"would it be practical to store syngas as a method of allowing IGCC-CCS plants to respond to the overnight fall in demand?" Fred Starr responds
Claverton Hydrogen Storage on IGCC Sites
You asked if it would be practical to store syngas as a method of allowing IGCC-CCS plants to respond to the overnight fall in demand
The prospects of the on-site storage of syngas, to enable an IGCC to vary its output seem limited. The gas that would have to be stored would have to be hydrogen. Otherwise, the processes by which the carbon in the syngas is removed would have continuously vary their throughput. Only the gasifier and air separation unit ( for supply of oxygen) would run at a constant output
Unfortunately, a very large amount of gas is produced when gasifying coal. It does not matter whether it is raw gas, purified syngas, or hydrogen. For a plant producing 350 MW of electricity, this would require the storage of about 180 thousand cubic metres of hydrogen an hour.
By pressurising the hydrogen to 100 bar, this results in the need for 1800 cubic metres of space. The cheapest way of doing this would be in a 42 inch pipeline, which would need to be two kilometres long.
Problem solved? I don’t think so:
1. The most obvious issue is that this is just one hour’s output from a medium sized plant. To deal with the overnight situation, while demand falls, one would need 5-8 hours storage, so the pipeline would have to be 10-15km long
2. This calculation assumes that all of the hydrogen can be removed from the pipe. In practice the pressure in the pipe would only be allowed to fall to 50 bar. There are several reasons for this restriction. These include:
- Avoiding the need to compress the hydrogen, once it falls below the required gas turbine burner pressure.
- Minimising fatigue of the pipeline
- Minimising temperature changes in the pipeline because of withdrawal of hydrogen
3. There are questions about embrittlement effects on the high strength steels that are needed for 100bar pipelines. I cannot get a clear answer on this.
This fact doubles the length of the pipeline to 20-30 km for just one night’s storage.
Natural gas was stored in large diameter bullets, but this seems to have been less popular than storing the gas in a liquefied form. Furthermore, because of the low calorific value of hydrogen, hydrogen bullets would have to be three times bigger.
Hydrogen storage in pipelines becomes practical once there is a large network of high pressure pipelines. This is what I have been saying for several years. As there is no prospect of this being built in the near future, my SNG option is probably the most practical solution, if we are going for an IGCC type process.
Dr Fred Starr FIMMM, C.Eng
18th Feb 2009