Prilling Bucket Modifications

1. NP PLANT PRILLING BUCKET EVALUATION FOR
CAPACITY UPRATE
Prepared by: Haider Ali- Business Development (BD) Engineer
Reviewed by: Mudussar Sharif- DM BD & Nitrates Sp.
Date: 16-November-20

2. CAPACITY ENHANCEMENT AREAS
• NP Plant capacity enhanced from 1200-MTPD to 1464-MTPD after successful NP Revamp
Phase I and II projects.
• Major Bottleneck(>1464MTPD):
• Prilling section
• Product cooling(in pipeline)
• Product belt(budget allocated in upcoming TA-21)
• Prilling:
• Prilling bucket design basis: 1500-MTPD
• Prilling bucket overflow issues
• Scrapper floor cleaning requirements
• Prilling tower fan’s capacity for additional plant load(aligned with product cooling,
increment in fan blade pitch angle*)
* ~3o increase in pitch angle increases air flow rate by ~10-15%
DWG FFL
DWG PFL

3. DROP FORMATION DYNAMICS FROM VISCOUS JET
(PLATEAU RAYLEIGH INSTABILITY)
Liquid jet emerging from an orifice develops perturbations on it’s surface.
Once growth rate is maximum i.e. the optimum wavelength(λopt) of the jet
exceeds its circumference, the jet breaks into droplets of same volume but
decreased surface area. λopt is a function of:
(a) Orifice diameter (b) Surface tension (c) Outlet velocity (d) Viscosity
DROP FORMATION DEPENDENCY ON OUTLET VELOCITY
1. Dripping- Oscillations cause jet to disintegrate into drops
2. Jetting- optimum wavelength for jet breakup and jet diameter reduced
3. Transition dripping jetting- unstable growth of small waves in
droplets
4. Atomization occurs rapidly on high outlet velocity
High Pressure
Low Pressure
*A stream with uniform drops that appear immediately is
established by vibration at a frequency near that of the
drop
1 4
2 3

4. NP PLANT-PRILLING
• NP melt is pumped into a perforated rotating bucket(truncated cone)
• High speed rotation of bucket induces centrifugal force which pushes melt against
the wall forming a thin film. It takes shape of a vortex and exits through perforations
established as a curved jet
M
Length of emerging jet is a function
of tangential velocity(𝑽𝒄) and
pressure drop across thin film
M
𝑽𝒄 = Ω ∗ 𝑟
Where:
• Ω = Angular speed (rad/s)
• r= bucket radius(m)
• ΔP = Pressure difference (N/m2)
• p = Density of solution (kg/m2)
• Vc = Exit/tangential speed (m/s)
• D = Diameter (m)
• ߜ = Liquid layer’s thickness
𝑽𝒄
Δ𝑷 = 𝑝 ∗
𝑉𝑐2
𝐷
∗ ߜ

5. DIMENSIONLESS NUMBERS
Where:
-μ = dynamic viscosity (m-2sec) -ρ = density (kg/m3) -U = jet velocity (m/s) -L= Length(m)
-a = Orifice (m) -σ = surface tension (N/m) -f = Coriolis frequency
# Number Abbr. Formula Ratio
1 Reynold Re ρU𝐿
μ
𝐼𝑛𝑡𝑒𝑟𝑖𝑎𝑙 𝑓𝑜𝑟𝑐𝑒𝑠
𝑉𝑖𝑠𝑐𝑜𝑢𝑠 𝑓𝑜𝑟𝑐𝑒𝑠
2 Weber We ρU2a
σ
𝐾𝑖𝑛𝑒𝑡𝑖𝑐 𝐸𝑛𝑒𝑟𝑔𝑦
𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑡𝑒𝑛𝑠𝑖𝑜𝑛
3 Rossby Ro U
L𝑓
𝐼𝑛𝑡𝑒𝑟𝑖𝑎𝑙 𝑓𝑜𝑟𝑐𝑒𝑠
𝐶𝑜𝑟𝑖𝑜𝑙𝑖𝑠 𝑓𝑜𝑟𝑐𝑒𝑠
4 Ohnesorge Oh μ
√ρaσ
𝑉𝑖𝑠𝑜𝑐𝑢𝑠 𝑓𝑜𝑟𝑐𝑒𝑠
𝐼𝑛𝑒𝑟𝑡𝑖𝑎𝑙 & 𝑆𝑢𝑟𝑓𝑎𝑐𝑒 𝑡𝑒𝑛𝑠𝑖𝑜𝑛 𝑓𝑜𝑟𝑐𝑒𝑠

6. MECHANISM OF BREAKUP OF LIQUID JET
# Mode Viscosity Jet velocity Description
1 M1 Normal Low
Rapid formation of primary droplets close to orifice with few or
absence of satellite droplets
2 M2 Normal High Largest number of secondary droplets are formed
3 M3* High High
Jet breaking up simultaneously at several points into a
continuous stream of droplets.
4 M4 High Low Large swell disturbances which rupture back to orifice
*Current prilling bucket operating mode
M1 M2 M3 M4

7. MECHANISM OF BREAKUP OF LIQUID JET(CONTINUED)
Breakup regime map: Ohnesorge No vs Weber No to predict breakup mode
# Case UoM 1 2 3 4
1 Flow Rate tph 50 62.5 65 65
2 No of Holes - 6632 6632 6632 7975
3 We No. - 8 12 13 9✓
1 2
4 3

8. CAPACITY ENHANCEMENT OPTIONS
Parameter UoM Existing Remarks
1 Flow rate t/h 62.5 Target
2 Bucket Diameter mm 355
3 Height mm 812
4 Angular velocity min-1 ~350 Throughput and tangential velocity
5 Hole Diameter mm 1.7 Product specifications
6 No of holes - 6779
a Pitch mm ~8.2
b Bucket Height mm
c Bucket Diameter mm
7 Bucket Angle Deg 15.7
8 Choking - Scrapper reconfiguration
Step height
Pitch
15.7o
Scrapper
355 mm
812
mm
M
550
mm
125 mm

9. CONCLUSION & WAY FORWARD
Conclusions
• Theoretical calculations of We and Oh number indicate current jet breakup mode @62.5tph is
same as at 50tph, but We number has increased indicating high velocities. Hence capacity is to
be increased while minimizing velocities
• Angular velocity (bucket rpm) and flow rate can be varied to handle throughput without any
change in bucket dimensions however bucket diameter, bucket height and pitch can be varied to
increase throughput
• Step Height (6.0-5.5mm) & pitch (8.2-7.52mm) can be decreased to increase number of holes
i.e. increased from 6632 to 7975 (~20%)

10. CONCLUSION & WAY FORWARD
Way forward
• Draft drawing of bucket for different cases of uprate Action : HA, TD: Nov-20
• Contact local vendor for modified prilling bucket manufacturing Action : HA, TD: Nov-20
• Trial run of manufactured prilling bucket on plant scale Action :SR & HA, TD Q1-21

11. REFERENCES
1.VICTORIA LOUISE HAWKINS (2010) Curved Liquid Jets: Effect Of Scale, Rheology And Forced
Disturbances, University of Birmingham
2.K. D. SHAH and A. G. ROBERTS (n.d.) Properties of Ammonium Nitrate, Imperial Chemical
Industries PLC, Billingham, Cleveland, England:
3.Ahmet Ozan Gezerman and Burcu Didem Corbacioglu (2011) 'New approach for obtaining
uniform- sized granules by prilling process', Elixir Chem. Engg. 40 (2011) 5225-5228, (), pp. 5225-
5228.