Plants seal their fate

By Seán Ottewell, editor at large

ChemicalProcessing.com

Contending with fugitive emissions becomes more of a priority

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Fugitive emissions from U.S. chemical plants top 300,000 tons every year, according to estimates from the Association Francaise de Normalisation (AFNOR), La Plaine Saint-Denis, France, an international standardization organization. This represents roughly a third of the total organic emissions from the sites. It’s exactly the same story in Europe, too.

“There’s no doubt that in the future there will be more regulation and inspection to decrease fugitive emissions,” says Dana Mathes, corporate director, environmental, health and safety operations for Dow Chemical, Midland, Mich.

However, sealing technology hasn’t received the attention it deserves, says Brian Ellis, director general of the European Sealing Association (ESA), Tregarth, U.K. “The EU (European Union) didn’t realize that it’s very hard to reduce emissions if seals aren’t doing their jobs properly. This has been the major focus for all of our members for over the last ten years or so.” He adds: “Sealing should be seen as much more of a support industry these days.”

“Market forces are pushing the development of ever-tighter sealing materials, but those forces depend on where you are. In the U.S., the driver is mainly regulation and compliance,” notes Jim Drago, manager, business development, for Garlock Sealing Technologies, Palmyra, N.Y.

However, the diversity of chemicals makes sealing a challenge, he adds. “The chemical industry is processing so many different oxidizing materials that we can’t use the carbon and graphite which are ideal for refinery hydrocarbon applications,” says Drago. The move away from large plants manufacturing one or two products to smaller facilities making a large range of products via batch processes adds to the challenge, he notes.

Another complication comes from the increasing popularity of piping made from polymers. “The challenge here is to generate enough pressure to create a proper seal without cracking the flange.”

Key resource

The crucial importance of sealing is highlighted in “Sealing Technology BAT Guidance Notes.” This 71-page document gives advice on the best available techniques (BAT) for industrial installations covered by the EU’s integrated pollution prevention and control directive. It’s published by the ESA, following close consultation with the Fluid Sealing Association (FSA), Wayne, Pa., and a number of seal suppliers.

Available on the ESA’s website, it provides an introduction to all aspects of fugitive emissions. Red bullet points highlight where the authors believe specific challenges might arise while green bullet points indicate their recommended approaches to achieving BAT.

According to the document, the scale of fugitive emissions depends on nine factors:

1. Equipment design
2. Equipment age and quality
3. Standard of installation
4. Vapor pressure of the process fluid
5. Process temperature and pressure
6. Number and type of sources
7. Method of leak determination
8. Inspection and maintenance routine
9. Rate of production

Disregarding unsealed sources such as storage tanks, vents, flares and spills, many losses stem from leaks in the sealing elements of particular types of equipment, including agitators, compressors, flanges, pumps, tank lids and valves. Overall, valves typically account for 60%, relief valves 15%, tanks and pumps 10% each and flanges 5% of fugitive emissions, notes the document.

According to an estimate cited in the Guidance Notes, for every pump in an average plant there will be 32 valves, 135 flanges, one safety valve and 1.5 open-ended lines. Hence, with so many potential sources, leaking losses can be hard to determine. The age of equipment and how well an installation is maintained can significantly influence the extent of emissions, but generally the important causes of leaks include equipment failure, pollution of the sealing element, incorrect process conditions and ill-fitting internal or external sealing elements.

A changing relationship

Ellis offers a number of observations on how the drive to tackle fugitive emissions is dramatically changing the relationship between sealing suppliers and the chemical industry.
“Traditionally the sealing suppliers went through a large number of distributors, creating a huge gap between themselves and the industrial users. So the person who actually carried out the final installation was not necessarily qualified at all.”

In the days of asbestos, he says, this wasn’t really an issue because asbestos had such a wide variety of uses but, with its phasing out, new sealing materials are much more application specific. “For example, you might only get three or four applications per material now, where there would have been 15 or 20 for asbestos. Of course, the new ones way outperform asbestos but they must be used by the user in the right application and be installed properly. This is a real challenge that faces the chemical industry — installation is absolutely crucial now, in a way that it never used to be. There is also the challenge of overcoming the conservatism of engineers on chemical plants, particularly in some European countries where there is a very great reluctance to adopt new solutions.”