What Is Steam Condenser?
Steam condensers are a mechanical device that converts low-pressure exhaust steam from a turbine into water. Or in other words, it is a device used to condense turbine exhaust steam into water. It does this with the help of cold water circulating in it from the cooling tower.
It works to achieve two main objectives. To supply pure water to the hot well and water from the hot well is again pumped into the boiler with the help of a boiler feed pump. To maintain pressure below the atmospheric pressure at the outlet of the steam turbine so as to obtain the maximum possible energy.
A steam condenser is a closed vessel heat exchanger that is used to convert low-pressure steam into water. The pressure inside a steam condenser is kept below atmospheric pressure to increase efficiency.
A steam condenser is a closed vessel that is maintained at a lower pressure, lower than atmospheric pressure. The condenser acts as heat exchangers where heat is exchanged between steam and cold circulating water. In this system, heat rejection occurs at atmospheric temperature by condensing the steam emanating from the prime mover.
Condensate can be reused as feed water to the boiler. Condensate can be supplied to the boiler through a high-capacity feed pump. The hot water coming out of the condenser is pumped into the cooling tower so that it cools down and supplies it to the condenser.
The process is repeated over and over. The thermal’s efficiency of the plants can be improved by the use of condensers. A steams condensers is a closed vessel in which steams are cooled by water and condensed by dissipating heat and where the pressure remains below atmospheric pressure.
The condensed steam is known as condensate. The use of condensers increases the efficiency of the steam power plant. A steam condenser is an essential component of all modern steam power plants.
Working Principle of Steam Condenser:
Inside the steam condenser, there is a flow of cooling water that continuously flows from the condenser to the cooling tower and from the cooling tower to the condenser. So when the exhaust comes from a low-pressure steam turbine and passes through the condenser, it (steam) condenses into the water; because the steam loses heat, the heat extracted from the steam is passed through the circulating cooling water.
There are two types of equipment on the condenser, one is the condensate extraction pump, and the other is the air extraction pump. And through an air-extraction pump, a vacuum is created inside the condenser so that cold water can easily circulate and also stabilize the flow of the condensate.
So when steam is condensed into water, it is again circulated in a steam generator with the help of a condensate extraction pump. This is the basic phenomenon of how steam condensers work; in the next part, we will look at the classification of steam condensers and how each type of condenser works.
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Types of Steam Condensers:
The steam condenser is broadly classified into two types:
- Surface condenser (or non-mixture type condenser).
- Jet condenser (or mixing type condenser).
#1. Surface Condenser
The surface condensers are designed to condense and deactivate the steam coming out of the main turbine and provides a heat sink for the turbine bypass system. There are no direct contacts between the exhaust stream and cold water in the surface condenser.
The steam coming out of the LP turbines is condensed by passing over the tubes containing water from the cooling system. Steam, when exposed to the cold surface of tubes and condenses due to the transfer of heat to cold water by conduction & convections.
This tube is usually made of stainless steel, copper alloy, or titanium-based on several selection criteria such as thermals conductivity or corrosion resistance. Titanium condenser tubes are generally the best technical choice; however, titanium is a very expensive material, & the use of titaniums condensers tubes is associated with a very high initial cost.
In generals, there are two types of surface condensers: waters-cooled surface condensers, air-cooled surface condensers. In thermal power plants, where cooling waters are in short supply, an air-cooled condenser may be used. An air-cooled condenser, however, is significantly more expensive and cannot achieve a lower steam turbine exhaust pressure and temperature than a water-cooled surface condenser.
The hot water in the condenser is released into the cooling systems, i.e., cooling tower, river, sea, or cooling pond. Condensates collected from these condensers are reused as feedwaters in the boiler. Since cold water and steam do not mix, condensate is reclaimed, and any type of cold water can be used. Compared to jet condensers, a higher vacuum can be maintained in the surface condenser; therefore, the greater thermal efficiency can be achieved.
On the other hand, surface condensers are heavier, require a larger area, and higher capital costs. But this capital cost can be recovered by saving the cost of running better thermal efficiency (i.e., higher). Thus, these condensers are best suited for modern thermal power plants.
They are commonly used where a large amount of substandard water is available, and better quality feedwater is supplied to the boiler.
Downflow Surface Condenser:
The figure shows two-pass downfalls surface condensers. This arrangement is compact & heat exchange is more efficient. Surface condensers have a major advantage over jet condensers, as condensate is not mixed with cold water. As a result, the entire condensate can be reused in the boiler. This type of steam condenser can be used when the supply of cold water is limited.
