Keywords: circular economy pilot enterprises; Mining circular economy; Intensified sintering method; Bayer process of mineral processing; Cleaner production; tailings
Zhongzhou Branch of Chinalco Co., Ltd. (hereinafter referred to as Zhongzhou Branch) is an alumina production enterprise under Chinalco, and it is an aluminum industrial base with priority development in the industrial policy planning of China aluminum industry. The main products are metallurgical grade alumina and chemical alumina. At present, the annual output of metallurgical alumina is 6.5438+0.8 million tons, and the annual consumption of bauxite is about 3.6 million tons.
In recent years, Zhongzhou Branch has firmly established the concept of "endless waste" and "no waste in aluminum industry", vigorously developed circular economy, supported by science and technology, focused on cost reduction, standardized management as a platform, and mass participation as the source, advocated energy conservation and emission reduction, and constantly promoted cost reduction and efficiency improvement. On June 5438- 10, 2005, Zhongzhou Branch, as the only representative of alumina industry, was included in the list of the first batch of circular economy pilot enterprises in China. This has strengthened the confidence and determination of Zhongzhou Branch to adhere to people-oriented, implement Scientific Outlook on Development and create a resource-saving enterprise.
Circular economy is an economic growth model of "resources → products → renewable resources", a social production and reproduction activity characterized by efficient utilization and recycling of resources, a fundamental change to the traditional extensive economic growth model of "mass production, mass consumption and mass abandonment", an important measure to build a conservation-oriented society, and an essential requirement for people-oriented and sustainable development. The party and the country have put the development of circular economy on the important agenda.
Under the new situation, especially a typical resource-consuming enterprise like Zhongzhou Branch, in order to achieve the goal of "building a world-class enterprise and a century-old shop of Chinalco" and sustainable development, it is necessary to take the development of circular economy, especially the development of mining circular economy, as a very urgent and important strategic task and persist in it.
1. Developing mining circular economy is an inevitable choice for the sustainable development of Zhongzhou Branch.
China is rich in bauxite resources, with proven reserves of 2.3 billion tons so far, ranking fourth in the world, which has the resource conditions for developing alumina industry. Because China's bauxite is different from foreign countries, most of them belong to diaspore type with high aluminum and high silicon, and more than 80% bauxite has an aluminum-silicon ratio (A/S) of 5 ~ 8, so it is impossible to produce alumina by the conventional Bayer process widely used abroad. Based on the characteristics of bauxite in China, the production process of alumina by alkaline lime sintering mixed process has been adopted and developed in China for decades, and has achieved low alkali consumption and high alumina output, which has made important contributions to the development of aluminum industry in China. At present, these two methods have become the main production methods of alumina in China, and their production capacity accounts for 90% of China's total production capacity. However, compared with the conventional Bayer process for treating high-grade bauxite abroad, these two production methods have the following disadvantages:
First, the production energy consumption is high. The comprehensive energy consumption per ton of products is 2 ~ 4 times that of Bayer process plants at home and abroad. In the manufacturing cost, energy consumption accounts for about 50%, which makes the production cost high. The operating cost per ton of products in 1998 is 176 USD, which is about 36 USD higher than that in foreign countries.
Second, the technological process is long and the construction investment is large. For large and medium-sized alumina plant construction projects, the unit product construction investment of mixed method is more than 20% higher than that of conventional Bayer method.
Thirdly, with the gradual decline of bauxite grade in China, the technical and economic indicators of the existing series-parallel process plants will gradually deteriorate, and the manufacturing costs will increase accordingly.
Fourth, China's private alumina enterprises have sprung up in recent years, with too many construction projects and disorderly over-exploitation. At the same time, due to the limitation of production technology, the phenomenon of mining rich bauxite and abandoning poor bauxite is serious, which makes bauxite resources more tense.
These deficiencies are not conducive to the further healthy and sustainable development of China's alumina industry. With the increase of energy price and the decline of bauxite grade year by year, this restriction will become more and more serious.
