Burning of fossil fuels leaves a combustion residue known as Ash. Bulk portion of this Ash is carried out of boiler with flue gas. Some of the ash, deposits over the internal furnace tubes and heat transfer area of the boiler during flue gas movement over these parts. These deposits are called soot deposits. A soot blower in boiler is a device used to clean soot deposits. To maintain boiler efficiency a certain number of soot blowers are equipped in boiler design.
Basic Working of Soot Blower in Boiler
The soot blowing medium is injected on the heating surfaces at high velocity by soot blower for a short time. The blowing medium (Steam/Water/Compressed air) strikes the deposit and dislodges it from the heating surface. The type of blowing medium is selected based on the system requirement in a particular installation.
Classification of Soot Deposits
High Temperature Deposits
These deposits occur on convection heating surfaces (Superheater & Re-heater) not exposed to radiant heat from furnace.
Low Temperature Deposits
These deposits are formed on low temperature zones (Economizers & Air heater)
Types of Soot Blowers
Soot blowers are made according to the surface to be cleaned and exact mechanism of these soot blowers depends on the manufacturer. Some commonly used soot blowers are:
Furnace Wall Soot Blower
Furnace wall soot blowers are used for water walls. A short nozzle of blower enters the boiler and expel hot steam or compressed air to clean the surrounding area. The nozzle retracts when not in use, making furnace wall blowers ideal for areas that reach high temperature.
Long Retractable Soot Blower (LRSB)
LRSB is a device that extends a long “lance” or nozzle into the boiler. The LRSB starts at the beginning of the boiler and slowly moves through it, rotating 360 degrees to remove soot from all surfaces. Once the cleaning is complete, the lance withdraws. They are perfect for high temperature areas.
Air Heater Soot Blowers
They are designed to clean the air heaters of boiler. Over time, moisture accumulates at the cold end of your air heater when the flue gas temperature falls below the condensation point. This moisture mixes with soot and other by products, creating a fine-grain deposit.
Air heater soot blowers are installed on the cold end of air heater and can consist of retractable blowers or blowers with nozzles installed on swinging arms. The device will move across the face of air heater, while a swinging arm will move in an arc across the face of the heat transfer surface, cleaning a large area.
Rotary Soot Blower
This type of blower is affixed to the boiler and does not retract like other types of blowers. Instead, the blowing tube or element of the blower remains in the boiler at all times. This tube is often equipped with multiple nozzles and rotates to clean a large portion of the boiler.
Because they do not retract, rotary soot blowers cannot be used in the high-temperature areas of boiler.
Parts of Soot Blower
It consists of four parts which is mentioned below:
- Nozzle for spraying the soot blowing medium
- Lances or Elements to carry soot blowing medium
- Drive mechanism for rotating, advancing and retracting the soot blowers
- Control loop for drive mechanism