Burners

Outline

• Burners• Burner Components• Parts of Burning System• Orientation of Burners• Classification• Solid Fuel Burners• Liquid Fuel Burners• Gaseous Fuel Burners

BurnerA part of the burning system used to burn the fuel in

the presence of some oxidizer.The primary purpose of a burner is to transfer heat

from the combustion products to some type of load.It is important to match the burner to the load to

ensure heat transfer is maximized in order to maximize the system thermal efficiency.

This reduces operating costs and indirectly reduces pollutant emissions because less fuel needs to be combusted for a given production rate.

The heat transfer from burners is often a complicated process because of the turbulent fluid flow, high-temperature chemical reactions, and spectral gaseous radiation.

Burner inside a Furnace

Burner ComponentsNoseBurner tileBodyMounting plateFuel connectionAtomizerPilotObservation Port

Parts of Burning System

Source of airSource of fuelA burnerValves and

proportioning devices

Valve or Proportioning device

Burning System

Orientation of Burners

There can be three orientations of burners1. Hearth fired2. Wall Fired3. Roof Fired

Classification of BurnersMixing TypeFuel TypeOxidizer TypeDraft TypeHeating TypeBurner Geometry

Classification of Burners(According to fuel)

Liquid Fuel Burners

Gaseous Fuel Burners

Solid Fuel Burners

Solid Fuel BurnersSr No Type of Coal

UsedBurner Type

1 High Volatile Short flame with self-induced turbulence

2 Medium Volatile

Short flame with externally induced

burners

3 Low Volatile Long flame or U-type

Liquid Fuel BurnersOil burners are of two types according

to the way with which they may be burnt.

1. Vaporizing Burners2. Atomizing burners

Vaporizing Oil BurnersIn vaporizing burners the volatile fuel is

passed at a low pressure through a tube adjacent to the flame, where vaporization takes place.

The vapour stream issues out of an orifice at a high velocity and entrains primary air.

The fuel-air mixture passes through a mixing tube and burns at the burner head.

Wick-type vaporizing burners A wick raises the liquid fuel from a trough by capillary

action. Radiation from the flame and adjacent hot surfaces

vaporizes the kerosene from the wick head. The vapours enter into an annular space between two

vertical, perforated metallic cylinders and burn in the air drawn through the perforations by natural draught.

The combustion takes place throughout the annular space with a blue flame.

These burners are used as cooking stoves.In ordinary wick-type burners, the burning rate is

controlled by varying the length of the exposed portion of the wick and is less satisfactory.

Pot-type BurnerThere is a fuel reservoir at the bottom, supplied by an oil

line. The oil surface is heated by radiation from the flame and the

hot walls. Vapours mix with the primary air admitted through a central

pillar and perforations in the pot wall. The fuel-air mixture is too rich at the oil surface to support

combustion. Further up, it is diluted with air and becomes inflammable. Flame is supported at the top of the pot. These burners work on natural or forced draught. Superior kerosene or light fuel oil is used. Soot formation necessitates the pot burner cleaning

periodically.

Wall-wiping flameUses coarse atomization before the fuel is

vaporizedA centrally located centrifugal spinner

distributes the oil in the form of a spray of coarse droplets striking the hot stainless steel wall of the burner.

The vapours mixed with the air (which is directed towards the wall by a fan) rises upwards and burns on a stabilizing grill with a blue flame.

The flame burns around the inner circumference of the furnace only, and from this fact gets its characteristic name.

Power requirement is low and operation is noiseless.

Kerosene and light fuel oil are used.

Petromax stovesBurns kerosene.An upward moving fuel jet strikes against a

hot metal surface at a high velocity and the vapours produced burn with a short and intense flame over the metal surface.

The fuel is stored in a small reservoir below the fuel line and the oil pressure is supplied by compressing air into the reservoir by a hand-driven piston.

It has risk of accidents and has noisy operation.

High speed vaporizing burner A high rate of vaporization is achieved

by atomization of the volatile liquid fuel and recirculation of hot combustion gases within the burner.

The burner bears out the difference between vaporizing and atomizing burners.

The combustion chamber receives fuel vapours in the former and fuel droplets in the latter.

Atomizing Oil Burners Atomization of oil creates enormous surface area per unit

weight of the fuel Atomizing burners have an arrangement for the atomization

of liquid fuels before the actual combustion takes place. For atomization, initially a jet or a thin film of liquid is

obtained and allowed to emerge into the open atmosphere at a suitable velocity.

Both the jet and unsupported film are unstable and break up into drops.

Disturbances like swirling of the jet or rotation of the film hastens the disintegration process.

Low viscosity and low surface tension are desirable for ease of dispersion and formation of small drops.

The atomization is assisted by the resistance, friction and turbulence of air.

Local turbulence in the air causes deformation and disruption of the drops.

Types of Atomizing burnersThere are three types of atomizing burners

(differing from one another on the principle of atomization) namely

1. Pressure jet atomizing burner2. Twin-fluid or blast atomizing burner, and3. Rotary atomizing burner

Pressure Jet Atomizing Burners

These are of two types namely

1. The plain orifice type (used for fuel injection in diesel and other internal-combustion engines)

2. Centrifugal swirl type (used in large industrial boilers). In the former, very high pressure of oil up to 350 kg/cm2 or

even higher are used. Much lower oil pressures (7 to 35 kg/cm2) are required in the

swirl type burners. The pressure jet atomizing burners are very quiet, have low

operating cost and power requirement is the lowest of all atomizers.

These are the most widely used of all atomizing burners. The pressure jet atomizers are susceptible to choking by dirt in

the oil. The oil should be strained/filtered for this reason.

Twin Fluid or blast atomizing burners

These burners use air or steam to atomize the oil and are of three main types :

1. low pressure (LP) types using air at 35 to 70 cm w.g.,

2. medium pressure (MP) types using air at 0.4 to 1 kg/cm gauge

3. high pressure (HP) types using air or steam at pressures exceeding 1 kg/cm2 gauge.

Each of these types may again be either ‘inside-mix’ or ‘outside-mix’ type.

Rotary Atomizing BurnersThese have a central stationary fuel line which delivers the

oil to the inner surface of a rotating hollow tapered cup. The cup is rotated (at 3,600—10,000 rpm) and the friction

between the oil and the cup surface causes the oil to rotate with the cup.

The centrifugal force, assisted by the tapering of the cup causes oil to flow towards the brim.

Finally, the oil is flung off in a thin film which disintegrates into fine droplets.

Rotary atomizers can tolerate higher viscosity than the others.

They may however lose atomizing efficiency at low viscosities.

Rotary atomizing burners are extensively used in boilers and small installations.

Gaseous Fuel Burners

There are two methods of burning gaseous fuels:

1. Premix burner or inside mixing type

2. Outside mixing type or diffusion flame burner or nozzle mix type burner

Premix burnerThe gas and air is pre-mixed and then

fired in the furnace chamber.

Outside mixing typeThe gas and air flow separately and mix

together in the furnace as combustion proceeds.

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