6 replies to this topic

[Dev 009]

Dear All, being first time here first of all would like to say Hello & thanks every member in this forum who are sharing there valuable thoughts & experience here. I would also like to share my experience & problems here with all you guys so please bear some pain for me.

Regards

My concern regarding the problem is that I am not able to calculate the required mixing time in a large tanks for which i have designed a Jet mixing nozzles.
I have searched a lot for proper equations for calculation of blending time but couldn't get through.

For eg we are having a 17000m³ tank storing Hydrocarbon liquid (DHDT Unit feed) with a pump of 275m³/hr for homogenization of stored fluid ( density difference of 30m³ has been assumed)

Can any body help me to find out proper correlations.
I have used one correlation stating blend time as

Blending time = ( Fo *rho * Z) / mu

where Fo = Fourier number = k_Z/Re
rho = density of fluid
Z = jet path length = sqrt ( dia²+hight²)
mu = Viscosity of fluid

this gives me a shorter mixing time of around 30 minutes to 1 hr.

Whether I can go ahead with this or not , I am not so confident about .



Any one please help me out. If u require further information just ask I will submit asap.


Regards
Rohit

[ankur2061]

Rohit,

I do have a few guidelines from the company standard of a very reputed chemical company.

For a jet mixer consider a minimum jet nozzle velocity of 9 m/s.

The jet mixing time can be calculated from the following equation:

t_m = 30*V*D_j / q*(Z_l*D_T)^0.5

where,

V = Volume of the liquid to be jet-mixed, m³
D_j = jet nozzle diameter, m
q = flow rate through the jet, m³/s
Z_l = liquid depth in the tank, m
D_T = Inside diameter of tank, m

Hope this helps.

Regards,
Ankur

[Qalander (Chem)]

Dear Rohit,

Further to the above valuable design related info.I will add:

The type of tank (i.e. Floating Roof, Fixed Roof & Fixed Roof with Floating deck/screen) is also critical as sometimes rotations develop in the liquids under mixing and may damage the floating roof or deck in case adequate and strong anti-rotating mechanism is not in-place.

Also, do not forget that this involves <b>eddies generating turbulence phenomena</b> and, as such, the generation of static charges is to be <b>duly taken care off</b>.

Finally, the extent of mixing for large storage storage tank may have to be very carefully/efficiantly designed considering all available incoming steams safe/econmical utilyzation; thus to optimize the <b>Time needed</b>,<b>Mixing affected</b> and <b>Exclusive mixing Needs through special separate higher pressure and/or flowrate pumps</b>.

Hope this helps
Qalander(chem)

[cesaredu]

Hi everbody , I was reading this information about jet mixers, the equation its very usefull but i couldnt find out the reference (books) (papers) , Qalander, please how could i know where is it? or another source about mixing in tanks, its true the information its very poor on the intenet.


If anyone have an information about this,

Thanks a lot

PD: Sorry about my english

[Dev 009]

Dear Ankur Sir,

thanks a lot for sharing such a good information, my doubt is that whether its a empirical equation or a derived equation .

Also having a concern that this doesn't include the density difference factor of fluid to be blended.

With the equation I am getting a reasonable time of mixing of around 4-6 hrs for the various hydrocarbon product ranges.

Regards
Rohit

[Qalander (Chem)]

Dear Rohit,

Sorry for somewhat belated response.Probably you might have already got info from Mr.Ankur

Since this is an information related to another company, you may send your email address and I may give you the specific equation(s) and conceptual info details that might be useful.

Regards
Qalander

[Qalander (Chem)]

Dear Rohit,

Further to today's email to your address and my first reply's <b>possible Static Charges generation / accumulation, if not duly safeguarded through proper bonding/grounding of system components,</b> then possible serious hazardous consequences may result;as depicted in the attached CSB case study. Although (not directly indicating eddies) but <b>turbulence, heterogenous system conditions & not verifiable Bonding/Groundimg conditions are possible contributary factors to create sufficiant energy static discharge in presence of air/ H-C's vapours containing empty space of Tank(s).</b>

All these should be carefully taken care of to avoid similar disastrous possiblities to occur.

Best Regards
Qalander