Drying of materials Part 2.

In the previous installment we gave the basis of the drying process, in that we need to heat the material up, run a dry air stream over it and allow the moisture in the pellet to jump into the air stream passing over it.

So let us start as previously stated with factor “a” Airflow over the pellets.

When researching the airflow for dryers you will find that it states so many cubic feet of air per minute per pound of material processed per hour. Basically the industry standard is considered 1 cubic foot per minute (cfm) per pound of material processed per hour.

Thus if we were processing 20 pounds an hour we would need 20cfm of air flow. If we were processing 100 pounds an hour we would need 100cfm. It is fairly simple and straight forward calculation, and so we now have a relationship between the airflow and pounds of material processed per hour.

Is it okay to run more airflow than pounds per hour process? Yes in this direction there is no issue as you are exceeding the demand and things will work. Is it okay to run less than the necessary air flow? NO… The 1 cfm per pound is some what a minimum, though there are materials and this is material specific that can run less than the 1 cfm rate.

What factors within the drying process effect air flow? Many and yet few if you have a clear understanding of what is going on.
1- Clogged filters, a dryer must be maintained and clogged or non maintained filters within the system tend to be one of the biggest issues I have run into.
a. At the exit from the dryer there should be an air filter that should be checked on a daily basis.
b. If you are running regrind material and notice many fines it may be needed to be checked more often.
2- Materials clogging the air flow at the hopper exit return entrance.
a. The material handler puts in material to the top and it flows down the hose to cause an obstruction to the air flow.
3- Kinked hoses
a. Both the supply and return hoses must be fully opened.
4- Non- sealed hoses
a. Holes in hoses
b. Junction to hose not sealed,
c. Air leaks in supply and return that allow air-flow to escape
5- Non full hoppers
a. The hopper and air flow through it is design based on a full hopper. If the hopper is only 1/3 full air flow will flow through the path of least resistance and you material will not dry.

Thanks for the time; the discussion will continue next month...

TA
Steven L Silvey
Silveys Plastic Consulting
silveysplastics@aol.com
360-882-3183