Honghi Tran - Academia.edu (original) (raw)

Papers by Honghi Tran

Tappi Journal, May 1, 2023

Mud ball formation in lime kilns has been a persistent problem in many kraft mills, particularly ... more Mud ball formation in lime kilns has been a persistent problem in many kraft mills, particularly for older kilns that are equipped with chains. A systematic laboratory study was conducted to examine how mud balls are formed and the key factors that affect ball formation. The results confirm the general mill experience that high moisture and high sodium contents in lime mud are the main contributing factors to ball formation. The high moisture content allows lime mud to agglomerate and grow to form balls, while the high sodium content helps make the balls hard and retain their shape. A ball formation mechanism is proposed to explain how mud balls form and grow near the kiln feed end.

Tappi Journal, Apr 1, 2006

Removal of fireside deposits from the heat transfer tubes in kraft recovery boilers is carried ou... more Removal of fireside deposits from the heat transfer tubes in kraft recovery boilers is carried out by sootblowing and occasionally "chill-and-blow" practices. During chill-and-blow, black liquor flow is reduced to rapidly cool the deposits. Thermal stresses generated in the deposit as a result of thermal shock can effectively weaken the deposit, facilitating its cleaning. For this study, we investigated the mechanical weakening effect of thermal stresses generated by the transient temperature gradients. We quantified the mechanical weakening effect due to thermal shock by measuring the decrease in biaxial flexure strength of a preheated sodium chloride disk at various quenching times and surface heat transfer coefficients. We observed that the mechanical weakening occured by transient thermal stresses as well as crack propagation. Approximately 35% loss in biaxial flexure strength could be achieved at heat transfer coefficients above 3.3.10 3 W/m 2 K, and at quenching durations above 40 s.

Tappi Journal, Jul 1, 2023

Poor settling and filterability of green liquor dregs has been a persistent problem in many kraft... more Poor settling and filterability of green liquor dregs has been a persistent problem in many kraft pulp mills. While the concentration and settling/filtering behaviors of dregs are expected to be related to how black liquor is burned in recovery boilers, the effect of boiler operation is not well understood. A systematic study was conducted to examine how recovery boiler operation may affect the dregs concentration in the raw green liquor (RGL) at three kraft pulp mills using SIMCA, a multivariate data analysis (MVDA) program. Daily average boiler operating data from three kraft mills were analyzed over a 3-year period. Results of both principal component analysis (PCA) and partial least squares regression (PLS) suggest that the main boiler operations contributing to high dregs concentrations in RGL are low liquor firing load, low bed temperature, poor char burning, and unstable char bed.

ABSTRACT Difficulties in dewatering of biosludge result in economical and environmental issues fo... more ABSTRACT Difficulties in dewatering of biosludge result in economical and environmental issues for wastewater treatment plants. Various attempts have been made to overcome this problem by achieving some pretreatment on biosludge. The main purpose of all pretreatment methods is to modify the biosludge characteristics in such a way to boost settling of cells and solid particles of sludge, and to ease the release of water molecules from extracellular polymeric substances and cells and to facilitate flow of water through forming filter cake. The present work presents an overview of different properties of sludge and their measurement, the main reasons of sludge dewatering difficulty, the fundamentals of sludge dewatering and various proposed methods for sludge pretreatment. The advantages and drawbacks of different methods are described and the dominance of one over the others is discussed mostly with respect to energy requirement and environmental impacts. Some recommendations have been made for optimal application of each method.

Tappi Journal, Dec 1, 2009

Researchers analyzed high resolution operational data from three recovery boilers using the princ... more Researchers analyzed high resolution operational data from three recovery boilers using the principal component analysis (PCA) feature of a multivariate statistical analysis program to identify major operating variables that contributed to fouling and plugging. The results show that PCA can be used to visualize the variability relative to long-term fouling trends in the boilers and to graphically distinguish changes in the boiler fouling condition caused by operational variability over a short period. This represents a major step forward in identifying operating variables that might be adjusted to minimize fouling, and in developing an online fouling monitoring technology based on PCA.

