Effects of Chloride, Potassium, and Sulfate on the Causticizing Reaction in the Kraft Recovery Process

Saeidi, Sona; Tran, Honghi; Papangelakis, Vladimiros G.

doi:10.32964/tj8.3.21

2009

DOI: 10.32964/tj8.3.21

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Effects of Chloride, Potassium, and Sulfate on the Causticizing Reaction in the Kraft Recovery Process

Sona Saeidi¹,

Honghi Tran²,

Vladimiros G. Papangelakis³

Abstract: We studied the effects of chloride (Cl), potassium (K), and sulfate (SO4) on the equilibrium of the causticizing reaction over a wide range of causticizing conditions, using OLI, an advanced thermodynamic program for equilibrium calculations in aqueous solutions of ionic salts. Cl, K, and SO4 were shown to have little or no effect on the causticizing equilibrium. Under a given causticizing condition, coastal mills, due to their much higher NaCl concentration, are predicted to have a causticizing efficiency 1%–… Show more

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Cited by 5 publications

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Influence of chlorine and potassium on operation and design of chemical recovery equipment

Hamaguchi¹,

Vakkilainen²

2011

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The main objective of this study is to evaluate the effect of chlorine (Cl) and potassium (K) on the operation and design of equipment in the chemical recovery cycle. Due to stricter environmental regulations, mill closure tends to increase, causing the accumulation of undesirable elements such as Cl and K in the kraft liquor cycle. Total inorganic solids in pulping liquors increase in the presence of Cl and K, which affects the operation of chemical recovery equipment. The objective here is to show the magnitude of these impacts and estimate operational cost differences by using different Cl and K contents in liquors. Pulp mill material and energy balances for each case are used for this purpose, and a modern Brazilian pulp mill served as a base case model. The results show that for one specific range, the solids content in black liquor can be 6.6% higher by increasing the mass percentage of Cl and K in black liquor. This difference reduces the black liquor higher heating value by 6.2% and increases the amount of dry solids to burn in the recovery boiler, also by 6.6%. The evaporation load increases along with steam consumption. This lowers total electricity output by up to 1.6 MW due to reduced flow to the condensing stage of the steam turbine. The balances also demonstrate that some pumping costs can be 12% higher when operating from a low to high concentration of Cl and K in black liquor.

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Influence of chlorine and potassium on operation and design of chemical recovery equipment

Hamaguchi¹,

Vakkilainen²

2011

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Formation of pirssonite in green liquor handling systems

Zakir¹,

Tran²,

Vladimiros³

2013

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The formation of pirssonite is commonly believed to be the cause of hard-scale buildup in green liquor handling systems in kraft pulp mills. The precipitation occurs when the concentration of sodium carbonate in the liquor exceeds the solubility of pirssonite. A laboratory study was conducted to systematically determine the causticizing conditions under which pirssonite precipitates. The results confirmed literature data showing that the solubility of pirssonite increases with temperature but decreases with increased concentrations of sodium carbonate and other sodium salts present in the green liquor. The solubility data obtained were used to create a database for pirssonite formation in OLI, a thermodynamic program for predicting phase stabilities of alkali salts in aqueous solutions. The OLI program, with the newly created database, was subsequently used to generate a series of pirssonite solubility curves in terms of saturated total titratable alkali that can be used as operational guidelines to prevent pirssonite precipitation and hard-scale formation in green liquor handling systems. A case study was performed using these solubility curves to explain the occurrence of the pirssonite deposition problem at a kraft pulp mill.

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Measurement of free lime content in lime mud

Mao¹,

Wei²,

Tran³

2015

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Overliming and the consequent presence of unreacted lime (or free lime) in the lime mud are commonly believed to be the cause of many problems in the operation of causticizing plants and lime kilns in kraft pulp mills. The free lime content in lime mud is typically determined in mill laboratories using a so-called ammonium chloride (NH4Cl) method and in commercial laboratories using a thermal decomposition (TD) method. Over the years, we analyzed many lime mud samples from mills and found that the free lime content was consistently low, < 3 wt% calcium hydroxide (Ca(OH)2), even in cases where overliming was suspected to have caused problems. A systematic study was therefore conducted to investigate the validity of free-lime measurement methods, the reason for the consistently low free lime content in lime mud, and if free lime values can be used to indicate overliming. The results show that the NH4Cl method is not suitable for determining free lime. The TD method is good, but the possible interference of magnesium hydroxide (Mg(OH)2) must be taken into account. Since most pulp mills perform their free lime analysis on mud samples collected from pre-coat filters which have been washed, the resulting free lime value is low, and thus, cannot be used to assess the extent of overliming in the causticizing plant.

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Effects of Chloride, Potassium, and Sulfate on the Causticizing Reaction in the Kraft Recovery Process

Cited by 5 publications

References 9 publications

Influence of chlorine and potassium on operation and design of chemical recovery equipment

Influence of chlorine and potassium on operation and design of chemical recovery equipment

Formation of pirssonite in green liquor handling systems

Measurement of free lime content in lime mud

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