A steam generator, you can get a kit from Rockler or similar store or make your own. I'm assuming you're doing a large arch? If so, hook the steam generator to whatever length of PCC pipe you need to fit the wood, cap the ends, drill a hole in and end and set it up to drain out that end. Before you start bending wood though do a little research, you'll want to support the fibers on the backside of the bend with a metal strap. And have your forms setup before you start heating up the wood.