PERFORMANCE, COST AND EMISSIONS ANALYSIS OF COAL-TO-LIQUIDS PLANTS WITH DIFFERENT GASIFICATION TECHNOLOGIES, UNDER CARBON CONSTRAINTS

摘要

Coal-to-liquids (CTL) processes generate synthetic liquid fuels like gasoline and diesel fuel from coal. The process involves gasification of coal to produce synthesis gas which is then catalytically converted into liquid fuels in a Fischer Tropsch (FT) reactor. A variety of gasification technologies (GE/Texaco, Shell, E-Gas) can be used to convert coal into syngas. Similarly, FT technologies can be classified into high temperature (HTFT) and low temperature (LTFT) reactors which produce different liquid fuels from syngas. One main concern of coal liquids, however, is the large emissions of carbon dioxide (CO_2) from the CTL process. These emissions can be mitigated using carbon capture and sequestration (CCS) technology. Two configurations are possible for CTL plants. In a typical commercial CTL plant, the unconverted syngas from the FT reactor is recycled to the reactor to increase the productivity of the liquids. In this work, such plants are called 'liquids-only' plants. The unconverted syngas from the FT reactor, instead of being recycled, can be combusted in a gas turbine steam turbine combined cycle power plant to generate electricity, which can be sold to the grid to add another stream of revenue. Plants with such configuration are called 'poly-generation' plants here. Different combinations of these component technologies (gasification, FT ami CCS) and plant configurations (liquids-only or poly-generation) affect the performance, cost and emissions of a CTL plant. In this paper, CTL processes using different commercial gasification technologies (GE, E-GAS and Shell) are techno-economically evaluated. Effect of implementing CCS or carbon constraints that impose a price or cost on CO_2 emissions is also studied. To study these effects, a comprehensive techno-economic assessment model of liquids-only and poly-generation CTL plants, capable of incorporating CCS is developed. To illustrate this model, a CTL plant producing 50,000 barrels/day of liquid products is considered as a case study. Capital costs ($/barrel/day) and cost of liquid products ($/barrel) are presented for a combination of different component technologies and plant configurations, under carbon constraints.