This is the successor of old Mod Weaponry v0.2.0
Type: Mod
Name: General Improvements
Description: Adds many updates of various stuff, new turrets, equipment, ammo, thermal power station (energy source), Wireless electricity transmitter and more
License: GNU GPLv3
Version: 0.4.1
Release: 10.03 ...

Ever heard of Carbon Filters?
And Coals main component is carbon. So you're basically changing the main filter-part (the carbon) when you recycle air filters. So using coal there is very logical.

Coal is still a main part of recipe of a new filter, using the only one filter seems to me "too cheap ...

I took a look on mod and I'm sorry to say but it's definitely overpowered. I've tried change values to:
-my value (original value)
-0.08 (-0.2)
-0.15 (-0.4)
-0.24 (-0.8)
and still is seems too much. Power usage changed to:
200KW (200KW)
500KW (2MW)
1MW (3MW)
Now I'd set the values (these should ...