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Reduce Cost of Ownership with DRY VACUUM PUMPS
The use of dry vacuum pumps in the chemical process industries brings many benefits, not least a significant reduction in installation and operating costs. This article reviews the technology and gives examples from some recent dry pump installation experiences.

Vacuum technologies used in the chemical process industries include wet and dry mechanical pumps. Wet technologies require lubrication fluids, such as oil or water. Oil-sealed pumps require regular maintenance. External oil cleaning devices or regular oil changes may increase the reliability of these pumps, but when pumping solvents, corrosive vapours or dusts there can also excessive wear on internal parts. This can reduce performance often translating into increased production costs. There is also the issue of proper disposal of contaminated oil. In addition to the cost of treatment and disposal, this waste poses a significant threat of pollution to the environment, particularly when contaminated with solvents.

Steam ejectors, whilst usually reliable and robust, can require very large quantities of steam and cooling water, which often create a condensate that is contaminated with process vapour, requiring costly disposal. Liquid ring pumps (LRPs), although simple and reliable, can require large amounts of cooling water. This water can become contaminated with process materials and require appropriate disposal. Proper disposal of wastewater or oil in these systems can be difficult and costly.

The key advantage of all dry pumps is that they do not use water or oil for sealing or lubrication of the vacuum stages. They have a lower environmental impact with no contamination of the process stream or cooling water, and little or no effluent generation. Even though dry pumps are made from ductile cast iron there is no corrosion when operating in the vapour phase. (See figure 1) This is because the pressure and temperature profile inside the pump is maintained above the dew point of the process media, ensuring reliable operation, even when pumping highly aggressive chemicals. Dry pumps require little maintenance, and are often more reliable than oil-sealed pumps, therefore dry vacuum is used to pump some of the most aggressive and problematic gases in a broad range of chemical processes.

Cost of Ownership
The capital cost of a dry vacuum pump is often higher than that of an equivalent wet pump, but there tends to be very little difference when the total installation cost is considered. The installation cost of the latest “fit and forget” dry pumps can be significantly less than for other process vacuum technologies, including other dry pumps. When running costs are taken into account, the dry system often shows a considerably lower cost of ownership. The latest dry pumps with integral pressure control will generally have a lower installation cost than other options. Dry pumps offer the best thermal efficiency of any process vacuum-producing system. Not only does the dry system use significantly less energy when it is running but, unlike a steam ejector, it can be switched off between cycles so that it uses no energy at all when it is not required. Inverters can also be used to minimise the power usage when in standby mode. Reduced power consumption results in lower carbon footprint and environmental impact.

cost of ownership of the dry system means that it often pays for itself very quickly.

Case Studies Highlighting Cost Reductions
The following case studies highlight some examples of companies who have reduced their costs by using dry vacuum pumping solutions.

Precision Control
A manufacturer of chemical intermediates for the pharmaceutical industry based in Hyderabad, (India) had been relying on traditional steam ejectors, which can be unreliable.The comapny began a trial using a dry pump with discrete, tapered variable pitch screws on an acetone recovery process that requires precisely controlled vacuum. The pump is now in regular operation, and the company reports enhanced end-product quality. The vacuum is being applied accurately and consistently, and batches are no longer interrupted. Of particular interest is that they have confirmed they will see a return on investment in less than three months. The reliability of the dry vacuum system allows for a more efficient process, and the substantial improvement in end-product quality means an increase in market value, further reducing the cost of ownership.

Prevent Condensing of Aggressive Chemicals
A major global agrochemicals manufacturer based in Gujarat (India) needed to pump aggressive chemicals including phosphorus oxy chloride, thionyl chloride and hydrogen chloride. Faced with these very aggressive chemicals, the existing liquid ring pumps would have needed to be protected with an expensive up-stream scrubber with high operating costs and potential pollution issues. A reverse claw dry vacuum pump was installed and configured to operate relatively hot so that the pumped vapours could not condense internally during compression. After two years of operation the pump was still in pristine condition.

In another corrosive application, pumping phenol, thanks to the staged and controlled compression and temperature profile within the pump, the supplier was able to offer operation above the saturation temperature, even when pumping a high boiling point material like phenol.

Reusable Uncontaminated Speciality Chemicals
Another agrochemical manufacturer based in Andhra Pradesh (India) wanted to reduce their energy consumption while pumping speciality chemicals. Dry vacuum pumps replaced their multi-stage steam ejectors and in a 12-month trial project they calculated significant savings as a result of reduced energy consumption. The customer also found that they were able to recover almost all of the valuable uncontaminated speciality chemicals at the exhaust for reuse in the process. The results were so impressive that the customer ordered a further 12 systems, and has now replaced all its steam ejector systems with dry vacuum pumps. (See figure 2)

Energy and Water Savings
A specialised fine-chemicals company that produces brominated organic compounds for the pharmaceutical, agrochemical and photographic industries was looking to replace the liquid-ring pump (LRP) and steam ejectors on its distillation system. Bromine and brominated compounds are aggressive chemicals that pose a high risk of corrosion to a pumping system and the production of wastewater was another issue. A large volume of wastewater used to be produced by both the LRP and steam ejectors at the plant, which was costly to treat. As well as standing up to the corrosive application, the ideal system also had to produce no polluted effluent. Further, a very tightly controlled vacuum environment was required, capable of providing a very high vacuum of less than 2 Torr.

A reverse claw dry pump was installed and as a result, the company has achieved higher margins thanks to the increased control over their processes and lower pressures. There have also been considerable savings on energy and the cost of water from not using steam ejectors and liquid-ring pumps. This system has been running successfully since 1996, followed by similar ones on the same site since then.

Environmental Considerations
Green credentials are becoming increasingly important for India’s chemical and pharmaceutical industries. The proper disposal of effluent and other pollutants can be an expensive proposition. Dry pumps, as well as having little or no effluent to dispose of, are energy efficient and the reduced power consumption results in lower carbon footprint and environmental impact.

Conclusion

Dry pumps are clean, reliable and provide low to high vacuum and require minimal maintenance. They can be used quite safely even when pumping flammable and corrosive vapours. Innovation in this sector continues, producing ever more ‘utilitarian’ high performing, highly controllable vacuum equipment that allows processors to reduce environmental impact and minimise running costs.