Typically 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 the intention to fulfill the operational wants of the unit. Please see the attachment for an instance of a Modular HRSG Common Association (Common Association).
Modular HRSGs could also be labeled in quite a lot of methods, together with the route wherein exhaust gases circulation and the variety of strain ranges out there. HRSGs are labeled into vertical and horizontal varieties based mostly on the route of the circulation 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 based mostly on the strain ranges they function at: single strain and multi strain. Single strain HRSGs have only one steam drum and steam is created at a single strain degree, whereas multi strain HRSGs have two (double strain) or three (triple strain) steam drums and generate steam at a number of strain ranges. Due to this, three parts are utilized in triple strain HRSGs: the decrease strain (low strain) part, the intermediate strain (reheat/IP) part, and the upper strain (HP) part. Every portion is comprised of a steam drum and an evaporator part, each of that are liable for the conversion of water to steam. After that, the steam flows by superheaters, which increase the temperature over the saturation level of the water.
It is not uncommon for the steam and water strain sections of an HRSG to expertise quite a lot of deterioration processes, together with creep, thermal fatigue, creep-fatigue, mechanical fatigue, Movement Accelerated Corrosion (FAC), corrosion, and corrosion fatigue, amongst others.
Some HRSGs have auxiliary or duct firing capabilities. These further burners supply better vitality to the HRSG, which ends up in extra steam being produced and, because of this, a rise within the output of the steam turbine. Usually, duct firing produces extra electrical output for a less expensive preliminary funding. Consequently, it’s typically utilized in peaking actions.
Diverter valves might also be utilized in HRSGs to manage the circulation of water coming into the HRSG. This permits the gasoline turbine to proceed to operate even when there isn’t a want for steam or when the HRSG have to be shut down.
Emissions controls might also be discovered within the HRSG, though this isn’t assured. Some might embrace 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 typically must be divided and the SCR will must be put in between the 2 sections. There have currently 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 specific type of HRSG that doesn’t have any boiler drums. The consumption feedwater is routed in a steady course, slightly than being divided into parts for economizers, evaporators, and superheaters. As a result of nice diploma of flexibility offered by this design, the sections are in a position to broaden or shrink in response to the quantity of warmth load obtained from the gasoline turbine. As a result of there aren’t any drums, the steam output might be modified rapidly, and there are fewer variables to manage, making it glorious for cycle and base load functions. Utilizing the appropriate materials choice, it’s doable to function an OTSG dry, which implies that the new exhaust gases might go by the tubes with none water operating by 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 not needed.
Warmth restoration has the potential to be employed extensively in energy-related initiatives. The steam from the HRSG is used to energy desalination amenities within the Persian Gulf space, which has loads of vitality. Universities are glorious candidates for Human Assets 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, giant ocean tankers (such because the Emma Maersk) use warmth restoration expertise.