Formation of pirssonite in green liquor handling systems

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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Fate of phosphorus in the recovery cycle of the kraft pulping process

TAPPI Journal ◽

10.32964/tj19.3.139 ◽

2020 ◽

Vol 19 (3) ◽

pp. 139-148

Author(s):

MARYAM SADEGH MOUSAVI ◽

NIKOLAI DEMARTINI

Keyword(s):

Kraft Pulp ◽

Pulp Mill ◽

Field Studies ◽

Kraft Pulping ◽

Pulp Mills ◽

Recovery Cycle ◽

Green Liquor ◽

Green Liquor Dregs ◽

Kraft Pulp Mills ◽

Negative Effect

The accumulation of nonprocess elements in the recovery cycle is a common problem for kraft pulp mills trying to reduce their water closure or to utilize biofuels in their lime kiln. Nonprocess elements such as magne-sium (Mg), manganese (Mn), silicon (Si), aluminum (Al), and phosphorus (P) enter the recovery cycle via wood, make-up chemicals, lime rock, biofuels, and process water. The main purge point for these elements is green liquor dregs and lime mud. If not purged, these elements can cause operational problems for the mill. Phosphorus reacts with calcium oxide (CaO) in the lime during slaking; as a result, part of the lime is unavailable for slaking reactions. The first part of this project, through laboratory work, identified rhenanite (NaCa(PO4)) as the form of P in the lime cycle and showed the negative effect of P on the availability of the lime. The second part of this project involved field studies and performing a mass balance for P at a Canadian kraft pulp mill.

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Effect of polysulfide pulping process on the energy balance of softwood and hardwood kraft pulp mills

Nordic Pulp & Paper Research Journal ◽

10.1515/npprj-2021-0026 ◽

2021 ◽

Vol 0 (0) ◽

Author(s):

Satu Lipiäinen ◽

Katja Kuparinen ◽

Esa Vakkilainen

Keyword(s):

Kraft Pulp ◽

Energy Use ◽

Process Development ◽

Black Liquor ◽

Pulp Mill ◽

Electricity Production ◽

Pulp Yield ◽

Pulp Mills ◽

Kraft Pulp Mill ◽

Kraft Pulp Mills

Abstract Polysulfide pulping is a method to increase the pulp yield in a kraft pulp mill. Higher production is in the core of pulp mill process development, but modifications in cooking raise questions on their effects on the other parts of the process. This study focuses on the impacts of polysulfide pulping on the energy use and production of kraft pulp mills. The impacts are estimated by calculating and analyzing the steam and electricity balances of reference softwood and hardwood mills. Energy generation using residual biomass is an essential part of the operation of a kraft pulp mill, and often a notable source of income. The results show that implementation of polysulfide cooking affects both energy consumption and production. Higher hemicelluloses content of pulp cooked using polysulfide liquor means that less organic material ends up in the black liquor. Subsequently, the recovery boiler energy production suffers. The reduced steam production together with increased steam consumption decreased electricity production, corresponding to a decline in sellable electricity of 22.4 % in the hardwood mill and 28.4 % in the softwood mill. The study shows that increasing the pulp production by investing in polysulfide cooking in stand-alone kraft pulp mills can be economically feasible.

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Study on Experimental Device of Removing TRS Gas with ClO2

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.834-836.1710 ◽

2013 ◽

Vol 834-836 ◽

pp. 1710-1717

Author(s):

Xue Ping Song ◽

Qiu Xia Xie ◽

Dong Hua Liang ◽

Wei Qiang Zhou ◽

Kai Huang ◽

...

Keyword(s):

Kraft Pulp ◽

Removal Rate ◽

Pulp Mill ◽

Sulfur Cycle ◽

Experimental Device ◽

Pulp Mills ◽

Kraft Pulp Mill ◽

Emission Standards ◽

Kraft Pulp Mills ◽

Designed Experiment

In order to remove the malodorous pollutants of total reduced sulfur (TRS) produced by kraft pulp mill, the experimental device was designed to remove the TRS gases in accordance with the principle of ClO2oxidizing TRS gases. After ClO2oxidizes TRS gases, the substances produced are absorbed by lye, which achieve the purpose of removing TRS gases. At the same time, these alkali absorber can be reused to the sulfur cycle of kraft pulp mills. With the self-designed experiment apparatus, the removal rate of H2S and CH3SH are 99.40% and 99.8% respectively, the concentration of H2S reduces from 1.275g/m3to 0.137mg/m3, the concentration of CH3SH reduces from 1.457g/m3to 0.032 mg/m3, which both reach national grade iii emission standards.

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The solubility of calcium carbonate in green liquor handling systems

TAPPI Journal ◽

10.32964/tj18.10.595 ◽

2019 ◽

Vol 18 (10) ◽

pp. 595-602

Author(s):

ALISHA GIGLIO ◽

VLADIMIROS G. PAPANGELAKIS ◽

HONGHI TRAN

Keyword(s):

Calcium Carbonate ◽

Systematic Study ◽

Kraft Pulp ◽

Thermodynamic Simulation ◽

Solubility Data ◽

Pulp Mills ◽

Persistent Problem ◽

Green Liquor ◽

Kraft Pulp Mills ◽

Salt Systems

The formation of hard calcite (CaCO3) scale in green liquor handling systems is a persistent problem in many kraft pulp mills. CaCO3 precipitates when its concentration in the green liquor exceeds its solubility. While the solubility of CaCO3 in water is well known, it is not so in the highly alkaline green liquor environment. A systematic study was conducted to determine the solubility of CaCO3 in green liquor as a function of temperature, total titratable alkali (TTA), causticity, and sulfidity. The results show that the solubility increases with increased temperature, increased TTA, decreased causticity, and decreased sulfidity. The new solubility data was incorporated into OLI (a thermodynamic simulation program for aqueous salt systems) to generate a series of CaCO3 solubility curves for various green liquor conditions. The results help explain how calcite scale forms in green liquor handling systems.

