Can handling process
The world recycled aluminum industry is an integral part of the world aluminum industry, an indispensable resource for the sustainable development of the world aluminum industry, and an industry with great market potential and development prospects. Recycled aluminum has the advantages that electrolytic aluminum does not have. It saves 95% of energy per ton of recycled aluminum compared to electrolytic aluminum per ton. CO2 and harmful emissions are greatly reduced, which is conducive to environmental protection.
As an important part of recycled aluminum recycling, cans are complex components and difficult to recycle, and they are always the short boards in the waste aluminum recycling industry in China. Although the recycling rate of China's cans is relatively high, compared with other developed countries' recovery technologies, China's recycling technology is extremely backward. It shows that the recovery rate of smelting is low (only 80%-90%), and the technology of recycling equipment The level of low pollution is serious (mainly still furnace-based), which has virtually caused an extremely wasteful use of resources in our country.
This article makes a preliminary discussion on the recycling process and equipment of cans. The components of the cans are relatively complex due to the composition of the waste cans. In addition to the impurities contained in the cans, the composition of the cans is mainly composed of three kinds of aluminum alloys. The can and tank bottom of the cans are 3004 aluminum alloy. The can cover is 5182 aluminum alloy and the pull ring is 5042 aluminum alloy. The composition and content are shown in Table 1.
Table 1: Ingredients of cans
Components of each part Si Fe Cu Mn Mg Cr Zn Ti 3004 barrel, bottom 0.3 0.7 0.25 1.0-1.5 0.8-1.3 0.25 / 5182 Cover 0.2 0.35 0.15 1.2-1.5 4.0-5.0 0.1 0.25 / 5042 Pull ring 0.2 0.15 0.15 0.2-0.5 3.0 -4.0 0.1 0.25 0.1
Second, processing technology analysis and existing problems The ideal treatment method for waste cans is to separate the can body from the lid and pull ring, and then to conduct melting separately to produce the original brand of alloy.
However, due to various reasons, the recovered waste cans have been damaged and some of them have been squeezed and packed. Therefore, it is difficult to separate the body, lid, and ring from the waste cans shipped to the factory. At present, the internationally accepted method is not to separate and directly produce 3004 aluminum alloy. At present, the following problems exist in the production of 3004 aluminum alloys from the use of waste cans: the texture of the waste cans is thin, and the surface area is large. During the smelting process, the oxidized burns are serious and the metal recovery rate is low.
2. There is a lacquer layer on the surface of the waste cans, which has a certain influence on the quality of the aluminum alloy, and it is prone to pollution during the recycling process;
3. The shape of the waste cans is damaged. Some of them have been packaged into pieces and are difficult to separate. Pretreatment is difficult.
4. After the mixing of waste cans, the complexity of the composition adjustment becomes more difficult. Third, the process for the above technical problems, and now the international advanced technology using crushing, preheating treatment stripping, mixed smelting method, compared to the end product is the production of cans of 3004 aluminum alloy tank. The core equipment is the use of a dual-chamber side-well melting furnace, which greatly reduces burn-in during melting and increases productivity.
The process flow for the production of 3004 aluminum alloys from waste cans is as follows: The crushing of waste cans - The removal of iron by magnetic separation - The carbonization of rotary kiln paint - Vibration decarburization of rotating screens - Melting of dual chamber reverberatory furnaces - Removal of impurities Magnesium - adjusting components - refinement refining degassing - filtration - ingot casting process description:
1. Crushing: The form of the recovered cans has been destroyed. Some imported waste cans have been packaged into pieces. Therefore, they must be broken before removing the paint.
2. Paint stripping and drying: Loose waste cans (including crushing waste cans) can be stripped directly into the paint stripping kiln. The stripping paint is treated with a rotary paint stripping kiln. At the beginning, a certain amount of heat energy needs to be added. After reaching a certain temperature, the heat energy mainly depends on the exothermic heat of the paint carbonization process on the surface of the can. In a rotary paint strip kiln, the paint layer of the can is charred, and the paint peels off due to its own vibration during the rotation process. In this process, the moisture in the can is also dried, eliminating the possibility of reaction between water and aluminum in the remelting process, and the safety of production is guaranteed. The temperature of the rotary kiln is controlled at about 500°C.
