You should try to learn Particle flow, its much more flexible than superspray/snow or any other particle arrays that came before 3dsmax 6.
But about your question, is it emitting some particles, then stopping the emission for about two or three frames, and then starting emitting again?
If so, try the settings of "particle birth/speed", i dont really remember exactly where it is, and i don't have 3dsmax in this machine =)
The smoke material is cool indeed =D. Noise gradient? But i think power plant's smokes are heavier, and next to grey/white, not black as your image show. look this image:
http://www.ens-newswire.com/ens/pics11/coalplant.jpg
Good luck =)