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Vacuum Technology Tackles Voids

July 16, 2012
Innovative use of existing technology and new developments improve performance.

Many chemical companies are striving to improve the reliability of vacuum systems, lower total cost of ownership, and meet regulatory requirements for noise reduction. To address these demands as well as specific vacuum technology problems, vendors are responding with novel applications of established equipment as well as new technologies.

Reliability is the number one issue for end-users — more so even than price — and noise is becoming more important, too, reports Peter C. Studer, director of sales and marketing for Wintek Corp., Flanders, N.J. "We had a customer that was looking to add vacuum capacity to their facility and had a dry vacuum pump that was noisy. Besides increasing the capacity, they wanted a pump that was quieter. We installed an oil-sealed liquid ring vacuum pump system that tested on-site at 70 dBA."

Wintek is carrying out an increasing amount of custom design for vacuum technologies. "Chemical companies today simply don't have the same engineering expertise and time to carry out these projects; where they might have had 100 engineers before, now they maybe have ten. It's definitely going to be more about service than new technologies over the next five years or so — and the operating companies don't really want to take a risk on newer technologies until they are very well established, either," notes Studer

That goes for solving plant problems, too, he adds. "Some of the most recent and most interesting of these actually focus on utilizing proven existing technologies in new applications."

Figure 1. Using methanol from solvent recovery system avoids potential water contamination. Source: Wintek. One such application involved replacing water or oil in liquid ring pumps with the same solvent being used in a customer's distillation process (Figure 1). "In this case, the methanol is passed to a reboiler for reheating to vapor and then through an inductor to create a vacuum. This provided 20,000 acfm at 0.2 psia for a methanol recovery system that was waterless. So there is no contamination," he explains.

Another customer needed to dry a product to remove heptane. Here, Wintek extracted the heptane vapor, collecting it in a condenser and condensate receiver in front of the liquid ring vacuum pump, which was sealed with heptane to avoid contamination if all the vapors weren't collected. "We were able to use a small 30-acfm vacuum pump at 1.9 psia, because we could condense out most of the heptane vapors with a colder 5°C cooling water before reaching the vacuum pump. It also helped that the dryer was easily sealed and the air leakage was quite low, less than 0.2 psi/hour."

The company also is finding that chemical makers that need to deal with solvents increasingly are moving to solvent-sealed vacuum pumps with a condenser/receiver on the discharge side rather than the standard condenser/receiver before the pump — so vapor goes through the vacuum pump and then is condensed at atmospheric pressure on exit. "One of our most recent systems of this type was again on heptane, but the cooling water was at 10°C and the vapor flow was approximately 450 kg/hr. We condensed some vapor before the pump and the rest after the pump, which allowed the end-user to make full use of the existing cooing system," notes Studer.

GEA Wiegand, Ettlingen, Germany, which specializes in multistage jet vacuum pumps, is seeing greater use of product vapor as motive medium, particularly in the production of polyester and textiles. Its completely closed systems are characterized by their ecological and economic efficiency, e.g., vacuum steam jet cooling plants provide cooling without recourse to additional refrigerants, says the firm.

Figure 2. New line features long service intervals, low noise and built-in control. Source: Edwards.TACKLING TOUGH SERVICESThe chemical industry increasingly is taking a "fit and forget" approach to vacuum systems, says Bolton, U.K.-based Don Collins, market development manager – chemicals for Edwards, Sanborn, N.Y. "Like utilities, you want to start it off and forget all about it." In response, the company has launched a line of dry vacuum pumps called CXS that boast innovative screw design and temperature control (Figure 2). "The CXS is intended to bring improvements to even the best vacuum pump on the market. These include better solids- and liquid-handling capability without special measures, longer service intervals (up to five years before any service), low noise (<64 dBA), integral control and best-in-class cost of ownership," notes Collins.

