7 replies to this topic

[daraj]

Hi,

 

There is an existing chemical plant with known design. If the plant has to be scaled-up to say 125% or 150% of its current capacity and for want of time, a rough conceptual design has to be made for CAPEX estimation purposes, I wanted to know what are thumb rules, if any, that can be used to scale up equipment quickly, atleast the distillation columns, heat exchangers, pumps, storagetanks,static mixers etc. I know priprietary design equipment and some special equipment have t be rigorously sized. But for these other types of storage vessels and separation equipment are there good thumb rules for scaling up for a given capacity? For storage tanks, for example, I can use linear scale-up for a quick design. That is the volume of tank for new design=125% of volme for current design.

But for something like packed/tray columns, S&T exchangers, statix mixers, compressors, blowers,cyclones, are there any thumb rules? They all cannot be linearly varying.so what is a good approximation to make in such cases?

 

assume the feed rate to each of these equipment has gone up linearly. Any references on this will also be helpful.Not looking for rigorous design, just for a quick scale-up in order to do preliminary cost estimation and such.

[Steve Hall]

The rule of thumb for capacity scale-up is six-tenths rule.

 

Cost_B = Cost_A (Size_{B ^/} Size_A) ^ 0.6

 

The exponent may vary (0.4 to 0.6) depending on complexity. Don't use a linear scale-up factor.

[breizh]

Consider this link :

http://www.sugartech...ation/index.php

 

Breizh

[daraj]

Hi Steve and Breigh, sorry for my late response, but no, the final CAPEX is not what Iam only interested in. I know tat yo can use  apower rule to arrive at that. What Iam more interested in knowing is design scale-up rules of thumb for common processing eqipment to arrive at the final equipment design and thereby a PFD, with minimum rigorous design involved. Like I said vessels or tanks can be sized just linearly with capacity. But are there any rules of thumb or heuristics based quick scale-up methods for the followng?: 

shell&tube heat exchangers

cyclones'

centrifugal pumps

blowers

static mixers

agitated vessels/reactors

packed columns

tray columns

decanters

fixed-bed adsorbers/reactors

 

Thanks

[gegio1960]

The concept behind the pro-rating is that the two plants (ie the reference plant already sized and the new one to be sized) have the same operating conditions. You've available the two Heat & Material Balances.

Based on that, the job is quite simple:

- S&THEs: area prorated on duty

- pumps, blowers: flow prorated, head constant

- columns, adsorbers, reactors: height constant, volume prorated on flow (so D1^2 / D0^2 = Q1 / Q0 ===> D1 = D0 * (Q1 / Q0)^.5 

good luck!

[Padmakar Katre]

Hello,

What is % +/- capex requirement? If it is +/- 30%, cost scale up may help, but if are quoting a commercial bid, get in touch with your technical team (process design) to get the realistic equipment sizes then decide.

[daraj]

Thanks gegio. For a packed column, would you size up just the packng volume based on flow? for example if my tangent to tangent height of current column is say 10m, and my packed bed height is 6m, and I have a 2m diameter.If I want to double the capacity here,i would just double the packed section volume? and while doing so, would I keep the L/D ratio the same? THese are the questions i have.

and for a tray column, how would you deal with this?

 

Padmakar,actually like I mentioned, the emphasis here is not on capital cost, maybe I shouldnt have mentioned it in my first post. That may be will come later on. Accuracy needed there isnt high. But my interest hereis only in a heuristics rule of thumb based scale-up aproach, for a conceptual design. I needed some thumb rules for separation equipment.For storage tanks I generally use linear sizing up. But for others, without the beenfit of a rigorous design exercise or simulation model, if I needed a rough scale-up(but not too far off) I wanted to know an experience-based quick and dirty aproach, thanks

[gegio1960]

daraj,

please kindly and carefully read and understand what I've written above.

You should find the answers to your additional questions.

And, if you want to be proactive, you could submit your prorating work for benefit of other members.

good luck!