[Aluminum Road Network] China's renewable aluminum industry has developed rapidly in recent years, both in terms of output and production scale, ranking first in reclaimed non-ferrous metals, and it has occupied an important position in China's aluminum industry. However, incongruous with the rapidly developing renewable aluminum industry is the poor environmental awareness of the industry. Environmental protection work is very backward and has seriously affected the development of this area.

As the state attaches great importance to environmental protection work, relevant departments continue to strengthen the management of the recycled aluminum industry environment, and some heavily recyclable aluminum companies will be eliminated. It can be asserted that in the future, the competition in the recycled aluminum industry will be a competition in the environment, and environmental issues will not be solved. Enterprises will be unable to survive. We should have a clear understanding of this.

Judging from the current environmental status of China's regenerated aluminum industrial enterprises, the main pollutant that causes pollution to the environment is exhaust gas. Therefore, this article will introduce the source, main components and processing technology of waste gas from the recycled aluminum industry, and according to the characteristics of China's recycled aluminum industry, recommend a more applicable environmental protection process for the reference of recycled aluminum enterprises in the construction of environmental protection. .

First, the source of smoke pollutants

China's waste aluminum recycling mainly uses pyrometallurgical melting, and the process of generating waste gas and possibly causing environmental impact is mainly smelting. In the smelting process, the main fuels used are coal, coke, heavy oil, diesel oil, coal gas, natural gas, etc. After the fuel is burned, the generated exhaust gas contains a lot of soot and sulfur, carbon, phosphorus and nitrogen oxides and other gases. After the charge (aluminum scrap) is heated, the oil of the waste itself and the combustibles mixed will burn, and a large amount of sulfur, carbon and nitrogen oxides will also be produced.

In the smelting process, a certain amount of covering agents, refining agents and degassing agents are added to react with various impurities in the molten aluminum in order to reduce burn-in, improve aluminum recovery and ensure the quality of the aluminum alloy. Produce a large amount of exhaust gas and smoke, which contain various metal oxides and non-metal oxides, and may also contain harmful substances, which may cause environmental pollution.

Second, the classification and composition of recycled aluminum fumes

1. Classification of waste gas from recycled aluminum industry

According to the regulations of the environmental protection department, the exhaust gas generated by the industrial sector can be divided into two categories: particulate matter-containing exhaust gas and gaseous pollutant-containing exhaust gas. Due to the complexity of raw materials in the recycled aluminum industry, both of the above two types of exhaust gases exist in the production process, both particulate-containing exhaust gas and gaseous pollutant-containing exhaust gas. Therefore, while treating the exhaust gas, we must comprehensively consider dust and harmful substances in the exhaust gas. The effect of gas on the environment.

2. Main components of exhaust gas

Due to different sources of raw materials for the recycled aluminum industry, different types of waste materials and different levels of pollution, different fuels, different additive components, and different smelting technologies, the pollutants in the exhaust gas are different. There can be the following:

(1) Particulate wastes are mainly metal oxides and non-metal oxides produced during the smelting process, such as oxides and chlorides of Mg, Zn, Ca, Al, Fe, Na, Mg, K, and a large amount of carbon. Grain ash, etc., constitute the dust we often talk about.

(2) Main components of gaseous pollutants

The regenerated aluminum industry may have the following gaseous pollutant emissions: CO, CO2, NOX, SO2, HCl, HF, hydrocarbons, and volatile metal oxides or volatile metals, possibly with chlorine, etc. All ingredients are harmful, but most of them will have a great impact on the environment, and some may endanger the lives of workers.

Third, dust governance

The purpose of dust control is to maximize the collection of dust in the flue gas, so that harmful gases can be converted into harmless and stable substances and meet the national emission standards. The management of the environment must first be controlled from the source. For recycled aluminum, it is necessary to strengthen the pretreatment and classification of wastes, make comprehensive use of various wastes as much as possible, and reduce the generation of pollutants; second, try to use pollution-free Additives; third is to improve the smelting technology to reduce the amount of waste generated. The commonly used smoke treatment technology is as follows:

1. Dust collection room

Dust collection chamber is a simple method in flue gas dust collection equipment. The principle is that when the velocity of the fluid suddenly decreases, the particles will settle due to their own gravity. The flue gas produced from recycled aluminum flows in the flue at a certain speed. When the space of the flue gas suddenly increases, the velocity of the air flow also suddenly slows down. As the velocity of the particles decreases, the particles are deposited under the action of their own gravity. There are many kinds of dust chambers.

