Because the technologies are relatively immature, and much development work is going on, it is still much too soon to say definitively what will prove to be the most cost effective way of capturing carbon from coal fuelled plants. According to Chris McLarnon, Powerspan’s vice president, R&D, as quoted on p 26 of this issue, his company’s ammonia-based ECO2 process – recently the subject of a collaborative agreement with BP – “could be installed on current or new coal plants and be economically preferable over IGCC for coal-based plants with CO2 capture.”

Nevertheless the current consensus seems to be that if you factor in provision for carbon capture the economics of IGCC improve significantly relative to supercritical pulverised coal – going from 7-14% more expensive to 9-15% cheaper according to one recent study. This is a point not lost on gasification enthusiasts and a perceived advantage that IGCC proponents are very happy to latch on to, after many years in the wilderness. “Gasification – effective carbon control”, was for example the title of IChemE’s September conference in Antwerp. And as GE pointed out in a paper to that conference a key advantage of gasification is that it “cleans the coal before it is burned instead of cleaning up the pollution after it is produced” – ie it is pollution prevention rather than pollution control.

Dealing with carbon, or at least showing that consideration has been given to being “carbon capture ready”, has become a central issue that new build power plant proposals must contend with in many areas of the world.

Indeed we are seeing increasing signs of a drive from some quarters for new coal plants to be capturing carbon from the outset. In the case of the United States, for example, a report put out

earlier this year by an interdisciplinary MIT faculty group (The future of coal) gives a flavour of the way things are going. The MIT group recommends, among other things, that “Congress should remove any expectation that construction of new coal plants without CO2 capture will be ‘grandfathered’ and granted emission allowances in the event of future regulation.” According to the academics, “This is a perverse incentive to build coal plants without CO2 capture today.”

The growing preoccupation with carbon dioxide is proving to be a powerful driver in the resurgence of interest we are seeing in the use of IGCC for coal fuelled power generation. Siemens, for example, now a big player in the gasification business through its acquisition of the GSP entrained flow technology some 18 months ago, sees “major potential for the IGCC process” when it comes to carbon capture, “particularly when efficiency is considered” – envisaging that “in the longer term, IGCC plants with CO2 capture should be able to achieve an efficiency of around 43%” (see p 19).

However there is no shortage of challenges to keep IGCC developers busy over the next few years. Although there are projects in the pipeline in the USA and in Europe (notably Nuon Magnum, Powerfuel Hatfield, E.On Killingholme, Centrica Teesside and RWE’s 450 MWe plant somewhere in Germany) the number of operating coal based IGCC power plants in operation worldwide remains a meagre handful and the number under construction is precisely zero.

An issue of increasing concern is capital cost escalation, a problem not confined to IGCC of course, but to which the technology may be more prone than certain of its competitors because of its relative complexity. Recent estimates suggest costs per kW may have doubled from the $1600/kW that was the going rate for many years.

It is cost concerns that are proving troublesome for the proposed Mesaba plant in the USA, which is something of a flagship project for coal based IGCC technology in that country. In August the Minnesota Public Utilities Commission, while generally supportive of IGCC and rightly dismissing some of the more eccentric conclusions contained in a report issued by two administrative law judges earlier this year (see MPS, May 2007, p 11), nevertheless ruled the power purchase agreement (PPA) between Excelsior (developer of the project) and Minnesota utility Xcel “not in the public interest.”* This was “primarily because the pricing provisions are likely to impose unreasonable and excessive costs on Xcel’s ratepayers.”

The PUC has sent the two parties back to the negotiating table, and is also going to explore the possibility of extending the market for power produced by the Mesaba plant to other entities in the state.

In the longer term, improving the performance and competitiveness of IGCC is clearly of vital importance if it is ever to be deployed on a significant scale for coal based power generation – which is hardly surprising in view of the relatively small experience base that exists to date. This is widely recognised by the developers of the technology. Siemens is, for example, working towards larger scale gasifier units and also radically improved integration of the gasifier with the combined cycle plant components (see pp 20-23).

Another area where there seems to be scope for improvement is in the design of gas turbines, at least according to a position paper recently issued by the Brussels based European Turbine Network (ETN). ETN argues that there are currently no turbines available that can provide low NOx and high efficiency on undiluted hydrogen-rich syngas, which is what gasifiers produce. Such turbine technology, developed specifically for IGCC applications and fully optimised for them, rather than adapted from turbines designed to run on natural gas, could play a major role in improving the performance and competitiveness of IGCC. The DOE H2 Turbine Program is aiming to develop just such a new generation of machines in the USA (for use in FutureGen and elsewhere), and such a programme would also be a good use of FP7 R&D funding in Europe.

* Under 2003 Minnesota state legislation designed to provide an incentive to develop an IGCC plant on the Iron Range, the IGCC developer is entitled to enter into a 450 MWe PPA (subject to PUC approval) with what is described somewhat mysteriously in the legislation as “a public utility that owns a nuclear generating facility in the state” – ie Xcel.