Papers

Permanent URI for this collectionhttps://hdl.handle.net/1807/96978

Browse

Now showing 1 - 20 of 117

Effects of rings on flow and temperature in lime kilns
(Annex Publishing & Printing, Inc., 2022) GAREAU, PATRICK; BUSSMAN, MARKUS; DEMARTINI, NIKOLAI; TRAN, HONGHI
A steady state, 2D axisymmetric model has been developed to help understand how rings form and grow in a typical lime kiln. Rings of varying length, thickness, and geometry of the front and back faces were modelled to study the effects on flue gas flow and temperature. The results show that ring growth causes the gas velocity to increase and insulates the adjacent refractory, resulting in a lower kiln shell temperature. The results also reveal the formation of recirculation zones immediately downstream of the rings, as well as temperature deviations upstream and downstream of the rings that might promote recarbonation and further ring growth. The model was applied to a kiln from a kraft mill with front-end and mid-kiln rings and good agreement was obtained between the measured and predicted kiln shell temperatures, providing confidence in the modelling.
Effects of agitator blade scaling on mixing in dissolving tanks
(Annex Publishing & Printing, Inc., 2022) Gareau, Patrick; Bussman, Markus; DeMartini, Nikolai
Hard calcium carbonate scale often forms on the agitators in smelt dissolving tanks. The effects of this scale on mixing are not well understood. While mixing in tanks has often been modelled in the literature, there have been no studies involving agitator scaling. To better understand the impact of agitator scaling on hydrodynamics and tank concentrations, a steady state, 3D model has been developed for a smelt dissolving tank at a kraft pulp mill. In this work, four cases are compared: an agitator with no scaling, mild scaling, moderate scaling, and extreme scaling. The extreme scaling case is representative of scale build-up on a dissolving tank agitator that was significant enough that the agitator had to be stopped and cleaned. The reduction in the agitator fluid jet velocity is relatively small for the mild and moderate scaling cases, but it becomes more significant for the extreme scaling case, for which the results indicate that the mixing of the smelt with the weak wash is likely poor and that there would thus be a risk of smelt pooling.
Enhancement of biosludge dewatering using proteins through dual conditioning
(Annex Publishing & Printing, Inc., 2022) Ghazisaidi, Hamed; Tran, Honghi; Meyer, Torsten; Allen, D. Grant
In pulp and paper mills, effective biosludge dewatering is essential in wastewater treatment to reduce the large volume of biosludge that needs to be treated and disposed. The dewatering process normally requires the use of polymers from petroleum-based sources. This study explores the potential of using cationic proteins such as protamine for biosludge dewatering through dual conditioning with a small amount of a synthetic anionic polymer such as anionic polyacrylamide (APAM). The results show that dual conditioning provides substantial synergistic enhancements in dewatering. The maximum cake solids content of biosludge achieved by adding protamine (7.5%) alone was 12%. By dual conditioning with a small amount of APAM (0.1%), not only the cake solids content was increased to 16%, but also the amount of protamine addition was substantially lowered to 2%. These results, coupled with the change in zeta potential of the particles in the biosludge samples, suggest that the cationic protamine reduced the negative charge of the particles, allowing smaller particles to agglomerate and providing a positively charged framework for the subsequent addition of the negatively charged APAM. After adding APAM, substantial floc-bridging occurred, allowing smaller flocs to aggregate into larger flocs. These synergistic effects can lower the wastewater treatment cost by reducing the amount of synthetic polymer and by applying low-value proteins from natural sources.
Determining the performance of lignin-based flocculants in improving biosludge dewaterability
(Annex Publishing & Printing, Inc., 2023-01-01) Ghazisaidi, Hamed; Wang, Vincent; Fatehi, Pedram; Tran, Honghi; Meyer, Torsten; Allen, D Grant
In the wastewater treatment plant of pulp and paper mills, biosludge dewatering is needed to reduce the sludge handling and disposal costs. It is usually facilitated by means of the addition of synthetic polymers. There is increasing interest in replacing synthetic polymers with biopolymers derived from low value by-products or industrial residuals to improve the environmental footprint of dewatering. In this study, lignin-based flocculants (LBF) were tested for their ability to improve the biosludge dewaterability based on Capillary Suction Time (CST) and dry cake solids achieved with a Crown Press. The results demonstrate that LBFs alone can significantly enhance dewatering with a decrease in CSTs from 72.7 ± 5.1 s (unconditioned biosludge) to 23.3 ± 0.4 s and an increase in dry cake solids after pressing from 7.1 ± 0.5% to 13.9 ± 1.3% with a relatively high dosage of 7.5% w/w. However, with dual conditioning a LBF and 0.1% w/w anionic polyacrylamide (APAM), the required dosage of LBF was reduced to 3% w/w to achieve a dry cake solids content of 13.8 ± 0.4%, the same as that achieved with Zetag8165, a commercial synthetic polymer. LBF addition lowered the particle surface charge, allowing the particles to agglomerate and enhancing for the biosludge dewaterability. The application of LBFs for sludge dewatering offers novel considerable promise for providing more sustainable approaches by optimizing the use of lignin from different extraction processes, applying various types of lignin modifications in combination with anionic polymers, and exploring different methods of disposal or utilization of the dewatered sludge.
