A paper that looks at how the earlier PTA production method involving a multi-stage process with pressure and atmospheric centrifuges and a re-slurry tank can be replaced with one stand-alone device – the rotary pressure filter (RPF).
Sometimes the smallest parts — such as seals and gaskets — can have the greatest impact on plant performance. For this reason, seal and gasket manufacturers are developing innovative new materials and designs that will help these diminutive, but important, components stand up to the harsh operating conditions of the chemical process industries (CPI).
“With multiple seals and gaskets responsible for essentially ‘making or breaking’ the entire system, the ultimate driver is to eliminate or severely reduce the cost of maintenance and downtime whenever possible,” says Marion Fisher, market development manager with Victrex (West Conshohocken, Pa.).
Marcus Pillion, president of Eagle Burgmann (Houston) agrees. “While this is not a new story, chemical processors need equipment to last longer and handle more upset conditions,” he says. “The run-ability of a plant is vital these days, so equipment must last longer and be more efficient. For this reason there’s a strong drive for new materials and better products in the seals and gasket industry.”
High-performance thermoplastics, such as polyether ether ketone (PEEK; Figure 1), are more often being specified for sealing applications due to its advantageous physical properties, such as high-temperature durability, creep resistance, stiffness and compatibility with a range of chemical environments, says Fisher. “PEEK polymer can be used as a rigid primary seal. However it needs to be manufactured to very tight tolerances to be used this way,” she continues. Elastomeric materials are commonly used as primary seals, but their mechanical properties require changes to the seal design in high-pressure applications. Where many elastomeric materials may fail by extruding under pressure, a thermoplastic backup seal ring will increase the pressure limits of elastomeric O-rings and maintain their seal integrity in many demanding environments.
“Many applications are using injection molded PEEK and PEEK films to fulfill these needs in chemical processing operations,” says Fisher. This is because PEEK polymer is a much tougher material option and has excellent creep resistance under high-pressure, high-temperature (HPHT) conditions, which helps reduce downtime and maintenance costs in that it needs to be replaced less frequently, she says. Back up rings prevent the extrusion of elastomeric seals in blow-off preventers, risers and valves and allow communication and power connectors to function in demanding and corrosive environments.
Another material innovation includes the use of microcrystalline diamond coatings. “The use of this new material allows operators to have more upset conditions and have a seal that lasts and survives without breaking down as quickly as other materials,” says Pillion.
A diamond coating of 8 µm or more in thickness makes the seal faces extremely hard and wear resistant, he says. In addition, the diamond material gives the seals excellent heat conductivity, maximum chemical resistance and low friction.
“The faces can now handle more upset conditions like run dry, which the operators appreciate because now the process itself doesn’t need to be perfect,” says Pillion. “And, processes rarely are, so this innovation allows operators room for improvement.”
Developing new designs
“When plants have a leakage problem with their gasketed joints, in many instances, they end up installing the same style gasket, using the same installation procedures and three months later they have the same old problem,” says Ed Crowley, Northeast regional manager with Flexitallic (Deer Park, Tex.). “But the industry is constantly working on new designs to improve gasket performance, allowing them to compensate for harsh conditions or deficiencies in the equipment or process, and plants are updating their installation procedures to incorporate best practices,” he says.
One example of a new gasket design includes Flexitallic’s launch of the Change gasket, which testing has shown to provide superior compression and recovery compared to traditional gaskets. The Change gasket consists of a metallic core and can be supplied with a variety of facing and filler materials such as Thermiculite, polytetrafluoroethylene (PTFE) or flexible graphite, making it suitable for a range of applications.
Crowley says the new gasket is a hybrid of a spiral wound gasket and Kammprofile gasket to offer the best performance characteristics of both traditional designs. “This allows it to seal better than conventional gaskets in cyclic conditions, because the Change gasket acts like a spring and therefore maintains a tight joint during thermal cycles,” he notes.
