Techno-Economic Comparison of Onshore and Offshore Underground Coal Gasification End-Product Competitiveness

Natalie Nakaten,Thomas Kempka

doi:10.3390/en12173252

Abstract

Underground coal gasification (UCG) enables utilization of coal reserves, currently not economically exploitable due to complex geological boundary conditions. Hereby, UCG produces a high-calorific synthesis gas that can be used for generation of electricity, fuels, and chemical feedstock. The present study aims to identify economically-competitive, site-specific end-use options for onshore- and offshore-produced UCG synthesis gas, taking into account the capture and storage (CCS) and/or utilization (CCU) of produced CO 2 . Modeling results show that boundary conditions favoring electricity, methanol, and ammonia production expose low costs for air separation, low compression power requirements, and appropriate shares of H 2 /N 2 . Hereby, a gasification agent ratio of more than 30% oxygen by volume is not favorable from the economic and CO 2 mitigation viewpoints. Compared to the costs of an offshore platform with its technical equipment, offshore drilling costs are marginal. Thus, uncertainties related to parameters influenced by drilling costs are negligible. In summary, techno-economic process modeling results reveal that air-blown gasification scenarios are the most cost-effective ones, while offshore UCG-CCS/CCU scenarios are up to 1.7 times more expensive than the related onshore processes. Hereby, all investigated onshore scenarios except from ammonia production under the assumed worst-case conditions are competitive on the European market.

Highlights

Underground coal gasification (UCG) can provide an economic approach to increase worldwide coal reserves by utilization of coal deposits that are currently not mineable by conventional methods.Hereby, the target coal seam is converted into a synthesis gas within a controlled, sub-stoichiometric gasification process [1,2,3,4,5]
In line with the assessment related to the economic competitiveness of UCG-based methanol on the European market, mass and energy flows, as well as the amount of CO2 that is not emitted, we considered a commercial-scale methanol production scenario based on UCG synthesis gas at an average scale of already operating MeOH synthesis plants in Europe
Gross power generation for all electricity production model setups was automatically adjusted to the energy demand that changes with the underlying synthesis gas composition, while power output was maintained constant at 100 MWel to ensure comparability between the different scenarios assessed within the sensitivity analysis

Summary

Introduction

Underground coal gasification (UCG) can provide an economic approach to increase worldwide coal reserves by utilization of coal deposits that are currently not mineable by conventional methods.Hereby, the target coal seam is converted into a synthesis gas within a controlled, sub-stoichiometric gasification process [1,2,3,4,5]. UCG synthesis gas is applicable for different end-uses as, e.g., provision of chemical raw materials, liquid fuels, hydrogen, fertilizers, or electricity (cf Figure 1). Since the 1930s, more than 50 pilot-scale UCG operations have been carried out worldwide, e.g., in the former Union of Soviet Socialist Republics (USSR), Europe, the U.S., South Africa, Australia, and China. These tests have been undertaken at shallow depths, e.g., at Angren (110 m) in Uzbekistan, Chinchilla (140 m) in Australia, and Hanna (80 m) and Hoe Creek (30–40 m) in the U.S [1,2,3,4,6]. One recent pilot-scale UCG installation in Poland was Energies 2019, 12, 3252; doi:10.3390/en12173252 www.mdpi.com/journal/energies

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Results

Conclusion