The Passive Vacuum Degasser; Research Test Setup and Preliminary Observations

Some form of vacuum-assisted degassing is often required in both production and research facilities to bring the total pressure of dissolved gasses in the culture water below the saturation value. One form of vacuum degasser is the passive vacuum degasser, a device that consists of a column, packed or unpacked, that has its tailpipe exiting below the surface of the water in the receiving vessel. Such an arrangement causes a vacuum to self-form in the column. The strength of this vacuum appears to correlate to both geometric and operational parameters in relationships that have not yet been clearly defined. An elaborate recirculating apparatus, with degassing columns equivalent in size to a commercial system, has been set up to explore the various physical parameters of passive degassers. Initially, to observe the degassing process, the column being used is a 10 ft (3 m) long, 1 ft (0.3 m) diameter clear plastic pipe into which water, supersaturated with air, is introduced at its upper end. The pump has been selected to operate at rates adjustable up to 210 USGPM (800 Lpm). A chiller is used to maintain a constant temperature. The re-saturation of the water is accomplished by means of a separate pressurized packed column. The geometric parameters that will be investigated are: column diameter to length ratio, distribution plate design, tailpiece diameter and length, and packing/no packing. The operational parameters include water flow rate, air saturation rate, water temperature, and column water height. Instrumentation includes a paddle wheel flowmeter, ultrasonic flowmeter, total gas pressure, oxygen level, temperature sensors before and after the column, column vacuum probe, column height differential pressure transducer, cross-over pipe pressure and pump pressure. The entire setup is linked to a computer for data logging. The aim of this paper is to describe the apparatus and its instrumentation, and report some preliminary findings.