Techno-Economic Analysis And Life Cycle Assessment Of Coal-to-Olefins Processes

Olefins are one of the most important oil derivatives widely used in industry. Their production capacity is an important symbol to weigh development level of petrochecmial industry. At present, olefins production are heavily dependent on oil and natural gas, however, world oil are increasingly depleted, especially in China. Therefore, developing alternative resources for olefins production is imminent. Large project of olefins production from coal route has been attracting more attention of the chemical process industry, in the light of the scarcity of oil resources and richness of coal in China. The coal based methanol-to-olefins（CMTO） plant adopting DMTO technology was built by Shenhua Group and successfully put into commercial production. The current production capacity of CMTO and methanol-to-olefins（MTO） are about 10 Mt/y. In China, olefins production from coal is expected to become an important alternative route. How much impact of fluctuation of ineternational oil price on coal based olefins projects? The product cost of coal route become the key factor of making decision. Therefore, techno-economic comparison between the two processes under different scenarios is particularly important. The study on their environmental impact and quantitative evaluation is also scare.Therefore, this paper investigates the main technologies of coal based olefins production process and then selectes a typical process route as a case study. On the basis of modeling of main process units of the CMTO, the techno-economic analysis is conducted in comparison with oil-to-olefins（OTO）, natural gas based methanol-to-olefins（NGMTO）, coke-oven gas based methanol-to-olefins（CGMTO）, and oversea imported methanol-to-olefins. It was found that CMTO suffers from high energy consumption and serious CO₂ emssions from the aspect of technical performance. In economic aspect, its product cost is about 9% higher than that of the OTO at present raw material prices. While product cost of the CMTO is only 70% of the OTO in 2012 with high oil price. The relationship between coal and oil prices with coal route competivity is obtained, which could provide suggestions for enterprises decision. There is also a large room for technical improvement and system optimization for the CMTO process, and its plant scale remains to be futher improved. To address the serious CO₂ emissions of coal route, this study conducts a process design of CMTO with CCS, which could significantly reduce CO₂ emissions. However, its electricity consumption increases significantly with increase of carbon capture rate. The corresponding mitigation cost of the process is roughly equivalent to the current international carbon price.The life cycle environmental impact and cost assessment model was established in this study. From life cycle environmental aspect, the CMTO suffers from high air pollutant emssions, especially CO₂ and PM. From the perspective of internal cost under current feedstock prices, the CMTO is the lowest in these alternative olefins production routes. The internal cost of the CGMTO is 12% higher than that of the CMTO. The NGMTO suffers from highest cost because of domestic higher natural gas price. However, the life cycle cost of the CMTO is about 1.4 times that of the OTO because of its large external cost caused by environmental punishment. To address the high energy consumption and pollutant emissions of the CMTO, developing coal based olefins production with moderate carbon capture process, coal and natural gas or coke-oven gas co-feeding methanol-to-olefins process is expect to promote element complementary between carbon-rich resources and hydrogen-rich resources, carry out CO₂ and PM reduction, and improve energy utilization efficiency. Updating existing coal pulverization and dust removal equipment could reduce PM emissions and correspongdingly improve its life cycle economic performance.Life cycle water consumption model for olefins production has been conducted in this work. Analysis results show that the coal route and coke-oven gas route suffer from high water consumption. On the other side, the water consumption in China of oversea imported-methanol route is only 17% of the CMTO, while its life cycle water consumption is about 62% of the CMTO. The coal route is water intensive, but unfortunately, coal chemical plants are mainly located in the arid northern China. To address this predicament, this paper proposes three suggestions:（1） Adjusting water prices system to arouse the enthusiasm of saving water and energy;（2） Promoting olefins production from co-feeding of coal and gas in areas with rich coal and gas;（3） Moderate Encouraging to develop oversea importedmethanol-to-olefins plants in coastal areas by using convenient transportation and relative cheap methanol imported from abroad.