Cracking the code

A major project is under way to boost the responsiveness of new ‘cleaner’ coal-fired power stations in a bid to bring them into line with National Grid standards.


A major project is under way to boost the responsiveness of new ‘cleaner’ coal-fired power stations in a bid to bring them into line with National Grid standards, The Engineer has discovered.

While dozens of countries are building less polluting and more efficient supercritical coal-fired plants, the UK has none — and any that are built would currently fail to meet the National Grid Code, which governs the ability to meet excess demand.

The problem could hamper plans to replace existing coal-fired units with ones using supercritical technology, including that proposed by E.ON UK at Kingsnorth in Kent.

Now, E.ON is working to address the issue with engineers at the University of Birmingham and Scottish Power Generation through a collaborative effort that aims to bring supercritical and ultra-supercritical plants into line with the National Grid’s requirements.

Supercritical plants run more efficiently by using extremely hot steam. While they are being built at a rate of one a month in China, the UK National Grid Code makes it difficult for power plants to adopt supercritical boilers, said Andrew Barrow, a spokesman for E.ON.

The code dictates that power plants must be prepared to significantly increase output if a power station drops off the grid, he added. The requirement is much stricter than for other European countries because of the relatively limited size of the UK’s electricity network.

While conventional coal-fired power plants have reserves of steam that can be tapped into in these situations, supercritical plants are extremely efficient and use the steam created straight away. Therefore, according to Barrow, an individual supercritical plant would struggle to produce the response required by the National Grid Code.

‘There are engineering ways around it,’ he said, adding that work would focus on the design of the overall system and its individual components.

This view is echoed by University of Birmingham engineers who believe that process and control strategies can be developed to help supercritical plants quickly meet increased demand on the grid.

Jihong Wang, a reader in control and power systems at Birmingham, is leading a £750,000 government-backed project that will spend four years creating computer models and simulations to attain a better understanding of the dynamic responses of supercritical plants. The project kicks off this August.

Wang and Bushra Al-Duri, a senior chemical-engineering lecturer at Birmingham, will work with partners from countries where these plants are currently up and running.

The Birmingham researchers will collaborate with academic colleagues at Tsinghua University and North China Electric Power University in China, which operates 24 of the 400 supercritical power plants up and running worldwide.

Wang said that their colleagues in China will provide data from a working 660MW supercritical plant that can be used to create mathematical models.

‘Electricity generation, distribution and transmission is a complicated set of processes,’ she added. ‘Every single component cannot be viewed individually. Every stage affects another stage and this is why we need to model and simulate the whole system.’

Wang said that she and Al-Duri also intend to create a laboratory-scale prototype of a supercritical boiler to examine its response to increased electricity demand.

‘The boiler can provide extra information you cannot get from a real power plant,’ she said. ‘In a real power plant, you cannot build extreme experiments.’

The resulting information will help Wang and Al-Duri make suggestions on how to optimise each stage of the process, from electricity generation to transmission.

Al-Duri said that industrial partners, such as E.ON, Scottish Power Generation and Emerson Process Management, will advise on the practicality of the solutions.

‘What may look like a very good idea in a 10-litre beaker or 10ml beaker will be quite different when we’re talking about two tonnes of coal being incinerated,’ she said. ‘They will provide advice on a practical and commercial level.’

Wang and Al-Duri believe that there is an urgent need for supercritical and ultra-supercritical technology in the UK. The researchers pointed out that, by 2015, the UK is due to face an electrical power shortage of more than 20GW based on projected economic growth and life expectancy of a number of existing power plants.

According to Al-Duri, coal is the only viable option to meet the UK’s energy needs in the short term, but the challenge will be to make sure that the electrical power generation from it is cleaner.

Conventional coal-fired power plants make water boil to generate steam that moves a turbine. Supercritical power plants operate above the temperature and pressure at which the liquid and gas phases of water coexist in equilibrium, meaning that there is no difference between water gas and liquid water.

Power plants using supercritical generation have energy efficiency up to 46 per cent, which the researchers say is 10 per cent above current coal-fired power plants. The improved efficiency means that a power plant will burn less coal and emit less CO2 for each unit of electricity it generates.

Wang and Al-Duri claim that supercritical and ultra-supercritical plants can be fully integrated with CO2 capture technology. Indeed, the plants will have to do so to meet new government requirements. Climate secretary Ed Miliband said in April that any new coal-fired power station built in the UK must have the ability to capture and bury at lease 25 per cent of its emissions.

Barrow said that E.ON backed the idea of a fleet of supercritical power plant stations across the UK. This would mean that energy storage would be less of an issue as there would be plenty of efficient plants to keep up with demand. However, this option would require initiatives such as the above to succeed or for a review of the code.

Siobhan Wagner