How to reduce the standard thickness of building gypsum

How to reduce the standard thickness of building gypsum
Shijiazhuang Jingjin Mechanical Equipment Installation Co., Ltd. --- Zhou Yanhui
As a quality index of building gypsum, the standard thickness of building gypsum is not only an important index to measure the quality of building gypsum, but also an index to measure the modification effect of ball mill. Therefore, it has always been our goal to keep the quality of building gypsum high and stable, especially the relative stability of crystal water and standard thickness.
At present, there are several methods to reduce the standard thickness of building gypsum:
(1) Use raw materials reasonably. At present, no matter phosphogypsum or desulfurized gypsum is used alone, the standard thickness of calcined building gypsum is inconsistent, and the difference is great. Therefore, reasonable collocation of various gypsum is an effective method to stabilize building gypsum. At the same time, limit the impurity content in gypsum, especially the metal salts of K, Na and Mg. According to relevant information, these metal salts can promote coagulation. This is also restricted in international standards.
(2) Good phase composition means the highest active ingredient. That is to say, the total content of soluble anhydrite and hemihydrate gypsum is the largest! Among the phase composition, soluble anhydrite and dihydrate gypsum have influence on the standard consistency of building gypsum. Both of them can promote coagulation to a certain extent, thus increasing the standard consistency.
Dihydrate gypsum is a harmful component in building gypsum. The content of dihydrate gypsum in building gypsum should be reduced as much as possible.
Although soluble anhydrite is an effective component, its content should also be reduced as much as possible due to its extremely unstable nature and its characteristics of increasing standard thickness. There are two places where soluble anhydrite appears: one is in the hammer dryer. This is described below. The other is in the electrostatic precipitator. Therefore, the dust collection effect of electrostatic precipitator should be as good as possible. According to the practice of Jingmen, Jiangxi and Guangdong branches, the effect of dense phase dust collection is not good, and the three electric fields of electrostatic precipitators can still collect a large amount of powder. Therefore, we suggest adding a group of cyclone dust collectors in front of the electrostatic precipitator. Therefore, we should strive to reduce the amount of dust collected in the electrostatic precipitator and reduce the probability of the occurrence of soluble anhydrite.
Increase the content of hemihydrate gypsum as much as possible.
Methods to improve the effective ingredients. First, use gypsum with high grade as much as possible. The second is to reduce the grade loss in the calcination process as much as possible.
At present, the only way to reduce the grade loss is to reduce the inlet flue gas temperature of the hammer dryer. When contacting with gypsum, insoluble anhydrite A Ⅱ shall be avoided as much as possible. After reducing the inlet flue gas temperature of the hammer dryer, the heat required for gypsum calcination will be insufficient. The problem of insufficient heat can only be solved by increasing the air volume and wind speed. However, fast wind speed means that the calcination zone and calcination time of gypsum are shortened. This requires that the entire air duct behind the hammer dryer should be appropriately extended, that is, the entire calcination belt should have enough length to allow sufficient residence time for gypsum to complete calcination.
(3) Give full play to the role of ball mill in reducing standard thickness. According to the tracking practice of long-term comparison of the relationship between surface area and standard thickness, the specific surface area is large, but the standard thickness is not necessarily low! Compared with Jingmen ball mill, its specific surface area is not large, but the range of reducing the standard thickness is large. Through analysis, it is estimated that the reason is the grading of ball forging.
For the mechanism of ball mill modification, I think it is mainly to use ball forging to crack the crystal of building gypsum to expose the unburned part. Other edges exposed by the crystal have poor water absorption and enhanced hydrophobicity. Thus, the standard thickness of building gypsum is reduced.
According to this mechanism, the following measures are taken to give full play to the role of the ball mill in reducing the standard thickness:
A. It is recommended to add external cooling measures for ball mill barrel, such as water spraying for cooling.
B. Control the internal ventilation of the ball mill.
A There should be a certain wind speed in the ball mill. The micro powder produced in the grinding process can be timely taken away by the air flow, reducing the buffering effect of the micro powder, improving the grinding efficiency, and the product quality will not be affected. When the ventilation is good, the water vapor in the ball mill will be discharged in time, the grate hole of the compartment plate will not be blocked, the adhesion of the grinding body will also be reduced, and the temperature in the mill can be reduced, which is conducive to the operation of the mill and the improvement of product quality. The ventilation speed in the mill varies with the grinding of different materials, generally 0.3~1.0m/s. The dedusting fan with low wind speed shall be selected as far as possible in production. It is recommended to install an air regulator at the same time according to a fan with large air pressure and air volume for easy adjustment.
B Control the grate hole diameter of the grinding tail grate plate of the ball mill. The control principle is to ensure that the smallest ball forging can not go out from the largest hole diameter, and it is best if it can be adjusted.
C. Add water reducing agent into the mill. It is better to pre add a certain amount of water reducing agent in the ball mill than to add it at the forming station. At the same time, the water reducing agent plays a role as a grinding aid here. Because the water reducer has the characteristics of hydrophobicity and retards the initial setting. In the ball mill, the water reducer encloses a part of the building gypsum crystal.
D. Optimize the grading of steel ball and forging. According to relevant information, large balls and forgings play the role of impact, while small balls and forgings play the role of grinding. Combined with the modification mechanism of the ball mill, large balls and forgings should be added appropriately. Basically, large forgings account for 60-70%, and ball and small forgings account for 30-40% (of which small forgings account for 80%).
Suggestion: We should first fill 70% of the target filling volume in the initial ball matching, and then gradually adjust it after tracking and verification in production. At the same time, as long as the mill motor allows, the ball forging shall be filled as much as possible!
E. Control the feeding amount of the ball mill. In fact, controlling the feeding amount is to control the residence time of building gypsum in the ball mill and extend the modification time of gypsum. It is necessary to add a buffer bin in front of the ball mill. This is the most effective way!
(4) Make good use of homogenizing silo. According to the working principle of the homogenizing silo, it is felt that the homogenizing silo should be as large as possible, and the Roots blower under the homogenizing silo should be increased. In this way, the building gypsum can be fully mixed, stirred and cooled in the homogenizing bin before entering the chute. In this way, the temperature and standard consistency of building gypsum can be reduced and relatively stable to the greatest extent.
(5) Fully age the building gypsum. At present, the aging position in our process is mainly the chute between the board making warehouse and the board making warehouse. The aging method is relatively simple. The first is to extend the time, the second is to add moist air, the third is to cool, and the fourth is to fully mix in the whole process.
As the chute fan blows in cold air, it cools the building gypsum and adds wet air during the conveying process, so that the building gypsum can be aged. We can add a cooling device in front of the board making warehouse to cool the building gypsum to a reasonable range (60 ° C). At the same time, make full use of the advantages of the four large warehouses for board making, appropriately increase the storage capacity, extend the aging time, and increase the aging effect. In order to prevent caking, 4 large warehouses can store appropriate amount for recycling. According to the statistical analysis of production data, after 5-8 hours of aging, the standard thickness of building gypsum is reduced by about 3%.