removal, resulting in using less than half of the biomass carbon with the remaining part emitted as CO

Summary

Chemical products play a significant role in the energy system. To reduce fossil-fuel consumption and mitigate the impact of climate change from the production of chemicals using natural gas and coal, the investigation of green chemical production processes become essential.

Biomass is a promising renewable carbon resource substitute for fossil fuels to produce chemical products. However, state-of-the-art biomass-to-chemical conversion requires an increased hydrogen concentration in the syngas derived from biomass gasification, which is achieved by water-gas-shift reaction and CO

removal, resulting in using less than half of the biomass carbon with the remaining part emitted as CO

. To overcome this problem, biomass- to-chemical technologies integrated with renewable power-to-hydrogen systems come into being as an alternative concept.

In this thesis, renewable-driven chemical processes using solid-oxide electrolyzer are implemented and compared with the state-of-the-art ones for various products (i.e., methane, methanol, dimethyl ether, jet fuel, ammonia, and urea) through innovative conceptual process design, thermochemical modelling, energy integration, techno-economic evaluation, and multi- objective optimization. Experimental data from the literature and industrial data are adopted to develop and verify thermochemical models, such as entrained-flow gasification, syngas purification processes, chemical synthesis processes, and others. For the economic models, capital expenditure and operating expenditure are examined, and the main economic assumptions are proposed on the basis of literature and industrial data. Although the economic information was taken from a variety of sources, it can predict the investment feasibility of the above processes, and provide a reference for policymakers from the industry or government.

Compared with the state-of-the-art chemical process, the solid-oxide electrolyzer-based

chemical process achieves higher overall system efficiency because (1) biomass-to-chemical

processes can fully convert carbon, (2) solid-oxide electrolyzer for steam- or co-electrolysis is

highly efficient, (3) high-temperature solid-oxide electrolyzer has the best heat integration

opportunity with entrained-flow gasification and chemical synthesis to enhance system-level

heat utilization. For instance, solid-oxide electrolyzer based biomass-to-synthetic natural gas

process increases the overall system efficiency by more than 15 percentage points compared with state-of-the-art biomass-to-synthetic natural gas. The solid-oxide electrolyzer based power-to-ammonia process enhance the overall system efficiency by over 30 percentage points in comparison with biomass-to-ammonia processes. The economic evaluation reveals that solid-oxide electrolyzer based chemical process is hardly economically viable at present. The stack price and lifetime of solid-oxide electrolyzers are highly sensitive to the investment feasibility of the project, and they reflect the significant impact of commercialization of solid- oxide electrolyzers on economic feasibility. The solid-oxide electrolyzer based processes require a large amount of renewable power to drive the solid-oxide electrolyzer; thus, both the price and available annual hours of renewable electricity have a significant impact on their economic feasibility. A lower price of renewable electricity significantly reduces the levelized cost of products. Biomass-to-chemical with steam electrolysis is hugely affected by available annual hours of renewable electricity. When renewable electricity is not available, the system might need to be shut down due to a lack of large-scale storage of hydrogen or electricity.

Nevertheless, the concept of state-of-the-art biomass-to-chemical integrated with co-

electrolysis allows for additional operational flexibility without renewable electricity, resulting

in high annual production. It is more economically convenient than that with steam electrolysis.