NOVEMBER 2016
| WORLD FERTILIZER |
23
and subsequently urea is formed by the
dehydration of the carbamate in the shell side. The
reaction heat of carbamate formation is recovered
to generate 5 barG steam in the tube side. A
packed bed is provided at the top of the VSCC in
order to absorb any uncondensed ammonia and
CO
2
gas into recycle carbamate solution from the
MP absorption stage. Inert gas from the top of the
packed bed is sent to the MP absorption stage.
A major feature of ACES21 is that it reduces the
amount of equipment needed in the urea synthesis
loop, simplifying the system. By introducing the HP
carbamate ejector, the urea reactor is laid out
quite compactly in low elevation. In addition, since
the operating condition of the synthesis section in
ACES21 is optimised under a lower operation
pressure than the previous process, a reduction in
energy consumption is achieved.
Spout-fluid bed urea granulation
process
The spout-fluid bed urea granulation process is a
urea process technology designed to produce a
large-size, high-quality urea product while saving
energy. It has been applied to 23 urea plants from
50 tpd to 4000 tpd production capacities in a
single train as a proven and reliable process.
TOYO established a urea granulation process
that was based on a spouted bed type urea
granulator and expanded its technical range to
provide a variety of urea fertilizer products,
including the addition of a conventional urea prill
product and urea solution product.
In the late 1990s, the company furthered the
design of the granulator by applying spout-fluid
beds to the granulator. The combination of the
spouted beds and fluidised beds reduce energy
consumption and improve the quality of the
product granules (Figure 4).
In the granulator, a spouted bed is formed by
an upward stream of air that is introduced into the
bottom of the granulator and a fluidised bed is
formed surrounding the spouted beds. The air
introduced into the spouted bed maintains the
particles in suspension. The droplets of urea
solution fed to the bed through the spray nozzles
are deposited on the surfaces of suspended seed
particles. Thus, the particles gradually grow
layer-upon-layer.
Since the air introduced for spouting and fluidising has
a cooling and drying effect, the spout-fluid bed granulator
functions as a cooler and a dryer. 96% of the urea solution
can be fed to the granulator to obtain a product with a
moisture content of 0.3% or less. This function provides a
lower biuret product and a lower utility requirement
compared to a molten urea feeding case.
Deciding the droplet size of the sprayed urea solution
on the seed particles is one of the key parameters in
improving the drying function and the shape of product.
The smaller the droplet size results in more surface area
in contact with the spouting hot air at the spouting pipe,
and a more uniform and thinner film on the seed
particle’s surface. They will accelerate the vaporisation of
water in the urea solution through this efficient contact
with the spouting and fluidising air. A more uniform film
will help to realise the sphericity (roundness) of the
product’s shape and the smaller droplet size also
eliminates the agglomeration of product.
Figure 5 shows the process flow of TOYO’s granulation
process, including this spout-fluid type granulator.
The urea solution, or molten urea, is fed into the
spouting urea seeds through multi-spray nozzles to enlarge
Table 1.
Performance test results of the Kaltim No.5 urea plant
Item
Unit
Actual Target
Production capacity
tpd
3545 3500 minimum
Total quality
Total nitrogen content
Wt%
46.2 46 minimum
Biuret content
Wt%
0.9
0.9 maximum
Moisture content
Wt%
0.3
0.3 maximum
Product size
Between 2 – 4.76 mm Wt%
97.2 94.9 minimum
Less than 1 mm
Wt%
0.0 0.1 maximum
Between 1 – 2 mm
Wt%
3
4 maximum
Above 4.76 mm
Wt%
0
1 maximum
Emission
Urea dust emission
mg/Nm
3
21
35 maximum
Ammonia emission
mg/Nm
3
66
125 maximum
Utility consumption
HP steam
T/T-urea
0.746 0.775 maximum
MP steam
T/T-urea
0.033 0.055 maximum
Electric power
kWh/T-urea 44
54 maximum
Total energy consumption
*)
Gcal/T-urea 0.82 0.89
*) The following basis have been applied to calculate the total energy
consumed in urea plants:
n
n
Excluding energy for cooling water.
n
n
Steam: Inlet steam enthalpy based on 50˚C steam condensate
return from urea plant.
n
n
Electricity: 2100 kcal/kWh.
Table 2.
Product specification of the IEFCL urea plant
Item
Unit
Actual
Target
Nitrogen content
Wt%
46.4
46.2
minimum
Biuret content
Wt%
0.8
0.9
maximum
Moisture content
Wt%
0.3
0.3
maximum
Product size
Between 2 – 4 mm
Wt%
93
90 minimum
Less than 2 mm
Wt%
1
5 maximum
Above 4 mm
Wt%
6
7 maximum
