Cooling coil orientation changes

[Mutt]

Practical experience needed here!
Have small well stirred (multi-bladed impeller) reactor - 2m diameter by about 3 m height - has internal cooling coil on 1.5m pitch - coil has failed and needs to be replaced. To do so means removing reactor from site - mission in itself - and cutting off bottom etc to replace. Coil can be removed on site by cutting out but new coil has to be cut into 1/4 coils and rewelded inside - impossible to do with limited space for back of coil. Proposal is to install pre-assembled packs of vertical tubes to give same or more surface area. The installation is feasible - just -

Now for the question : will having vertical tubes vs coil greatly change the mixing and heat transfer characteristics? Yeah, I know lot of variables to be considered but just hoping somebody might have clue!

 

[25362]

Is the given coil pitch correct or is there a typographical error ? Could 1.5 m be the diameter of the coil ?

 

[Mutt]

Yep - coil is 1.58m diameter, 11.5 turns, 3" ND Sch 80 Stainless steel, 160mm between turns!

Question still the same - do vertical serpentine pipes affect heat transfer / mixing patterns dramatically in well stirred vessel when compared to coil of same surface area?

 

[25362]

Before analyzing whether or not a vertical serpentine can be exploited to enhance turbulence and reduce mixing time, by acting as baffles, one should:

1. Estimate whether the present H/E surface could be supplied by a vertical configuration; I think with difficulty or not at all.

2. Consider whether a vertical serpentine would provide a reasonable HT since the (up and down) hydraulics may interfere. An alternative would be vertical pipes connected to two ring (manifold) headers, as a cage.

Please comment on whether you are cooling or heating the reactor, what is the residence time of the reactants, the reasons for the strong mixing, for example, two immiscible liquid phases, etc., and whether a loop reactor is applicable in this case.

 

[Mutt]

Thanks for response - client has decided to go for removal of reactor and to replace coil - doens't like to mess with the recipe!

Have sat with drawings and is possible to match surface area with double bank of staggered serpentine coils - dificult to explain but possible!

I have checked hydraulics - have increased velocity on cooling medium side slightly, pump has plenty of head - RO to be replaced - loop reactor is possible and done on newer reactor designs but delivery time for specialised new pump (solids present in some recipes) required in excess of 6 weeks.

The strong mixing is really to allow for heat transfer - extremely exothermic reaction - need to maintain uniform temp in product as is temp sensitive.

 

[quark]

I basically don't see any problem with vertical pipes, provided you have the same heat transfer area. The advantage of a coil is to make more space for the agitator.

BTW, most of the reactors of the size you mentioned and above (3m dia. x 5 m height, acidification and salination reactors in dye intermediate plants) have a removable top dish. I did maintenance of the coil and stirrer, at the start of my career, plenty of times withuot having problem by removing the top dish.

Regards,