Solubility of Sodium Salts in Kraft Black Liquor and the Impact on Evaporator Fouling
(2023-03) Khafhafera, Ahmed; DeMartini, Nikolai; Chemical Engineering Applied Chemistry
The evaporation of black liquor is a key step in the chemical recovery cycle of kraft pulp mills. Black liquor is concentrated stepwise by evaporating water in multiple effects evaporators (MEE). The majority of the scaling and fouling instances during black liquor evaporation are attributed to sodium salts. The focus of this thesis is to obtain the necessary solubility data for sodium oxalate and sodium carbonate-sodium sulfate salts and thus generate empirical models for sodium salt solubility that can be applied in mills to help reduce evaporator scaling. Sodium oxalate solubility was studied in the temperature range of 50 °C to 140 °C and a dry solids range of 14% to 70% dry solids. Four mill liquors were studied for the work done below 100 °C, and sodium oxalate solubility was not found to be liquor-dependent but rather depended only on the concentration of sodium, concentration of oxalate, and temperature. Two different empirical formulas were developed for solubility below 100 °C and solubility above 100 °C. These formulas were applied by a mill with sodium oxalate scaling in several of their evaporator effects. Double salts of sodium carbonate and sodium sulfate precipitate in the evaporation sets of all kraft pulp mills. Most of the solubility work focused on the transitions between the different salt species and the solubility of the carbonate-rich salts, about which there is relatively little data in the present literature. Empirical formulas were developed for use by mills and were utilized in the following studies with electrostatic precipitator (ESP) ash. Electrostatic precipitator (ESP) ash is used by the pulp and paper industry in two different ways to try and reduce sodium salt scaling. The first is to dissolve it in black liquor so that a sulfate-rich double salt precipitates first rather than carbonate-rich salts, which causes more severe scaling. The second approach is to add the ash above the solubility limit to increase the crystal surface area for precipitating salts to precipitate onto. The experiments showed that ash added below the solubility limit dissolves quickly, reaching saturation as fast as 10 min. It also found that ash, when added to carbonate-rich black liquor above the solubility limit, remains as burkeite and sodium sulfate and, within 24 h, does not undergo dissolution and re-precipitation to a carbonate-rich salt. This may help explain the varied success of using precipitator ash to reduce sodium salt scaling in kraft black liquor evaporators.
Effect of Steam on the Release of K and Cl during Biomass and Black Liquor Combustion
(Annex Publishing & Printing, Inc., 2022) Ng, Jerry; DeMartini, Nikolai
The supercritical steam temperatures achieved in biomass and kraft recovery boilers are limited by alkali and chlorides in the fuel because these elements contribute to fouling and corrosion in the convective passes. There is a lack of experimental data on the effect of steam in the combustion gases on the release of alkali and chloride from biomass and black liquor. In this work, the release of K and Cl from three biomass fuels in different gas environments is measured. The gas environments studied were balanced with N2 and contained 11% CO2, 1% O2, and either 8 or 17% steam. The mass loss and particle temperature throughout combustion were measured. Measurements show that the presence of steam slows the release of K and Cl during char oxidation in wood. Temperature measurements during char conversion experiments show that the particle temperature drops in the presence of steam as a result of endothermic gasification reactions on the char surface by steam and CO2. The decrease in the char temperature results in a lower KCl vapor pressure, lowering the KCl vaporization rate; however, experiments show that this lower temperature alone does not explain the decrease in KCl release. For black liquor, steam and CO2 did not affect the mass loss or the release of K and Cl, but this appears to be due to the small black liquor droplets fully burning before reaching a high enough temperature for significant K and Cl release.
