Abstract SYMPHOS 2011

Figure 2
From the 1960’s to Date
The changes to processing techniques since the 1960’s have been evolutionary
rather than revolutionary.
I have the following memories from when I first started out in the fertilizer
industry back in 1975 in the U.K.
The plants that we operated were old, probably dating back to the 1940’s and
50’s.
MATERIALS OF CONSTRUCTION
A lot of wood was used, especially for floors and roof beams etc. Today
practically no wood is used for any purpose – steel and concrete have taken
over as cheaper and superior materials. Not much stainless steel was in
evidence – rubber, and, where appropriate, brick lining, on carbon steel was
employed. As better stainless steels have become available, these have tended to replace lined carbon steel in
many duties due to lower maintenance costs.
PRODUCT SIZE
At the time our focus was on maximizing capacity rather than maximizing product quality. Standard product size
was maybe 85% between 1 and 4 mm. Today’s customer requires a much tighter and larger size specification to
optimize distribution of the fertilizer by mechanical spreaders. Typically a size distribution of 95% between 2 and
4 mm is required.
This has become a practical proposition as the available screening machines have improved considerably. The
machines that we operated when I first started work were essentially horizontal, frame vibrated machines with no
in-built mechanism for keeping the cloths clean. The cloths tended to blind quite quickly leading to progressively
more and more fines in the product. As a result we actually had an operator with a long handled brush whose job it
was to physically clean the screens (“the screen man”)! Luckily the current generation of screens that are available
are inclined at some 35deg. to the horizontal, have static frames and the cloths are directly vibrated by electric
motors, meaning that they are, to a large extent, self-cleaning.
CONTROL SYSTEMS
The plants that we operated back in 1975 had a very rudimentary measurement and control scheme. Such controls,
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A major break-through came in 1956 when
Frank Nielsson of TVA patented the Ammoniator-Granulator
(See Figure 3). This invention
allowed large quantities of ammonia to be
injected beneath the rolling bed of wet solids
in a rotary drum with reasonable efficiency. In
the TVA process only one “preneutralizer” vessel
was used, operating at the point of maximum
solubility (mole ratio 1.4-1.45) to minimize the
slurry moisture (16-20%). This enabled recycle
ratio to be reduced to about 5/1. Modern plants
Figure 3