Typically talking, HRSGs are composed of 4 key parts: the economizer, the evaporator, the superheater, and the water preheater[clarification required]. The assorted parts of the unit are assembled to be able to fulfill the operational wants of the unit. Please see the attachment for an instance of a Modular HRSG Basic Association (Basic Association).
Modular HRSGs could also be categorised in quite a lot of methods, together with the course wherein exhaust gases stream and the variety of stress ranges out there. HRSGs are categorised into vertical and horizontal varieties based mostly on the course of the stream 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 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 superheaters, which increase 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, Move Accelerated Corrosion (FAC), corrosion, and corrosion fatigue, amongst others.
Some HRSGs have auxiliary or duct firing capabilities. These additional burners supply larger power to the HRSG, which leads to extra steam being produced and, consequently, a rise within the output of the steam turbine. Basically, duct firing produces extra electrical output for a less expensive preliminary funding. Consequently, it’s typically utilized in peaking actions.
Diverter valves may additionally be utilized in HRSGs to manage the stream of water getting into the HRSG. This allows the gasoline turbine to proceed to operate even when there is no such thing as a want for steam or when the HRSG have to be shut down.
Emissions controls may additionally be discovered within the HRSG, though this isn’t assured. Some could embrace a Selective Catalytic Discount system to lower nitrogen oxides (that are a major 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 general 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 selected type of HRSG that doesn’t have any boiler drums. The consumption feedwater is routed in a steady course, fairly 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 increase 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 could be modified shortly, and there are fewer variables to control, making it glorious for cycle and base load functions. Utilizing the fitting materials choice, it’s attainable to function an OTSG dry, which implies that the new exhaust gases could cross 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 now not obligatory.
Warmth restoration has the potential to be employed extensively in energy-related initiatives. The steam from the HRSG is used to energy desalination services within the Persian Gulf space, which has quite a lot of power. Universities are glorious candidates for Human Assets Technique Group submissions. They could make use of a gasoline turbine to generate energy with nice dependability for utilization on the campus. The HRSG could use the warmth recovered from the gasoline turbine to generate steam or sizzling water to be used in district heating or cooling techniques. As a way to enable their oil-fired boilers to be shut down when at sea, massive ocean tankers (such because the Emma Maersk) use warmth restoration expertise.