[China Aluminum Network] Electrolytic aluminum is aluminum obtained by electrolysis. The modern electrolytic aluminum industry uses cryolite-alumina molten salt electrolysis. Molten cryolite is a solvent, alumina as a solute, carbon body as an anode, and aluminum as a cathode. After a strong direct current is passed, an electrochemical reaction is performed at two poles in the electrolytic cell at 950°C-970°C. Both electrolytic.
Chinese name electrolytic aluminum
Substantially aluminum obtained by electrolysis
Method cryolite-alumina molten salt electrolysis method
Temperature requirement 950°C-970°C
modern industry
Alumina is used as a solute, carbon is used as an anode, and aluminum is used as a cathode. After a strong direct current is passed, an electrochemical reaction is performed at the two poles of the electrolytic cell at 950°C to 970°C, that is, electrolysis.
The aluminum electrolysis production can be divided into three categories: side-inserted anode rod self-roasting tank, upper anode rod self-baking tank and pre-baked anode tank.
The production of electrolytic aluminum from self-baking tanks is characterized by simple equipment, short construction period, and low investment. However, there are smoke gas can not handle, serious pollution, mechanization difficulties, labor intensity, not easy to large-scale, single-groove production and other low The shortcomings that have been overcome have now largely been eliminated.
At present, most of the countries and production enterprises in the world are using large pre-baking cells. The current intensity of the cells is very high. It not only has a high degree of automation, but also has a low energy consumption, high single-cell output, and meets the requirements of environmental regulations.
China has completed industrial trials and industrialization of 180kA, 280kA and 320kA modern prebaked cells. The technological improvement and transformation centering on energy conservation, production increase, and environmental protection standards has promoted the conversion of self-baked cell production technology into pre-baked cells and has achieved great success.
According to the electrolytic aluminum production process, the production cost of electrolytic aluminum is roughly composed of the following parts:
(1) Raw materials: Alumina, cryolite, aluminum fluoride, additives (calcium fluoride, magnesium fluoride, etc.), anode materials;
(2) Energy costs: electricity (DC and AC), fuel oil;
(3) Labor costs: wages and other administrative expenses;
(4) Other expenses: equipment loss and depreciation, financial expenses, transportation costs, taxes, etc.
Process flow
Aluminum electrolysis process: The modern aluminum industry uses cryolite-alumina molten salt electrolysis. Molten cryolite is a solvent, alumina as a solute, carbon body as an anode, and aluminum as a cathode. After a strong direct current is passed, an electrochemical reaction is performed at two poles in the electrolytic cell at 950°C-970°C. Electrolysis. The chemical reaction is mainly performed by this equation: 2Al2O3+3C==4Al+3CO2. Anode: 2O2ˉ+C-4eˉ=CO2↑ Cathode: Al3+3eˉ=Al. Anode products are mainly carbon dioxide and carbon monoxide gas, which contains a certain amount of harmful gases such as hydrogen fluoride and solid dust. In order to protect the environment and human health, it is necessary to purify the anode gas, remove harmful gases and dust, and discharge it into the atmosphere. The cathode product is aluminum liquid. Aluminum liquid is pumped out from the tank by vacuum lifting and sent to the foundry. After being purified and clarified in the holding furnace, it is cast into aluminum ingots or directly processed into wire blanks and profiles.
The production process is as follows:
Alumina Fluoride Salt Carbon Anode DC
↓ ↓ ↓ ↓↓
Exhaust anode gas ------ electrolytic tank
↑ ↓ ↓
Exhaust gas ↠gas purification liquid aluminum
↓ ↓
Recovery fluoride purification and clarification
↓ ↓ ↓
Return to electrolytic tank
Casting rolling or casting
↓ ↓
Aluminum ingots or profiles
equation:
Electrolytic aluminum is aluminum obtained by electrolysis.
Important through this equation: 2Al2O3+3C-powered→4Al+3CO2.
Anode: 2O2ˉ+C-4eˉ=CO2↑
Cathode: Al3+ +3eˉ=Al
Newer technology
Electrolytic aluminum energy-saving new technologies come out, the industry saves 27.5 billion kWh annually.
On March 17, 2012, China's electrolytic aluminum industry made new breakthroughs in energy conservation and emission reduction. “Low-temperature low-voltage aluminum electrolysis new technology†passed the acceptance of the National Ministry of Science and Technology at Zhongfu Industry Linfeng Aluminum Power Company on that day. The year of 13235 degrees has been reduced to 11,819 degrees, a drop of 10.7%, and a number of technologies have reached internationally advanced levels. If the whole industry is promoted, China's electrolytic aluminum industry can achieve annual electricity savings of 27.5 billion kwh.
