Techno-economic and environmental analyses of a novel, sustainable process for production of liquid fuels using helium heat transfer

Abstract

In this paper, several new processes are proposed which co-generate electricity and liquid fuels (such as diesel, gasoline, or dimethyl ether) from biomass, natural gas and heat from a high temperature gas-cooled reactor. This carbonless heat provides the required energy to drive an endothermic steam methane reforming process, which yields H2-rich syngas (H2/CO > 6) with lower greenhouse gas emissions than traditional steam methane reforming processes. Since downstream Fischer-Tropsch, methanol, or dimethyl ether synthesis processes require an H2/CO ratio of around 2, biomass gasification is integrated into the process. Biomass-derived syngas is sufficiently H2-lean such that blending it with the steam methane reforming derived syngas yields a syngas of the appropriate H2/CO ratio of around 2. In a prior work, we also demonstrated that integrating carbonless heat with combined steam and CO2 reforming of methane is a promising option to produce a syngas with proper H2/CO ratio for Fischer-Tropsch and methanol/dimethyl ether applications. In this study, we presented another novel design called gas-nuclear-to-liquids process which can be applied for liquid fuel production without needing H2/CO adjustment. Chemical process simulations of several candidate processes were developed, which used the rigorous multi-scale, two-dimensional, heterogeneous models for the carbonless-heat-powered steam methane reforming and mixed reforming of methane processes developed in prior works in gPROMS. In addition, 1D process models within Aspen Plus were also used (Aspen Plus simulation and gPROMS models are provided to the reader). The performance of the presented systems was compared with a biomass-gas-to-liquids plant where heat from gasification drives the steam methane reforming instead of the high temperature gas-cooled reactor. Techno-economic analyses and greenhouse gas life cycle analyses of each case were completed to investigate the economic and environmental impacts of the proposed processes. Optional carbon capture and sequestration technology is also considered. The analysis demonstrates that carbonless heat integration leads to thermal efficiencies of up to 55% (high heating value based) as well as suitable profits in the right market conditions. It is also found that net negative life cycle greenhouse gas emissions of the final products can be achieved owing to use of biomass, carbonless heat, and carbon capture and sequestration. Even without carbon capture and sequestration, the life cycle greenhouse gas emissions of the proposed process are 25–57% lower than traditional natural gas-to-dimethyl ether and coal-to- dimethyl ether processes.