In this article, I will share the function of a superheater, its type, working principle land advantages of using this unit.
Superheater is an important unit that is used to superheat the steam that is produced by the boiler or any type of steam generator.
The steam produced by the boiler is usually nearly saturated. Saturated steam contains moisture that is not good for the steam distribution lines and components that are going to use the steam.
Moisture in the steam will also end up resulting in the corrosion of the distribution lines and blade turbines.
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At the same time, the saturation extent in the steam reduces the quality of the steam.
Whether the steam will be used in the steam power plant for driving the steam turbines or mainly for energy production it should be dry for it to produce the highest efficiency.
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For the steam to be dried, its temperature has to be increased by the superheater after it has left the boiler unit.
The construction of the superheater mainly consists of tube circuits that are in parallel with one or more return tube bends that are connected between headers.
For the superheater to be effective, the tube’s diameter should be considerably small (about 1 to 2 inches) this is what will enable the steam to be dried efficiently.
The superheater has the capability of supplying steam at different loads but at a constant temperature.
The action of superheating the steam increases the steam turbine and boiler efficiency.
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Types Of Super Heater And Their Working Principles
There are three types of superheaters namely as follows;
- Convective superheater
- Radiant superheater
- Convective and radiant superheater (combined superheater)
Convective superheater
This type of superheater uses heat from the flue gasses to heat the steam in the tubes using the method of convection.
The flue gasses are passed through the tubes of the superheater and the heating happens entirely through convection.
The flue gasses used to supply heat to the superheater should have higher temperatures than the saturated steam.
This is what will ensure that the saturated steam is super-heated and it’s not the flue gasses taking heat from it.
The temperature of the flue gasses should be 1750C higher than the saturated steam for the process of superheating to be effective.
Radiant superheater
It heats the saturated steam by the method of radiation.
A radiant superheater is usually placed inside the furnace to absorb the heat directly (through the process of radiation) from heat energy from the burning fuel and use it to superheat the saturated steam.
Convective and radiant superheater (combined superheater)
It uses the principle of convection and radiation to superheat the saturated steam from the boiler.
A combined superheater is the most effective one because it has multiple ways to receive heat energy and use it to superheat the steam.
The heat transfer in the superheater varies with the load of saturated steam fed into the superheater; as the load of the saturated steam increases, so does the heat transfer.
This is to ensure that the heat provided to the superheater can handle a load of saturated steam fed into the superheater.
The lower the heat transfer in the superheater, the lower the efficiency of the superheater and vice versa is true.
The final temperature of the steam leaving the superheater depends on the temperature of the gasses used to superheat the steam, the gas flow rate and the quantity of gas flow.
The above factors can affect the efficiency of the superheater. For the superheater to perform with high efficiency, it mainly depends on the heat from the furnace or flue gasses.
A negative change in temperature, flow rate and quantity of these gasses will decrease the efficiency of the superheater.
Since the superheater deals with receiving heat from the flue gasses and the furnace, it has to be designed to withstand higher temperatures; special steel alloys like chromium molybdenum are used to design the tubes of modern high-pressure boilers.
The steel alloys have excellent strength to withstand high temperatures from the gasses and the steam and they also have high resistance to oxidation.
The superheaters are also classified according to where they are placed in the boiler system.
The superheaters classified according to location are as follows;
- Over deck superheater.
- Inter deck superheater.
- Inter tube superheater.
- Interbank superheater.
Sugden Superheater
The Sugden superheater is used in the Lancashire boiler. This superheater uses steel U tubes that are connected to the headers to superheat the steam.
These steel U tubes that are used to heat the saturated steam in the superheater system are usually arranged in pair of four.
A single header of the superheater can carry about 10 of these pair (which are a total of forty tubes).
This clearly shows that the superheating capacity of the Sugden superheater is massive because of the number of steel U-tubes they can carry.
The more the number of steel U tubes, the higher the rate of heat transfers thus a higher efficiency.
The Working Principle Of Sugden Super Heater
Sugden superheater operates under the principle of convection. The flue gasses are passed through the superheater steel tubes in the Sugden superheater.
The flue gasses heat up the steel superheater U tubes thus transferring the heat energy into the saturated steam entering the tubes from the boiler through the right header.
The flue gasses transferring heat energy to the steel U tubes are released from the section of the steel U tubes and out of the Sugden superheater by the damper to allow another fresh volume of flue gasses to enter the section.
The superheated steam leaves the left header via the other side of the steel U tube that is also connected to a steam distribution line that takes the superheated steam out of the Sugden superheater to the point of application.
Lastly…
And that summarizes the working principle of superheaters. If you have any questions or additional points feel free to leave your comment.
Thanks for reading, see you in my next article.
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