4 replies to this topic

[yclee99]

I'm not sure I am asking a very noob question or not. But I need some help from you guys expecially those have experience with multitube reactor (oxidation) - Tube = process fluid, Shell = cooling water/others

How is the temperature profile (Th = process fluid/hot side fluid temperature, Tc = cold side fluid temperature, Twt = tube wall temperature, Tws = shell wall temperature) look likes?

The reason I'm asking this question is I would like to know these temperature profiles to help me do the simulation.

Thank you

[Pacsal]

I'm not sure I am asking a very noob question or not. But I need some help from you guys expecially those have experience with multitube reactor (oxidation) - Tube = process fluid, Shell = cooling water/others

How is the temperature profile (Th = process fluid/hot side fluid temperature, Tc = cold side fluid temperature, Twt = tube wall temperature, Tws = shell wall temperature) look likes?

The reason I'm asking this question is I would like to know these temperature profiles to help me do the simulation.

Thank you

Hi there,

My experiance comes from partial oxidation of Methanol to Formaldehyde over a "mixed oxide" catalist tube reactor.

The way the reactor is filled up is 4-5 different levels of catalist. When MeOH is fed from top, then it first comes in contact just inert to increase the temp to adequate level then with low concentration catalist (only 20-25% of its total strength) then with the layer of 50% and so on.
The reason for that is to keep the reaction happening in a constant margin of temperature not being too low (so reaction speed will be low) not too high (to damage the catalist).
In the reactor I have in mind, in 4 tubes (out of 200-300 tubes), there were 10 temperature indicators installed in each one of them to be able to observe the profile temp.
Overall, the temp was increasing suddenly right after the inert part and then almost linearly decrease as the fluid was heading towards the end/bottom of the reactor but always within the recomended temp window.

If in your design, there is no catalyst or one of your products is a catalist of the reaction, then consider:
1. Introdusing reactants in various positions of the reactor
2. Separate the cooling side in various cooling fluid flow rates for better temperature control
3. Having reactors in series (expensive).

I hope I have helped.
Pascal

[KIENG]

I'm not sure I am asking a very noob question or not. But I need some help from you guys expecially those have experience with multitube reactor (oxidation) - Tube = process fluid, Shell = cooling water/others

How is the temperature profile (Th = process fluid/hot side fluid temperature, Tc = cold side fluid temperature, Twt = tube wall temperature, Tws = shell wall temperature) look likes?

The reason I'm asking this question is I would like to know these temperature profiles to help me do the simulation.

Thank you

Hi vclee99,

I worked with tubular Phthalic Anhydride reactors for many years. The reactors are cooled by circulating heat transfer salt on the shell side and air + feed stock on the tube side. The reactors have vertical tubes filled with ceramic pellets impregnated with the catalyst. Air + feed stock flow is down through the tubes. The tubes in the older reactors are 3200 mm long, newer reactors have longer tubes.

The air flow for a PAA reactor is typically 3.5 to 4 normal cubic meters per tube. The feed stock concentration is typically between 40 and 80 grams per normal cubic meter. Higher loadings are possible in new reactors. The feed stock is naphthalene or orthoxylene.

The tube temperature is measured with multipoint thermocouples. The top of tube temperature is the same as the air+feed stock coming into the reactor. The top part of the catalyst bed heats the reactants. Once the temperature is high enough to start the oxidation process the temperature continues to rise to the maximum temperature. The peek of the maximum temperature is controlled by regulating the salt bath temperature. After the peek temperature, the temperature slowley drops through the remainder of the bed. The bottom of the tube temperature approximates the salt bath temperature. Inlet temperature is approximately 180 C, peek temperature is about 480 C and the outlet temperature is about 360 C.

The salt bath temperature changes very little. The salt flow is from bottom to top with a change in temperature of about 1 deg. C. This temperature rise is small because the salt has a very high specific heat, is very dense and its circulation rate. The salt bath is cooled by generating steam. The salt bath temperature is typically 350 C to 380 C.

Hope this helps.

[Andrei]

yclee99,

Your question is not noob at all, it is just incomplete.
The temperature profile is very specific to each type of reaction, reactor configuration and heat transfer medium. A nuclear reactor is also a tubular reactor. What system do you want to study?

Hi

Anyone knows how the the catalyst in the tube is hold or supported? Is there any screen at the bottom of the tube plate?