According to the statistics of Henan Provincial Department of Land and Resources, by the end of 2005, the bauxite resources in Henan Province were 698 million tons. Theoretically, according to the final alumina production capacity of 0. 1 100 million tons/year in Henan province and the bauxite consumption of 2.5, the required bauxite amount is 200 million tons/year, while that of other non-aluminum industries is 500 million tons/year, and that of * * is 300 million tons/year. According to the recovery rate of 60%, bauxite mining needs to consume 500 million tons/year. Therefore, it is roughly estimated that the service life of bauxite resources in Henan is 6.98/0.5= 13.96.
It can be seen that it is imperative to change the traditional production technology, vigorously develop the mining circular economy, accelerate the construction of conservation-oriented enterprises, and take the development road of saving resources, protecting the environment and harmonious coexistence between man and nature, which is the inevitable choice for the sustainable development of Zhongzhou Branch. In order to fundamentally change the status quo of alumina industry, Zhongzhou Branch, on the one hand, based on theoretical research, improves the aluminum content in the process materials by regulating the reaction behavior between aluminum and silicon in the production process, and realizes the systematic strengthening and innovation of sintering method. On the other hand, actively promote the industrialization of Bayer alumina production new technology projects. At the same time, Zhongzhou Branch vigorously carries out energy conservation and emission reduction, clean production, and reuse of tailings and red mud to realize the sustainable development of aluminum industry and build a harmonious society.
Second, the main practices of Zhongzhou Branch in developing mining circular economy
Zhongzhou Branch always adheres to the road of combining Industry-University-Research's cooperation with independent innovation, and takes the difficulties of resource recycling, environmental protection and process equipment improvement as the key points of scientific and technological research. In recent years, more than 200 scientific and technological achievements have been made, of which more than 20 are the first at home and abroad. 32 scientific and technological achievements passed the provincial and ministerial appraisal, and 13 won the second prize at the provincial and ministerial level; More than 50 patents were applied, of which 40 were accepted by China National Intellectual Property Administration and 26 were authorized. The successful development and industrial application of the national high-tech industrialization demonstration project "Bayer process for producing alumina by 300,000 tons/year mineral processing" and the intensified sintering process for alumina production have attracted great attention from the same industry at home and abroad. Among them, the new process of intensified sintering was called a technological revolution of alumina production theory in China by well-known domestic experts, and won the eighth China patent gold medal and the second prize of national scientific and technological invention; The industrial implementation of Bayer process in mineral processing has pioneered the application of mineral processing technology in alumina production in the world, and found a new technical route with reliable technology and reasonable economy for the production of alumina from low-grade diaspore bauxite in China. The post-ore-adding concentrated solution project pioneered the application of diaspore and diaspore in a production line of alumina industry. At present, these three technologies have become the core technologies of alumina production in Chinalco, and have been recognized by domestic authorities as the major key technologies for the future development of China alumina to change the resource situation, develop mining circular economy, improve core competitiveness and ensure the sustainable development of China alumina.
(A) improve the traditional technology, reduce the consumption of resources and energy.
Sintering is the oldest alumina production process, which has the disadvantages of high energy consumption, long process and high cost. In order to improve the process, Zhongzhou Branch cooperated with Central South University to transform and upgrade the traditional industry by using advanced and applicable technologies, and realized the "new process of intensified sintering to produce alumina", and successively implemented industrialization and reconstruction and expansion projects, with an annual output of 300,000 tons higher than that of the traditional sintering method. The energy consumption of alumina sintering process decreased from 182 1 kg standard coal in199 to the current 1 kg, and the energy consumption decreased by 4 1.7%. Only one energy consumption can save 690 thousand tons of standard coal and create economic benefits of more than 654.38 billion yuan every year. Zhongzhou Branch also focuses on the digestion and absorption of "strengthening sintering production process". Through the whole process of technical research, the operating rate of clinker kilns has increased from less than 90% to more than 95%, the kiln hourly capacity has increased from 58 tons to 63 tons, and the kiln age has increased from less than 1.20 days to an average of more than 200 days, making the annual output of seven clinker kilns about 1.05 million tons. At the same time, Zhongzhou Branch invested more than 20 million yuan to transform environmental protection projects such as electrostatic precipitator of clinker kiln, dust collector of thermoelectric boiler and zero discharge of industrial wastewater in the whole plant, especially adopting advanced foreign technology, which reduced the dust discharged by electrostatic precipitator of clinker kiln by more than 40%, far below the national emission standard, recovered 725 tons of alkali and 2 million tons of water annually, and reduced the total pollutant discharge of 10,000 yuan output value by more than 200%.
