An apparatus and method for processing materials in a batchwise or continuous fluidised bed, such as a drier, in which the fluidised bed is subdivided into a plurality of smaller areas, to each of which two separately controlled gas flows are provided. The first lower gas flow is provided to the bed preferably all of the time, and is sufficient at least to maintain the bed in an expanded state. The second higher gas flow is provided to each separate area of the bed in sequence by means of a rotary valve arrangement, and is high enough to induce fluidisation in the bed, but not high enough to induce significant solids loss by entrainment in the offtake gas. The higher flow sequence can be chosen to provide almost any desired sequence to the separate parts of the bed. The sequence can be chosen to induce a travelling wave within the bed which can be across or along the bed, and can be skewed relative to the sides of the bed. In a continuously operated bed, the travelling wave can move either co-currently with, counter-currently to, or cross-currently to, the direction of flow of the solids through the bed. This form of operation, particularly with a skewed travelling wave, improves bed operating efficiency. Since the rotary valve cannot be closed completely, problems associated with abrasive dust in the gas feed, of valve lubrication, and valve differential thermal expansion are all substantially avoided.
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