Process and plant for drying lignite in a fluidised-bed dryer

摘要

In the case of known processes for drying moist bulk materials in a fluidised bed, the drier is fed from outside not only the fluidising medium but also a high-energy heating medium, whereas the vapours discharged remain unutilised. By the process according to the invention, the feeding of heating medium from outside is to be avoided, the energy balance improved and the emission of vapours reduced. For this purpose, a partial stream (15) of the vapours (10), subjected to dust separation in an electrostatic precipitator (11), is compressed into saturated steam for use as a heating medium (18) in a compressor (14), with the supply of electric energy and the injection (17) of vapour condensate (29). A second partial stream (13) serves as fluidising medium for the preheated bulk material (5) passed through the drier (6). The preheating takes place in a heat exchanger (2), which has a partial stream (3) of the vapour condensate (21) flowing through it. After phase separation in an expansion vessel (4), the vapour phase (23) of the condensate is fed to the partial stream (16). The process is suitable in particular for the drying of pit-moist lignite or of moist sewage sludge. IMAGE