The majority of today’s wastewater treatment plants utilize
a n a e robic digestion techniques for biological stabilization of
municipal sewage sludge. These plants which today are an integral
p a rt of any community are tremendous consumers of energy Wi t h
energy costs constantly on the rise and consumption closely monit
o red, existing plants, some of them re t rofitted, and new plants
alike are installing plate and spiral heat exchangers in an effort to
reduce energy consumption, and so improve operating efficiencies.
Each type, however, is considered for very different reasons. Plate
heat exchangers may be selected for their high thermal efficiency
and minimum capital investment. Spiral heat exchangers, on the
other hand, are turned to for their ability to effectively handle fluids
containing solids and fibers, similar to those encountered in
wastewater treatment plants.
First time users will want to become familiar with the basic construction
features, advantages, limitations and applications of
these heat exchangers.
Readers familiar with the heat exchangers may find some fresh
information regarding their installation or operation.
Spiral heat ex c h a n g e r s in their normal orientation are true counter
current flow heat exchangers, with hot and cold fluids flowing in
opposite directions relative to each other. Basically, each exchanger
is an assembly of two long strips of metallic plate wrapped
around a mandrel to form a pair of concentric passages.
Normally, alternate edges of the passages are welded closed so fluids
flow through continuous, isolated channels. Fluid cross
contamination is not possible under normal conditions.
The passage spacing is maintained primarily by sealing bars
mounted at the passage edge and spacing studs. Depending on
the fluid handled, the spacing may range from 1/4” to 1 1/4”.
Certain designs do not contain spacing studs, such as units
applied to handle sewage sludge. The lack of spacing studs
reduces the likelihood of plugging. Depending on thermal and
pressure drop requirements, passage width may range from 9” to
96”. Covers with full face gaskets are fitted to each side of the
unit. Complete units are available from 5 ft 2 to 3000 ft 2.