Components of a Boiler - Part 3

Soot Blowers

Soot Blowers are devices used for cleaning in boilers.  The Soot Blower is a mechanical device which cleans the deposits due to fouling in the furnace.  The Soot Blower consists of a cleaning medium such as steam, compressed air or water.

It directs jets of the medium on the surfaces and tubes to be cleaned.  Special injectors which can precisely focus the jets on to the tubes are used.  Removing the soot deposits greatly improves the efficiency of the boilers. 

There are different types of Soot Blowers such as the insertable soot blowers which can be inserted into the tubes as well as the rotating kinetic type of soot blowers. 

The soot blower can be operated manually by an operated or it can be made automatic to operate at specific intervals.  Boilers will have a specific cleaning cycle which depends on the size of the boiler, type of coal used, operating load, etc.

Soot Blowers which are powered by compressed air will have a dedicated air compressor for soot blowing.  The soot blowing equipment is generally galvanized to withstand the corrosive effect of the gases


Screen Tubes

In radiant super heaters, where the tubes of the superheater are placed directly in the furnace, special tubes are used to protect the superheater tubes from the high temperature of the furnace.  These tubes are called Screen Tubes as the screen the superheater tubes from the intense heat.

Slag Screen

The Slag Screen is a bank of specialized Boiler tubes which is fitted at the entrance of the convection passes in a boiler furnace.  The slag screen cools the hot gases and the ash before the entry to the convection shaft.  This minimizes the risk of slag. 

The slag screen can be arranged in an inline arrangement where the slag screen tubes are parallel to the boiler tubes or a staggered arrangement where the tubes are at an angle to the boiler tubes.

Water Walls Tubes are tubes which run along the inner surface of the boiler.  The function of the water wall tubes is to transfer the heat of the furnace to the water which flows in them.

Water Wall Tubes are more efficient than water tubes which were used earlier.  Water wall tubes help to better capture the heat of the boiler.  Since they are located in the walls, they prevent the heat from leaving the boiler and improve its efficiency.  They also keep the boiler surroundings cooler.

The water Wall Tubes are connected to the steam drum by means of risers. 

Super Heater

The Super heater Tubes serve to super heat the steam from the steam drum.  Steam from the steam drum is saturated steam.  It may still have droplets of water in it.  This steam is passed through tubes passing through the furnace to heat it.  Superheated steam has very high energy and is used to drive the turbines.

The capacity of a boiler is dependent on the amount of superheated steam it can generate.  Super heater tubes must be able to withstand very high temperature and pressure.  The steam-water ratio is designed such that it does not overheat.    Hence, super heater tubes are one of the most important parts of the boiler. 

Super heaters are classified into

  1. Radiant Super heaters which are placed directly in the furnace
  2. Convectional Super heaters which are placed in the path of the hot gases
  3. Separately fired super heaters are heated by a separate heat source.

Steam Drum

Steam drum is the reservoir at the top of the water tube boiler.  The water tubes which carry water are connected to the Steam drum.  The steam drum serves to extract the steam from the water and send it for superheating.  The difference in density causes the steam to rise.

The pressure in the steam drum regulates the steam generation within the boiler.  As the steam is extracted, further steam is generated.

The water is sent back to the water drum for further heating.