Simulation and Techno-Economic Analysis of Pressurized Oxy-Fuel Combustion of Petroleum Coke

Abstract

The research presented in this thesis was part of the International Partnership for Carbon Neutral Combustion, which was sponsored by King Abdulla University of Science and Technology. The thesis focuses on oxy-fuel combustion under pressurized conditions and assesses the technical and economic viability of combusting petroleum coke (petcoke) for electricity generation, while capturing CO2. The technical evaluation was conducted through simulating, in Aspen PlusTM, an oxy-combustion power plant that uses petcoke as fuel. The basis for all simulations was a constant heat input of 1877 MWth, while a 3% (on dry basis) excess oxygen was maintain in the flue gas along with an adiabatic flame-temperature of 1866°C. Comparisons with the oxy-combustion of Illinois No. 6 coal showed that oxy-coal combustion was 0.6% points (on HHV basis) more efficient than oxy-petcoke combustion (29.0% versus 29.6%). However, operating oxy-petcoke combustion at elevated pressures improved the net efficiency to a maximum of just over 29.8% (on HHV basis) at 10 bar. A sensitivity analysis on the impact of operating pressure was conducted on the fuel intake, O2 required, recycle ratio and removal ratio of SOx and NOx via flash distillation; along with how the operating pressure within the carbon capture unit affects the recovery and purity of the CO2 being separated. The sensitivity analysis showed that pressure had minimal impact on the fuel intake and O2 required but affected recycle ratio by up to 3% points, while increasing pressure improved the removal ratio of SOx and NOx. As for the operating pressure of the carbon capture unit, the recovery and purity of the CO2 produced was preferred at 35 bar. In addition, a modification to the steam cycle is presented that utilizes the latent heat of the flue gas to heat the feed water, which improves the net efficiency of the power plant at all pressures by 1.9% points. As for the economic evaluation, the oxy-petcoke combustion power plant was assumed to be built in the US and in KSA. The levelized cost of electricity (LCOE) for oxy-coal combustion was 11.6 ¢/kWh (in 2017 USD) compared to 10.4 ¢/kWh and 6.5 ¢/kWh for atmospheric oxy-petcoke combustion in the US and in KSA, respectively. The LCOE further drops to a minimum of 9.2 ¢/kWh in the US, or 5.7¢/kWh in KSA, when oxy-petcoke combustion takes place at 10 or 15 bar. However, based on a profitability analysis, operating at 10 bar has the highest net profit, highest net present value and lowest discounted payback period, compared to the plants operating at 1, 5 and 15 bar, whether in the US or in KSA. A sensitivity analysis was also conducted that showed that the cost of manufacturing (COM), LCOE and costs of CO2 avoided and CO2 capture are most sensitive to total capital cost, and to a lesser extent the cost of the fuel, which in this case is petcoke. Overall, the technical and economic evaluation help conclude that using petcoke as a fuel to generate electricity is viable in oil-refining countries like the US or KSA, in which pressurized oxy-petcoke combustion is better than atmospheric as the highest net efficiency and lowest LCOE are achieved at an operating pressure of 10 bar.