HTGR-Integrated Coal To Liquids Production Analysis (2010)

As part of the DOE’s Idaho National Laboratory (INL) nuclear energy development mission, the INL is leading a program to develop and design a high temperature gas-cooled reactor (HTGR), which has been selected as the base design for the Next Generation Nuclear Plant. Because an HTGR operates at a higher temperature, it can provide higher temperature process heat, more closely matched to chemical process temperatures, than a conventional light water reactor. Integrating HTGRs into conventional industrial processes would increase U.S. energy security and potentially reduce greenhouse gas emissions (GHG), particularly CO2. This paper focuses on the integration of HTGRs into a coal to liquids (CTL) process, for the production of synthetic diesel fuel, naphtha, and liquefied petroleum gas (LPG). The plant models for the CTL processes were developed using Aspen Plus. The models were constructed with plant production capacity set at 50,000 barrels per day of liquid products. Analysis of the conventional CTL case indicated a potential need for hydrogen supplementation from high temperature steam electrolysis (HTSE), with heat and power supplied by the HTGR. By supplementing the process with an external hydrogen source, the need to “shift” the syngas using conventional water-gas shift reactors was eliminated. HTGR electrical power generation efficiency was set at 40%, a reactor size of 600 MWth was specified, and it was assumed that heat in the form of hot helium could be delivered at a maximum temperature of 700°C to the processes. Results from the Aspen Plus model were used to perform a preliminary economic analysis and a life cycle emissions assessment. The following conclusions were drawn when evaluating the nuclear assisted CTL process against the conventional process: • 11 HTGRs (600 MWth each) are required to support production of a 50,000 barrel per day CTL facility. When compared to conventional CTL production, nuclear integration decreases coal consumption by 66% using electrolysis and nuclear power as the hydrogen source. In addition, nuclear integration decreases CO2 emissions by 84% if sequestration is assumed and 96% without sequestration, when compared to conventional CTL. • The preliminary economic assessment indicates that the incorporation of 11 HTGRs and the associated HTSEs impacts the expected return on investment, when compared to conventional CTL with or without sequestration. However, in a carbon constrained scenario, where CO2 emissions are taxed and sequestration is not an option, a reasonable CO2 tax would equate the economics of the nuclear assisted CTL case with the conventional CTL case. The economic results are preliminary, as they do not include economies of scale for multiple HTGRs and are based on an uncertain reactor cost estimate. Refinement of the HTGR cost estimate is currently underway. • To reduce well to wheel (WTW) GHG emissions below baseline (U.S. crude mix) or imported crude derived diesel, integration of an HTGR is necessary. WTW GHG emissions decrease 8% below baseline crude with nuclear assisted CTL. Even with CO2 sequestration, conventional CTL WTW GHG emissions are 24% higher than baseline crude emissions. • Current efforts are underway to investigate the incorporation of nuclear integrated steam methane reforming for the production of hydrogen, in place of HTSE. This will likely reduce the number of HTGRs required for the process.