nssc process optimization

NSSC PROCESS OPTIMIZATION: I. PULPS QUALITY  María C. Area, Fernando E. Felissia Programa de Investigación de Celulosa Y Papel, FCEQYN, Universidad Nacional de Misiones  Alberto Venica Celulosa Argentina- Fábrica Zárate  Jacques L. Valade Université du Québec à Trois-Rivières

PULPING PROCESSES: CURRENT TRENDS Processes of smaller daily production capacity. Use of smaller quantities of chemical

products. Use of products that are not harmful to the environment.

NSSC : TRENDS Actual principal use: hardwood corrugating medium. Other uses: printing and writing papers, business forms, reply cards and tissue paper.

Current trends: partial Kraft pulp replacement in linerboard and bag grades. F.A.O. Projections: new NSSC installations will be required until the 21st century.

NSSC PROCESS: CHARACTERISTICS Flexibility: use of different buffers, anthraquinone addition, etc. Higher yields than kraft for similar

resistance. Easier bleaching. Less refining energy requirement.

OBJECTIVE

Obtain the best physical properties of NSSC pulps, using low chemical charges in order to reduce inorganic solids in spent liquors.

MILLS IN THE WORLD 100%

Kraft

80%

Sulfite

60%

CMP+CTMP

40%

Cold Soda

20%

NSSC

0%

LABORATORY TRIALS Raw material: • Industrial chips of hybrid poplar (Populus deltoides), delta of Paraná river, Argentina.

Chemical composition: • Extractives in hot water: 2.3%

• Extractives in alcohol-benzene content: 2.6 % • Lignin content (Klasson): 24.2 % • Lignin content (soluble): 3.0 % • Cellulose content (Seiffert): 41.8 % • Hemicelluloses (difference): 26.1 % • Ash content: 0.84%

EXPERIMENTAL DESIGN Design type CCD: 4 variables at 5 levels. 29 runs:16* + 6* + 2* alpha of T (154 and 181 ºC )+ 5 central points (experimental error detection). T= 162 and 178ºC (16 runs*)

T= 170ºC (6 runs*)

11.60

alpha

* sulfite

sulfite

9.8

* 3.05

6.2

time 15

25

4.40

0.05

10

time

30

VARIABLES STUDIED Process conditions: Cooking time (time at maximum temperature, t): 10 to 30 minutes. Temperature (T):

154 to 186ºC. Sodium sulfite charge on wood, (% SO3=): 4 to 12% o.d. Sodium carbonate charge on wood (% CO3=): 0 to 3% o.d.

NSSC REFERENCE MILL « Productos Pulpa Moldeada »  (Cipolletti, Río Negro, Argentina).

Capacity: 20 000 tmy. Technology: Sunds Defibrator (Sweden). NSSC market pulp from hybrid poplar: Bleached to 80% ISO for tissues, printing and writing papers. Bleached to 63% for light boards. Unbleached pulp for corrugating medium.

Exported to: Brazil,Uruguay and Turkey.

PULPING METHODOLOGY H factor Energy of activation : 32 000 cal/mol. Reaction rate constant used for the H factor:

K= EXP((43.2-16 113 / (273 + T)) • T : liquor temperature measured each 30 sec.

PRE-CHEMICAL STAGE CHIPS (20 kg OD) AIR DRYING CLASSIFICATION

FINES AND OVERSIZED CHIPS ELIMINATION

CHIPS WASHING BY FLOTATION STEAMING REFINING CENTRIFUGATION OF THE DESTRUCTURED MATERIAL MIXING AND SCREENING OF THE CENTRIGUGATED MATERIAL DESTRUCTURED MATERIAL FOR THE CHEMICAL STAGE

