It will run on a mix of Rice and Buckwheat. But Pea coal is way to big to go through the stoker mechanism... I can't imagine anyone mixing rice and pea..
Can you post a photo of a sample of the coal?? Pea coal is a big as a golf ball, Buckwheat is supposed to be no bigger than 9/16" so about like a martini olive. Put a golfball or a nickel and a quarter in the photo for size comparrison.