Typically talking, HRSGs are composed of 4 key elements: the economizer, the evaporator, the superheater, and the water preheater[clarification required]. The varied elements of the unit are assembled in an effort 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 a wide range of methods, together with the course through which 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 fuel that flows vertically over vertical tubes, and horizontal HRSGs have exhaust fuel 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 answerable for the conversion of water to steam. After that, the steam flows by way of 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 a wide range 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 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. In consequence, it’s typically utilized in peaking actions.
Diverter valves may additionally be utilized in HRSGs to regulate the stream of water getting into the HRSG. This allows the fuel turbine to proceed to operate even when there isn’t any 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 embody 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 environment. 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 should be divided and the SCR will should be put in between the 2 sections. There have recently 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, quite than being divided into parts for economizers, evaporators, and superheaters. Because of the 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 fuel turbine. As a result of there are not any drums, the steam output may be modified shortly, and there are fewer variables to manage, making it glorious for cycle and base load purposes. Utilizing the appropriate materials choice, it’s potential to function an OTSG dry, which signifies that the new exhaust gases could move by way of the tubes with none water operating by way of them. A bypass stack and exhaust fuel diverter system, that are wanted to run a combustion turbine whereas a drum-type HRSG is out of service, are 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 amenities within the Persian Gulf space, which has quite a lot of vitality. Universities are glorious candidates for Human Sources Technique Group submissions. They could make use of a fuel turbine to generate energy with nice dependability for utilization on the campus. The HRSG could use the warmth recovered from the fuel turbine to generate steam or scorching water to be used in district heating or cooling techniques. To be able 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.