Utilization of kraft pulp mill residuals
(Annex Publishing & Printing, Inc., 2022-02-02) MEYER, TORSTEN
Kraft pulp mills produce on average about 100 kg of solid residuals per metric ton of pulp produced. The main types of mill waste are sludge from wastewater treatment plants, ash from hog fuel boilers, dregs, grits, and lime mud from causticizing plants and lime dust from lime kilns. Of these, about half is disposed of in landfills, which highlights the need and potential for waste recycling and utilization. Sludge is either incinerated in hog fuel boilers to generate steam and power or used in various forms of land application, including land spreading, composting, or as an additive for landfill or mine waste covers. The majority of hog fuel boiler ash and causticizing plant residues is landfilled. Alkaline residuals can be conditioned for use in land application, manufacture of construction materials, and production of aggregates for road work. This technical review summarizes residuals utilization methods that have been applied in pulp and paper mills at demonstration- or full-scale, and therefore may act as a guide for mill managers and operators whose goal is to diminish the costs and the environmental impact of waste management.
Methane production potential of pulp mill sludges: microbial community and substrate constraints
(Oxford University Press, 2021-11) Chan-Yam, Kelly; Meyer, Torsten; Scott, J Ashley; Basiliko, Nathan
Sludges from pulp and paper mills represent a major ecological and environmental cost, and anaerobic digestion represents a method of waste reduction and energy recovery for these mills. This study compared methane production potential and microbial communities across 11 primary- and biosludges from five pulp and paper mills using various mill processes. We measured methane production from sludges in anaerobic batch reactor experiments over 64 days. Sludges were incubated with and without added substrate to test for organic substrate limitation versus inhibition of methanogens. Initial microbial communities and changes to community composition were determined using Illumina MiSeq for metabarcoding of bacterial and archaeal 16S rRNA genes. Mean methane production potential varied greatly between sludges (0.002-79 mL CH4 g-1 TS). Among primary sludges, kraft mill sludge produced more methane than other mill types. For these other mills, biosludge produced more methane than primary sludge, which had evidence of methanogen inhibition. Microbial communities and diversity were influenced by the initial community composition, and high methane production was only seen in sludges with high diversity. A number of sludges innately produced substantial methane and may be targets for further modelling and larger scale testing of anaerobic digestion.
Enhancing pulp and paper mill biosludge dewaterability using enzymes
(Elsevier, 2015-01-01) Bonilla, Sofia; Tran, Honghi; Allen, D. Grant
There have been limited studies on the potential use of enzymes for enhancing the dewaterability of biosludge. The mechanisms for such enhancement have not been investigated despite the environmental advantages of using enzymes over synthetic polymers for biosludge conditioning. In order to find enzymes with this potential, a screening of commercially available enzymes was carried out using capillary suction time to assess biosludge dewaterability. The only enzyme that showed dewatering improvements in the screening tests was a lysozyme which reduced the capillary suction time by 36% and increased the cake solids content from 5.6 to 8.9 DS%. Lysozyme aided in the flocculation of particles reducing the polymer demand from 11% to 6%. Active and inactive lysozyme exhibited a similar ability for enhancing sludge dewatering, indicating that the conditioning mechanism of lysozyme is similar to that of a flocculant.
Modeling Deposit Breakup Under Sootblower Jet Impingement
(PAPTAC, 2018) You, Shenglong; Bussmann, Markus; Tran, Honghi; Tandra, Danny
This paper presents, for the first time, an integrated numerical model of sootblowing and deposit breakup. The model couples a 3D Computational Fluid Dynamics (CFD) solution to a Finite Element Analysis (FEA) model, to simulate jet dynamics and the stress distribution within the deposit, respectively. A one-way Fluid-Structure Interaction (FSI) approach is used to couple the CFD and the FEA simulations: the pressure on the deposit surface predicted by the CFD simulation is exported to the FEA model as a boundary condition. In addition, a 2D Finite-Discrete Element Method (FDEM) code is used to simulate crack initiation and propagation through a deposit cross-section. The integrated model is validated against lab experimental results [1] with reasonable agreement, identifying the initiation and propagation of cracks similar to those observed in the experiments. The model provides a better understanding of the deposit removal process, and could be used to improve sootblowing efficiency.
Factors Affecting Chloride and Potassium Removal Efficiency of a Recovery Boiler Precipitator Ash Treatment System
(PAPTAC, 2007) Gonçalves, C.; Tran, H.; Shenassa, R.
A laboratory study was performed to examine the main factors affecting the removal efficiency of chloride (Cl) and potassium (K) of ash treatment systems operated at a temperature between 60 and 100°C. The results show that the removal efficiency is directly proportional to the amounts of Cl and K in the liquid that have been separated from the ash-water slurry. For a given system, the Cl and K removal efficiency is determined by the concentration of Cl and K in the liquid and by the degree of solid-liquid Separation (DS). DS, in turn, is greatly affected by the ash concentration in the slurry and the CO3 content of the ash.