After more than 30 years of development, the electrolytic aluminum industry has gradually become an important basic industry in China. However, due to the high power consumption in the production process, it has always been called the “high energy-consuming industry†and is also one of the industries that the country has regulated. The research and development of low-temperature and low-voltage new technologies is the development direction of energy saving and consumption reduction in the electrolytic aluminum industry, and it is also a major technical problem faced by the world aluminum industry.
In 2009, "low-temperature low-voltage aluminum electrolysis new technology" was included in the National Science and Technology Support Program. The project leader Liang Xuemin and other project team experts persistently worked hard to develop the world’s first successful electromagnetic and magnetic fluid stabilization technologies, low-temperature and low-voltage electrolytic cell structures, and low-temperature and low-voltage process operation technologies, and were pioneered by Zhongfu Industry Linfeng Aluminum Power Company. The more advantageous 400KA “static flow†aluminum electrolytic cell achieves high-efficiency, low-voltage, long-term, high-cycle, stable operation under large-scale industrial production and a series of high current densities.
According to reports, according to the estimated 2012 domestic electrolytic aluminum production of 20 million tons, after the promotion of this technology in the entire industry, China's electrolytic aluminum industry can achieve annual electricity savings of 27.5 billion kwh, equivalent to electricity consumption in Henan Province in 2011 265.9 billion kilowatts More than 10% of the time, according to the calculation of 0.53 yuan per kilowatt-hour, directly creating economic benefits of 14.575 billion yuan, equivalent to 8.8 million tons of standard coal, while reducing carbon dioxide and other greenhouse gas emissions of 15.66 million tons, will promote the aluminum industry and China's energy reduction Rows of work play a good role model.
Industrial characteristics
All aluminum in the world is produced by electrolysis. The production of aluminum electrolysis adopts Hall-Elu cryolite-aluminum salt molten salt electrolysis method, that is, the fluoride salt mainly composed of cryolite is used as the flux, and the alumina is the multiphase electrolyte system composed of the solute. The Na2AlF6-Al2O3 binary system and the Na3AlF6-AlF3-Al2O3 ternary system are the basis of industrial electrolytes. The electrolytic aluminum industry has a greater impact on the environment and belongs to the high energy-consuming and highly polluting industries. The exhaust gas emitted from the production of electrolytic aluminum is mainly CO2, and gas-solid fluoride such as HF gas. CO2 is a greenhouse gas and is the main cause of global warming. The effect of CF4 and C2F6 in fluorides is 6500-10000 times that of carbon dioxide, and it will affect the ozone layer to varying degrees. HF is a highly toxic gas that enters the body through the skin or respiratory tract and can be killed by only 1.5g.
There is a problem
The actual operation index is poor. Due to the short development time, the deep development of China's large-scale aluminum electrolytic cells in the production field is obviously insufficient, resulting in a large gap between the production indicators of actual operational indicators and the international advanced level. Most of them are operated under large-load and small-grid power grids, and there are many hidden safety hazards. Aluminium electricity and joint ventures are one of the trends in the development of electrolytic aluminum companies in China, but at the same time there are also technical problems. Due to the large scale of large-capacity electrolyzers (a series of production capacities of up to 200,000 tons or more), huge electricity loads are concentrated on one production series (generally more than 400,000 KW), and any fluctuations in electrolysis series production will result. The greater impact of the power grid or captive power plant may even threaten the safety of the power supply.
The lack of a "fine design" technique based on a thorough grasp of the mechanism and laws of cathode damage and a comprehensive technical measure to increase the service life of the cell makes it difficult for the electrolytic cell to reach the design life and the early breakage rate is high. Problems affecting the life of large troughs in China In addition to the quality of cathode carbon materials commonly considered in China, there are some problems in the design of electrolyzers, furnace construction materials, furnace quality, roasting start-up, normal production operations, and production management. . The underlying reason for these problems is that China still lacks an in-depth grasp of the mechanism and laws of aluminum cell damage (often referred to as cathodic failure) and the "fine design" techniques and integrated technical measures to improve the life of the cells. With the continuous expansion of the capacity of the electrolytic cell, the problem of the service life of the cell becomes even more pronounced.
