Combined-cycle gas steam turbine power plants free download

In cogeneration plants CHP studied in Chapter 18, problems arise in a similar manner, especially if steam needs at medium and high pressure are important. In a combined cycle plant, the vein of hot gases exiting the gas turbine must be cooled by water of the steam recovery cycle. In a single pressure cycle, water enters the heat exchanger in the liquid state at about 30 C after being compressed by the feedwater pumps downstream of the condenser.

It is heated at the boiling temperature corresponding to its pressure economizer , then vaporized at constant temperature and superheated before being expanded in the steam turbine. The diagram in Figure The associated enthalpy diagram shows that if we set for technical reasons a pinch minimum value temperature difference between both luids between points 6 and 9 on the one hand, and between points 4 and 11 on the other hand, heat exchanges take actually place with much larger differences in nearly all of the heat exchanger.

The example in Figure Hot gases exit the gas tur- bine at C and maximum pressure of the steam cycle is equal to bar. In these circumstances it is impossible to cool gases below C, which represents a signiicant loss.

Other losses are spread fairly evenly among the various components and exhaust. In descending order, they take place in the air compressor, gas turbine, steam turbine, economizer, evaporator, superheater, exhaust and condenser. Manufacturers continue in their efforts to reduce them, and very signiicant progress has already been made in recent decades.

Therefore opportunities for improvement are becoming fewer. Losses in the HRSG and those in the exhaust are linked, as we have already seen. They represent Their reduction is therefore an important issue. The ideal heat exchange corresponds to the case where the curve of gas cooling and that water of heating would be parallel.

The heat exchanger would then operate in counter-low and irrevers- ibility would be minimal. This is not feasible with water, and the single pressure cycle has strong internal irreversibilities. To improve the cycle performance, we use multiple steam cycles at different pressure levels two, three or even four. Figure In all three cases, the grey surface represents work provided for the same heat input in the gas turbine.

The rectangle in the dashed line is the Carnot cycle. The gain provided by the increased number of pressure levels is very clear, but designing the HRSG is a complex optimization problem and quite new, which does not arise in conventional boilers.

The optimization of such cycles is a complex problem, because to get the better cooling of the hot gas stream, there are many degrees of freedom on the pressure levels, on the corresponding low rates, and on placement of heat exchangers in series or in parallel. This optimization problem is quite new.

It did not arise in old power plants, in which very large irreversibilities occurred for technical and economic reasons related to the thermal resistance of steel boilers and sulfur content of fumes. There is no proven method to solve it. The optimization method presented in Chapter 22, known as Systems Integration, is the exten- sion to the case of power generation or cogeneration plants, of the pinch method developed in the context of chemical engineering to optimize the coniguration of very large exchanger networks such as those of a reinery.

They will be presented in Chapter 24 of Part 4. Two of them are particularly interest- ing and can yield high eficiencies, because the heat exchange with the exhaust gases is made with very low irreversibility: the humid air cycle and the Kalina cycle. In the humid air cycle, the air leaving the compressor is humidiied in a saturator with water heated by exhaust gases. It leaves the saturator cooled and is then preheated in a regenerator before being directed to the combustion chamber and then into the turbine.

This cycle looks a little like a steam injection cycle, but its performance is much better. The Kalina cycle is a combined cycle variation where water is replaced by a water-ammonia mix which vaporizes and condenses with a temperature glide. Furthermore, many variations are possible in combined cycles: for example it is possible in the gas turbine, to make an intermediate cooling during compression, or a reheat. More complex cycles are under investigation. Their detailed presentation is beyond the scope of this book: we limit our- selves to some thermodynamic considerations on a key combined cycle component: the recovery steam generator.

For other developments, the reader may refer to the thesis of H. Abdullah referenced at the end of Chapter Finally, we will study in the next chapter cogeneration plants, for simultaneous production of mechan- ical power and heat, among which will appear some variants of the combined cycles considered above.

It is therefore easier to locate them close to consumption areas. One major limitation is that gas turbines require the use of clean fuel expensive , such as natu- ral gas or light distillates, which excludes the use of heavy fuel oil or coal, traditional basic fuels for power plants. Title: Gas--steam turbine combined cycle power plants. Full Record Other Related Research. Abstract The purpose of this technology evaluation is to provide performance and cost characteristics of the combined gas and steam turbine, cycle system applied to an Integrated Community Energy System ICES.

Authors: Christian, J. Publication Date: Research Org. Christian, J. Gas--steam turbine combined cycle power plants. United States: N.