Usually talking, HRSGs are composed of 4 key parts: the economizer, the evaporator, the superheater, and the water preheater[clarification required]. The varied parts of the unit are assembled with a purpose to fulfill the operational wants of the unit. Please see the attachment for an instance of a Modular HRSG Normal Association (Normal Association).
Modular HRSGs could also be labeled in quite a lot of methods, together with the route through which exhaust gases movement and the variety of stress ranges accessible. HRSGs are labeled into vertical and horizontal varieties primarily based on the route of the movement of exhaust gases. Vertical HRSGs have exhaust gasoline that flows vertically over vertical tubes, and horizontal HRSGs have exhaust gasoline that flows vertically over horizontal tubes. HRSGs could also be divided into two teams primarily based on the stress ranges they function at: single stress and multi stress. Single stress HRSGs have only one steam drum and steam is created at a single stress degree, whereas multi stress HRSGs have two (double stress) or three (triple stress) steam drums and generate steam at a number of stress ranges. Due to this, three parts are utilized in triple stress HRSGs: the decrease stress (low stress) part, the intermediate stress (reheat/IP) part, and the upper stress (HP) part. Every portion is comprised of a steam drum and an evaporator part, each of that are chargeable for the conversion of water to steam. After that, the steam flows by means of superheaters, which enhance the temperature over the saturation level of the water.
It’s common for the steam and water stress sections of an HRSG to expertise quite a lot of deterioration processes, together with creep, thermal fatigue, creep-fatigue, mechanical fatigue, Circulate Accelerated Corrosion (FAC), corrosion, and corrosion fatigue, amongst others.
Some HRSGs have auxiliary or duct firing capabilities. These further burners provide higher vitality to the HRSG, which ends up in extra steam being produced and, consequently, a rise within the output of the steam turbine. Generally, duct firing produces extra electrical output for a less expensive preliminary funding. Because of this, it’s usually utilized in peaking actions.
Diverter valves may be utilized in HRSGs to manage the movement of water coming into the HRSG. This allows the gasoline turbine to proceed to perform even when there isn’t any want for steam or when the HRSG have to be shut down.
Emissions controls may be discovered within the HRSG, though this isn’t assured. Some might embody a Selective Catalytic Discount system to lower nitrogen oxides (that are a big contributor to the event of smog and acid rain) and/or a catalyst to extract carbon monoxide from the ambiance. Due to the presence of an SCR, the HRSG’s total configuration is considerably altered. Optimum efficiency of the NOx catalyst is achieved at temperatures of between 650 levels Fahrenheit (340 levels Celsius) and 750 levels Fahrenheit (400 levels Celsius). To do that, the evaporator a part of the HRSG will usually should be divided and the SCR will should be put in between the 2 sections. There have these days been a number of low-temperature NOx catalysts launched to the market, permitting the SCR to be positioned between the Evaporator and Economizer sections (350°F – 500°F (175-260°C)).
The once-through steam generator is a selected type of HRSG that doesn’t have any boiler drums. The consumption feedwater is routed in a steady course, reasonably than being divided into parts for economizers, evaporators, and superheaters. As a result of nice diploma of flexibility supplied by this design, the sections are in a position to develop or shrink in response to the quantity of warmth load acquired from the gasoline turbine. As a result of there aren’t any drums, the steam output could be modified rapidly, and there are fewer variables to control, making it glorious for cycle and base load purposes. Utilizing the correct materials choice, it’s attainable to function an OTSG dry, which implies that the recent exhaust gases might go by means of the tubes with none water operating by means of them. A bypass stack and exhaust gasoline diverter system, that are wanted to run a combustion turbine whereas a drum-type HRSG is out of service, are now not mandatory.
Warmth restoration has the potential to be employed broadly in energy-related initiatives. The steam from the HRSG is used to energy desalination services within the Persian Gulf space, which has numerous vitality. Universities are glorious candidates for Human Sources Technique Group submissions. They might make use of a gasoline turbine to generate energy with nice dependability for utilization on the campus. The HRSG might use the warmth recovered from the gasoline turbine to generate steam or sizzling water to be used in district heating or cooling programs. As a way to permit their oil-fired boilers to be shut down when at sea, massive ocean tankers (such because the Emma Maersk) use warmth restoration expertise.