Gas-powered gensets have pick of fuel options: engine generator sets running on natural and other gases are renowned for their versatility. In part two of this feature our Special Correspondent checks out the many applications that are now possible--and takes a peek into the future.

ONE OF THE most widely applied uses of gas-powered generating sets has been in the combined heat and power field. Some generating sets are designed from the outset for the expanding CHP market and gas engines or gas turbines are normally used.

For example, Caterpillar's G3500C and G3500E series--burning either natural gas, landfill or biogas--have been designed for extended-hours distributed generation and CHP applications. They provide one of the highest power densities available, and at up to 43.5 per cent thermal engine efficiency also provide a lower electricity cost. With a CHP system using both heat and electrical power--almost 50/50--and exhaust heat use, thermal efficiency up to 90 per cent has been achieved.

CHP systems are used for a multitude of applications wherever a gas supply is provided. Examples such as tomato growing, with dozens of such installations in the Netherlands and the UK, for hospitals where the heat is used for kitchens, laundry and central heating in addition to electrical independence, swimming pools where again the heat output is well used, can all be cited. Some factories now use CHP such as the motor industry in the UK and in France where the Peugeot Mulhouse factory uses ten Cummins 12-cylinder engines running on natural gas.

Local heating for communities with district heating networks is used where the gas supply is either free or the offshoot of a gaseous process. Rolls Royce has one of their own B-gas engines producing over 5 MW in Denmark for such a scheme. With Nigeria still flaring off some gas this could be utilised as electrical energy.

Other applications include locations where gas is surplus to requirements such as refineries, gas pipelines, landfill sites and at wellheads. Petrochemical plants are very large consumers of heat and gas and many have gas-powered generation stations on-site, although the larger installations use high-output gas turbines. One unusual cogeneration plant operates in Brussels, Belgium where Cummins supplied two 1.36MW gas-powered generators for the Electrabels Distribution Centre, who are the country's main distributor of gas and electricity. Heat from the Cummins engines' exhaust is used to preheat gas that arrives by pipeline up to a suitable temperature prior to feeding a large gas turbine.

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In the San Alberto Gas Field in Bolivia, Cummins also supplied three 1.25MW gas-powered generating sets powered by their QSV91G 18-cylinder engines. Fed from the incoming pipeline, two generators provide 2.5MW to drive gas distribution pumps. The third set is on permanent standby.

Landfill gas

On the same continent is a gas site in Sao Paulo, Brazil. The power source consists of 24 Caterpillar GS3516 generating sets each rated at 925kW, all located in one building. The landfill site receives 7000 tons of waste daily, about half of the 16mn population from the city. Built 30 years ago it now contains 30mn tons of waste.

The resultant gases were originally flared off. In a spirit of global warming-prevention, the city of Sao Paulo opted to bring in Biogas, the company that operates the landfill gas collection system. This comes from 200 vertical drains and 43km of piping which produces 12,000 [m.sup.3] of gas per hour. The 22MW of electrical power supplies 250,000 in the city and is likely to do so for the next 25 to 30 years.

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Another 'free gas' use has been at a coal mine in Scandinavia, where seven Jenbacher gas engines produce 12MW of electrical power fed from coal-mine gas, also known as 'firedamp'. The main component of this gas is methane (25-60 per cent) which develops during the geochemical conversion of organic substances into coal (carbonisation). Closed mines produce a source of high-quality gas which emerges from fissures, faults and pores and in the coal itself. Up to 100m3 of mine gas per ton of coal is liberated during mining. By using this gas, which is very heavy compared to carbon dioxide, some global warming is averted, saving 35,000 t/year of CO2 based on the generators working 8000 hours a year. In Spain a company installed 26 gas-engined generators for a CHP system using gas from their steel industry--gases coming from the coke ovens.

Bio fuels

Market research reports suggest that the European biomass power plant markets earned US$1,685mn in 2005 and are likely to reach US$2,204mn in 2012.

"The parallel needs of emission reduction and energy generation have increased the focus on renewable energy sources," says Frost & Sullivan Industry Manager Rajat Kumar. It is the European Union's target of achieving 12 per cent contribution to total power production using renewable sources that is driving this market.

Biomass-fuelled power plant needs to be near to 'feedstock' sites and are thought able to produce up to 30 MW at one site using gas engine-powered generating sets. A popular feed is likely to be E-grass, also called elephant grass. It is fast growing, reaching a height up to 3.5m in a period of five to six years. One project in the UK is designed to burn E-grass and is expected to supply electricity for some 2,000 homes (approximately 10 MW). Another benefit from burning grass is that the carbon dioxide when released is simply absorbed by the new grass which needs it for growing.

Brazil has been converting sugarcane into fuel and even Rudolf Diesel stated that "the use of vegetable oil for engine fuel may seem insignificant today [1900], but such oils may in the course of time become as important as petroleum and the tar products of the present day."

Wartsila has been carrying out research using rape seed and palm oil and has installed generating sets running off bio-oil for Italgreen Energy in Italy. And in the UK Caterpillar's distributor Finning Power Systems installed 2.3MW of green electricity for the Thames Water Long Reach Sewage Treatment Works near London.

This utilises the methane gas given off by the treatment process and provided as fuel for two Caterpillar sets both of which are fully hardened for running on aggressive bio-gas. The CHP system provides all the electricity for the Dartford site, running 24/7 and remotely monitored by Finning's service centre.

Future trends

Gas, like oil, will eventually run out. The supply is finite and already we are consuming something like four barrels of oil for every new one now being discovered. We are consuming electricity at a four per cent a year growth rate and only producing enough power station capacity to meet just three-quarters of this new demand. The world is power hungry and newly-developing countries throughout for example Africa, have only just got started as major consumers.

The world has about half a century to wake up and find an alternative solution. Renewable sources such as elephant grass, wind, tides, geothermal and waste gases will be unlikely to meet anywhere near the total new demand, even with the best will in the world.

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Electrical storage would help, although limited to specific locations. Fuel cells will certainly be one of the main solutions and are already becoming a commercial reality in small kW sizes at present--but 1MW units are not far away. These may, with paralleling, eventually be able to produce up to 10MW installations but for the really large 200-400-600MW power stations currently being used the volume of fuel, in what ever shape or form, is likely to be difficult to find if not impossible. Nuclear power is probably the only alternative left for this required new capacity of electrical output. Back to the 1960's ... but what is going to fuel the jumbo aircraft of tomorrow? Power rationing will probably be necessary in the future if the remaining fossil fuel reserves have to be carefully conserved for essential uses--whatever these are deemed to be.

Cases of power production crises are already upon us. From drought cases in Africa causing power rationing to Norway where a shortfall in electrical power has prompted the authorities to consider 120 mobile gas-powered generating sets. Consisting of individual 4 to 10MW units, two such stations each of 800 MW will be installed to meet a power deficit of over 1500MW by 2010. What happened to the massive hydro capacity from the mountains of Scandinavia?

Gas turbines currently power 15 to 20 per cent of total installed global capacity. But demand is increasing by 1GW every three days--and this is expected to continue for the next 30 years.

Novel energy

Other novel forms of energy are being used by Shell in Norway to build the world's largest project using carbon dioxide from power generators to enhance oil recovery in an offshore oil and gas field. The CO2 is pumped into the area holding oil and gas and will store 2-2.5mn tons annually.

This will help to increase oil recovery, as after 15-20 years of extraction the natural pressure and oil production drops. This system will recreate the natural gases and at the same time the gas-powered generating sets will have zero C[O.sup.2] and NOx emissions from this plant.