Vacuum Technology Tackles Voids

Innovative use of existing technology and new developments improve performance.

By Seán Ottewell, Editor at Large

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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."

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.

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