Sand Drying
Sand Drying
(OP)
Client wishes to convert a totating kiln, counterflow grain dryer to a sand dryer. The sand is aproximately 5% moisture, and they want to dry to less than 1% moisture. How do I determine the heat required and the airflow rate required through the dryer.
they wish to dry 90 tonnes/hr.
the dryer is 1.5m in diameter and 8 m long.
Do not know the rpm available.
Do know they have a 18,000,000 btuh oil fired burner.
they wish to dry 90 tonnes/hr.
the dryer is 1.5m in diameter and 8 m long.
Do not know the rpm available.
Do know they have a 18,000,000 btuh oil fired burner.





RE: Sand Drying
Need to know the entering temperature of the wet sand, and the temperature and absolute humidity of the entering air.
What you need to do is raise the vapor pressure of the water in the sand above the vapor pressure of the water in the air at the exit of the drier.
RE: Sand Drying
How do I determine the vapour pressure of the water in the sand?
Thanks for your help.
RE: Sand Drying
This is a bit of a simplification, but essentially evaporation is driven by the difference in vapor pressures. The higher the difference, the faster the evaporation rate. Having air with a relative humidity of 80% makes the job a lot harder, as it just can't hold much more water.
The partial pressure of the water in the air is a function of temperaure and humidity. If you heat the air the absolute humidity (mass of water per mass of air) remains constant, but the relative humidity decreases. Unfortunately the vapor pressure of the water in the air also increases.
Also, the hotter the air, the hotter the sand needs to get to maintain a decent driving differential. Of course the air heats the sand as they pass. Fortunately you can't damage sand by overheating it.
Its really best if you can take some of the water out of the air before it enters the drier.
I hope this at least gets your thinking headed in the right direction.
Of cousrs you could always take the brute force approach. Just heat the sand above 100C. But this is hardly efficient, and not nearly as much fun.
I found these two web sites interesting.
http://van.hep.uiuc.edu/van/qa/section/States_of_Matter_and_Energy/Boiling_Evaporating_and_Condensing/20020321122324.htm
http://www.pdh-odp.co.uk/GasLaws.htm
RE: Sand Drying
you don't have enough residence time and the moc's of most grain driers are incompatible with sand.
RE: Sand Drying