Optimal Steam Pressure for Jacket

[BenjaminM]

I am trying to decide how to go about determining the optimal steam pressure for a reactor jacket. For the sake of argument, I'll just say we're heating water.

The jacket is rated for 150 psig, and we have somewhere around 145 psig steam available. Historically we'd stick a 50 psi regulator in line and move on with life. But I'm trying to decide why? Are there savings to be had running at a higher (or lower) pressure.

Obviously higher pressure = hotter.

Lower pressure = more btu / pound of steam.

No regulator = one less thing to break.

No regulator = additional hazard if something else breaks.

Time = probably the most important.

Utilization rate probably factors in. Are we running 10% uptime or 95% uptime?

I'm guessing lower pressure is cheaper.

Is it a problem worth solving? I'm thinking so.

 

[georgeverghese]

If the skin temp on the reactor side of the jacket is too hot, you may have thermal decomposition of the reactor fluid. If this concern is valid for your application, adjust the steam temp to be below what corresponds to this limiting skin temp. Calculation of this skin temp may be complicated by things like agitator speed or if it is a batch type heating application or if the reactor fluid viscosity and / or specific heat capacity changes as it heats up.

 

[pierreick]

Hi,
Pay attention to the properties of the fluid, is it thermal sensitive with risk of decomposition and built up on the wall of the reactor?
To me this is not the way to approach the problem, lab scale, pilot test to be performed to define all the parameters.
My 2 cents.
Pierre

 

[seuenergy]

Hi,
This one is big MOC.
For process, you need to evaluate the risk of higher temperature. For example, decomposition, reaction tiem .eg.
For equipment, you need to evaluate the risk of reactor, related pipelines...

I think higher temperature would improve yield by reducing batch time, but before you get the advantages, the risk must be evaluated.

 

[MintJulep]

Optimized for what?

Lowest fuel cost? Lowest lifecycle input cost? Maximum profit? Process throughput? Product quality? Something else?

 

[BenjaminM]

Thanks all.

This is a new installation in an old factory. The vessel isn't going to be dedicated to one single product, we may run a variety of chemistries in it.

George, Pierre, Seuenergy, thank you all three. You all hit on the same point about problems with over heating the product and thermal decomposition. This point is not lost on me. For the question though I stated "For the sake of argument, I'll just say we're heating water". I am sorry for not making that clearer that I was looking past (for the time being) any possible problems from thermal decomposition.

MintJulep, you're closer inline to what I am asking. To your questions, the answer is Yes.

If I had to pick one I would say what is the lowest fuel cost is what I am working towards.

 

[LittleInch]

Then I think if your heat demand can stand it the lower the pressure / temperature the better as then your condensate doesn't flash off quite as much flash steam?

There are multiple inputs into this such as area of the jacket, heat losses, energy amount going into the water, how do you deal with flash steam and condensate - where does that energy go?

Any fixed steam pressure is going to be good / efficient / required in some conditions and not in others.

 

[georgeverghese]

Its probably safest to use the lowest operating steam pressure that will enable gentle heating with less risk of thermal decomposition on the inside heating surface, and that will keep batch heating time just about acceptable.
Steam pressure at the jacket will also influence the safety relief capacity of the heating vessel, for the case when temp control goes awry and temp safety controls also fail to act. The hotter you run the steam, the higher the relief capacity will be. So you dont want to exceed the installed relief capacity on this vessel. Q = U. A. MTD