Techno-economic metrics of carbon utilisation: Part 2
Explaining the technological and economical parameters of carbon utilisation and how these vary widely depending on external as well as technology-specific variables.
Joris Mertens, Mark Krawec and Ritik Attwal
KBC (A Yokogawa Company)
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Currently, there is a common misconception that carbon capture, utilisation, and storage (CCUS) means carbon storage (CS) rather than carbon utilisation (CU). The confusion between storage and utilisation is understandable since they both help reduce carbon emissions. The difference between storage and utilisation is that storage involves disposing of waste, whereas utilisation involves efficient use of resources. Since utilisation is more expensive than storage, some utilisation technologies need further development, which explains the current focus on storage.
To help curb carbon emissions, NEDO (New Energy and Industrial Technology Development Organization) entrusted Yokogawa, a leading provider of industrial automation and test and measurement solutions, to perform a strategic decarbonisation study of the Goi industrial area in the Chiba Prefecture at Tokyo Bay, opposite the capital (Yokogawa, 2021). KBC carried out the research related to carbon utilisation for Yokogawa. This research aims to make the industrial area net carbon neutral by 2050, preferably using carbon utilisation rather than storage.
KBC conducted a techno-economic evaluation of the nine carbon utilisation technologies. These technologies and feeds, other than CO2, are listed in Table 1, an abridged version of Table 1 from Part 1.
Part 1 of this two-part article assessed how key variables such as hydrogen requirements, CO2 utilisation, and product price affect operating costs (KBC, 2022).
Table 2 shows hypothetical price scenarios for green hydrogen and CO2 utilisation in 2030 and 2050. Whereas the 2030 scenario assumes a high price for green hydrogen and a low price for CO2 utilisation, the 2050 scenario speculates a much lower price for green hydrogen and a much higher price for CO2. The primary purpose of this comparison is to demonstrate the sensitivity of the carbon utilisation economics with carbon and green hydrogen pricing.
Price estimates for the 2030 and 2050 scenarios have been established with a more rigorous market analysis for the other feeds (propylene, propylene oxide, slag) and the carbon utilisation products. For most feed and product pricing, KBC relied on third-party market intelligence supplied by Argus Media. The investigation concluded that making hydrogen-intensive carbon utilisation technologies available in a scenario depicting high-priced green hydrogen must impose either product mandates or high CO2 prices of USD 350/t.
Part 1 of this article accounted for the carbon impact of imported electricity and fuel and assumed the hydrogen had a zero carbon intensity (CI). Figure 1 recaptures the carbon utilisation, carbon utilisation intensity (CUI) charts presented for the different technologies. Different power, fuel, and steam emissions factors are assumed for the 2030 and 2050 scenarios illustrated in the bar chart in Figure 1.
Part 2 further develops the techno-economics of carbon utilisation by investigating the impact of the CI of green hydrogen, power, and fuel consumed. The capital expenditure for the different technologies is also compared.
Utility balance: impact of power, fuel, and steam imports on carbon emissions
The carbon utilisation units may import and export electricity as well as steam and/or fuel. However, the balance is primarily determined by the reaction heat, and the heat required for amine regeneration.
Exothermic processes have the potential to use the excess heat for steam generation and export. Synthesis processes using hydrogen tend to be highly exothermic. The methanation, Fischer-Tropsch (FT), and xylenes technologies indeed generate considerable amounts of reaction heat, ranging from 1.8 to 2.9 MWh of product for the xylenes and methane processes, respectively. However, this does not always translate into steam exports. Some technologies use medium-level and high-level heat above 120ºC for preheat, while the lower-level heat (<120ºC) is lost in cooling. The intermediate-level heat (150-200ºC) is often used to produce the necessary steam to regenerate the amine solution, which is used to capture CO2. Carbon capture is used in the methanation, FT, and Oxo production processes. Capturing and recycling CO2 are required to avoid large purges of CO2. However, it requires a significant amount of relatively low-level heat for amine regeneration and electricity for the compression and recycling of captured CO2.
Ultimately, all technologies are net utility importers except the xylenes process. The xylenes process is a net steam exporter that assumes CO2 capture is optional, and the best technology available for heat integration has been considered, unlike other technologies studied. In addition, caution should be exercised with respect to the xylenes technology because it is still in its infancy. Consequently, the available yield information was limited. KBC anticipates that further improvements in product selectivity will be achieved once the technology matures.
Figure 2 shows the net import requirements of electricity and fuel/steam, respectively.
The use of import electricity and fuel/steam will lead to emissions that occur outside the carbon utilisation unit. These will be categorised as Scope 1 or Scope 2 emissions depending on whether they occur within a unit located elsewhere on the same production site or outside the site. In Figure 1, the utility import-related emissions were subtracted from the CUI, as shown. Note that the hydrogen consumed was assumed to be imported green hydrogen with a zero carbon footprint.
Naturally, emissions related to imported electricity and fuel/steam will depend on their CI. Table 3 shows the CI of these utilities in the 2030 and 2050 scenarios. It should be noted that the 2030 scenario assumes an initial degree of decarbonisation of the utility imports, whereas the 2050 scenario forecasts total decarbonisation. A worst-case scenario has been considered as a sensitivity case assuming coal is used to produce electricity while heavy residual oil is the imported fuel.
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