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Bureau of Mines / Minerals yearbook: Metals, minerals, and fuels 1972
Year 1972, Volume 1 (1972)

Briggs, Ted C.
Nitrogen,   pp. 881-896 PDF (2.1 MB)

Page 896

tough and rigid and have low permeability to gases such as oxygen and carbon
dioxide so that carbonated drinks contained in them had a long shelf life.
The potential market for these materials is, of course, large.e1 
 A coal gasification process, marketed by Koppers Co., was said to have the
potential to relieve the developing shortage of natural gas. The Koppers-Totzek
process used commercially proven technology to produce a gas rich in carbon
monoxide and hydrogen that could be converted into fuel and process gases
or synthetic natural gas of pipeline quality. The process was in operation
in 16 plants around the world, primarily to gasify coal of all kinds to produce
synthesis gas for ammonia production.62 
 The prilling process for manufacturing solid ammonium nitrate and urea gained
worldwide acceptance since its introduction over 30 years ago. In the prilling
process, a concentrated solution of ammonium nitrate or urea was sprayed
from the top of a tall tower into a rising stream of air which cooled the
droplets, which then solidify into spherical pellets. 
 There are two problems inherent in the prilling process. The first is that
the large volume of cooling air used to solidify and cool the prills requires
the installation of dust scrubbing equipment on the prilling tower to remove
entrained dust. The second is the regulation of product size. The maximum
prill size that can be obtained is limited by the economics of the tower
height, 70 to 170 feet, required to provide sufficient free fall for solidification
and cooling of the liquid spray. The size limitation is more serious with
urea because of its lower melting point, 271° F, compared with 337°
F for ammonium nitrate. Also, urea has a higher heat of crystallization,
104 Btu's per pound, than ammonium nitrate, 61 Btu's per pound. 
 Typical ammonium nitrate prills are 95% plus 16 mesh on a Tyler screen and
about 65% plus 10 mesh. Urea prills are 95% plus 16 mesh and about 30% plus
10 mesh. These sizes and size distributions were said to be less suitable
for bulk blending than product sizes obtained by granulation. 
 A number of studies have shown that segregation occurred when products having
different size ranges were blended or handled. The greatest single factor
in producing segregation was size distribution, while differences in shape
or density had little effect. Granulated ammonium nitrate or urea, as contrasted
with prills, is not limited to a particular size range that can be produced,
and the size of granule produced can be regulated as desired by choice of
suitable screen sizes. 
 Originally developed for the production of granular complex fertilizers,
a C&I/ Girdler, Inc., granulation process utilized the principle of accretion,
or layering, to build up onionskin-like layers of ammonium nitrate or urea
on small seed particles. This was accomplished by spraying a slurry or solution
onto a rolling bed of solid particles in a rotating drum. 
 The C&I/Girdler, Inc., process differs from that used in most granulation
processes. Other granulation processes depend on the agglomeration, or sticking
together, of small particles by using a solution or slurry as the binding
agent. The agglomeration method was found to be unsuccessful for the granulation
of ammonium nitrate.63 
 61 Chemical Marketing Reporter. Nitrile Resins of IC! Groomed for Containers.
V. 202, No. 24, Dec. 11, 1972, p. 27. 
 "Farm Chemicals & Croplife. Answer to Natural Gas Shortage? V. 135,
No. 8, Aug. 1972, p. 
 "Reed, R. M., and J. C. Reynolds. The Spherodizer Granulation Process. Chem
Eng. Prog., v. 69, No. 2, February 1973, pp. 62—66. 

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