基于生物质热解的高炉渣余热回收工艺基础研究

【作者】 杨艳华；

【导师】 雷霆；

【作者基本信息】 昆明理工大学 ， 钢铁冶金， 2023， 博士

【摘要】 钢铁工业是国民经济的重要基础产业,是技术、资源、能源密集型产业。目前,以高炉-转炉为主要工序的长流程仍然是今后很长一段时间的主流工艺,其中,高炉炼铁工序能耗占据整个流程能耗的70%。因此,高炉炼铁工序的节能降耗对整个钢铁产业意义重大,特别是要注重该工序过程中产生的余热、余能、余压的回收。在实现高炉渣高附加值利用的同时,高效回收其蕴含的巨大热量,对于减少资源消耗、提高能源利用率,推动钢铁工业实现双碳目标具有重要意义。高炉渣的综合利用主要包括高炉渣资源的高附加值利用和余热高效回收两个方面,高附加值利用的关键在于形成高活性非晶体,余热高效回收的关键在于热量的梯级回收。随着高炉渣干法粒化工艺地深入研究,为炉渣品质和余热高效回收兼顾提供了一种新方法。基于此,本论文提出将干法粒化得到的高温颗粒作为热载体,用做热解生物质的热源。系统研究干法粒化得到的高温渣粒,在降温过程中的热释放规律,同时研究典型生物质的热解行为,筛选出适宜的生物质种类进行热解实验,从而实现二者的能级匹配,并对高炉渣热载体热解生物质过程进行了模拟仿真,解析了热交换过程,明确了温度场分布情况,为后续工艺优化提供理论支撑。具体研究成果如下:采用蓝宝石法系统研究了高炉渣成分和结晶度对比热容的影响规律,获得了不同条件下的高炉渣比热容表达式,明确了高炉渣在降温过程中的热释放规律。渣中Al₂O₃和Ca O/Si O₂对炉渣在1100℃-1300℃温度区间的比热容影响较大,渣中Mg O对炉渣在800℃-900℃温度区间的比热容影响较大;炉渣结晶度对比热容的影响主要取决与结晶物相的相对量,结晶度越大,炉渣中的结晶物相越完整,比热容随温度变化曲线越平滑。化学成分对高炉渣热量释放影响较大,Al₂O₃影响最明显,其次是Mg O和Ca O/Si O₂;Al₂O₃含量为15.00 wt.%时热量释放最大,为2.9144×10⁶ k J/t,显热占95%以上;Mg O含量为9.00 wt.%时释放热量最大,为2.3281×10⁶ k J/t,显热占90%以上;Ca O/Si O₂为1.17时释放热量最大,为2.2791×10⁶ k J/t,显热占80%以上。炉渣结晶度越大,物理显热逐渐增大,结晶度为100%时热量最大为1.7018×10⁶k J/t。在10℃/min-25℃/min的冷却速率范围内,高炉渣释放总热量在0.70×10⁶ k J/t以上,且以物理显热为主,冷却速率对热量释放的影响较小。采用DSC热分析法研究了生物质种类（花生壳、水稻秸秆、小麦秸秆和玉米秸秆）、粒度和升温速率等条件下典型生物质的热解需热量及热解表观活化能,确定了与高炉渣热释放规律相匹配的生物质为玉米秸秆。在升温速率为15℃/min,终点温度为1000℃,生物质粒径为120μm条件下,玉米秸秆热解需热量最大为608.4 k J/kg。同一种生物质,热解升温速率对生物质热解需热量影响较大,粒度对生物质热解需热量影响较小。在5℃/min、15℃/min、20℃/min和25℃/min四种升温速率下玉米秸秆的热解需热量明显高于其他三种生物质,5℃/min升温速率下,其热解需热量达到891.09 k J/kg。玉米秸秆的热解需热量随着粒度减小而下降,粒径从180μm减小到75μm时,热解需热量下降量达到20%。升温速率升高、生物质粒径减小,得到的生物质热解反应活化能降低,有利于热解反应的发生。开展了以高炉渣为热载体定温热解和降温热解实验,考察了高炉渣掺混比、温度和粒度对热解过程得影响,采用烟气分析仪测得不同条件下生物质热解产物,计算出能量转换效率。定温热解温度越高,越有利于生物质热解气相产物的生成,热解温度为1000℃时气相产物产率高达61%,其热解气组成主要为H₂和CO,并且温度越高越有利于H₂的生成。降温热解实验表明,高炉渣掺混量、高炉渣温度均有助于热解反应进行,但高炉渣粒径不宜过大和过小,粒径在2-3 mm时热解产气率最大,该过程热解气体主要以CO、CO₂为主,H₂的生成量显著减少。降温热解过程中的能量转换效率最高达46.96%。分析了高炉渣颗粒与生物质颗粒热解传热过程,联用高炉渣、生物质、异质颗粒的传热方程,建立了固体颗粒传热模型。其中生物质的传热方程为（?）T/（?）t=（（?）²T/（?）r²+2（?）T/r（?）r）（λ/ρC）+Qdυ/Cdt。本文系统地研究了高炉渣热解生物质过程中关键科学问题,其结果为高炉渣干法粒化——化学法余热回收工艺的开发和设计具有理论指导意义,同时为生物质的资源化利用提供一种新途径。更多还原

【Abstract】 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.更多还原