There are better uses for old tires than burning them for energy. TXDOT uses ground up tires mixed with asphalt to pave dangerous curves on roads. It is designed to let rain water soak through it, and not stand on the road surface.
They paved a 2 mile, extremely dangerous section of the road I use every day. Prior to the "new" pavement, there were 5 - 6 deaths on that short stretch of road. Since the repave two years ago, only two accidents and no deaths or injuries.
Tghe problem with that is, it wears out eventually. Then what are you gonna do with it? It can't be recycled.