My concern would be that a forge fire with an air blast is goind to be a lot hotter than a normal fire. So, the clay chimenea may be subjected to more thermal stress and possibly crack or simply fall apart. You may be able to minimize the risk by keeping your forging fire smalish and in the center of the grate. Also, the grate has slots all over it to provide a draft to the wood fire. You probably want to block most of these slots except what is feeding the fire in the center. Possibly clay or a circular sheet of metal with a hole in the canter. You have to tear everything down to clean the ashes and clinker out.