贺冲,白进,郭晶,鲁浩,黄磊
HE Chong,BAI Jin,GUO Jing,LU Hao,HUANG Lei

• 1:太原理工大学环境科学与工程学院
• 2:中国科学院山西煤炭化学研究所煤转化国家重点实验室
• 3:太原理工大学安全与应急管理工程学院

摘要(Abstract)：

生物质中碱金属(钾和钠)在气化过程中易释放至气相，导致气化炉腐蚀、积灰、结渣等问题，严重影响气化炉的长周期运行。采用热力学模拟，分别从碱金属释放和分布规律、物相演化机理、熔渣结构单元和熔渣固定碱金属吉布斯自由能，阐明添加高岭土对秸秆气化过程中碱金属释放的影响机制。结果表明，800℃秸秆灰渣中碱金属钾主要存在于钾镁硅酸盐和长石，而钠存在于长石，温度升高促进灰渣中碱金属释放至气相；此外，矿物质种类和熔渣结构分别是决定碱金属释放行为的关键因素；800℃时添加高岭土促进灰渣中固钾矿物质由钾镁硅酸盐转变为白榴石，固钠矿物质由钠钙硅酸盐转化为霞石，减弱碱金属释放行为。高温下添加高岭土，熔渣解聚参数G下降，熔渣中Si-Si-O-O结构单元转变为Al-Si-O-O结构单元，促进碱金属以电荷补偿形式与四配位Al~(3+)结合，Si-KAl-O-O结构单元和Si-NaAl-O-O结构单元含量升高，抑制碱金属释放。此外，1 400～1 600℃时，添加高岭土导致熔渣固定碱金属反应的吉布斯自由能降低，熔渣固定碱金属能力增强，碱金属释放减弱；熔渣固定碱金属钾反应的吉布斯自由能高于碱金属钠，因此碱金属钾更易释放至气相。
Alkali metals(potassium and sodium) in biomass are easy to be released into the gas phase during gasification, causing corrosion, ash deposition, slagging and other problems in the gasifier, seriously affecting the long-term operation of the gasifier. In this study, the effect of kaolin addition on the release behavior of alkali elements during straw gasification was explored in the aspects of the distribution of alkali elements, phase evolution behavior, slag structure, and the Gibbs free energy of alkali element capture by slag, via thermodynamic modelling. The results indicate that K and Na are mainly in the form of the K-Mg silicate and feldspar, respectively, while sodium exists in feldspar, and the increase of temperature promotes the release of alkali metal in ash to gas phase. The released content of alkali elements increases with the gasification temperature. In addition, the mineral species and slag structure are the key factors governing the release behavior of alkali elements at low temperature and high temperature, respectively. The addition of kaolin at 800 ℃ promotes the transformation of potassium fixing minerals from potassium magnesium silicate to leucite in the ash, and the transformation of sodium fixing minerals from sodium calcium silicate to nepheline, reducing the release behavior of alkali metals. At high temperature, the addition of kaolin decreases the depolymerization parameter G value of slag, leading to the conversion of the structure unit Si-Si-O-O to Si-Al-O-O. The resulted Si-Al-O-O is the key structure unit of capturing alkali elements in the slag by forming the structure unit Si-KAl-O-O and Si-NaAl-O-O, and this process is driven by the charge compensation effect. Furthermore, the kaolin addition decreases the ΔG of the reaction of slag capture alkali elements at 1 400-1 600 ℃, which enhances the ability of alkali metal fixation of slag and inhibits the alkali element release. In contrast to Na, the ΔG of the K capture reaction by slag is higher, indicating that the K is easier to be released than Na during biomass gasification.

关键词(KeyWords)： 生物质气化;碱金属;高岭土;熔渣结构;吉布斯自由能
biomass gasification;alkali elements;kaolin;slag structure;Gibss free energy

Abstract:

Keywords:

基金项目(Foundation): 国家自然科学基金资助项目(22108190)