A Multivariate Analysis of Recovery Boiler Fouling
(PAPTAC, 2007) Versteeg, P.; Tran, H.; De Leo, V.
Operating data from two recovery boilers was analyzed using Principal Component Analysis (PCA) and Partial Least Squares Analysis (PLS). PCA allowed visual and operational comparisons between periods of high fouling and low fouling in both boilers. PLS extracted the correlation structures between vari-ables and provided a better understanding of overall boiler operation and a focus on which variables might be adjusted to improve boiler performance. Together these two techniques can help identify the main operating variables that cause fouling in recovery boilers.
Fate of phosphorus in the recovery cycle of the kraft pulping process
(TAPPI Press, 2020-03-01) Sadegh Mousavi, Maryam; Demartini, Nikolai
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 magnesium (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.
Enhancing Biosludge Dewaterability with Hemoglobin from Waste Blood as a Bioflocculant
(2020-11-22) Ghazisaidi, Hamed; Garcia, Rafael A.; Tran, Honghi; Yuan, Runlin; Allen, D. Grant
Synthetic polymers are widely used in the treatment of biosludge (waste activated sludge) to enhance its dewaterability. This paper discusses the results of a systematic study using hemoglobin (Hb) from animal blood and methylated hemoglobin (MeHb), a derivative in which a methyl group replaces the hydrogen carboxyl groups, to replace synthetic polymers to improve the dewatering efficiency of biosludge. With regular hemoglobin, no improvement in biosludge dewatering was found. With 10% of methylated hemoglobin per total solids content, however, the dry solids content of biosludge increased from 10.2 (±0.3) wt% to 15.0 (±1.0) wt%. Zeta potential measurements showed a decrease in the negative surface charge of the particles in biosludge from −34.3 (±3.2) mV to −19.0 (±2.1) mV after the treatment with methylated hemoglobin. This, along with an unchanged particle size distribution after conditioning, suggests that charge neutralization is likely the main cause of particle flocculation. With charges neutralized, the extracellular polymeric substances (EPS) around the biosludge flocs become loose, releasing the trapped water, thus increasing dewaterability.
The sticky temperature of recovery boiler fireside deposits
(Annex Publishing & Printing, Inc., 2002-09) Tran, H.N.; Mao, X.; Kuhn, D.C.S.; Backman, R.; Hupa, M.
The sticky temperature of carryover particles in kraft recovery boilers is an important parameter in boiler design and operation. Results of a collaborative study show that the sticky temperature depends strongly on pat tide size and liquid content. A series of sticky temperature contour maps have been constructed which can be used to predict the sticky temperature of any sulphide free carry over particle as a function of chloride, potassium and carbonate coment.
Characterization of deinking sludge and its ashed residue
(Annex Publishing & Printing, Inc., 1994-10) Latva-Somppi, J,; Tran, H.N.; Barham, D.; Douglas, M.A,
Deinking sludges from three drinking plants, their laboratory-prepared ashes and ash samples from a deinking sludge incinerator were characterized. Sludges consist of degraded cellulose fibres mixed with particulate solids and water. As received, sludges contain 30 to 55 wt% solids which consist of 55 to 85 wt% volatiles and 15 to 45 wt% ash. Dried sludges have heating values ranging from 12 to 16 MJ/kg and are reasonable fuels if dried to a low moisture content. Ashes consist mainly of Si02 , Al203 and CaO derived from coating materials, melt at tern* peratures higher than 1400" C and do not sinter below 1050" C. Laboratory ash particles are smaller than 10 μm, while incinerator ash particles are much larger and partially fused.
Removal of recovery boiler fireside deposits by thermal shedding
(Annex Publishing & Printing, Inc., 1993-11) Tran, H.; Reeve, D.W.; Cole, T.; Damon, R.A.; Clay, D.T.
Recovery boiler fireside deposits are occassionaly removed by thermal shedding, which rapidly cools the boiler to cause deposits to contract, crack, and be readily blown off by sootblowers. A laboratory study on deposit thermal expansion and two field studies on the effectiveness of thermal shedding have led to development of a new shedding procedure, which requires less boiler downtime. but still achieves the same deposit removal efficiency with minimal damage to boiler tubes.
