Boiler Components - Part 2

Lagging in Boilers

Lagging in Boilers refers to the covering over the boiler.  The principal function of the lagging is to cover the insulation and prevent heat loss from the boiler.  It also provides a cool surface over the boiler for fitment of accessories.  It provides a formal shape to the boiler after the insulation has been fitted.

Lagging is a essential part of boiler design.  Lagging is usually made of aluminium or steel.  The Lagging should be adequately supported so that it maintains its shape. 

The surface of the Lagging should also be provided with drainage so as to drain the excess water in case of rain or other water leakage.  This is important particularly in outdoor design. 

Adequate allowance should be made in the design for expansion and contraction of the lagging during operation as the temperature varies. 

The expected lifetime of the insulation and lagging is 15 years.

Level Indicators are very important instruments in any boiler.  Level indicators tell the operator how much water is there in the boiler.  The Level indicator is a vertical tube made of glass which can withstand high temperature.  This glass is mounted on the boiler drum.  One end of the level indicator is placed below the water level, the other end is placed above the water level.  This is called the steam end.

As the level of water rises and falls in the boiler, the level in the indicator also changes.  The glass tube of the indicator is covered by another protective layer of toughened glass.
The indicator has a drain cock which can be opened to drain the water in the level indicator.  This is used to check the functioning of the level indicator. 

The level indicator has two safety balls at each of the inlets, the water inlet and the steam inlet.  If the glass of the level indicator gets broken, the balls seal the two outlets and prevent leakage.
The Level indicator is a simple device which provides a direct reading of the level inside the boiler. 

Conductivity Probes for Level Monitoring in the Boiler

Maintaining level is an important aspect of Boiler Control.  Automatic Boiler Controls work by sensing the level of water in the boiler based on conductivity and and taking the necessary action.  Level monitoring is done by means of conductivity probes which are inserted through the boiler wall.

These probes are placed at different levels of the boiler.  When the water reaches the particular level, the contacts are bridged and a current flows through the probes and a signal reaches the controller.  If the water level falls no current flows signalling that the level has fallen.

These probes are specially designed to withstand the temperature and pressure of the boiler.

Steam Throttling Valve

The function of a throttling valve is to reduce the steam flow rate of the boiler.  This is necessary to prevent steam flashing.  

If a throttling valve is not used, a false temperature reading may reach the boiler blowdown controller.  This will result in wrong operation of the boiler blowdown.  The boiler throttling valve must be installed before the sensor. 

Baffles in Boilers

Baffles are used in Boilers to reduce turbulence in the flow of the hot combustion gases over the boiler tubes.  The baffles maintain proper velocity of the gases which enables efficient energy transfer.

Baffles also guide the fly ash and slag to the proper place for deposition from where they an be easily removed.  

If the Baffles are damaged, it will result in overheating at certain places and poor heating in others.