NOVELTY - In a biomass combustion system, for converting biomass to energy and useful products, a combustion method (m1) comprises feeding the biomass into a combustion chamber through an airlock and supplying oxygen and nitrogen-free diluent to the biomass, to control the combustion process in the combustion chamber.    USE - For converting solid biomass material to usable heat energy and related byproducts (claimed).    ADVANTAGE - The new system is a zero emission solid fuel fed combustion system, and improved gasifier system. The new method: (i) has controlled oxygen quantity, which minimizes the heat loss of the process and also minimizes the amount of carbon monoxide and volatile organic carbons that are produced; (ii) utilizes high temperature, which eliminates formation of nitrogen oxide; and (iii) minimizes the amount of air supplied to the process, thus the amount of energy required to move gas in the combustor and ancillary is also minimized. The new method provides electrical energy costs of 20 - 25 % less than similar combustion systems where the air is used.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for;    (1) a system for converting solid biomass material to usable heat energy and related byproducts comprising an air separator (a1), a solid fuel combustion chamber (b1), a first burner stage (c1), a second burner stage (d1) and a third burner stage (e1), where (a1) is for separating oxygen from air and providing a supply of oxygen, (b1) has a first chamber portion with an airlock inlet feed for feeding a metered amount of solid fuel to it, (c1) has a first traveling conveyor firebelt and device (D2) for feeding oxygen from the supply along the length of the first traveling conveyor firebelt, (d1) has a second traveling conveyor firebelt and device (D3) for feeding oxygen from the supply along the length of the second traveling conveyor firebelt, and (e1) comprises a steam boiler having a firetube for collecting fuel gases from (c1) and (d1), and combusting the collected fuel gases with oxygen from the separator and device to generate steam from the heat of combustion in (e1) and heat utilization device connected to the steam boiler;    (2) a solid fuel fed gasification system comprising:    (i) a first chamber having an airlock inlet feed for feeding a metered amount of solid fuel to it;    (ii) a first burner stage having a first traveling conveyor firebelt with a first oxygen-introducing means for introducing a metered amount of oxygen in progressively increasing proportions along the lengths of the first traveling conveyor;    (iii) at least one additional burner stage having at least one additional traveling conveyor firebelt with a second oxygen introducing a metered amount of oxygen in progressively decreasing amounts along the length of the further traveling conveyor firebelt;    (iv) a steam boiler connected to the gasification chamber for receiving gaseous products resulting from the combustion of the solid fuel;    (v) a device for introducing oxygen into the boiler for converting the thermal energy to steam; and    (vi) a cyclone and baghouse for particulate collection and a scrubber for removing noxious gaseous from the exhaust stream.