The Heat Recovery Steam Generator, or HRSG, is configured in various shapes, designs, configurations, arrangements, and so on. To streamline our dialogue herein, we shall 1st say that the kind of HRSG we are now reviewing is what may perhaps be referred to as a water tube(as opposed to a fire tube) sort heat recovery unit. This refers to the process fluid, i.e., the steam or water being on the inside of the tubing with the products of combustion being external of the tube. The products of combustion are typically at or about atmospheric pressure, therefore, the shell side is normally not regarded as to be a pressure vessel.
In the style of any HRSG, the 1st step generally is always to perform a theoretical heat balance which is able to provide us with the correlation of the tube side and shell side process. Before we can calculate this heat balance, one needs to determine the water side components which will make up your HRSG unit. Despite the fact that these elements may perhaps consist of other heat exchange components, right now we will primarily take into consideration the 3 major coil varieties that may be present, i.e., Evaporator, Superheater, and Economizer. Whenever I allude to an Evaporator Section, this encompasses all the evaporator coils making up the complete evaporator for the Pressure System. A pressure circuit consists of all of the components incorporated within the many streams associated with that pressure level.
4.1.3.1 Preheater
Condensate from the condenser is heated in the preheater to a temperature close to the saturation temperature of the deaerator. The preheater inlet temperature is controlled using condensate recirculation. The preheated water is fed to the deaerator/feed water tank.
4.1.3.2 Economizers
The Economizer Section, often known as a preheater or preheat coil, is utilized to preheat the feed water being introduced towards the system to replace the steam (vapor) becoming removed from the method via the superheater or steam outlet and the water loss via blow down. It can be normally located inside the colder gas downstream in the evaporator. Because the evaporator intake and outlet temperature conditions are both near to the saturated steam temperature for the HRSG pressure, the quantity of heat that could be removed from the flue gas is limited on account of the approach to the evaporator, known as the pinch which is explained later, while the economizer inlet temperature is actually low, allowing the exhaust gas temperature to be reduced lower.
The feed water pumps pump feed water from the feed water tank to the IP and HP economizers. In the respective economizers the water is heated close the saturation temperature and fed to the IP or HP drums.
4.1.3.3 Evaporators
The most essential component would, certainly, be the Evaporator Section, given that without this component (or coils), the unit would not be an HRSG. an evaporator section might consist of 1 or more coils. In these coils, the water/steam flowing through the tubing is heated to near the steam saturation point for the operating pressure it can be at. The HRSG contains three evaporator systems, one for each pressure level. Fig. (4.5) shows HRSG water circulation methods.
4.1.3.4 Superheaters
The Superheater Section of the HRSG is utilized to dry the saturated vapor becoming separated within the steam drum. In some units it may perhaps only be heated to small above the saturation point where in other units it may well be superheated to a substantial temperature for additional energy storage. The Superheater Section is commonly situated in the hotter gas stream, in front of the evaporator. Saturated steam from the drum is fed to the superheaters where it is superheated. The HP superheated steam temperature is controlled by an inter-stage attemperator. The attemperator is located in between two superheater sections. The HP steam is fed to the steam turbine. The IP steam is mixed with the cold reheat steam and fed to the reheater. The LP superheated steam is fed to the deaerator/feed water tank and to the LP section of the ST.
4.1.3.5 Reheaters Cold reheat steam returning from the outlet of the HP stage of the steam turbine is mixed with the IP superheated steam and fed to the reheater where additional heat is added increasing the temperature before it is fed to the IP part of the steam turbine. The outlet temperature is controlled by an inter-stage attemperator.
4.1.3.6 Lp, Ip & Hp Steam Drum
Economizer water is fed to the drum through a feed water distribution pipe, which distributes the feed water evenly over the length of the drum, below the water level. The drum water is fed to the evaporator through the down comers.
