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