Knowledge Management System Of Guangzhou Institute of Energy Conversion, CAS
| 硫酸盐黑液高温水蒸气气化与直接苛化实验研究 | |
| Alternative Title | Kraft Black Liquor High Temperature Steam Gasification with Direct Causticization using Titanium Dioxide and Titanates |
| 袁洪友 | |
| Thesis Advisor | 阴秀丽 |
| 2009-05-31 | |
| Degree Grantor | 中国科学院广州能源研究所 |
| Place of Conferral | 广州能源研究所 |
| Degree Name | 硕士 |
| Keyword | 黑液 热解 气化 回收锅炉 直接苛化 |
| Abstract | 黑液是碱法制浆的副产物，其中含有需要回收的制浆化学品和能源。Tomlinson型碱回收锅炉是当今处理黑液的主要设备，燃烧黑液有机物生产蒸汽并以熔融态回收制浆化学品。始终无法消除的熔融物遇水爆炸隐患以及热力学效率低等问题使得业界开发替代回收方案的努力一直在进行，其中气化技术获得了广泛和持久的研究。 本文首先全面回顾国际上黑液低温和高温气化技术30多年来的发展历程，找出高、低温气化各自存在的主要问题。低温气化由于运行温度低因而碳转化速率较低，高温气化以熔融态回收碱因而耐高温耐腐蚀材料问题成为制约其发展的障碍之一。二氧化钛直接苛化技术可以将Na2CO3在炉内直接脱去CO2，因而苛化和气化在一个反应器中即可进行，固体产物五钛酸盐可水解出氢氧化钠，难以进一步水解的三钛酸盐则回收继续用于直接苛化反应，省去了传统的石灰苛化循环；直接苛化产物具有较高的熔点因而可以在相对较高的温度(例如800℃)运行而又不引入熔融相。 黑液气化结合直接苛化工艺目前处于试验研究阶段，提高温度(800℃以上)的黑液水蒸气气化结合直接苛化目前未见任何研究报导，本文将以此为方向探索可行的黑液气化工艺路线。 实验方面，首先对硫酸盐黑液的热膨胀特性进行了初步了解，分析了热解产物得率与热解气体组成。硫释放到气相是气化不同于燃烧的一个特点，对热解导致的硫释放及其形式做出了分析。 在对黑液的热解特性有了基本了解之后，模拟黑液低温气化的温度和气氛条件对黑液气化过程的碳转化、硫酸盐还原和硫释放进行了研究。实验结果表明硫酸盐还原在低温气化工艺所要求的温度范围内是可以进行的，提高温度有助于硫酸盐还原，但是允许提高的温度范围有限。低温气化条件下，除未还原硫酸盐硫之外，其它所有形式的硫如有机硫、Na2S等通过一定转变全部排入气相。试验中发现黑液热解焦中有机碳气化速率非常缓慢，除了温度较低的原因外，传质阻力使得气固接触不够充分可能是重要原因。 流化床是黑液低温气化工艺普遍采用的反应器，为了比较理想地考察硫酸盐黑液气化过程硫的行为，以及考虑到提高温度的直接苛化试验的需要，建立了外加热的小规模流化床水蒸气气化反应器，进料量约500g/批。该流化床采用石英砂、木屑、碳酸钠二氧化钛混合物均可实现稳定运行。黑液液体进料试验未能成功，原因主要在于没有实现黑液的快速干燥热解成焦；黑液干燥固体进料也因膨胀没有顺利流化；当采用二氧化钛与黑液固体混合进料高温运行时虽然流化仍然失败，但是发现有机碳转化速率相比低温气化有极大提高，遗憾的是固体产物有比较严重的结块。 高温直接苛化工艺成功的几个关键之处在于苛化反应是否足够迅速以避免形成熔融物，产物是否具有良好的颗粒性，水解是否容易进行，三钛酸钠能否循环利用等。流化床试验遇到的严重结块的问题原因已经找到，而后对直接苛化工艺涉及的一系列热点问题进行了试验探索。试验结论认为：高温水蒸气气化与直接苛化是一条可行的黑液气化法碱回收方案，在有机碳气化、碳酸钠脱CO2、五钛酸盐水解、三钛酸盐循环利用等方面均不存在问题。含硫化合物的转变还需要进一步研究，探索减少有机硫排放和提高芒硝还原率的工艺条件。 |
| Other Abstract | Black liquor is the residue from the cooking of wood, straw or other fibrous plants in the alkali pulping process. Recovery of the chemicals used, as well as of the energy contained in the organics, is important for the economics of the paper mill. Nowadays, Tomlinson recovery boilers are used to generate heat from the organic compounds and to recover the cooking chemicals contained in the black liquors, but there are some safety problems and the energy efficiency is relatively low. Gasification of black liquor is a promising alternative for recovery systems in the pulping process. Two gasification processes have been commercialized: a low temperature process operating at about 600℃, and a high temperature process operating at 950-1000℃. Low temperature processes have problems achieving good conversion while avoiding ash agglomeration; high temperature processes suffer material problems caused by extremely corrosive conditions. It is of interest to combine direct causticization of black liquor by TiO2 with gasification. Firstly, a high temperature needed for both gasification and direct causticization can be realized in a single reactor. Secondly, direct causticization with TiO2 produces high melting point products which minimize the smelt formation problem associated with high temperature gasification processes. Thirdly, the sodium penta-titanate formed in the gasifier is leached with water, forming solid sodium tri-titanate and sodium hydroxide, The sodium tri-titanate is separated and recycled to the gasifier. Illuminated by the black liquor gasification with steam at low temperature, one