Dry vacuum pumps

Figure 12-2C. Dry vacuum pump cyiinder for very iow absoiute suction pressures. Vaives in heads for iow ciearance and high voiumetric efficiency. (Used by permission Bui. L-679-BiA, 1957. Dresser-Rand Company.)...

Positive displacement pumps are self-priming by their normal operating action and are designed to cope with mnning dry. Centrifugal pumps are not inherently selfpriming, and need to be provided with assistance in the form of ejectors, as in Figure 32.56 or dry vacuum pump systems. In these systems, a dry vacuum pump allows air to be drawn out and where an automatic valve prevents... 

Fig. 2.29.1. Working schema of a dry vacuum pump operating on the so-called claw principle. 1 rotors 2, compression chamber 3, suction chamber 4, exhaust slit 5, suction slit 6, purge between stages (Figure from [2.241).

Fig. 2.29.2. Working schema of a four-stage dry vacuum pump, type Leybold DRYVAC .

One option involves the condensation of (or part of) the permeate under atmospheric instead of vacuum conditions. This requires the use of dry-vacuum pumps , able to compress the permeate vapour from vacuum to atmospheric pressure, after which condensation is performed at a higher temperature [23]. In this case, the operating conditions have to be carefully monitored since these pumps may lead to unsuitable heating of the vapour and eventually aroma deterioration, despite the low residence time. Alternatively, the use of liquid ring vacuum pumps where the service liquid can take some of the aromas from the permeate stream has been proposed [24]. 

Fig. 2.44. Dry vacuum pump combination with Such combinations are available for pumping a dry Roots pump for fast evacuation, a high speeds from 250 to 4000 m3/h [2.25]. pumping speed and a low ultimate vacuum.

Fig. 2.45.1. The diagram shows the pumping speed for a pump set combination consisting of an EH 500 Roots pump and a GV80 dry vacuum pump (BOC Edwards). The advantage of...

Vacuum is applied to the chamber and vapor is removed through a large pipe which is connected to the chamber in a manner such that, if the vacuum is broken suddenly the inrushing air will not greatly disturb the bed of material being dried. This line leads to a condenser where moisture or solvent that has been vaporized is condensed. The noncondensable exhaust gas goes to the vacuum source, which may be a wet or dry vacuum pump or a steam-jet ejector. 

A vacuum source this can be a water pump (see p. 29) with an anti-suck-back trap producing a vacuum of 15-25 mm Hg, at best or a rotary vacuum pump (consult your instructor about its use since it is an expensive piece of equipment and easily contaminated or damaged), which will evacuate down to 0.1 mm Hg. Two-stage dry vacuum pumps produce a vacuum of 1-5 mm Hg, are resistant to organic and acid vapours and are easy to use. 

Ryans, J., Bays, J., Run Clean with Dry Vacuum Pumps, Chem. Eng. Prog., 97,10, 32,... 

Vacuum / / / —whose flow-rate depends largely upon the in take of air at the various fittings, connections, etc. Different kinds of vacuum pumps can be used e.g., rotary—water/oil sealed, reciprocating dry vacuum pump. 

In the past, environmental problems associated with the commonly used pump fluids, namely water and oil, have led to the development of dry vacuum pumps that compress without contact. Rotary lobe and screw-type vacuum pumps (Fig. 5 and 6) are the types most commonly used for industrial applications. 

Install pre-condensers cooled with cooling/chilled water. Use multi-stage steam ejectors arranged in series/series-parallel arrangement. Use liquid ring or dry vacuum pumps... 

Dry Vacuum Pumps (DVPs) These use the operating principles of rotary-lobe roots blowers, claw compressors or screw compressors, and hence require electrical power. They run dry and hence at very high temperature due to the heat of compression. Usually,... 

Chemical Process Retrofitting and Revamping 11.3.4 Dry Vacuum Pumps... 

Figure 11.11 Surface condenser retrofitted with dry vacuum pumps values shown are for...

Ryans, J.L. and Bays, J. (2001) Run clean with dry vacuum pumps. Chemical Engineering Progress, 97(10), 32-41. 

Dry vacuum pumps Three-stage rotary-lobe 1.5 60-240... 

Liquid-ring pumps are limited to a suction pressure of 10 torr with a moderate capacity and efficiency (25-50%). Dry vacuum pumps can achieve very low pressures at higher efficiencies. 

Dry vacuum pump size for usual discharge pressure 20-35 kPa gauge to allow for downstream discharge. Vacuum pumps run hot 50-70 °C. Allow 30 min warmup period before putting on-line. Allow 60 min purge before shutdown. Try not to have the pump discharge into a common header. Multistage pumps... 

Figure 19 (a)-(c) Oil free vacuum pump sets, (a) Schema of a dry vacuum pump... 

The temperature of the product and the reactor wall has to be kept about 20 °C below the melting temperature of the polyester to prevent sticking. The reaction products, glycol and water, are continuously removed from the reactor to keep the polycondensation going. Therefore, the reactor is equipped with a vacuum system, which reduces the pressure inside the reactor to <5 mbar. The vacuum systems used are either based on a series of steam ejectors (option in combination with a watering pump) or dry vacuum pumps. 

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