Power from gas + CCS at 54% efficiency?

Jul 22 2013

Engineers at Technology Centre Mongstad of Norway believe that it might be possible to generate electricity from gas with CCS at 54 per cent efficiency – compared to 59 per cent efficiency for a gas turbine without CCS.

Technology Centre Mongstad (TCM), the world’s largest CO2 capture research facility based in Norway, is currently enabling electricity to be generated from gas, with carbon capture, at 50-51 per cent efficiency.
TCM is connected to a nearby gas electric power plant.
TCM Engineers think that 52 per cent should be achieveable and 53-54 per cent possible. Bear in mind that the record efficiency for a gas power plant without CCS is currently around 59 per cent.
If there is a 51 per cent efficiency using CCS, this means that around 16 per cent of the electrical power, which would otherwise be available for electricity, is being used to run the capture plant ((59-51)/51= 0.156).
This is a lot of power, but still less than the 30 per cent power requirement estimates of early carbon capture plants.
TCM is engaging in intensive research to try to improve the 51 per cent figure.
Olav Falk-Pedersen, Technology Manager at Mongstad, believes that it might be possible to run the plant at 54 per cent efficiency, which would mean that the capture plant is drawing just 8.5 per cent of the electrical power ((59-54)/59=0.084).
If this could be achieved, it would make a massive reduction to the overall cost of CCS and improvement to its viability. 
Oil and coal prices are constantly changing, but if (for example) the coal price per megajoule was to drop to 9 per cent less than the gas price (due to it being easier to get planning permission to build new gas plants than coal plants, and a surplus of coal in the US due to the shale gas boom), then it could be equally viable to construct a coal power station with CCS, as a gas power station without CCS.  
Since it is currently viable to build gas plants without CCS, that would mean that a coal plant with CCS is economically viable.
There are the capital costs to take into consideration, but the main cost over the lifetime of the plant is the cost of the fuel.
Mr Falk-Pedersen believes that 52 per cent efficiency is “achievable”.
Technology Centre Mongstad
Technology Centre Mongstad claims to be the world’s largest facility for testing and improving CO2 capture, with an investment budget of  6bn NOK (approx. USD $1billion). 
It is designed to capture 100,000 tonnes of CO2 per year. It is a joint venture between the Norwegian state, Statoil, Shell and Sasol. 
The plant receives effluent gas from a Statoil oil refinery and a gas fired power station. The gas power plant has CO2 of 3.5 per cent and the refinery cracker has CO2 of 13 per cent. 
The capture plant is still 200 times smaller than a capture plant that would be required to capture all the CO2 from a large coal power station, which can emit 20m tons of CO2 per year, but if the technology works efficiently at 100,000 tons a year that is a great step towards a 20m tons a year plant. 
TCM is testing two carbon capture processes, chilled ammonia from Alstom and an amine process from Aker Clean Carbon. They are both post-combustion capture with solvents, designed to capture 85 per cent of the CO2 in the flue gas.
Aker Solutions builds its plant at its own factory in modules which can then be brought to the site and put together – this is because it does a lot of construction work for offshore facilities, and modular construction is much more practical for offshore construction if the plant can be built onshore rather than offshore. All of its modules can be delivered to Mongstad on barges.
Alstom goes for the on-site construction approach, which might be less expensive.
People often ask of Alstom and Aker are competing to see whose technology is best, but Mr Falk-Pedersen says that both companies are winners because they are learning more about their own technology.
The research work is learning how the operation of a carbon capture plant can be fine-tuned for maximum efficiency, separation, purity, reliability, long life, maintainability, and construction.
It is working out how to get the best balance between energy requirement, amount of CO2 separated, and purity of the output stream.
It is learning how to keep the plant running reliably for long periods of time, and how to maintain the quality of the solvents so they can be reused over and over again and do not degrade.
The challenge is to “close the heat and mass balance,” Mr Falk-Pedersen says, or in other words keep all flows into and out of the system in a steady state and measure energy consumption per ton of CO2 removed and other important key performance parameters with a high accuracy.. This way, the plant can be operated most efficiently. 
You can do lots of theoretical studies and simulations about how the plant should run, but it is all slightly different when you do it for real.
An important parameter is the capture rate, how much of the CO2 in the gas stream going into the plant should be separated from the exhaust gas which comes out. The plant is designed for  a capture rate of between 50 to 95 per cent.
You could argue that there isn’t much point to a plant which can only capture 50 per cent of the CO2 going in – but the energy costs of getting a 95 per cent capture might be so high, you might choose a lower capture rate.
The plant has a very stable (constant) exhaust gas as its input flow in terms of its composition. The input flow rate can be varied between 20,000 and 60,000m3 an hour. There is possibility to add air to the input flow, so you can experiment with a stream with an even lower CO2 concentration.
Research is also going into working out the best packing type for the absorber, and the optimum height of the absorption tower.
The researchers take 100 manual samples a day from the plant, and analyse them for concentrations of different substances, sometimes at levels of parts per billion. They also collect data from around 4,000 measuring points. 
“People are working hard to see how we can totally optimise the process,” he said.
The centre will be open for other companies to test their carbon capture equipment in early 2014, and Mitsubishi, Hitachi, Siemens and A ker are already showing interest. They will be able to test the technologies in our amine plant  and see how well it can function in a larger scale capture plant.
Perhaps most importantly, if the centre can prove that carbon capture can work, then coal power companies (when asked by regulators if they will put carbon capture on their new coal plant) will no longer be able to reply that the carbon capture technology does not exist.
The project is planned to run for 5 years at least, and after that might be used to also research other capture technology (other than post combustion).


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