La-mont Boiler

La-Mont BOILER

A Forced Circulation Boiler was first introduced by La-Mont in the year 1925 which is used in power plants. This is a modern high pressure water tube type steam boiler working on forced circulation system.

Description [Fig. 9]

Fig. 9 shows the flow-circuit of La-Mont boiler.

1. Furnace

In the furnace, water wall pipes are used to provide a large heating surface, thereby to increase the capacity of the boiler and also to cool the furnace wall. Water Wall Pipes are vertical or inclined pipes in the interior walls of the furnace. These pipes are connected at the top and bottom to the other parts of the boiler so that there is continuous rapid circulation of water through the water wall.

2. Steam Separator Drum (Boiler)

Steam Separator Drum is placed wholly outside the boiler setting.

3. Circulating Pump

It is a centrifugal pump used for forced circulation of water. Forced circulation of water prevents the tubes from being overheated.

4. Evaporator Tubes

These are provided above the furnace.

5. Convection Superheater

The wet steam should not be used in the steam turbine. The presence of moisture in it will cause corrosion of turbine blades. To raise the temperature of steam and thereby to increase the turbine efficiency, wet steam is passed into the Superheater.

6. Economiser

The feed pump supplies feed water to the economiser.

7. Air Pre-heater

A blower draws atmospheric air and supplies compressed high pressure air (forced draught) to the air preheater.

Working Principle

Water from the Circulating Pump is circulated through the Evaporator Tubes. Hot gases from the Furnace heat the water and evaporate into steam. Wet steam from the evaporator enters the steam space in the Steam Separator Drum.

In the Convection Superheater, the moisture in the wet steam is removed and superheated steam is produced. The principle of convection superheater is similar to steam generating tubes of the boiler. The hot flue gases at high temperature sweep over convection superheater tubes and raise the steam temperature, producing superheated steam.

The superheater, thus, receives heat from the flue gases flowing from the furnace, entirely by convective heat transfer. Such a superheater is conveniently located, since it is not necessary for it to “see” the furnace.

Feed water is supplied by the Feed Pump to the Economizer. Economiser is used to preheat the feed water using the waste hot gases before going to the Chimney. Thus, some of the heat in the hot gases, which otherwise gets wasted, is used to preheat the feed water. This results in an increase in the boiler thermal efficiency.

The heat of the exit gases cannot be fully extracted through the economizer. These exit gases preheat the air from the blower in the Air Preheater. The preheated air is supplied to the furnace for combustion.

Capacity

Due to forced circulation of water, the rate of heat transfer and the steam capacity of the boiler are increased. The capacity of La-Mont boiler is about 50 Tonnes/hr of superheated steam at a pressure of 170 bar and at a temperature of 500°C.

Important Note:

The main difficulty experienced in the La-Mont boiler is the formation and attachment of bubbles on the inner surfaces of the heating tubes. The attached bubbles to the tube surfaces reduced the heat flow and steam generation, since it offers high thermal resistance than water film.

Boiler Mountings

This boiler is fitted with mountings, viz., water gauge, pressure gauge and block-off cock. Also, three safety valves are fitted as per Indian Boiler Act. The design, manufacture and erection of these boilers are very difficult. It requires skilled personnel and huge investment.