Investigation and recovery of purge gas streams to enhance synthesis gas production in a mega methanol complex

Nowadays, methanol has gained great importance as an alternative fuel and a product which can be considered as a CO2 utilization in novel processes; nevertheless, there is no adequate work on purge gas streams in current conventional methanol complexes. This study aims to specify main waste gasses in one of the biggest methanol plants in the world, located in the Pars Special Economic Energy Zone of Iran. The calculations in this work show that every hour, 50106 Sm3 purge gas including unreacted gas (60% hydrogen, 17% CO and CO2, and 23% N2 and CH4) is burnt in the complex. A new process design has been proposed to recovery of available purge gasses in that methanol plant. The Auto-Thermal Reformer (ATR) of the complex has been modeled in detail and various cases were considered to analyze the effects of this new strategy. The results indicate noteworthy improvements in both quality and quantity of the produced synthesis gas by injecting the recoverable stream into the ATR. In this way, emission of 26.7 ton carbon dioxide per hour to the atmosphere is prevented and it converted to valuable methanol. This process can bring annual profit ranging from 20 to 40 million US dollars per year with the Rate of Return (ROR) between 29 and 56%.