An introduction to two different systems, the Dynamic distribution system,
and the Static distribution system.
An evenly distribution of the production into all the tubes in the calandria
is required for a good coverage. The product distribution system requires
special attention during the design of an evaporator.
DYNAMIC DISTRIBUTION SYSTEM
In the dynamic distribution
system (Fig. 18), the necessary kinetic energy for distribution is
obtained by a drop in pressure of the product over a full-cone nozzle. As the
product is superheated in relation to the pressure inside the tubes, flash
vapour is instantaneously formed. The mixture of product and vapour is sprayed
into the inlet of the tubes thus being covered by product.
Fig. 18 Dynamic product
distribution system
The ability of a nozzle to spray optimally depends on the pressure drop
determined by the quantity of the liquid to be handled and the degree of
flashing when entering the room above the tubes. This distribution system is
not considered adequate in modern evaporators where flexibility, and thereby
differences in the feed quantity are required. Further, in multi-effect
evaporators the flashing, and therefore the distribution, is minimal due to low
∆t.
STATIC DISTRIBUTION SYSTEM
In the static distribution system
the incoming superheated product is first separated in flash vapour and
product. The product enters a distributor plate placed inside an
open cone, when entering the calandria. The cone is placed above a
distributor bowl with a number of holes, where a certain level of product is
maintained. The product flows through the holes in the plate by gravity. Each
hole is placed just above the area between the tubes. Thus the product flows
onto the tube plate and then over the edge down along the surface of each tube.
The flash vapour also enters the tubes and pushes the product against the inner
surface of the tubes giving it its initial velocity. (Fig. 19)
Fig. 19 Static product
distribution system
This distribution system is much more flexible in respect of capacity, as an
increase in the level within the distributor bowl - as a result of increased
capacity - will make the product flow through the holes at a higher velocity,
thus maintaining the level.
