Another concept that is being studied is the humidified air turbine (HAT) cycle. This is an intercooled, regenerated cycle with a saturator that adds a considerable amount of moisture to the compressor discharge as shown in Fig. 1.20. The combustor inlet contains 20-40% water vapor, depending on whether the fuel is natural gas or gasified […]

One of the variations in cogeneration systems using gas turbines is the Cheng cycle. This system is ideal for plants with varying electrical and steam loads. It consists of a gas turbine with an HRSG, which has a superheater, evaporator, and economizer (Fig. 1.19). A duct burner is located between the superheater and evaporator. The […]

Several teams of large companies in the United States are developing a coal-fired high performance system, also called HIPPS. In this combined cycle plant, a fluid bed air-blown pyrolyzer converts coal into fuel gas and char. The char is fired in a high temperature advanced furnace, which heats up both air for a gas turbine […]

Before going into this option, one should clearly understand when multiple — pressure options are justified. From the discussion on HRSG simulation, it can be seen that the exit gas temperature in an HRSG depends on the steam pressure and temperature. The higher the steam pressure, the higher the exit gas temperature. Hence when high […]

Because single-pressure HRSGs are not very efficient, one may consider adding secondary surfaces such as as a deaerator coil or condensate heater or a heat exchanger as shown in Fig. 1.18 To lower the stack gas temperature.

The advantages of fired HRSGs were discussed earlier. Firing increases the steam generation and lowers the HRSG exit gas temperature with a fuel utilization of nearly 100%. The additional fuel fired increases the HRSG duty by the same amount compared to, say, 92% in a steam generator.

Pinch and approach points determine HRSG temperature profiles. If we have to work with only a single-pressure HRSG and there is no additional heat recovery equipment such as a deaerator coil or condensate heater, we can use low pinch and approach points to maximize steam generation. However, the surface area requirements increase due to the […]

By nature, HRSGs are inefficient, particularly the unfired units, because of the large gas mass flow associated with the low exit gas temperature from the gas turbine. The large mass flow forces one to use a boiler with a large cross section, though the steam generation may not be compatible with the size of the […]

The HRSG simulation concept is helpful in predicting the performance of an HRSG at various modes of operation. The HRSG need not be designed to perform this study. Figure 1.17a Shows a multiple-pressure HRSG used in a combined cycle plant with nine modules. Module 1 superheater is fed by module 3, which consists of a […]

Exhaust gas flow from a gas turbine is 250,000 lb/h at 1000°F. Gas analysis in percent by volume (vol %) is CO2 = 3, H2O = 7, N2 = 75, and O2 = 15. Super­heated steam is generated at 600 psia at 875°F, and about 20,000 lb/h of saturated steam is required for process, which […]