7 replies to this topic

[knapee]

Dear Sir/Madam

I have a polyester acrylate plant design project, and found the vertical type condenser installed on the top of the reactor(required to recycle the solvent ).
But, I don’t quite understand the reason why the vertical instead horizontal condenser to be installed. In spite of saving the limitation of space, is any idea for this kind of vertical type condenser to be chosen here ?

And, it seems that the solvent won’t boil out from the reactor cause the feed ,acrylic acid bp=141C is greater than water bp.= 100C, biphenol epoxy, bp=unspecified here.
So, could any pro here can kindly tell me why this condenser to be installed here to recycle the acrylic acid back ?


Thank you very much for your time and help.

Regards,

Attached Files

•  Quick Start v - page 27 - 20120219_194620.pdf   101.2KB   102 downloads

[amirentezari.k]

heat transfer coefficient of vertical condenser is bigger than horizontale type

[Art Montemayor]

Knapee:

Thank you for the submitted sketch. It tells all I would ask for in the query with the exception of a scope of work.

What you depict is what is known as a “knockback” condenser. This type of equipment is very specialized in its application and when the total condensation and return of a volatile overhead product is required (as in a batch reactor where one of the reactants is volatilized and carried off in the overheads product) it is almost always the condenser of choice.

I don’t quite understand your statement that you have a polyester acrylate plant design project. Since this is the Industrial Professional Forum, I have to assume that you are not a student and that this “project” is a real-life assignment.

Additionally, I don’t understand that you “found the vertical type condenser installed on the top of the reactor”. What do you mean to say? Have you been given an EXISTING batch reactor unit that produces polyester acrylate? Or are you designing a NEW unit and have been told to employ a vertical condenser? Which is it that you are trying to say?

If the reactor already exists, it may be that it is what is available and you have to use it as-is. I really don’t know because you haven’t told us your scope of work. I have worked on and operated a lot of reactors – some setup just as you sketched yours. And although I didn’t require a vertical unit, I still used the same setup because it didn’t make a difference to the production product. But I don’t know your situation.

I don’t know the reaction kinetics of the acrylic reactor, but I note that you are adding water (and also recycling it). One guess is that the knockback condenser is for the vaporized water. But I’m guessing. Since you are the designer of record, what do you need to make the reaction work? That is a much smarter and more efficient manner of analyzing the requirements for the process.

[knapee]

Dear Mr. Montemayor

Thank you very much for your professional and helpful response. The design project is real-life assignment, but the scale may be quite small and it is brand new.

Besides that, I also found other similar post “Horizontal Partial Condenser Design” in this forum, and it really helpful. Since this vertical condenser will be sized by vender, we don’t have to do much basic design work for this exchanger. My concern is that we may have to find the bubble point for this mixture by simulation software (biphenol epoxy, toluene, acrylic acid and water), but we don’t know the relative percentage of this mixture since client don’t know this. So, we may find the lowest boiling point of component in this mixture to decide which component will be stay in the reactor or boil out. Please give me any professional comment if you think it is not trivial.

Thank you very much.

Regards,

[Dazzler]

Hi Knapee
I think the vertical arrangement will give lower pressure drop for a given exchanger (and nozzle sizes) and this means more of the free water and solvents can be removed at the end of batch and at lower final batch temperature (product may be temperature sensitive?).

I have also observed similar setups in the past with 2 condensers. Polyester resin and Phenolic resin reactors. The lower vertical condenser is a partial condenser, the top condenser sloped angle condenser so liquid drains towards knockout put.

The arrangement in your sketch is odd because having a top outlet pipe on the only condenser it seems that the boiled out solvent or water is to mostly pass through the knockout pot then to vent somewhere (perhaps an incinerator). Not much solvent liquid will condense and collect in the pot and minimal will flow back to the reactor via the u-leg as an additional coolant.

I don't know your particular reaction, but some polymerisations are done with a solvent to help control exotherm (so no reaction runaway) and to keep the reaction mix temperature down so slower more controlled reaction rate and lower reactor pressure.

If liquid water/solvent/distillate recycle to the reactor is important through the reaction stage then I suspect the sketch is not drawn correctly. There should be a liquid line from somewhere lower on the condenser as well as a vapour line, or there is another total condenser at the very top that has not been noticed.

Dazzler

Edited by Dazzler, 25 February 2012 - 05:24 AM.

[knapee]

Dear Dazzler

Thank you very much for your comment.

Hi Knapee I think the vertical arrangement will give lower pressure drop for a given exchanger (and nozzle sizes) and this means more of the free water and solvents can be removed at the end of batch and at lower final batch temperature (product may be temperature sensitive?).

