removal system 22 includes a first siftings hopper 54 second siftings hopper 56 and third siftings hopper 58 the siftings hoppers 54 56 and 58 are divided by air seal plates 60 62 and 64 into two air sections for each siftings hopper siftings hopper 54 is divided into a first air chamber 66 and second air chamber 68 siftings hopper 56 is divided into a first air chamber 70 and a second air chamber 72 and siftings hopper 58 is divided into a first air chamber 74 and a second air chamber 76 three buffers 61 63 and 65 are attached to the top of seal plates 60 62 and 64 respectively to extend the air chambers 66 68 70 72 74 and 76 upward to the underside of the grate 16 first secondary air duct 44 thereby directs combustion air into the first air chamber 66 of siftings hopper 54 likewise second secondary air duct 46 directs combustion air into the second air chamber 68 of siftings hopper 54 air duct 48 directs combustion into the first air chamber 70 of siftings hopper 56 and air duct 50 directs combustion air into the second chamber 72 of siftings hopper 56 finally air duct 52 directs combustion air into the first air chamber 74 of siftings hopper 58 in this case however the second air chamber 76 of siftings hopper 58 does not have a separate.