Usually talking, HRSGs are composed of 4 key elements: the economizer, the evaporator, the superheater, and the water preheater[clarification required]. The assorted elements of the unit are assembled with a view 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 categorized in a wide range of methods, together with the path during which exhaust gases circulate and the variety of stress ranges obtainable. HRSGs are categorized into vertical and horizontal varieties primarily based on the path of the circulate 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 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 accountable for the conversion of water to steam. After that, the steam flows by means of superheaters, which increase the temperature over the saturation level of the water.
It is not uncommon 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, Movement Accelerated Corrosion (FAC), corrosion, and corrosion fatigue, amongst others.
Some HRSGs have auxiliary or duct firing capabilities. These further burners provide larger power to the HRSG, which ends up in extra steam being produced and, in consequence, 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 usually utilized in peaking actions.
Diverter valves might also be utilized in HRSGs to regulate the circulate of water getting into the HRSG. This allows the fuel turbine to proceed to operate even when there is no such thing as a want for steam or when the HRSG should be shut down.
Emissions controls might also 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 environment. 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 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, reasonably 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 fuel turbine. As a result of there are not any drums, the steam output might be modified rapidly, and there are fewer variables to control, making it glorious for cycle and base load purposes. Utilizing the best materials choice, it’s potential to function an OTSG dry, which implies that the recent exhaust gases might cross by means of the tubes with none water working by means 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 needed.
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 plenty of power. Universities are glorious candidates for Human Assets Technique Group submissions. They might make use of a fuel turbine to generate energy with nice dependability for utilization on the campus. The HRSG might use the warmth recovered from the fuel turbine to generate steam or sizzling water to be used in district heating or cooling methods. To be able to permit their oil-fired boilers to be shut down when at sea, giant ocean tankers (such because the Emma Maersk) use warmth restoration know-how.