Utilizing the by-product oxygen of the hybrid sulfur process for synthesis gas production
Conradie, Frederik Hendrik
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This study introduces an evaluation of the downstream utilization of oxygen produced by the hybrid sulfur process (HYS). Both technical and economic aspects were considered in the production of primarily synthesis gas and hydrogen. Both products could increase the economic potential of the hybrid sulfur process. Based on an assumed 500MWt pebble bed modular nuclear reactor, the volume of hydrogen and oxygen produced by the scaled down HYS was found to be 121 and 959 ton per day respectively. The partial oxidation plant (POX) could produce approximately 1840 ton synthesis gas per day based on the oxygen obtained from the HYS. The capital cost of the POX plant is in the order of $104 million (US dollars, Base year 2008). Compared to the capital cost of the HYS, this seems to be a relatively small additional investment. The production cost varied from a best case scenario $9.21 to a worst case scenario of $19.36 per GJ synthesis gas. The profitability analysis conducted showed favourable results, indicating that under the assumed conditions, and with 20 years of operation, a NPV of $87 mil. and an IRR of 19.5% could be obtained, for the assumed base case. The economic sensitivity analysis conducted, provided insight into the upper and lower limitations of favourable operation. The second product that could be produced was hydrogen. With the addition of a water gas shift and a pressure swing adsorption process to the POX, it was found that an additional 221 ton of hydrogen per day could be produced. The hydrogen could be produced in the best case at $2.34/kg and in the worst case at $3.76/kg. The investment required would be in the order of $50 million. The profitability analysis for the base case analysis predicts an NPV of $206 million and a high IRR of 23.0% under the assumed conditions. On financial grounds it therefore seemed that the hydrogen production process was favourable. The thermal efficiency of the synthesis gas production section was calculated and was in good agreement with that obtained from literature. The hydrogen production section’s thermal efficiency was compared to that of steam methane reforming of natural gas (SMR) and it was found that the efficiencies were comparable but the SMR process was superior. The hydrogen production capacity of the HYS process was increased by a factor of 1.83. This implied that for every 1 kg of hydrogen produced by the HYS an additional 1.83 kg was produced by the proposed process addition. This lowers the cost of hydrogen produced by the HYS from $6.83 to the range of approximately $3.93 - $4.85/kg. In the event of a global hydrogen economy, traditional production methods could very well be supplemented with new and innovative methods. The integration of the wellknown methods incorporated with the new nuclear based methods of hydrogen production and chemical synthesis could facilitate the smooth transition from fossil fuel based to environmentally friendly methods. This study presents one possible integration method of nuclear based hydrogen production and conventional processing methods. This process is technically possible, efficient and economically feasible.
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