The coal-to-SNG process is an energy-intensive process, and optimizing the heat recovery network can improve the economy and energy efficiency. This study proposes a branched, triple pressure level heat recovery steam cycle (HRSC) to recover waste heat, in which one branch is responsible for recovering the waste heat from the water gas shift (WGS) unit, and the other branch is responsible for the methanation (METH) unit. The extended Duran–Grossmann model is used to optimize two heat exchanger networks to match the branched HRSC superstructure. The temperature/pressure/flow rates of the HRSC streams and the operating temperature of the WGS and METH units are optimized. The optimal bypass ratio of the WGS unit as well as the recycle ratio and split ratio of the METH unit, are 0.506, 0.681 and 0.456, respectively. The exergy efficiency of the coal-to-SNG plant is improved by 1.28% compared with the industrial plant, which can reach 54.17%.

煤制天然气过程是一个能源密集型过程，优化热回收网络可以提高经济性和能源效率。这项研究提出了一个分支的三压力级热回收蒸汽循环（HRSC）以回收废热，其中一个分支负责从水煤气变换（WGS）单元回收废热，而另一个分支负责该废热。甲烷化（METH）单位。扩展的Duran–Grossmann模型用于优化两个热交换器网络，以匹配分支的HRSC上部结构。优化了HRSC流的温度/压力/流速以及WGS和METH单元的工作温度。WGS装置的最佳旁路比以及METH装置的循环比和分流比分别为0.506、0.681和0.456。