static mixer

[rika kose]

We got two quotes for a static mixer.
The same dimention,
a, is PTFE coating, 3 elements, 0.25 bar pressure drop
b, is ETFE coating, 0.35 bar pressure drop with 6 elements.

Option b is 5 times more expansive.

IS the ETFE so much more expansive?
based on what we should make the decision?

 

[Latexman]

What is being mixed? More details; better answer.

 

[rika kose]

What is being mixed? More details; better answer.

Two liquids.
liquid 1. viscosity is 100cP flow = 95m3/h, liquid 2 viscosity is 1.4 cP flow flow is around 2 m3/h. solubility of liquid 2 in liquid 1 around 10% wt

 

[shvet]

based on what we should make the decision?

On homogenity of the mix downstream.
The cost of the most expensive static mixer is negligible compared to the risk of potential profit losses. A static mixer isn't a compressor, reactor, or furnace. It's a small, easy-to-manufacture piping element that someone could even make themselves from a sheet of plastic in a carport with a hand tool in about an hour.
How are you going to prove that both of these mixers provide the same level of homogeneity? Why would you score them based on cost alone (assuming that pressure drop results in processing costs)?
Pricing isn't a simple or obvious issue, especially in a science-intensive field like fluid mixing.
I'd guess the first one was designed using CFD modeling, while the second one relied on pilot testing, which is far more expensive.

 

[EdStainless]

More elements with slightly more pressure drop infers that the mixing will be more through.
Do you really want to use a coated one?
Are you injecting liquid 2 through a centerline quill?

 

[Latexman]

shvet and Ed align with my thinking. Option B mixes better. What is the cost of failure? Is a coating really needed, or will SS be okay? IIRC, standard MOC in static mixers is SS.

 

[georgeverghese]

Ask them about flow turndown range - that should also be weighed in for selection criteria. At low flow, mixing will be more difficult.

 

[pierreick]

Hi,
Probably good to read:

https://www.klmtechgroup.com/PDF/EDG-SYS/ENGINEERING-DESIGN-GUIDELINES-static-mixer-Rev2.1web.pdf

Agree with comments above, what is important is the end result (good mixing) at the operating point.

You did not answer the reason why the static mixer is coated. Are your materials corrosive?

note : You may have 2 different types of SM in the offers,
the first being LPD (Low pressure drop), the second being ISG (interfacial surface generator)
https://www.staticmixers.com/models#isg ,
construction wise this will explain the cost difference.
base of design:

https://www.mwa.co.th/wp-content/uploads/2022/12/รายการคำนวณออกแบบระบบกวนเร็วแบบ-Static-Mixer-Noritake.pdf

Static Mixers for Process Industry Applications

Static and motionless - no moving parts inline continuous mixers for food, chemical, petrochemical, wastewater applications

www.staticmixers.com

2nd and third links are similar , except the calligraphy .

Pierre

 

[shvet]

Given 7kPa per 1 element I bet on those are not coated with plastic but made of instead as buckling is not an issue. The perforated plastic ~1/4" sheets squeezed with plastic spools by long studs and inserted in a piping straight run.

Assuming the turndown 1:2 the pressure drop per element is 1.5 kPa. Wondering how can 2nd liquid dispersing be possible at 1.5 kPa? Given the 1st liquid viscosity is 100 times higher than water one how low the LL surface tension should be to provide any dispersing of any degree at 1.5 kPa? Is it physically achievable?

1,5 kPa is the pressure a cup of espresso (total 150g) with bottom diameter 5mm puts on a table desk.

update&offtop
I love @rika kose whose topics have always been being so immense, so impressive. So contrast to the topics nearby: "10 or 11 cfps is preferred?" or "should I pick up globe or gate valve?". No, @rika kose is not like that.

if a liquid then 100 times denser than water
if a mixing then 1:50 and in a pipe
if a dispersing then 1psi of pressure drop
if a fluid than a highly corrosive one and corrosive-immune fluoroplastics
if a price then 6 times difference

That is the scale, the real chem engineering challenges! Not a rat races at the neighbourhood. The brain is emerging from a rut, gears between the ears start turning and squeaking. Awesome. More such please.
But are you sure that @rika kose is a human, not an AI conducting a behavioristic experiment?

