The power plant consists of basic components like a boiler, turbine, condenser, and pump. Each component serves a basic function in the power plant.
Condensers are heat exchangers that convert the extracted steam from the turbine into liquid form without changing temperature and pressure. They are usually categorized into two types, i.e., based on direction flow(Parallel flow, counter flow, and cross flow) and cooling action(jet and surface type condenser).
The surface condenser is a close heat exchanger where the steam extracted from the turbine is condensed by giving off its latent heat to the cooling water.
Here steam and cooling water don’t come in contact with each other and are called indirect heat exchangers. Here the condensate we get is entirely pure and can be used directly in the boiler. This condenser is mainly used in places with limited good-quality water, like ships or land installations.
Parts Of The Surface Condenser.
The surface condenser is a cylindrical shape condenser. It comprises the following components.
The shells are the outer part of the surface condenser and consist of tubes and baffles. The shell is usually airtight and is made from cast iron.
The cooling water flows inside the tubes. These tubes are placed parallel inside the cylindrical shape surface condenser.
The tubes are divided into upper and lower sections—the cooling water flow in opposite directions in the upper and lower section.
The water entering the surface condenser is used twice to condense the steam. That is why the surface condenser is known as a double-pass surface condenser. The tubes are mainly made from stainless steel.
3. Extraction Pump
In the surface condenser, the extracted steam from the turbine enters from the top side of the cylindrical vessel and condenses on the downside. An air extraction pump is in between the upper and lower section of tubes to suction the steam. It is present only in the central flow surface condenser.
4. Coolant Water Valve
Coolant water valves are in the surface condenser from where the cooling water can enter and leave the surface condenser.The cooling water inlet valve is at the bottom of the cylindrical surface condenser. The impure water goes out from the top of the surface condenser.
It supports the tubes inside the surface condenser and controls the flow direction inside the tubes.
6. Two Vertical Tube Plates
Two vertical tubes on both sides of the surface condenser hold the horizontal tubes properly.
7 Rapture Disc
A rupture disc is present on the top of the surface condenser. It is used for safety purposes when the pressure inside the condenser increases. The pressure may increase due to multiple reasons like air leakage or an increase in the level of the hot well as a result of which the accumulation of non-condensable gas increases.
So for such a situation, a rapture disk is installed in the surface condenser which breaks when the pressure inside the surface condenser reaches 1kg/cm2 or 2kg/cm2 and the pressure inside the surface condenser is released.
Working Of Surface Condenser
The cold water from the cooling tower enters from the inlet valve of the surface condenser. It first enters into the lower section of the horizontal tubes.
The cooling water goes from one shell’s end to the other. It then rises and flows in the opposite direction in the upper section of the tubes. There is an outlet water valve where the water returns again to the cooling tower.
A steam inlet is at the top of the cylindrical vessel or surface condenser. The exhaust steam from the turbine enters through it and flows outside the tubes.
As a result, the cooling water flowing inside the horizontal tubes absorbs the latent heat from the steam. Now the water leaving from the surface condenser will be hot.
The steam will change its phase, i.e., convert into liquid form without changing its temperature and pressure.
The condensate will finally be collected in the hot well by the condensate extraction pump. It is called a hot well because the water collected here is hot. The hot well level is always maintained at a 50 percent level. A level transmitter installed in the hot well will show the hot water level present in the hot well.
A feed pump is located just below the hot well, which transfers the hot water into the boiler.
Noncondensable gases accumulate when the steam is condensed into the liquid inside the cylindrical vessel. The noncondensable gases are rejected outside through the ejector.
There is a ruptured disc present at the top of the cylindrical vessel. The pressure inside the surface condenser may sometimes rise because of numerous reasons. For example, it may be because of air leakage or the level of hot water can increase because of malfunctioning the condensate pump.
The rupture disc is a safety device that raptures at a specific pressure to prevent excess pressure build-up inside the surface condenser.
The temperature between water entering inside the surface condenser and leaving water should be 10o Celsius. It is the reason why the volume of the surface condenser is quite large. Again in this condenser, a large amount of water is needed to condense the exhaust steam coming from the turbine.
Efficiency Of Surface Condenser:–
The efficiency of the surface condenser is defined as the ratio of the rise in temperature of the cooling water inside the condenser to the difference between the vacuum temperature and cooling water inlet temperature.
