Vacuum systems with surface condensers

Steam-jet vacuum systems combine ejectors, condensersand interconnecting piping to provide relatively low-cost and low-maintenance vacuum pumping. During system design, critical decisions must be made regarding process conditions, component orientation and layout. Disposal of contaminated water is of growing concern in process operations, particularly in the chemical industry, Where an ejector system is  drawing in contaminants, a condenser that discharges directly to the drain may not be used. In these applications, ejectors using surface condensers are being

utilized more. The surface condenser prevents discharge to the drain and permits recovery or treatment of undesirable wastes. A reliable source of steam and cooling water must be available, and provisions must be made to carry out condensate removal under vacuum. Finally, the appropriate monitoring and control instrumentation must be specified. Specific guidelines should be followed during equipment layout and installation, to optimize system performance. These systems operate on the ejector-venturi principle, which relies on the momentum of a high-velocity jet of steam to move air and other gases from a connecting pipe or vessel. Shell-and-tube surface condensers may be installed either horizontally or vertically. The vapors to be condensed can be routed through either the inside or the outside of the tubes. However, once a unit has been designated for tubeside or shellside vapor duty, it should remain dedicated to that type of service. A steam jet system with surface condensers normally requires more motive steam and condensing water than one with directcontact condensers. This is the most expensive type of multi stage ejector. Customised SANADID multi-stage vacuum systems offer a wide variety of applications. In the field of process engineering surface condensers have proven to be ideal. The decisive advantage is to separate the cooling and the process medium. There are different options of SANADID vacuum systems with surface condensers available.

The figure on the right illustrates a 3-stage system. In this example two jet ejector stages are connected in series to achieve a suction pressure of 1 mbar with a minimum of motive medium. The temperature of the available cooling water determines the achievable pressure in the first surface condenser. A further jet ejector stage compresses the suction flow components of the first surface condenser which can’t be condensed to atmospheric pressure. The motive steam of the upstream jet ejector is condensed in the downstream surface condenser.

Advantages

• separation of process and cooling medium
• decades of experience, proven technology

Disadvantages

• process and cooling water-sided pollution possible