June 03, 2011

Process Intensification - 4, Loop Reactor

Process Intensification has been our focus since last few posts and I have already covered two most common and most discussed equipments under this topic. Static mixer - which are already in use by the industry and Micro Reactors which are still waiting for good response from industry.

Similarly the third one which is specifically used in few of the industries is Jet Loop reactors which also qualifies to PI category - One particular configuration developed by BUSS Chem Tech



So we are going to discuss loop reactors with different variations in the configuration e.g. simple circulation loop reactors, venturi reactors etc. & then finally Jet reactors which are derived from above systems.

Now let us start from the beginning on these reactors. In the beginning only CSTR were there & at that time need was felt of increasing the mass transfer as well as heat transfer but the invention of putting a circulation loop with one heat exchanger was only based on the objective of increase in heat transfer area so as to reduce the batch cycle time & this is how the concepts of various loops came into picture.

CSTR

The above CSTR configurations were developed around 1930s.

Simple Loop Reactor
So simple configuration was similar to the following diagram for a general circulation reactor. They were developed around 1950s.


Now as you see, the exchanger in the loop is for providing faster heat transfer outside the reactor due to limitation of heat transfer area in the given volume of CSTR type vessel. So basically it was due to very low surface area to volume ratio of CSTR (As shown in Micro Reactors article).

Another version was developed with static mixer in the upstream of exchanger for very quick reactions to remove the heat as soon as reactants react. They were developed around 1960s.



Loop With Spray at Top
The next generation of loop reactors was with spray type nozzle at the top as shown in the picture. In fact, they are designed for enhanced GAS LIQUID interaction by providing a top spray in the gas zone.




Loop Reactor with Venturi
Further improvements in the loop reactors were done by introducing a venturi in the system. This was slightly different than first picture of this post. The difference was in the discharge zone of venturi, the discharge in this type of reactor was at the inlet of reactor - no mixing in liquid zone as shown in the picture. This was mainly developed to enhance the circulation of gas from the top headspace of the reactor to minimize the safety issues with hazardous & explosive gases.

Jet Loop Reactor
The Next generation loop reactors are Jet Loop reactors as shown in the first picture from BUSS reactor. The difference here is that the Jet mixes with liquid with a very high speed & therefore the reaction speed goes very high in the mixing zone of the Ejector. For example, the reaction rate can be increased by a factor of say 25 - 40 times in a jet reactor compared to CSTR.

So if you think you need higher capacity from your existing system of CSTR etc. OR if you are planning to design a reactor for slow gas liquid reactions then think on considering a loop reactor with circulation exchanger for faster heat transfer + plan for either a SM in the piping or plan for a eductor at the bottom of reactor which will thoroughly agitate your liquid mass.

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