Modeling of a methanol synthesis process to utilize CO₂ in the exhaust gas from an engine plant

Abstract

We investigated the conversion of CO₂ in the exhaust gas of an engine plant into methanol. The process consists of CO₂ purification by an acid gas removal unit (AGRU), mixed reforming, and methanol synthesis. The AGRU removes a large amount of inert gas, yielding CO2 of 98% purity at a recovery rate of 90% for use as feed to the reformer. The reformer temperature of 900 °C led to the almost total consumption of CH4. In the methanol synthesis reaction, the utility temperature had a greater influence on the conversion and methanol production rate than the inlet temperature. The optimal temperature was determined as 180 °C. Because the amount of hydrogen in the reformer effluent produced by dry reforming was insufficient, the steam available in the engine plant was used for mixed (dry and steam) reforming. The steam increased the hydrogen and methanol production rate; however, the compression cost was too high, and there exists an optimal amount of steam in the feed. The techno-economic analysis of the optimal conditions showed that utilization of CO₂ in the exhaust gas along with freely available steam is economically feasible and reduces CO₂ emissions by over 85%.