"The range is aimed at the nastiest chemicals that can be pumped, including aromatics, benzene, halides, vinyl chloride, acids and flammable materials, together with a limited amount of solids," he adds. Site tests particularly are targetting difficult applications. The toughest of these involves pumping phenol. Here a CXS pump has been installed side-by-side with an existing Edwards EDP dry pump. The EDP doesn't have an upsteam knockout pot (KOP) with automatic drain to prevent large liquid slugs from tripping the pump from time to time. If the pump cools down and phenol solidifies within it, the unit can suffer damage upon restart. This happens two or three times a year, primarily due to an incorrect manual KOP draining procedure.

"The CXS has taken these same slugs without tripping and, even when stopped unexpectedly, for example during an emergency plant shutdown, it restarts without damage even after it cools down. This is exactly what we expected from the pump. It has been running well for several months in this condition, so we have extended the trial," notes Collins.

In trials at a chemical plant in Italy, the low noise level has proven to be an important factor. Electrical engineers there also have praised the pump's ease of installation: the CXS comes with its own controls and hardwired safety interlocks and software and just needs the power, water and pneumatics connected to be up and running. It can be remotely monitored and controled via several communications interfaces including Ethernet. "What we would like to do in the future is to make the control system even better, for example by including software for its own predictive diagnostic testing."

Figure 3. Small units create a vacuum from compressed air and can be placed at point-of-use. Source: Piab. POINT-OF-USE VACUUMPiab USA, Hingham, Mass., is promoting the benefits of miniaturization and decentralization in vacuum system design. For instance, the company has introduced a new concept for vacuum conveying of powders. Its piFLOWi design promises to allow users to double the conveying capacity for many materials.

The company's patented COAX cartridge technology (Figure 3), which creates a vacuum with compressed air, underpins piFLOWi. Based on Piab's multistage technology, the cartridges are smaller, more efficient and more reliable than conventional ejectors, the company says. It adds that a vacuum system based on COAX technology can provide three times more vacuum flow than conventional systems, allowing users to increase speed with high reliability while reducing energy consumption.

"Traditional, centralized vacuum systems are inherently inefficient, because of the dead volume from tanks, manifolds and longer vacuum lines connecting the pump to the devices utilizing the vacuum. The pumps also have to be sized to accommodate for the 'worst case scenario' and they must compensate for additional volumes. Because of these factors, mechanical vacuum pumps are often oversized, resulting in increased capital costs and energy consumption," says Piab's Peter Tell, Sjöflygvägen, Sweden-based inventor of COAX.

The latest COAX multistage vacuum ejector cartridges are made of lightweight composite materials and are only the size of a pencil; so they are small enough to be directly integrated with end-use devices. By eliminating all tubing between the vacuum generator and the point-of-use, the ejector cartridges are said to significantly improve performance and save energy.

The company also has introduced various integrated vacuum-sensing control options, such as "cruise control," and automated vacuum management, which enable even greater energy saving. "Such energy savings, coupled with improvements in productivity and reduced maintenance costs, are the tangible benefits of the miniaturization and decentralization of industrial vacuum systems," Tell notes.

Meanwhile, Gardner Denver, Wayne, Pa., is talking up the efficiency and economic advantages of its Claw series of vacuum pumps and compressors, which utilize a highly evolved claw design for dry frictionless compression. The company says its rotary vane vacuum pump line also boosts efficiency by requiring less power to operate than other oil-lubricated pumps.

For its part, Tuthill Vacuum & Blower Systems, Springfield, Mo., now is offering the KDS425 vertical-flow dry screw vacuum pump. It features a vertical cantilever design to keep condensables from collecting in the pump process chamber, relatively high internal pump temperatures to thwart vapor condensation in the pump, and dry running operation to stop pump oil contamination. "Customers told us loud and clear there were definite advantages they liked about dry vacuum pumps versus wet vacuum, especially the benefits as to operations and environmental impacts," notes Dave Reader, lean product development manager.

Seán Ottewell is
Chemical Processing's Editor at Large. You can e-mail him at [email protected].

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