2 replies to this topic

[RBS]

Hi All,

My design project requires me to do a full chem eng design for a precipitation growth tank for alumina processing. Alumina Hydrate crystallises and forms in the tanks. Any help/advice on where to start would be helpful, few chem eng books have the design methology

[kkala]

Crystallization kinetics is not known to me, even though I had worked (~1990s) in an alumina project that was eventually cancelled. Unfortunately files have been lost, but some notes below might be useful.
1. Introduction to Bayer Process with few approx process parameters (as applied in above case) can be seen in http://www.cheresources.com/invision/topic/9656-bayer-process. Mentioned precipitation yield seems to be on the high side, yet possible http://www.alcortechnology.com/documents/3.ALUMINAYIELD-TMS2007.pdf, depending on conditions. Residence time of ~70 hr was conservative, and so was seed to product ratio (~6:1). Following data concerned that project.
2. Only two classifiers were used, no hydrocycles (or combination), but all alternatives are possible. Seed to product ratio was ~6 : 1. Filters separated Al2O3.3H2O from spent liquor, evaporated and reused.
3. http://www.cheresources.com/invision/topic/15287-tank-height-vs-soil-load-bearing-capacity/.
http://www.cheresources.com/invision/topic/12134-ammonia-storage-tank (posts 6 and 8).
can give a picture of precipitator (structural) design and dimensions (*). Contrary to fuel tanks, these precipitators are "long" tanks (high L/Dia), so that agitators can effectively keep their Al2O3.3H2O particles in suspension (and probably to save space). All precipitators had identical dimensions.
4. Agitators (of blades at several depths) were of special design to minimise energy spending (suppliers EKATO, Robin, etc). A non classical option at ~1990s was the draft tube, to produce agitation through internal circulation in each precipitator. Now the draft tube seems to have references in alumina precipitators, so it can be applied http://www.lightninmixers.com/industries/mining-minerals/draft-tube-precipitators.
5. Another issue is that sandy alumina is required today, not floury, which affects the design of precipitation - classification. More growth is needed for the crystals to result in coarser alumina. I do not know whether the matter is too complicated for a student project, data seemed to be experimental in ~1990s. For information see http://sourcedb.cas.cn/sourcedb_ipe_cas/zw/lwlb/200909/P020090909612456827645.pdf and http://www.freepatentsonline.com/6296819.html. Alussuisse was probably the first to have developped sandy alumina process in Europe in ~1980s.
(*) Thickness of these atmospheric tanks was high (60 mm?). Weldings between plates needed annealing due to caustic content of liquor.

Edited by kkala, 11 October 2012 - 10:59 AM.

[nabroos]

Dear sir

 

We are a group of students working on the project graduated from the University for the extraction of aluminum  by Bayer process.

Currently faced with difficulty in terms of the process that we use most of the equipment and the lack of information available to us and also we faced difficulty in currency balancing of energy and matter.

 

We hope anyone who has information about this industry to tell us

 

Thank you a lot