Liquid-ring vacuum system

Fig. 2 Liquid ring vacuum system with closed pump fluid circuit, Dr.-Ing. K. Busch GmbH...

In general, liquid ring vacuum systems are operated with simple particle separators on the intake side. The idea is to have the vapour components separated out on the intake side, provided that this is a low-maintenance option, and controlled compression and condensing of the process vapours occurs in the vacuum pump. 

Liquid ring vacuum systems are standard systems for creating cost-effective and generally low-maintenance installations. 

The simplest designs are volume separators in which droplets of pump fluid are separated from the exhaust gas flow by the reduction in the flow speed. These separators are used in liquid ring vacuum systems. The separation can be improved by fitting swirl bodies. A mixture of saturated vapours that varies according to the operating temperature of the vacuum pump always emerges from the exhaust gas nozzle. 

Dual-phase extraction cannot remediate heavy chlorinated compounds, pesticides, or heavy hydrocarbons including polychlorinated biphenyls (RGBs), dioxin, fuel oil No. 6, or metals (with the possible exception of mercury). High-velocity pump systems (such as liquid ring vacuum pumps) tend to form emulsions, especially when diesel fuel is part of the recovered fluids. The problem of emulsion can be solved with prepump separation or a de-emulsification unit. 

Noncondensable gas-removal system, to remove and compress the noncondensable gases. A typical system uses two stages of compression. The first stage is a steam jet ejector. The second stage is another steam jet ejector, a liquid ring vacuum pump, or a centrifugal compressor. 

The chemical plant consists of a single-effect vacuum evaporator system for regenerating the solution and liberating the sulfur dioxide. Indirect heat is supplied to the forced-circulation evaporator by using exhaust steam from the refinery. The vacuum is supplied by a liquid ring vacuum pump which also pumps the sulfur dioxide back into the front of the Claus plant. 

Vacuum systems with rotary vane vacuum pumps may be used where the process requires vacuums < 50 mbar or if liquid ring vacuum pumps cannot be used in the installation. These vacuum systems are designed to separate out as much of the process vapours and particles as possible on the intake side or to condense the process vapours into the atmosphere as moist air. Rotary vane vacuum pumps may be operated as recirculahng lubrication or blow-by vacuum pumps. The vacuum pump is built with a rotor turning eccentrically in a cylinder. The rotor has axial slots and rotating vanes are pressed against the cylinder by centrifugal force in these slots (Fig. 3). 

Bannwarth, H. (2005) Liquid Ring Vacuum Pumps, Compressors and Systems, WUey-VCH Verlag GmbH Co. KGaA, Weinheim. 

Heuristic 46 For pressures down to 10 torr and gas flow rates up to 10,000ft /min at the inlet to the vacuum system, use a liquid-ring vacuum pump. For pressures down to 2 torr and gas flow rates up to 1,000,000 ft /min at the inlet to the vacuum system, use a steam-jet ejector system (one-stage for 100 to 760 torr, two-stage for 15 to 100 torr, and three-stage for 2 to 15 torr). Include a direct-contact condenser between stages. 

Figure 3.10 Reduction of the maximum power requirement for liquid ring vacuum pumps with variable outlet slots in open systems depending on the altitude.

Figure 3.12 Necessary motor power requirements for open systems depending on the height above sea level for the operation employment of liquid ring vacuum pumps with...

Liquid Ring Vacuum Pumps, Compressors and Systems... 

Brine Dechlorination. In the mercury and membrane processes, the depleted brine leaving the cells must be dechlorinated before resaturation. Further acidification with hydrochloric acid to pH 2-2.5 reduces the solubility of chlorine by shifting the equilibrium point of hydrolysis and inhibits the formation of hypochlorite and chlorate. Chlorine discharged in the anolyte tank prior to dechlorination may be fed into the chlorine system. The dissolved chlorine of the brine then is still 400 -1000 mg/L, depending on pH and temperature. The brine is passed down a packed column or sprayed into a vacuum of 50 - 60 kPa, which reduces the chlorine concentration in the brine to 10-30 mg/L. The vacuum is produced by steam jet or liquid-ring vacuum pump. The pure chlorine gas obtained is fed into the chlorine stream. 

A useful summary of the typical equipment used for developing and maintaining process system vacuum is presented in Table 6-1. Also see Birgenheier [33]. The positive displacement type vacuum pumps can handle an overload in capacity and still maintain essentially the same pressure (vacuum), while the ejectors are much more limited in this performance and cannot maintain the vacuum. The liquid ring unit is more like the positive displacement pump, but it does develop increased suction pressure (higher vacuum) when the inlet load is increased at tlie lower end of the pressure performance curve. The shapes of these performance curves is important in evaluating the system flexibility. See later discussion. 

Vacuum capacities and operating ranges, table, 344, 355 Ejectors, 344, 357 Integrated systems, 344 Liquid ring pumps, 344 Rotary lobe blowers, 344 Rotary piston pumps, 344 Rotary vane pumps, 344 Vacuum equipment, 343 Applications diagram, 352 ASME Code, 344 Pumps, 382 Steam jets, 357 Vacuum flow,... 

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