The steam parameters of combined cycle and cogeneration plants differ signifi­cantly. Combined cycle plants typically use unfired HRSGs and generate multiple — pressure-level steam with a complex arrangement of heating surfaces to maximize energy recovery. Fired HRSGs in combined cycle plants are often the exception to the rule owing to their impact on cycle efficiency […]

Today’s cogeneration plants have both HRSGs and packaged steam generators. To generate a desired quantity of steam efficiently, the load vs. efficiency character­istics of both the HRSG and steam generator should be known. Although the generation of steam with the least fuel input is the objective, it may not always be feasible, for reasons of […]

It is generally believed that combined cycle plant efficiencies with fired HRSGs are lower than those with unfired HRSGs. The reason is not the poor performance of the HRSG. In fact, a fired HRSG by itself is efficient. However, the large losses associated with the Rankine cycle, particularly when the steam turbine power is a […]

Supplementary firing is an efficient way to increase the steam generation in HRSGs. Additional steam in the HRSG is generated at an efficiency of nearly 100% as shown in Q8.38. Typically, HRSGs in combined cycle plants are unfired and those in cogeneration plants are fired. The merits of auxiliary firing in HRSGs are discussed in […]

Combined cycle plants today operate in sliding pressure mode; if extraction steam is desired at a given pressure for process reasons, then a constant pressure may be required at the steam turbine inlet. Typically the steam pressure is allowed to float by keeping the turbine throttling valves fully open and ensuring full arc admission. The […]

Generally gas turbines perform poorly at low loads, which affect not only their [11, 12] performance but also that of the HRSG located behind them. Because of the low exit gas temperature at lower loads, the HRSG generates less steam and also has the potential for steaming in the economizer. Table 1.4 Shows the exhaust […]

The power output of a gas turbine without inlet air temperature cooling or conditioning suffers at high ambient temperature owing to the effect of lower air density, which in turn reduces the mass flow of air. The power output could drop by as much as 15-25% between the coldest and hottest temperatures. The exhaust gas […]

Though combined cycle plants based on natural gas (Fig. 1.9a) are widely used, with the increasing cost of natural gas several coal gasification technologies are gaining acceptance. The technology is proven, and there are several plants in operation throughout the world. The advantages of integrated coal gasification combined cycle (IGCC) are Ability to use of […]

In order to handle the high firing temperatures, in the range of 2500-2600°F, gas turbine suppliers are doing research and development work on turbine blades for protection against corrosion and thermal stresses. Thermal barrier coatings have been used on turbine blades for several years. The base high alloy material ensures the mechanical integrity, while the […]

Evaporative cooling boosts the output of the gas turbine by increasing the density and mass flow of the air. Water sprayed into the inlet air stream cools the air to Table 1.2 Typical Combined Cycle Plants Simple cycle data System 7FA 9FA 6FA W501F Simple cycle output, kW 159,000 226,500 70,140 187,000 Simple cycle heat […]