Proportion of gypsum powder in different processes

Proportion of gypsum powder in different processes

1 One step method of internal fired rotary kiln
Structural characteristics: high temperature hot flue gas is in close contact with gypsum powder in the downstream, which is bound to cause excessive dehydration of very small powder particles, forming anhydrite II and III, usually up to 20%. If the anhydrite component is reduced, the content of dihydrate gypsum will be increased. In general, this process has low investment, low power consumption, and can also produce various performance gypsum powders according to user requirements. The disadvantage is that the water content of raw materials should be relatively stable. If the water content fluctuates too much, the product components will change accordingly, affecting the product quality. The operator needs to observe the product outlet temperature at any time, adjust the feeding amount properly, and ensure that the discharge temperature is constant, so as to ensure the product quality. In addition, the discharge temperature is 150 ° - 180 °, and the flue gas temperature should be more than 40 ° higher than the material temperature. In this way, the flue gas takes away more heat, consumes more energy, gypsum powder is taken away more by the flue gas, and the dust removal load is large. (1.8m * 18m, output 66000 tons)
2 One step method of external firing rotary kiln
Structural features: This is the most traditional process, which is the first generation deformation of intermittent frying pan. The gypsum powder contacts the frying pan, and the heat is transmitted from the iron plate to the gypsum powder. The product quality is relatively stable. Semi hydrated gypsum accounts for about 90% of the effective components. The proportion of anhydrite and dihydrate gypsum is small, and the product has wide adaptability. Small investment, simple equipment and low power consumption. Disadvantages: the indirect heat transfer efficiency is low. Affected by the heat transfer area and heat transfer mode, the effective heat utilization rate is only about 30%, and the energy consumption is high. As the iron plate is both a heat transfer medium and a load-bearing carrier, it is not suitable for the production line with large output, limiting the scope of use.
3 Boiling furnace
(1) Structural characteristics of the indirect heating fluidized bed furnace: the heat transfer oil is used for indirect heat transfer, the secondary heat source is used, the heat flow is stable, the fluidized bed furnace is large, the heating time is long, the typical low temperature slow burning, the composition of the finished product is easy to control, and the hemihydrate gypsum content is the highest. The disadvantage is that the secondary heat source equipment has large investment, low overall thermal efficiency, high input and high output of raw materials, particles and relatively heavy components in raw materials can enter but not exit, and the furnace needs to be shut down for cleaning after a period of operation. Moreover, the raw materials into the furnace must have sufficient fluidity, and the raw materials must be dry and free of particulate matter.
(2) Structural features of the direct heating fluidized bed furnace: the material circulation process is the same as that of the heat transfer oil fluidized bed furnace, except that the secondary heat source is changed to direct flame heating, which has the advantage of reducing the intermediate links of the heat transfer oil furnace, but the flame and gypsum powder cannot have the same heat exchange area as the heat transfer oil fluidized bed furnace, so the exhaust gas temperature is bound to be higher, and the material requirements will also be improved. The thermal efficiency is slightly lower than that of the heat transfer oil fluidized bed furnace.
4 Flash firing method
(1) Take Dongda powder as the representative, air flow drying flash firing method.
(2) Take Pingshan Taihe Branch as the representative, in the form of Peter Mill.
The inevitable common disadvantages of the two methods are that the setting time of gypsum powder is too fast, the calcination process of gypsum powder is extremely short, the phase composition is dispersed, and the process control is extremely strict, which can not meet the requirements of various users.
5 Combined process
(1) Combined with the advantages of the two methods, the externally fired rotary kiln waste heat air drying is only suitable for small lines.
(2) The waste heat air flow drying of direct fired fluidized bed furnace is suitable for medium-sized lines.
(3) Rotary kiln pre drying, fluidized bed furnace calcination, suitable for large lines.
6 Effect of gypsum transformation agent on gypsum performance
(1) When 0.2% of the total amount of sodium succinate (Na2C4H4O5 · 6H2O) gypsum is added, the crystallization effect is the best, α The gypsum has the highest strength.
(2) Potassium citrate (K3C6H5O7 · 5.5H2O or K3C6H5O7 · 2H2O)
The effect is slightly worse than (1).