How to Make Rice Coal From Larger Sizes

I bought a Alaska Channing coal stove and a friend of mine has about 5 ton of coal some is rice some is bigger. Does anyone have a easy way of making the bigger coal rice size? The bigger coal burns but not completely. Should I sift my ashes and reburn? Alaska co said that it really does not matter but you will have unburnt coal in you ash pan since it was free I guess I should not worry but I hate to waist . Thanking in advance I love the stove already its a balmy 74 on lowest settings. I am from just south of buffalo n.Y