Well, the "clips" specified in that article were measured at between 7 and 16 ohms, so you need at least 1.2 Amps - at 12V.
Judging by the comments, you do not need 18V from two 9V batteries in series. Big question is - just what sort of 9V battery did you have in mind - surely not a little "PP3" - that would be absolutely useless unless you used half a dozen alkaline in parallel. A pack of six alkaline AA cells would probably suffice, but better to use eight for 12V in this case. A 12V "Gel Cell" (lead acid) rated at least 4 AHr would be a better choice overall (and is rechargeable). Or ten NiMh.
And further complications if you plan to use igniters in parallel, though since they fuse, what you can actually do is to fire them in rapid sequence at 200 mS intervals, leaving each switched on for 400 mS.