Techno-economic analysis of coke oven gas and blast furnace gas to methanol process with carbon dioxide capture and utilization

Abstract

This paper documents a process for converting coke oven gas (COG) and blast furnace gas (BFG) from steel refineries into methanol. Specifically, we propose the use of blast furnace gas (BFG) as an additional carbon source. The high CO2 and CO content of BFG make it a good carbon resource. In the proposed process, CO2 is recovered from the BFG and blended with H2O, H2, and CH4-rich COG to reform methane. Optimized amounts of H2O and CO2 are used to adjust the (H2 – CO2)/(CO + CO2) molar ratio in order to maximize the amount of methanol that is produced. In addition, the desulphurization process was modified to enable the removal of sulfur compounds, especially thiophene, from the COG. The process design and simulation results reported herein were then used to determine any potential environmental and economic benefits. This research is based on off-gas conditions provided by ArcelorMittal Dofasco (AMD), Hamilton, Ontario. In order to determine which conditions are most desirable for this retrofit strategy, potential greenhouse gas reduction and economic benefits were analyzed. In particular, this analysis focused on the heating utility chosen for methane reformation prior to methanol synthesis. To this end, COG, BFG, and natural gas (NG) were compared. The results showed that using BFG/NG as a heating utility can produce greater economic gains, and that synthesizing COG + BFG to methanol results in greater economic and environmental gains than solely producing electricity (the status quo). Compared to current operating procedures, the proposed process could potentially increase net present values by up to $54 million. The carbon efficiency achieved was up to 72%. An additional 0.73 kg of CO2 from BFG is needed for every 1 kg of MeOH produced. About 52% of feedstock energy is converted to MeOH, with another 33% recovered in the form of utilities. The exergy efficiency of the recommended version of the system is about 61%. The business case for converting CO2 into methanol highly depends on the local electricity grid carbon intensity. For Ontario, it can reduce direct CO2 emissions by 228 ktonne per year, and fix up to 246 ktonne CO2 into methanol per year. In addition, analyses of location effects, CO2 taxes, electricity prices, electricity carbon intensity, methanol prices, and income taxes indicated that MeOH production is highly recommended for Ontario, Mexico, the USA, and China applications. For USA, build MeOH plant is recommended for Finland, whether to do this retrofit or not is inconclusive. For Finland, the results are inconclusive, other strategies may be equally suitable. Aspen Plus Simulation files and other source code have been open-sourced and are available to the reader.