would naturally consider gasification with steam at relatively high temperature, fortunately, using TiO2 this process maybe feasible without smelt formation. The steam gasification research began with the pyrolysis experimental study. The swelling of kraft black liquor was tested at 400-800℃ under nitrogen atmosphere with a visualized single droplet reactor. The main permanent pyrolysis gas components of three kraft liquors were investigated at temperatures up to 850℃. The measurements of H2S release during pyrolysis were realized by iodometry, the total sulfur release was evaluated through char analysis. Steam and CO2 gasification of black liquor at low temperature were conducted with tube furnace. The effect of temperature, atmosphere and reaction time on carbon conversion, sulfate reduction and sulfur release were investigated. Nearly all sulfur release to gas phase except for sulfur in sulfate. Sulfate can be reducted by carbon at solid state. the gasification rates of organic carbon by steam at these low temperature(600 and 650℃) are very slow, though we already know this according literature before, compare with fluidized bed, mass transfer limitation may worsen this problem. For improving of gas-solid contact, a small bench scale fluidized bed was constructed, with an external heater and a steam blowing system. The feedstock of quartz sand, sawdust can be easily fluidized in the small FB. Regretfully, the liquid feedstock of black liquor never successfully realized fluidization. Unlike MTCI low temperature process, the material sprayed into the bed cannot be quickly dried and pyrolyzed, poorly design may account for the failure. When switch to solid feedstock of black liquor mixed with titanium dioxide, fluidization condition cannot be gained all the same, but after 30 min of steam gasification at 800℃, the agglomeration of feedstock in the middle of the bed was found but without any organic carbon remaind. Given the presence of titanium dioxide, the reason for agglomeration was not clear then. Puzzled by the serious problem of agglomeration, and Encouraged by the good carbon conversion at high temperature, we conducted experimental of kraft black liquor high temperature steam gasification with direct caustisization using tube furnace or called fixed bed which can be easily operated. Fortunately, mass transfer limitation doesn’t show too much negative effect on the carbon conversion at relatively high temperature. When choosing pure anatase titanium dioxide as the direct causticization agent, agglomeration of bed material never appeared. All reactions concerned gained high conversion at high temperature, including organic carbon gasification, decarbonization, penta-titanate hydrolyzing. Recycling titanates show similar effects with fresh titanium dioxide, no agglomeration was found either. Anyhow, we reckon the high temperature steam gasification using titanates a promising alternative to conventional recovery process. Method of decreasing organic sulfur emission and improving sulfate reduction need further research. |
| Pages | 103 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.giec.ac.cn/handle/344007/5860 |
| Collection | 中国科学院广州能源研究所 |
| Recommended Citation GB/T 7714 | 袁洪友. 硫酸盐黑液高温水蒸气气化与直接苛化实验研究[D]. 广州能源研究所. 中国科学院广州能源研究所,2009. |
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