REGENERATIVE FEED WATER HEATING SYSTEM
REGENERATIVE FEED WATER HEATING SYSTEM
In regenerative feed water system steam is bled from the turbine from various stages and is made to give up its latent or any super-heat to the condensate in a heat exchanger, this system is called regenerative system.
What is Regenerative Feed Heating?
A small portion of steam expanding through the turbine is bled off from different stages of turbine before reaching condenser and used to heat feed water in the feed water heaters.This is called regenerative feed heating system.
Why Regenerative Feed water heating?
Loss of work that could have been obtained by expanding the extracted steam in the turbine (because of if we expand more steam from the turbine then after doing work this steam condensed in the condenser due to which its losses latent heat after condensation).
Reduction in the energy supplied in the boiler (reduction of coal required in boiler which release energy after burning) to raise the temperature and pressure of the feed water.
Heat gained in this way outweighs the loss of mechanical power but ae get much efficiency because of in it energy flow in a closed cycle.
There is a reduction in the amount of Cooling water required which results in the reduction in pumping power.
if we not take bleading from turbine
and whole heat comes out from lp turbine than mare water is required for
cooling this steam.
Surface Type :-
Here feed water is passed through tubes with bled steam surrounding them. In it water and steam does not mix together. After heat transfer both fluid leave the feed water heater from seprate line. In modern Power plant several numbers of closed type feed water are used.
Here feed water is passed through tubes with bled steam surrounding them. In it water and steam does not mix together. After heat transfer both fluid leave the feed water heater from seprate line. In modern Power plant several numbers of closed type feed water are used.
Direct contact type :-
Here steam and water is mixed together. In it both fluid are mixed and leave together from same line. In modern Power plant minimum one open type feed water is used.
Here steam and water is mixed together. In it both fluid are mixed and leave together from same line. In modern Power plant minimum one open type feed water is used.
Various components of the feed water heating system involve in a thermal power plant. Most of these are dual function i.e. these system work primary their function and then secondary is feed heating.
In a power plant feed heating is devided in to two parts as according to working pressure as:-
Low pressur feed water system
High pressure feed water system
Low pressure feed water system also called as condensate system and high pressure feed water water system is called as boiler feed water system.
Different components of regenerative feed water system.
Ejector:-
The purpose of ejector is evacuate air and other non condensing gasses from the condenser and thus maintain the vacuum inside the condenser.
In Power plant there are two types of ejectors are used.
1:-Main ejector.
2:-Starting ejector.
Working principle:-
Steam is supplied at a pressure of 4.5 to 5 kg/sq.cm to the 2 or 3 nozzles. Steam expands in the nozzles thus giving a high velocity eject which creates a low pressure zone in the throat of the ejector. This throat is connected to the air suction line of condenser so it suck the air from the condenser. The working steam which expanded in volume after flowing through a diffuser come in contact with cluster of tube through which condensate is flowing and get condesed. In these tubes condensate water is flowing which absorb the heat of steam & noncondensable gases. This process is again repeated two times.
Steam is supplied at a pressure of 4.5 to 5 kg/sq.cm to the 2 or 3 nozzles. Steam expands in the nozzles thus giving a high velocity eject which creates a low pressure zone in the throat of the ejector. This throat is connected to the air suction line of condenser so it suck the air from the condenser. The working steam which expanded in volume after flowing through a diffuser come in contact with cluster of tube through which condensate is flowing and get condesed. In these tubes condensate water is flowing which absorb the heat of steam & noncondensable gases. This process is again repeated two times.
The non condensing gas of air are then further sucked with the 2nd stage of nozzle of the ejector then 3rd stage and finally air with small quantity of steam is exhausted into the atmosphere through the outlet.
Now a days in large size units ejector are eliminate and vacuum pumps are used in place of ejector.
1. Starting ejector :-
It is used for accelerating the initial pulling of vacuum.
It is used for accelerating the initial pulling of vacuum.
It operates in parallel with the main ejector.
When vacuum pressure reaches 500-600 mm of Hg column, the starting ejector is switched off.
When vacuum pressure reaches 500-600 mm of Hg column, the starting ejector is switched off.
In it there are no any condensation takes place and discharge of ejector is dumped directly to the atmosphere.
Generally this is used when light-up processes is carried out.
2. Main ejector :-
Main ejector with a standby unit is usually provided for normal operation.
Nunber of stages in a main ejector depends upon the cooling water condition.
There are two numbers of main ejectors named as ejector-A and ejector-B. One ejector is running while other is standby available.
CEP
The function of these condensate extraction pumps is to pumps out the condensate to the deaerator thrugh ejectors, gland steam cooler, and L.P. heaters.
This pump is a multistage pump.
So also called as turbine type pumps.
It's suction is under negative pressure . So special arrangement is provided for providing sealing of pump. It's sealing is done by water.
For the sealing water are taken from two sources. One is from makeup line which is used at starting time. Second is from discharge header which is used when pump is running. Both are make common line with NRV. When pump started thne sealing line from makeup is closed and due to pressure difference.
Gland steam cooler (GSC)
Type-1 :- It cools the air-steam mixture sucked from the turbine end seals by the flow of condensate from the condenser .
Construction details:-
It is of vertical type and has two sections.An ejector is mounted on the cooler which maintains constant vacuum in the first section and sucks the remaining air steam mixture to second section where air is let off and steam is condensed.
A part of main condensate, after main ejector, flows through cooler tubes consisting of U-shaped brass tubes rolled in steel tube plate.
Drain from this cooler is then led to condenser.
