1. Study on crushing strength of granulated salt
1.1 Water addition affects crushing strength
The crushing strength of granulated salt is mainly determined by two methods: throwing high crushing strength mainly characterizes the strength properties of secondary crushing of granulated salt and determines the design of technological process. However, the pressure crushing strength is mainly a pre-degree property that characterizes the pile pressure and process conditions of granulated salt. As can be seen from the data, In the high throwing strength, when the granulated salt with different water addition falls freely at the position with the throwing height of 4 meters, the number of broken particles is also different with the different water addition. Among the 10 granulated salt with water addition range of 0.5-2.0%, 1-3 particles are broken, and the breaking rate is relatively low. When the water addition is 1%, only 1 particle is broken. For the first time, judging from the pressure crushing strength data measured by the particle strength meter, the crushing strength of the granulated salt is also relatively ideal in this interval, with the average strength reaching more than 40N/cm2. 1% water addition has the best effect, and the crushing strength reaches 50N/cm2, which exceeds the technological requirements and product requirements for the crushing strength of the granulated salt ≥ 45 N/cm2. When the water content is 0% and 2.5%, the crushing strength per 10 grains is as high as 5-6 grains, the crushing rate is relatively high, and the pressure crushing strength is also less than 20N/cm2. In this range, the granulation salt strength is low and easy to crush, so it is not conducive to granulation. Therefore, reasonable and accurate control of water addition range is one of the effective ways to effectively improve salt granulation strength.

1.2 Speed Affects Crushing Strength
From the data of the influence of rotational speed on the granulation salt crushing strength, it can be seen that in the experiments of three different raw salts, with the continuous decrease of rotational speed, the granulation salt crushing strength of the three raw salts increases with the decrease of rotational speed, indicating that the slower the rotational speed, the higher the granulation salt strength. It can be seen from the data that when the rotating speed drops to 24r/min, the crushing strength of dry salt adding water and centrifuge wet salt is greater than 40N/cm2, which is very close to the design requirement value we conceived. Therefore, in order not to affect the production capacity, the rotation speed can be determined to be 24r/min.
 
2. Study on technological conditions
2.1 Process Angle
The natural fluidity of salt in process pipelines and equipment is related to the setting and installation of process pipelines, process angles of equipment, process flow and other related parameters in process design. Therefore, before process design, it is necessary to master the natural flow process conditions of salt under different moisture conditions. The data show that the accumulation angle of refined salt with different moisture content increases with the increasing amount of water added, and the accumulation angle increases continuously. It means that with the increase of water addition, the accumulation angle becomes larger and larger. At the same time, the worse the natural fluidity of salt, the steeper the process pipeline, and the more unfavorable it is to the process trend of small angle.

2.2 Drying process
The raw salt of granulated salt adopts dry salt plus water and centrifuge wet salt, and the granulated products contain a certain amount of water. Its water content is kept between 0.3-2.0%. In order to meet the quality requirements of different users, it is necessary to carry out drying and water removal process on granulated salt.

When the granulated salt is subjected to drying at 100 ℃, 120 ℃ and 140 ℃ respectively from the original strength of 45.4 N/cm2. When the strength reaches 100N/cm2, the required time is 5min, 3min and 3min respectively. Moreover, when the temperature is 140 ℃ and dried for 1min, the strength of granulated salt rapidly increases to 90.95 N/cm2, indicating that the higher the temperature, the shorter the drying time. It is analyzed that in the same drying time, the crushing strength of granulated salt increases with the increasing drying temperature and the crushing strength of granulated salt also increases. At various temperatures, the crushing strength of granulated salt is also increasing rapidly, and the higher the temperature, the greater the increase of strength with time, which is conducive to enhancing the strength of granulated salt in a short time. On the contrary, the strength of granulated salt increases slightly with time at low temperature, which is not conducive to improving the strength of granulated salt in a short time. For example, at 80 ℃, after drying for 5min, the crushing strength of granulated salt basically does not change. Therefore, we can draw a conclusion that drying and heating is one of the effective methods to rapidly improve the crushing strength of granulated salt. At the same time, we also found that drying amount and drying area are important factors that mainly affect drying efficiency.
 
2.3 Cooling Temperature and Cooling Time
The surface temperature of the granulated salt after drying is ≥ 100 ℃, and the temperature is too high to be directly packaged. The granulated salt needs to be cooled before entering the packaging barrel. Here we adopt a packaging temperature of < 40 ℃ and a cooling temperature difference of 60 ℃. Natural cooling and fan cooling are adopted to carry out cooling experiments. Through experiments, it is known that the blowing and cooling time of the fan from 100 ℃ to 40 ℃ takes 3-4 minutes. The natural cooling time depends on the ambient temperature and takes longer, usually 7-9 minutes. If the cooling time required for natural cooling is too long, the conveying distance will become longer, which is not conducive to the arrangement of process flow.