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| Sulphuric Acid on the WebTM | Technology Manual | DKL Engineering, Inc. |
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Knowledge for
the Sulphuric Acid Industry Introduction
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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.
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.
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Copyright© 2005,
2006, 2007, 2008 DKL
Engineering, Inc., All Rights Reserved |
