Jump to content

  • Log in with Facebook Log In with Google      Sign In   
  • Create Account


ChExpress Blog - 12/17/14

Read the latest news from the chemical industry in Christa's blog.

Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Multiphase Slug Length and Volume Calculator

Precipitation Unit

mixing tank stirred tank

This topic has been archived. This means that you cannot reply to this topic.
3 replies to this topic
Share this topic:

#1 Tamilselvi

Tamilselvi

    Brand New Member

  • Members
  • 2 posts

Posted 02 March 2013 - 06:30 AM

Hi, 

 

I am a final year chemical engineering student and I'm working on a tannery waste water treatment design project.

 

I am supposed to design and size a precipitation unit. The reactants are calcium hydroxide and chromium(III) sulphate ( precipitating chromium out). Can you please advise me if a mixing tank or stirred tank is sufficient for this process. And Right after this unit i have a settling tank to remove the precipitate.

 

Inlet flow : 1,727,741 kg/day

Outlet flow: 1,728,395 kg/day 

Lime added: 654 kg/day 

Inlet temperature: room temp

Outlet temperature: 297 K

Enthalpy : -8,196,232 kJ/day (endothermic)  

 

Please advice me of any books that has info to design this. 

P.S. I have tried Coulson and Richardson and David Hendrick's book on water treatment unit processes.

Thank you!! :)

 

Selvi



#2 kkala

kkala

    Gold Member

  • Banned
  • PipPipPipPipPip
  • 1,939 posts

Posted 02 March 2013 - 09:16 AM

So you actually need the residence time of the mixing tank(s), as I understand. I am not aware of "tannery wastewater treatment". One article probably of some usefulness can be <http://www.academia....GE_OF_POLLUTION>. Total time of chromate precipitation + settling (reaction to Cr(OH)3 slowly continues in settling) is about 3.5 h, but agitation lasts a few minutes (para 2 and Fig 3) (solubility of Cr(OH)3 less than Ca(OH)2, <http://faculty.ncc.e...PY4=&tabid=1903>).

Googling "tannery wastewater chromates treatment", or similar, returns a lot of data, probably containing some more precise info, if looked into.



#3 Tamilselvi

Tamilselvi

    Brand New Member

  • Members
  • 2 posts

Posted 02 March 2013 - 09:55 PM

@kkala, 

 

Thank you for the links. I have found them before. :)But I'm just curious if a mixing tank is sufficient or would I need to design a reactor? 

Thanks again!

 

Selvi 



#4 kkala

kkala

    Gold Member

  • Banned
  • PipPipPipPipPip
  • 1,939 posts

Posted 03 March 2013 - 09:54 AM

"Extrapolating" precipitation unit from alumina plants (alumina crystallization), I  think of a well agitated atmospheric tank, so that its content is almost homogeneous. This is actually a sort of  stirred tank reactor. Residence time (say half an hour) is the critical parameter for tank size. There are not high temperatures during formation of Cr(OH)3. Then settling occurs.

Precipitation and mixing may not be clearly separated in actual industrial practice, see fig 3 of infogate's report <http://www.gate-inte.../w019e_2002.pdf>. However better to show design steps clearly in a new project, equipment "merging" can be considered later.

 

Note: Attached reference may be useful.

 

 

 

 

 

Attached Files






Similar Topics