Patent DE-10011177-A1 (DE)
Title: Drying of wood particles as chips or fibers and the like has an initial drying stage partially heated by cleaned exhaust gas from the main drier where hot gases are the drying medium from a combustion chamber
Inventor: SCHMIDT WERNER
IPC: F26B21/04
Filed: 2000-03-08
Abstract: For the direct drying of wood particles, as chips or fibers and the like, a burner generates a hot gas flow for a drier. A part-flow of the exhaust gas is taken from the return flow to the burner, to be passed directly into the drier.  The deflected part-flow of the exhaust is mixed with the hot gas flow before entry into the drier, and the remainder of the exhaust is returned to the burner. The wood particles are mainly dried in the drier, where a part-flow of the hot gas from the burner is directed at the material without mixing, for an initial direct drying action in an initial drying chamber before it enters the drier. The initial drying action is at a lower or higher temperature than the main drying phase, or it is at the main drying temperature level. The initial drying phase is shorter than the main drying action. The wood particles are carried out of the initial drying station by the exhaust gas from it, to be separated from the exhaust and the exhaust gas is cleaned of impurities for mixing with the hot gas flow through an exhaust gas channel for the cleaned gas. The impurities are separated from the exhaust gas by an eddy tube, emerging from the initial drying station. The wood particles are passed to the main drier, after the initial drying stage. The gas mixture for the initial drier is set at 250-500 deg C and preferably 300-350 deg C, using a part-flow of heated gas with cleaned exhaust from the initial drier and added fresh air if necessary. The hot gas in the combustion chamber is heated to \-800 deg C so that any fine dust or odorous matter is completely incinerated in the returned exhaust part-flow. Particles are separated by a cyclone from the exhaust gas flow and/or the exhaust gas from the initial drier. An Independent claim is included for an assembly to dry wood particle material with a branch channel (17) from the gas recirculation (16), as a bypass for an exhaust gas part-flow around the combustion chamber (3) to the drier (5). Preferred Features: A section (4') of the hot gas tube channel (4), at the combustion chamber side, leads from the combustion chamber (3) to an entry (6) at the mixing chamber (7). An outlet (8) of the mixing chamber (7) is linked to the drier (5) by a pipe channel section (4) at the combustion chamber side. The branch channel (17) is connected to a further entry (18) into the mixing chamber (7). A further branch channel (19) leads from the pipe channel section (4') at the combustion chamber side of the hot gas pipe channel (4) to the initial drying section (1). The branch channel can lead to a combustion chamber for the initial drying stage (1), with the chamber outlet linked to the initial drier (1) by a further branch channel. The branch channel(s) (19) are connected to an additional mixing chamber (21), with its outlet connected to the entry of the initial drier (25) by a further hot gas channel (24), at the initial drying stage (1). A second entry (39) into the second mixing chamber (21) is a connection for the exhaust gas from the initial drier (25) from its gas recirculation system (32,38). The initial drier (25) has a feed unit (26) for the wood particle material. A separator (28) in the initial gas recirculation channel (32) separates impurity particles from the initial drier exhaust gas, linked to the feed unit (9) by a carrier channel (30) to pass the initially-dried wood particles into the main drier (5) as a carrier flow for them. A further separator (34) is after the exhaust gas separator (28) at the initial drying stage (1), to clean the exhaust of particles, linked to the additional entry (39) into the second mixing chamber (21). At least a part of the separators (11,28,34) is a cyclone or eddy pipe, to clean the gas flows of particles, and at least the third unit (34) is an eddy pipe. The gas recirculation channels (15,16,38) are fitted with one or more fan blower impellers (16,33).