Page 22 - Microsoft Word - Sulfo and Sulfa 1.doc

regenerates the off-line air dryer. During the air dryer cooling cycle in smaller plants, the
regeneration/utility air vents to the atmosphere or is sent to other processes where the
heat in the air can be used. In larger plants (greater than 4000 kg/hr) the heat may be
recovered as steam. In this case, the gas plant is modified so that it produces steam
instead of hot air and a portion of this steam heats the regeneration air.

In the sulfur supply system shown in Figure 21, bright Frasch or by-product sulfur flows
by gravity to one of two gear pumps. Typically dual strainers, pumps, and flow meters
are provided minimize down time during maintenance. The sulfur passes through a
highly accurate mass flow meter prior to delivery to the sulfur burner. Because the mole
ratio is the most important process variable, control of the sulfur flow to the sulfur
burning air/SO gas plant is one of the two most important process control functions in
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the plant. The entire sulfur supply system is steam jacketed because the sulfur has a
freezing point of 112.8°C.

Sulfur is normally handled at its viscosity minimum, which is 136°C. A steam
and condensate system supplies the necessary tracing circuits for the sulfur supply
piping.

Figure 21. Sulfur Feed System

SC FIC
FE
SULFUR MELTER SULFUR TO
SULFUR BURNER

In the SO gas generator, illustrated in Figure 22, the metered sulfur is delivered to the
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refractory-lined atomizing sulfur burner where combustion with the dry process air
generates sulfur dioxide (SO ). The atomizing burner ensures instant, constant sulfur
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burning. The sulfur dioxide gas leaving the burner is cooled to 420°C and delivered to a
three-stage vanadium pentoxide catalytic converter, where the gas is filtered and
converted to sulfur trioxide (SO ). The conversion efficiency of the converter is between
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99.0 and 99.5%. Prior to entering the inlet mist eliminator, the sulfur trioxide gas leaving
the converter is cooled to nearly ambient temperature in an SO double pipe cooler
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Page 21 of 36 © 1997 The Chemithon Corporation