Improving Mill Extraction

IMPROVING MILL EXTRACTION BY SUMIT BHATI DY. MANAGER-ENGG.

Triveni Engineering & Industries Ltd. Sugar Unit- Ramkola, Kushinagar (U.P.)

OBJECTIVE OF MILLING n

Maximum possible extraction of sucrose

n

Minimum extraction of non sugars

n

Minimum sucrose in final bagasse

n

Optimum moisture in final bagasse

n

Optimum power/ energy consumption

THRUST AREAS FOR EFFICIENT MILLING 1. 2. 3. 4. 5. 6. 7. 8. 9.

CANE MANAGEMENT PREPERATION OF CANE SPECIFIC FIBRE LOADING HYDRAULIC LOAD PROPER SETTING OF MILLS PRIMERY EXTRACTION SECONDARY EXTRACTION IMBIBITION MILL SANITATION

CANE MANAGEMENT u

u

Quality cane supply 1. Minimum extraneous matters and binding materials 2. Clean and fresh Uniform supply of cane to avoid reduced crushing situation

Thrust area

PREPERATION OF CANE A

Optimum cane preparatory Index as 85

A

Long fibrous preparation

A

Avoid excess of cane preparatory devices

A

Avoid dusting of cane

Thrust area

CANE PREPARATION n

n n n n n n n n n

Good cane preparation Improve Bulk density and higher number of juice open cells Make easy to extract free juice Improve mill extraction Reduction in power consumption Improve feedability to mills Lower down mill opening Lower mill speed Lower hydraulic loading Effective imbibition Lower down reabsorption

BULK DENSITY AND PREP ARATORY INDEX Relationship between bulk density and preparatory index at 15% fibre B.D.(kg/cm2) P.I. 400 450 500 550 600 650 700

44.5 52.85 61.25 69.65 78.05 86.45 94.85

HYDRAULIC LOAD a. To be decided by Specific Hydraulic loading (SHP ) SHP = F/ 0.1LD Where F = Total load on top roller (Tons) L = Length of roller (Mt.) D = Dia. Of roller (Mt.) b. To curb excessive lift of top roller

Thrust area

Mean Value Of SHP 12 Roller

1st 2nd 240 220

3rd 250

4th 275

5th

15 Roller 240 220 230 250 275 Above values of SHP are in tons/ft2 Nitrogen gas pressure in accumulator should be in the range of 70 to 90% of the hydraulic pressure. Nitrogen gas pressure should never be higher than the oil pressure

SPECIFIC FIBRE LO ADING n

n

n

n

This is the maximum fibre load to be given to a milling tandem This is influenced by type of feeding devices Optimum range of SFL is 20kg/m3 to 25kg/m3 for mills with D chute and UFR Optimum range of SFL is 27kg/cm3 to 30kg/m3 for mills with GRPF/TRPF

REABSORPTION Speed of bagasse is lesser than roller surface speed when it comes in contact to rollers gripping zone and reaches equal to roller speed at neutral plane. The speed of bagasse is higher than roller speed between neutral plane and axial plane. This phenomenon of excess speed causes the extrusion of bagasse which gives higher volume of bagasse than the escribed volume generated by the opening between the rollers called Reabsorption

REABSORPTION FACTOR The ratio of actual volume of bagasse emerged to escribed volume generated by the opening between rollers at axial plane is known as reabsorption factor

RF CALCUL ATIONS RF RF RF RF

1ST Mill 2ND Mill 3RD Mill 4TH Mill

0.75+ 0.0052V + 0.01F 0.65+ 0.0052V + 0.01F 0.60+ 0.0052V + 0.01F 0.60+ 0.0052V + 0.01F

Where V Roller surface speed (ft/min)

F Fibre index (lbs/ft3 )

FACTORS INCRE ASES REABSORPTION n n n

n n n

Poor cane preparation Higher surface speed Higher hydraulic loading than required Inefficient juice drainage Roller polishing Increase in pressure

PROPER SETTING OF MILLS n

n

n n

Relative positioning of three rollers (Top, Feed & Discharge) Trash plate properly drawn and positioned Setting of feeding devices Proper setting of scrapers knives

Thrust area

MILL SETTINGS n

n

Fibre method of mill setting Fibre % bagasse after each mill 12 roll 15 roll 18 roll

I 33 32 32

II 42 41 40

III 47 47 47

IV 52 52 53

V

VI

55 57

60

MILL SETTING n

0 1 fb x H

n

wt. of bagasse after each mill (W) (kg/hr)= TCHxfbx1000 TC Fibre% bagasse Where fb fibre % cane Assume bagasse density after each mill (d ) in kg/m3 I II III IV 1200 1210 1220 1230

MILL SETTING n

Discharge opening (operating )

