Debate

Carbon Capture: A mixed picture

Carbon capture is becoming a topic of interest in the waste industry. Being hailed as a weapon against climate change, it’s a technology that can make zero-emission waste incineration plants a reality. But it’s not without its pitfalls.

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It’s certainly an exciting prospect: if CO2 is removed from processes in which it is produced, it can subsequently either be stored underground or reused. If all CO2 emitters did this, we could – in theory – soon find ourselves in a climate-neutral world. For waste incineration plants, carbon capture could mean that these plants would in practice have zero emissions – because to capture the CO2 effectively, all other pollutants would need to be removed beforehand.

The carbon itself can then be transported to a suitable site for long-term storage. The options being discussed at the moment include the idea of storing the captured carbon dioxide in sites where natural gas reserves have been depleted, either on land or underwater, for in- stance in the North Sea.

A lot of question marks

The great unknown, however, is how the CO2 would behave when stored in this way. The hope is that it will remain trapped, as the natural gas once was, and not escape. The circumstances are completely different, however. Natural gas forms over millions of years. The captured CO2, on the other hand, is injected in one go into rock that, like all depleted fields, still contains natural gas or crude oil residues.

In the best-case scenario, the CO2 could be used to help recover these residues using tertiary recovery methods. In the worst-case scenario, however, the gas or oil residues might surface in undesirable locations and cause damage to the environment. The CO2 itself could also start to leak out after a certain amount of time. This is why Germany, for exam- ple, holds the view that geological storage of CO2 should only be an option if sufficient moni- toring of the storage sites can be ensured.

Useful interim step

An additional factor comes into play here: the geological storage sites available may be large, but they are not infinite. At some point they will be exhausted. As a result, carbon capture and utilisation (CCU) is being explored as an alternative to carbon capture and storage (CCS). In this process, the captured CO2 can be used to produce methane in order to store excess electricity from renewable energy sources. This is already a mature technology, but the disadvantage of this elegant solution is obvious: the CO2 is only stored until the methane produced in this way is used. When it is used, the CO2 escapes into the atmosphere or must be recaptured.

The overall picture therefore remains mixed. As an interim step, carbon storage and carbon utilisation could help to mitigate the CO2 problem. Minimising the CO2 emissions released into the atmosphere is the only sustainable solution, however. For the waste industry, this means minimising the proportion of plastic that enters the waste stream before thermal recycling takes place. This is because the plastic fraction is responsible for virtually the entire CO2 load of thermal recycling.

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Does carbon capture offer a new role for the waste-to-energy sector? >>