The solubility of calcium carbonate  in green liquor handling systems

TAPPI Journal ◽  
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.

scholarly journals Characterization of hard scale formed in the kraft mill green liquor processing equipment

TAPPI Journal ◽  
2013 ◽  
Vol 12 (1) ◽  
pp. 53-59 ◽  
Author(s):  
TASNUVA ZAKIR ◽  
HONGHI TRAN ◽  
VLADIMIROS G. PAPANGELAKIS
Keyword(s):  
Kraft Pulp ◽  
Selective Dissolution ◽  
Pulp Mills ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Persistent Problem ◽  
X Ray ◽  
Green Liquor ◽  
Kraft Pulp Mills

Scaling, the formation of hard deposits, in green liquor handling systems is a persistent problem in many kraft pulp mills. Scaling is commonly believed to be a result of pirssonite (Na2CO3·CaCO3·2H2O) formation when the green liquor total titrateable alkali (TTA) is high. In this study, we characterized 12 scale samples obtained from 10 kraft pulp mills using various analytical methods, including TGA/DSC (thermogravimetric analysis/differential scanning calorimetry), XRF (X-ray fluorescence spectrometry), XRD (X-ray diffraction spectrometry), SEM (scanning electron microscopy), and EMPA (electron microprobe analyzer). The analysis identified only four of these samples as pirssonite; the remaining consisted mostly of calcite (CaCO3). The reason for the predominant presence of calcite in the majority of the scale samples is not known. It may be a result of selective dissolution of sodium carbonate (Na2CO3) from the pirssonite scale during the time when the green liquor total TTA was low, leaving the insoluble CaCO3 behind.

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

TAPPI Journal ◽  
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.

Mill experience of calcium carbonate scale formation in green liquor pipelines

TAPPI Journal ◽  
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.

Cleavage of acetyl groups from northeast hardwood for acetic acid production in kraft pulp mills

TAPPI Journal ◽  
2013 ◽  
pp. 57-67 ◽  
Author(s):  
RAVIKANT PATIL ◽  
JOSEPH M. GENCO ◽  
HEMAND PENDSE ◽  
ADRIAAN VAN HEININGEN
Keyword(s):  
Acetic Acid ◽  
Kraft Pulp ◽  
Ion Concentration ◽  
Alkali Concentration ◽  
Extraction Temperature ◽  
Pulp Mills ◽  
Hydroxide Ion ◽  
Green Liquor ◽  
White Liquor ◽  
Kraft Pulp Mills

This study identified the optimum conditions for cleavage of acetyl groups from wood hemicelluloses for possible conversion to salts of acetate or to acetic acid in kraft pulp mills. Acetyl groups in wood hemicelluloses can be hydrolyzed by either OH- (hydroxide) or H+ (hydronium) ions. Experimental data are presented for the extraction of industrial northeast hardwood chips using alkali streams that are available in the kraft pulp mills: caustic, green liquor, and white liquor. The effects of extraction time, chip soaking temperature, alkali concentration, and extraction temperature on cleavage of acetyl groups were investigated. Soaking at elevated temperature was found to be more effective than no soaking or soaking at room temperature. The rate of cleavage of acetyl groups from wood hemicelluloses was proportional to the initial hydroxide ion concentration in the liquor. Both white liquor and 0.5 N sodium hydroxide had higher rates of hydrolysis of acetyl groups compared to green liquor, which contained fewer hydroxide ions. The initial hydroxide ion concentration in the liquor also determined the mechanism by which acetyl groups were hydrolyzed from the hemicellulose backbone. If the extraction liquor contained excess hydroxide ions, then most acetyl groups were directly hydrolyzed from the xylan polymer to form sodium acetate, and the xylan remained in the wood, provided the temperature was low. The extraction temperature had a negligible effect on rate of cleavage of acetyl groups if the liquor contained excess hydroxide ions.

