Factors and measures affecting the amount of dust in granulators and crushers

【Crusher】-Factors and measures that affect the amount of dust in the granulator and crusher
 
1. The main factors affecting the amount of dust produced by the granulator and the countermeasures
 
(1) The particles stay in the granulator for a long time, and the collision and friction between the particles generate a large amount of fine powder;
(2) If the wind speed is too high, the small particle seed crystal or the atomized urine can be directly sucked into the dust scrubber before it can be wrapped on the seed crystal;
(3) If the bed height is controlled too high, it will increase the collision and friction between particles, and if it is too low, the amount of atomized urine sucked into the dust scrubber will increase;
(4) The bed temperature is higher than 118℃, and the particle powdering is obviously intensified;
(5) The return ratio is too large, and the amount of dust brought into the granulator is large;
(6) If the amount of added formaldehyde is small or not added, the particle strength will decrease and be easily broken (when formaldehyde is not added, the dust will increase by about 20%).
 
In view of the above influencing factors, the following countermeasures can be adopted in actual production.
 
(1) Strictly control the negative pressure (-0.25~0.30kPa) in the granulator through the adjustment of fluidized air volume and induced draft fan;
(2) The height of the control bed is appropriate (about 3/4 of the field window);
(3) Reduce the operating temperature of the granulator from the original 120°C to 112°C. The evaporation system is adjusted to increase the urine concentration, reduce the water evaporation burden of the granulator, reduce the generation of dust, and change the intercrystalline structure of the urea particles. In order to reduce the bed temperature, the temperature of fluidizing air and jet air needs to be adjusted;
(4) Choose an appropriate return ratio (0.4~0.5);
(5) The strength of urea particles. When the mass fraction of the added formaldehyde is controlled at 0.55%, the urea particles are easy to bond into agglomerates. Moreover, the particle crushing strength easily exceeds the upper control limit of 30N. If the formaldehyde content is too low to achieve the desired effect, the mass fraction of formaldehyde added is controlled at 0.35% to 0.45%, and the effect reaches the ideal state.
 
2. The main factors affecting the amount of dust produced by the crusher and the countermeasures
 
The crusher can be said to be mainly used to control the return ratio. In the crusher, the ultra-large granular urea needs to be ground into fine particles and returned to the granulator. The greater the amount of grinding, the greater the amount of dust generated. The roller spacing of the crusher is well controlled. The key to reducing the amount of dust in the crusher. When the load of the granulator and the load of the crusher reach the corresponding level, the distance between the rollers crushed by the crusher is proportional to the average particle size of the product particles. The particles with a particle size of less than 0.8mm out of the crusher are basically all due to their smaller mass. The exhaust gas enters the dust scrubber.
 
Therefore, ensuring the normal working conditions of the crusher is the key to reducing its dust emission. It is not only necessary to ensure the accuracy of the adjustment of the roller spacing, but also to ensure that the surface of the roller is clean, and try to avoid the adhesion of urea dust on the surface of the roller. Since the adjustment principle of the roller spacing of the crusher is determined by the factors such as meeting the technological production requirements and the crushing effect, it is generally not easy to change it after setting in the production. Through the extreme value method of the crushing number coefficient n and the production practice of similar devices, it is proved that when the crusher roller spacing is adjusted so that the seed crystal with a certain effect after crushing is about 75% to 80% in the range of 1.2 to 2.0mm, the finished product The particle size is ideal, and the amount of dust generated by the crusher is significantly reduced.
 
3. Other main factors affecting the amount of dust generated and countermeasures
 
The main factors for the generation of dust in the urea screen are: the collision and friction between the particles cause the particles of the outer layer of the particles to break to generate dust, and the dust generated by the collision and friction between the particles and the urea screen. If the urea screen is damaged, the proportion of dust generated by urea will increase. The main factors that produce dust from product coolers and other equipment are: due to the collision and friction of particles, the factors that generate dust in product coolers (including super-large particle product coolers) include excessively high bed negative pressure and excessively high particle temperature, etc. Will increase the amount of dust. In view of the above causes of dust, control the air volume of product cooling air and dust collection fan air in actual operation to prevent excessive air volume.