6 replies to this topic

[Jorge_RZ]

Hi,

 

Does anyone know of a process in the industry where a multi-tube catalytic reactor is used for a heterogeneous G-S reaction at low pressure (<5 barg)?

 

I'm working on a project for the partial oxidation of a hydrocarbon. The reaction is highly exothermic and takes place at 380-450 C and around 2 barg.

 

I'm finding it extremely hard to come up with a design for this application. The reasoning behind my design is the following:

 

- Reactors with larger tube diameter are more cost effective than those with small diameter for the same capacity.

- Tube heat transfer area decreases when the tube diameter increases, making more difficult to remove heat of reaction.

- Limit pressure drop of reactor to 0.5 bar because of high cost of compression and recycle.

- High space velocity increases selectivity to desired product (according to experimental data).

 

Basically, I'm trying to find the maximum tube diameter that allows to remove the heat of reaction, and a tube length that will give me a reasonable pressure drop and number of tubes at a given space velocity (I'm assuming 40,000 max). Obviously this two trade-offs are dependent and have an effect on each other, but I wanted to state it like this for matter of simplicity.

 

The only way I can achieve this is at a very low space velocity, that results in a sharp decrease in selectivity to the desired product and increase in selectivity to undesired products (CO2 and CO that result from a total oxidation). 

 

I suspect the biggest issue is the low operating pressure and pressure loss limitation that does not allow me to operate at higher space velocities. This is why I ask if anybody knows of this kind of reactor being used in a similar low pressure application.

 

Maybe a fluidized reactor is a better choice in this scenario? 

 

Looking forward to hear your comments,

 

Thanks,

 

 

[Jorge_RZ]

I'm sorry, in my post there is a omission that may create some misunderstanding for some of you.

 

When I say "I'm assuming 40,000 max" i mean 40,000 tubes, not space velocity, that would be a little too much!

 

Thanks,

[bmsharad]

Oxidation reactors for production of formaldehyde, acetaldehyde by vapor phase oxidation are similar in design, construction & operation & have been around for last 50+ years, you would be able to get literature if you search on the net & the library, and that will enable you to design

[Bobby Strain]

The question seems more academic. Are you really an engineer?

 

Bobby

[bmsharad]

Oxidation of ortho & para xylene respectively, in vapor phase as well toluene to benzaldehyde in vapor phase are similar

All are practiced industrially for last 30-40 years at least.

You have not indicated what is the throuhput capacity, no of tubes depend on that also, 40000 tubes appears a very high number

[Jorge_RZ]

Thanks bmsharad, that fully answers my question. I´ll do some reading. I spent a big deal of time looking for similar applications in the internet, I found some processes, but always at higher pressure. Obviously I was not using the right keywords.  I´ve seen in the literature reactors being built with as many as 45,000-50,000 tubes...but maybe that´s a rare case and not the general rule as you say.

 

Bobby, your answer was not very helpful. Yes, I´m an engineer... a young one though. This was not an academic question, I don´t give much data because my question had nothing to do with the reactor design. Just wanted to know similar applications so I can do my homework and learn from them. The only reason I explained my approach to design the reactor is to comply with this forum´s guidelines of giving some background related to the question being asked. Maybe you should create a forum for guys with 30+ years of experience where guys like me can´t ask "academic" questions.

 

Thanks,

[Bobby Strain]

We always like to help. Often students disguise themselves as professionals. When you supply the most complete information, you will find that you get a lot more help from the old guys. And always be nice.

 

Bobby