Tappi Journal, Oct 1, 2010

HLORIDE (CL) AND POTASSIUM (K) are known to have a negative impact on the operation of the kraft ... more HLORIDE (CL) AND POTASSIUM (K) are known to have a negative impact on the operation of the kraft chemical recovery process. These elements, despite their small quantities in black liquor, can drastically lower the melting temperature of fly ash deposits, and contribute to severe fouling and corrosion of heat transfer tubes in recovery boilers [1,2]. As pulp mills have tightened their liquor cycle in recent years in order to improve spill control and decrease chemical losses, Cl and K concentrations in the mill liquor have increased, causing problems in recovery boiler operation. This has led to a renewed interest in chloride and potassium removal. Due to their highly volatile nature at high temperatures, NaCl and KCl vaporize from the recovery boiler char bed, and from inflight burning black liquor particles. As the flue gas temperature decreases in the back side the boiler, these compounds condense as fume and become enriched in the precipitator ash. The enrichment factors of these species in the ash are typically about 2.5 for Cl and 1.5 for K. As a result, efforts to remove Cl and K from the recovery cycle have been directed at the precipitator ash. Besides purging precipitator ash periodically, several ash treatment processes are presently available for selectively removing Cl and K from the recovery cycle, using distinctly different principles: leaching, evaporationcrystallization, freezing-crystallization and ion exchange [3]. While the first three ash treatment processes use different principles, they all follow a basic scheme, as shown in Fig. 1. Ash and water are fed into an ash treatment C Abstract: Results of an analysis of the operating data of an ash leaching system show that the system removed 90% of the chloride (Cl) and 82% of the potassium (K) introduced to the system with the precipitator ash. The Cl concentration in the ash was significantly lower, compared to that before the ash system installation, while the K concentration remained at about the same level as before, when the mill was purging ash. The dramatic decrease in Cl concentration and the insignificant change in K concentration in the precipitator ash are likely due to the ash leaching system installation and the high sulphidity operation of the mill.

Journal of Pulp and Paper Science, 1999

L'enlevement des depots sur la surface exposee aux flammes des chaudieres de recuperation kra... more L'enlevement des depots sur la surface exposee aux flammes des chaudieres de recuperation kraft est un probleme complexe impliquant une interaction entre la mecanique des fluides du jet du souffleur de suie et la mecanique des solides des depots. La presente communication discute des effets de la pression de vapeur ainsi que du type de tuyere de soufflage et de sa dimension sur la pression d'impact maximale de la tuyere, le rayon de nettoyage et la consommation de vapeur. Une analyse de la mecanique d'enlevement des depots solides est aussi presentee. Nous avons montre que les principales proprietes d'un depot solide influencant le processus d'enlevement sont la resistance a la traction des depots etla force d'adhesion des depots aux tubes. Des etudes en laboratoire indiquent que ces proprietes sont fortement fonction de la temperature. Le rayon de nettoyage d'un souffleur de suie a n'importe quel endroit d'une chaudiere de recuperation peut etre evalue si les proprietes physiques de dependance des depots sur la temperature et les caracteristiques d'exploitation du souffleur de suie sont connues.

Pulp & paper Canada, Oct 1, 1984

ers, and summarized by Bill Darmstadt of BE & K Engineering Co., Alabama. Following is a summary ... more ers, and summarized by Bill Darmstadt of BE & K Engineering Co., Alabama. Following is a summary of the highlights of the colloquium.

Tappi Journal, May 1, 1997

A field trial was performed to examine the chemistry and leachability of ash and gaseous emission... more A field trial was performed to examine the chemistry and leachability of ash and gaseous emissions from boilers burning deinking residue together with natural gas and bark. The results show that, for the boiler firing deinking residue with natural gas, increasing the combustion temperature by increasing the gas flow rate had little effect on NO x emissions and ash chemistry. Fly ash consisted of mostly calcined clay, CaO and TiO 2 . Bottom ash was similar but had higher SiO 2 , Fe 2 O 3 , Na 2 O, K 2 O, and PbO contents than fly ash. Pb likely originated from clay used as a coating material. Hg was enriched in fly ash and particulates, but its concentration was too small to be of concern. The leachability of both bottom ash and fly ash was low, particularly for boilers that burn deinking residue with bark due to the high CaO content. Application: Disposal of ash from boilers burning deinking residue with natural gas, or particularly with bark, should not be a concern because of the low heavy-metal content and the low leachability of the ash.

Tappi Journal, 2006

This paper is also published on TAPPI's web site <www.tappi.org> and summarized in the January So... more This paper is also published on TAPPI's web site <www.tappi.org> and summarized in the January Solutions! for People, Processes and Paper magazine (Vol. 89 No. 1).

