The reason why gas for Delimara is now not possible
The writing of Evarist Bartolo on the Delimara power station extension has left a few loose ends. Further arguments about natural gas as a start-up fuel are now futile. The combination of procrastination and the EU deadline for Marsa closure have put paid to that possibility. As of 2010, supplies of natural gas in amounts adequate for electricity generation will not be available before another four or five years.
We now have significant experience of Combined Cycle Gas Turbine (CCGT) technology, but our ‘gas’ turbines are run on diesel oil. This has provided a fall-back position for a power station extension, with a choice of either a second CCGT for Delimara or of medium speed piston engines. The latter offer a choice – a Hobson’s choice some might say – of fuels, once the EU allowed us to modify Legal Notice 329: either diesel or Heavy Fuel Oil (HFO). The latter, while having a hefty price advantage over the former, needs expensive pollution removing equipment for the emissions to conform to EU standards; as well as an efficient method of export of hazardous waste.
Worse than that, it carries with it an ‘environmental deficit’ in the minds of the public, partly the result of past performance of Enemalta in power station pollution control, but also because of somewhat casual treatment of the problem of disposing of the heavy sludge left as a HFO residue. Despite this, Enemalta has committed itself to the use of piston engines burning HFO.
The arguments about the choice of fuel have obscured other aspects of this business. Enemalta has always maintained that piston engines run on HFO will produce cheaper electricity than a CCGT running on diesel, even when costs of pollution control and eventual conversion to gas are included; Evarist Bartolo says otherwise: a CCGT running on diesel will do better. But neither side has produced detailed numbers to back their case, just as neither side has discussed the inherent suitability of the two generating systems for our grid.
In fact, eight piston engines of 18MW each make more technical sense than one large turbine, particularly if our grid has to cope with a significant amount of wind-generated electricity. For while a single turbine will lose efficiency when working at less than maximum power – which it will be at times when there is a relatively low demand and a high output from wind farms – single diesel engines can be switched off in that situation, keeping the rest delivering maximum power at their best efficiency. Incidentally, the piston engines would have an efficiency which would be a few percentage points higher than that of a CCGT, so that for the same fuel, the engines would use less to generate one unit of electrical energy.
To conclude: all arguments about questionable tendering procedures apart, the solution best calculated to satisfy technical as well as environmental and public health requirements seems to be to have the piston engines – which have a ‘combined cycle’ aspect as well, given that a 10MW steam turbine can be operated using the engine exhaust to raise steam – consuming diesel rather than HFO. That would go a long way towards meeting public concern about power station emissions, without compromising the technical advantages. It should not be beyond the ingenuity of Minister Tonio Fenech to find the extra cash that might be needed to cover increased costs of generation, if these do indeed exist. On the other hand, consumers of electrical energy must not be hyper-sensitive to utility charges, once Enemalta can be seen to be pursuing sensible fuel-procurement policies and doing its best to achieve good operational efficiency.
Edward Mallia is a physicist at the University of Malta
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