作者(Author): 贺冲,白进,郭晶,鲁浩,黄磊
HE Chong,BAI Jin,GUO Jing,LU Hao,HUANG Lei

DOI: 10.13226/j.issn.1006-6772.RE22090901

参考文献(References)：

• [1] ZENG X,MA Y,MA L.Utilization of straw in biomass energy in China[J].Renewable and Sustainable Energy Reviews,2007,11(5):976-987.
• [2] GE Z,CAO X,ZHA Z,et al.The influence of a two-step leaching pretreatment on the steam gasification properties of cornstalk waste[J].Bioresource Technology,2022,358:127403.
• [3] HU Z,WANG X,ZHOU Y,et al.Assessment of the effect of alkali chemistry on post-flame aerosol formation during oxy-combustion of biomass[J].Fuel,2022,311:122521.
• [4] 颜婷珪，白进，孔令学，等.煤灰流动性研究方法进展[J].洁净煤技术，2020,26(1):90-98.YAN Tinggui,BAI Jin,KONG Lingxue,et al.Advances in research methods of coal ash fluidity[J].Clean Coal Technology,2020,26(1):90-98.
• [5] 吾买尔江·卡瓦，林雄超，杨远平，等.新疆高碱煤四喷嘴气化炉结渣特性研究[J].洁净煤技术，2019,25(3):62-67.KAWA Omarjiang,LIN Xiongchao,YANG Yuanping,et al.Study on the slagging characteristics of Xinjiang high-alkali coal in four-nozzle gasifier[J].Clean Coal Technology,2019,25(3):62-67.
• [6] TURN S Q.Chemical equilibrium prediction of potassium,sod-ium,and chlorine concentrations in the product gas from biomass gasification[J].Industrial & Engineering Chemistry Research,2007,46(26):8928-8937.
• [7] FATEHI H,HE Y,WANG Z,et al.LIBS measurements and numerical studies of potassium release during biomass gasification[J].Proceedings of the Combustion Institute,2015,35(2):2389-2396.
• [8] LI X,HE F,SU X,et al.Evaporation rate of potassium chloride in combustion of herbaceous biomass and its calculation[J].Fuel,2019,257:116021.
• [9] CAO W,LI J,LIN L,et al.Release of potassium in association with structural evolution during biomass combustion[J].Fuel,2021,287:119524.
• [10] LIU Y,WAN K,HE Y,et al.Experimental study of potassium release during biomass-pellet combustion and its interaction with inhibitive additives[J].Fuel,2020,260:116346.
• [11] CLERY D S,MASON P E,RAYNER C M,et al.The effects of an additive on the release of potassium in biomass combustion[J].Fuel,2018,214:647-655.
• [12] ZHANG H,HAO Z,LI J,et al.Effect of coal ash additive on potassium fixation and melting behaviors of the mixture under simulated biomass gasification condition[J].Renewable Energy,2021,168:806-814.
• [13] LI F,YU B,LI J,et al.Exploration of potassium migration behavior in straw ashes under reducing atmosphere and its modification by additives[J].Renewable Energy,2020,145:2286-2295.
• [14] MIAO H,WANG Z,WANG Z,et al.Effects of Na2CO3/Na2SO4 on catalytic gasification reactivity and mineral structure of coal gangue[J].Energy,2022,255:124498.
• [15] GE Z,CAO X,ZHA Z,et al.The mineral transformation and molten behaviors of biomass waste ashes in gasification-melting process[J].Fuel Processing Technology,2022,226:107095.
• [16] LI F,WANG X,ZHAO C,et al.Influence of additives on potassium retention behaviors during straw combustion:A mechanism study[J].Bioresource Technology,2020,299:122515.
• [17] GAI C,DONG Y.Experimental study on non-woody biomass ga-sification in a downdraft gasifier[J].International Journal of Hydrogen Energy,2012,37(6):4935-4944.
• [18] WU C Z,YIN X L,MA L L,et al.Operational characteristics of a 1.2 MW biomass gasification and power generation plant[J].Biotechnology Advances,2009,27(5):588-592.
• [19] KNUDSEN J N,JENSEN P A,DAM K.Transformation and release to the gas phase of Cl,K,and S during combustion of annual biomass[J].Energy & Fuels,2004,18(5):1385-1399.
• [20] CAO W,MART-ROSSELLO T,LI J,et al.Prediction of potassium compounds released from biomass during combustion[J].Applied Energy,2019,250:1696-1705.
• [21] REBBLING A,FAGERSTROM J,STEINBALL E,et al.Reduction of alkali release by two fuel additives at different bed temperatures during grate combustion of woody biomass[J].Energy & Fuels,2019,33(11):11041-11048.
• [22] HU X,ZHANG Z,WU X,et al.Sodium capture mechanism by simulated silica/aluminosilicate slag at high temperatures[J].Fuel,2022,328:125344.
• [23] VARGAS S,FRANDSEN F J,DAM K.Rheological properties of high-temperature melts of coal ashes and other silicates[J].Progress in Energy and Combustion Science,2001,27(3):237-429.
• [24] HU X,WUX,ZHANG Z,et al.Sodium retention behavior of Xinjiang high-alkali coal in a 20 kW slag-tapping combustor test[J].Fuel,2022,317:123298.