steam-generating equipment
In our previous blog, we discussed the boiler. Still, in our today’s blog, we will discuss boiler furnace, superheater, reheater, economizer, and air preheater. These are the Steam-generating equipment of the steam power plant.
boiler furnace:Steam-generating equipment
A boiler furnace is a chamber in which fuel is burnt to liberate heat energy.
In our previous blog, we have seen that a boiler is used to convert water into steam, but we need something to burn the fuel and generate heat energy. Therefore, we use a boiler furnace to burn the coal, and hot gases are transferred toward the boiler.
The boiler furnace provides an enclosure for burners.
The furnace walls are made from refractory material such as fire, clay, silica, kaolin, etc. The refractory material shows resistance to high temperatures. This type of material is used to reduce the heat loss in the furnace and stop the spreading of heat in the surrounding. It acts like a surrounding container that contains heat inside. This refractory material also possesses the resistance change of shape, weight, or physical property at high temperatures.
Construction of boiler furnace varies according to the following points:
- Characteristics of fuel used and ash produced
- Firing methods
- Nature of load demand
- Combustion space required
- Operating temperature
Superheater: Steam-generating equipment
A superheater is a device that removes the last traces of moisture from the saturated steam leaving the boiler tubes.
As you can imagine, by reading the name superheater, it superheats the steam. It makes that steam very dry so that no moisture content shall remain in the steam that will expand on turbine blades.
If all the moisture has been removed from the steam, that means its temperature increases above the saturation temperature,
For heating the steam at this high temperature, some heating medium must be needed, but as if you see the layout of the steam power plant, you can observe that there is no place or no provision is there to insert a boiler furnace,
So the superheater tubes are heated by the heat of combustion gases during their passage from the furnace to the chimney. This causes the recycling of waste gases that are going out as wastage from the chimney.
This close loop cycle of the power plant increases efficiency and reduces the wastage of flue gases from the plant.
Superheater can be further classified into two types:
- Radiant
- Convection
Radiation superheater
The radiant superheater is located in the furnace between the furnace water walls. It absorbs the heat from the burning fuel through radiation.
Radiation: The transfer of heat occurs through electromagnetic waves without having a solid contact.
Convection superheater
The convection superheater is located well back in the boiler tube tank. It receives its heat entirely from flue gases through the convection process. Hence the name convection superheater is used. This type of superheater is usually ahead of the economizer.
Convection: the transfer of heat is within the solid/ liquid material.
reheater
After expanding the steam on turbine if not used then that remaining steam goes wastage through the chimney.
Reheater superheats the partly expanded steam from the turbine.
So why do we need the reheater, because there is not just a single turbine is used? Still, the set of turbines are used to expand the steam. In this process, sometimes the steam temperature gets reduced, so a steam Reheater is used for reheating.
economizer
Economizer is the device that recovers the heat from flue gases to the chimney and raises the temperature of feed water and air supplied for combustion, respectively.
The temperature of feed water in economizer is raised about 247˚ to 276˚.
The economizer chamber should be leak-proof against air filtration; otherwise, boiler draught may be adversely affected.
air preheater
An air preheater is a device that preheats the air passing to the boiler.
The main function of an air preheater is to recover the heat from the flue gases leaving the economizer and heat the incoming air required for combustion.
This raises the temperature of furnace gases, improves combustion rates and efficiency.
Air preheaters lower the stack temperature and thus increase the overall efficiency of the boiler.
If we calculate approximately drop in 20˚-22˚ in fuel gas temperature, increase boiler efficiency by about 1%.
Advantages of air preheater are:
- High thermal efficiency
- Reliability of operation
- Fewer maintenance charges
- Occupies small space
- Reasonable initial cost
- Economizer is easily accessible.
The air preheater is basically of two types –
- Recuperative (plate type or tubular type).
- Regenerative type.
The recuperative type of air preheater is continuous in action. In contrast, the regenerative types are discontinuous in action and operate on a cycle.