Effects of added materials on black liquor combustion

TAPPI Journal ◽  
2016 ◽  
Vol 15 (7) ◽  
pp. 479-486
Author(s):  
LIMING ZHAO ◽  
DANIELLY CORTES ◽  
HONGHI TRAN
Keyword(s):  
Systematic Study ◽  
Sodium Sulfate ◽  
Kraft Pulp ◽  
Black Liquor ◽  
The Other ◽  
Pulp Mills ◽  
Combustion Behavior ◽  
White Liquor ◽  
Other Hand ◽  
Kraft Pulp Mills

Black liquor is often mixed with various types of materials before being burned in a recovery boiler to meet specific needs of kraft pulp mills. A systematic study was conducted using a thermogravimetric combustor to examine how added materials might affect the combustion behavior of black liquors obtained from several pulp mills. The results show that adding soap, caustic, white liquor, and sawdust significantly reduces the liquor swelling tendency, thereby requiring a longer time for the liquor to burn completely. Adding makeup saltcake, precipitator ash, sodium sulfate, and biosludge, on the other hand, has little or no effect on the liquor combustion behavior.

Formation of pirssonite in green liquor handling systems

TAPPI Journal ◽  
2013 ◽  
Vol 12 (7) ◽  
pp. 33-41 ◽  
Author(s):  
TASNUVA ZAKIR ◽  
HONGHI TRAN ◽  
VLADIMIROS G. PAPANGELAKIS
Keyword(s):  
Sodium Carbonate ◽  
Kraft Pulp ◽  
Pulp Mill ◽  
Pulp Mills ◽  
Hard Scale ◽  
Kraft Pulp Mill ◽  
Green Liquor ◽  
Kraft Pulp Mills ◽  
Alkali Salts

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.

Measurement of free lime content in lime mud

TAPPI Journal ◽  
2015 ◽  
Vol 14 (7) ◽  
pp. 481-489 ◽  
Author(s):  
XIAOSONG MAO ◽  
WEI REN ◽  
HONGHI TRAN
Keyword(s):  
Thermal Decomposition ◽  
Systematic Study ◽  
Kraft Pulp ◽  
Measurement Methods ◽  
Pulp Mills ◽  
Free Lime ◽  
Lime Content ◽  
Lime Kilns ◽  
Lime Mud ◽  
Kraft Pulp Mills

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.

Toward Production of Bioethanol Using Pulp Rejects from Kraft Pulp Mills as Raw Materials

2013 ◽  
Vol 67 (11) ◽  
pp. 1248-1251
Author(s):  
Masanori Kishino ◽  
Ken Orihashi ◽  
Akira Harada
Keyword(s):  
Kraft Pulp ◽  
Raw Materials ◽  
Pulp Mills ◽  
Kraft Pulp Mills

Activated Sludge Treatment of Kraft Mill Effluents from Conventional and Oxygen Bleaching

1991 ◽  
Vol 24 (3-4) ◽  
pp. 427-430 ◽  
Author(s):  
J. Nevalainen ◽  
P.-R. Rantala ◽  
J. Junna ◽  
R. Lammi
Keyword(s):  
Activated Sludge ◽  
Kraft Pulp ◽  
Activated Sludge Process ◽  
Chlorinated Phenols ◽  
Pulp Mills ◽  
Main Interest ◽  
Sludge Treatment ◽  
Kraft Pulp Mills ◽  
Activated Sludge Processes ◽  
Oxygen Bleaching

Conventional and oxygen bleaching effluents from hardwood kraft pulp mills were treated in laboratory-scale activated sludge processes. The main interest was the fate of organochlorine compounds in the activated sludge process. In the treatment of conventional bleaching wastewaters the BOD7-reduction was 80-91 % and in oxygen bleaching wastewaters 86-93 %. The respective CODCr removals were about 40 % and about 50 %. The AOX reductions were on average 22 % and 40 % in the treatment of conventional and oxygen bleaching effluents, respectively. The reductions of chlorinated phenols, guajacols and catecols were usually more than 50 % in both reactors. Very little accumulation of AOX into the sludge was observed. The stripping of AOX from aeration unit was insignificant.

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