NOVELTY - Burner unit for (10) burning particulate biomass to form hot gas comprises: combustion unit (14) and static mixing unit (16); where combustion unit has two horizontal heat-resistant ducts (18, 20), second duct is above first duct and communicates with it through plenum (24) and to static mixing unit via hot combustion gases outlet (32) and device (28) to supply air and particulate biomass fuel to first duct end remote from plenum; and static mixing unit has gas inlet (40) and baffles (42-48) arranged to progressively mix hot combustion gases with gas from inlet in several mixing stages.    USE - As a burner unit for burning a particulate biomass fuel and for obtaining a flow of hot gas (preferably a stream of hot gas or a superheated steam), which is useful for drying particulate biomass (claimed), and minerals.    ADVANTAGE - The burner provides a burner for burning biomass to produce hot gas for drying applications (preferably for drying particulate biomass). The burner allows a high heat output to be achieved from a compact unit i.e. 250-700 kW heat can be produced from burning wood chips. The hot combustion gases emerging through the combustion gases outlet at above 200 degrees C, which are too hot for many drying processes, such as can cause charring of wood chips, can be brought to a temperature of (7O-110, preferably 85-110) degrees C, suitable to rapidly evaporate moisture from wood chips, by passing hot combustion gases to pass through the static mixing unit, where they are mixed with a flow of gas at a lower temperature (preferably air or steam), to provide an out-flowing hot gas stream at a desired temperature. The lower temperature gas flow is significantly larger than the flow of the hot combustion gases, to achieve the desired temperature of the hot gas stream e.g. the gas flow is 5-10 times the flow of the hot combustion gases (by mass). This air flow is brought in contact with hot combustion gases by baffles that are arranged to progressively mix hot combustion gases with gas from the inlet of the mixing unit in several mixing stages. Hence, the burning unit allows for drying particulate biomass material using hot air from the burner unit; and is also provides a supply of hot gas for a wide range of applications i.e. for drying other materials e.g. minerals. The effective drying further provides a burner with a much smaller footprint for drying the biomass, and can be installed in a container (such as a 20'International organization of standardization (ISO) container) or on a skid so that it can easily be transported to different places where biomass is available and hot gas is required.    DETAILED DESCRIPTION - A burner unit (10) for burning a particulate biomass fuel and obtaining a flow of hot gas, comprises: a combustion unit (14), and a static mixing unit (16); where the combustion unit has a first horizontal duct (18) of heat-resistant material, a second horizontal duct (20) of heat-resistant material above first duct communicating with first duct through plenum (24) and also communicating via a hot combustion gases outlet (32) with static mixing unit, and a device (28) to supply air and particulate biomass fuel to end of first duct remote from plenum; and the static mixing unit comprises an inlet for gas (40), and several baffles (42-48) arranged to progressively mix hot combustion gases with gas from the gas inlet in several mixing stages. The first horizontal duct includes a grate onto which particulate biomass fuel can be introduced. Each of the horizontal ducts is sufficiently long, such that ash particles settle out and are not carried through the combustion gases outlet. The ducts have a diameter of 300-500 mm, and a length of 3.5-4.5 m. The burner unit also comprises a mesh filter at the hot combustion gases outlet. The burner unit is mounted in a container or on a skid so as to make it transportable. The hot combustion gases passing through the static mixing unit are mixed with a flow of steam to provide an out-flowing stream of steam at a desired temperature. An INDEPENDENT CLAIM is included for process for drying particulate biomass involving: contacting the biomass with a stream of hot gas or a superheated steam that is created by mixing combustion gases with an air stream or a stream of steam, respectively using a static mixing unit comprising several baffles.    DESCRIPTION OF DRAWING(S) - The figure shows a sectional view of the burner unit.    Burner unit (10)    Combustion unit (14)    Static mixing unit (16)    First duct (18)    Second duct (20)    Plenum (24)    Grate (28) Inlet/device to supply air and particulate biomass fuel to end of first duct (26)    Hot combustion gas outlet (40) Inlet for gas static mixing unit (32)    Baffles. (42-48)