brown stock washing
TRANSCRIPT
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Improving Brown Stock Washing by
On-line Measurements – Mill
Investigations
Contents
1. The purpose of brown stock washing
2. Refractometer measurements
3. Real-time refractometer measurement results for washer performance optimization
4. Implications of process and mill levels
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Target
Series of investigations to find solutions, which will minimize
washing loss and consume less energy, water and chemicals.
Pulp Washing in
Bleaching
Brownstock Washing • Digester
• Post-digester
• Post O2-stage
• Post screening
Rationale
1. There is a need to improve brown
stock washing and its monitoring, for
economic and environmental reasons.
2. Conventional on-line and traditional
lab sampling methods do not reveal
all process variations.
→ Better real time monitoring tools
are needed.
Basic Concepts
• The reason for brown stock washing
• Washing before and after Oxygen
delignification
• The parameters, which describe the
washing performance and its
effectiveness: wash loss and
dilution factor
• Wash loss evaluation
Refractometer
• Indicates total dissolved solids in solution, suitable for all concentrations
• Measures the washable liquid substances concentration exactly
• Detects organic materials with large molecular size, like lignin
• Not influenced by COD caused by methanol
Refractometer
• Not influenced by suspended solids,
bubbles or fibres
• In-line real-time measurement
• Short response time → suitable for
control
• Mounts directly in pulp line
Principle
Light
source
Optical image
Process medium
Critical angle
Prism
Arrangement
Process Analyses
• A software tool Wedge was used for washing
result analyses and for calculating the
different factors, which define the washing
line performance
• The Wedge was used to calculate liquor
balances and dilution factors in the washing
line, as well as to calculate E-value
91ln
1ln211
21
10DF
yxL
yyDF
E
Experiments
Experiments were divided into three parts:
1. Washing in the digester
2. Washing before oxygen delignification
3. Effects of washing loss on oxygen
delignification
Digester washing
Bypass was decreased and the amount of
wash liquor fed into the digester was
increased (into the central distribution
chamber). The same amount of filtrate from
the wash circulation was extracted.
700,0
720,0
740,0
760,0
780,0
800,0
820,0
840,0
860,0
880,0
900,0
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Wash
ing
lo
ss,
(kg
DS
/BD
t)
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
Extr
acti
on
fro
m w
ash
cir
cu
lati
on
, (t
/BD
t)
Washing loss from digester Extraction from wash circulation
Digester washing
The digester’s washing result can be increased by utilising radial displacement washing.
6,50
7,50
8,50
9,50
10,50
11,50
24.7.2009 11:31 24.7.2009 19:46 25.7.2009 4:01
DS
-co
nte
nt,
(%
)
Liquor in blow Wash liquor to digester Wash liquor to PDs
Pressure Diffuser’s Feed
Consistency Effect
With a higher feed consistency,
the washing efficiency is increased.
0,4
0,6
0,8
1,0
1,2
1,4
1,6
1,8
9,0 9,5 10,0 10,5 11,0 11,5 12,0
Feed consistency, (%)
E10
Effect of the Downward Velocity
of the Pressure Diffuser Screen
• The downward velocity of the screen notably affects the
pressure diffuser’s washing result
• In literature: “The optimum velocity ratio should be
slightly higher than one being from 1.1 to 1.3.”
0
1
2
3
4
5
6
0,110 0,115 0,120 0,125 0,130 0,135
Downward velocity of the screen, (m/s)
E10
640
660
680
700
720
740
760
0,110 0,115 0,120 0,125 0,130 0,135
Downward velocity of the screen, (m/s)
Wash
ing
lo
ss,
(kg
DS
/BD
t)
Optimum range Poor wash results Optimum range
Effect of Dilution Ratio on E10
The dilution ratio notably affects the
pressure diffuser’s washing efficiency
0
1
2
3
4
5
6
7
0,90 0,92 0,94 0,96 0,98 1,00 1,02
Dilution ratio
E10
slinliquorwash
sloutfiltratewashratioDilution
/),(
/),(
Effects of Washing Loss in
Oxygen Delignification
• The oxygen delignification response was highly affected
by the amount of washing loss
• This is due to the oxygen being consumed in the
oxidation reactions of the washing loss
18
20
22
24
26
28
30
32
34
100 150 200 250 300 350 400 450
Washing loss to oxygen delignification, (kgDS/BDt)
Kap
pa r
ed
ucti
on
in
oxyg
en
deli
gn
ific
ati
on
, (%
)
Optimum range Process difficulties
Effect of Washing Loss in
Oxygen Reactor’s Temperature
88,0
89,0
90,0
91,0
92,0
93,0
94,0
95,0
96,0
100 200 300 400 500
Washing loss to oxygen delignification, (kgDS/BDt)
Te
mp
era
ture
in
ox
yg
en
rea
cto
r, (
ºC)
Temperature in the oxygen reactor correlates
with the amount of washing loss
Conclusions
• By using refractometer measurements, TDS changes in the incoming washer flows (liquid and pulp suspension) can be detected immediately and reliably
• TDS changes also had a clear effect on washing loss in the brown stock line’s oxygen delignification performance
• By using refractometers and data-analyses tools, it is possible to discover the black spots of the washing line and to evaluate the washing result continuously, thus improving the washing efficiency
Implications
• Digester and diffuser washing can be improved by utilising refractometer measurement results
• Real-time measurements provide whole new possibilities for implementing higher level process optimization, e.g. throughout the entire washing department
Refractometer
Thank You
Thank you for your attention!
Any questions?