6 replies to this topic

[K.K.]

Any one has any idea of how to simulate Fluorine Washing Section of Phosphoric Acid Plant. The main problem is that the SiF4 reacts with water to form silicic acid and Silicon hydroxide, and both of these components are not present in Aspen Plus Data bank. Then how to figure this out.
I would highly appreciate any expert opinion.

[Adam_K]

You can create custom chemicals in Aspen, it would require a lot of information but is probably worth it in the end. Otherwise, there are likely basic simulators for the process available on the internet or you couuld try doing it in Excel or similar, really depends on the complexity of the simulation.

[K.K.]

Thanks Adam. You correctly mention the need of defining custom components, but it requires a lot of input of properties. Secondly, the reaction kinetics are not known. I am trying to find on internet but cannot find. Almost stuck.

[Adam_K]

Thanks Adam. You correctly mention the need of defining custom components, but it requires a lot of input of properties. Secondly, the reaction kinetics are not known. I am trying to find on internet but cannot find. Almost stuck.

That's disappointing. If youn can attach information on the process in your next post, I'll have a read through it and give you tips on setting up the calculatioins. Your best bet is to wait until someone who knows about the process and simulations comes and finds your topic, but in the meantime we can keep bumping it to the top of the forum.

Also, what information have you been provided with, and what are you results are you trying to achieve with the simulation?

[Adam_K]

One last question: have you tried using different chemical names/formulae/CAS numbers for the silicic acid and silicon hydroxide? I've sometimes found that HYSYS uses old or uncommon names for chemicals, and the ones you are looking for should be available, as phosphoric acid production is a relatively large industry.

[K.K.]

Thanks Adam for you reply.
I have tried by all means, but now its confirm that both of these components are not present in the component databank of HYSYS/Aspen Plus/ProMax and Pro-II. Looks like its never been simulated before. I tried to define a custom component, but Aspen plus ask for heat of formation and similar properties, which I am unable to find on internet. Even the density of pure Silicic acid is not available, it is available against some solution concentrations of 25% and so. Only the molecular weight is available.

Secondly, if any how we succeeded in defining the components, the second big issue is the reaction kinetics. The practical industrial processes apply huge access water quantities compare to stiocheometery.

Getting no clue.

[kkala]

Having worked in a phosphoric fertilizer plant (1975-81) producing phosphoric acid from African phosphates, I can recall following that might offer some indirect help to the effort of simulation.
1. Phosphoric acid fluoride emissions was treated "easier" that those of phosphoric fertilizers, the latter containing particulates in addition. Spray columns or scrubbers had been installed, using water (soda was expensive). Purge of water was lead to waste water treatment unit.
2. Adsorption kinetics determined the size of treating equipment rather than equilibrium, as we concluded from suppliers and rough industrial measurements. We did not know the kinetics, but suppliers did.
3. According to a supplier, SiF4 was easier to "catch" than HF. A series of measurements in the phosphoric acid plant (autoclave temperature=80 oC max) revealed that most of gaseous F was in the form of HF, not of SiF4, even though silica was in excess in the phosphates used. This obliged supplier to modify equipment to maintain F emission guarantees (900 to 30 mg/l, approx).
4. We had found equilibrium pressures of HF over aqueous solutions in a German magazine (that I can't remember). Kohl & Riesenfeld in "Gas purification" (Gulf, 1974), Chapter "Water as an absorbent" report partial SiF4 and HF pressures over their solutions, but not so detailed.
5. An article on F emissions treatment pointed out that condensation plays an important role in increasing abatement efficiency. And condensation occurs in the off gases of phosphoric acid plants.
6. The theory that efficiency depends on spent energy per unit volume of gases (either as gas or liquid ΔP) has some weight in gaseous fluoride abatement.
7. Problems can be in cases (that simulation is not expected to look into) when: (a)water forms thin dropplets entrained with gases (so increasing F emmision). Scales are formed plugging water circulation (purge decanted slurry, not settled water).
Hopefully the above could give a general useful idea, as well as complexity of the case.