It consists of horizontals cast-iron cylindrical vessels filled with tubes through which cool water flows. The ends of the condenser are cut by vertical perforated type plates, to which water taps are attached. The condensate extractions pump, which is located at the bottom, creates suction. The exhaust steam enters from above and flows over the nesting of the tubes.
Coldwater enters the lower tubes and passes through the upper half of the tubes. A portion of the tubes is examined with a baffle. This reduces the amount of water vapor that escapes with the air.
Central Flow Condenser:
In the central flow condenser, steams enter the top of the condenser and flows downstream. This suction pipe has an air extraction pump in the center of the tube nest. Due to these placements of the suctions pipes in the center of the tube nesting, and the exhaust steam passes radially inside the tubes towards the suction pipe. Condensate is collected at the bottoms of the condenser & pumped into the hot well.
In a regenerative surface condenser, the condensate is heated using the regenerative method. In this, the condensation passes through the exhaust steam emanating from the turbine or engine. It raises its temperature and is used as feed water for boilers.
Evaporative condensers are another type of surface condensers. When the supply of cold water is limited, evaporating the circulating water at small partial pressures can reduce the amount required to condense the steam. This principle is employed in evaporative condensers.
#2. Jet Condenser
In the jet condenser, the cold water is sprinkled on the exhaust stream, and there is a direct contact between the exhaust stream and the cooling water. The process of condensation is very fast & efficient, but here cold water and condensed steam are mixed.
The condensate then boilers cannot be reused as feedwater. The temperature of the condensate is similar to that of cold water coming out of the condenser. Jet condensers require less amount of cold water for condensation of steam due to a more intimate mixture of steam and cold water.
In general, jet condensers require fewer building spaces & are simpler to manufacture and lower in capital costs. Despite these advantages, jet condensers are not common in thermal power plants, especially due to the loss of condensate.
Parallel Flow Jet Condenser:
In a parallel flow jet condenser, both steam and water enter the top & the mixture is removed from the bottom. The principle of these condensers is shown in the figures. The exhaust steams mix with the water and condenses.
Condensate, cooling water, and airflow are diverted downstream and by two separate pumps known as air pumps and condensate pumps. The condensate pump moves the condensate to the hot well.
Counterflow Jet Condenser:
A low-levels or counter-flow jet condensers are shown in the figure. In this type of steam condenser, cold water enters the top and is sprayed through the jet. The steam enters from the bottom and mixes with a fine spray of cold water.
A separate pump removes the condensate. The air is removed from the top separately by an air pump. In the parallel flow type of this condenser, cold water and condensed steam move in the same direction. From top to bottom.
Barometric Jet Condenser:
High-level jet condensers are shown in the figure. It is similar to a lower-level condenser, except that the condenser shell is placed at the height of 10.36 m (barometer height) above the hot well. Coldwater enters the condenser from above and is sprayed through the jet.
The steam enters the bottoms and mixes with a fine spray of cold water. The water column in the tailpipe pushes condensate into a hot well by gravity.
Ejector condensers are shown in the figure. In these condensers, the water is 5 to 6 m. It enters the top of the condenser and is passed through a series of converging nozzles. Pressure falls on the nozzle’s throat. The pressure reduction draws exhaust steam into the nozzle through a non-return valve.
The steam is condensed by mixing it in water. In the converging cone, the pressure energy is partially converted to kinetic energy. In divergent cones, the kinetic energy is partially converted into pressure energy. The pressure obtained is greater than the atmospheric pressure, and this pushes the condensate towards the hot well.
Working of Steam Condenser:
The steam condensers receive exhaust steam from one end and come into contact with the cooling water circulating within it from the cooling tower. As low-pressure steams comes in contacts with cold water, it condenses and transforms into water.
It is connected to the air extractions pump & condensation extraction pump. After condensation of steams, the condensate is pumped into the hot well with the help of a condensate extraction pump. The air extraction pump expels air from the condenser and produces a vacuum inside it.
It is connected to the air extractions pump & condensate extractions pump. After condensations of steams, the condensate is pumped into the hot well with the help of a condensate extraction pump. The air extraction pump expels air from the condenser and creates a vacuum inside it.
The vacuums create circulations of cold water and the flow of condensates downstream. As low-pressure steams comes in contact with cold water, it condenses and transforms into water. The vacuums produced helps in circulations of cold water and the flow of condensate flow.
Advantages of Steam Condenser:
- This allows the reuse of condensate for feed water and therefore reduces the cost of electricity generation.
- The temperatures of the condensates are higher than the feed water. This reduces the heat supply per kg of steam.
- This increases the efficiency of the plant.
- This reduces the backpressure of steam and can result in more work.
- This exhaust lowers the steam temperature and allows more work to be achieved.