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Oil Burner Refractory Failure Causes & Cure

written by: Dr V T Sathyanathan edited by: Lamar Stonecypher updated: 5/13/2010

Oil burner throat is made of refractory play a major role in the performance of the burner. Its

damage leads to many problems during combustion and results in non-availability of the burner.The reasons for such failure are quality of refractory chosen and the way it is prepared and

applied.

IntroductionMany designers of oil burners prefer to provide a good refractory lined throat which provides the

right kind of flame quality. This is in addition to the spinner vanes provided in the burner to givea spin to the primary air. The secondary air also comes out through the throat and mixes with the

flame at such a location that the hydrocarbons will be ensured of oxygen to burn. The main

functions of the burner throat are to provide proper shape to the flame, to mix the fuel and air,

and to provide the stabilizing heat back to the flame.

Construction & Materials

The burner throat is normally made of high alumina plastic refractory or castable refractory ofGrade A is used. This refractory must have a maximum permanent linear change of plus/minus 6

% at 1550 degree C. Crushing strength must be more than 300 kg/cm2

after drying at 110 degree

C and cooled to ambient temperature. After heating to 1200 degree C to 3 hours and cooling to

ambient temperature the crushing strength should be more than 210 kg/cm2

and at 1750 degree C275 kg/cm

2. It should be able to with stand a service temperature of not less than 1750 degree C.

The bulk density must be 2900 kg /m3

after drying at 110 degree C and cooling to ambient

temperature. The Grog size must be maximum 5mm and Ferric Oxide (Fe2O3) should be only5% max. These properties are only a typical one, however the designers do specify the refractory

best suited to their design. Some burner designers use pre-formed ceramic shaped tiles for the

burner throat.

Ensuring Longetivity

While making the burner throat from refractory the following will have to be ensured to achievemaximum life of the burner throat.

o Check the shelf life of the refractory being use, normally refractory material have a shelflife of one year, some may even have as low as three months. Use the refractory only if it

is within the shelf life period.

o Mix the refractory with the correct quantity of water specified by the refractory supplier.Using higher or lower quantity of water will not ensure the required life of burner throat.

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o Use only soft water of the quality specified by the refractory supplier.o Use thin plywood while making the throat at the specified intervals and shape to allow

for the required expansion gaps.

o Allow the setting time and dry the throat at the specified temperaturenormally 110degree Cand time. Many practice this by doing the throat job just before boiler light up

and continue to operate the boiler after drying operation is completed rather than coolingit to ambient temperature.

o It is a good practice to make a template of the throat shape on a thick wood with a centerpivot leg for keeping it at the center of the burner and rotating the template to achieve the

correct shape of the burner throat. Care must be taken to make the template with thecorrect inside diameter and curve profile.

Inspection

The burner throat must be inspected periodically and closely during all boiler outages. The

longitudinal cracks seen on the burner throat surface is not uncommon and is not severe.

However circumferential cracks are generally an indication that the burner throat has to berepaired or replaced. It is advisable to replace the burner throat if the circumferential cracks are

more and deep.