循环灰热载体煤热解催化反应机理及油气提质净化研究

Based on the development of the grading conversion process which combines combustion and coal pyrolysis by using circulating ash heat carrier, an integrated technical route of non-regenerative dolomite catalytic reactor and the existing grading conversion process is proposed. This research investigates the catalytic effect of circulating ash and deactivated dolomite catalyst after oxidative combustion on the primary pyrolysis products and clarifies the catalytic reaction characteristics of typical components in the circulating ash for pyrolysis volatiles and pollutants. Combined with the theory of granular bed filter, this research reveals the dust trapping mechanism in the environment of high-temperature pyrolysis volatiles and establishes the mathematical model of the dust removal efficiency and clarifies the catalyst deactivation mechanism as well as the cooperative and inhibitive effect of deposited dust on the tar cracking activity of non-regenerative dolomite catalyst. Aiming to investigate the reaction characteristic of pollutants such as sulfurated, chlorinated and mercuric contaminants in coal pyrolysis volatiles with dolomite catalyst, in a two-stage fixed bed reactor, this research investigates the effect of different degrees of tar catalytic cracking reaction and dust deposition on the reaction of pollutants with dolomite catalyst and the competition mechanism. On the experimental platform of the integrated system, this research examines the evolution characteristics of pollution elements comes from the raw coal between the combustion furnace, pyrolysis reactor and catalytic reactor and ascertains the key technological factors which affecting the modification and purification of the volatiles. This research will provide a theoretical basis for the poor quality of tar, oil product with ash and other technical bottlenecks of the coal pyrolysis process development.

以基于循环灰热载体的煤热解/燃烧分级转化工艺开发为应用背景，提出将非再生型白云石催化反应器与已有分级转化工艺耦合的技术路线。考察循环灰及失活白云石催化剂氧化产物对一次热解产物的催化作用，阐明热解油气及污染物与循环灰中典型组分的催化反应特性。结合颗粒床除尘理论探明高温热解油气环境下粉尘的捕集机理，建立除尘效率的数学模型，阐明粉尘沉积对非再生型白云石催化剂焦油裂解活性的协同/抑制作用及催化剂的失活机理。研究煤热解油气中的含硫、含氯、含汞污染物与白云石催化剂的反应特性，在两段固定床反应器上，考察不同程度的焦油催化裂解和粉尘沉积作用对污染物与白云石催化剂反应的影响及竞争反应机理。在耦合系统实验平台上，考察原煤中的污染元素在燃烧炉、热解反应器、催化反应器间的迁移特性，探明影响油气提质净化的关键工艺因素。通过本项目研究，可望为煤热解工艺开发中焦油品质差、油中带灰等技术瓶颈问题的解决提供理论依据。

本项目以煤热解/循环流化床（CFB）燃烧分级转化工艺为应用背景，将非再生型白云石（D）催化剂作为油气提质净化和粉尘过滤的介质。考察循环灰及失活白云石氧化产物对一次热解油气产率、成分的影响规律，阐明了循环灰中典型组分对油气产物及污染物的催化反应特性。结合颗粒床除尘理论建立了可预测高温油气环境下粉尘在颗粒床内捕集效率的数学模型。考察含硫、含汞污染物与白云石反应对焦油催化裂解特性的影响，明确污染元素在失活催化剂上的赋存形态，揭示非再生型白云石催化剂的失活机理。开展煤热解/燃烧双阶段脱硫、脱汞实验，获得煤中硫、汞等污染元素在燃烧炉、热解反应器、催化反应器间的迁移规律，揭示影响油气提质净化的关键工艺因素。热载体对焦油的催化能力强弱顺序为：循环灰>新鲜白云石>失活白云石。循环灰中Fe2O3和CaO对长链脂肪烃和C-O键的催化裂解效果明显。0-20μm粒径范围内的粉尘难以被颗粒床捕集，滤料层高度越高、表观气速越慢、过滤介质尺寸越小，越有利于粉尘的捕集。Ni的硫中毒和积碳的形成是1%Ni-D活性逐渐降低的重要原因。Fe助剂能显著改善白云石催化剂的耐硫性能，还有一定的消碳作用。白云石中MgO促进了硫醇和甲基苯基硫醚向二硫化合物的转化。煤中汞主要以Hg0形式释放，白云石可使部分Hg0转化为Hg2+。1%Ni/2%Fe-D中主要组分对Hg0的氧化作用顺序为NiO＞Fe2O3＞CaO＞MgO。高温抑制Hg0向Hg2+的转化，当温度＞750℃时Hg0向Hg2+的转化率降低至10%。在以循环灰做热载体并以天然白云石作催化剂时，煤中62.43%的硫被固定在循环灰中，CFB锅炉排放的含硫污染物相较直接燃烧减少了55%。煤中汞在热解过程中完全脱除，相比直接燃烧，分级转化工艺需处理的气量少。本项目可为该分级转化技术的后续工艺开发及污染物的迁移控制提供理论依据。