How a person burns depends on their body fat and whether or not they were embalmed.
Still, regardless of all the other arguments, it would be possible to do in a quiet way. As, at the end of the day, all crematoriums do is create heat all day long, surely someone could come up with a way of harnessing that heat, creating steam and running turbines and all that jazz, just a modification of the present building?

I'm not comfortable with rounding up dead folk and dumping them at a big power station, but those that are going to be burned anyway could be done more efficiently.