To kenvlach - Cont'd 2 1

[bbqnw12]

You know what? Lemme break it down to you as best as I can without giving away too much confidential information. See if I can give you a slightly better picture of what is going on.

Naphtha, the proposed carrier fluid, will be passed to a heat exchanger where it will be heated to about 60°-65°C, 15°-20° higher than the temperature of the eventual site of reaction. This is done to allow for heat loss during the conveyance of the fluid or the slury. This will then be passed on to a jacketed container where the CaO 'meets' it. The slurry is then passed to the pump and is pumped through a pipe (of limited diameter) to the site of reaction.

Here, it encounters some water within which the main process subject is situated, and the CaO should react with the water present to form Ca(OH)2. There will not be a reactor required in this case. This Ca(OH)2 then reacts with the organic acid impurity (which is difficult to disclose without giving away the application) and the heat given off is very useful in another aspect of the process. Contrary to what you said before, taking into account the fact that we will be heating the carrier fluid before its use AND the initial neglect of the heat of neutralisation, there should be a fair bit of 'useful' heat left over. But of this or how much I am uncertain. Also, the use of CaO reflects cost significance - in answer to your question.

Please also note that vaporisation of the water and the organic fluid are not important, particularly at this stage of the study. Due consideration will be awarded them if need be later on.

So what do you reckon about using naphtha? And what suggestions do you have? Hope the above made a bit of sense.

Thanks for all your help. Hope to hear from you soon.


kenvlach (Materials) Jul 31, 2003
More questions.

What acid impurities are you talking about? An unspecified main process?

Preheating the organic liquid will not help in moving the CaO slurry. The liquid may flow easier, but a denser liquid would be better for moving the solid.

“Calculated temperature rise from the CaO + H2O rxn is <300deg.C, on the basis of 1kg CaO : 1kg H2O”

Your calculated temperature rise may be high. The heat absorbed by vaporization of your organic carrier and the excess water will prevent the temperature from rising much above 100oC (depends upon how strongly the 'water of hydration' is held). For equal weights, the overall rxn. is

CaO(s) + 3.11 H2O(l) + organic --> Ca(OH) 2(hydrated) + 2.11 H2O(l) + organic

Available enthalpy is ÄHRxn + ÄHhydration = -15.56 kcal/mol + ? [do you have a value?]

But, for the temperature rise, we have to subtract 2.11 x ÄHvap, H2O and ÄHvap, organic before dividing by Cp(RHS).

Since ÄHvap, H2O ~ 10 kcal/mol, not much useful heat left over.

If you have some other process that contains acid and requires heating, why not just feed the CaO directly into that reactor? Or, feed the CaO into a feedstock stream. Avoids setting up a 2nd reactor for CaO hydration, pumping slurry in, separating off a hot organic (condenser?) and pumping a hot Ca(OH)2 slurry.

P.S. For neutralizing acidity, it only makes sense to bother with CaO or Ca(OH)2 if the material cost is significant. I use NaOH solution since pumpable, faster reacting and small quantities.

 

[kenvlach]

Naptha is more dense and has a lower vapor pressure than an alkane, so better for moving the CaO. I don't really know a lot about naptha, but in the US it is considered a health hazard (has an OSHA exposure limit).

When you get to the point of worrying about vapors, consider fractional condensation.

P.S. Don't start any more threads (unless a new subject). Just continue the existing one.

 

[bbqnw12]

Thanks. Sorry for the whole thread thing. I'm new to this thing, so I'm not good at using it properly yet. I just thought that you probably would not look at the old threads after having answered to them, regardless of the increase in number of replies. Will continue in existing threads in the future.

Erm... about naphtha, I know nothing about OSHA exposure limits. Is that an American thing? I perceive it is the Occupational Safety and Health Administration or something. We don't seem to have limits on naphtha here. But even if we did, I have been advised that we will have it contained, and where it isn't people handling it will be taking appropriate safety measures.

Well, thanks ever so much for all your help. I now know who specifically to disturb with my many problems. Ta for now.