Energy Reclamation from HT Furnaces for Industrial ventilation

I've been given a bit of a problem... 960,000 sq. ft. building (almost 30 mill cu. ft.) of manufacturing. Inside, about 10 heat treat lines, 4 Endothermic gas generators, Lots of heat, to say the least. The real problem... right now, we've got about 1/2 to 3/4 air changes per hour on the supply side and the building is approximately 1 mill cfm negative, with some CO Problems developing in the winter, once the 'summer' ventilation supply air is shut down. What kind of luck has the collective had with the use of 'run-around' systems to supply heat to ventilation units? Heat Wheels are out of consideration due to the amount of dirt and dust.

thanks!

Twangy