Study On The Impact Factors Of Closed White Water Circuit

The effects of chemical additives decreased because the wet-end environment deteriorated along with closing white water circuit. It will influence the papermaking processes and properties of paper. The past works mainly focused on the influence of anionic DCS (dissolved and colloidal substance) and inorganic salts. However the impact by the interaction of anionic DCS with inorganic salts is usually ignored. In the same time, hard degree is failure to take as consideration when conductivities are chose as the parameter. For the reasons above, bleached Eucalyptus globulus kraft pulp was chose as fiber material in this paper. Beside that, calcium salt and sodium salt which were common in the white water circuits were chose to represent the inorganic salts, saponify rosin, sodium oxalate and saponify stearic acid were chose as the anionic DCS simulacra. The effect on the properties of wet-end and paper sheets by inorganic salts, anionic DCS and the synergistic effect between them were investigated. As results, calcium ions were the key reason to influence the effect of chemical additives for forming deposits with DCS simulacra, screening the anionic charge of the adsorption sites in fibers. Main results as follows:The adsorption between calcium ions and bleached Eucalyptus globulus KP fibers conformed to Pseudo-second-order kinetics model but not the first-order kinetics model. The adsorption isotherms of Ca2+ by bleached Kraft eucalyptus pulps agrees with the ionic reaction model between carboxyl groups of fibers and Ca2+. In 298K, pH 7.5, the molar ratio of carboxyl to Ca2+ is close to 2:1. Because of the strong binding capacity with carboxyl groups, Ca2+ can screen the anionic charge of carboxyl acid groups, so the electrostatic adsorption between cationic addition agents like CPAM, AKD, CS, etc and the adsorption sites of fibers are affected. The binding capacity with carboxyl groups and Na+ is weaker; it has a small effect on the properties of cationic addition agents compared to Ca2+.The wet-end and hand sheets properties will be affected in the following ways when the concentrations of metal ions increasing:1, Bringing up the Zeta potential of pulp, the Zeta potential reducing effect of calcium ions are stronger than sodium ions. The mathematic relationship of the Zeta potential of the pulp(ζ), the conductivity of pulp(σ) and the original Zeta potential of pulp(ζ0) met the following mathematic models:when regulating conductivity of pulp by calcium chloride:ζ=-0.388+0.988ζ0+0.2021na-0.09141na×ζ0; When regulating conductivity of pulp by sodium chloride:ζ=-0.806+0.960ζ0-0.3161na-0.1021nσ×ζ0.2, Enhanced the retention and drainage ability of pulp when no addition agents was added; when addition agents were added in pulp, the retention and drainage ability of pulp declined, the effect on reducing retention and drainage ability of pulp from calcium ions was stronger than from sodium ions.3, Reducing the sizing effect of AKD, the reducing effect from calcium-ion was stronger than from sodium-ions.4, Affecting the strength properties of hand-sheets, the tensile, folding endurance and burst lifting effects of sodium ions are strong, the tear reducing effect of calcium ions are worse.The effects of three different kinds of DCS simulacra on paper making were investigated:1, The properties of pulp fluctuated because of the appearance of DCS simulacra, but when PDADMAC, CPAM, etc are added in the pulp, because their abilities of capturing DCS simulacra, the retention and drainage properties of pulp become stable.2, Sodium oxalate impairs the sizing effect of AKD. However, the sizing effect of hand-sheets increased and then decreased when saponify stearic acid and saponify rosin content of the pulp increased.3, DCS simulacra reduced the strength properties of hand-sheets.The deposits formed by Ca2+ and DCS simulacra will affect wet-end and paper sheets properties:1, Reduced the retention and drainage abilities of pulp.2, Increasing the concentration of calcium ions in the pulp which already contained certain concentration of DCS simulacra, the sizing effect of hand-sheets increased and then decreased.3, Inorganic salts restrain the impact to strength properties of hand sheets by DCS simulacra. However sodium salts had small effect on the retention and drainage abilities of pulp and the sizing effect of hand-sheets.Calcium ions were the most important factor that made the achievement of closing white water circuit so difficult. It would increase the effect of cationic additives by controlling the influence of calcium ions. Even though the accumulating sodium ions make the conductivity of white water still high, the properties of wet end and paper sheets will be improved by means of removing of calcium ions from the paper making system. So, calcium ions controlling was very important for closing white water circuit.A home made chemical addition agent (ACS) had been used to control the bad influence of calcium ions in closing white water circuits. Good results had been made when put ACS into the pulp that contained a certain concentration of CaCl2 (the conductivity of pulp was 4051μs/cm regulated) and DCS simulacra (0.02g/L saponify rosin; 0.02g/L sodium oxalate; 0.02g/L saponify stearic acid). Main results as follows:when the dosage of ACS was 0.12%, the CSF of pulp increased from 200ml to 340ml; the turbidity of white water dropped from 105NTU to 47.6NTU. In paper properties, when the dosage of ACS was 0.4%; the white degree of hand-sheets increased from 80.61% to 83.56%; the Cobb value dropped from 73.5g/m2 to 42.2g/m2, the strength of hand-sheets also increased in different degrees.Changing the dosage of ACS and the concentration of calcium ions in the pulp, detected the properties of pulp and paper sheet. The order autoregressive scheme of the dosage of ACS in pulp (AACS), concentration of calcium (CCa) to the properties of pulp and hand sheets as follows:Freeness=422-0.771CCa+269AACs +2.06AACS×CCa-2321(AACS)2+3×10-4(CCa)2; Turbidities of white water=37.2-0.117CCa-221AACS-0.782AACS×CCa+1290(AACS)2+1.2×10-3(CCa)2;Cobbvalue=19.5+1.43×10-3CCa-10.1AACS-5.48×10-2AACS×CCa+78.3(AACS)2+5.1×10-5(CCa)2; Tear index=0.335+5.28×10-4CCa+0.321AACS-6.23×10-4AACS×CCa-0.996(AACS)2+10-6(CCa)2; Tensile index=41.6-2.62×10-2CCa+28.0AACS +0.119AACS×CCa-153(AACS)2+1.01×10(CCa)2; Burst index=2.11+4.18x10-3CCa-0.201AACS +8.28×10-3AACS×CCa+3.55(AACS)2-1.3×10"5(CCa)2; Folding index=6.86+5.44×10-2CCa+18.7AACS +0.128AACs×CCa-129(AACS)2.The correlation coefficients of the order autoregressive scheme of the dosage of ACS and concentration of calcium to the properties of pulp and hand sheets were high; it proved that the increased properties of pulp and paper were based on the controlling of calcium ions. For achieving the needed properties of pulp and paper, the dosage of ACS can be calculated according to the concentration of calcium. This will be meaningful to carry out closing white water circuit.