You actually don't need to know the force on the wheel to work on the power.  Just look at the kinetic energy of the powder.  Kinetic energy = $(1/2)mv^2$.  For 0.013 kg of powder, the kinetic energy is $(1/2)(0.013)(104.72)^2=71$ Joules.  You need to provide that much Joules every second, so the power is just 71 Joules/second = 71 Watts.  

Of course, this assumes that the bearings in your wheels are frictionless.  They are not.  It will take some amount of power just to spin the wheels with no powder. This will depend on how good your bearings are.  That's something that you could easily measure if you have the wheels already.  If not, probably just round up to something like 100W and that should be more than enough.