AIR REGISTER
This is the name given to an assembly of vane air swirler plates etc fitted within the boiler casing in association with each burner ,its functions is to divide air into primary and secondary streams and to direct them such as to give the correct air flow pattern.
The air must pass through the air check to enter the register . In some cases the check can be formed by the swirl vanes themselves by rotating them about their axis, in other cases a sliding sleeve is used.
The inner primary air flows until it reaches the tip plate ( stabiliser ) then spills over to form a series of vortices which reduces the forward velocity of the air. This retains the primary flame within the quarl . The outer , secondary air passes over the swirler vanes which causes the air to rotate thus assisting the mixing of air and fuel.
The secondary air shapes the flame, short and fat for side fired, longer and thinner for roof fired.
A small amount of cooling air is allowed to flow to the tip plate and atomiser tip.
It is important that the air check forms a tight seal otherwise thermal shock can damage the quarls when the burner is not in use
The front plate is usually insulated , the complexity of the air control is related to the TDR .The steam jet types have the steam providing additional energy for the mixture of air and fuel.
- see 'burners' for description of profiled registers
PREPURGING OF FURNACES
Furnace explosions caused by oil vapour and air present in furnace in explosive proportions. To a lesser extent a blowback is a furnace explosion. Prevention is by purging with air.
Usually adequate purging is provided within the combustion control however makers timings should be strictly followed .
N.B.
This is particularly important with membrane wall boilers where the pressure wave is contained within a strong cell which if ruptured, has disastrous consequences.
Modern design