For better efficiency of the Surface Condenser following parameters has to be maintained:-
|Cooling Water Temperature
|Outlet temperature of cooling water
|Vacuum gauge pressure
To calculate the vacuum pressure, first absolute pressure (Pa) is to be calculated:-
Absolute pressure (Pa)= Atmospheric pressure – Vacuum Gauge Pressure ( Pr )…… (2)
We know that atmospheric pressure = 1.0322
and vacuum gauge pressure =0.92
Absolute Pressure (Pa )= 1.0322 – 0.92
= 0.1122 …. (3)
From the standard table, we get the vacuum temperature for Pa = 0.1122 is 48ocelsius. This temperature has to be maintained for better efficiency.
ηCondenser = [ (40o-32o) / (48o-32o)] * 100 = 50% ….. (4)
So, 50% efficiency in surface condenser can be achieved by maintaining above parameters.
Advantages Of Surface Condenser
- High Vacuum efficiency
- Pure condensate is obtained, which can be fed directly to a boiler.
Disadvantages of Surface Condenser
- More water is required.
- The surface condenser requires ample floor space.
- Complex design
- Maintainance cost is high
Types Of Surface Condenser
There are usually four types of surface condenser which is listed below.
- Downflow surface condenser
- Central flow surface condenser
- Evaporative surface condenser
- Regenerative surface condenser
1. Downflow surface condenser
In a downward flow surface condenser, the water enters from the lower section of the tubes and then moves to the upper section tubes. The direction of the water flow between the upper and lower section tubes is opposite.
The steam flows from the top part of the surface condenser over the horizontal tubes, and then the condensate steam is collected in a hot well. An extraction suction pump is located at the bottom of the surface condenser, sending the condensate steam further to the boiler.
The steam flows from the top to the bottom of the surface condenser, called a downward flow surface condenser.
2. Central Flow Surface Condenser
Central flow surface condenser is an improved version of downward flow surface condenser. It works on the same principle as the downflow surface condenser, but here, there is an air extraction pump located at the center of the surface condenser so that the flow of the stem will be towards the center.
The steam flows inwardly over the horizontal tubes, hence the radial flow surface condenser.
3. Evaporative Surface Condenser
The design of an evaporative surface condenser is entirely different from the downward surface condenser and central flow surface condenser. There are serpentine shape grilled tubes inside this condenser. The exhaust steam from the turbine enters from one end of the grilled tubes.
There is even a colling pond where cool water is stored. The cool water rises through the pump, and the nozzle sprays water in the mist over the tubes, carrying exhaust steam from the turbine. At the same time, the air even enters from the bottom of the surface condenser and flows over the tubes.
As a result, the steam flowing inside the tubes gives off its latent heat to the water and finally condenses to liquid form without change in pressure and temperature.
There is a condensate pump that extracts the condensate. It is then fed to the boiler with the help of a feed pump. The heated water is now cooled by the air supplied inside the evaporative condenser.
4. Regenerative Surface Condenser
The regenerative surface condenser is a special surface condenser that uses regenerative methods to improve efficiency. After leaving the tubes, the condensate is further heated by the exhaust steam coming from the turbine or engine. The temperature of the condensate increases, and then it is directly fed to the boiler.
One advantage of using a regenerative surface condenser is that amount of fuel required to heat the feed water in the boiler will be less. Thus it saves the energy of the powerplant.
Applications Of Surface Condenser
1. Refrigeration And Airconditioning
Surface condensers are extensively used in Central air condition units or refrigeration plants. The vapor refrigerant enters the surface condenser and finally condenses into liquid form. It then enters the evaporator and cools the surrounding air.
2. Thermoelectric power plants
The surface condenser is extensively used in power plants, including nuclear and thermal power plants. The surface condenser condenses the steam from the turbine, and then pure, quality water is fed directly to the boiler.
3. Industrial Plants
Surface condensers are used in various industries like food processing and petrochemical refineries where steam is used.
4. Desalination plants
Surface condenser plays a vital role in Desalination plants. These plants convert seawater into fresh and clean water.
We have discussed surface condensers, their types, and their applications above. You can ask in the comment section if you have any queries.