Бурение грунтовых зондов, установка энергетических колодцев

The most widespread gas turbine cycle is the aircraft engine, which operates an open cycle using essentially air as a working fluid. In power applications the open cycle is mainly used for peak-shaving installations. The flow scheme and the T-s diagram of the Joule cycle are given in Figures 7-14 and 7-15 respectively below. Air (A) is compressed in a compressor, and the pressurized air (B) is used for the combustion of the fuel. The resulting very hot gases (C) then enter the turbine, and the still hot gases (D) are sent to the stack. Although this simple cycle has at best about the same efficiency (43%) as a fairly advanced steam cycle, the efficiency as a percentage of the Carnot potential is about 10% lower (see Table 7-Ю). This problem can be remedied by using the hot gases leaving the gas turbine as a heat source for a steam cycle in a heat recovery steam generator (HRSG). In this case the efficiency increases to almost 60%, which corresponds to over 70% of the Carnot potential.

The flow scheme and the T-s diagram for this combined cycle (CC) is given in Figures 7-16 and 7-17, respectively. In the T-s diagram it is clearly shown that part of the space below the area of the Joule cycle is occupied by a relatively small steam cycle. The ratio of the shaded areas to the area below the upper line of the cycle, which is a measure for the overall efficiency, is thus considerably increased.

The open cycle is used in airplanes and for peak shaving in power stations. Larger and more efficient gas turbines are now entering the marketplace with firing temperatures of about 1500°C. These advanced turbines claim additional economies of scale, reduced capital costs, and higher overall net efficiencies of 45-50% (LHV basis). This illustrates how gas turbine manufacturers have concentrated on higher turbine inlet temperatures. But the efficiency gain achievable by this means has its limits. Taking the Carnot criterion (Figure 7-10) illustrates that increasing the inlet temperature from 1200 to 1500°C will increase the efficiency from 80 to 83%. Assuming a high 60% thereof can be realized, in actual practice this implies that the cycle efficiency will increase by a mere 2%. Further, one should keep in mind that blade cooling and low NOx requirements, which are problems that increase

with temperature, will imply a higher parasitic power consumption, all of which casts some doubt on too great expectations of further increases in gas turbine inlet temperatures.

In base load power stations combined cycles (CC) are generally used. Although the Joule cycle is not very efficient, it has the advantage of a very low capital cost. From the point of view of the Joule cycle it is advantageous to achieve as low a gas outlet temperatures as possible. Typically, the gas outlet temperatures of the gas tur­bine are about 550°C. This is, however, a disadvantage for the steam part of the combined cycle, since high superheat temperatures cannot be achieved. The steam cycle is therefore relatively capital intensive (expressed in dollars per installed kW). The main disadvantage of the use of gas turbines is that only gas and light petroleum distillates can be used as a fuel. To take full advantage of the high efficiency of the CC in combination with dirty feedstocks as coal and heavy oils, these fuels must first be gasified.

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