What’s the future for carbon capture and storage?

It’s long been established that each of the three vital elements of CCS – capture, transportation and storage – is technically possible. What’s been missing is how they could be integrated into a chain that benefits all parties. It’s not just valuable to power, pipeline and offshore industries, but also manufacturing and heavy industry, for example.

Without this chain, it’s a question of who should pick up the extra cost of reducing carbon. Should it be the power station owner through the loss of efficiency that results from installing CCS? Should it be the taxpayer, or the energy customer? Nobody seems keen to pick up the tab.

What’s needed is a way of generating an income from the CO2. Could it be used for enhanced oil recovery, forcing extra gas and oil out of wells? This could generate revenue that would otherwise remain untapped, and producers around the world are already using natural and captured CO2 to do exactly this.

Applying this technology in the North Sea could extend the life of aging assets, increase hydrocarbon recovery and defer decommissioning costs, while simultaneously permanently storing large volumes of CO2.

Allam Cycle potential

But what if power generation produced less CO2 in the first place? A promising new approach does exactly that. In May 2018, WSP’s client NET Power fired up a 50MWt demonstration plant in Texas, USA, using a new process called the Allam Cycle. We’ve been working with NET Power since 2013, helping to take the technology from conceptual design to a demonstration of the combustor and testing of the process.

The Allam Cycle effectively captures all the carbon dioxide it produces, generating electricity at an efficiency comparable with a conventional natural gas combined cycle power plant, without carbon capture.

NET Power’s plant mixes fuel (natural gas) with pure oxygen, which is combusted with CO2 recycled from within the process, to reach the high temperature and pressure needed to drive a turbine. Using pure oxygen rather than air eliminates any chance of producing oxides of nitrogen, some of the world’s worst air pollutants, and enables the plant to generate all of its CO2 as high-pressure, high-purity by-product.

The bulk of the CO2 is reheated and used again in the combustor, but the remaining by-product can be sequestered underground without further compression – or used for enhanced oil recovery or other industrial applications.

The Allam Cycle could provide a useful stepping stone to a zero-carbon future. In the long term, decarbonising without a direct replacement for gas would be challenging due to high infrastructure costs. This is where hydrogen comes in.

Large-scale production of hydrogen would require vast quantities of low-carbon electricity for electrolysis. Or it would result in lots of CO2 – if either steam reforming of natural gas or underground gasification of untapped coal seams were employed. But we don’t need to produce vast quantities right away.

The current thinking is that the gas distribution network could handle up to 20% hydrogen (by volume) without requiring customers to make radical changes to their boilers or other plant, the HyDeploy program will shortly be testing this theory thoroughly. If rolled out nationwide, this blending approach could save the equivalent of 6 million tonnes of CO2 every year. And there is already enough waste hydrogen from industrial processes to start injecting it into the gas distribution network.

A step-by-step approach like this could then see smaller-scale hydrogen and CCS developed hand-in-hand, reducing the barriers to entry for both. Indeed, Cadent’s HyNet North West project and the Acorn Project in the north-east of Scotland are following this path – producing hydrogen from natural gas and developing accompanying CO2 storage.

Cadent estimates HyNet will save over one million tonnes of CO2 emissions every year, the equivalent of taking more than 600,000 cars off the road. This is why hydrogen, and accompanying CCS, have a vital role to play in the UK government’s aspirations for a low-carbon future.

Dr Andrew Jackson is a Principal Engineer within the Oil and Gas Projects team of WSP’s Energy division.