Loeffler Boiler is the improved version of the Lamont Boiler. Lamont boiler has a major defect that salt and sediments were deposited in the inner surface of the water tube through which water flows. Due to deposition of salt and sediment in the inner surface of the water tube the heat transfer reduces. Lamont Boiler also has an overheating problem due to deposition of salt. In Loeffler Boiler all these problems are solved by preventing the flow of water in the boiler tubes.
Loeffler Boiler is a forced circulation, high pressure and water tube boiler with internally fired furnace.
Loeffler Boiler can carry high salt concentration due to the presence of an evaporating drum.
It works on the principle that the feed water is evaporated by using superheated steam from the superheater.
The total steam produced in the superheating process is used in two processes. Nearly 2/3rd of the superheated steam is used to evaporate the water and again produce steam and 1/3 rd of the superheated steam is used to rotate the turbine and produce electricity.
Construction and Main Parts of Loeffler Boiler :-
Main parts of Loeffler Boiler are:-
1) Water feed Pump:-
Water feed pump is used to feed water to the boiler. Quantity of feeded water should be equal to the quantity of water evaporated in the boiler. In some of the case, injector is used to inject water to the boiler.
Economizer is used to increase the efficiency of the boiler. It uses flue gases to produce heat. Economizer is used to preheat the water before sending it to the evaporating drum. It increases the efficiency of the boiler by preheating water so that less amount of heat is needed to evaporate the water in further process.
3) Evaporating Drum:-
Evaporating drum is used to convert feed water into saturated steam with the help of superheated steam from the superheater. It contains a mixing nozzle. Mixing nozzle is used to mix the steam from superheater with feed water and evaporate them.
4) Radiant Superheater:-
Radiant superheater is a chamber where saturated steam is heated to make it superheated steam. It uses radiant heat transfer method to create superheated steam and transfer heat from the combustion chamber to steam. This section is near the combustion chamber
5) Convective Superheater:-
Convective superheater heats the steam to the desired temperature of about 500-degree Celcius. In this superheater, convection is used to transfer heat from the flue gases to the steam.
The superheated steam from the convective superheater is then sent to the turbine to produce electricity.
7) Steam Circulating Pump:-
It is present between the evaporating drum and radiant superheater. It circulates the steam inside the boiler.
A drain is provided to the evaporating drum where the mixing of the superheated and water takes place. It is open when the salts and sediments are settled in the drum. It is also used to release the water when cleaning is required.
9) Safety Valve:-
A safety valve is provided to release excess steam present in the vessel. When the pressure of steam exceeds its prescribed limit, the safety valve automatically opens and the excess steam rush out to the atmosphere and the valve automatically closes when the pressure reaches the normal value.
- At first, normal water is feeded to the economizer from the water feed pump. In the economizer, water is preheated using the flue gases. These gases are produced in the furnace where the coal burns.
- This preheated water from the economizer is sent to the evaporator drum. In this evaporator drum, water mixes with the superheated steam coming from the superheater. This evaporator drum has a nozzle and the superheated steam from the superheater enters into the nozzle and this nozzle mixes the superheated steam with water.
- As the superheated steam mixes with feed water, this feed water changes into saturated steam. This saturated steam is drawn from the evaporator drum using a steam circulating pump.
- Then it is passed through a radiant superheater. The radiant superheater superheats the saturated steam by using radiant heat produced by the burning of fuel. The tubes of the radiant superheater are placed in the furnace.
- After the radiant superheater, superheated steam is passed to the convective superheater. Convective superheater is placed in the path of the flue gases. In the convective superheater, the superheated steam from radiant superheater is further heated to a temperature of about 500-degree Celcius.
- Then the superheated steam from the convective superheater is divided into two parts. Nearly 2/3rd of the superheated steam goes to the evaporating drum for evaporating water and 1/3rd of superheated steam goes to the turbine through steam main. Steam main is the path through which superheated steam is supplied to the turbine to produce electricity.
Advantages of Loeffler Boiler :-
- It can use salt water for steam generation as the depostion of salt and sediments in the boiler tube are eliminated in this boiler.
- This boiler is compact in design.
- Operation of this boiler is salient and clean.
- High circulated of steam over the tube.
Disadvantages of Loeffler Boiler :-
- Bubble formation reduces the heat transfer rate.
- Evaporating drum is used which is very expensive that increases overall cost and also make it bulky.