The production of synthetic fuels (synfuels) in coal–to–liquids (CTL) facilities has contributed
to global warming due to the huge CO2 emissions of the process. This corresponds to
inefficient carbon conversion, a problem growing in importance particularly given the limited
lifespan of coal reserves. These simultaneous challenges of environmental sustainability and
energy security associated with CTL facilities have been defined in earlier studies. To reduce
the environmental impact and improve the carbon conversion of existing CTL facilities, this
paper proposes the concept of a nuclear–assisted CTL plant where a hybrid sulphur (HyS)
plant powered by 10 modules of the high temperature nuclear reactor (HTR) splits water to
produce hydrogen (nuclear hydrogen) and oxygen, which are in turn utilised in the CTL
plant. A synthesis gas (syngas) plant mass–analysis model described in this paper
demonstrates that the water–gas shift (WGS) and combustion reactions occurring in
hypothetical gasifiers contribute 67% and 33% to the CO2 emissions, respectively. The
nuclear–assisted CTL plant concept that we have developed is entirely based on the
elimination of the WGS reaction, and the consequent benefits are investigated. In this kind of
plant, the nuclear hydrogen is mixed with the outlet stream of the Rectisol unit and the
oxygen forms part of the feed to the gasifier. The significant potential benefits include a 75%
reduction in CO2 emissions, a 40% reduction in the coal requirement for the gasification
plant and a 50% reduction in installed syngas plant costs, all to achieve the same syngas
output. In addition, we have developed a financial model for use as a strategic decision
analysis (SDA) 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 than that produced in the conventional
CTL plant when the average cost of producing nuclear hydrogen is US$3/kg H2. The model
also evaluates the cost of CO2 avoided as $58/t CO2. Sensitivity analyses performed on the
costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen
production cost of US$2/kg H2 or at a delivered coal cost of US$128/t coal. The economic
advantages of the nuclear–assisted plant are lost above the threshold cost of $100/t CO2.
However, the cost of CO2 avoided in our model works out to below this 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. / Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/4840 |
| Date | January 2010 |
| Creators | Chiuta, Steven |
| Publisher | North-West University |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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