Lack of advanced production and operation techniques, high operating costs. China's 300KA grade super large-scale pre-baked aluminum electrolytic cell has been put into industrial application for a short time. The previous experience in large prebaked tanks cannot be fully replicated (these experiences are also very limited). The problem of unequal current distribution during the roasting start-up process is more prominent and the energy consumption during the roasting start-up process is large; the physical field (electric field, magnetic field, flow field) of the electrolysis cell after the operation is apt to fluctuate, and it is difficult to maintain the heat balance; the slot resistance electrode It is susceptible to external disturbances and fluctuates. It is difficult to extinguish after the anode effect occurs. Due to the large inertia of the electrolytic cell, it is difficult to quickly return to normal if the fluctuation of the tank condition or abnormality of the slot condition occurs. As far as the overall production status of China's electrolytic aluminum is concerned, the comprehensive utilization efficiency of energy is about 15% lower than the international advanced level. The main manifestation is: current efficiency differs by 2-3 percentage points; the difference between tons of aluminum power consumption is 300-800Kwh; anode for electrolytic aluminum The energy consumption of the production process differs by about 3Gj/t; the anode consumption of the electrolytic aluminum differs by 30-60Kg (equivalent to about 75-150Kg of standard coal); the service life of the electric tank differs by about 1000 days; the anode effect coefficient is advanced internationally by 0.1 times per day. China's better level is around 0.3 times per day.
Overcapacity
Since the electrolytic aluminum industry in China began in 2002, the production of electrolytic aluminum began to be surplus. Affected by the declining demand from downstream industries, China’s electrolytic aluminum surplus in 2008 is expected to reach 500,000 tons. Demand for electrolytic aluminum slowed down. Affected by the economic crisis, demand from real estate and automotive industries fell sharply. Demand from the power equipment industry continued to grow rapidly. The demand for electrolytic aluminum in the packaging industry remained stable. 2008 The demand for electrolytic aluminum grows at around 10%. China's bauxite resources are scarce and aluminum resources can only be maintained for another 10 years. It is no longer possible to support an average annual expansion rate of about 20% in the electrolytic aluminum industry. The production cost of electrolytic aluminum is between 15,000 yuan/ton and 17,500 yuan/ton, while the price of electrolytic aluminum is only 13,400 yuan/ton, and the industry suffers serious losses. As raw materials fell further, the average production cost of China's electrolytic aluminum enterprises was also around 15,000 yuan, so the possibility of a sharp drop in aluminum prices was very small. Around June 2009, aluminum prices may return to 15,000 yuan/ton.
As energy prices continue to rise, the world's major aluminum companies have begun to ensure the price competitiveness of aluminum production by reducing the cost of all aspects of electrolytic aluminum production. From the perspective of domestic policy analysis, the national industrial policy is to position the aluminum industry to meet domestic demand, and there will be differences in the policies for high-precision products and low-tech products. Therefore, it is the main direction for the development of the current aluminum company to grasp the development trend of transportation, electricity, packaging, home appliances and other industries, and actively introduce advanced equipment, improve technical capabilities and reduce production costs.
How to further resolve the excess capacity of electrolytic aluminum
On the basis of the "Guiding Opinions of the State Council on Resolving the Contradiction of Serious Overcapacity," which has just been promulgated, hereinafter referred to as the "Guiding Opinion," the China Industry Insight Network researcher believes that policy enforcement and support should be strengthened to further pressure supply and demand, and to improve supply and demand. Policy, efforts to resolve electrolytic aluminum excess capacity. Here are some specific suggestions.
On the supply side, it is recommended that multiple measures should be adopted to strictly reduce the electrolytic aluminum production capacity. In particular, the reform of electricity price should be accelerated and the impulse of rapid expansion of production capacity should be dispelled.
First, it is necessary to strictly implement the "Guiding Opinions," and "prohibit the construction of new capacity projects," "classify and properly handle illegal projects under construction," "clean up and rectify built-up illegal production capacity," and "eliminate and retire backward production capacity." The construction of production capacity will receive fines to establish the elimination of outdated production capacity funds, and a concrete supportive policy will be issued in respect of the phase-out of production capacity and withdrawal of financial subsidy, enterprise conversion, and employee placement.
Secondly, it effectively eliminates policy obstacles, implements "integration of batches", and promotes mergers and reorganizations of enterprises. Specifically, it proposes to promote mergers and acquisitions of electrolytic aluminum in the "Implementation Plan for Merger and Acquisition, Reorganization, and Auditing of Road System" of the China Securities Regulatory Commission. Key industries entered the rapid exemption/quick auditing channel to further study and reduce the cost of mergers and reorganizations of listed companies in the industry; it is recommended to adjust the electricity policy and allow existing power companies constructed or absorbed by leading companies to provide low-cost electricity for their electrolytic aluminum production. Supply; It is recommended to increase financial support, taxation, and other aspects, encourage leading companies to take the integration as the main body, and effectively promote cross-regional, cross-industry, cross-ownership corporate restructuring.
