基于热解/燃烧分级转化的循环灰热载体煤热解模拟及硫迁移特性研究

Aiming at development of a grading conversion process that combines moving-bed coal pyrolysis with circulating fluidized bed combustion, based upon the typical coal pyrolysis kinetics and ash/coal mixing flow model, and taking into consideration of the complex transfer phenomenon of coal pyrolysis by circulating ash heat carrier in the moving-bed reactor, this research will set up a mathematical model of industrial application value to describes coal particles' heating-up process and coal pyrolysis devolatilization behavior in moving-bed reactor and predict the distribution of temperature of circulating ash-pyrolysis gas-coal three phases and concentration of pyrolysis products under different operating conditions.Through pyrolysis/combustion dual-process principle experiment by using high sulfur coal as raw material, and by applying multiple analyzing methods,this research investigates the key technical factors that influences the circulating ash's sulfur retention capacity and activity in coal pyrolysis process and reveals transformation mechanism of sulfur in heat carrier and residual sulfur in semicoke in the process of combustion. Based on this, by comparingthe sulfur transfer characteristics in single circulating fluidized bed combustion process and desulfurization economic and technical indicators, this research suggests optimized desulfurization scheme applicable to this grading conversion technology. This research deepens the understanding of the heat transfer and reaction law in the circulating ash heat carrier moving bed reactor,expounds different forms of sulfur's transfer in grading converstion process, and provides powerful theoretical evidence for the future industrial development of pyrolysis/combustion grading conversion technology.

以移动床煤热解/循环流化床燃烧分级转化工艺过程开发为应用背景，在典型煤种热解动力学、灰/煤混合流动模型的基础上，综合考虑移动床循环灰热载体煤热解反应器内复杂的传递现象，建立具有工业应用价值的数学模型，描述煤颗粒受热升温历程和热解脱挥发分行为，预测不同工况下反应器内的循环灰-热解气-煤三相温度、产物浓度分布规律。以高硫煤为原料，进行热解/燃烧双阶段过程原理性实验研究，利用多种分析表征手段，探明热解阶段影响循环灰固硫容量、活性的关键工艺因素，揭示固定于热载体中的硫化物和热解半焦中残余硫在燃烧阶段的转化机理。在此基础上，对比单一循环流化床燃烧过程的硫迁移特性和脱硫经济技术指标，提出适于该分级转化工艺的优化脱硫方案。通过本课题的研究，加深对移动床循环灰热载体煤热解反应器内传递和反应规律的认识，阐明煤中不同形态硫在分级转化过程中的迁移特性，为热解/燃烧分级转化技术的后续工业开发提供有力的理论依据。

本项目以煤热解与循环流化床燃烧耦合的分级转化多联产工艺为应用背景，在二维移动床冷态实验平台考察移动床内的灰/煤混合及流动特性。综合考虑移动床循环灰热载体煤热解反应器内气-固-固三相传递规律、典型煤种热解动力学和煤热解脱挥发分行为，建立循环灰热载体煤热解二维数学模型。通过热解/燃烧双阶段过程原理性实验，结合多种分析表征手段，明确热解阶段影响循环灰固硫容量、活性的关键工艺因素，揭示了固定于热载体中的硫化物和热解半焦中残余硫在燃烧阶段的转化机理。旋转放置6层30°挡板对不同比例硅胶/石英砂的混合度范围在0.0125~0.0253。最佳实验条件为热载体/煤比例为6:1，改流体角度20°。由于热阻的存在，煤颗粒表面和中心的最大温差在床层高度为0.05 m处达到406 K。与煤颗粒的升温过程不同，煤颗粒外层的脱挥发分过程是经过一个短暂的升温过程（~0.016 m）才开始的。挥发分释放主要集中在0.08-0.24 m。与其他气相产物相比，CO2在~0.1 m处首先到达其释放速率最大值，C10H8在~0.16 m处达到其释放速率最大值。较慢的床层移动速度、较大的灰煤比、较高的煤预热温度和较高的灰初始温度都会减小煤热解所需的理论床层高度。传热机理对热解行为的影响强弱为：辐射换热 > 煤与热解气体之间的对流换热 > 煤热解吸热。不同煤种的脱挥发分特性因煤质不同而明显变化。与石英砂为热载体相比，以循环灰为热载体时，由于大部分H2S被循环灰固定，从而导致释放到气相中H2S大大降低。半焦表面的硫形态以噻吩为主，并且高温下体内的硫向体表迁移明显。循环灰中的主要固硫组分是CaO和Fe2O3，并且相同质量Fe2O3的固硫效果优于CaO。CaO固硫产物CaS燃烧时释放SO2比Fe2O3固硫产物FeS燃烧低~30%。与原煤直接燃烧相比，以循环灰为热载体650℃热解，800、850、900℃燃烧时减少的循环流化床脱硫负荷分别为43.71%、41.87%、38.80%。本研究可为热解/燃烧分级转化技术的后续工业开发、移动床热解反应器的放大设计及污染物迁移与控制提供理论依据。