Cycle plants combined as a solution to the growing energy demand

To meet the increase in the demand for electric power, Spanish power system has prompted the development of renewable energies, including wind and solar that, given their cost, capacity and variability of supplythey can not cope reliably to the important growth of demand for the next few years. This circumstance, together with the commitments signed by the Spanish Government in the Kyoto Protocol, confer an imperative character to the introduction of technologies that work with fossil fuels whose efficiency is much greater and whose emissions make it a cleaner technology. Therefore, combined-cycle thermal power stations are a great alternative, as they are able to provide the electrical system of the safety and reliability.

Technology of combined cycle electric generation is one of the most efficient, with less environmental impact, and for this reason, it is already widespread in the world. It's a system that will be replacing with renewable energy, to the already traditional, with a consequent reduction of emissions. Environmental characteristics, given that their specific emissions for each kWh of electricity generated are much lower that those produced by conventional thermal plants, this technology is supported and driven by the State Spanish in its multiannual planning of the electricity and gas sectors and the own European esstadosthat they recognize the need to increase the capacity of generation according to criteria of respect for the environment.

Technology of combined for electric power generation cycle is that harmonizes better efficiency and environmental respect, because it combines the direct potential of burning, usually natural gas, and steam obtained by reuse of the waste gases from the combustionstill hot to generate electricity. That is, from a single primary energy source, usually natural gas, is obtained electricity in two stages. The first is based on gas turbine, which directly generates electricity from the combustion. And the second, which re-uses the energy contained in the remaining hot gases of the first phase to generate steam, which is used by steam turbine to generate more electricity in a heat recovery boiler. The combined efficiency of the whole process is between 55% and 60%, compared to the 30% to 40% of electric power plants that use a single stage of transformation of the energy contained in fuel.

Basically, a combined cycle is composed of a gas turbine, a boiler for heat recovery, a steam turbine, a capacitor and an electrical generator or alternator, as well as any related ancillary services required (rest of plant) to obtain a system capable of producing electricity. Combined cycle thermal power plants can be classified according to the type of fuel used and, on the other hand, depending on configuration and its main equipment available.

Considering the type of fuel used, combined cycle plants can be natural gas, diesel, or mixed, though he is usually prefers the use of natural gas as the cleanest fossil fuel available: it contains no sulphur and produces fewer CO₂ for the same energy generated (smaller relation C/H). Thus, in the case of combined cycle plants are mixed, the fuel used base practically at all times of operation will be natural gas and alternative fuel, which exclusively recourse in case of emergency, will be the diesel. As for your configuration, a combined cycle plant can have one or more gas turbines, connected to its own boiler heat recovery which, in turn, feed paths or a single steam turbine. And according to the number of main axes that comprises a group of combined cycle, a new classification based on the provision of the pillars of gas and steam turbines, if they are in the same line and trailers or not can bespeaking in this case monoeje and multiaxis configuration.

How does a combined cycle plant?

The process of generation of electricity in a combined cycle plant begins with the admission of air from the outside, which is led to the gas turbine compressor, through successive stages of filtering, to be compressed andthen mixed with the fuel, usually natural gas in the combustion chamber. In this, after start and keep the combustion process, occurs continuously the oxidation of the fuel in the presence of oxygen. The result is a stream of hot gases that expand, spin the gas turbine providing useful work; an alternator allows you to transform such useful work in electricity.

The exhaust gas which are expelled from the turbine of gas (600 ° C) preserved still an important part of the thermal energy gained in combustion, approximately 60%, by what passed for its use to the heat recovery boilerwhere most of the heat still available in the exhaust gases is removed producing steam from water pressure in the conditions required for the steam turbine. They are later driven to the chimney of evacuation, where they are released into the atmosphere at a much lower temperature (between 90 ° C and 100 ° C).

The steam coming out of the steam turbine is a condenser where it is transformed into water. This condenser is cooled by air or water, so that you get the dissipation of latent heat in the steam to the cooling water or the atmosphere. Subsequently, resulting condensation water is pumped to high pressure until the recovery boiler to start again the water-steam cycle.

Against the conventional thermal power stations, based on the combustion of coal or fuel oil, combined cycles using natural gas as a fuel base. In response to specific emissions per kWh of electricity generated, if it is next to the use of natural gas as a fuel base the effect of high efficiency, the advantage provided by the combined cycles is clear in comparison with the conventional generation from coal or fuel oilallows to achieve average reductions of up to 60% in emissions of carbon dioxide, up to 57% in the oxides of nitrogen and the practical elimination of sulfur compounds and particles; all of this to obtain a same amount of electrical energy. Thus recognized in countries with strict regulations to protect the environment, where the consumption of natural gas is growing in applications where contamination is reduced.

To generate a same amount of electricity, the combined cycles needed for up to 35% less than consumption of fuel than conventional power stations and water consumption reduced front of those (1/3 of what it consumes a simple cycle of fuel or coal plant) because the gas turbine does not need of any cooling and water for the water-steam cycle is required. Currently, NOx emissions are controlled in the cycles combined by the use of premix burners by dry process of low NOx and CO emissions through complete reaction in the combustion chamberwhich is achieved through the selection of a few teams with the proper design, the use of monitoring and control systems. With regard to the emissions that are generated, various effluents are treated before discharge. Solid waste and liquids are few in this type of installation, and most of them come from keeping or waste water treatment. When they cannot be treated in the systems installed in the plant, are delivered to an authorised Manager. On the other hand, in the combined cycles there are noise sources such as fans, pumps, turbines, steam systems, cooling towers and transformers, which comply with existing labour and environmental legislation. The criteria for noise mitigation include venues with special measures attenuation and silencers at the entrance of air and exhaust gases exit.

The combined cycles require under time limits construction and delivery than conventional thermal power stations, as well as lower initial investment, allowing to reduce the repayment terms. There is a great modularity and standardization in its design, which gives uniformity to the technology. In addition, they have greater flexibility operational and, thereby, smaller times of starting and stopping and increased capabilities of regulation, and require less space and smaller building, allowing to reduce its visual impact and territorial.

The National Plan of allocation of emissions provides a greater generation with natural gas and renewable energy sources to reduce the generation with coal and fuel oil, less efficient and more polluting. The forecast until 2012 considers a reduction of 3.7% annually in the use of coal and an increase of 9% per year in the natural gas. For this reason, are currently in Spain more than 40 groups combined working cycle or forthcoming entry into service.

The example of Natural Gas as a bet on the combined cycle

The strategy of the Group Natural Gas in power generation business is focused on having a mix of production balanced, competitive and respectful with the environment, based on combined cycles and renewable energies, and in line with the objectives of the Kyoto Protocol. The recent integration in the Natural Gas group in the Electrical Union Fenosa, does that at this time the Group has consolidated its position within the Spanish electricity market.

At the moment the company has 7,600 MW operating in combined cycle with its ten centers in the flat of the Vent (Tarragona, 800MW); Palos de la Frontera (Huelva, 1,200 MW); Campo de Gibraltar (Cádiz, 800 MW-) 50% with Cepsa-; Sant Adrià de Besòs (Barcelona, 400 MW); San Roque (Cádiz, 400 MW); Arrúbal (La Rioja, 800 MW); Cartagena (Murcia, 1,200 MW); Sagunto (Valencia, 1,200 MW); Sabón (A Coruña, 400 MW); and Aceba (Toledo, install). Also, the company is in building a combined cycle of 400 MW in Malaga and two groups, 800 MW in total, in the port of Barcelona, is expected to come into operation during 2010.