Third, balance the regional electricity prices, accelerate the reform of the power system, and eliminate the expected profits. Although in the long run, high-energy-consuming industries such as electrolytic aluminum have a large-scale transfer to energy-rich western regions such as Xinjiang, there is a need for a gradual process of full transfer of production capacity between regions in the short to medium term. As far as transport capacity and resources and environment are concerned, the capacity expansion caused by the preferential electricity prices in the western regions such as Xinjiang should not be accelerated by leaps and bounds. Therefore, it is recommended that measures be taken to balance the regional electricity prices and accelerate the reform of the national grid system. For example, it could be piloted in the national electrolytic aluminum industry, unified the service charge for on-grid interconnection to 1 penny to 3 cents nationwide, or allow the construction industry to be located in various regions. The regional transmission network eliminates the inequality of electricity prices caused by policy reasons, and eliminates the expectation that related companies will obtain excess profits in western regions such as Xinjiang, thus curbing the impulse of investment in production capacity and enabling companies to voluntarily stop building new production capacity.
On the demand side, based on the current reality of weak external demand and the upgrading of trade frictions, it is recommended that domestic demand for aluminum be increased by means of purchasing and storage, widening the scope of application, effectively "digesting a batch", and raising the level of aluminum processing through technological innovation. For higher income. The first is to appropriately increase the country's reserves of aluminum. The country’s expansion of its storage and storage scale as the current aluminum price hits a new low in two years is not only conducive to digesting part of production capacity, promoting the maintenance and appreciation of assets, but also establishing market confidence. The second is to increase research and development and taxation support, and actively expand the application of aluminum. Third, we must actively work through technological research and innovation to improve the level of aluminum processing in China to obtain higher returns.
Supply and demand situation
The global output of electrolytic aluminum has grown steadily, and the power to increase production still comes from China. In 2005, the world output of electrolytic aluminum was 31.91 million tons, an increase of 6.45% year-on-year, of which China's output was 7.67 million tons, a year-on-year increase of 15.07%. In 2006, the global output of electrolytic aluminum reached 33.8 million tons. In June 2006, the global average daily output (excluding China) was 82,200 tons, which was an increase of 700 tons compared with the average daily output in May, which was a 0.09% increase from the previous period. In June, the domestic output of electrolytic aluminum was 780,300 tons, and the average daily output of electrolytic aluminum production was 26,000 tons, which was an increase of 1975 tons compared with the average daily output in May, which was an increase of 7.59%. China is still the main driving force behind the global increase in electrolytic aluminum production. Because China’s output accounts for a global share of 24.9%, the change in China’s output has played a decisive role in the global supply of electrolytic aluminum. The development status of China's electrolytic aluminum industry has determined that China's domestic electrolytic aluminum supply has been relatively abundant. In 2005, the average electrolytic aluminum production capacity was 10.7 million tons, and the capacity utilization rate was 75%. From the domestic data in June, China’s production capacity has been released to some extent. . China has built 11 electrolytic aluminum projects with a total capacity of 1.12 million tons. There are still 10 proposed electrolytic aluminum projects with a total capacity of 1.4 million tons. In 2006, electrolytic aluminum production capacity reached 11.6 million tons, and in 2007 it reached 12.5 million tons. The electrolytic aluminum construction process is simple. The technical content is low. The construction period is short and there are sufficient capital inputs. It takes only 9 months from start of construction to completion and production.
The alumina production capacity of the electrolytic aluminum upstream industry rapidly expanded, and the industrial chain extended to the electrolytic aluminum industry, becoming the main driving force for the growth of electrolytic aluminum production capacity. The stage of growth and development of the electrolytic aluminum industry determines that production growth is the main tone, electrolytic aluminum companies compete, mergers and acquisitions, and continuous expansion, the increase in industry concentration, will also promote the growth of production capacity. The aluminum consumer, the purchaser of the electrolytic aluminum industry, is rapidly developing the economy in China. In the process of urbanization in China, consumer products such as infrastructure, public utilities, housing, and automobiles have greatly stimulated the demand for electrolytic aluminum in China. The electrolytic aluminum industry is in a period of high-speed development and the industry has survived the survival of the fittest and the industry has become more concentrated. From 2003 to 2005, the total output of electrolytic aluminum increased from 5.54 million tons to 7.67 million tons, and the output increased by 2.13 million tons, of which only China's top ten electrolytic aluminum plants achieved an increase of 910,000 tons. The number of manufacturers decreased from 141 to 95. The average production scale of individual manufacturers increased from 39,000 tons in 2003 to 80,000 tons in 2005.
industry analysis
From January to November of 2012, the output of primary aluminum in China was 18.15 million tons. The output showed a slight downward trend year-on-year, and the situation of serious overcapacity was eased. By the end of October, the industry had eliminated more than half of the target of 2.7 million tons of backward production capacity.
