I've drafted my own provisionals for years and it didn't pose a problem -- but I'm also a lawyer. Self-drafted provisionals often create problems by accidentally hitting a third rail of patent law, like saying "In one obvious application of this invention...." or "while people have done this using pencil and paper, this invention automates it...."
As for the patentability question, you need to check with your lawyer, as a high level and vague description like you posted may well miss a point of patentability. You should be aware that there are two ways that prior art can be a problem: Obviousness and novelty.
Obviousness asks "knowing what people skilled in the art knew at the time of invention, would it have been obvious to combine other stuff that is well known to create the invention"? If the new use of a known process wouldn't be obvious, you don't have an obviousness problem.
Novelty asks "has this thing existed or been done before"? Normally, something that not novel is also obvious, but there are exceptions -- and this may be one. For example, I can't patent a jet engine that already exists just because I propose we attach it to a boat instead of a jet. Or using a real world example, Amazon's "one click" patent covers keeping somebody logged in and then buying and shipping it based on a single click. If I proposed using the same invention in a car's console to order gas while parked at a gas station, the one click portion would not be novel even though it might not be an obvious use of the one-click invention. Of course, actually implementing it in a gas station might create new twists that are novel and non-obvious, such as where you also determine fuel level and capacity and trigger an automated pump to open the gas cap, extend a fuel line to the car, and fill the car. But the baseline "this already exists, but look, I'm using it in an unexpected way" would normally present a novelty problem (although with processes the new way you use it may be part of the process, so that may get around the novelty issue).