The Use of the Parry Process for the Thermal Drying of a Lignitic Feed to a Mine-Mouth Generating Plant

摘要

Victor F. Parry of the US Bureau of Mines initially developed the Parry Process as a means to dry the low rank 'slack' (finer size fractions) not used as feedstock in the coarse coal saturated steam Fleissner drying process. The Parry Process was published in 1949 and is the first recorded utilization of gas recirculation thermal drying with coal. Gas recirculation thermal drying consists of the tempering of the furnace exit / dryer inlet gases with recycled process gas (as opposed to air) resulting in a vitiated air stream (i.e. less than 5% oxygen v/v). Low rank coals have low ignition temperatures with the gas recirculation thermal drying process permitting the direct drying of low rank coals without ignition occurring. In 1954, the US Government in conjunction with private industry built nine Parry gas recirculation lignite entrainment dryers to feed nine adjacent carbonizers. The gasified product from the carbonizers was to be the feedstock for the plastics industry. The char from the process was to be the feedstock to three adjacent cyclone fired boilers providing steam to three generating units. Before construction of the carbonizers was completed, a less expensive plastics feedstock was developed from liquid hydrocarbons. The nine carbonizers were never used and the nine gas recirculation thermal dryers were retained to upgrade the lignitic feed to the three coal fired boilers that were designed for a higher BTU char feedstock. These nine thermal dryers are still operating today representing 51 years of continuous operation. These thermal dryers process a 35% moisture lignite producing a 3 to 5% moisture product and have been used as the prototype for both other low rank and bituminous fitlercake thermal coal dryers. This paper presents the design and operation of these thermal dryers.