Calcium oxide products have a large demand and large production scale due to their wide application. Due to the many disadvantages of the traditional calcination production method, they all have high energy consumption, large pollution emissions, poor product quality uniformity, and harsh working conditions for workers. And other issues.
Energy saving, consumption reduction, and emission reduction have become the common and urgent needs of the world. Restricting harmful gas emissions is the first to bear the brunt of the calcined production of calcium oxide due to the high demand for products. If the calcination of calcium carbonate does not need to recover carbon dioxide as raw material, it will increase the emission of a large amount of carbon dioxide gas to the environment, and the NO2 harmful gas emitted by the kiln gas will not only pollute the environment but also endanger the health of workers. Recycling carbon dioxide and reducing the unit energy consumption index can reduce the total emission of NO2 harmful gas. It is of great significance for reducing the production cost of calcium oxide and reducing the pollution to the environment.
Theory and a large number of production practices have proved that calcium carbonate with a characteristic particle size of only a few tens of μ can achieve a decomposition rate of 98% in only 1-3 seconds under high temperature conditions close to 1,000 degrees. Based on this feature, a feasible industrial design can be developed, which can revolutionize the traditional way of calcining to produce calcium oxide.
We produce calcium oxide by calcining and decomposing calcium carbonate: CaCO3 △ CaO+CO2
In theory, when calcium carbonate is heated to 530°C, the decomposed CO2 is greater than the partial pressure of CO2 in the air, and CO2 can continue to diffuse into the air. When the temperature reaches 898°C, the theoretical equilibrium pressure of calcium carbonate decomposition is equal to the total pressure of the surrounding air. When the pressure is equal, calcium carbonate will decompose violently. However, in the actual production of the kiln, the calcium carbonate block we use for calcination has a certain physical size, and the calcium oxide formed on its surface at a temperature of 898°C forms a thermal resistance, which makes the temperature of the decomposition surface that gradually moves to the inner core of the block It cannot reach 898°C, so the calcination and decomposition reaction of calcium carbonate is difficult to proceed quickly without increasing the furnace temperature.
Assuming that the calcining reaction interface of calcium carbonate in the process of calcining and decomposing is always at the temperature of 898°C for the first time, then the calcining and decomposition reaction of calcium carbonate can be completed quickly. The rate at which calcium carbonate completes the calcination decomposition reaction. Limited by the displacement speed of the calcination reaction interface to the inner core of the block, and the displacement speed of the calcination reaction interface depends on the calcination temperature. Therefore, the completion of the calcination decomposition reaction process of calcium carbonate is not only related to the characteristic particle size of the calcium carbonate block, but also related to the calcination temperature. Although the displacement rate of the reaction interface has nothing to do with the particle size of the calcium carbonate block. But for a block with a certain particle size, the higher the calcination temperature, the shorter the time to complete the decomposition reaction. Calcium carbonate with a characteristic particle size as fine as tens of μ can achieve a decomposition rate of 98% in only 1-3 seconds at a temperature close to 1000°C. It is because the specific surface area of the fine particles is large and the heat transfer speed is extremely fast. In this case, the high-temperature hot air flow can instantly “penetrate” the particle core, so that the calcium carbonate can quickly complete the calcination decomposition reaction.
We simply refer to the excellent characteristics of calcium oxide products with a suitable degree of calcination as “activity”. The key to the preparation of activated calcium oxide lies in the appropriate degree of calcination. Percalcined calcium oxide is produced by calcining calcium carbonate in a high-temperature environment exceeding 1,000 degrees for too long. This situation cannot be completely avoided in the production of kilns using bulk materials as raw materials. It is an ideal way to obtain highly active calcium oxide by using powder materials with fine particle sizes as raw materials, mixing them rapidly in high-temperature hot air, and detaching them after completing the thermal decomposition reaction in an instant.
Calcining powdered calcium carbonate with fine particle size to produce highly active calcium oxide requires solving the following problems:
1. Material particle size
When the material particle size is fine to a certain extent, its free movement is in the “Brown” state of non-gravity acceleration. In the collection system composed of cyclone collectors, this kind of material placed in the high temperature and high pressure hot air will bring a lot of trouble to our product collection system, so the selection of material particle size, in order to simplify and compress the collection system For equipment investment, it is best to choose the lower limit of the ultimate capacity of the cyclone collector. In order to achieve the effect of instantaneous penetration, decomposition and detachment, the selection of the appropriate characteristic particle size of the material also needs to be comprehensively considered from the effect that can be achieved by the process design of the system equipment.
2. Dispersion of materials
Naturally accumulated powder materials have low bulk density, large volume, and extremely poor thermal conductivity. It cannot be calcined directly. Only when it is uniformly dispersed in the unit volume space and adjusted to a suitable gas-solid concentration, is it most conducive to the calcining of powder materials. Therefore, it is necessary to use powder materials for calcination, and it is essential to have equipment that can fully and evenly disperse the materials before calcination or at the same time as calcination.
3. Calcination method
Suspension calcination, the powder material is dispersed and mixed directly with the heated hot air flow, and a higher heat ratio can be obtained. However, when product purity is required, the choice of fuel species is limited. In addition, impurities such as silicon and aluminum in materials and fuels can easily generate carbonate products such as silicon and calcium aluminate in high-temperature kilns, which can cause nodules and scarring to the kiln, which is not conducive to prolonging the life of the kiln and Stable operation.
Calcination of calcium carbonate causes chemical and physical changes in calcium carbonate. Calcium carbonate with less impurity elements theoretically contains about 55% calcium oxide and about 44% carbon dioxide. Calcination and decomposition of calcium carbonate will precipitate a large amount of carbon dioxide. Calcium oxide obtained by calcination and decomposition is measured by its degree of calcination. It can form over-fired, medium-fired, light-fired and under-fired profiles. The burnt part is usually a polycrystal above 10μ, and the medium-burned and light-burned part is mostly a single crystal below 5μ. Compared with overburned calcium oxide products, light-burned and medium-burned calcium oxide has the characteristics of small crystals, large specific surface area, large total pore volume and strong reactivity. Relevant tests show that the specific surface area of lightly burned calcium oxide is about 9000-25000㎝2/g due to the small crystal size, medium-burned calcium oxide is about 3000-9000㎝2/g, and perburned calcium oxide is only 300-3000㎝2 /g.
Calcium oxide is added with water to form calcium hydroxide (commonly known as “slaked lime”). Continue to add water to digest to obtain lime milk. The emulsification rate of light-burned calcium oxide is more than 1.5 times higher than that of per-burned calcium oxide. The emulsified particle size of light-burned calcium oxide is more than 90% at 0.01- Between 1μ, and after emulsification of calcium peroxide emulsification, the emulsified particle size is only about 20% in the range of 0.01-1μ. The characteristics summarized above are decisive for the direct use of calcium oxide products or as raw materials for subsequent deep-processing products. Especially when it is used as a raw material for the production of nano-calcium, it directly restricts the product yield of nano-calcium.