Lignite drying process

Several common lignite drying processes: 1. Vibratory mixed flow drying This technology can remove about 10% of the moisture from lignite, increase the calorific value to about 3500 kcal, and have a large drying capacity of a single equipment, which can reach 3 million tons per year, but the dehydration rate is low. The principle is to crush the raw coal to 35-50mm and dry it with a hot air dryer. The dryer is a closed box with 4-5 layers of zigzag vibrating inclined screen inside. The high temperature hot air generated by the hot air stove is mixed with the cold air to about 230C ° C to form a medium temperature hot air that passes through the drying oven from bottom to top. Coal particles pass through the vibrating screen surface from top to bottom, fine particles leak from the mesh hole, and drying is quickly completed. Coarse particles slowly roll down through the screen surface, and undergo heat exchange between hot air and coal blocks to obtain drying. The drying process varies from 10 to 60 minutes depending on the dehydration rate requirements. If necessary, the dried coal can also be sent to a coal separator for separation, which will discharge the gangue and mud blocks, further improving the calorific value of lignite. 2、 Belt furnace drying and upgrading technology This technology can reduce the moisture content of lignite to below 10% and increase its calorific value to over 5000 kcal. The principle is similar to that of vibrating bed drying, which uses hot air drying, but the temperature of hot air used in this technology can be as high as 300C °. Using preheating, drying, and cooling processes, in addition to drying lignite, it can also modify and improve the quality - decomposing oxygen-containing functional groups, allowing partial oxygen atoms to precipitate, resulting in higher dehydration rates. Lignite is placed on a mesh heat-resistant metal belt for transportation. The strong wind generated by the fan passes through the mesh of the mesh conveyor belt and the gap between the lignite and the hot wind for heat exchange, allowing the lignite to be dried and modified for upgrading. The large amount of water vapor evaporated during the drying process can also be condensed for recovery. This technology can adjust the drying time, and the process is controllable. However, there is no very mature technology in China, but it has a high technological content and a promising future. 3、 Drum drying technology Rotary dryer This technology can reduce the moisture content of lignite to about 15%, achieve high dehydration rate, and increase the calorific value to about 4500 kcal. The principle is to crush the feed coal to 0-50mm and then put it into a drum filled with high-temperature hot air of about 500C °. In the inclined rotating drum, the lifting plate on the drum wall makes the lignite travel stably in the drying drum to form a completely broken fabric curtain, allowing the flue gas to fully exchange heat with the raw coal, with an exchange time of about 30 minutes, thereby drying the lignite. Compared to the vibrating bed drying technology, the processing capacity of a single equipment of the drum drying technology is relatively small, and due to the high drying temperature, it is prone to spontaneous combustion and even explosion of lignite, with a high rate of lignite breakage and great operational difficulties.