(2) Actively research and develop new technologies to improve the economic service life of bauxite resources.
Focusing on the "Bayer process for alumina production by mineral processing", the company has continuously improved the process and achieved many scientific and technological achievements, such as selective grinding, double-stream leaching, research and development of key technologies and equipment of Bayer process for mineral processing and industrial application. Among them, "Research and Development and Industrial Application of Bayer Process, the key technology and equipment of mineral processing" won the only first prize of scientific and technological progress in the second scientific and technological conference of China Aluminum Company. After the process was put into production practice in 2004, the aluminum-silicon ratio of Bayer process system decreased from the traditional 10 to about 5.7, which opened up an effective way for the full utilization of low-grade diaspore bauxite resources in China. It is predicted that the application of the new Bayer process can increase the economic service life of bauxite resources in our province by more than three times. Compared with the main series-parallel processes in China, the new Bayer process can save 15% ~ 20% in construction investment, 10% in production cost and 50% in production energy consumption. At the same time, Zhongzhou Branch applied the technology of adding ore after Bayer digester, and adding imported gibbsite to the last digester. Under the condition of little investment increase, the production capacity was increased by 60,000 tons, and the heat energy was fully utilized, which not only improved the production capacity, but also facilitated the production of sandy alumina. The unit investment of alumina was saved by 50% compared with the conventional investment. The project was successfully put into production on September 30, 2006.
(3) Develop high value-added products, optimize product structure and utilize resources step by step.
In order to make full use of the resource advantages of alumina production by sintering method and realize the industrial chain of resource cascade utilization. Zhongzhou Branch has continuously increased the development of chemical alumina, and independently developed three series 10 of dry white aluminum hydroxide, ultra-fine aluminum hydroxide and high white aluminum hydroxide. Among them, SH-M75 dry white aluminum hydroxide was recognized as a national new product, and ultra-fine high white aluminum hydroxide was recognized as a high-tech product in Henan Province. Products not only have high added value advantages, but also have environmental protection advantages. Its raw material comes from the solution in the middle of alumina production, and the waste liquid from the production of chemical alumina can be returned to alumina production, so the production process does not produce any pollution, and the production cost of alumina can be reduced, which is incomparable to a single chemical alumina factory. With the development of chemical alumina, the economic activities of the branch become a feedback process of "resources-products-renewable resources", and materials and energy are reasonably and permanently utilized in the economic cycle, thus making "reduction, reuse and recycling" a reality. At present, the production scale of chemical alumina has reached the annual output level of 6.5438+300,000 tons, the whiteness of products is generally above 94%, and the annual export earnings exceed 9 million US dollars.
(d) Promoting alternative technologies and recycling energy.
In the promotion of alternative technologies, advanced technologies and processes such as intensified sintering, Bayer process, high-temperature double-flow digestion and lump coal instead of coke have been continuously improved. In the popularization of reduction technology, the technical conditions of new equipment such as indirect heating desilication of alumina, tube falling film evaporation of mother liquor and high-efficiency CO2 compressor were continuously improved, so that the tube falling film evaporation technology of mother liquor was applied to sintering system for the first time, and the steam consumption was significantly reduced.
(5) Promoting cleaner production and comprehensive utilization of resources.
