Physical methods of preventing scaling in heat- and mass-transfer equipment
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NEW MATERIALS AND CORROSION CONTROL
PHYSICAL METHODS OF PREVENTING SCALING IN
HEAT- AND MASS-TRANSFER EQUIPMENT
V. M. Sheptun UDC 66.023.23:621.187.3
In the course of the physicochemical treatment of industrial solutions the working surfaces of heat- and mass-transfer equipment become covered with salts, which leads to a reduction in the performance of the equipment. This phenomenon is taken into account in the design stage by increasing the working surface area of the equipment by about 1.1-1.3 times depending on the rate of growth of the scale. In addition, it is necessary to provide additional lines of equipment and auxiliary equipment for removing the scale.
These measures make it possible to maintain the required performance of equipment, but lead to considerable increases in the consumption of materials and in the operating and capital costs. These costs can be reduced to a minimum if the project includes physical methods for preventing the scaling, of the working surfaces (for example, ultrasonic or acoustic means, which are regarded as the most reliable and effective methods). Ultrasonic scale prevention is based on the contact introduction of vibrations into the equipment by means of magnetostrictors and ultrasonic generators.
The end of the waveguide of a magnetostrictor is rigidly connected to the working surface of the equipment. During the contact introduction of the vibrations into the equipment the scale is broken up as a result of deformations of the working surfaces. The acoustic method of preventing scale on working surfaces is based on the direct superposition on the heat- or mass-transfer medhnn of vibrations of the sonic frequency range (f = 20-20,000 sec-X). As the emitters use is made of electromagnetic, electrodynamic and hydrodynamic energy transformers.
Apart from the hydrodynamic transformers, the transformers are fed from an alternating current network using frequency multipliers and by electromechanical generators [i]. The hydrodynamic devices transform the energy of a liquid stream provided by a pump into wide-band acoustic vibrations. For this purpose, gear pumps, screw pumps, and other types of pumps with flow rates Q = 3-10 m3/h and pressures p = 0.5- 1 MPa are used.
The scale is broken up by the sound-pressure field of varying sign. The effective sound pressure needed for breaking up the scale depends on the salt concentration in the liquid, the liquid velocity in the channel, and falls in the range of values.
The acoustic vibrations can be imposed on the heat- and mass-transfer media either by the continuous or periodic operation of the transformer (without shutting down the equipment for the removal of the scale). For continuous conditions, the sound pressure is selected to satisfy the conditions that the rates of growth and break-up of the scale should be equal.
Translated from Khimicheskoe i Neftyanoe Mashinostroenie, No. 9, pp. 28-29, September, 1986. No. 9 1987 Plenum Publishing Corporation