If you already own a vacuum unit
Keep it for planned dewatering campaigns, then fit a small offline loop to hold the tank dry.
Comparison
Water removal technologies compared
Vacuum dehydration, centrifuges, coalescers, headspace dehumidifiers and Desorbers all remove water from oil, at very different running costs. Whether the water is free, emulsified or dissolved decides which fits.
We sell Desorber and depth filtration equipment, so keep that in mind. Where a vacuum unit or a centrifuge is the better tool, the table says so.
The comparison matrix
| Vacuum dehydration | Centrifuge | Coalescer | Headspace dehumidifier | CJC Desorber and depth filtration | |
|---|---|---|---|---|---|
| How it works | Oil is heated and exposed to vacuum so water boils off at reduced pressure | High speed rotation separates by density | Fine droplets merge on a media surface until they are heavy enough to drop out | A desiccant unit dries the air in the space above the oil, so less moisture is absorbed from the tank atmosphere | Cellulose media absorbs water and traps particles. For heavier loads the Desorber preheats the oil to 70 °C and meets it with a counter flow of cold dry air, which takes up the water. Cooling the air condenses that water out, and the dried air recirculates |
| Free water | Yes | Yes | Yes | Slowly | Yes |
| Emulsified water | Yes | Partly, poorly with stable emulsions | Partly, fails with low interfacial tension oils | No | Yes, and it breaks stable emulsions |
| Dissolved water | Yes, down to low ppm | No | No | Yes, slowly | Yes. The Desorber takes oil down to below 500 ppm |
| Removes particles at the same time | Not without a separate filter stage | Heavy solids only | No, and solids blind the media | No | Yes, 3 µm absolute in the same pass |
| Removes oxidation products and varnish | No | No | No | No | Yes |
| Heat applied to the oil | Yes, typically 60 to 80 °C under vacuum | Often pre-heated | None | Sometimes | Media alone: none. Desorber: oil preheated to 70 °C at atmospheric pressure. No vacuum, so the oil never boils |
| Risk to additives | Controlled units are fine. Run too hot, too long, or at too deep a vacuum and lighter additive fractions and antioxidants can be stripped along with the water | Can throw out additive-rich sludge and some water soluble additives | Surfactant additives disarm the coalescing media, and the media can strip those additives out of the oil | Low | Low. Without vacuum there is nothing to draw volatile additives off, and C.C.JENSEN states the process is unaffected by the additive package |
| Rotating or vacuum machinery | Vacuum pump, heater, condenser, controls | High speed bowl, drive, balancing | Pump only | Blower or dryer | A circulation pump, plus a heater and fan on the Desorber. No vacuum pump and no high speed rotating parts |
| Capital cost | High | High | Low | Medium | Medium |
| Running cost | High. Heater and vacuum pump draw continuous power | Medium. Energy plus periodic bowl service | High. Frequent media replacement | Medium | Low. Fractional kW motor plus insert changes on condition |
| Operator attention | Skilled operation and regular maintenance | Scheduled cleaning and balancing | Media changes | Desiccant changes | Insert changed on gauge indication |
| Usual deployment | Mobile unit brought in for a campaign | Permanent on large lube systems and marine plant | Fuel and clean fluid duties | Fitted on a reservoir headspace | Permanent on the tank, running continuously |
| Best suited to | Large one-off dewatering jobs and systems where dissolved water must reach very low ppm, such as some turbine and EHC duties | Heavy free water plus solids, high volume systems, marine engines | Clean fuels and low solids fluids where free water is the only issue | Holding a dry reservoir dry after it has been cleaned up | Continuous control of water and particles together, on systems that must keep running |
| Not the right tool for | Continuous low level water control, where the energy and maintenance cost is hard to justify | Emulsified or dissolved water, and fine particle control | Emulsified water, detergent oils, dirty oil | Free or emulsified water, particles | Oil that is heavily flooded. Drain the free water first, then let the Desorber and the loop hold it dry |
Swipe sideways for all columns.
The additive question
A vacuum dehydrator run within its design envelope will not damage a modern turbine oil. Run too hot, too long or at too deep a vacuum, it can strip antioxidants along with the water. The Desorber works at atmospheric pressure, so there is no vacuum to pull volatiles out. C.C.JENSEN state the process is unaffected by viscosity and by the additive package.
Which method suits your oil
Send the water figure in ppm, the oil type and where the water is getting in. We will say which method fits, even if it is not ours.