077

Figure 7.9 Steam turbine part-load/speed correction curves. Courtesy Elliot Co.

Figure 7.8 Approximate steam turbine efficiency chart for multistage steam turbines (>3,000 kW. Courtesy Elliot Co.

Figure 7.9 Steam turbine part-load/speed correction curves. Courtesy Elliot Co.

d) Hence, the waste heat recovery steam generator should be able to generate about 185,000 lb/hr. A unit with a 200,000 lb/hr nominal capacity will likely be specified.

Example 3. Find the ASR and steam flow required when the turbine of Example 2 is operated at 14,800 kW and 4,500 RPM.

From Figure 7.9 the power correction factor is 1.04 and the speed correction factor is 1.05. Then, the total correction factor is:

high pressure steam is generated to be subsequently expanded in a steam turbine-generator; this constitutes the so called combined cycle (See Fig 7.4).

If the demand for steam and/or power is even higher, the exhaust gases are used (1) as preheated combustion air of a combustion process or (2) are additionally fired by a "duct burner" to increase their heat content and temperature.

Recent developments include combined cycle systems with steam injection or STIG—from the HRSG to the gas turbine (Cheng Cycle)-to augment and modulate the electrical output of the system. The Cheng Cycle allows the cogeneration system to handle a wider range of varying heat and power loads.

All these options present a greater degree of CHP generation flexibility, allowing a gas turbine system to match a wider variety of heat-to-power demand ratios and variable loads.

Therefore, the part-load ASR is 7.68 lb/kWh

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