The steam/water mixture coming from the evaporator enters the drum in the primary steam separator (baffle type), where water and steam are separated. Before leaving the drum, the steam passes the secondary separator (wire mesh type) and leaves the drum through the saturated steam line, and prevents water droplets to be carried over to the superheater under normal operating conditions. The drum as shown in Figure (4.6) is designed with a storage volume of water to produce steam for a certain time during failure of feed water supply. This so called hold-up time is (minimum values as calculated): • 3.0 minutes for HP • 8.3 minutes for IP • 11.4 minutes for LP
In the style of any HRSG, the 1st step generally is always to perform a theoretical heat balance which is able to provide us with the correlation of the tube side and shell side process. Before we can calculate this heat balance, one needs to determine the water side components which will make up your HRSG unit. Despite the fact that these elements may perhaps consist of other heat exchange components, right now we will primarily take into consideration the 3 major coil varieties that may be present, i.e., Evaporator, Superheater, and Economizer. Whenever I allude to an Evaporator Section, this encompasses all the evaporator coils making up the complete evaporator for the Pressure System. A pressure circuit consists of all of the components incorporated within the many streams associated with that pressure level.
4.1.3.1 Preheater
Condensate from the condenser is heated in the preheater to a temperature close to the saturation temperature of the deaerator. The preheater inlet temperature is controlled using condensate recirculation. The preheated water is fed to the deaerator/feed water tank.
4.1.3.2 Economizers
The Economizer Section, often known as a preheater or preheat coil, is utilized to preheat the feed water being introduced towards the system to replace the steam (vapor) becoming removed from the method via the superheater or steam outlet and the water loss via blow down. It can be normally located inside the colder gas downstream in the evaporator. Because the evaporator intake and outlet temperature conditions are both near to the saturated steam temperature for the HRSG pressure, the quantity of heat that could be removed from the flue gas is limited on account of the approach to the evaporator, known as the pinch which is explained later, while the economizer inlet temperature is actually low, allowing the exhaust gas temperature to be reduced lower.
The feed water pumps pump feed water from the feed water tank to the IP and HP economizers. In the respective economizers the water is heated close the saturation temperature and fed to the IP or HP drums.
4.1.3.3 Evaporators
The most essential component would, certainly, be the Evaporator Section, given that without this component (or coils), the unit would not be an HRSG. an evaporator section might consist of 1 or more coils. In these coils, the water/steam flowing through the tubing is heated to near the steam saturation point for the operating pressure it can be at. The HRSG contains three evaporator systems, one for each pressure level. Fig. (4.5) shows HRSG water circulation methods.
4.1.3.4 Superheaters
The Superheater Section of the HRSG is utilized to dry the saturated vapor becoming separated within the steam drum. In some units it may perhaps only be heated to small above the saturation point where in other units it may well be superheated to a substantial temperature for additional energy storage. The Superheater Section is commonly situated in the hotter gas stream, in front of the evaporator. Saturated steam from the drum is fed to the superheaters where it is superheated. The HP superheated steam temperature is controlled by an inter-stage attemperator. The attemperator is located in between two superheater sections. The HP steam is fed to the steam turbine. The IP steam is mixed with the cold reheat steam and fed to the reheater. The LP superheated steam is fed to the deaerator/feed water tank and to the LP section of the ST.
4.1.3.5 Reheaters Cold reheat steam returning from the outlet of the HP stage of the steam turbine is mixed with the IP superheated steam and fed to the reheater where additional heat is added increasing the temperature before it is fed to the IP part of the steam turbine. The outlet temperature is controlled by an inter-stage attemperator.
4.1.3.6 Lp, Ip & Hp Steam Drum
Economizer water is fed to the drum through a feed water distribution pipe, which distributes the feed water evenly over the length of the drum, below the water level. The drum water is fed to the evaporator through the down comers.
The steam/water mixture coming from the evaporator enters the drum in the primary steam separator (baffle type), where water and steam are separated. Before leaving the drum, the steam passes the secondary separator (wire mesh type) and leaves the drum through the saturated steam line, and prevents water droplets to be carried over to the superheater under normal operating conditions. The drum as shown in Figure (4.6) is designed with a storage volume of water to produce steam for a certain time during failure of feed water supply. This so called hold-up time is (minimum values as calculated): • 3.0 minutes for HP • 8.3 minutes for IP • 11.4 minutes for LP
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