Molecular Sieve Dryer Switching Valve - High Temperature

Valves Supplied

Size:  4”, 6” ANSI 300 Class
Body Material:  WCC Carbon Steel
Internals:  Carbon Steel – Electrolysis Nickel Plated  
Trim:  Teflon Seat / Kalrez Seals      
Port:  Reduced Port
Connections:  Raised Face Flanged

Service Conditions

Media:  Nitrogen Dryer – Switching Valve  
Manual / Actuated:  Actuated w/ Override
Temperature:  450F norm / 500F Max  
Orientation:  Vertical
Pressure:  450psig  
Cycles / Frequency:  Approx. 4X / day

Application/Service Conditions

The targeted valve installation is a molecular sieve dryer valve (also known as: mole sieve switching valve, de-hydration switching valve, gas de-hy switching valve, among others). Brief overview on molecular sieve dryer; a cyclical adsorption desorption system to transfer contaminants – or non-desired gas molecules from one stream to another.  Mole sieve drying systems are utilized in processes where the end user is ultimately trying to purify (remove moisture and contaminates or isolate specific gas strains).

•    Natural Gas Processing - Removes CO2, H20, H2S, RSH, COS, Hg, S, etc.
•    Petrochemical and Specialty Gas Manufacturing – Allows the separation of specific gas molecules (example methane for liquefaction)
•    Regeneration done thermally with high temperature gas flow

Common application: valve cycles 4-6 times each day - year round. Pneumatically actuated. High temperature swings from ambient to 500°F (some as high as 620°F max). Potential Issues: On occasion, drying material is upset (desiccate) and is blown into valving during operation. This desiccate dust (material is as small as dust and as large as one inch in diameter) is extremely hard and has the tendency to crush in between the more commonly utilized valve design and damages the seating surfaces to the point that a positive seal cannot be achieved to isolate the dryer beds. Customer has to de-pressure entire system to repair in-line and they cannot repair themselves. Other designs require special tools. Multiple customers with this application complain about the accessibility/availability and cost of the certified repair technicians.

The first Hemiwedge valve was shipped to this customer in February ‘09 and they independently tested to approximately 4100 cycles (estimated 4 years of service) on their site. The valve was noted in the engineer’s report to have “no visible leakage” after the test period. After the successful test, the customer immediately installed four additional Hemiwedge® valves in their next outage in June 2009. They have subsequently ordered additional valves to replace other valves around their dryer beds.