Method for drying high moisture, low calorific value lignite for a generating set and recovering water contained therein and apparatus thereof

A method for drying high moisture, low calorific value lignite for a generating set and recovering water contained therein, comprising the following steps:

• step 1:
• by means of Level 1 drying, wet coal is crushed, passed through a wet coal bunker, fed into a rotary steam tube dryer in sequence, and then heated and dried in heating steam and a dry carrier gas for a certain time to obtain coal particles B with a certain proportion of water and dry gas F at a certain temperature;
• the dry exhaust is fed into a first bag filter and dedusted therein to obtain exhaust D containing water vapor and pulverized coal T, the pulverized coal T is directly fed into a collecting tank, and at the same time the exhaust D is fed into a washing cooling tower;
• step 2:
• by means of Level 2 drying and milling, the coal particles B are fed into a surge bunker and then into a coal mill, and milled under preset conditions for a preset time to obtain the dried, pulverized coal C;
• after nitrogen gas P is heated by a nitrogen gas heater to a preset temperature, a portion of the nitrogen gas P is introduced into the coal mill to dry and mill the coal particles B so as to obtain pulverized coal C;
• the other portion of the nitrogen gas P is introduced into the coal mill through a sealing fan and sealed for later use;
• exhaust G discharged from the top of the coal mill is introduced into a second bag filter and collected therein to obtain pulverized coal C and the dedusted exhaust H, wherein the pulverized coal C is directly fed into a pulverized coal collecting tank and collected therein, a portion of the exhaust H is sent back to the nitrogen gas heater and heated therein to a preset temperature, and then introduced into the coal mill, while the other portion of the exhaust H is fed into the washing cooling tower and treated therein;
• step 3:
• the exhaust D and the exhaust H are cooled and dehumidified in the washing cooling tower to form bottom liquid J in the bottom of the washing cooling tower, water vapour obtained by vacuum flashing cooling of the bottom liquid J is dehumidified and then introduced into a steam condenser to be condensed, so as to form clean water M which is transported to a condensate water recovery tank and stored therein, and while non-condensable gas that cannot be condensed is discharged into the air;
• step 4:
• a portion of nitrogen gas E discharged from the side of the washing cooling tower is introduced into a carrier gas heater and heated therein, and then introduced into the input end of a rotary steam tube dryer for use as a dry carrier gas;
• the other portion of the nitrogen gas E is introduced into the nitrogen gas heater and heated therein, and then introduced into the coal mill for use as a medium for drying and milling, so as to form a nitrogen gas closed loop system;
• step 5:
• the pulverized coal T and the pulverized coal C are mixed together in the pulverized coal collecting tank, then fed into the Venturi jet pump, mixed with air and burned in a boiler.