MVR for Wastewater Treatment (Mechanical Vapor Recompression Evaporators)

Increasing energy costs have justified the increased use of mechanical recompression evaporators. 

The principle is simple. Vapor from an evaporator is compressed (with a positive-displacement, centrifugal or axial-flow compressor) to a higher pressure so that it can be condensed in the evaporator heat exchanger. Various combinations are possible, including single-effect recompression, multiple-effect recompression, multiple-stage recompression, and single-effect recompression combined with a multiple-effect evaporator.

Based upon a 75% isentropic (adiabatic, reversible) compressor efficiency and a combined electric drive motor and gear reducer efficiency of 92%, the energy required to compress a single pound of vapor from 14.1 to 22.8 psia is only 49.3 BTU. To produce the equivalent steam from one pound of 234 oF evaporator condensate requires 999 BTU. The energy savings possible through the use of a recompression evaporator are significant. In some cases multiple-effect evaporators have been converted to MVR to take advantage of changes in the relative cost of electric power and steam.

The compression ratio required is comprised of three components which are:
The boiling-point rise, i.e., the temperature of the boiling liquor minus the temperature of boiling water at the same pressure.
The Delta-T required for heat transfer.
The pressure drop in the vapor pipe to and from the compressor.

Vapor bodies use the ZONTEN vertical-inlet baffle design, which has proven to be effective in minimizing short circuiting. Vapor from the body is compressed with either a single-stage centrifugal compressor, a multiple stage fan or a turbine and condensed in the heat exchanger. Condensate is sprayed into the vapor discharged from the compressor to control super-heat. Depending on the application a small amount of make-up steam may be required.

Most submerged-inlet evaporators short circuit. That is, some of the heated liquor which enters the vapor body short circuits to the outlet instead of rising to the boiling surface. The boiling temperature of the liquor is increased above the equilibrium value (denoted as degrees of short circuiting), which decreases the, Delta-T available for heat transfer. It is particularly important to minimize short circuiting in recompression evaporators because this reduces the available temperature difference to drive the system. Overcoming this requires a higher compression ratio which increases power consumption.

Mechanical recompression is not limited to single-effect evaporation. It is sometimes economical to compress vapor from the last effect of a double- or triple-effect evaporator so that the vapor can be condensed in the first-effect heat exchanger.

ZONTEN can design and supply many different types of equipment to achieve processing requirements.
Our specialty is designing and installing innovative systems to convert liquid solutions into dry solids using evaporation, crystallization and drying.

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        Shanghai ZONTEN Environmental Protection Technology Co., Ltd is a New Hi-tech Enterprises, specialized in developing, designing, manufacturing, installing & commissioning MVR Evaporator with 10,000 square meter working plant.

        We are a perfect organization, ISO9001-2008, ISO14001, OHSA18001, OHSAS18001:2007 past, Evaporation & Crystallization Member of CPCIF (the China Petroleum and chemical industry association). We warmly welcome you visit us.