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dear friend..
i would like to know how spray drying method could use to produce gum arabic.. i'm also intersted to know the process flow diagram for this method

dear friend..
i would like to know how spray drying method could use to produce gum arabic.. i'm also intersted to know the process flow diagram for this method

Hi

I recently did an assignment on spray drying. Your best bet is to get a hold of a text book called Spray Drying by K. Masters. This text covers pretty much everything you'll ever need to know about the subject. All the academic papers refer to it and even the manufacturers recommend the book, so make it your first point of call. I wouldn't know anything about the P&ID's Im still a student and we are only covering those in two weeks time, however all the comments on this site seem to say you won't find any useful P&ID's for the process or any other process, just representatvie ones giving the overall summary.

Spray drying is basically the transformation of a slurry/solution to dried product by spraying the solution into a heated medium where upon the solvent evaporates and solid particles are formed.

A number of configurations are possible with respect to atomizer, flow of the heated medium.

The solution is atomised by a forcing the slurry through the spraying nozzle. The atomizer used depends mainly upon the characteristics of the solution being sprayed. There are two main categories two fluid and single fuid nozzles. Single fluid atomizers the spining wheels, pressurized nozzles (often relying on giving the fluid a lot of angular momentum prior to spray formation) and to a lesser extent pizo electric atomisers (I've only seen one reference to using these though). For two fluid atomisers the spray is made by pumping a gas at high velocity over the feed point of the slurry, this entrains the slurry into the gas flow and atomizes it at the same time.

With regards to the heated medium. this can flow co-current or counter current to the spray. In the former case the formed particles are exposed to much milder heating conditions then in the latter. So it is more suitable to temperature sensitive materials like milk and coffee. The explanation is that in co-current flow the wet particle is exposed to the hot inlet gas temperature, the solvent evaporates and cools the warm gas around the particle so when the particle is dry it is exposed to the cooled heating medium. In the other case the particle flies towards the heating medium inlet so when it is dry it is exposed to far hotter air and can be damaged if it is heat sensitive. There is also a mixed flow configuration which has the particle move both with and against the heated medium. I've also heard of the heated medium being cold enough so that the solvent freezes instead of evaporates the frozen powder was then removed and dried by freeze drying, this was for some drug application if i remember correctly.

Particles typically undergo two phases of drying in the first case the particle is very wet and the solvent can flow freely to the surface of the particle, the evaporation rate at this point is relatively constant, however it should slow down as the amount of solvent is reduced due to boiling point elevation effects. In the second phase one could imagine the solids in the particle forming 'continents' on the surface of the particle as the surface becomes completely covered in these 'continents' the solvent now has to diffuse through this upper layer to evaporate. If diffusion is fast enough the surface remains damp and evaporation occurs quickly enough so as not to heat up the particle. It is common for particles to shrink in such cases similar to a soccer ball going flat. In the other case evaporation occurs faster then diffusion, the particle's surface becomes dry and heats up and any solvent that is in it's interior evapourates and expand within the particle causing it to puff up and even explode like a balloon would.

With regards to gum arabic there are two kinds they sell at my local arts store one is granular while the other is plate like flakes. The granular form has been sprayed dried and it appears the solvent they used could easily diffuse through the gum arabic, this is seen from the way in which the particles all have a deflated soccer ball look to them. I also know the plate like gum arabic is easier to re-dissolve in water as it has a larger surface area then the granular form and may be more preferred by artists so if your planning on making the stuff do some market research before installing a Spray drier. Hope this helps. Please forgive any typos i'm writing a test in the morning and don't currently have the time to spell check, sorry.

Oh yeah spray drying is used in a number of fields including medicine, coffee, milk, plastics, soap and detergents and ceramics, you shouldn't have any trouble finding more info. Definitely check k. masters' book though. He also gives a number of case studies where the process has been used. I can't remember the name of the company who produced the gum arabic I used in the project i was doing. I know gum arabic has been used in paints and a bit of pyrotech as a binder but this was back in the sixties, you'd probably know this though if you'd googled it. Also it doesn't easily dissolve in water (which could be a nice way of making fiine powder gum arabic) but is prob better in i think some one said MEK (Methyl ether ketone, beware this is hazardous stuff apparently you'll need safety stuff, check msds's) or was it acetone, google is your friend she'll tell you. Oh yeah, I do not assume any responsibility for something that you might do with the solvents, I have listed, that may prove hazardous to your health. If your an idiot it is not my problem.