Comparative study on life cycle energy consumption, carbon emissions and economic performance of various coke-oven gas utilization schemes

Coke-oven gas (COG) is the by-product of coking process and can be used as feedstock in energy and chemical processes. However, the relative advantages and comprehensive competitiveness of various mature and widely -used utilization schemes still need to be investigated, which will be helpful in exploring better ways to use COG. From the perspective of energy supply, this paper investigated the energy consumption, carbon emissions, capital investment and product cost of COG-to-hydrogen (COGtH), COG-to-natural gas (COGtNG), COG-to-methanol (COGtM) and COG-to-power (COGtP) through LCA method, and compared the comprehensive competitiveness using entropy weight method. The results show that COGtP performs better in all aspects, only consumes 2.669 MJ of energy and generates 0.14 kg CO2-eq of carbon emissions when outputting 1 MJ of energy, and product cost is only 1.11E-02 RMB/MJ, making it the most competitive utilization scheme. COGtM consumes the highest 8.525 MJ of energy and generates 0.708 kg CO2-eq of carbon emissions when outputting 1 MJ of energy, and it is superior to COGtNG only in terms of capital investment, making it the least competitive utilization scheme. The comprehensive competitiveness of COGtNG is slightly higher than COGtH, with comprehensive score of 0.49 and 0.46 respectively, and it can be further improved by reducing the equipment investment of methanation, while the performance of COGtH in economic aspect needs to be improved, especially to reduce product cost. Further analysis shows the extent to which the energy consumption and carbon emissions is affected by allocation principle is determined by the proportion of energy consumption and carbon emissions in the coking and up-stream coal mining, washing and transportation stages, and under value allocation, the energy consumption and carbon emissions is almost directly linearly proportional to COG price, but non-linearly inversely proportional to coke price. In addition, the value allocation is favorable than mass and energy allocation in view of its reduced energy consumption and carbon emissions of utilization schemes if COG price decreases to 0.38 RMB/Nm3 and 0.47 RMB/Nm3 respectively, or coke price increases to 1122 RMB/t and 899 RMB/t respectively.