Dwo = W x 1000 d x 3.14xDxnxLx60 Where D n L d n

Diameter of mill roller Mill rpm Mill roller length Bagasse density

Reabsorption correction as under Dwo / RF

MILL SETTING n

Mill Ratio

Conventional With GRPF/TRPF n

Feed/Discharge 2.0 to 1.80 1.75 to 1.6

Trash plate/Feed ratio

Conventional With GRPF/TRPF TP toe angle Heal angle TP slope

TP/Feed 1.9 to 2.2 1.7 to 1.8 Mill apex angle 6 >25 and < 30 4.5% to 5.5 %

UFR setting n n

n

n

Speed Ratio for UFR= 1.1 Average speed of UFR = Mill speed + UFR speed 2 Fibre Compaction (kg/m3 )= 85 to 120 UFR work opening= Fibre/minx1000 V x L x Fibre compaction Where

V = surface speed of UFR (mt./min) L = Length of UFR (mt )

DONNELLY CHUTE SETTING n

n

n

Average speed for D chute = Mill speed + UFR speed 2 Fibre Compaction (kg/m3 ) 50 to 85 D chute opening = Fibre/minx1000 V cosF x L x Fibre compaction Where

V cosF = L =

Surface speed of UFR (mt./min) Length of UFR (mt )

GRPF/TRPF SETTING n

n

GRPF SETTING 1. Speed ratio (A) 1.2 to 1.4 2. Volumetric ratio (B) 1.3 to 1.5 TRPF SETTING 1. Speed ratio (A) 1.0 to 1.2 2. Volumetric ratio (B) 2.0 to 3.0

PRESSURE CHUTE SETTING n

n

n

n

Normal value of inlet pressure chute angle is 21 degree Normal value of out let angle of pressure chute is 45 degree Divergence angle of pressure angle varies from 5 to 7 degree Pressure chute should be symmetrical to the axis joining mid point of PF opening and mill feed opening

PRIMERY EXTRACTION n n

High purity extraction To be achieved maximum

Thrust area

SECONDARY EXTRACTION n n

n n

Low purity extraction Extraction based on imbibition efficiency Extraction of more non sugars High power consumption

Thrust area

IMBIBITION n n n n

By cold water By hot water Preferably by hot water Optimum temperature of hot water 70oC.

Thrust area

MILL SANITATION n n n n

n

To avoid bacterial growth Rapid growth of Luconostics in acidic and Low Brix juice Regular steaming Regular chemical spray - 30-40 ppm shock dosing under extreme conditions - 10 ppm for regular dosing Chemicals 1. Quaterrery Ammonium salts 2. Carbonates bases Thrust area 3. Bleaching powder

NORMAL MILL PRACTICES Æ Æ

Æ

Æ

Æ

Æ

Æ

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Not to monitor lift of top roller It is assumed that top roller lifts only that value considered during mill setting calculations Normally actual lift of top roller during operation is higher than considered in mill setting calculation Higher thickness of cane/bagasse blanket passes through mills due to excessive lift of top roller This leads to poor extraction of sucrose and results in higher sugar loss in final bagasse Hydraulic load applies on top roller simply by assumption/experience It is seldom to consider the lift of top roller while deciding the hydraulic pressure To compromise with mill performance due to power constrain

PERFORMANCE OF INDIVIDUAL MILLS Æ

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Plotting of Brix curve for feed and discharge side To monitor lift of top roller Analysis of bagasse leaving the mills for free pol and total pol Measurement of temperature of juice on feed and discharge Measurement of pol for bagasse leaving a mill and juice from back roller of same mill

OVER-ALL PERFORMANCE OF MILLS

Æ Æ Æ Æ

Pol percent final bagasse Brix of last expressed juice Primary extraction (PE) Reduced mill extraction (RME)

MAINTENANCE FOR QUALITY PRODUCTION AIM OF MAINTENANCE IS TO KEEP DOWN TIME MINIMUM AND TO ACHIEVE DESIRED CAPACITY UTILIZATION WITH EFFICIENCY AND QUALITY PRODUCTIVITY

PRESENT STATUS OF MAINTENANCE Æ

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There is seldom preventive/predictive maintenance No records of individual equipments No records about repair of equipments No proper training programme No proper house keeping works No separate inspection cell Lack of motivation among staff

PROPER MAINTENANCE SYSTEM

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Complete repair and overhauling during off-season Preventive/ predictive maintenance during crushing season

STEPS FOR GOOD MAINTENANCE Æ

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Right selection of equipments and their components Correct orientation of wrongly placed equipments Quality repair during off-season Planning and scheduling of various jobs Equipment cards Provision of stand by equipments

PREVENTIVE MAINTENANCE CONSTANT MONITORING ON OPERATIONAL PARAMETERS THROUGH SYSTEMATIC INSPECTION SO AS TO TAKE TIMELY REPAIR/REPLACEMENT OF COMPONENTS UNDERGOING WER AND TEAR TO AVOID DOWNTIME DUE TO FAILURE

ELEMENTS OF PREVENTIVE MAINTENANCE Æ

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Preventive maintenance cell with proper motivation Proper inventory to be maintained Categorization of plant and machinery Analysis of wear and tear and evaluation of service life

PREDICTIVE MAINTENANCE IT IS MORE ADVANCE ON STREAM NON DESTRUCTIVE TESTING WITH A VIEW TO AVOID UNNECESSARY SHUT DOWNS BY TAKING FULL HELP OF TROUBLE PREDICTING AND TROUBLE SHOOTING TEST INSTRUMENTS