Reactor pressure control trouble shooting

[rika kose]

The reactor at client is design at 6 barg, 250ºC, volume 10m3. Client wants to produce a new product at 4 barg, 140ºC. PSV of reactor is set at 6 barg. PCV is set at 5 barg.
The reactor is full jacket reactor. heating medium is 6 barg steam.


During the test, 8m3 water is filled and heated to 110ºC. But the pressure is 2.5 barg.
Our explanation is vapor phase and liquid phase are heated separately, because the water level is lower than the jacket height.

Then we come up with the question, how can we control the pressure in the production.
Reactants are dissolved in a acetone like solvent. boiling point of the reactants mixture is around 70ºC.
Filling level is 80%. Reaction starts at 140ºC. exothermic reaction. It mostly like before the liquid is heated to 140ºC, pressure is already over the PCV pressure.

Anyone has some experiences with this kind of situation?

 

[Latexman]

What about the vapor space? What temperature does the water go in? Is the vapor space trapped up to the PCV setting? If so, the pressure of the gases will increase with increased temperature. PV = nRT, right?

Do you need a higher boiling solvent? Diacetone alcohol?

Good Luck,
Latexman

 

[Compositepro]

Do you allow the air that is initially in the vessel to vent out? If not, the pressure in the reactor vessel will be one barg higher than expected from vapor pressure.

 

[TiCl4]

You most likely had non-condensable gases that caused the issue. Total pressure was the sum of partial pressure of the non-condensable gases and the water vapor pressure because each behave as an independent, ideal solution/gas. Total pressure in that system would have been the vapor pressure of the water + vapor pressure of the non-condensables.

In your proposed setup, your PCV will need open up to relieve pressure (i.e. the non-condensables) at the start of the batch when you are heating (I am assuming it is a batch process or CSTR-type reaction where level in the reactor is constant). You will continue to need to relieve pressure until the non-condensables are purged in order to achieve normal operating pressure and temperature that you expect.

You will, of course, need to verify that the reaction mixture actually has a vapor pressure of 4 barg at 140C. Is this based off of VLE calcuation or experimental determination? NIST has the vapor pressure of 140 C acetone at 8.5 barg! You will need to make dead sure your understanding of the VLE is accurate, even with the non-condensable gases removed.

Also, what is the viscosity of the mixture? 6 barg steam is 275 C! If mixing is poor in the vessel, localized hot zones near the heat transfer zones could cause an increase in vapor pressure above what you might expect by measuring the bulk material temperature.