Hi Friends,
In earlier post, we have already published the systematic approach for Design of Bauxite slurry heat exchangers. In present post, we will discuss the major reasons of scaling in Bauxite slurry discharge pipelines and solutions to avoid such serious operating problems. Generally, Bauxite slurry lines are always observed as metal clean with surface shining like silver in majority of Alumina refineries. But, there are a few Alumina refineries in the World wherein acute scaling problems are faced in the bauxite slurry discharge lines. Now, there are two questions before us to resolve-
(i) What are the probable reasons for this scaling ? and
(ii) What are the practical solutions to avoid such scaling ?
In general, most of the people engaged in Alumina refineries will often say that scaling is a chronic problem in Alumina refineries so we have to do descaling periodically. In addition, further punch from a few people will come who will firmly utter that scaling frequency in Bauxite slurry discharge line occurs due to operational lapses. You may be satisfied with these answers but I am not. The reason being incorrect observations supplemented by pessimistic approach. I will request the readers to analyse my observations outlined below and compare with your own personal observations to arrive at realistic simple solutions.
I have analysed this problem very critically with variations in process and operating conditions. I can firmly mention here that the chances of scaling in Bauxite slurry pipeline is minimal due to operational lapses rather it is mostly due to design defects of discharge pipelines as elaborated below-
Design defect # 1: Over designed capacity of bauxite slurry discharge line causes lower velocity of slurry and thus faster settling of Bauxite slurry particles ultimately causing scaling in pipelines. Such pipelines must be designed as per design norms with adequate slurry velocity.
Design defect # 2: Inadequate slope in the discharge line is the second reason which causes scaling. In such lines, a minimum slope must be provided on the reverse side as per design guidelines for slurry pipelines to ensure complete draining of slurry at the feed end soon after stoppage of grinding circuit for any reason.
Design defect # 3: If the discharge line is provided with any jacketed steam heating arrangement then heating of Bauxite particles results in partial dissolution of alumina, reactive silica and formation of Sodalite complex forming rock hard scales in the inner surface of the pipelines. Thus heating arrangement should never be provided in Bauxite slurry discharge lines.
Trust, the topic has been covered with required details. Please put your views / suggestions / remarks / comments, if any.
Regards.
Kunwar Rajendra
(i) What are the probable reasons for this scaling ? and
(ii) What are the practical solutions to avoid such scaling ?
In general, most of the people engaged in Alumina refineries will often say that scaling is a chronic problem in Alumina refineries so we have to do descaling periodically. In addition, further punch from a few people will come who will firmly utter that scaling frequency in Bauxite slurry discharge line occurs due to operational lapses. You may be satisfied with these answers but I am not. The reason being incorrect observations supplemented by pessimistic approach. I will request the readers to analyse my observations outlined below and compare with your own personal observations to arrive at realistic simple solutions.
I have analysed this problem very critically with variations in process and operating conditions. I can firmly mention here that the chances of scaling in Bauxite slurry pipeline is minimal due to operational lapses rather it is mostly due to design defects of discharge pipelines as elaborated below-
Design defect # 1: Over designed capacity of bauxite slurry discharge line causes lower velocity of slurry and thus faster settling of Bauxite slurry particles ultimately causing scaling in pipelines. Such pipelines must be designed as per design norms with adequate slurry velocity.
Design defect # 2: Inadequate slope in the discharge line is the second reason which causes scaling. In such lines, a minimum slope must be provided on the reverse side as per design guidelines for slurry pipelines to ensure complete draining of slurry at the feed end soon after stoppage of grinding circuit for any reason.
Design defect # 3: If the discharge line is provided with any jacketed steam heating arrangement then heating of Bauxite particles results in partial dissolution of alumina, reactive silica and formation of Sodalite complex forming rock hard scales in the inner surface of the pipelines. Thus heating arrangement should never be provided in Bauxite slurry discharge lines.
Trust, the topic has been covered with required details. Please put your views / suggestions / remarks / comments, if any.
Regards.
Kunwar Rajendra
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