African Petrochemicals Edition_16.2

ZWICK FOR MOLTEN SULPHUR OR SULPHUR TAIL GAS
If you work with Molten Sulphur or Sulphur Tail gas, please take time to read more.
Design engineers at Zwick in Germany have looked at solving on-going
problems being experienced with valves on sulphur units.
Typical valve problems on large bore line sizes range from seizing of the
packing to severe seat damage when valve need to be operated after long
periods of time of inactivity. Valves should be specified as steam jacketed
valves as this is a standard mandatory type of valve requirement.
Generally a standard valve may be suitable in an ideal line were there are never
any shutdowns or upset conditions as once the valves body temperature has
reached that of the hot sulphur or tail gas passing through it will not allow for
any solidification, however in an upset condition were the valve body cools
down with sulphur cooling also, then this will solidify in the bearing / shaft
areas which will consequently generate a seizure of these elements.
Based on international experience, Zwick engineers recommend the use
of steam jacketed valves as these would maintain the critical areas under a
constant temperature, thus eliminating any potential seizure.
Zwick are capable of supplying valves in both wafer and double flanged style
with steam jackets, and we can also apply a steam traced trim (stem and disc).
Zwick Tri-Con series valves come with bearing protectors, which reduce the
ingress of the medium into the critical areas, which coupled with the bearing
flush purge ports constitute a true cleansing and protection of these critical
areas.
The following explanation highlights the technical differences between the Zwick
Tri-Con valve and other manufacturers of valves ranging from double eccentric to
unjacketed valves which will fail in this type of application.
The Zwick Tri-Con series valve is a specially designed process isolation, on/
off and control valve, which has a wide range of application uses limited
only by that of the actual materials used, in fact Zwick manufacture valves
for applications which range from -196ºC up to +815ºC. Valves can be
manufactured in any machinable form of alloy available on the market for
specific client requirements.
The Zwick Tri-Con series valve is a triple offset valve with true cone in cone
design which totally eliminates any rubbing of the seats, hence eliminates
any wear and tear which would generate leakages across the seat, this is
technically not possible for other typical high performance valves, which
means it is limited to a double eccentric design, rubbing sealing in the last 15-
18º which will generate leakage as the time goes by.
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The other standard double eccentric are not designed for these severe
applications therefore any attempt to use it for particular process applications
may result in a problematic outcome.
Self Centering disc
With it’s unique self centering temperature compensating disc, the Tri-Con
series construction guarantees the optimal position of the laminated seal
against the seat. Jamming due to thermal expansion is therefore eliminated.
The torque transmission with keys
The disc is keyed to the shaft and not pinned, providing equal torque
transmission and eliminating the danger of pins sheering off.
Ideal lamination and disc design
The strong disc with it’s elliptical supporting surface offers the best fixing of
the lamination. The zero leakage is achieved by the special machining of thre
lamination.
Supporting bearing bushing
The optimal position of the bearing reduces the bending of the shaft. This
guarantees bi-directional tightness under maximum pressure.
General characteristics
• Triple eccentric design
• Metal seating
• Zero leakage
• Pressure classes
• Full bi-directional shutoff tp API & DIN, ZERO Leakage
• Temperature range -196ºC up to +815ºC
• Size range 2” to 72” (DN50 to DN1800)
• Friction free opening and closing
• Vacuum tight
• Laminated seal and seat made of stainless steel
• Anti blow-out shaft to API 609
• Steel casting, stainless steel and special alloys
• Fire-safe acc. To BD 6755 and API 607 for both flow
directions
• Fugitive emission control acc. To “TA-Luft II”
Valve & Automation are the agents for Zwick products. Please
contact Desmond Delport on 011 397 2833 or sales@valve.co.za