It is a forced circulation- water tube boiler which was first introduced in 1925 by La
The feed water from hot well is supplied to a storage and separating drum (boiler) through the economizer. Most of the sensible heat is supplied to the feed water passing through the economizer
The feed water from hot well is supplied to a storage and separating drum (boiler) through the economizer. Most of the sensible heat is supplied to the feed water passing through the economizer. A pump circulates the water at a rate 8 to 10 times the mass of steam evaporated. This water is circulated through the evaporator tubes and the part of the vapour is separated in the separator drum. The large quantity of water circulated (10 times that of evaporation) prevents the tubes from being overheated.
The centrifugal pump delivers the water to the headers at a pressure of 2.5 bar above the drum pressure. The distribution headers distribute the water through the nozzle into the evaporator. The steam separated in the boiler is further passed through the super-heater.
To secure a uniform flow of feed water through each of the parallel boiler circuits a choke is fitted entrance to each circuit. These boilers have been built to generate 45 to 50 tons of superheated steam at a pressure of 120 bar and temperature of 500°C.
1. Steam separating drum – The feed water from the hot well is stored in the drum. The steam is separated from water in the drum and the steam is usually collected at the top
of the drum.
2. Circulating pump – Water from the steam separating drum is drawn by a circulating pump and it circulates water through the evaporator tubes. Pump circulates water at a rate of 8-10 times the mass of steam evaporated. Forced circulation is necessary to prevent the overheating of tubes.
3. Distribution header – The distribution header distributes the water through the nozzle into the evaporator.
4. Radiant evaporator – Water from the drum first enters the radiant evaporator through the pump and header. The water is heated by the radiation heat from the combustion chamber. In radiant evaporator, the hot flue gases do not pass over the water tubes.
5. Convective evaporator – The mixture of water and steam coming out from the radiant evaporator enters the convective evaporator tubes. The hot flue gases passing over the evaporator tubes transfer a large portion of heat to the water by convection. Thus, water becomes steam and the steam enters to the steam separating drum.
6. Superheater – The steam from the steam separating drum enters the superheater tubes where it is superheated by the hot flue gases passing over them. The superheated steam then enters the steam turbine to develop power.
7. Economiser – The waste hot flue gases pass through the economiser where feed water is pre-heated. By pre-heating the feed water, the amount of fuel required to convert water into steam is reduced.
8. Air pre-heater – The hot flue gases then passes through the air pre-heater where the air required for combustion is pre-heated.
1. La-Mont boilers can generate 45 to 50 tons of superheated steam at a pressure of 120 bar and temperature of 500°C.
2. Drum is of small size.
3. Tendency of scale formation is eliminated due to forced circulation of water.
1. Bubbles are formed on the inside of the water tubes and this bubbles reduce the heat transfer rate.
2. Initial and operating costs are high.
3. Maintenance costs are very high.