HRSG design features
The HRSG generates steam, the quality and quantity of which depend on the flow and temperature of the exhaust gas entering it. Large co-generation and combined-cycle plants generate high-pressure/high-temperature superheated steam (600-1,500 psig at 650-950°F), while small capacity plants (10-MW gas turbines and below)
may generate low-pressure saturated steam (100-300 psig).
The superheated steam temperature in a HRSG is controlled using spray desuperheaters as in conventional boilers. Steam temperature varies with gas inlet conditions, so performance should be
verified at various off-design cases.
Multiple-pressure steam generation is employed in cases where the exit gas temperature from single-pressure-level
generation would be considered too high or uneconomical.
There are three types of HRSGs: unfired, supplementary-fired, and exhaust-fired Figures.
. This is not a rigid classification, but it is widely used. The main features and the typical steam outputs that can be
expected for each of the three types. Figure also shows a freshair-firing system, where a supplementary-fired
HRSG is operated using air from a fan, a situation that arises, for example,when the gas turbine trips or is shutdown for maintenance. Figure 4c shows a typical duct burner for asupplementary-fired HRSG.
The HRSG generates steam, the quality and quantity of which depend on the flow and temperature of the exhaust gas entering it. Large co-generation and combined-cycle plants generate high-pressure/high-temperature superheated steam (600-1,500 psig at 650-950°F), while small capacity plants (10-MW gas turbines and below)
may generate low-pressure saturated steam (100-300 psig).
The superheated steam temperature in a HRSG is controlled using spray desuperheaters as in conventional boilers. Steam temperature varies with gas inlet conditions, so performance should be
verified at various off-design cases.
Multiple-pressure steam generation is employed in cases where the exit gas temperature from single-pressure-level
generation would be considered too high or uneconomical.
There are three types of HRSGs: unfired, supplementary-fired, and exhaust-fired Figures.
. This is not a rigid classification, but it is widely used. The main features and the typical steam outputs that can be
expected for each of the three types. Figure also shows a freshair-firing system, where a supplementary-fired
HRSG is operated using air from a fan, a situation that arises, for example,when the gas turbine trips or is shutdown for maintenance. Figure 4c shows a typical duct burner for asupplementary-fired HRSG.