I don't quite get that the vertical type exchanger will give lower delta P. It seems very trivial, but I would like to ask you explain a little more, please. And, the feed composition of acrylic acid, cyclohexane(not shown in the attached graph), water, and Biphenol epoxy. are already known, and the cyclohexane, water will be boil out after feed went through precondenser. So, I conclude there is 3 phase (gas, oil/liquid, and water) at equilibrium state in the precondenser.
The degree of freedom = composition no. - phase no. + 2 = 4 - 3 + 2 = 3, and the feed compositions of acrylic acid, cyclohexane, water, and Biphenol epoxy are already known.

Therefore, the degree freedom = 4 -3 = 1, and is this means once the delta pressure is fixed, the outlet temperature will be fixed. If we can get the outlet temperature of precondenser lower, is that means more of the free water and solvents could be removed ?

I have also observed similar setups in the past with 2 condensers. Polyester resin and Phenolic resin reactors. The lower vertical condenser is a partial condenser, the top condenser sloped angle condenser so liquid drains towards knockout put.

It is odd to me that we call the vertical condenser as partial condenser instead of calling horizontal one as partial condenser. Cause the solvent will be boiled out in the first condenser(vertical one), and then the partial condenser(horizontal one) can take care of the remaining solvent, so logically the vertical one be called as condenser is much reasonalbe for me.

The arrangement in your sketch is odd because having a top outlet pipe on the only condenser it seems that the boiled out solvent or water is to mostly pass through the knockout pot then to vent somewhere (perhaps an incinerator). Not much solvent liquid will condense and collect in the pot and minimal will flow back to the reactor via the u-leg as an additional coolant.

There is short pipe connected from the superstar to the U-leg (Please see attached drawing.). But, I am not sure it is that you mentioned " a liquid line from somewhere lower on the condenser as well as a vapour line"?

I don't know your particular reaction, but some polymerisations are done with a solvent to help control exotherm (so no reaction runaway) and to keep the reaction mix temperature down so slower more controlled reaction rate and lower reactor pressure. If liquid water/solvent/distillate recycle to the reactor is important through the reaction stage then I suspect the sketch is not drawn correctly. There should be a liquid line from somewhere lower on the condenser as well as a vapour line, or there is another total condenser at the very top that has not been noticed.
Dazzler

I also don't know what exactly reaction is. This is a typically polyester-acrylate reaction, and we only get little information form our client.
The simple reaction is bellow :
Epoxy + acrylic acid + inhibitors + catalyst + pure air and heated to 90 C -> cool down and add some diluted monomer ->epoxy acrylates


Please correct me if I make any wrong statement.

Thank you very much.

Good day

Best Regards,

Attached Files

•  Quick Start v - page 27 - 20120227_231542.pdf   113.96KB   44 downloads

Edited by knapee, 27 February 2012 - 11:06 AM.

[Dazzler]

I see a second condenser has now appeared in the top of the sketch (sketch 2). That is what I was expecting. Now that this is here, there is no need for a liquid line fromt helower or partial condenser.

It is called a partial condenser becasue some components in the vapour are condensed and some are not. Those that are not condensed continue on to the final or total condenser.

The top condenser then condenses as much as possible, so only the "non-condensibles" get lost to the vent.

Sometimes in the partial condenser there is a section with some trays in order to improve separation, a little like stages in a distillation column.

By pressure drop in the vertical condenser being lower, I mean nozzle pressure drop, due to less sudden changes in flow direction compared to what would happen for a horizontal condenser. Yes only small dp. Remember any pressure drop in the "overhead" system will put a back pressure on the boiling surface in the reactor and raise the boiling point slightly.

Dazzler

[knapee]

Dear Sir

In the design of acrylic acid total condenser (horizontal) for the epoxy acrylate reactor, Acrylic acid (10%) and air (80%) in the tube side was cooled from 80 C
@0.5 kg/cm2g to 50 C@ 0.2 kg/cm2g by using cooling water (shell side
inlet = 30C@ 3kg/cm2g, and outlet = 40C @ 2.3kg/cm2g).

Cooling water which is usually more prone to fouling flow in the shell side, and
Acrylic acid vapor and gas (almost N2) flow in the tube side.

My question is following:

• Are the vertical or horizontal cut and the vent nozzle properly situated in HTRI critical for the result of HTRI or not? (There is already a vent line to waste gas flare in this total condenser, and indeed properly situated vent can prevent accumulation of non-condensable )

Also, the baffles are cut vertically for side to side flow (parallel-cut baffle); it will facilitate drainage of the condensate. However, the parallel-cut baffles have the potential for significant flow and temperature misdistribution in the end zones, which can induce local tube vibration and reduce the effective heat transfer rate in the inlet and outlet baffle spaces.

• Is TEMA type(BEM), and single segmental baffle proper for this case or not ? Single segmental baffle is operated well in single phase (if 2 phase case, which one is proper ?), and cross flow heat transfer (across the tube) is greater than

the longitudinal heat transfer ( through the windows). However, it may not be

effective with very viscous fluids. ( Is that means not proper condenser in the polymer plant ?)

Above is my silly question, and hope not bother you too much time.

Please kindly give me any comment or guide in this case.

Thank you so much.

Best regards,