Type:-2 in this type of Gland steam condenser a blower or fan is mounted direct to the shell.
Construction details:-
It is of vertical type and has two sections.An ejector is mounted on the cooler which maintains constant vacuum in the first section and sucks the remaining air steam mixture to second section where air is let off and steam is condensed.
A part of main condensate, after main ejector, flows through cooler tubes consisting of U-shaped brass tubes rolled in steel tube plate.
Drain from this cooler is then led to condenser.
Type:-2 in this type of Gland steam condenser a blower or fan is mounted direct to the shell.
This fan is maintained a negative pressure in the gland steam condenser.
This gland steam condenser is connected to the last glant chamber of the turbine end. Due to negative pressure in side the gland steam condenser steam-air mixture is sucked and condenser in to the GSC.
After condensation condesed water is goes back to condenser and non condensable gas are vented out with the help of fan in to the atmosphere.
DRN Cooler (DRAIN COOLER)
Low Pressure Heaters
A Feedwater heater is a component used to pre-heat water delivered to the boiler. Preheating the feedwater reduces the amount of energy needed to make steam and thus reduces plant operation costs. This improves the thermodynamic efficiency of the system.
Turbine has been provided with non-controlled extractions which are utilised for heating the condensate, from turbine bleed steam. There are 3 or 4 low pressure heaters in which steam is extracted from LP turbine.
A Feedwater heater is a component used to pre-heat water delivered to the boiler. Preheating the feedwater reduces the amount of energy needed to make steam and thus reduces plant operation costs. This improves the thermodynamic efficiency of the system.
Turbine has been provided with non-controlled extractions which are utilised for heating the condensate, from turbine bleed steam. There are 3 or 4 low pressure heaters in which steam is extracted from LP turbine.
Deaerator
Deaerator is a device for air removal from water to make it non-corrosive. Deaerator generally implies not only the deaerator but also the feed water tank below where deaerated water is stored and fed to the suction of boiler feed pumps.
The presence of certain gases, principally oxygen, carbon-dioxide and ammonia, dissolved in water is generally considered harmful because of their corrosive attack on metals, particularly at elevated temperatures.
Deaerator is a device for air removal from water to make it non-corrosive. Deaerator generally implies not only the deaerator but also the feed water tank below where deaerated water is stored and fed to the suction of boiler feed pumps.
The presence of certain gases, principally oxygen, carbon-dioxide and ammonia, dissolved in water is generally considered harmful because of their corrosive attack on metals, particularly at elevated temperatures.
Function of Deaerator is to remove the noncondensable gases from the water. The process of removing noncondensable gases are called as deaeration and it is mechanical process.
For deaeration inndeaerator steam is supplied from following source
APRDS.
CRH line.
Turbine extraction.
.....
Principle of Deaeration:
Henrys law: The mass of gas with definite mass of liquid will dissolve at a given temperature and is directly proportional to the partial pressure of the gas in contact with the liquid. This holds within close limits for any gas, which does not unite chemically with the solvent.
Pa =Ma/(Ms + Ma)
Pa= partial pressure of air
Ma= mass of air
Ms= mass of steam
Solubility Law: Solubility of gases decreases with increase m solution temperature and/or decrease in pressure.
In Deaerator there are several instruments and transmitters are installed.
The deaerator comprises of two chambers:
Deaerating column.
Feed storage tank.
High Pressure Heaters
After the deaerator water is pumped by the Boiler feed pumps near and above the boiler drum pressure. This high pressure feed water is taken through the high pressure feed water heating system which is the last stage of the regenerative feed water heating.
Steam bled from the turbine stages is introduced in the H.P. heaters where it gives up its heat to the feed water.
The H.P. heaters are connected in series. The condensed steam from the last heater is either cascade through the previous heaters or given to the deaerator through a set of interlocked valves depending on the pressure conditions inside the heaters.
These are regenerative feed water heaters operating at high pressure and located by the side of turbine.
HP heaters are connected in series such that the feed water, after feed pump enters the HP heaters.
The steam is supplied to these heaters from the bleed-off point from the turbine through motor operated valves.
There are two HP heaters, may have a group bypass protection on the feed waterside.
The H.P. heaters are connected in series. The condensed steam from the last heater is either cascade through the previous heaters or given to the deaerator through a set of interlocked valves depending on the pressure conditions inside the heaters.
These are regenerative feed water heaters operating at high pressure and located by the side of turbine.
HP heaters are connected in series such that the feed water, after feed pump enters the HP heaters.
The steam is supplied to these heaters from the bleed-off point from the turbine through motor operated valves.
There are two HP heaters, may have a group bypass protection on the feed waterside.
Feed water flows through the tube spirals and is heated by steam around the tubes in the shall of the heaters.
These heaters are cylindrical vessels with welded dished ends and with integrated, de-superheating, condensing and sub cooling sections.
The internal tube system of spirals is welded to the inlet and outlet headers.
Following fittings are generally provided on the HP heaters:
Gauge glass for indicating the drain level.
Pressure gauge with three way cock.
Air Vent cock.
Safety valve shell side.
Seal pot.
Isolating valves.
High level alarm switch.
These heaters are cylindrical vessels with welded dished ends and with integrated, de-superheating, condensing and sub cooling sections.
The internal tube system of spirals is welded to the inlet and outlet headers.
Following fittings are generally provided on the HP heaters:
Gauge glass for indicating the drain level.
Pressure gauge with three way cock.
Air Vent cock.
Safety valve shell side.
Seal pot.
Isolating valves.
High level alarm switch.
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