Summary: A number of common industrial processes require vacuum, such as distillation or drying operations. The necessary vacuum has historically been supplied using a variety of technologies that have high operating costs in terms of both consumables (e.g., oil, water) and maintenance costs. With recent advances in pump technology, process vacuum can now be supplied using a number of ‘dry’ vacuum pump technologies. By using dry vacuum pumps, significant operating cost savings can be achieved. Similarly, by eliminating the consumption of process water and the need for disposal of contaminated fluids, switching to dry vacuum pumps also yields environmental benefits. Part 1 provides the detailed background of one case where using dry process pumps offers numerous benefits. Part 2 will quantify the benefits of switching to dry, chemical-resistant diaphragm pumps.
One common application for process-scale vacuum is to use vacuum distillation to separate components of a multi-part mixture. A New Jersey-based chemical recycling company uses vacuum distillation in order to remove liquid contaminants from common industrial chemicals. Historically, they have used a liquid ring vacuum pump to reduce the pressure level within the distillation apparatus to the point that water and other contaminants boil off, leaving behind purified industrial chemicals. However, operational challenges related to the liquid ring pump require that the company identify an alternative vacuum source in order to scale-up their throughput, and thus their revenues. There are three specific operational problems associated with the current liquid ring pump.
The first operational concern is the operating cost of the pump. By their nature, liquid ring pumps require a steady flow of process water, along with electric power as would be required for any motor-driven piece of equipment. In this particular case, the installed liquid ring pump consumes over 700,000 gallons of water per year, based on the 6,000 annual operating hours of this New Jersey chemical recycling firm. This equates to operating costs of several thousand dollars per year – as much as the initial purchase price of the pump. The high operating cost has a notable, negative impact on the firm’s net margins. Identifying a vacuum solution with lower operating costs can therefore have an important impact on the bottom line.
The second limitation of the liquid ring pump relates to the required maintenance and associated downtime. On an annual basis, the primary pump must be taken down for 1-2 working days in order to be overhauled. During this time, and during other, briefer periods of downtime throughout the year, it is necessary to switch over to a back-up pump. The back-up pump is the same model as the primary pump; however, the back-up does not perform as well as the primary unit. This therefore limits throughput and revenues. Finding a new pump solution that is more reliable, requires less frequent maintenance, and does not require duplicative investment, would simultaneously reduce capital costs and operating costs.
The final operational concern relates to the use of the water/anti-freeze solution as the sealing fluid. The throughput of the system is directly dependent upon the liquid ring pump’s ability to reach a specified vacuum level, and simultaneously maintain sufficient flow for the distillation process to progress at the optimal rate. Due to seasonal temperature variations, the flow rate through a liquid ring pump varies significantly throughout the course of the year. On warm days, when the vapor pressure of water is relatively higher, the flow and vacuum level attainable by the pump are reduced, thus reducing the throughput rate significantly. On cold winter days when the local temperature drops below freezing, the sealing fluid can actually freeze in the discharge line, shutting the pump down entirely. This happens because the discharge line is plumbed to discharge outside of the building.