Coal cleans up its act

Researchers from Imperial College London have designed a system which uses coal to generate hydrogen.

Team leader Rafael Kandiyoti believes that the ZECA (zero emissions carbon alliance) technology could make a significant contribution to low-emissions energy generation.

The technology combines several different systems. First, the coal is brought into contact with hydrogen at 70 bar and 700 degrees C using hydrogasification, which converts the carbon in the coal into methane. Steam is then pumped into the reactor, absorbing some of the heat given off by hydrogasification, and providing the reaction mixture for the second phase.

Here, gases pass into another reactor containing calcium oxide (lime) and a catalyst which promotes the ‘water-shift’ reaction, converting the methane and steam into carbon dioxide and hydrogen. The lime reacts with the CO2 to form calcium carbonate (limestone), leaving near-pure hydrogen.

Next, the limestone is passed into a third reactor called a calciner, where it is heated, reversing the first reaction and releasing a pure steam of CO2. This, say the researchers, can be captured and sequestered.

The hydrogen produced by phase two of the reactor splits into two streams. One is recycled to form the hydrogen feed for the hydrogasifier; the other is ‘polished’ — purified to a high degree — and fed into a solid oxide fuel cell to generate electricity.

According to Kandiyoti the technology should help the UK meet its targets for emissions reduction. He said: ‘The present strategy seems to be to increase the proportion of our energy that is produced from sustainable sources. However, there are serious concerns that sustainable fuels will not fill the energy gap that will exist if the UK reduces its fossil-derived energy to the level that will be required to meet the Kyoto emission levels.

‘Therefore, the concept of generating power from coal, with zero or near-zero emissions of CO2, is receiving serious consideration in both Europe and the US.’

The concept of ZECA technology was developed at Los Alamos National Laboratory and LouisianaStateUniversity. However, the theory has not yet been put into practice, and several conceptual plant models are being developed, according to the researchers.

Kandiyoti’s team is currently studying a novel type of hydrogasification reactor, where the gases pass through a heated wire mesh, which can perform the reaction at the required conditions.

In the next phase of the research, they hope to optimise the conditions inside both the hydrogasifier and the second-phase reactor, while another team at CambridgeUniversity studies the thermodynamics of the processes.

‘The data obtained will be used to test the concept and progress the design on a novel zero-emission power plant,’ said Kandiyoti.