Knowledge for the Sulphuric Acid Industry
Sulphuric Acid on the Web
Acid Plant Database
Boiler Feed Water
Materials of Construction
DKL Engineering, Inc.
Sulphur Burning - Sulphur Burners
May 14, 2002
Rotary Cup Burners
There are basically two types of sulphur burners in use in sulphur burning acid plants; Sulphur Guns using an atomizing spray nozzle and Rotary Cup Burners. Two fluid atomizing nozzles are not commonly used.
A sulphur gun consists of a steam jacketed pipe with a atomizing spray nozzle mounted on the end. The steam jacketed pipe is long enough to place the spray nozzle at the front on the furnace an serves to keep the gun cool and maintain the sulphur in the molten state.
Early sulphur guns used a standard ‘Spraco’ type nozzle screwed onto the end of the sulphur gun. More sophisticated design are now available but the all work on the same principal.
An atomizing spray nozzle is a device which breaks up a mass of liquid into a multitude of droplets, serving the general purpose of increasing the surface area. Spray nozzles create droplets by using the energy in a pressurized liquid to break up the liquid stream into droplets as the liquid passes through an orifice. In this case, the formation of droplets and the increase in surface area allows for the efficient and thorough combustion of sulphur in the sulphur furnace.
Spray nozzles require a high pressure drop to effectively atomize the molten sulphur. Pump delivery pressures for molten sulphur are typically 690 kPag (100 psig) or higher.
Spray nozzles with fixed orifice sizes are limited in their turndown ability. Typically the flow of molten sulphur is controlled by an upstream control valve. As the valve is closed a greater portion of the pressure drop is taken across the valve reducing the pressure at the spray nozzle. The effectiveness of the spray nozzle is greatly reduced as the inlet pressure is reduced. To overcome this problem the orifice in the spray nozzle must be changed to a smaller size. This requires a stoppage in the plant in order to change the spray nozzle.
This problem is partially overcome by having multiple sulphur guns installed in the furnace. As plant production is reduced, sulphur guns are taken out of service so pressure at the spray nozzle is not significantly reduced. For small plants, multiple sulphur guns are not as practical or necessary as in larger plants.
Some sulphur gun designs have been developed where the control of sulphur flow is done right at the spray nozzle. This eliminates the turndown problem of fixed orifice spray nozzles. A control rod runs down the length of the sulphur gun and extends through the spray nozzle orifice creating an annular space for sulphur flow. To increase sulphur flow, the control rod is extracted increasing the size of the annular space (i.e. orifice area). The advantage is that high pressures are maintained right at the inlet of the spray nozzle providing for good atomization at all flow rates. One disadvantage is that as the size of the orifice is reduced, the nozzle is more prone to blockage.
A rotary cup burner consists of a spinning cup spinning at high speed which atomizes the molten sulphur. The spinning cup is driven by an electric motor through a drive belt system. Sulphur is fed to the burner at a low pressure (< 1 bar g) compared to a pressurized spray nozzle. The high speed rotating cup ensures that the sulphur is atomized to a high degree. The result is a short intense flame that provides for complete combustion of the sulphur to sulphur dioxide. The burner permits a high specific furnace load (2 Gcal/m³) compared to the pressurized spray nozzle (0.75 Gcal/m³).
Since the burner does not rely on a high pressure drop, burner turndown ratios of 1:5 are possible the need to change any spray nozzles. The capacity of the burner is controlled by a control valve on the molten sulphur line. Typical burner capacities range from 5 to 600 tpd of sulphur.
The burner can also be used to burn fuel oil during the preheating step and can be quickly switched over to sulphur when required.