Fuel For Combined Cycle Power Plants
The turbines used in Combined Cycle Plants are commonly fueled with natural gas. Global natural gas reserves were expected to be fully consumed by 2070, however the improvement in shale gas extraction has increased gas supplies and reserves dramatically. Because of this fact, it is becoming the fuel of choice for an increasing amount of private investors and consumers because it is more versatile than coal or oil and can be used in 90% of energy applications. Chile which once depended on hydro-power for 70% of its electricity supply, is now boosting its gas supplies to reduce reliance on its drought afflicted hydro dams. Similarly China is tapping its gas reserves to reduce reliance on coal, which is currently burned to generate 80% of the country’s electricity supply.
Where the extension of a gas pipeline is impractical or cannot be economically justified, electricity needs in remote areas can be met with small scale Combined Cycle Plants, using renewable fuels. Instead of natural gas, Combined Cycle Plants can be filled with biogas derived from agricultural and forestry waste, which is often readily available in rural areas.
Combined cycle plants are usually powered by natural gas, although fuel oil, synthesis gas or other fuels can be used. The supplementary fuel may be natural gas, fuel oil, or coal. Biofuels can also be used. Integrated solar combined cycle power stations combine the energy harvested from solar radiation with another fuel to cut fuel costs and environmental impact. The first such system to come online is Yazd power plant, Iran and more are under construction at Hassi R'mel, Algeria and Ain Beni Mathar, Morocco. Next generation nuclear power plants are also on the drawing board which will take advantage of the higher temperature range made available by the Brayton top cycle, as well as the increase in thermal efficiency offered by a Rankine bottoming cycle.
Low-Grade Fuel for Turbines: Gas turbines burn mainly natural gas and light oil. Crude oil, residual, and some distillates contain corrosive components and as such require fuel treatment equipment. In addition, ash deposits from these fuels result in gas turbine deratings of up to 15 percent. They may still be economically attractive fuels however, particularly in combined-cycle plants.
Sodium and potassium are removed from residual, crude and heavy distillates by a water washing procedure. A simpler and less expensive purification system will do the same job for light crude and light distillates. A magnesium additive system may also be needed to reduce the corrosive effects if vanadium is present. Fuels requiring such treatment must have a separate fuel-treatment plant and a system of accurate fuel monitoring to assure reliable, low-maintenance operation of gas turbines.
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