design of a digester tank

Hello alienitmeca, you seem to be starting multiple threads on the same subject, which I find confusing...

Should you not be consulting a biological / chemical engineer so as to determine the optimum pressure and temperature for the process under consideration, based on material being digested, type of biological process being used, desired gas production rate, raw material feed rate, sludge removal rate, whether there will internal agitation of the slurry or if straight gravitational top-down flow is to be employed, etc., etc.?

Once you have this information you will be in a much better position to develop a successful design.

CR

Thank you CR for your response, it seems that you have a knowlage on the subject of vertical tanks used for digestion and production of biogaz, it woold be thankful if you were to indicate some threads that can help me or maybe an example related to such topic, actually, all the data that i should have put on my thread are not specified.

Question:

* should these data be handed to me (as a mechanical engineer) by a process engineer or should i try to understand how digester works and design it according to my calculations ?

Digestion is not digestion. Digesters can be very simple (gas tight tank with mixers, overpessure ~5mbar) to very complex (high pressure, fixed bed for bacteria). Understand your process first.

For most digesters I have seen you don't need a chemical engineer to design, but someone with experience in the field. I don't know what you plan to do, so I can't advise you further.

Thank you MartinLe, actually i have been looking for someone with an experienc in the field, i think you'd be the one, could you indicate the standards used for the design of the complex digester type.

In fact, i have been given the data sheet for the design of a vertical tank indicating an overpressure of 5 bar, i couldn't decide which standard to use since API 620 are only for tanks with a maximum overpressure of 15 PSI (2.03 bar).

An exemple of the tank design woold be also very informative



i'm really looking forward to receiving your reply

I'm assuming you're designing an anaerobic digester. Can you answer the following:
- Throughput (lbs/day, GPD) (what flow needs to be handled?)
- Biological Oxygen Demand of the feedstock
- Makeup of feedstock (industrial? Municipal)
- Desired solids retention time (days)

i currently do not have the information since i 'm doing a general design according to potential features but i can give some indications to the question but not precise answers:

-the diameter of the tank is suppose to be 15m, this information may give an idea about the tank size, and the flow to be handled.

-i don't understand the second question.

-Municipal

-30 days approximately


it would be very helpful to indicate the bio-gas release out of the tank.

i am looking forward to receiving your answer

First of all, I never dealt with American standards or high pressure processes. One steel tank was quoted to us as according to DIN/ ÖNORM EN 15282 version 2007-06-01 but this probably wont help you in the US, and it was lower pressure. We mostly use concrete.

We understand correctly that you do the mechanical design of a steel tank and that it's the first time you do this for this process? Do you need to design the tank only, or also equipment (mixer, piping, heating ...)? Do you know what is requested in terms of manholes, portholes? Insulation?

Do you size the tank? Do you define the pressure you require (15psig is still what you aim for?)?

MAybe I'm wrong, but I feel you should straighten out with your collegues who does what (process design, equipment specification, tank design) because maybe that's not totally clear.

Maybe look at one of your competitors that do a lot of digesters:
http://www.glstanks.com/en/index.php

MartinLe, thank you for your respond, yes this is my first attempt to design a tank, actually we are not working in the US, we're working in north africa (Tunisia), digesters seems to be the trend in our country nowadays, and i need to be a pioneer in the subject, that's why im asking so much,

to answer your questions:

- i only need to design the tank (no mixers, no heater), but knowing the overall of the process could only better my work

-as far as the tank size is concerned, i am doing a design for various kind of shapes (dome roof, cone roof) and sizes (exemple:diameter=15m).

- the pressure was only chosen (less than 15 PSIG) so the standard API 620 could be used for the design.

- you were right, i have recently contacted the process engineers and things are going better now.

thank you for your responds and i will keep this thread open in case i need any more help.