Introduction

Coal tar and fuel oil are the widely used fuels for high temperature furnaces.  Both these fuels have the same potential for use as a source of heat energy.  They give brilliantly luminous flames which radiate heat effectively in the melting chamber.  But, the slightly higher carbon content in tar makes the tar flame even more luminuous than that of oil.  One of the major factors influencing the cost of production of steel is the fuel cost.  The open hearth furnaces of SMS-3, Tata Steel, used both coal tar and LSHS as liquid fuel.  Petro fuels becoming more dearer day by day, and coal tar being in heavy demand, particularly after having established as a blast furnace injectant, it was imperative to explore the best possible device to derive the maximum heat value from these liquid fuels.  This would not only benefit by way of cost savings in terms of rupees but also would save large foreign exchange. 

Conventional Emulsion Atomizer

Atomisation of liquid fuels can be accomplished in number of ways in practice, using different types of atomizers.  However, heavy and viscous fuels, like coal tar, LSHS, etc.  are generally atomized using steam, primarily by dint of its mechanical action.  Such conventional atomizers can not effectively atomise the fuel, thus resulting in incomplete combustion and soot formation.

Problems of conventional Atomiser

Fluctuations in fuel and steam pressures required frequent adjustment of the spindle which was difficult to maintain in practice, at the optimum level, all the time because it was manually controlled.  This resulted in poor atomization leading to incomplete combustion and soot formation near the burning zone.  Moreover, the high solid content in the liquid fuels, particularly in coal tar, gave rise to clogging of the burner nozzles. 

All the above mentioned problems, associated with the conventional atomizer have been take care of by the use of emulsion designed and developed.  It is well known, that emulsification of liquid fuels prior to burning, not only enhances the combustion efficiency through effective atomization but also reduces the emission levels of particulate solids and inter alia saving fuel. 

New Emulsion Atomiser

In the New Emulsion Atomiser, developed, the emulsification and atomization of liquid fuels take place simultaneously prior to burning. The Atomiser consists of a tar nozzle, concentric to which, a primary steam nozzle is provided.  It is imperative for the steam to attain supersonic velocity for diffusion of the two steams to form a stable emulsion.  Such supersonic velocities are attained by using “Laval Nozzle”.  The secondary steam injection mainly helps in  transporting the atomized emulsion to the burner before the emulsion breaks. 

Basic Principle

The basic principle of using emulsified fuel is that, when droplets of the emulsified fuel are heated, they explode into many tiny fragments.  The micro explosion is referred to as secondary atomization.  Improved atomization, thus achieved, not only enhances the combustion efficiency but also reduces the particulate (soot) emission, resulting in reduction in the level of atmospheric pollution. 

Achievements / bene fits 

The performance of the furnaces with the new liquid fuel emulsion atomizer continuously excelled the conventional one in all aspects and the operation of the furnaces were also more steady and stable.  

            The benefits achieved can be summarized as follows:

• Brighter, more luminuous, intense and stable flame.

• Reduction in fuel rate by 8%

• Increase in gross productivity by 8%

• Decrease in mean thermal Input (MTI) by 1%

• Reduction in soot formation and NOx emission level due to improved combustion.

• Emulsion atomizer is very simple in construction and has no moving parts hence it costs less and offers easy maintenance.

PATENT : Patent No. 187182 dated 24-9-1996