Swenson Technology,
Inc.| Swenson Technology,
Inc. |
LTV FALLING-FILM EVAPORATOR |
| A Swenson
single-effect, LTV falling-film evaporator with
separate vapor body and heat exchanger is shown in Fig. 7.
Liquor is fed into the top liquor chamber of the heat
exchanger where it is distributed to each tube.
Swenson provides several different distribution devices
for falling-film evaporators; a distribution plate is
shown in Fig. 7. The liquor accelerates in velocity as it descends inside the tubes because of the gravity and drag of the vapor generated by boiling. Liquid is separated from the vapor in the bottom liquor chamber of the heat exchanger and with a skirt-type baffle in the vapor body. A supplemental entrainment separator can be installed in the upper portion of the vapor body to reduce liquid entrained with the vapor to a minimum. The Swenson direct-contact condenser (shown in Fig. 7) is used to condense the vapor with water. Concentrated liquor is discharged from the bottom liquor chamber and cone bottom of the vapor body. The vapor body can also be provided as an integral component of the heat exchanger, similar to that shown in Fig. 5, except the heat exchanger would be located above the vapor body in the falling-film configuration.
Fig. 6. Triple-Effect, Falling-Film, Membrane Cell, Caustic Soda Evaporator |
Evaporation also occurs inside the tubes of the
falling-film evaporator. The unit can be used to
concentrate the same non-salting liquids concentrated in rising-film
evaporators, and it is suitable for
concentrating more viscous liquors. Tube sizes and
lengths are comparable to those for rising-film
evaporators. The falling-film evaporator is particularly useful in applications where the driving force in temperature difference between the heat-transfer medium and the liquid is small (Delta-T's of less than 150F). The retention time for liquor in this evaporator is less than that for a rising-film evaporator. The combination of short liquid retention time and the ability to operate at a low Delta-T makes the falling-film evaporator ideal for concentrating the most heat-sensitive materials. High heat-transfer coefficients are attained in falling-film evaporators when a continuous film of liquid, preferably at its boiling point, flows down the inside tube wall with a vapor core in the tube center. For some applications, however, it is necessary to supplement an insufficient quantity of feed liquor with product liquor pumped to the top liquor chamber to avoid vapor blanketing of the inside tube surface.
Fig. 6A. Two, 4-Stage, Mechanical Recompression, Falling-Film Evaporators |
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Copyright 2002 Swenson Technology, Inc. |