The branch has invested more than 40 million yuan to transform environmental protection projects such as electric dust collection in clinker kiln, dust collection in thermoelectric boiler and zero discharge of industrial wastewater, and actively promoted recycling technology. At present, water (zero discharge of industrial wastewater, red mud backwater, ash backwater and evaporation backwater reuse) has been realized many times; Cascade utilization of heat (high pressure steam power generation, medium pressure steam dissolution, low pressure steam evaporation, exhaust steam heating); Not only did it realize zero discharge of industrial wastewater, but it also recovered more than 700 tons of alkali and 2 million tons of water every year.
(six) around the comprehensive utilization of tailings, ash and red mud, actively carry out scientific and technological research work and extend the road of mining cycle.
In 2003, Bayer alumina production process was successfully industrialized in Zhongzhou Branch of China Aluminum Company. With the continuous in-depth research and secondary development of Bayer process technology in Zhongzhou Branch, the process economic and technical indicators are continuously optimized, the production cost of alumina is continuously reduced, and the technical advantages are becoming more and more obvious.
As an innovative process, the Bayer process of mineral processing also brings a new topic: compared with the conventional Bayer process, which has only one waste-red mud, the Bayer process of mineral processing also has another waste-bauxite flotation tailings. With the continuous and stable operation of two Bayer process production lines in Zhongzhou Branch, the total discharge of flotation tailings is also accumulating, which has caused great pressure on the long-term stable operation of the existing tailings pond in Zhongzhou Branch. Therefore, solving the problem of safe storage and resource utilization of bauxite flotation tailings has become an important problem to be solved urgently after Bayer process industrialization.
The development and utilization of bauxite flotation tailings is a new subject and a technical problem. It is necessary to obtain good economic benefits and realize zero discharge of flotation tailings as far as possible. Developing comprehensive utilization technology of bauxite flotation tailings can not only enrich and improve the connotation of resource utilization technology of bauxite flotation tailings, promote the formation of new industrial chain and establish new economic growth points, but also effectively reduce the environmental and safety risks in the storage process of bauxite flotation tailings and realize zero discharge of bauxite flotation tailings. It has resource, environmental and ecological effects, and has important practical significance for China's alumina production enterprises to realize circular economy, benign development and improve economic benefits.
Chinalco and Zhongzhou Branch attached great importance to the safe storage and resource utilization of bauxite flotation tailings, and organized scientific and technological forces to tackle key problems at the beginning of Bayer process industrialization in Zhongzhou Branch. In recent two years, through the unremitting efforts of scientific and technical personnel of Zhongzhou Branch, the research on paste storage technology of bauxite flotation tailings has completed all the research contents, and the paste technology has been innovatively applied to treat flotation tailings, and the paste storage technology of bauxite flotation tailings has been established. Flotation tailings slurry, base material and gelling activator are mixed in a certain proportion to form an easily cemented paste with certain strength. At present, this technology has entered the stage of industrialization in Zhongzhou Branch. From 2005 to 2006, the research on the technology of producing low-temperature ceramic wood from bauxite flotation tailings completed all the research contents specified in the project, and successfully developed the technology of producing low-temperature ceramic wood from bauxite flotation tailings, the technology of producing imitation stone from bauxite flotation tailings and the technology of producing cement admixture from bauxite flotation tailings. In 2006, "Study on Preparation of Al-Si Alloy from Bauxite Flotation Tailings" made a great breakthrough in iron removal technology from bauxite flotation tailings, and the research on preparation of Al-Si-Fe alloy from bauxite flotation tailings is under way.
At present, the feasibility study report of dry ash storage scheme has passed the expert review and can be implemented before the end of 2007. Comprehensive utilization scheme of tailings and red mud cooperates with relevant universities to tackle key problems.
Mineral resources are non-renewable resources, which are increasingly tense. Therefore, it is the unshirkable responsibility of Zhongzhou Branch, a resource-saving enterprise with high energy consumption, to create a resource-saving enterprise, reduce production costs, realize the resource utilization of industrial wastes, develop mining circular economy, increase product output, improve product structure and enhance enterprise competitiveness.