Apparatus for the continuous gelatinisation of starch and starch derivatives

摘要

Apparatus for the continuous gelatinization of starch, partly degraded starch or starch derivatives by means of steam or a chemical solution, comprises a tube having at least one construction through which a starch suspension is passed, and having in the tube wall, beyond the constriction in the transition region to full cross-section, one or more inlet orifices for the steam or chemical solution. The constriction in the tube, e.g. a diaphragm with one or more passages or a nozzle, may be followed by a gradual widening of the tube cross-section. Since the starch pastes formed are generally used at a temperature below that of their formation, e.g. 50-100 DEG C., the apparatus may be extended by provision, after the inlets for gelatinizing agents, of at least one further constriction which is followed by orifices in the tube wall for supply of cooling, diluting and/or preserving liquids. The apparatus may be yet further extended by provision, after the orifices for inlet of cooling liquid, by a further constriction followed by orifices in the tube wall for return of the already gelatinized starch to a point upstream, e.g. to a point immediately after the commencement of paste formation. In a preferred form of the apparatus there is provided, in the direction of flow of the suspension, after the inlets for gelatinizing agent, a screen for the temporary subdivision of the suspension into a number of partial streams, to assist the formation of a homogeneous paste. In such an embodiment (Fig. 2) the starch suspension is passed through tube 1 surrounded by jacket 2, defining annular space 3 for the gelatinizing agent, e.g. steam which is admitted to the tube by orifices 6 and 7 following constricting diaphragms 4. The stream of supension is subdivided by screen 8. The orifices 6 and 7 may be individual holes, or annular gaps. In further embodiments, the apparatus may be provided with means for adjustment of relative quantities, pressures and velocities of the starch suspension and of the gelatinizing agent to ensure that a homogeneous product is obtained in spite of varying flow conditions. In Fig. 5, tube 1 has a conical constriction 17 provided with inlet orifices 19 which can be covered or uncovered by movable closed sleeve 20, which is coaxial with tube 1. Axial displacement of the sleeve 20, permitting variation in the number of open inlet orifices is achieved by rack 21 meshing with gear-wheel 22. This mechanism may be operated by automatic regulating device 27 which is sensitive to throughput quantity of gelatinization temperature. In Fig. 7, the free cross-sectional area for the suspension in the transition region 18 following constriction 17 is varied by means of coaxial displacement rod 24, the position of which may be controlled by device 271, which is sensitive to throughput quantity of suspension or increase in temperature. The surfaces of the apparatus coming into contact with the suspension or paste are desirably formed with irregularities such as annular or helical recesses, e.g. screw-threads or protuberances, e.g. pins or hooks, to promote mixing. The starch moves continuously through the reaction zone along a pressure gradient, and is subjected to compressive and shearing forces on passing through the constriction and mixing with the gelatinizing agent. The apparatus may form part of any paste-using machine, e.g. fermentation, papermaking or sizing plant, and may be used for gelatinizing natural starches, mechanically, chemically or enzymatically degraded starches or starch derivatives, e.g. ethers, phosphates or oxidation products of starch.