Boiler arrangement & Fuel oil burning process - various designs burners
Various design burners :
Marine boilers currently burn residual low-grade fuels. This fuel is
stored in double-bottom tanks from which it is drawn by a transfer
pump up to settling tanks. Here any water in the fuel may
settle out and be drained away.
The high-pressure fuel is supplied to a burner which it leaves as an
atomised spray . The burner also rotates the fuel droplets
by the use of a swirl plate. A rotating cone of tiny oil droplets thus leaves
the burner and passes into the furnace. Various designs of burner exist,
the one just described being known as a 'pressure jet burner' .
The 'rotating cup burner' atomises and swirls
the fuel by throwing it off the edge of a rotating tapered cup. The 'steam
blast jet burner', atomises and swirls the fuel by
spraying it into a high-velocity jet of steam. The steam is supplied down
a central inner barrel in the burner.
The air register is a collection of flaps, vanes, etc., which surrounds
each burner and is fitted between the boiler casings. The register
provides an entry section through which air is admitted from the
windbox. Air shut-off is achieved by means of a sliding sleeve or check.
Air flows through parallel to the burner, and a swirler provides it with a
rotating motion. The air is swirled in an opposite direction to the fuel to
ensure adequate mixing . High-pressure, higb-0i»tput
marine watertube boilers are roof fired . This enables a
long flame path and even heat transfer throughout the furnace.
The fuel entering the furnace must be initially ignited in order to
Fig:pressure jet burner
Fig:Rotating cup burner
Fig:Steam blast jet burner
Fig:Air register for side fired boiler
Once ignited the lighter fuel elements burn first as a primary flame
and provide heat to burn the heavier elements in the secondary flame.
The primary and secondary air supplies feed their respective flames.
The process of combustion in a boiler furnace is often referred to as
'suspended flame' since the rate of supply of oil and air entering the
furnace is equal to that of the products of combustion leaving.
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