Analysis of the techno-economics and CO2 emissions of DME production using by-product gases in the steel industries

Abstract

A dimethyl ether (DME) synthesis process using steelmaking by-product gases (a mixture of coke oven gas (COG) and furnace top gas (FTG)) was developed to evaluate the effects of process configurations on techno-economics and CO2 emissions based on a natural gas-based conventional process. The performance of a catalytic reactor combining pellet-type methanol synthesis and methanol dehydration catalysts through physical mixing was validated against experimental data. Two separation strategies––flash vessels vs. absorber––for DME separation were considered. The recycling of the entire light gas or pure hydrogen was also compared, resulting in four combinatorial cases for the DME production process. Further analysis, exploring variations in the purge and bypass fractions of the recycling stream, showed that recycling pure hydrogen achieved the most favorable techno-economics and CO2 emissions. When auxiliary hydrogen feed was applied, gray hydrogen deteriorated the techno-economics and CO2 emissions, whereas green hydrogen enhanced the CO2 emissions but led to poor techno-economic outcomes. The sale of partial amounts of pure hydrogen by pressure swing adsorption (PSA) adversely affected both CO2 emissions and DME production, though an increase in hydrogen price could potentially improve techno-economics. The case of absorber-based separation and recycling of pure hydrogen showed the highest CO2 reduction, approximately 8.5% reduction compared to the use of natural gas for DME production at the cost of techno-economics (an increase of minimum selling price by 2.2 $/kgDME), indicating that CO2 reduction comes at a cost. The developed model offers valuable insights into the design of efficient CO2 utilization processes within the steel industry.