The main composition of desulfurized gypsum is the same as that of natural gypsum, which is calcium sulfate dihydrate (CaSO4 · 2H2O), slightly yellow, neutral or slightly alkaline. The physical and chemical properties of gypsum are the same as those of natural gypsum. However, as an industrial by-product, desulfurized gypsum has its own characteristics compared with natural gypsum, which is mainly reflected in the obvious differences between desulfurized gypsum and natural gypsum in appearance, chemical composition, especially impurities and particle morphology. In addition, the grade of desulfurized gypsum is slightly higher than that of natural gypsum and contains less impurities. It is a kind of chemical gypsum with good quality.
If the desulfurized gypsum is treated by stacking and landfill, it will cause serious pollution to the land, groundwater and atmospheric environment. Active use of these gypsum can reduce environmental pollution, turn waste into renewable energy, realize sustainable development and save valuable natural gypsum resources, which is of great significance.
Desulfurized gypsum cannot be directly applied. It usually needs to be calcined before it can be used. The calcination process is an important factor affecting desulfurized gypsum. Next, let’s introduce the calcination process of desulfurized gypsum. There are usually two calcination processes: high-temperature calcination and low-temperature calcination.
Desulfurization gypsum calcination process
The industrial by-product desulfurized gypsum is fed into the steam tube bundle calcining kiln through box feeder, belt conveyor, vibrating feeder and other conveying equipment, and then calcined with 240 ℃ supersaturated steam; The calcined products are sent to the cooling bin for cooling through conveying equipment such as screw conveyor and plate chain elevator; The cooled semi-finished products are sent to the pre grinding bin through screw conveyor, belt conveyor, plate chain elevator and other conveying equipment, and then sent to the ball mill for grinding after metering; The milled finished products are sent to the finished product warehouse for storage; After the finished product warehouse, a packaging machine can be set for packaging and sale, or the powder material can be directly transported by bulk truck for external sale.
High temperature calcination
The high-temperature calcination method (equipment) is that the desulfurized gypsum is in direct contact with the high-temperature flue gas for heat exchange, rapid dehydration and calcination. The heat source temperature of high-temperature calcination is greater than 600 ℃, and the materials stay in the calcination device for only a few seconds. The surface temperature of gypsum particles is high, and the internal temperature of particles varies according to the size of agglomerated particles, such as direct heating rotary kiln calcination Air flow calcination equipment adopts high-temperature rapid calcination process, which is difficult to control and has high production efficiency. The high-temperature calcination process is characterized by high production efficiency and low investment.
Low temperature calcination
The low-temperature calcination method (equipment) is to indirectly heat the desulfurization gypsum through the built-in heating pipe. The heat source adopts steam and heat transfer oil. Because it is indirectly heated, the heat transfer speed between the material and the heat source is slow. After the gypsum is slowly heated and heated, it is slowly dehydrated to form hemihydrate gypsum. Low temperature slow calcination means that the materials stay in the calcination equipment for a long time, the surface temperature of gypsum particles is in a low state, and the internal and external temperatures of particles are close, such as frying pan and indirect rotary kiln. The outstanding advantages of low-temperature calcination are uniform and stable product quality, stable quality of building gypsum powder generated by low-temperature slow calcination, stable phase composition and slow setting speed.
Desulfurization gypsum calcination equipment
The direct heating rotary kiln calcination technology is to directly contact the hot gas flow with the desulfurized gypsum powder in the rotary kiln barrel, dehydrate the dihydrate gypsum into hemihydrate gypsum, and directly calcine the gypsum by using the direct heating rotary kiln. Before calcination, the desulfurized gypsum does not need drying treatment, the calcined gypsum is of good quality, and the gypsum powder rotates slowly in the rotary kiln barrel, The thermal medium generally moves in the same direction with gypsum powder, and the gypsum powder is in the stacking state in the rotary kiln.
Rotary kiln performance advantages of Fodamon
Thermodynamic calculation and analysis shall be carried out for the kiln cylinder to leave a specific gap between the tire and the cylinder, so as to ensure that the cylinder can closely cooperate with the tire under normal working state (hot state), effectively improve the stiffness of the cylinder and prevent the cylinder from necking due to too tight cooperation.
The main drive system adopts a new AC frequency conversion speed regulation technology, which is more energy-saving and environment-friendly than the traditional electromagnetic speed regulation and DC speed regulation, and has a wide speed regulation range, high efficiency, high speed regulation precision and stable operation.
The lifting plate or retaining plate arranged in the rotary kiln can ensure that the gypsum is evenly dispersed in the cylinder section and contacts with the hot air flow, reduce the generation of wind tunnel and improve the heat exchange efficiency.
The equipment operates stably and is suitable for industrialized large-scale production. It can be produced continuously and automatically. It has large production capacity, low energy consumption, no dust leakage in the calcination process and meets the environmental protection standard.