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Mill experience of calcium carbonate scale formation in green liquor pipelines

TAPPI Journal ◽

10.32964/tj19.8.387 ◽

2020 ◽

Vol 19 (8) ◽

pp. 387-397

Author(s):

ALISHA GIGLIO ◽

HONGHI TRAN ◽

MARIA BJORK ◽

RICKARD WADSBORN ◽

HAL LAGIMODIERE ◽

...

Keyword(s):

Kraft Pulp ◽

Temperature Drop ◽

Metal Substrate ◽

Scale Formation ◽

Operating Conditions ◽

Pulp Mills ◽

Green Liquor ◽

Kraft Pulp Mills ◽

High Degree ◽

Calcium Carbonate Scale

Experience of hard calcite (CaCO3) scale formation in green liquor pipelines at four kraft pulp mills was systematically investigated to determine if there is any correlation between the severity of the scaling problem at each mill and the design and operating conditions of its causticizing plant. The results show that the high degree of supersaturation of calcium ions (Ca2+) in the liquor is the main contributing factor. Mills that operate at a lower green liquor total titratable alkali (TTA), higher causticity, and a larger liquor temperature drop are more likely to pro-duce a green liquor that is supersaturated with Ca2+, and thus experience more severe scaling problems. In order to minimize CaCO3 scaling, the green liquor handling equipment should be operated as steady as possible to avoid conditions that allow Ca2+ to be supersaturated. The strategies include minimizing variations in liquor TTA, insulating the green liquor pipelines to reduce temperature gradients, and adding lime mud to weak wash to provide seeds for precipitation to occur on mud particles instead of on metal substrate.

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Method for analysis of ClO2 and Cl2 air emissions from pulp mill

Nordic Pulp & Paper Research Journal ◽

10.1515/npprj-2018-0012 ◽

2019 ◽

Vol 34 (1) ◽

pp. 19-27

Author(s):

Kimona Häggström ◽

Magnus Gunnarsson ◽

Katarina Bremert-Jirholm ◽

Nina Simic

Keyword(s):

Chlorine Dioxide ◽

Analytical Method ◽

Kraft Pulp ◽

Pulp Mill ◽

Air Emissions ◽

Pulp Mills ◽

Limit Of Quantification ◽

Regulatory Standards ◽

Low Concentrations ◽

Kraft Pulp Mills

Abstract Chlorine dioxide is commonly used as a bleaching agent in kraft pulp mills. Scrubbers are required to remove any remaining ClO2 from the plant tail gases. To control the air emissions of chlorine compounds, chlorine dioxide and chlorine contents must be monitored to ensure that the strict regulatory standards are met. However, the currently used analytical method is not suitable for detection of low concentrations of chlorine and chlorine dioxide. A new method for measuring chlorine dioxide and chlorine emissions was developed, which ensures compliance with the stringent requirements imposed by the authorities. The two species could be measured separately with a limit of quantification of 3 ppm. The method was robust and easy to use in the pulp mill environment and it was validated both in the laboratory and the field. The specificity of the method was demonstrated, Cl2 analysis was not sensitive to the presence of ClO2 and vice versa. The uncertainty (±2×RSD) of the analytical method in the field was estimated from duplicate measurements performed in the range of 3–500 ppm for ClO2 and 3–300 ppm for Cl2, and was found to be ±20 % and ±10 %, respectively. Possible interferences in the analytical method are also discussed.

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Some Toxic Constituents of Chlorination-Stage Effluents from Bleached Kraft Pulp Mills

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f81-100 ◽

1981 ◽

Vol 38 (7) ◽

pp. 739-743 ◽

Cited By ~ 23

Author(s):

A. B. McKague

Keyword(s):

Gas Chromatography ◽

Rainbow Trout ◽

Kraft Pulp ◽

Pulp Mill ◽

Salmo Gairdneri ◽

Pulp Mills ◽

Juvenile Rainbow Trout ◽

Bleached Kraft Pulp ◽

Toxic Materials ◽

Kraft Pulp Mills

Constituents responsible for the toxicity of a sample of bleached kraft chlorination-stage effluent to juvenile rainbow trout (Salmo gairdneri) were investigated. Tetrachlorocatechol, 3,4,5-trichlorocatechol, and 2,6-dichlorohydroquinone were identified and evidence was obtained for the presence of other chlorodihydroxybenzenes in toxic acidic fractions of the sample. Concentrations of 0.46 mg/L 3,4,5-trichloro- and 0.74 mg/L tetrachloro-catechol were estimated in the sample by analytical gas chromatography. Toxic materials in the nonacidic fraction were not identified although the nontoxic dichloromethyl methyl sulfone was isolated.Key words: chlorination-stage effluent, toxicity, pulp mill, chlorocatechols, chlorodihydroxybenzenes

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