GRAND is an
integrated software for fertilizer granulation plant simulation which
includes a comprehensive module RDSIMUL for rotary dryer
simulation. It considers the influence of all the practical
parameters like solids feed rate, temperature and particle size, gas
flow rate and temperature, material critical relative humidity (CRH),
critical moisture content (to account for surface and internal moisture
evaporation), fuel type, water and steam injection etc. and even such
usually neglected (but important) parameters like gas leakages (false
air) into the system, entrainment of dust from the dryer and cooler and
their subsequent capture in overhead cyclones.
RDSIMUL predicts the
overall heat and mass balances and reports the important parameters at
various stages and additionally predicts the following :
The integrated system GRAND
predicts other important parameters pertaining to granulator,
cooler and recycle system as well. Specifically, the various
moisture contents and temperatures, water and steam addition rates in
granulator, heat balances for granulator and cooler etc. are
predicted. The important input parameters that affect the
performance are the solids and gas flow rates, feed particle size,
material CRH vs. T relationship, equipment dimensions, slope, rpm etc.
If one set of operating data is available, the software can be
"tuned" for the particular plant and the resultant customised
software would accurately predict for all other combinations of
operating conditions. A technical report entitled
"Methods for Design and Optimisation of Rotary Granulator, Dryer
and Cooler in Fertilizer Granulation Plants" has also been
published which outlines the complete mathematical model with several
worked-out examples, and the same is included as part of the software
RDSIMUL is especially
useful for designing optimum rotary dryers for any specific application.
It is possible to study before-hand the effect of changing equipment
dimensions like diameter and length, and design conditions like rpm and
slope on performance, thereby facilitating the optimum design choice.
Further, the software is extremely useful to offer after-sales technical
support for troubleshooting and getting the maximum from the equipment
supplied. By showing the predictive strength of RDSIMUL to
prospective equipment buyers, it can be used also as an effective sales
tool. The software can also be bundled along with the
equipment supply which will be greatly appreciated by the buyer as the
same would enable continuous optimal running of the plant.
The various methods and
calculational procedures employed in GRAND and RDSIMUL are
presented in our technical report No.PTC:02-4.
Both GRAND and RDSIMUL
are completely menu-driven and user-friendly and come with detailed
Three sets of rotary dryer
simulations using RDSIMUL are given below. Although
detailed predictions are obtained in tabular formats, we give below only
the salient features of the profiles of solids moisture content,
temperatures of gases, solids and
dew-point, and relative humidity along the dryer length. Further,
the overall granulation plant flowsheet, directly obtained from the
software, is also shown. It can be seen from Figs.
4.2 and 8.2 that the solids reach a maximum temperature
inside the dryer at around a length of 13 m. In this case, the
last 2.5 m of the dryer actually performs the function of a
cooler, and the dryer could therefore have been that much shorter in
length. While Figs. 4.1- 4.4 refer to the case of a plant
operating in an extremely cold country during summer, Figs. 8.1- 8.4
refer to the same plant operating during winter. Figs. 13.1-
13.8 refer to another plant operating in a relatively warm country.
The software as such has been put to use for a variety of materials and
operating environments. The tabular result of the software is
extremely comprehensive and can be furnished for a typical case upon
The air balance of a rotary
dryer for one case is shown in Figs. 13.4-13.6. While Fig.
13.4 shows the various contributions to air flow in three different
units, Fig. 13.5 shows the same for two sets of units, namely Nm³/h
and kg/h. Fig. 13.6 represents the same in pie-graph.
The heat balance is similarly shown graphically for the above case in Figs.
13.7 and 13.8. While both heat input and output are
shown side by side in Fig. 13.7, the distribution of heat in the
various output terms is shown in Fig. 13.8 in an alternate
pie-graph. Several combination of graphical analysis are possible
using the integrated graphics system in GRAND and only a few are
shown here for illustration. For a comprehensive and complete
understanding of the operation of a rotary dryer and a granulation
plant, the use of GRAND is indispensable. Its use at the
design stage is still higher and simply can not be over-stated.