 

[dgeesaman]

On homogenity of the mix downstream.
The cost of the most expensive static mixer is negligible compared to the risk of potential profit losses. A static mixer isn't a compressor, reactor, or furnace. It's a small, easy-to-manufacture piping element that someone could even make themselves from a sheet of plastic in a carport with a hand tool in about an hour.
How are you going to prove that both of these mixers provide the same level of homogeneity? Why would you score them based on cost alone (assuming that pressure drop results in processing costs)?
Pricing isn't a simple or obvious issue, especially in a science-intensive field like fluid mixing.
I'd guess the first one was designed using CFD modeling, while the second one relied on pilot testing, which is far more expensive.

I used to design static mixers. Typically 316 or carbon steel pipe section, 4-12" dia. While they are mechanically simple, they are NOT cheap carport fabrications when they are welded to a code. The cost and labor that goes into welding paperwork for just a single small pipe section like this is significant, which is completely negligible in a 500ft run of piping or vessel.

As for the coating options, the first question in my mind is surface prep and application. You can get a blasting or spray nozzle on the first one or two mixing elements easily enough, but when you stack six and weld them in-place, it could be much harder or more manufacturing steps to get to the middle two. Some static mixers have removable elements - so that begs the question if a removable element option will be more practical.

The other question is the coating supplier - the two coating materials may be different vendors who have different costs being passed through. Some coating suppliers are in high demand and their prices quickly go up. Or they heavily discount their key accounts and make their low volume customers eat the difference. I've been on the receiving end of all of that.

 

[EdStainless]

dgee, we used to have to mix a very corrosive chemical into a blend.
We found a source for investment case Ni alloy mixers.
I can't imagine how a coated unit would be effective.

 

[rika kose]

Thanks for all the replies.

Yes, the main stream liquid is corrosive to SS/CS. the old pipe lines are all glass lined.

I agree that cost is negligible compared to better performance. However, how can we determine if the more expensive option performs significantly better than the less expensive one? The more expensive option is even pricier than a centrifugal pump/or a small heat exchanger. There must be a very strong argument to convince the person who is going to pay, right? I didn't receive much detailed information along with their quote.

Shvet, I read your reply three times and tried to figure out it was a compliment or sarcasm, but I didn't succeed.

Anyway, this is an open forum where people share their thoughts or ask questions. It's not about being right or wrong. Some questions might sound stupid to experts, but not everyone is an expert, and not everyone works alongside an expert.

 

[shvet]

However, how can we determine if the more expensive option performs significantly better than the less expensive one?

Testing at a lab or pilot scale.

Your case is unique. You are mixing two immiscible liquids 1:50 and one of them is highly viscous at extremely low energy spent on the interface developing. I guess the result expected from mixing is a chem reaction at liquid-liquid interface which, combined with a mass transfer rate from a droplet center to the perimeter, determines the results of the mixing.

All this is a kind of stuff called know-how and leads to commodities market domination or patents licensing which are million times more costly than the price of a pump or a mixer.

Ask a process designer which elelement of the flowsheet has more impact on the process performance - the mixer or a pump.

 

[dgeesaman]

dgee, we used to have to mix a very corrosive chemical into a blend.
We found a source for investment case Ni alloy mixers.
I can't imagine how a coated unit would be effective.

I agree, we didn't do coated options. 316 S/S, 2205, C-276, etc.

David

 

[shvet]

I ... tried to figure out it was a compliment or sarcasm

This is the prompt you to start with the basics and rely less on the beliefs of unknown people.
This is chemical engineering, which is not rocket science, correct? Many generations of engineers have gone this road before you, correct? Is it wise to ignore their experience? If you have truly been diving so deep into process design/engineering, then it's time to dust off a couple of hefty handbooks and start making bookmarks.
There is no stupid questions in engineering, only unproductive behaviour. Ability and willingness to ask a stupid question is one of the most valuable, as per my personal experience (no sarcasm).
Each challenge you encounter you have been solving by relying on opinions of random people instead of personal skills developing. Nobody wins from such actions: not you, not your clients, not the community, not the pumps&mixers.