Mining, metallurgy & exploration, Nov 1, 2006

Causes for nodule formation in lime kilns were investigated using rotary batch kilns. The results... more Causes for nodule formation in lime kilns were investigated using rotary batch kilns. The results show that the size of the mud lumps and the sodium content in the mud are important factors in determining the final lime nodule size. Under the test conditions, lumps smaller than 13 mm appear to agglomerate to form larger nodules. while lumps larger than 19 mm do not agglomerate and, therefore, do not form larger nodules. The melting of sodium compounds in lime mud appears to be responsible for particle agglomeration once the sodium content exceeds 5%. Passing air through the bed material in the batch kiln prevented particles from agglomerating and adhering to the kiln wall.

Les dommages importants subis par les tubes de la chaudiere de recuperation a VCP Luis Antonio on... more Les dommages importants subis par les tubes de la chaudiere de recuperation a VCP Luis Antonio ont ete causes par le choc de gros morceaux de depots tombant du toit du fourneau de la chaudiere et du bord d'attaque des plateaux des surchauffeurs. Nous avons pu reduire considerablement le probleme grâce a une surveillance periodique de l'accumulation des depots sur le toit en installant une camera speciale et un souffleur de suie supplementaire, et aussi en augmentant la frequence des soufflages de suie dans les secteurs a probleme et en provoquant le detachement thermique afin de controler la taille des depots.

Tappi Journal, Aug 1, 2016

Black liquor is often mixed with various types of materials before being burned in a recovery boi... more 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.

Pulp & paper Canada, Dec 1, 1986

L'appareil Sootprobe mesure le taux d'accumulation de depot et la temperature des gaz de ... more L'appareil Sootprobe mesure le taux d'accumulation de depot et la temperature des gaz de carneau dans le surchauffeur et la chaudiere

DIGITAL.CSIC (Spanish National Research Council (CSIC)), Nov 4, 2017

B ioenergy and Carbon Capture and Storage (BECCS), is an interesting option to remove CO 2 from t... more B ioenergy and Carbon Capture and Storage (BECCS), is an interesting option to remove CO 2 from the atmosphere, thus mitigating the CO 2 emissions from the use of non-renewable sources, i.e., fossil fuels. BECCS has been identified as a relevant measure to achieve the target enforced by the United Nations Framework Convention on Climate Change (UNFCCC) in the Paris Agreement: To limit the increase in the average world temperature to 2 º C above pre-industrial levels. However, implementing CO 2 capture in bioenergy through common technologies has the drawback of high economic and energetic costs. In this sense, the Chemical Looping Combustion (CLC) technology allows inherent CO 2 capture at low cost during combustion. The benefits of CLC are based on avoiding the costly separation steps required in commercial CO 2 capture processes, e.g., CO 2 separation in flue gases or O 2 production for oxy-fuel combustion, by the use of an oxygen carrier. The purpose of the oxygen carrier, usually a particulate metal oxide, is to transfer oxygen from air to fuel in order to avoid the direct contact between them. Thus, the oxygen carrier provides the oxygen required for combustion in the so-called fuel reactor. The oxygen carrier is later regenerated by air in the air reactor. The most common design of a CLC unit includes two fluidized bed reactors, being those mentioned fuel and air reactors with the oxygen carrier continuously circulating among them. CLC has been widely investigated for the use of gaseous fuels and coal but the interest of using biomass has recently increased considering that negative CO 2 emissions would be possible. The objective of this work is to contribute to the development of biomass combustion by CLC evaluating the use of new and highly reactive Mn-based materials as oxygen carriers. Experiments were performed in a continuous 500 Wth CLC unit at Instituto de Carboquimica (ICB-CSIC), consisting of two interconnected fluidized-bed reactors. After determination of both gas streams composition, the performance of the CLC process was assessed by calculating the CO 2 capture rate and the combustion efficiency as a function of the operating conditions. During the experimental campaign, the temperature in fuel reactor and the circulation rate of the oxygen carrier were varied. In general, CO 2 capture rates close to 100% were obtained, which increased with temperature. In addition, high values of combustion efficiency were obtained. When the combustion was incomplete, the major unburnt compounds from the fuel reactor were H 2 , CO and CH 4. Likely, these unburnt gases could proceed from the volatile matter as a high conversion of char would be expected. Interestingly, the amount of tar detected was low and they do not contribute significantly to the combustion efficiency.