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We are well aware that Digesters are the reaction vessels used for dissolution of alumina present in Bauxite in Caustic soda forming Sodium aluminate. Digesters are also known as Autoclaves in Alumina refinery. In present post, we will discuss the basic criteria and methodology used for design of digesters.
Basic Design Criteria: Since digesters are the pressure vessels fabricated with boiler quality steel in workshop by certified welders. The thickness of steel plate used for fabrication is 20 mm minimum. Thus the dimensions of digesters are decided based on the condition of connecting road for its transportation from workshop to project site. Number of digesters is decided based on the volumetric flow rate of digestion liquor and residence time in digestion circuit for designated plant capacity.
Design Calculations: The net volume of each digester has been taken as 200 m3 in arriving at the straight height of cylindrical vessels. Here, we have assumed the diameter of each digester as 4000 mm for sample design calculations. The cone angle of 60o is kept at the bottom for easy discharge of digested slurry. The height of bottom discharge pot has been considered as 1115 mm. Cone end of the vessel has been added with a pipe having nominal diameter of DN900. The gross volume of each digester works out to 226 m3. Detailed sizing calculations are presented below-
The digesters of any volumetric capacity can be designed easily by following above stated procedures.
Please put your views / suggestions / remarks / comments, if any.
If you like this article, then please press your rating as +1 .
Thanks and regards.
Kunwar Rajendra
Dear Sir,
ReplyDeleteCould you explain the procedure to choose feed entry configuration for digesters?
With profound regards,
Ravi Kumar.
Hi Ravi Kumar,
ReplyDeleteYour question is not clear to me. Will you please put your question with clarity in expression so that we can process your reply?
Sorry for inconvenience caused to you.
Regards.
Kunwar Rajendra
Dear Sir,
ReplyDeleteslurry inlet configuration to digesters.
I mean to say ,Feed entry from center of the digester or side entry etc.,
With Profound regards,
Ravi Kumar.
Dear Mr. Ravi Kumar,
ReplyDeleteThe slurry entry is always from the top any where in the dished end portion. To gain on extraction efficiency, top entry agitators are generally provided in Digesters. Thus the entry for liquor and slurry is always from the top side.
Trust, the above clarifies your doubts.
Regards.
Kunwar Rajendra
Dear Sir,
ReplyDeleteCould you explain how the cone end diameter (Dc) and Discharge pot height(Hp)values are selected in above calculations?
With Profound regards,
Ravi Kumar.
Dear Sir,
ReplyDeleteWhat is the preferred range for aspect ratio(H/D) in digester design?
with profound regards,
Ravi Kumar.
Hi Ravi Kumar,
ReplyDeleteYou have put two simple questions in continuation. I appreciate your interest in design of critical process equipment of Alumina refinery. Your 1st question simply reveals that you are not putting efforts while carrying out design calculations. I do not understand, why are you not in position to arrive the desired results just by using the reference formula indicated in the last column.
Now, coming to your 2nd question, there is no fixed H/D ratio for the equipment fabricated in workshop by highly qualified and certified welders. Rather, length and diameter are decided based on the connecting roads from Workshop to Project site as the pressure vessels can not be fabricated at site. This aspect has been described in the write up of the post which you have not bothered to go through sincerely.
While carrying out any assignment, never be casual and always put concerted efforts with positive attitude.
Trust, you will arrive the desired results and will acquire expertise in design calculations with your sincere efforts in future.
Regards.
Kunwar Rajendra