Integrated Process Of Coal And Coke-Oven Gas To Chemicals With Low Carbon Emission

Coal gasification technology is one of the clean and efficient coal utilization technologies. Coal gasification based chemical industry develops rapidly in recent years. However, coal gasification based chemical processes suffer from the problems of high carbon emission and high energy consumption due to the high carbon contents of coal. This paper investigates the coal to methanol process, coal to olefins process, and coal to SNG process. Derived from coal gasification, high CO2 emission and energy consumption of these processes is due to low H/C ratio of the coal gas, while the required H/C ratio for chemicals synthesis is very high. CO of the coal gas is needed to convert to H2 by water gas shift reaction. It results in a high emission of CO2 and waste of carbon resource, as well as very high consumption of energy in the water gas shift unit. Thus, supplying hydrogen-rich source as the raw material to the coal gasification based chemical processes is a good way to tackle with these problems. This paper proposes the conceptual design for coal to methanol process, coal to olefins process, and coal to SNG process, using the waste coke-oven gas of coking industry as the hydrogen-rich source. Techno-economic analysis methodology is using in this paper to find the advantages and disadvantages of the co-feed processes of coal and coke-oven gas to chemicals.This paper proposes an integrated coke-oven gas assisted coal to methanol process(GaCTM), in which the tri-reforming unit makes the CH4 of COG react with CO2 of coal gasification for the purpose of CO2 mitigation and efficiency improvement. Compared to conventional coal to methanol process, the CO2 emission per ton methanol product of GaCTM is 1.6 ton, which decreases by 45%. Energy efficiency is 62%, which increase by 11%. The economic analysis shows that the production cost for GaCTM is 8% higher than that of coal to methanol process.Based on the research on GaCTM, this paper proposes a novel co-feed process of coal and coke-oven gas to olefins(CGTO), in which CH4 of COG reacts with CO2 in a dry methane reforming unit to reduce emissions, while the steam methane reforming unit produces H2-rich syngas. H2 of COG can adjust the H/C ratio of syngas. Techno-economic analysis result shows that CO2 emission from the CGTO process is reduced by 85% and decreases to as low as 0.8 t CO2/t olefins, when compared to coal to olefins process. The energy efficiency of the CGTO is 46.5%, which 10% higher than that of coal to olefins process. The economic analysis shows that the production cost for the co-feed process is 7150 CNY/t olefins, which is 14% higher than that for coal to olefins process. However, the co-feed process will show economic superiority over the conventional coal to olefins process when the carbon tax would be fixed at the level of 150 CNY/t CO2 or higher.This paper also proposes a novel co-feed process of coal and COG to SNG(CGtSNG). In the co-feed process, methane in COG is used for DMR reaction for reducing CO2 emission. And H2 in COG is used for adjusting the H/C ratio of the methanation syngas. A process of coal and COG to SNG without DMR unit(CGtSNG w/o DMR) is also proposed. Although CGtSNG w/o DMR process do not make use of CO2, the CO2 emission and energy consumption are also decreased by system integration. CGtSNG has high energy efficiency and low emission. The energy efficiency of CGtSNG and CGtSNG w/o DMR is 4.1% and 7.6% higher than that of CtSNG. CO2 emission of CGtSNG and CGtSNG w/o DMR decrease by 60% and 27.8% in comparison to the CtSNG process, with the effluent discharge decrease by 72% and 30.9%. CGtSNG has advantaged in economic performance. Production cost of CGtSNG and CGtSNG w/o DMR is 16.7% and 5% lower than that of CtSNG.