10 min ATMOSPHERIC 20 mm OF DISKS CLEARANCE

CHARGE OF THE RAW MATERIAL

CHEMICAL STAGE

500 g INCLUDING 25 g IN A 100-MESH BASKET FOR YIELD DETERMINATION SATURATED STEAM ENTRANCE

AIR EXTRACTION

4L STAINLESS STEEL DIGESTER BEGINNING OF RECIRCULATION TEMPERATURE CONTROL H-FACTOR CALCULATION

SYSTEM REFRIGERATION WITH COLD WATER

LIQUORS PREPARATION: SODIUM SULFITE, SODIUM CARBONATE, WATER. VACUUM LIQUOR CHARGE - L:W=6.5:1

FOUR 600 WATTS HEATING WIRES CONTROLLED INDEPENDENTLY ONE FROM THE OTHER

CLOSING OF STEAM ENTRANCE STOPPING OF THE REACTION

REMOVE OF SPENT LIQUORS

WASHING OF THE MATERIAL

MEASURE OF FINAL pH, RESIDUALS, SOLIDS, DENSITY, AND VISCOSITY IN SPENT LIQUORS

BASKET WASHING WITH 2 L + 10 L OF WATER

SPENT LIQUORS CONSERVATION ON CHLOROFORM OVER TOLUENE

YIELD CALCULATION

INCORPORATION OF 2L OF WATER AND CENTRIFUGATION

MECHANICAL STAGES

COOKED MATERIAL

FIRST STAGE: ATMOSPHERIC DEFIBRATION

SINGLE DISK REFINER: BAUER, 8 in, 5 HP,. DISK CLEARANCE: 0.003 mm 590 CSF

PULP CENTRIFUGATION ENERGY MEASUREMENT CSF AND SOMERVILLE SHIVES DETERMINATION

DEFIBRATED PULP

SECOND STAGE: REFINING

PULP CENTRIFUGATION

PHYSICAL TESTS

REFINED PULP

VALLEY BEATER : CSF DETERMINATION EACH 5 min, 260 CSF TIME MEASUREMENT

RESULTS Yield Defibration and refining energy Physical properties of pulps Sulfonic and carboxylic acids content in pulps Process variables optimization (resolution of the matrix of derived equations)

90

88 87 86 85 4.406.20 8.00

9.80 11.60

Sulfite

3.05 2.30 1.55 0.80 90 0.05 88 Yield

Yield

89

86 84 82 154162 170 178 186 Temperature

3.05 2.30 1.55 0.80 0.05

Energy

2.30 1.55 0.80 0.05 1.62 1.48 1.34 4.40 6.20 8.00 9.8011.60 Sulfite

0.51 0.65 0.79 0.92 1.06 1.20

2.4 2.2 Bulk

Carbonate

3.05

2 1.8 1.6 1.4 154 162 170 178 186 Temperature

60 Tensile Index

50 40 30 20 59

0

56 154 162 170 178 186 Temperature

Brightness

10

53 50 47 44 41 154 162 170 178 186 Temperature

106 96 86 76 66 154 162

170 178 186 Sulfite

3.05 2.30 1.55 0.80 0.05 Sulfonic acids

Sulfonic acids

116

97 94 91 88 85 82 79 10

15

20 Time

25

3.05 2.30 1.55 0.80 0.05

30

SELECTION OF BEST OPERATIONS (OPTIMUM CONDITIONS) Best points are in general near point 12. To minimize the inorganic/organic solids ratio: “Optimum”: 26 min, 177 ºC, 6.0 % NaSO3, 2.54% NaCO3.

To maximize physical properties:  “Alpha”: 30 min, 186 ºC, 11.6 % NaSO3, 3.05% NaCO3.

Points selected for scaling up verification: “4 pilot plant”: 25 min, 178 ºC, 6.2 % NaSO3, 0.8% NaCO3. “12 pilot plant”: 25 min, 178 ºC, 6.2% NaSO3, 2.3% NaCO3.

PILOT PLANT TRIALS Raw material: Spanish hybrid poplar. Chemical composition: • Extractives in hot water: 2.67% • Extractives in alcohol-benzene content: 1.94 %

• Lignin content (Klasson): 22.9 % • Lignin content (soluble): 1.91 % • Cellulose content (Seiffert): 43.3 % • Hemicelluloses (difference): 27.5 %

Trials

4 pilot plant 12 pilot plant

Optimum

alpha

85.4

87.6

87.0

78.0

Time to 260 CSF

20

20

18

15

Tensile I. (N.m/g)

30.9

35.57

33.2

55.9

Burst I. (kPa.m2/g)

1.38

1.6

1.58

2.83

Tear I. (mN.m2/g) Bulk (cm3/g)

3.73

3.87

4.08

4.16

1.76

1.76

1.76

1.46

Sulfonic acids (mmol/kg)

47.2

58

57.05

82.7

Carboxylic acids (mmol/kg) 75.65

86.05

91.15

99.9

Total acids (mmol/kg)

122.85

144.05

148.2

182.6

RCT (kN/m)

1.31

1.24

1.19

1.36

CMT (N)

202

223

204

291

STFI (kN/m)

2.97

3.13

3.34

4.10

Yield(%)

CONCLUSIONS Temperature presents the most important effect on all the studied properties. Sodium carbonate effect on yield is important only at low sulfite charges or high temperatures. Sodium sulfite charge reduces strongly the energy consumption, followed by temperature.

CONCLUSIONS Carbonate charge does not affect the responses sensibly as an independent variable, but it presents high interaction effects.  Absence of this buffer in these cooking liquors produces an increment of energy consumption and a reduction of pulps resistance. Independent variables values to obtain highest mechanical properties were located toward the maximum levels of the experimental plan. Temperature:186ºC, cooking time: 30 minutes, sodium sulfite: 11.6% and sodium carbonate: 3.05%.

CONCLUSIONS Pulp brightness decreases as a consequence of strong pulping conditions  If the pulp is going to be bleached, this means an increase in bleaching costs

These conditions imply an important yield reduction (80% to 72%) Pilot plant results showed higher yields and lower properties than expected