The electrical stuff is beyond my ken, but one of the easiest ways to moderate the blast from an electric blower is to use some mechanism that limits the flow of air from the blower to the tuyere. The simplest way to do this is to leave the blower and the tuyere unconnected, but with the blower pointed towards the tuyere's intake; by changing their alignment and the gap between the two, you change the amount of air that can make it in.
Another option is to put some kind of valve that blocks the airflow, spills out the extra air, or both. One of our members used a conduit fitting with an adjustable cover to allow the extra air to escape, and I myself built a gate valve out of scrap lumber that worked really well.
Depending on the motor type, you can also regulate the blast by putting an adjustable cover on the air intake. Motors that rely on airflow to keep cool are not good candidates for this option.