Countercurrent drying In the drying process, the drying driving force is relatively uniform, which is suitable for the drying of the materials to be dried. The dust carried by the drying medium is filtered through the wet zone, and the airflow contains less dust.
The indirect heating cylinder dryer is composed of a fixed concentric cylinder mounted outside the axis of the rotary cylinder and directly passes through the combustion chamber as a flue, so that the high temperature flue gas from the combustion chamber is from the concentric cylinder gap of the dryer. Passing, thereby drying the material in the inner cylinder; or in the central chimney peripheral multi-tube return pipe, so that the material of the outer cylinder is heated and dried by the reciprocating flow of hot air. As shown in Figures 6 and 7, respectively, due to the low heat transfer efficiency of indirect heating and complicated structure, the indirect heating cylinder dryer is rarely used.
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(II) Selection and calculation of the cylinder dryer The selection of the cylinder dryer is mainly based on the characteristics of the material to be dried, such as the moisture content of the material, the particle size and the moisture of the dried product. In addition, should also consider economic factors, such as try to choose low-cost source of heat drying methods, drying methods such as the use of low-quality coal to boil the combustion chamber, while also considering the use of waste heat, and minimize material into the water before drying Wait.
The production capacity of the cylinder dryer is related to the moisture (calculated by the reset percentage) of the dried material entering and leaving the dryer and the drying strength. First, calculate the total volume of the dryer, the formula is as follows:
Where V 0 — the total volume of the dryer, m 3 ;
Q———Processing capacity of drying operation (kg/h according to the weight of solids in the dry matter section;
R 1 , R 2 — the moisture (in weight percent) of the dried material entering and leaving the dryer;
W S ——— Drying strength according to evaporation moisture meter, kg / (m 3 · h).
Dry strength is determined by actual production data for the test or drying of similar materials.
The dryer volume is related to the dry strength, the nature of the dried material, the moisture before and after drying, the temperature of the drying medium at the inlet and outlet of the dryer, the dryer type, the gas flow rate and the quality of the fuel. These factors are determined based on experimental studies and actual production data for drying similar materials.
Based on the calculated total volume, then the number of dryers selected is selected.
Where n——— select the number of units, Taiwan;
V 0 ——— Calculate the total volume of the required dryer, m 3 ;
V———Select a single volume of the dryer, m 3 ;
Determination of the diameter of the cylinder dryer:
Where D———the diameter of the cylinder dryer, m;
β———full coefficient, β value generally takes 20%;
V 2 ——— volume of exhaust gas discharged from the dryer, m 3 /h;
υ 1 ———The airflow velocity at the outlet of the cylinder, m/s;
n———The number of dryers, Taiwan. See formula (2).
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