Desulphurisation plant a success

15 October 2007

Dr Tony Clemens, programme leader for the government-funded “Hydrogen Energy for the Future of New Zealand” research programme has recently announced the completion of several milestones in CRL Energy’s efforts to produce high grade hydrogen from New Zealand lignite.

“Last year we had an objective to successfully operate a desulphurisation plant sufficient to handle 10% of the 200 kW syngas stream produced by our coal gasifier here at CRL Energy. This proved to be very difficult but through hard work by the team we’ve conquered the challenge and I’m pleased to say that this has not only recently been achieved, but in addition the desulphuriser was easily able to clean up 20% of the syngas stream.”

Achieving this milestone represents completion of a major milestone for the coal to hydrogen part of the programme because in order for the downstream syngas clean-up gear and fuel cell to work, it is essential that all traces of sulphurous gases are removed.

Last year the original desulphuriser (sulphur scavenger solution introduced into the gas stream) proved unable to remove all sulphur from the syngas stream. The team at CRL Energy had to redesign and build a completely new desulphurising tower (packed column with circulating caustic wash).

“The new tower is performing extremely well and is able to reduce hydrogen sulphide (H2S) in syngas from in excess of 1200 ppm to the point where it is undetectable on equipment designed to read down to 0.1ppm.”

A water gas shift reactor for treating volumes equivalent to 10% of the gasifier output has also been constructed and commissioned.

“Previous difficulties with activating the catalyst in the reactor have been resolved and a series of experiments were carried out in which catalyst bed temperature, steam feed rate and syngas flow were varied. Initial experiments used bottled syngas which mimicked the gasifier syngas, but we are now using genuine, gasifier-generated desulphurised syngas. The reactor was able to shift 60% of the CO in the syngas. This is sufficient to allow us to continue to the next stage.”

The next stage is a condenser and drying tower assembly to treat the wet shifted gas prior to pressurization and passing to the fuel cell. Construction of the drying tower has already begun.

“In addition we now have all the parts needed for testing the ECN hydrogen separation membrane (ECN: Energy Research Centre of the Netherlands - a major international energy research organization) and the test facility is currently being assembled. We will be testing its ability to produce pure hydrogen from our desulphurised, dry, shifted syngas.

“In all we expect the syngas slipstream clean-up line will be fully integrated with the gasifier (including testing of the new ECN membrane for hydrogen separation) by Christmas this year,” says Dr Clemens.