The simple method is to use bricks. If some baffles are made in the dust chamber, the dust collection effect of the particles can be improved. However, in general, the collection efficiency of the dust collection chamber is not good.

2. Whirlwind Dust Collector

Whirlwind precipitator is a more suitable dust collection setup, lower investment, better effect, and adopted in many enterprises. Cyclone dust collectors can also be called centrifugal dust collectors.

When the gas enters the dust collector in the direction of the tangential line, the air flow will continuously rotate at a high speed in the dust collector in a certain direction. The particles in the gas will generate centrifugal force during high-speed rotation and move around when they collide with the dust collector. On the wall, due to its own gravity, it descends into the dust collection chamber to achieve dust collection. The effect of the cyclone dust collector is obvious, and it is applied in many enterprises that produce dust.

3. Spray dust collector

The principle is to make droplets of a certain solution capture the particles in the gas during the descending process. After the particles are wetted, they will also absorb other particles and be collected due to their own gravity drop to the dust collection chamber.

A number of nozzles are arranged in a cylinder to control the nozzle hole degree, flow rate, pressure and angle, so that the sprayed liquid is misty, the gas rises from the lower end, the particles are trapped, and the spray dust collector is a simple Efforts to collect dust are widely used.

4. Splash Tower

The foaming tower is also a commonly used dust collector. The effect is higher than the above types of dust collectors, but the investment is large and the operation is difficult. The principle is to set a partition in the middle of a cylinder. There are countless holes in the partition. During normal operation, there is a layer of solution on the partition. Gas enters from the lower end of the tower and passes through the partition. In the liquid layer, the dust is trapped by the liquid, and the clean gas is removed from the upper end of the liquid.

When the pressure of the gas equals the pressure generated by the liquid on the partition, the gas-liquid two phases are stationary. When the pressure of the gas is greater than the water pressure, the gas flows through the liquid, but the pressure of the gas and the height of the water layer are designed by calculation. The pressure is too great to achieve the effect of dust collection. In actual production, the surface of the water is boiling.

5. Bag filter

Dry dust collection is mainly bag filter, the principle is to make dust gas through the filter bag, to achieve the effect of dust collection, there are two commonly used:

(1) External system: In the dust collector built a number of baghouses, the surface of the baghouse filter cloth, production, the exhaust gas into the dust collector, the room is negative pressure, dust gas into the dust collector, the particles are adsorbed On the surface of the filter cloth, the purified gas was excluded from the baghouse. After a certain period of operation, the dust on the filter cloth accumulates, and the air permeability deteriorates, which affects the dust collection and exhaust effect. Therefore, the dust must be promptly removed. The method is to start the compressed air, reverse air blow, and after the dust falls off. Enter the dust room.

(2) Internal bag filter: The principle is the same as that of the external system, except that the dusty gas enters the baghouse. The outside of the baghouse is under negative pressure. The gas passes through the filter cloth and the dust accumulates in the baghouse. After a certain period of time, After the vibration, the dust automatically falls off into the dust chamber to achieve the effect of dust removal.

The cost of bag dust collection is relatively high, but a dust remover is currently used. When choosing a bag filter, be sure to pay attention to the temperature of the bag, generally below 250 degrees. In addition to the above equipment, there are more advanced dust collection equipment such as electric dust collection, but due to the high cost, no one company in the recycled aluminum industry has adopted it.

Fourth, gas pollutants waste gas treatment technology

The composition of gaseous pollutants is described above. With regard to the treatment of such exhaust gas, there is currently no corporate governance. The main reason is that there are many types of harmful gases produced by the recycled aluminum industry and it is difficult to handle them separately. However, we can see that these gaseous pollutants still have common characteristics, which is to say that the pollutants in the exhaust gas are mostly acidic, which facilitates the disposal of the exhaust gas. In general, as long as the weak alkaline substance is added, it can be effectively treated. Na2CO3 is generally added to neutralize the discharge.

In the above-mentioned wet dust collection, such as a spray tower, a splash tower, etc., water is generally added. If alkaline substances are added to the water, harmful substances in the exhaust gas can be treated while collecting dust.

The above introduced several commonly used environmental protection equipment, and hope that companies can refer to the construction of environmental protection equipment. At the same time, enterprises must take into account the characteristics of smoke produced by recycled aluminum - not continuous generation of exhaust gas, and intermittent generation of exhaust gas. The bag filter, cyclone dust collector, and spray tower described above are all suitable for the characteristics of the industry.

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