Closed-loop liquid ring vacuum system with a non-water ring liquid (oil- or solvent-sealed, with Roots booster) for vapour recovery

01

Choose the ring liquid by its vapour pressure at the cooled loop temperature

Busch, writing in CPP, explains that the achievable vacuum of a liquid ring pump depends on the vapour pressure of the operating fluid, which is why the pumps work only in the rough-vacuum range. The fluid can be water or a liquid compatible with the gas or vapour pumped: ethylene glycol, mineral oils, organic solvents, or other liquids that are already part of the process. [1]

In a closed circuit, Busch describes the separated fluid passing through a heat exchanger before it re-enters the pump, so it stays at a constant temperature and only small amounts of fresh fluid are needed; the fluid absorbs the heat of compression and the pump runs close to isothermal. [1] Editorial note: with a non-water ring liquid it is the closed circuit that keeps the liquid, and the vapour condensed into it, inside the plant instead of going to drain.

Editorial calculation from NIST's Antoine parameters [4] [5] (water: A 5.40221, B 1838.675, C −31.737, valid 273–303 K; toluene: A 4.14157, B 1377.578, C −50.507, valid 273–323 K; P in bar, T in K): water's vapour pressure is 10.0 mbar at 7 °C, 17.0 mbar at 15 °C and 31.7 mbar at 25 °C; toluene's is 13.9, 22.1 and 37.9 mbar at the same temperatures. So a toluene ring at 15 °C (22.1 mbar) has about the vapour pressure of a water ring at 19 °C: a toluene-sealed loop has to run roughly 4 K colder than a water-sealed one to hold the same limit. [5] [4]

Editorial note: compare the ring liquid's vapour pressure at the loop temperature with the suction pressure you need; Busch's 33 hPa two-stage ultimate is already of the same order as these values, which is why the coolant temperature, not the pump size, decides how close to it a non-water loop can work. [1] [5] [4]

Give the supplier the vapour composition and flow, the ring liquid you propose and its vapour pressure curve, the coolant and its supply temperature, and how the recovered liquid will be bled from the loop.

02

Add a Roots booster: water ring 267 Pa against oil ring 80 Pa behind the same booster

Shandong Boke's JZJ2B Roots–liquid ring systems pair ZJP Roots pumps with 2BV or 2BE1 liquid ring backing pumps, and its table gives two ultimate pressures for the same set: 267 Pa as a water ring vacuum system and 80 Pa as an oil ring vacuum system. The 70 L/s JZJ2B70-2 (ZJP-70 on a 2BV5110) lists a maximum inlet pressure of 6,000 Pa and 5.5 kW total power. [2]

Editorial calculation: the oil ring brings the set's ultimate down by a factor of 267 ÷ 80 ≈ 3.3 with the same booster — the effect of a lower-vapour-pressure ring liquid in the backing pump carried through the booster stage. 70 L/s × 3.6 = 252 m³/h. [2]

A larger example of a booster train on a non-water ring: a Wintek vapour-recovery system listed by Phoenix Equipment uses two rotary-lobe vacuum boosters in series, followed by an intercooler and a two-stage liquid ring vacuum pump, and operates at about 4.7–5.2 torr absolute, with a booster liquid-injection system on the skid. [3] Editorial calculation: 5 torr × 133.3 Pa/torr ≈ 667 Pa. [3]

Boke also offers flow parts in stainless steel, duplex stainless steel or titanium alloys and protective coatings for corrosive duties, with mechanical or packing seals chosen to the operating conditions. [2] Editorial note: ask at what inlet pressure each booster is switched on and how it is protected above the listed maximum inlet pressure.

03

A biodiesel-sealed vapour-recovery skid on a distillation column, line by line

The Wintek system is a single published unit, but its listing gives the design data a buyer of a non-water-sealed system has to supply or check. [3]

Duty: designed for a biodiesel distillation column; 5,600 ACFM design capacity and 4,792 ACFM operating capacity; inlet flow 280 lb/h with a listed composition of 76% nitrogen, 23% methanol and 1% water vapour, at 60 °C. Ring liquid: biodiesel, circulated in a closed-loop recovery system through a plate heat exchanger by a circulation pump. Cooling medium: 45 °F water with 40% glycol. Skid: two Tuthill rotary-lobe boosters, intercooler, a Dekker DV0751B-DA3 two-stage liquid ring pump with a 75 HP motor, separator tank, instrumentation, valves and skid-mounted piping; 3-phase 60 Hz 460 V. [3]

Editorial calculation: 5,600 ACFM × 1.699 = about 9,510 m³/h and 4,792 ACFM about 8,140 m³/h at suction conditions; 280 lb/h is about 127 kg/h; 45 °F is about 7.2 °C. Using the product the column already makes as the ring liquid means methanol condensing in the loop ends up in a stream the plant can handle, rather than in seal water. [3]

Editorial note: the listing does not say how the methanol that condenses into the biodiesel ring is removed from the loop; ask any supplier how the ring liquid's composition, and with it its vapour pressure, is held steady over a campaign.

04

Ring-liquid loop, chilled exchanger, circulation pump, boosters and intercooler

05

Ring liquid, loop temperature, ultimate pressure and booster data for the quotation

06

Send the vapour, ring-liquid and coolant data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Process: [dryer, column or reactor; working pressure]
Vapour load: [composition; flow; inlet temperature]
Ring liquid: [proposed liquid; vapour-pressure data]
Coolant: [medium; supply temperature]
Boosters: [number; switch-on pressure]
Recovery: [how condensed vapour leaves the loop]
Site: [electrical supply; hazardous-area class]

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