Peterhead - capturing carbon

Materials World magazine
,
1 Dec 2014

Simon Frost looks into plans to create the world’s first carbon capture and storage project for a gas-fired power station in Scotland. 

Popular or not, fossil fuels will remain a major part of the global energy mix for years to come – Shell estimates that the world will still be 75% reliant on fossil fuels in 2050. But in order to meet ambitious emission reduction targets while supplying the world’s growing energy needs, carbon capture and storage (CCS) technology could prove essential, by making the carbon-heavy plumes of smoke that rise from power stations a thing of the past.

Shell’s Peterhead CCS project, at Peterhead Power Station, Aberdeenshire on the northeast coast of Scotland, is competing to become the world’s first gas-fired power station to integrate CCS on a commercial scale. The system will be retrofitted on one of the plant’s three 385MW combined cycle gas turbines and in operation by 2020. It is expected that around one million tonnes of CO2 will be captured every year – the equivalent of taking 250,000 cars off the road – to be stored in a depleted offshore gas field beneath the North Sea. With CCS technology still in the demonstration phase, the Peterhead project will run for 10 years.

Ed Daniels, former Chairman of Shell UK, said in a statement, ‘The project has the potential to make gas, already the cleanest burning fossil fuel, even cleaner. CCS could be critical to reducing carbon emissions at a time of growing global demand for energy. The successful demonstration of the technology at Peterhead would be a step towards proving its commercial viability as a tool for mitigating climate change. It could also help diversify the North Sea oil and gas industry and so contribute to the sector’s long-term commercial health.’


The billion pound question

Funding for the front-end engineering and design (FEED) study for the Peterhead CCS Project was granted to Shell UK in February 2014 by the UK Government, with the final investment decisions from Shell and Government expected to be made towards the end of 2015. The project is one of two in the running to secure funding as part of the UK Government’s £1bln CCS commercialisation programme, the other being the White Rose Project at Drax in North Yorkshire. Drax Power Plant, the largest coal-fired station in the UK, is currently in the process of converting its coal units to run on biomass. The White Rose Project is a planned oxyfuel power and CCS demonstration plant at the same site.

A previous Government-funded CCS project at Longannet Power Station in Fife, Scotland, was scrapped in 2011 due to doubts over its commercial viability. Since then, Shell has been working to drive down the cost of the technology. For the Peterhead project, Shell is collaborating with Scottish and Southern Energy (SSE), which owns the plant. SSE will be responsible for modifying the existing power station to support the carbon capture equipment, which Shell will install.


How will Peterhead work?

Post-combustion amine-based capture technology will be retrofitted to one of the three turbines at Peterhead Power Station, diverting the flue gases and, Shell claims, preventing around 90% of the turbine’s emitted CO2 from entering the atmosphere.

Shell owns the Cansolv absorption technology (right), by which feed gas is first quenched and saturated in a circulated water pre-scrubber. The gas then contacts a lean amine solution in a counter-current mass transfer-packed absorption column. Midway through the column, the partially-loaded amine is removed, cooled and reintroduced over a layer of mass transfer packing, and the CO2-rich amine is pumped through a lean-rich amine heat exchanger and through to a regeneration column. Rising low-pressure saturated steam regenerates the lean amine solution and the CO2 is recovered as a pure, water-saturated product. The lean amine can then be pumped back to the absorption column for reuse in capturing further CO2.

North Sea storage

The CO2 will be piped 102km offshore to the Shell-owned Goldeneye gas reservoir, which lies around 2.5km below the North Sea and has been depleted since 2011.It will then be absorbed by porous rock and trapped beneath a 100 metre-thick layer of impermeable cap rock. Goldeneye has the capacity for around 20 million tonnes of CO2.

Speaking at the Scottish Carbon Capture and Storage Conference, Scottish Energy Minister Fergus Ewing said, ‘We firmly believe that the North Sea’s vast CO2 storage potential – coupled with our existing oil and gas capabilities, ready supply chain and existing infrastructure – means that Scotland is in a strong position to be at the centre of CCS development in Europe.’

As an active power station since 1980, Peterhead boasts an existing local skills base, while the Goldeneye reservoir also has established infrastructure in the form of a subsea pipeline linked to the St Fergus Gas Plant, just a few kilometres north of Peterhead. A tie-in subsea pipeline will be constructed to link it to the Peterhead Power Station by Wood Group Kenny, which won the design contract in October 2014 and will provide 80 engineers from its Aberdeen and London offices for the project.

A global issue

While Peterhead will be the first to integrate CCS with gas power, the SaskPower-owned Boundary Dam coal-fired power station in Saskatchewan, Canada became the world’s first commercial-scale power plant to begin CCS operation in September 2014. A CCS project in Kemper County, Mississippi, is due to come online in 2015, and further projects are also underway in Australia and Saudi Arabia. Commenting on the launch of the Boundary Dam, Dr Luke Warren, Chief Executive of the CCS Association, stated his belief that international success in CCS will serve to maintain the building momentum bringing the technology into commercial use in the UK. ‘From a UK perspective, we need examples of successful CCS more than ever.’

Boundary Dam will use some of the captured carbon for enhanced oil recovery (EOR), a point of contention for environmental organisations, who argue that CCS is only commercially viable when used as a means to recover more crude oil, therefore leading to further emissions. The CO2 captured at Peterhead will be suitable for EOR, but Shell has publicly stated that it will not be serving the EOR industry through its CCS activities at Peterhead.

The UK Energy Technology Institute estimates that CCS could save the UK £32bln a year in achieving decarbonisation targets by 2050, and the Government, fossil fuel and heavy industrial producers are evidently looking at Peterhead as an example to set a wider CCS effort in motion. Ewing noted, ‘We cannot build an industry with one project. We also need follow-on projects to be supported, like the innovative Captain Clean Energy Project proposed for Grangemouth [Scotland], which could play a major connecting role between our existing onshore and offshore infrastructure, including the opportunity for EOR in the Central North Sea, and enable the infrastructure required for future industrial CCS.’  


How carbon is captured:

CSS is a technology to reduce the amount of CO2 pumped into the atmosphere by fossil fuel plants and heavy industrial processes such as cement and steel production. The carbon is captured at one of three stages:


Pre-combustion

The fuel is mixed with oxygen in a gasifier to form a synthetic gas (syngas) that combines hydrogen, carbon monoxide, CO2 and water. Steam is then added to convert the syngas to hydrogen and CO2, which are then separated, leaving a hydrogen fuel to be burnt and a stream of captured CO2.


Oxy-combustion

In order to capture carbon during combustion, the fuel is burnt in oxygen instead of air, so the waste products of the combustion are mainly water and CO2. These are easy to separate and, therefore, the carbon can be captured from an exhaust stream.


Post-combustion

The most widely-understood method and the one to be used at Peterhead. Exhaust gases are fed to a carbon-scrubbing column, where they are washed with a solvent – either chilled ammonia or advanced amines – that absorb the CO2. The CO2 and solvent are then separated.