3. Technology categorisation

Not all CO₂ reuse technologies require a concentrated stream of CO₂. Some technologies could utilise a dilute stream of CO₂ (e.g. flue gas) and hence would not require a conventional capture plant. Furthermore not all technologies permanently store CO₂. These attributes will lead to different effects when considering the objective of accelerating the uptake of CCS.

It is evident from the detailed investigation in Section 2 that the short-listed reuse technologies utilise varying sources of CO₂ (from a concentrated stream of CO₂ to a dilute stream of CO₂ such as untreated flue gas) and also have varying abilities to permanently store CO₂. The differentiation of these attributes is important as they will have a different impact on the objective of accelerating the uptake of CCS.

CO₂ reuse technologies which require conventional capture plants may contribute cost reductions in capture plant from capability building, learning and knowledge sharing. However reuse technologies that utilise flue gas directly might provide a lower cost option for capturing CO₂, and provide some form of revenue. Consequently they have potential to act as a transitional measure to conventional CCS, (for example if there are delays in developing integrated CCS projects due to the timing of access to viable storage sites).

Generally reuse technologies that do not provide permanent storage are likely to be exposed to risk due to the uncertainty around the carbon price liability (where a carbon price is present). This is explained in more detail in Part 2 – Section 4 of the report.

This section highlights the key differences between the reuse technologies and categorises them based on (1) CO₂ feedstock and (2) permanence of CO₂ storage.

3.1 CO₂ feedstock

Carbonate mineralisation, concrete curing, algae cultivation and potentially ECBM could utilise flue gas directly and therefore would not require a conventional capture plant to deliver a concentrated CO₂ stream.

Reuse technologies that require a concentrated stream of CO₂ require a source, such as natural gas processing, from which concentrated CO₂ is a by-product, or the addition of a conventional capture plant to concentrate dilute CO₂ emission streams from sources such as power, steel and cement plants. Reuse technologies that utilise flue gas directly from dilute sources however, do not require conventional capture plant, and may need no more than some lower cost form of gas clean-up treatment.

Figure 3.1 presents the reuse technologies that require concentrated CO₂ and those that can utilise dilute CO₂ in flue gas directly or a low cost form of capture or treatment.

Figure 3.1 Technologies operating on concentrated CO₂ versus dilute CO₂

^*ECBM – both CO₂ and direct flue gas ECBM is being considered.

In considering how reuse technologies can help to accelerate the uptake of CCS, the two categories above will have a different impact. Implementing reuse technologies that operate on a concentrated CO₂ stream and require a conventional capture plant to concentrate the stream may contribute to capability building, learning, and knowledge sharing, with some subsequent impact on cost reductions for conventional capture plants.

Implementing reuse technologies that use a diluted CO₂ stream, such as flue gas will not contribute to the development of conventional capture technology. However, these technologies could have potential for lower costs, enabling them to act as a transitional measure to conventional CCS (for example if there are delays in developing integrated CCS projects due to delays in access to viable storage sites). This issue is discussed further in Part 2 – Section 4 of this report.

There are differing purity requirements amongst the uses for CO₂ that require a relatively concentrated CO₂ stream. CO₂ for human consumption is typically a minimum of 99.8 per cent CO₂, with limits imposed on the nature of the allowable impurities. Chemical processes using CO₂ as a feedstock also tend to require an almost pure CO₂ stream, with specifications of 99.9 per cent + CO₂ not uncommon. EOR tends to have less stringent requirements, and 95 per cent CO₂ is a commonly accepted purity level. These differing purity requirements will inevitably have some cost implications for the final CO₂ product, but the market prices receivable for bulk gaseous CO₂ will remain low, as discussed in Part 2 of this report.

3.2 Permanence of CO₂ storage

Reuse technologies that permanently store CO₂ are considered to be an alternative form of CCS and hence are referred to as ‘alternative CCS’.

EOR, ECBM, EGS, carbonate mineralisation, concrete curing, bauxite residue carbonation and potentially algae cultivation (depending on the end product) are considered to be alternative forms of CCS.

The reuse technologies’ ability to permanently store CO₂ is another important attribute which is likely to have an impact on the viability of the technology and its ability to accelerate the uptake of CCS.

Some reuse technologies result in permanent storage of CO₂ considered suitable for hundreds to thousands of years (such as mineralisation). Urea fertiliser and polymers may start to breakdown and release CO₂ from one to six months after use, while products such as fuels will release CO₂ once utilised (combusted) releasing CO₂ back into the atmosphere.

Reuse technologies which permanently store CO₂ are considered to be an alternative form of CCS and may be referred to as ‘alternative CCS’ throughout the report.

Figure 3.2 shows the reuse technologies and their ability to store CO₂ in the derived end product.

Figure 3.2 Permanent versus non-permanent storage

Note: Algae cultivation can result in various products, which may result in semi-permanent and non permanent storage of CO₂. While the production of biofuels through algae cultivation does not permanently store the CO₂, it may have an equivalent mitigation effect where the algal biofuels effectively replace fossil fuels.

The two permanency categories above will have a different impact when considering how reuse technologies can help to accelerate the uptake of CCS. Implementing reuse technologies that also provide permanent storage of CO₂ may avoid any carbon price implications. Reuse technologies which do not permanently store CO₂ are exposed to greater risk due to the uncertainty of the carbon price liability between emitter and end product, which could affect the commercial viability of the technology or the competitiveness of the end product. This is discussed further in Part 2 – Section 4 of the report.

3.3 Technology categorisation

Section 3.1 highlighted that not all of the short-listed reuse technologies require a concentrated stream of CO₂ while Section 3.2 indicates that not all technologies result in permanent storage of CO₂. Considering both of these attributes together the reuse technologies fall into the following four categories:

1. Reuse technologies which require concentrated CO₂ (and a conventional capture plant for power, steel and cement sources) and permanently store CO₂.
2. Reuse technologies which require concentrated CO₂ (and a conventional capture plant for power, steel and cement sources) and do not permanently store CO₂.
3. Reuse technologies which do not require concentrated CO₂ (or a capture plant) and permanently store CO₂.
4. Reuse technologies which do not require concentrated CO₂ (or a capture plant) and do not permanently store CO₂.

Figure 3.3 presents the short-listed technologies into the four categories as outlined above.

Figure 3.3 Technology categorisation

This categorisation is important in the overall assessment and evaluation of reuse technologies and their ability to accelerate the uptake of CCS. This is discussed further in Part 2 – Section 4 of the report.