Hello Bernardo, welcome to the forum
Do a google search for the will burt company. it may be wil-burt . These folks make current bituminous coal under feed coal burning stokers, and they can help.
I contacted them looking for parts for my 'Iron Fireman' underfeed stoker. They were very helpfull
With burning Bituminous, you feed the coal into the retort, where the voltitiles are cooked off and burnt, then the coal burns and forms a clinker that accumulates around the retort. You have to remove the clinkers daily or more often with the burn rates you are talking about. Unlike burning Anthracite, where the ash can fall off the retort into an ash pan, Biturminous will stick together and clinker, and you have to remove the clinkers manually, using clinker tongs, rakes and hoes.
Hope this helps. Greg L