【作者】 刘阳；

【导师】 钱宇；

【作者基本信息】 华南理工大学 ， 化学工程， 2018， 博士

【摘要】 天然气是一种重要的清洁能源和化工原料,发展煤制天然气产业对缓解我国天然气供需矛盾具有重要作用。经过多年的发展和工程示范,煤制天然气项目已经成为我国天然气供应的一条重要来源。煤制天然气过程工艺流程长,全厂能量系统复杂,现有煤制天然气项目能量回收系统设计相对独立,从全局视角来看,尚未做到能量的“梯级利用”。煤制天然气过程能量系统配置仍存在不合理之处,全厂能量利用效率仍有提高空间。研究和解决能量系统瓶颈问题,将对我国煤制天然气项目进一步升级示范和行业的可持续发展起到积极的作用。本研究建立了煤制天然气过程各子系统基础模型,包括工艺系统与公用工程系统,并利用工业数据对模型参数进行校核。在模型准确可靠的基础上,对煤制天然气全流程进行模拟计算,得到全流程物料平衡和能量平衡数据。以此为基础,对典型煤制天然气过程技术经济性能进行了分析,弄清了现有工艺过程物质和能量利用的瓶颈问题。结果表明煤制天然气过程公用工程系统能源消耗和碳排放高:每生产一立方米合成天然气能源消耗为2.27kg标煤,其中公用工程系统燃料煤消耗占28.8%,平均单位产品碳排放为4.94kg,其中公用工程系统碳排放占42.4%。因此,通过能量系统集成优化,是实现煤制天然气项目的提质增效和过程的节能减排重要途径。全局夹点法是用于大型工业过程全局能量集成的一种图形化方法。该方法应用于石油化工等领域能量集成已取得了较好的效果。然而全局夹点法仅考虑了蒸汽的潜热,而忽视了锅炉给水预热和蒸汽过热的热量。这使得全局夹点法在应用于高温煤化工过程能量集成时,计算得到的全局回收的热量比理论上可以实现最大的热回收值存在明显高估,同时得到的公用工程结构无法满足工艺需求。我们提出了一种用于解决高温过程全局能量系统集成的考虑显热的全局夹点法,可应用于煤化工过程的能量集成。利用本文所提出的方法可以得到满足工艺过程需求的公用工程系统。因此,对于具有高温煤化工过程全局能量系统集成,本文所提出的考虑显热的全局夹点法在理论模型和工程实践两方面都具有价值。本研究旨在针对煤制天然气工业过程能量系统存在的瓶颈问题,提出相应的节能改造方案以实现全厂能量利用效率的提高。首先根据单元过程模拟数据,利用夹点技术对各单元过程的能量系统展开详细的用能分析,确定各单元能量系统特点。在此基础上利用本文所提出的考虑显热的全局夹点法,对现有煤制天然气全厂能量系统进行分析,确定全厂用能瓶颈以及实现能量系统改造的方向。提出从装置间热联合、低温热回收利用和蒸汽动力系统优化三个方面进行节能改造:通过将水煤气变换单元和甲烷化单元进行装置间热联合,可以实现过程?效率提高15.8%;构建了全厂低温有机朗肯循环发电系统,实现产电4.32MW;结合蒸汽产、用的变化对蒸汽动力系统进行相应改造,燃料煤节约14.3%。通过全厂能量系统集成,可以实现年收益1944万元,投资回收期为2.3年。更多还原

【Abstract】 Natural gas is an important clean energy and chemical raw material.The development of the coal-to-gas industry plays an important role in alleviating the contradiction between China’s natural gas supply and demand.Coal to synthetic natural gas(coal-to-SNG)process is consist of several sub-units,and energy system of the process is complex.Meanwhile,the existing heat recovery scheme for the coal-to-SNG project is designed by individual process.It is failed to achieve the step utilization of energy from a holistic view.There are several unmatched joints in existing energy system configuration of coal-to-SNG process,and the energy utilization efficiency still has room for improvement.Studying on the bottleneck problem of energy system could produce a positive effect on the further upgrading of China’s coal-to-SNG project and the sustainable development of the industry.This study established a basic model for each sub-unit of the coal-to-SNG process,including both chemical process and utility system,and the industrial data are used to check the model parameters.With accurate models,mass and energy balance of coal-to-SNG process is simulated.Based on this,the technical and economic performance of the typical coal-to-SNG process is analyzed,and the bottleneck problems of the material and energy utilization are clarified.The result shows that the utility system of coal-to-SNG process has a high energy consumption and carbon emissions: consume 2.27 kg of standard coal to produce one cubic meter of synthetic natural gas,of which the utility system’s fuel coal consumption accounts for 28.8%,the carbon emission of the average unit product is 4.94 kg,of which the utility system’s carbon emissions accounted for 42.4%.Therefore,energy system integration is an important way to achieve the quality improvement and efficiency of coal-to-SNG projects and the process of energy conservation and emission reduction.The Total Site Analysis method is a graphical methodology for heat integration study on large industrial processes.It has achieved great success in petrochemical industry.However,in that case,only the latent heat of steam is considered,while the heat for boiler feed water preheating and steam superheating is neglected.This leads the amount of heat recovered globally is significantly overestimated compared to the theoretical maximum heat recovery value.Besides,utility system designed cannot meet requirements of the chemical process,when the Total Site Analysis method calculated in the high-temperature coal chemical process energy integration.In this work,we propose a Total Site Analysis method considering sensible heat for heat integration of processes with high temperature and can be applied to energy integration in coal chemical processes.By take method proposed in this paper,a utility system which meets the requirements of the process better can be obtained.Therefore,for the total site heat integration of coal chemical process with high temperature,the total site analysis method considers sensible heat,which is much valuable in both theoretical model and engineering practice.The purpose of our study is to solve the bottleneck problem and propose a corresponding energy-saving transformation plan to achieve the improvement of the energy utilization efficiency.Firstly,the pinch point technology is used to carry out detailed energy analysis of each unit process,then,using the Total Site Analysis method to consider sensible heat.The energy system of the existing coal-to-gas natural plant is analyzed to determine the energy bottleneck of the whole plant and the direction of energy system transformation.It is proposed to carry out energy-saving transformation from three aspects: heat union between equipment,low-temperature heat recovery and utilization,and steam power system optimization.By combining the water gas shift unit and the methanation unit,the enthalpy efficiency is increased by 15.8%;the whole plant low-temperature organic Rankine cycle power generation system was constructed to realize 4.32 MW of electricity production.The steam power system was modified correspondingly with the change of steam production and use,and the fuel coal saved 14.3%.Through the integration of the entire plant energy system,the annual income can be 19.44 million yuan,and the investment recovery period is 2.3 years.更多还原