Plants seal their fate

Contending with fugitive emissions becomes more of a priority

By Seán Ottewell, editor at large

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Dow also focuses on comprehensive and company-wide training strategies.

“We did have concerns about how flanges were being put together, so we implemented a flange-fitting training strategy. When combined with our engineering standards, such strategies have led to a tremendous increase in productivity. The more we do this, the fewer emissions and leaks we have, the fewer spare parts are needed, etc: it’s an increased cost/productivity benefit,” Mathes notes.

Drago also stresses the importance of correct installation. “If you don’t adhere to the rules, you won’t get the performance. We can sell the best gasket or packing set in the world, but there’s no point if it isn’t installed properly.”

New options

To address sealing challenges and surmount the inherent conservatism of many operating companies, members of ESA and FSA are developing better technologies.

Figure 1. Suitable for top-mounted drives, this seal features a central rotating seal made of solid silicon carbide and wider sliding faces. Source: Burgmann.

For example, the new AGSZ agitator gas seal from Burgmann Industries, Wolfratshausen, Germany, targets low RPM machines. Designed for use on top drives in tanks with standardized connections, the central rotating seal (Figure 1) is made of solid silicon carbide and has wider sliding faces, which produce a gas film of much greater stability, says the company.

The result is safe, non-contact operation even in rugged agitator applications. Buffer gas consumption has been reduced by 75% compared to the previous AGS model while leakage measurement variations fall within a much narrower range. The stationary spring-backing of the seal faces makes the AGSZ less sensitive to radial movement such as shaft wobble or shaft skew. Such a stationary design has a proven track record on pump seals, notes the company.

A specially designed clamping ring for torque transmission allows up to ± 2-mm. axial movement of the shaft. The floating bearing on the shaft is integrated into the seal. Acting as the fixed bearing between the rotating shaft bushing and the stationary housing, it reportedly provides effective protection against the negative effects of movement at the sealing gap.

The high strength coating on the seal faces guarantees very good emergency running characteristics in start-up and slow-down phases or during failure of the buffer gas supply, according to Burgmann. Being double-balanced, the seal remains closed even when there’s no buffer gas. In addition, a reduction in the number of wearing parts helps to lower maintenance costs and simplifies installation.

Meanwhile, DuPont Performance Elastomers, Wilmington, Del., has added to its Kalrez Spectrum family of perfluoroelastomer parts that are specifically designed for touch services such as those involving amines. Hot primary amines are notoriously aggressive toward elastomers, causing their premature degradation.

In lab tests, Kalrez Spectrum 6380 parts exhibited what the company describes as excellent overall chemical resistance and mechanical properties for static and dynamic sealing applications in harsh processes at temperatures up to 225°C. In particular, they showed very low swell after 672 hours of exposure to ethylene diamine, ethanolamine and ammonium hydroxide, compared with alternative perfluoroelastomer parts commonly specified for such environments.

“Before introducing Kalrez Spectrum 6380, we subjected pilot seal samples to rigorous field testing in an aggressive primary amine process at 210°C, operated by a major chemical company located in the Texas Gulf Coast area,” notes Tony Dorta, global marketing manager. “Several perfluoroelastomer parts from various manufacturers were used, but none offered service in this process environment beyond four months. By substituting Kalrez Spectrum 6380, the company succeeded in tripling seal service life to one year. As a result of this field test and our own laboratory trials, we are confident in recommending the latest Kalrez product for processes involving hot amines, strong acids and oxidizing media.”

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