Gas turbine combined cycle

An important field of study for power plants is that of the combinedplant [ 1 ]. A broad definition of the combined power plant (Fig. 1.5) is one in which a higher (upper or topping) thermodynamic cycle produces power, but part or all of its heat rejection is used in supplying heat to a lower or bottoming cycle. The upper plant is frequently an open circuit gas turbine while the lower plant is a closed circuit steam turbine together they form a combined cycle gas turbine (CCGT) plant. 

Davidson, BJ. and Keeley, K.R. (1991). The thermodynamics of practical combined cycles, Proc. Instn. Mech. Engrs. Conference on Combined Cycle Gas Turbines, 28-50. 

Fig. B.5. Effect of carbon dioxide lax on electricity price for a combined cycle gas turbine plant.

In recent years there has been a rapid growth in the number of combined heat and power (CHP) and combined cycle gas turbine (CCGT) plants, driven mainly by gas turbines using natural gas, sometimes with liquid fuel available as stand-by. Governments have encouraged the construction of these plants, as their efficiency is high and they produce less carbon dioxide than conventional coal and oil-burning power stations. However, they present some hazards, as gas turbines are noisy and are therefore usually enclosed. 

Restructuring will promote the introduction of other advanced technologies and practices as well. For example, the use of combined-cycle, gas turbine power plants are expected to proliferate under restructuring. These plants are generally more efficient and more environmentally benign than many fossil fuel plants currently in use. 

In open cycle, the diesel has the higher efficiency, making it more attractive for light fuel oils. However, in combined cycle, the gas turbine often has the highest overall efficiency, but there is the penalty associated with the additional cost for boiler and turbine. Nevertheless, unless the prime fuel is of low cost, the use of combined-cycle gas turbine plant will prove to be the more economic. 

The required oxygen is produced in an air-separation plant. The electricity for the air-separation plant is provided by a natural-gas fuelled combined-cycle gas turbine (CCGT) power plant. 

In contrast, the yield of electricity from photovoltaics (PV) is about 337 500 kWh per ha and year, even if it is assumed that the area of the PV panels cover about one-third of the total plant area. If PV electricity were converted to liquid hydrogen (LH2), stored and then converted back to electricity by a combined cycle gas turbine (CCGT, efficiency 57.5%) about 104000 kWh electricity could be generated per ha and year. This yield is still more than three times the yield of the best biomass pathway (upper end of bandwidth electricity from biogas via large gas engine). 

Compressed-air energy storage Corporate average fuel economy California Air Resources Board Coal-bed methane Combined cycle gas turbine Carbon/carbon dioxide capture and storage Clean development mechanism Chlorofluorocarbon Computable general equilibrium Compressed gaseous hydrogen Combined heat and power... 

The main drivers for the utilization of natural gas in power sector is twofold 1) emission reduction by shifting fuel from oil and/or coal to gas, and 2) the possibility of introducing combined cycle gas turbine (CCGT) technology with high electric efficiency (58 %). 

Different generation technologies produce different levels of C02 emissions, and therefore the opportunity costs of C02 emissions per unit of power produced differ as well. For example, a combined-cycle gas turbine produces about 0.48 t of C02 per MWh of electricity, while a typical coal power station emits about 0.85 tC02/MWh. A C02 price of 20/tCO2, therefore, increases the generation costs for the gas plant by 9.6/MWh and for the coal plant by l7/MWh. 

Most phase I NAPs provide for NE allocations based on a general emission rate and predicted activity level. For example in The Netherlands (NL), new entrants are allocated allowances based on projected output or fixed cap factor multiplied by uniform emission rate in line with that of a combined-cycle gas turbine (CCGT). In France, Germany and Poland, C02-intensive power generators, such as coal-fired installations, receive the highest number of allowances per kW installed. The literature highlights the risk that NE provisions can create distortions (Harrison and Radov, 2002). In order to illustrate how these rules can impact electricity prices and C02 emissions in our GB simulations, we focus on two approaches one based on a uniform benchmark and one based on a fuel-specific benchmark. In both cases the forecast capacity factor of new entrants is fixed at 60%. 

In our simplified model we assume that the highest prices are set by demand side response or open cycle gas turbines, followed by combined-cycle gas turbines with high variable and low fixed costs, and coal-fired power stations with low variable and high fixed costs. We compare two cases. First, the system is small relative to the EU emission-trading scheme and the EU C02 price is not affected by changes in national emissions of C02. Second, the model represents the entire EU ETS, and we set a fixed C02 budget and endogenously determined C02 price. 

Recent very successful demonstrations of the high efficiencies that can be achieved with combined cycle gas turbine-steam turbine power plants using pressurized, fluidized... 

Unlike molten carbonates, solid oxides use a hard ceramic electrolyte instead of a liquid. That means the fuel cell can be cast into a variety of useful shapes, such as tubes. With higher temperatures, sofcs may be able to cogenerate steam at temperatures as high as i,ooo°f. The Siemens Westinghouse Power Corporation has built the first advanced hybrid system, which combines a gas turbine with a tubular sofc. As of 2003, the 220 kW hybrid system has operated in California for more than 2,000 hours with a respectable 53 percent efficiency, comparable to current combined cycle gas turbines. The ultimate goal is an efficiency of 70 percent or more. 

The present treatment of the conventional process will be based on the process diagram presented in Figure 1, which represents a steam reformer coupled with an ammonia synthesis plant [6], This is one of the two cases, which were considered in the project. The other was the use of the produced hydrogen as fuel in combined cycle gas turbines. In this chapter, the steam reforming part will be treated only, but some comments on the ammonia plant will be made, in view of the composition of the product stream leaving the steam reformer. 

In the 1980s, fundamental changes took place in the state-owned sector with the so-called privatization of the industry. First in Chile, then in the UK, the assets of the publicly-owned electricity authorities were vested in companies which issued equity shares to the general public. This change in ownership was coupled with a fundamental shift in the way electricity was produced and sold. New, cheaper, technologies such as gas-fired, combined cycle, gas turbine plant, which could be built more quickly than the traditional coal-fired steam turbine plant, and which is less labour intensive in its operation, was introduced extensively in the UK. The separate producers of electricity competed with each other on price (per kWh) to win market share. It is alleged, with some justification in the UK, that such competition has reduced the price to the end-user. 

A transfer provision was initially drafted for new plants which had been built to replace old plants. If the operators complied with the requirement of the three-month (without any further examination) to the two-year period (if the respective verifications could be provided) from the closure of the old plant and the opening of the new plant, the allocation to the old plants would be transferred to the new plants without restrictions, provided that the new plants produced comparable products. In addition to the transfer rule - which was considered as a standard - there should be a rule that provides additional new plants (as well as plant expansions) a free allocation on the basis of the planned capacity use and an emission benchmark. The emission benchmark should be orientated towards BAT procedure. Above all, it should not be differentiated by fuel or technologies. As far as electricity production is concerned, a benchmark orientated towards a modern natural gas-fired combined cycle gas turbine (CCGT) power plant (365 g CCh/kWh) was scheduled. The allocation calculated in this way should be subject to an ex-post adjustment in the course of the following years. Thus, a special procedure was scheduled for CHP plants. The allocation should be determined with the help of the benchmark for electricity generation as well as the benchmark for heat generation. 

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