Transcript 64555696-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
sugars
n
Minimum extraction of non
n
Minimum sucrose in final
bagasse
n
Optimum moisture
bagasse
n
Optimum power/ energy
consumption
in final
THRUST AREAS FOR EFFICIENT MILLING
1. CANE MANAGEMENT
2. PREPERATION OF CANE
3. SPECIFIC FIBRE LOADING
4. HYDRAULIC LOAD
5. PROPER SETTING OF MILLS
6. PRIMERY EXTRACTION 7.
SECONDARY EXTRACTION 8.
IMBIBITION
9. MILL SANITATION
CANE MANAGEMENT
u
Quality cane supply
1. Minimum extraneous matters and
binding materials
2. Clean and fresh
u
Uniform supply of cane to avoid
reduced crushing situation
Thrust area
PREPERATION OF CANE
Optimum cane preparatory Index as
A
85
A
Long fibrous preparation
Avoid excess of cane preparatory
A
devices
A
Avoid
dusting of cane
Thrust area
CANE PREPARATION
Good cane preparation
n
Improve Bulk density and higher number of
juice open cells
n
Make easy to extract free
juice n Improve mill extraction
n
Reduction in power
consumption n Improve
feedability to mills n Lower down
mill opening n Lower mill speed
n
Lower hydraulic loading
n
Effective imbibition n
Lower down reabsorption
BULK DENSITY AND PREPARATORY 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 CALCULATIONS
RF
RF
RF
RF
1ST
2ND
3RD
4TH
Where
Mill
Mill
Mill
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
V
(ft/min)
(lbs/ft3 )
Roller surface speed
F
Fibre
index
FACTORS INCREASES REABSORPTION
n
n
n
Poor cane preparation
Higher surface speed
Higher hydraulic loading
than required
Inefficient
juice
drainage
n
Roller
polishing
n Increase in pressure
n
PROPER SETTING OF MILLS
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
n
n
Thrust area
MILL SETTINGS
n
Fibre method of mill setting
n
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
n
wt. of bagasse after each mill (W)
Hxfbx1000
(kg/hr)=
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 =
Where
n
W x 1000
d x 3.14xDxnxLx60
D
Diameter of mill
roller n Mill rpm
L
M
Mill roller
length
d
B
Bagasse density
Reabsorption
under Dwo / RF
correction
as
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
Speed Ratio for UFR= 1.1
n
Average speed of UFR =
Mill speed + UFR speed
2
n
Fibre Compaction (kg/m3 )=85 to 120
n UFR work opening=
Fibre/minx1000
V x L x Fibre compaction
n
Where
V V =
surface speed of UFR
(mt./min) L = Length of UFR (mt )
DONNELLY CHUTE SETTING
Average speed for D chute =
Mill speed + UFR speed 2
n
n
n
Fibre Compaction (kg/m3 )50
to 85
D chute opening =
Fibre/minx1000
V cosF x L x Fibre compaction
Where V V cosF = Surface speed of UFR (mt./min)
L
= Length of UFR (mt )
GRPF/TRPF SETTING
n
n
GRPF SETTING
1. S Speed ratio (A)
1.2 to 1.4
2. V Volumetric ratio (B) 1.3 to 1.5
TRPF SETTING
1. S Speed ratio (A)
1.0 to 1.2
2. V 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
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PRIMERY EXTRACTION
High purity extraction
To be achieved maximum
n
n
Thrust area
SECONDARY EXTRACTION
n
n
Low purity extraction
Extraction
based
imbibition efficiency
Extraction
sugars
n
consumption
n
on
of more non
High
power
Thrust area
IMBIBITION
n
By
cold
By hot
water n
water
n Preferably by hot water
n Optimum temperature of hot water
70oC.
Thrust area
MILL SANITATION
To avoid bacterial growth
n
Rapid growth of Luconostics in acidic
and Low Brix juice
n
Regular steaming n
Regular chemical spray
-30-40 ppm shock dosing under extreme
conditions
-10 ppm for regular dosing
n
Chemicals
1. Q Quaterrery Ammonium
salts 2. C Carbonates bases
Thrust area
3. B Bleaching powder
n
NORMAL MILL PRACTICES
Not to monitor lift of top roller
It is assumed that top roller lifts only that value

considered during mill setting calculations
ormally actual lift of top roller during operation is higher
than considered in mill setting calculation
igher 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





Plotting of Brix curve
and discharge side
To monitor lift of top roller
for
feed
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
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

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


Complete repair and overhauling
during off-season
Preventive/
predictive
maintenance during crushing season
STEPS FOR GOOD MAINTENANCE


Right selection of equipments and their
components
Correct orientation
placed equipments
of
wrongly
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

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
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