3, rotary vibration decarburization: after drying carbonized cans on the fragments can also paint carbon particles after strong agitation, after shaking sieved so that all the carbon particles off the separation.
4. Smelting: The pretreated waste cans enter the smelting furnace for smelting. There are many kinds of regenerated aluminum melting furnaces, and the use of advanced double-chamber reverberatory furnaces is currently internationally preferred. The dual-chamber reverberatory furnace is divided into inner and outer chambers (side wells). The molten aluminum liquid is heated in the inner chamber (heating chamber), pumped into the outer chamber (side wells) by the aluminum liquid pump, and forms a downward aluminum suction in the side wells. The water whirlpool, cans of pieces of cans quickly absorbed into the aluminum liquid by the vortex, the debris is melted in the molten aluminum, and the molten aluminum water is then heated in the inner chamber. The cycle depends on a special aluminum liquid pump. Because the aluminum scrap is not in direct contact with the flame, it is directly added to the molten aluminum liquid, avoiding the burning of the scrap aluminum and increasing the metal recovery rate. The core technology of the dual-chamber furnace is the manufacturing technology of aluminum liquid pumps and side wells. Zhejiang Shengzhou Rongsheng Metallurgical Equipment Co., Ltd. is one of the few companies in the world that has this technology and is the promotion of domestic double-chamber reverberatory furnaces in China. The application provides technical assurance. The major characteristics of this type of smelting furnace are high metal recovery rate, which can reach over 97%; high thermal efficiency, low energy consumption, energy consumption can be reduced to 30Kg/T fuel consumption;
5. Melting process: After the waste cans are melted, after the slag is removed, the comparison of the obtained components and the 3004 alloy of the production tank is as follows: Item name Si Fe Cu Mn Mg Cr Zn Ti 3004 Tank 0.3 0.7 0.25 1.0-1.5 0.8 -1.3 0.25 / / Mixing 0.14 0.16 0.16 1-1.2 1.64 / / / From the table, silicon, iron, copper, manganese and other alloy components are all lower than the standard and need to be supplemented, in which silicon is directly added to industrial silicon, Other alloy components that need to be added are added as alloys. The content of magnesium in the melt exceeds the standard and it is necessary to control the operating conditions and add the scouring agent in addition to magnesium to allow the magnesium to enter the dross.
6, grain refinement: In order to ensure that the standard aluminum alloy ingot, in the smelting stage, grain refinement, add grain refiner. At present, there are several good effects of refiners. This process is intended to use two kinds, one is Al-Tl-B, and the other is rare earth refiner.
7, degassing: degassing is mainly to remove the hydrogen and sodium, calcium and other molten aluminum liquid. This process plans to use nitrogen or argon as a degasifier. The degasifier forms fine bubbles in the molten aluminum liquid. The bubbles come into contact with the aluminum liquid and absorb the surrounding hydrogen and oxides of calcium, sodium, etc., and then flow over the aluminum liquid.
8. Filtration: Since the aluminum liquid contains impurities, it is necessary to use a filter box composed of a ceramic filter plate to filter and remove impurities from the aluminum water to achieve the purpose of purifying the aluminum liquid.
9. Ingot casting: Using advanced semi-continuous ingot casting machine, aluminum water is solidified into aluminum ingots and made into products. The above-mentioned processes and technologies have been industrially tested. The experimental results show that the net aluminum recovery rate reaches 97% and the composition reaches the standard of 3004 aluminum alloy. IV. Environmental protection issues in production The main pollutants in this process are fumes from the rotary kiln, fumes from the smelting furnace, and scum of molten aluminum. In view of the characteristics of pollutants, this process adopts two dust collections for smoke and dust, and a cyclone type dust collector on the front to recover most of the smoke and dust. The second channel adopts spray technology, in a special spray tower, smoke and dust Due to the fact that acidic substances may be present in the added scouring agent, a weak alkaline spray is used and the waste water is recycled after treatment. After the scum generated in the smelting process is treated by the rotary kiln, aluminum is further recovered. The main components of the waste slag are oxides of alumina, calcium, and magnesium. Since the main component is an aluminum compound, the waste water is purified. Therefore, there is no pollution to the environment.
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