LTV Falling-Film Evaporator
A Swenson single-effect, Long Tube Vertical falling-film evaporator with a separate vapor body and heat exchanger are shown in Figure 2. Liquor is fed into the top liquor chamber of the heat exchanger where it is disturbed to each tube. Swenson provides several different distribution devices for falling-film evaporators; a distribution plate is shown in Figure 2.
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, as shown in Figure 2, is used to condense the vapor with water. Concentrated liquor is discharged from the bottom liquor chamber and cone bottom of the vapor body.
Evaporation occurs inside the tubes of the falling-film evaporator. The unit can be used to concentrate the same non-scaling liquids concentrated in rising-film evaporators, and it is suitable for concentrating more viscous liquors. Tubes are normally ¾” to 2” in diameter and from 10 to 30 feet long. 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 less than 15°F. The retention time for the liquor in this evaporator is less than that for a rising-film, and this fact paired with lower temperature differences makes the falling-film evaporator ideal for concentrating the most heat-sensitive materials.