NZ looks at reducing carbon emissions by storing and using it in industry

New Zealand is on target to fall short of its carbon reduction targets, but a series of projects are looking at how to help speed up the process of carbon dioxide (CO₂) removal.

University of Canterbury (UC) Associate Professor David Dempsey will lead a new team which will research how to store released carbon which would later be used by industry.

“The goal is to remove one million tonnes of carbon from the atmosphere each year,” Dempsey told Cosmos. “Right now, New Zealand is on course to overshoot its 2030 Nationally Determined Contribution (NDC) by 100 million tonnes. Engineered carbon removal processes can take a big bite out of this.”

The research, via UC’s Civil and Natural Resource Engineering Department, will focus on forestry, geothermal, agricultural and mining industries.

At first, some of the options appear counterintuitive. One example requires cutting down and burning pine forests.

Dempsey says this process would be a bit like crop farming. “You grow the crop (pine trees), cut them down and burn them. The burning process is where the CO₂ and some useful heat is released.

“Trees have spent hundreds of millions of years fine tuning removing carbon from the air. They are good for offsetting carbon emissions, providing you never cut them down, guarantee them against fire and storms, and never run out of land for more forest.

“Both of these are likely to become difficult in the future as forestry competes with agriculture for land, and as emerging climate hazards threaten the security of forest carbon,” he says. “So, if you have a fixed stock of land but want to keep pulling more and more CO₂ out of the atmosphere, you take the trees down (but extract and store their carbon) and plant new ones (for more CO₂ removal).

The aim is to capture the CO₂ and store it underground as negative emissions while making use of the heat.

“NZ has its own constraints and opportunities. We will take a look right across NZ, but I expect much of the focus to be in the upper North Island where we have a few advantages with forestry, geothermal and agriculture, as well as some major industries looking at decarbonisation pathways.

The research will among other things, explore injecting captured CO₂ in underground rocks that, when exposed to CO₂, trigger absorption.

“Another example would be ‘enhanced rock weathering,’ which uses use particular rock called dunite from the Nelson region.

“There is already a natural carbon cycle operating globally, where CO₂ dissolved in rainwater will naturally react with dunite and other similar rocks where they are exposed. The resulting reaction converts the CO₂ into a bicarbonate ion that is then washed into the oceans (eventually ending up in shells or coral or marine sediments).

This weathering happens naturally but the researchers would look at how much manual intervention could speed the process up. One way is to crush these rocks up and spread them on pasture.

“The idea of enhanced rock weathering is to speed up this natural carbon drawdown process by greatly increasing the exposure of ultramafic rocks – this is done by mining and crushing them (to increase surface area) and then spreading them out so they can start taking up the CO₂.

“The rates at which these particular rocks react chemically are not well known. Measuring these reaction rates helps us estimate the likely rate of carbon removal, and hence the total removal over some time frame.”

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