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- Dernegård, Henric C O, 1981, et al.
(författare)
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Characterization of a dusting lime kiln - A mill study
- 2017
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Ingår i: PEERS Conference 2017: Maximizing Success Through Innovation. ; 2017-November, s. 488-500
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Konferensbidrag (refereegranskat)abstract
- © 2017 TAPPI Press. All rights reserved. The white liquor preparation is one of the main purposes of the recovery cycle in a kraft pulp mill and the lime kiln, being the single unit operation handling bulk solid materials, poses particular challenges in the recovery cycle. In this study, the influence of a dusting lime kiln on the preparation of white liquor was studied. The investigation showed that the dusting lime kiln produced a burned lime with a substantial fraction of fines at the expense of the fraction of granules, whereas a clear lime kiln had virtually no fines and more granules instead. Burned lime from both dusting and clear periods were collected and separated into fines and granules. The different fractions were slaked and causticized in a synthetic green liquor. The study found that the fines always delivered a lower effective alkali in the resulting white liquor, and that the particle sizes of the lime mud were always larger than those originating from the granules, implying that the fines were sintered harder. The industrial consequence is that a dusting lime kiln increases the load on the kiln because the yield of effective alkali is lower; it also introduces a greater dead load into the liquor cycle.
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- Dernegård, Henric C O, 1981
(författare)
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Dusting in a lime kiln - Characterization of the material and unit operations
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The present thesis describes the background of, and gives some points of orientation for, the phenomenon of dusting in the burner zone of a lime kiln. The aim of this study is twofold: to increase knowledge of the factors that influence the degree of dusting and also to investigate the effect a dusting lime kiln has on the white liquor preparation process. The thesis covers parts of the historical development in the recovery process, earlier findings on dusting in the literature, the impact of dusting on the causticizing process and an explanation for the cause of dusting along with actions to avoid, or contain, it. A Kraft pulp mill utilizes a rotary lime kiln to regenerate CaO from CaCO3 by reburning. The CaO is used to regenerate the cooking chemicals for the digester. A lime kiln is around 70-100 meters long and around 2-4 meters in diameter. The kiln is typically equipped with product coolers at the discharge end where hot reburned lime meets incoming secondary air in a counter-current heatexchange process. Dusting in a lime kiln occurs when fine material chaotically swirls at the discharge end of the kiln. This is caused when the velocity of upward moving air through the discharge exceeds the terminal velocity of the material that drops back into the kiln from the product coolers. The reason for material dropping back is that some material remains in the cooler opening and is not transported further into the cooler, as intended. Both the terminal velocity and the tendency to get stuck in the product cooler inlet are connected to the size of the reburned lime. If the lime is powdery fines, dust will be formed in the burner zone. If the lime forms nodules, which is intended, dusting will not occur. A dusting kiln produces a fine particulate reburned lime that is very hard burned and has a low specific surface area. When this lime is slaked, the slaking and causticizing reaction is slower and might lead either to a lower yield of effective alkali or to a slower temperature rise in the slaker, and potential overliming. It is found that when dusting occurs in a kiln, the amount of material inside the kiln increases notably even though the feed rate of lime mud has not increased. Furthermore, during dusting conditions, the reburned lime mud contains a very large fraction of fine material. A possible explanation for the increased load could be that the fine material is present in a large part of the kiln. The fine material is likely subjected to stronger friction than the nodules. This in turn will lead to a slower material transport through the kiln and thus an increased amount of material inside the kiln. Through mill trials, it is found that removing the recirculated material from the electrostatic precipitator for a couple of hours has a positive effect on bringing a dusting kiln back to a clear one.
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- Dernegård, Henric C O, 1981, et al.
(författare)
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VARIABILITY IN LIME-MUD FEED RATE INDUCED IN THE LIME-MUD FILTER: CONSEQUENCES AND ACTIONS
- 2017
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Ingår i: Journal of Science and Technology for Forest Products and Processes. ; 6:3, s. 19-27
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Tidskriftsartikel (refereegranskat)abstract
- This study shows that despite keeping both lime-mud slurry flow and density constant, lime-mud moisture content and feed rate from the filter to the lime kiln can vary significantly. These variations, which were previously not detected in the mill, were revealed after installation of a band scale and a moisture detector. It was found that cleaning the doctor blade caused a periodic disturbance in the lime-mud feed rate to the kiln. The variations in moisture content, however, were too minor to disrupt the stability of a kiln equipped with a flash dryer. This work resulted in a new and better way of continuously estimating available CaO and reburned lime production rate.
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