Techno-economic evaluation of a nuclear-assisted coal-to-liquid facility

Abstract

The production of synthetic fuels (synfuels) in Coal-to-Liquid (CTL) facilities has contributed to global warming due to the enormous carbon dioxide (CO 2) emission footprint of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the severe consequences concomitantly posed by global warming and the rapid depletion of coal reserves. This paper seeks to address these simultaneous challenges of environmental and energy sustainability associated with CTL facilities. To reduce the environmental impact and improve the carbon conversion of CTL facilities, we propose and apply the concept of a nuclear-assisted synthesis gas (syngas) plant to a reference syngas plant in a CTL facility consisting of 36 dry fixed-bed gasifiers. In this kind of plant, a Hybrid Sulphur (HyS) plant powered by 10 high-temperature nuclear reactors (HTR's) splits water to produce nuclear hydrogen and oxygen. The nuclear hydrogen supplements the hydrogen-poor syngas from the Rectisol and the oxygen becomes part of the gasifier feed. The nuclear-assisted syngas plant concept that we have developed is entirely based on the premise that the water-gas shift (WGS) reaction is minimised by operating a dry fixed-bed gasifier under steam-lean conditions. A mass-analysis model of the syngas plant described in this paper demonstrates that the WGS reaction contributes 68% to the CO 2 emission output. The consequent benefits of eliminating the WGS reaction include reductions in the CO 2 emissions and gasification coal requirement of 75% and 40%, respectively, all to achieve the same syngas output as the conventional syngas plant. In addition, we have developed an economic model for use as a strategic decision analysis tool that compares the relative syngas manufacturing costs for conventional and nuclear-assisted syngas plants. Our model predicts that syngas manufactured in the nuclear-assisted CTL plant would cost 21% more to produce when the average cost of producing nuclear hydrogen is US$3/kg H 2. The model also evaluates the cost of CO 2 avoided, which at the average hydrogen cost is $58/t CO 2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO 2 avoided is zero at a hydrogen production cost of $2/kg H 2 or at a delivered coal cost of $128/t coal. The economic advantages of the nuclear-assisted syngas plant are lost above the threshold cost of $100/t CO 2. However, the cost of CO 2 avoided in our model is below the threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear-assisted CTL plant.