Plants seal their fate

Contending with fugitive emissions becomes more of a priority

By Seán Ottewell, editor at large

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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.”

A success story

One company not resistant to change is Dow Chemical. Indeed, Mathes says the company aims to outpace regulations. “So our own internal targets are designed to anticipate these changes and stay ahead of them.”

In fact, Dow has been setting corporate emissions targets for 15 years now. Many of these are focused on volatile organic compounds (VOC) and the fugitives that form a substantial part of them. Currently more than two million points of emissions are monitored at over 20 sites around the world. Since 1994, the result of these efforts has been a 62% cut in VOC emissions even though the company has increased production by 38% over that period.

Although bulk manufacturing still is an important part of Dow’s portfolio, its move to lower volume manufacturing of a larger number of products, especially performance chemicals, has brought new challenges in terms of fugitive emissions.

So, wherever possible, the company’s engineers try to design out the opportunities for fugitive emissions to arise — for example, by reducing the need for pipe connectors and their associated gaskets in new plants.

“By putting sections of pipe rack together and welding them, we’ve learned how to engineer out flanges. We also opt for seal-less or tandem seal pumps now, rather than single-seal pumps. These, of course, have implications for process safety and maintenance: fewer opportunities for spillages and simpler maintenance has important implications in terms of long-term cost of ownership,” notes Mathes.
At existing plants, Dow uses strategies such as live loading of gate valve packings to improve their performance. Such approaches are particularly important because 80% of the company’s fugitive emissions come from these valve packings and pump seals.

The issue of installation is extremely important at Dow, too. The company invests a lot of time and effort to make sure it has the best engineering standards. However, if field data from a Dow plant anywhere in the world suggest a change would be beneficial, it happens straightaway and is immediately implemented globally, says Mathes.

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