energy intensive industry.At present,the long process with blast furnace-converter as the main process is still the mainstream process for a long time in the future,in which the energy consumption of blast furnace ironmaking process accounts for 70%of the energy consumption of the whole process.Therefore,the energy saving and consumption reduction of blast furnace ironmaking process is of great significance to the whole iron and steel industry,especially pay attention to the recovery of waste heat,residual energy and residual pressure produced in this process.While realizing the high value-added utilization of blast furnace slag,the efficient recovery of the huge heat contained in blast furnace slag is of great significance for reducing resource consumption,improving energy efficiency and promoting the iron and steel industry to achieve the double carbon goal.The comprehensive utilization of blast furnace slag mainly includes two aspects:high value-added utilization of blast furnace slag products and efficient recovery of waste heat.The key to high value-added utilization lies in the formation of highly active amorphous crystals,and the key to efficient recovery of waste heat lies in the cascade recovery of heat.With the in-depth study of the dry granulation process of blast furnace slag,it provides a new method for both slag quality and waste heat recovery.Based on this,this paper proposes to use the high temperature particles obtained by dry granulation as the heat carrier and as the heat source of pyrolysis biomass.Systematically study the heat release law of the high temperature slag particles obtained by dry granulation in the cooling process,and study the pyrolysis behavior of typical biomass,select the appropriate types of biomasses,so as to realize the matching of the two energy levels.the process of pyrolysis of biomass by blast furnace slag heat carrier was simulated,the heat exchange process was analyzed,and the temperature field distribution was clarified,which provided support for the follow-up process optimization.The specific research results are as follows:The influence of blast furnace slag composition and crystallinity on the specific heat capacity of blast furnace slag is studied systematically by sapphire method,the expression of specific heat capacity of blast furnace slag under different conditions is obtained,and the heat release law of blast furnace slag in the cooling process is clarified.Al2O3 and binary basicity Ca O/Si O2 in slag have a great influence on the specific heat capacity of slag in the temperature range of 1100℃-1300℃,Mg O in slag has a great influence on the specific heat capacity of slag in the temperature range of 800℃-900℃,and the effect of slag crystallinity on specific heat capacity mainly depends on the relative amount of crystal phase.The higher the crystallinity is,the more complete the crystal phase in the slag is,and the smoother the curve of specific heat capacity varies with temperature.The chemical composition has a great influence on the heat release of blast furnace slag,and the effect of Al2O3 is the most obvious,followed by 2.9144×106 k J/t when the content of Mg O and Ca O/Si O2,Al2O3 is 15.00 wt.%,and sensible heat accounts for more than 95%.When the content of Mg O is 9.00 wt.%,the heat release is 2.3281×106k J/t,the sensible heat is more than 90%,and the heat release is 2.2791×106 k J/t.When binary basicity Ca O/Si O2 is 1.17,and the sensible heat accounts for more than 80%.The physical sensible heat increases gradually with the increase of slag crystallinity,and the maximum heat is 1.7018×106 k J/t when the crystallinity is 100%.In the cooling rate range of 10℃/min-25℃/min,the total heat release of blast furnace slag is more than 0.70×106 k J/t,and it is mainly physical sensible heat,and the cooling rate has little effect on heat release.The pyrolysis heat requirement and pyrolysis activation energy of typical biomass under different biomass（peanut shell,rice straw,wheat straw and corn straw）,different granularity and different heating rate were studied by DSC thermal analysis.It was determined that the biomass matched with the heat release law of blast furnace slag was corn straw.Under the conditions of heating rate 15℃/min,final temperature 1000℃and biomass particle size 120μm,the maximum heat required for pyrolysis of corn straw is 608.4 k J/kg.For the same kind of biomass,the heating rate of pyrolysis has a great influence on the heat requirement of biomass pyrolysis,while the particle size has little effect on the heat requirement of biomass pyrolysis.Under the heating rates of5℃/min,15℃/min,20℃/min and 25℃/min,the heat requirement of pyrolysis of corn straw was significantly higher than that of the other three biomass.At the heating rate of 5℃/min,the heat requirement of pyrolysis reached 891.09 k J/kg.The pyrolysis heat requirement of corn straw decreased with the decrease of particle size,and the reduction of pyrolysis heat requirement reached 20%when the particle size decreased from 180μm to 75μm.With the increase of heating rate and the decrease of biomass particle size,the activation energy of biomass pyrolysis shows a downward trend,which is beneficial to the occurrence of pyrolysis.The experiments of constant temperature pyrolysis and cooling pyrolysis with blast furnace slag as heat carrier were carried out.the effects of mixing ratio,temperature and particle size of blast furnace slag on the pyrolysis process were investigated.the pyrolysis products of biomass under different conditions were measured by flue gas analyzer,and the energy conversion efficiency was calculated.The higher the constant temperature pyrolysis temperature,the more favorable for the formation of gas phase products of biomass pyrolysis.When the pyrolysis temperature is 1000℃,the yield of gas phase products is as high as 61%.The pyrolysis gas is mainly composed of H2 and CO,and the higher the temperature is,the more beneficial to the formation of H2.The cooling pyrolysis experiments show that both the mixing amount of blast furnace slag and the temperature of blast furnace slag are helpful to the pyrolysis reaction,but the particle size of blast furnace slag should not be too large or too small,and the pyrolysis gas production rate is the highest when the particle size is 2-3 mm.In this process,the pyrolysis gas is mainly CO and CO2,and the amount of H2 is significantly reduced.The energy conversion efficiency in the process of cooling pyrolysis is as high as 46.96%.The pyrolysis heat transfer process of blast furnace slag particles and biomass particles is analyzed,and the heat transfer model of solid particles is established by using ANSYS Fluent software and the heat transfer equations of blast furnace slag,biomass and heterogeneous particles.The heat transfer equation of biomass is（?）T/（?）t=（（?）2T/（?）r2+2（?）T/r（?）r）（λ/ρC）+Qdυ/Cdt,where dυ/dt is the volatile formation rate of biomass.In this paper,the key scientific problems in the process of biomass pyrolysis of blast furnace slag are studied systematically.the results are of good guiding significance for the development and design of dry granulation of blast furnace slag-chemical waste heat recovery process.at the same time,it provides a new way for the resource utilization of biomass. |
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