13 replies to this topic

[Mainak Sarkar]

Why all the reactors are vertical and not Horizontal? Can any body suggest horizontal reactor in the chemical industry? Yes, there is horizontal reactor in cement industry, but that is not very common. So let discuss what are the reasons for which vertical reactor are preferred over horizontal reactors.

[Farzan Bashir]

Hey Mainak,

 

See the thing with vertical reactor is actually that they simulate Plug flow characterstics and hence are more efficient in achieving the higher conversions. One of the example is the Urea Synthesis Reactor in a fertilizer plant which is vertical and have trays in it to simulate plug flow characterstics.

 

and the thing with horizontal reactor is that they are mainly employed when a phase separation is also desired with the reaction.

 

Hope you have got the point.

 

Farzan

[Art Montemayor]

This is a very general, non-specific query.  It implies academic interest in horizontal reactors, but doesn’t specifically identify the reasons nor the incentives for such a physical orientation.  In order to discuss such a topic it is always best to identify specific examples or cases involved.  Beyond the classroom, engineering is fully reliant on practical, safe, and operable design - not merely conceptual.  That is the stuff that separates us from pure science.

 

As far as anyone suggesting horizontal over vertical orientation goes, anybody can do so.  However, in every reactor design and operation I’ve been involved in the past this idea would be quickly cast aside as impractical and ill-advised.  The reasons for this (in the case of continuous flowing reactors - NOT batch) would have been:

• Whenever there is a chemical reaction taking place, a chemical engineer has to take into account changes in composition, temperature, viscosities, densities, as well as physical state.
• It is essential to have a secure means of ensuring that ALL fluid flows in a continuous flow reactor and is kept constant and under control.
• In order to maintain constant flowing conditions, it is essential to avoid any internal bypassing or “dead” spots within the reactor.
• Stratification or segregation of the flowing mass phase(s) has to be prevented in order to ensure homogenous reaction and flows.  Any product gaseous compounds must be allowed to freely flow homogeneously out of the reactor and not elevate to secluded, internal dead flow spots where they can accumulate and hinder the reaction results.
• Fixed bed catalyst must be allowed to fully fill all of the design reaction volume within the reactor.  Additionally, such solid catalyst must be installed in such a manner that it allows for ease of installation as well as removal when needed.
• Vertical oriented reactor beds achieve the above requirements and allow for gravity-controlled flow of all fluids - especially gases - particularly when feed is introduced in the bottom and products exit the top (all in one pass; with no multiple passes within the reactor).

It is very difficult to achieve the above with a horizontal orientation in most type of reactions that I have been involved.  There may be a reaction that is favored by a horizontal orientation, but I've never run across one.  Every reaction should be studied for the best, practical, safe, and operable features when considering it physical orientation.

[Bobby Strain]

But, there are a few special designs that use radial flow in vertical vessels. Catofin dehydrogenation and family processes use horizontal reactors with fixed bed. Both for good reason.

 

Bobby

[PingPong]

Horizontal reactors are also in Claus process and in SCOT process.

Like in Catofin these reactors have flow from top to bottom through a relatively shallow, but wide, catalyst bed to minimise pressure drop.

 

Stratco sulfuric acid alkylation reactor/contactor is also horizontal, as it contains a tube bundle that is easier to pull when horizontal.

 

Shell SMPO process uses horizontal reactors to oxidise ethylbenzene to ethylbenzene hydroperoxide by bubbling air through it.

 

Vertical reactors need less plot space than horizontal. Moreover they are more suitable for mixed phase flow (trickle flow) from top to bottom. Vertical is also more suitable for fluidized bed reactors and ebulated bed reactors.

 

Based on my petroleum and petrochemical experience I would say that, when possible, a reactor is usually designed vertical, unless there is a very good reason to make it horizontal.

[PingPong]

Although Catofin, Claus and SCOT reactors are horizontal vessels, one could argue that these are actually vertical reactors because the flow through their catalyst beds is in vertical direction. If one could ask the fluid molecules and catalyst particles, I am sure they would be under the impression that they were inside a vertical reactor.

[Mainak Sarkar]

Thanks every body for participation in the discussion!! The points all of you discussed are very basic.

 

The query came to my mind from general inquisitiveness. The point all suggested are very basic and vital. But still I find no problem in designing horizontal over vertical reactor in some cases. For example lets say hydro-treating reactor in refining industry, if we change the orientation from vertical to horizontal what will happen? According to me nothing will happen, except for space, i.e. a horizontal reactor will occupy more spacer than a vertical reactor. We all know that a hydro-treating reactor operates in a trickle flow regime, i.e. Gas makes the continuous phase while the liquid is the dispersed phase.  If we operate the reactor in the same flow regime but in horizontal orientation will there be any specific problem?  

[PingPong]

You cannot design a hydrotreating reactor horizontally, as the liquid would separate from the gas and flow over the bottom, bypassing most of the catalyst.

[Mainak Sarkar]

But if it is liquid phase hydro-treating will it be possible to carry reaction in horizontal reactor.

 

Note: Liquid phase hydro-treating is the new concept introduced by Process Dynamics and marketed by DuPont, where hydrogen for the reaction is supplied is soluble form through multiple injection points. The flow regime for the process is liquid phase only.   

 

Please comment!!

[PingPong]

I assume you are referring to the DuPont IsoTherming process, which nevertheless uses a vertical reactor.

 

Licensors tend to exagerrate the benefits of their process.

In this process the reactor is not really isothermal either, although that is what the name of DuPont's process implies.

 

I was never involved in a project using that technology, but I have serious doubt that there is absolutely no free gas in such reactor. Especially if make-up hydrogen is also injected at reactor side nozzles, that gas is not dissolved immediately.

 

If a reactor is guaranteed liquid filled, so under no circumstances vapor is present, one could design such reactor horizontal instead of vertical, but it would not have any advantage.

 

I am getting curious why you seem so determined to advocate use of horizontal reactors.

Edited by PingPong, 01 August 2014 - 03:28 PM.

[Ali_gholamalian]

easily horizontal and vertical reactors can switch to another type. but the reason of "why vertical is common" is so simple, because of simplicity. assume a fix bed reactor, which one do you prefer? fill a vertical reactor with e.g. MS 13X or a horizontal reactor. at the other hand, even in vertical reactors, channeling of flow is so possible by poor distribution on inlet stream; so gas phase come from top and liq from bottom. by this mean, a great distributor needed to prevent channeling, and capacity of catalyst use well.

[Mainak Sarkar]

In hydrotreating reactor both gas and liquid come from the same direction i.e. from the top.

[AVINASH UTTAM WAGH.]

We were using Horizontal Carbonator (reactor)  for the reaction of Calcium hydroxide (Liquid phase)  with Carbon dioxide for the manufacture of Calcium carbonate.

[HABIB092]

Dear friends

 

I think that selection of vertical and horizontal reactors depend upon many theory and practical factors like such.

1. pressure drop : pressure in horizontal reactors are lower than vertical.

2. capacity: horizontal reactor can handle larger capacity than vertical.

3.Plot space: horizontal reactor take larger plot space than vertical.

4. Reaction kinetics: from case to case  which shape is better for higher conversion /yield cannot be ignored .