Abstract:

China is now vigorously developing coal-to-SNG process for clean energy supply. However, recent studies reveal that this process suffers from high energy consumption and greenhouse gas emissions. An effective way to solve it is to increase the plantwide energy efficiency by Total Site Heat Integration. The total site profile of coal-to-SNG reveals that the low temperature waste heat recovery and the heat integration between coal gasification unit and water gas shift unit could provide considerable energy savings. The total site analysis method was used to target the maximum heat recovery and the optimal site utility system. The results showed that the site utility consumption decreased from 1.26t/kNm³ to 1.07t/kNm³ SNG and the plantwide energy efficiency was increased from 57.2% to 59.6%. On the other hand, the CO₂ emission decreased from 5.02t to 4.66t CO₂ per kNm³ SNG. The water consumption of the integrated process decreased around 33.4% compared to that of the conventional process. Unit production cost decreased from 1.65 CNY/Nm³ SNG to 1.59 CNY/Nm³ SNG. Thus, an annual production cost of 120 million CNY could be saved for an annual production of 2×10⁹ m³ natural gas.

Key words: coal-to-SNG, total site heat integration, pinch technology, temperature-enthalpy curve, techno-economic analysis

摘要：

我国正在大力发展煤制天然气项目实现清洁能源供给。然而现有煤制天然气示范项目存在能耗大、CO₂排放高、生产成本缺少竞争力的问题。本文从煤制天然气能量系统出发，通过全局能量集成实现煤制天然气项目的节能减排与经济效益的提高。根据煤化工示范项目特点，提出了煤制天然气过程全厂能量系统集成优化策略：建立了煤制天然气各单元过程模型，对全流程的物流和能流展开了详细的模拟计算；利用夹点技术对全厂内各单元过程的能量系统展开了用能分析；利用全局温焓曲线对全厂能量系统进行了分析，揭示出全厂能量利用效率低是由于高品位热量降质利用和低品位余热未得到合理利用引起的。通过装置间热回收集成和增设有机朗肯余热回收装置可有效地提高热回收率。通过全厂能量系统优化集成，燃料煤消耗由现有过程1.26t/kNm³（0℃、101325Pa标准状态）天然气下降到1.07t/kNm³天然气。由于公用工程系统消耗的减少，全厂能量利用效率由原来的57.2%提高到59.6%，同时CO₂排放可以由原来5.02t/kNm³天然气下降到4.66t/kNm³天然气。相比于现有过程，改进过程的总投资仅增加了2%左右，而单位生产成本由1.65CNY/Nm³下降到了1.59CNY/Nm³，对于年产20亿立方米煤制天然气厂每年可节约生产成本1.2亿元。

关键词: 煤制天然气, 全局能量集成, 夹点技术, 温焓曲线, 技术经济分析