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Operation of Louisiana Low Turbulence (LLT) Clarifiers
Vadim Kochergin
Audubon Sugar Institute Presented at the
Jamaica Association of Sugar Technologists Annual Conference,
November 4, 2011, Ocho Rios, Jamaica
Rapidorr 444 CFD Modeling
Chetty and Davis, 2001
Large Scale Turbulent Eddies in an Industrial Clarifier
Design Concepts
Large scale turbulent eddies created by juice introduction need to be reduced.
Velocity in the feed channels should remain relatively high to eliminate plugging/scaling.
Uniform distribution of feed inlets and outlets in order to have uniform vertical juice velocities to make full use of the cross-sectional area of the clarifier.
Minimize any non-vertical flows within a clarifier.
Proof of Concept- 25 m3/hr flow
Proof of Concept
Basic TRD Layout
Side View
Top View
Industrial Trials – 2009 Grinding Season
Turbidity, suspended solids, and flocculant usage were monitored for the three clarifiers at Westfield Sugar Mill. – a 20 ft. diameter Graver – a 20 ft. diameter Graver retrofitted with the new design – a 30 foot diameter Dorr, with two mud boots * High mud levels -200-300 Lbs per ton of cane was not
uncommon
Turbidity- Comparison 2009 season
20
30
40
50
60
70
80
90
100
110
10/7/2009 10/27/2009 11/16/2009 12/6/2009 12/26/2009 1/15/2010
Turb
idity
(NTU
)
Date
GraverModifiedDorrPoly. (Graver)Poly. (Modified)Poly. (Dorr)
Results
Observations Season 2009/2010
Clarifier showed better performance compared to Graver and Dorr at the same mill
Bagacillo in clear juice was observed due to air entrainment in the pre-distributor
Turbulence Reduction Device
Updated clarifer design – 2010 Sterling, LA
Residence time 30-40 minutes
Redesigned feed distributor
Material of construction- Cromgard Steel (American Utility Metals)
Clarifier Retrofit
Water test –Sterling, Summer 2010
Sterling Clarifier Turbidity Comparison
Controlled Tests
Two separate tests were conducted in which the flowrate to the LLT was increased from 750 to
1000-1100 GPM to test the limits of the clarifier throughput
Effect of Upward Velocity on Turbidity
Controlled Tests Summary
No air entrainment at 1100 GPM ( 50 % increase compared to the standard operating flowrate of 750 GPM)
No mud flocs / bagacillo in clear juice
No significant change in turbidity
Using the same amount of flocculant as at 750 GPM
Mud consistency remained constant during second test. – Flocculant was increased with increased flowrate.
Conclusions
Air entrainment problem has been resolved with improved pre-distribution
No air entrainment was observed even at 50 % increase compared to nominal throughput
LLT design showed on average 20 % better performance than SRT design at lower residence time (35 min vs 45 min)
Slightly more flocculant was used as compared to the SRT. Flocculant use optimization has not been performed
Capital cost of LLT design was estimated at about 30-40 % of SRT design
Acknowledgements
American Sugar Cane League for providing partial funding for the project
Personnel of Sterling, Lula, Westfield and Enterprise Sugar Mills