Seal and Gasket Products
Mechanical seals in one assembly for mixers
Featuring both single and double cartridge configurations and designed for easy installation and maintenance, ChemSeal cartridge seals (photo) can be removed from the agitator as a complete assembly and repaired on the workbench before re-installation. The “swing-out” agitator seal-change design contributes to the ease and speed of seal replacement. The seals are available in a variety of materials to meet critical temperature and pressure ratings, satisfying a range of mixing/agitation applications. — Chemineer, Inc., Dayton, Ohio
A silver-filled sealant for bonding and sealing
Developed for bonding and sealing, the EP3HTSMED epoxy system (photo) features a rapid cure schedule and a tensile shear strength exceeding 1,000 psi. The silver-filled epoxy adhesive/sealant provides electrical conductivity with a volume resistivity less than 0.001 ohm cm. Serviceable over a temperature range of –60 to 400°F, the sealant is resistant to severe thermal cycling and many chemicals. The product is a thixotropic paste and requires no mixing. It needs only contact pressure during the heat cure of 20 to 40 minutes at 300°F. — Master Bond Inc., Hackensack, N.J.
Gaskets for high-temperature applications
Therma-Pur can be used to seal connectors in biomass gasification, marine and land-based exhaust systems, turbochargers and mineral and fertilizer processing. The gasket is made in a solvent-free process and combines a unique blend of raw materials with a fiber core. The material provides sealing effectiveness in temperatures to 1,800°F, including extreme thermal-cycling conditions. The low organic-fiber content and non-oxidizing formulation also exhibit low weight-loss ratio. The fiber core makes it safe to handle. The gasket is available in a range of configurations. — Garlock, Palmyra, N.Y.
A wear-resistant fluoropolymer for shaft seals
To address the compatibility requirement of synthetic lubricants used in industrial gears, a new fluoroelastomer material — a wear-resistant FKM — was developed for use in radial shaft seals that interact with aggressive oils in industrial-gearbox sealing applications. FKM material blends are used in applications containing synthetic oils, as they offer high temperature and chemical resistance. — Simrit, Elgin, Ill.
A conductive gasket suitable for food applications
The C2 gasket (photo; 24 to 72 in. round) is a co-extruded product of FDA white silicone and conductive black silicone, to produce a gasket that can be used in food and high-static processes. The FDA white silicone element is the only portion exposed to product contact, while the black conductive component of the gasket makes contact with the frames and the outer lip of the screen tension ring (for Sweco STP and spot-welded screens only). — Sweco, Florence, Ky.
Seal and bearing materials for sanitary applications
Turcon MF6 and Zurcon Z431 PEEK seal and bearing materials (photo, p. 27) conform to the latest version of the 3-A Sanitary Standard and are capable of withstanding high temperatures and the cleaning regimes used in food and beverage manufacturing. Suitable for a range of seal profiles, scrapers and wear rings, Turcon MF6 is part of the company’s range of PTFE-based sealing materials formulated for food contact, pharmaceutical and medical applications. Zurcon Z431 PEEK is suitable for valve and bearing applications. — Trelleborg AB, Trelleborg, Sweden
Seal and weld biotech-grade tubing
The AdvantaTube Sealer and Sterile Welder (photo) are programmed to seal and weld AdvantaFlex biopharmaceutical grade TPE tubing. TPE tubing works well in peristaltic pumps, may be molded to form sampling and batch filling assemblies and exhibits low levels of extractables. The welder produces tubing welds, where two open ends of tubing are heated and joined to form a leak-free, single length of tubing using an automated process. The welder maintains the sterility of wet, dry or fluid-filled tubing and works with gamma irradiated and autoclaved AdvantaFlex. The sealer offers simple operation. A 10-ft cord connects to a base and allows users to bring the remote sealing head to the tubing. The unit uses heat and compression to securely seal fluid-filled or unfilled tubing in two minutes. — AdvantaPure, Southampton, Pa.
Piston rings for oil-free, compressed-gas applications
Carbon-graphite is available for use in piston rings needed to seal high-pressure gas in applications requiring compressed gases that do not contain oil or grease. The piston rings are used in conjunction with carbon-graphite guide rings or carrier rings, which hold the piston centered on a cylinder bore. The self-lubricating, carbon-graphite piston rings and guide rings are used in reciprocating compressors, where oil-free gases, such as air, steam, refrigerants, hydrogen, hydrocarbons, chlorine, nitrogen and oxygen can be compressed to pressures greater than 800 psi. — Metallized Carbon Corp., Ossining, N.Y.
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