At this stage, electrolytic aluminum companies should avoid blindly expanding production capacity, transform their existing industrial advantages into profitability, use existing resources, and integrate coal-fired power, smelting, and processing in their original advantages to form a complete industrial chain and scale the company. Bigger, stronger production capacity and refined processing technology have become an important goal of electrolytic aluminum companies.
After more than 60 years of development, the electrolytic aluminum industry in New China has achieved tremendous achievements in all aspects, but it also faces many challenges and problems that must be properly resolved. Otherwise, it will be detrimental to the next step.
Excessive production capacity
As of the end of 2013, China's primary aluminum production capacity has exceeded 32,000 kt/a. This is a rather scary figure. It is necessary to stop the car and it cannot be developed anymore. The car that developed the aluminum electrolysis industry in the country can no longer do so. Reeling the whip, singing the wind song all the way to run wild. It is necessary to develop overseas, to mine bauxite in places where resources and energy are relatively abundant, to extract alumina and to produce aluminum ingots for remelting, to build joint ventures or wholly-owned enterprises, and to ship the obtained products back to China. The amount of aluminum and aluminum products that are destined for exports by 2020 is processed in imported remelted aluminum ingots instead of being processed using imported aluminum resources (bauxite, alumina, aluminum scrap). By 2030, about 50% of the remelting aluminum ingots for domestic apparent consumption will be imported. The ideas for the development of the original aluminum electrolysis industry in Japan, South Korea, and China's Taiwan region are worth learning from. The practices of some countries in the United States and Europe can also be studied.
Going out to develop aluminum resources is risky. In some places, the risk is still very high. It may be necessary to “pay a certain amount of tuition feesâ€. The payment of tuition fees may be unavoidable. At present, Japan and other countries have all shut down domestic primary aluminum production. Japan also maintains a Puyuan Aluminum Plant with a production capacity of 15 kt/a. This plant uses electricity from a small hydropower station in Mt. Fuji, and the power station is built on an aluminum plant. The aluminum plant will then extract high-purity aluminum by segregation to reduce the pollution to the environment. Moreover, in the past 30 years, the production of primary aluminum in the industrialized countries such as the United States, Germany, etc. has been reduced. The large aluminum company The output of primary aluminum in the country has declined somewhat, while the output of enterprises abroad has risen by more than 35%.
In 2013, per capita aluminum consumption (7 billion people, raw aluminum consumption 51,400 kt) was 7.34 kg/person, and per capita aluminum consumption in China (1.35 billion people, raw aluminum consumption 25,500 kt) was 18.89 kg/person. It has exceeded the average world consumption by 2.57 times, and it is close to 21.4 kg/person in industrialized countries. Our main task now is to improve the quality of raw material consumption and do as much as possible with as little raw material consumption as possible. The domestic scale will not be expanded any more, and measures such as “decrease by the east and increase by fire†may be adopted.
Technical challenges
Although the slot capacity of some electrolytic aluminum plants in China has surpassed or exceeded the comparatively advantageous level, the technical and economic indicators of the same type of trough are still relatively backward compared with the advanced level in foreign countries.
At present, the anode effect coefficient of electrolytic cells in China's electrolytic aluminum plants is relatively high; the aluminum ton electricity consumption is higher than that of Europe's leading level; the average cell lifetime is generally shorter; the current level of foreign leading current efficiency has reached 96%, while in China more than 75%. The current efficiency of the company is only 92.5%-93.5%, and there are quite a few plants whose calculation of rectifier efficiency is low; under the same power consumption conditions, the anode current density of the Chinese electrolytic cell is designed to be only 0.7-0.735 A/cm2. This means that the equivalent unit area electrolytic cell production is low, therefore, in the period to come, a major task of China's aluminum electrolysis is to greatly increase the electrolytic cell per unit area of ​​production.
China's current development of electrolytic aluminum industry also has many advantages, such as low investment in electrolytic aluminum plant unit products, about 1/3 of industrial developed countries; low labor costs, is 1/5-1/ corresponding labor costs in the primary aluminum costs of industrial countries. 4; The environmental protection requirements are relatively low, so investment in environmental protection facilities is also low. This is not the case. Now it is time to increase environmental protection investment. Thousands of provinces and provinces, can not save environmental protection, should improve the environmental protection standards, and those who do not meet the standard, should be shut down, environmental protection standards should become high-voltage lines.
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