T&T: air duct filter

[ed]

My engine space never had a blower to evacuate heat. I just installed one. 
The intake for this exhaust system is near the alternator. I do get some 
belt dust from the alternator. I'd like to keep that belt dust out of the 
blower.
So I'm looking for a simple filter at the mouth of the intake that can be 
easily cleaned and not interfere too much with air flow. The duct is 3" 
aluminum.

Ed K