[China Aluminum Industry Network] Alkaline recycling process features
Mixed alkaline circulation, fully illustrates the process characteristics and production organization of the hybrid process.
A. The hybrid process is a closed type, so Bayer... Sinter has a certain restriction on the production capacity between the two systems. That is to say, the main joint point of the hybrid method: the red mud produced by the Bayer process must be balanced (consumed) by the sintering method; the seed solution supplied to the Bayer process by the sintering method must satisfy the alkali output of the Bayer process (including loss ) The need for a hybrid approach to balance. The buffer for production fluctuations depends on the clinker silo, seed tank, and alkali slurry tank. From this perspective, the hybrid method is the same as the serial and parallel method, and the sintering method is subordinate to the Bayer method.
B. The sintering method has a complete production process, and has an independent alkali circulation system. There is an independent aspect besides the subsidiary aspect of the Bayer process system. That is to say, when the production capacity of the sintering process is surplus, the flow rate can be increased, so that the amount of alkali circulation can be increased, and more alumina production can be obtained than in the Bayer process. This point is different from the serial and parallel joint method. This is the basis for the name of the hybrid law.
C. In principle, the Bayer process cannot be independent and is limited by the sintering process capacity, ie, the amount of alkali that is added to the Bayer process by the sintering process and the alkali circulation rate of the sintering process itself. That is to say, when the production capacity of the sintering process is insufficient, the Bayer process's surplus production capacity will not be fully realized. If the red mud out of the row is used to excavate the surplus capacity, only the Bayer process can use the caustic soda to replace the alkali output, so as not to destroy the mixed joint method. The alkali balance relationship. From the standpoint of the basic balance of the blending method, the way to realize its comprehensive production capacity is to select the main technical indicators related to the alkali cycle. The selection of the main technical indicators should consider the ore A/S, Bayer, ... sintering capacity of the two major systems, and determine the overall balance.
Mixed alkaline circulation process
There is a problem of alkali circulation in the alkaline production of alumina. The so-called alkali circulation is actually the circulation of liquid (alkaline, water) in alumina production. Different production methods, different alkaline circulation, the amount of circulating alkali is proportional to the scale of production.
The process of alkaline blending is more complex. It relies on the supplement of soda ash to make up for the chemical and mechanical losses of alkalis in the production process. It maintains the balance of multiple (mainly two) alkaline circulatory systems. It renews the cycle, dissolves a batch of bauxite, obtains alumina, and discharges red mud. The two main alkaline circulatory systems of the hybrid method are:
A, Bayer process red mud and liquid, wet alkali and liquids and a part of the sintering method of seed mother liquor, aluminum hydroxide solution, through the clinker, evaporation of the mother solution through the mixed process flow of Bayer ... sintering Base cycle.
B. Alkaline cycle of the whole process of sintering between carbon evaporation mother liquor, clinker, sintering semen, carbon split mother liquor, carbon evaporation mother liquor.
In addition, there are Bayer's method of evaporation of the mother liquor, raw pulp, semen, seed mother liquor, seed evaporation mother liquor in the whole process of alkaline circulation; internal carbon segregation solution in the sintering process, between semen and seed mother liquor, semen Alkaline cycle of partial flow etc.
Process characteristics of the hybrid process
Based on the absorption of China's traditional sintering alumina production technology and experience, the hybrid approach has explored a series of alumina production technologies and experiences that are suitable for the characteristics of China's bauxite resources.
A, Bayer process production. The adoption of aluminum ore lime dissolution method not only reduces the dissolution temperature, but also improves the dissolution effect and reduces the caustic alkali consumption. With proper multi- ore blending, less recirculating mother liquor, and balanced dissolution as unbalanced dissolution process, the Bayer process cycle efficiency is improved, and the purpose of increasing production, saving energy, and reducing consumption is achieved. With the method of decomposing the initial low temperature, intermediate cooling, high seed ratio, and active seeds, the decomposition rate of the seed was improved. With a suitable method to reduce the alkali concentration of the evaporated mother liquor, the concentration of semen is increased. Reduce the amount of evaporation of the system, so that the vapor consumption decreases.
B. Sintering process production, the use of sintering process plant alkali ratio, calcium unsaturated formula experience, combined with the characteristics of high TiO2 material in the mixed-joint method, increase the calcium into the amount, so that TiO2 CaO. TiO2, increased Clinker dissolution properties. The use of raw material and coal in the raw material to suppress the excessive accumulation of Na2SO4 in the production system caused difficulties in evaporation. In terms of clinker dissolution, the use of medium-strength Na2CO3, using a low causticity coefficient dissolution method to prevent red mud expansion and degeneration, improve the clinker net dissolution rate, in order to achieve better alumina recovery, low alkali consumption purposes. With the flocculation sedimentation technology, the sedimentation filter is used to separate red mud from the sedimentation tank, which greatly reduces the labor intensity and working environment of the workers and also increases the power consumption of the breast augmentation. The use of Bayer red mud as seed in the crude liquor desilication of the sintering process increases the silicon content index of the semen and plays a greater role in improving the product quality and increasing the clinker production rate. In the decomposition, all of the aluminum hydroxide used as a seed for the Bayer seed decomposition will play a role in reducing the SiO2 value in the product and improving the product quality.
Mixed process flow
At present, the production process of alumina in the mixed-joint process in China is based on the in-line process and combines the technological conditions for adding some high-silica-aluminum ore to the sintering system to stabilize the sintering system, and fully utilizes the Bayer process and the sintering process. Part of the production capacity. In this process, the Bayer process system treats low-silica-alumina ore, and the sintering system removes the Bayer process red mud and further recovers the remaining alumina and sodium oxide, thereby achieving low alkali consumption and high alumina recovery. purpose. At the same time, the sintering method can also process a part of high-silica-alumina ore, which has created conditions for the comprehensive utilization of mine resources. The caustic alkali used in the Bayer process system is supplemented by the sintering system, which is beneficial for reducing production costs. In the hybrid method, Bayer process products contain low silicon and high iron content, while the sintering process products contain high silicon and low iron content. These two products, after mixing, complement each other and can produce superior alumina products.
Advantages of the hybrid approach
(1) The red mud of the Bayer process system recovers alumina and sodium oxide by sintering, which increases the total recovery of alumina and reduces the alkali consumption. For example, in the treatment of ore with an average aluminum to silicon ratio of 8.5, oxidation occurs. Total aluminium recovery is 90-91%, and soda consumption is less than 60Kg/t alumina.
(2) A considerable amount of low-grade ore is added to the raw slurry in the sintering system, which not only improves the aluminum-to-silicon ratio of the clinker, but also improves the sintering process. It also effectively uses a part of the low-grade ore. The production of a part of aluminum hydroxide through carbon makes it possible to flexibly adjust the production capacity of the Bayer process and the sintering process.
(3) Add Sintering with cheap soda to compensate for the loss of caustic during production
Disadvantages: The hybrid process is quite long, the equipment is numerous, and many operation processes are checked against each other.
