PROCESSWASTE HEAT EVAPORATORS - WHE
Protein rich raw materials from fish and animals can contain up to 70% water that needs to be removed by thermal drying which again
requires large amounts of steam produced by boilers that burn expensive oil, gas, coal or solid fuel.
The main purpose of a waste heat evaporator (WHE) is to save 30 to 50% of drying steam consumption in LTR – LOW TEMPERATURE
RENDERING fishmeal and rendering plants using cooker, twin screw press (or decanter) and dryer.
Such LTR plants separate the solids and liquid in twin screw press or decanter followed by separator to make clean and oil free stick
water with dissolved protein (like sugar is dissolved in water) content ranging from 7 to 12% that must be recovered
to produce high protein animal feed grade meal.
The WHE utilize the waste heat vapor from the steam heated disc drier to evaporate stick water UNDER VACUUM before
the concentrate is returned to the drier.
Especially fish and chicken raw materials have high content of water, up to 70% which makes the WHE more feasible.
Example:
LTR plants without WHE will use about 1 kg steam to process 1 kg raw material.
LTR plant with WHE will use 0.55 to 0.6 kg steam to process 1 kg raw material by using the waste heat.
This means the WHE will as an average remove 40% of the water in the raw material – almost “free of charge”.
Note that HTR = HIGH TEMPERATURE RENDERING and LFP = Lean Fish Plants evaporate all the water in the dryer and can not utilize the waste vapor
for energy saving as there is no separation of the stick water to be processed in the WHE. However, sometimes the waste vapor can be used to make hot water for use in a nearby abattoir – slaughter house
The WHE come in 1-stage or 1- effect if the plant is small and there is little stick water (tuna waste) and 2-or 3 stages
or effects for large plants that need maximum saving.
The 2 and 3 effect waste heat evaporator utilize the vapor more than one time under ever stronger vacuum and lower boiling point.
In principle, the Disc Dryer is a dryer for solids (fishmeal) with high steam consumption, while the WHE is a dryer for the stick water that works “free of charge”.
The WHE does not use steam from the boiler, but use the wasted
vapor from the disc drier that would normally be thrown away.
The disc drier will evaporate water at normal boiling point
100 deg C. The WHE will evaporate water under vacuum where
the boiling point is only 60 deg C. (that is the whole secret with
the WHE : vacuum!)
The design of a WHE is basically a stainless heat exchanger with
tubes, a circulation pump for the stick water which is pumped
around and around, a vacuum pump plus two in and out feed
pumps, and a condenser.
When the WHE has run for a while, the stick water will concentrate
to a thick syrup that is pumped into the drier and mixed with the
fishmeal.
WHE requires skilled operators and good maintenance and must
often be cleaned by flushing with caustic soda.
The WHE can be installed after the OFP fishmeal plant is installed.