Evaluating the effect of enzymatic pretreatment on the anaerobic digestibility of pulp and paper biosludge
(Elsevier, 2018-01-05) Bonilla, Sofia; Choolaei, Zahra; Meyer, Torsten; Edwards, Elizabeth A; Yakunin, Alexander F; Allen, D Grant
Anaerobic digestion of biosludge has not yet been implemented in pulp mills due to low biogas yields. Enzymatic pretreatment of biosludge has shown improvements in biogas yields but results are varied. A key limitation of previous studies is that they fail to consider the COD contribution from the enzyme solutions. The aim of this study was to systematically investigate the potential for enzymatic pretreatment on the anaerobic digestibility of pulp mill biosludge. Out of the six enzymes tested, four enhanced the anaerobic digestibility of biosludge. At the end of the BMP, a maximum improvement of 26% in biogas yield was observed with protease from B. licheniformis. There was no correlation between enzymatic activities on standard substrates and/or on biosludge and the effect of enzymes on biogas yields. Enzymes have potential for improving biosludge anaerobic digestibility but more research on optimal conditions and potential synergies with other pretreatment is needed.
Cationic proteins for enhancing biosludge dewaterability: A comparative assessment of surface and conditioning characteristics of synthetic polymers, surfactants and proteins
(Elsevier, 2018-01-31) Bonilla, Sofia; Allen, D. Grant
Synthetic organic polymers are commonly used to facilitate challenging solid-liquid separations such as biosludge dewatering. However, there is interest in reducing the use of polymers due to their toxicity and synthetic sourcing. Surfactants and proteins have shown potential to enhance sludge dewaterability but little is known about the properties and/or mechanism(s) that promote this enhancement. In this study, synthetic polymers, surfactants and proteins were investigated to evaluate whether surface properties such as charge, surfactant activity and hydrophobicity, play a role in how these conditioners affect biosludge dewatering. Capillary suction time (CST), dry solids content, filtrate rate and filtrate solids content were used to assess dewaterability. Results show that surface charge determines the potential of conditioners. The effect of charge was greater for surfactants and proteins than for polymers. In contrast with previous reports, surfactant activity negatively affected the dewaterability of biosludge. Cationic conditioners, regardless of the group improved biosludge dewaterability. However, the dose of cationic proteins is still high compared to currently used synthetic polymers (e.g. protamine is 0.1 g/g TSS vs. synthetic polymer 0.03 g/g TSS). Our results suggest that there is potential for using proteins to improve biosludge dewaterability but a further reduction in protein dose and/or an increase in the protein’s efficiency as a conditioner is needed.
Natural Freezing-Thawing and Its Impact on Dewaterability and Anaerobic Digestibility of Biosludge
(Mary Ann Liebert, 2017-05-01) Meyer, Torsten; Chen, Xu; Tran, Honghi N.; Allen, D. Grant; Edwards, Elizabeth A.
Dewatering of pulp and paper mill biosludge is challenging, and it can make up half of overall wastewater treatment costs. By harvesting energy provided by nature, freezing-thawing can notably alter the physical structure of sludge flocs, thereby influencing dewaterability and anaerobic digestibility. Samples of biosludge from three pulp and paper mills (sulfite, kraft, and semi-chemical pulping) as well as biosludge digestate (i.e., biosludge after anaerobic digestion) were subject to freeze-thaw treatment, and they were subsequently tested in terms of dewaterability by using a gravity filtration—crown press unit, and anaerobic digestibility by means of biochemical methane potential assays. Gravity filtrate from dewatering of freeze-thaw treated biosludge was also tested for anaerobic digestibility. Freeze-thaw treatment improved the dewaterability of biosludge mill samples to a larger extent than dewatering polymer. Treatment at −10°C before dewatering increased the dry solid content of the dewatering cake from 13% to 21% (sulfite mill), from 7% to 26% (kraft mill), from 10% to 20% (digestate after 35 days of digestion), and from 17% to 23% (digestate after 60 days of digestion). Biosludge from the semi-chemical pulping mill was only dewaterable after freeze-thaw treatment, which enabled a final cake solid content of 45%. In contrast, the anaerobic digestibility of biosludge and digestate improved, if at all, only to a relatively small extent. A strong improvement in digestibility was only observed in the case of gravity filtrate from dewatering of freeze-thaw treated biosludge (sulfite mill), where the specific biogas yield increased from 111 to 310 mL/g chemical oxygen demand added. Visual inspection on untreated and freeze-thaw treated biosludge confirmed the assumption that the strong effect on dewaterability was caused by irreversible compaction and dehydration of sludge particles. Evidence for widespread rupture of bacterial cells was not confirmed, which may explain the comparably small effect on anaerobic digestibility.

Browse

Recent Submissions