First grind and second bake. The largest advantage of this technique, compared with that of “first grind and second bake”, is energy consumption reduction. Large plaster stone shall be ground into powders with diameter less than 0.2mm, which increases the specific surface when calcining, enlarges the contact area with heat medium, improves calcination heat exchange efficiency and lowers energy consumption greatly. This equipment has small bulk, large production capacity, and simple structure and is hard to destroy.
Analysis on technique features:
I. Concept of technique
Crusher grinds large gypsum into small granules less than 25mm. After storage and measurement with weigh belt, transfer them into Raymond mill for milling. Transfer qualified calcined gypsum powder to clinker bin for storage or to board-manufacturing workshop for usage.
II. Technique’s advantages:
1.Features of first grind and second bake:
Compared with that of first grind and second bake, the largest advantage of this technique is great energy consumption reduction. The reason lies in: great plaster stones are ground into powders with diameter less than 0.2mm, which increases the specific surface when calcining, enlarges contact area with heat medium, improves calcining heat exchange efficiency and lowers energy consumption greatly; the disadvantages are three powder pollution positions in technical process, which shall be solved with dust-removing equipment.
2.Features of two other techniques:
First bake and second grind: due to high energy consumption and low production capability of this technique and that the quality of the products is hard to control and is unstable, at present, it is a kind of backward technique and is seldom adopted. Only a few small factories are still applying it.
Integration of grind and bake: this technique has good features: low energy consumption, small investment, high efficiency, stable quality of the products and small area coverage. Besides, the dust volume is concentrated and is easy for protecting environment. However, it is not mature at home and only BNBM imported from German one set of Peters-mill, which runs to manufacture thistle board.
III.Operating mode of ebullience calciner:
The bed state of gypsum ebullience calciner belongs to bubbling bed so this calciner is called “ebullience calciner”. The calcining part of the ebullience calciner is a standing box-type container with a gas distribution board at the bottom for the purpose of supporting solid powder materials to avoid leakage when stopping running and having the gas from the bottom into lathe evenly during running. Continuous feeding batch feeder is equipped above the upper bound of the bed. There are overflow holes on the furnace wall of the upper bound of the bed, which is used for discharging materials. Many heating pipes are equipped within the beds and the heating media within the pipes are saturated steam or heat oil; the heat is transferred through pipe walls to fluidized gypsum powder outside of the pipe and makes the gypsum powder dehydrate and decompose. One electrical precipitator is equipped on the upper calcination section and the dust brought by gas when leaving fluidized bed shall be collected by the electrical precipitator and return to fluidized bed automatically. The dusted tail gas shall be extracted by extract blower into the air. During normal operation, blast air from the bottom of ebullience calciner and enter into fluidized bed through the gas distribution board. Then the heat pipe flooded within the fluidized bed shall transfer a large amount of heat to materials and have the dehydrate gypsum powders reach the temperature of dehydration and decomposition. The dehydrate gypsum shall dehydrate crystal water in fluidized bed and become steam. The steam mixes with the blasted air at the bottom of ebullience calciner and they move upward through bed. Since the steam is much more than air, the fluidization of the whole bubbling bed is realized by the steam formed from gypsum dehydration. Due to violent tumbling and mixing of powder materials in the fluidized bed, the temperature and components of the materials at all positions of the whole fluidized bed are almost the same. The raw gypsum powder added continuously, once entering the bed, shall immediately mix with the hot powder materials within the bed evenly and quickly dehydrate and decompose in the hot powder. In order to avoid that the raw gypsum is extracted too early before finishing dehydration, the furnace is designed to add a separator to divide the fluidized bed into a large and a small sections. The bottoms of two sections are connected. Raw gypsum enters into the large section firstly and dehydrates most of crystal water; then comes to the small section through the lower part of the passage and completes the final dehydration and overflow the furnace from upper bed automatically
