Exchanger Technology Heats Up

Improved designs save space and energy and fend off fouling

By Seán Ottewell, Editor at Large

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Heat exchanger efficiency is crucial. Fortunately, the chemical industry is benefiting from improvements as equipment makers such as Alfa Laval, Klaren International and Heatric leverage the latest materials and technologies to boost performance.

Five main factors — energy efficiency, capacity, emissions, water use and uptime — drive the chemical industry’s demand for improved heat exchanger technology today, says Gert Ternström, market development manager, petrochemical industry, Alfa Laval, Lund, Sweden.

“The overall focus is very much on process optimization and here compact heat exchangers offer great benefits,” he stresses.

The company’s Compabloc range exemplifies this, he notes. The all-welded plate pack eliminates gaskets between plates and makes it possible to operate with a wide range of aggressive media and at high temperatures and pressures.

Balaji Amines, Tamalwadi, India, certainly has benefited. It installed 48 Compablocs on its amine production plant, resulting in a 40% reduction in overall steam use, says the chemical maker.

“It seemed risky at the time because Compabloc was more expensive than alternative products,” notes Prathap Reddy, chairman and managing director of the Indian company. “But I’m happy we took the risk. The first installation of eight Compablocs laid the foundation for savings of around $700,000 per year. The Compabloc is a reliable and efficient product. Furthermore, it can withstand aggressive media and high temperature and pressure. It is also almost maintenance-free and can be cleaned in a few hours instead of days, two more advantages over shell-and-tube models.” Reddy adds the payback period for a Compabloc is shorter because of the huge energy savings achieved — and the company is well on the way to replacing all of its old shell-and-tube exchangers with Alfa Laval’s technology.

Ternström also highlights a project with a major paraxylene producer in Asia that has a 500,000-mt/y plant. The company decided to replace its existing air-cooled heat exchangers used for condensing overhead vapors from three of the plant’s columns with four Compablocs. Two were installed on top of the paraxylene recovery column and are now recovering 20 MW of waste heat, resulting in annual fuel savings of roughly €2.3 million ($2.6 million). The other two, which are installed on top of the recycle and de-heptanizer columns in the xylenes isomerization area, recover 3.7 MW, leading to roughly €430,000 ($482,000) in fuel savings per year. The payback time for the revamp, including the cost for installation, was less than one year.

However, despite these successes, Ternström says there’s still a lot of resistance to compact heat exchanger technology — despite a number of companies standardizing on it for specific activities such as absorption systems for gas sweetening and carbon dioxide removal from ethylene oxide processes.

“Other users are not so technology focused, so we are still only scratching the surface of what compact heat exchangers can be used for,” he explains.

Part of the challenge is to get plant designers to stop falling back on old rules-of-thumb about how much heat can be recovered using standard shell-and-tube exchangers. “They simply don’t take advantage of the huge potential benefits of using compact heat exchangers,” he laments.

One chemical company that is more proactive in this regard is BASF. Its Ludwigshafen, Germany, site has more Alfa Laval compact heat exchangers — about 1,500 — than any other chemical complex in the world.

The Swedish company has been working on a two-part strategy at Ludwigshafen’s acetylene and naphthalene plants. The first is to swap out compact gasketed plate-and-frame heat exchangers that posed a safety risk and led to frequent production stops with equally compact units without gaskets. The second is replace carbon steel shell-and-tube heat exchangers suffering from erosion.

To date, the benefits of this strategy include savings of €300,000–€400,000/y ($336,000–$448,000/y), two-thirds of which comes from eliminating leaky gaskets and the rest from maintenance savings, says BASF. There’s also a huge reduction in the amount of floor space, foundations, piping and installation work needed for the new heat exchangers.

“The Compablocs were around 25% lower in cost compared to retubing the existing shell-and-tube heat exchang¬ers,” says Frank Steiglich, project operation manager acetylene, at BASF, “On top of that, a lot of space was freed up, which resulted in a safer plant for the operators.”

Boiling and condensing operations generally have the potential for large savings, Ternström counsels. He cites reboilers as a bastion of conservative design that demands a rethink: “The higher efficiency of the compact plate technology opens up the use of lower temperature/quality heat sources. For example, doing the same boiling duty but replacing high-pressure steam with medium-pressure steam often results in 30–50% lower operating costs.”

Alfa Laval now is planning to develop even larger compact exchangers.

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