Types and functions of dust removal systems in the recycled aluminum industry

Types and functions of dust removal systems in the recycled aluminum industry

Types and functions of dust removal systems in the recycled aluminum industry

As resource shortages and environmental pollution become more and more serious, scrap aluminum recycling and melting have gradually become an important environmentally friendly process to replace traditional melting.

In this process, scrap aluminum is converted into reusable aluminum, but at the same time, a large amount of pollutants, including harmful gases such as sulfides, are also produced.

In order to reduce environmental pollution and protect the health of employees, the use of flue gas desulfurization and dust removal equipment is essential.

The dust removal systems in the recycled aluminum industry mainly include the following categories and working principles:

1. Cyclone dust collector

Working principle:

Dust-containing gas enters the cyclone dust collector along the tangential direction, forming a high-speed rotating airflow in the cylinder.

Due to the different masses of dust particles and gas, the dust particles are thrown to the wall of the device under the action of centrifugal force, and then fall into the dust hopper along the wall under the action of gravity, while the purified gas is discharged from the central exhaust pipe at the top of the cyclone dust collector.

This dust collector has a simple structure and is easy to operate.

It can handle high-temperature and high-concentration dust-containing gases and is often used for the preliminary separation of coarse dust particles during aluminum melting and casting.

2. Baghouse dust collector

Working principle:

The dusty gas enters the air inlet of the bag filter and passes through the filter bag.

The filter bag is made of a variety of materials, such as polyester fibers, and the gaps between the fibers allow gas to pass through, but block dust.

The dust is trapped on the surface of the filter bag, and over time, a layer of dust forms on the surface of the filter bag.

When the dust accumulates to a certain extent, the filter bag is shaken by a pulse spray system (using compressed air to spray the filter bag in a very short time) or mechanical vibration, and the dust is shaken off into the dust hopper, so that the filter bag is regenerated, and the purified gas is discharged through the air outlet.

The dust removal efficiency of the baghouse dust collector is very high, and it can effectively remove fine dust, playing an important role in aluminum melting.

3. Electrostatic dust collector

Working principle:

In an electrostatic dust collector, the dusty gas enters the electrostatic dust collector and passes through a high-voltage electric field.

The discharge electrode (cathode) releases a large amount of electrons, causing the dust particles to carry a negative charge.

The charged dust particles move toward the dust collecting electrode (anode) under the action of the electric field force.

After reaching the dust collecting electrode, the dust particles lose their charge and deposit on the electrode plate.

The electrode plate is vibrated by a regular vibration device, and the deposited dust falls into the dust hopper for collection.

The purified gas is discharged from the outlet.

The electrostatic dust collector can handle large volumes of dusty gas, and has a high efficiency in capturing fine dust.

The functions and principles of the dust removal system in the recycled aluminum industry are as follows:

1. Desulfurization

Function: Remove sulfur dioxide from exhaust gas, reduce acid rain formation and environmental damage.

Working principle: The most common method is limestone-gypsum method.

Using limestone (calcium carbonate) slurry as absorbent, sulfur dioxide reacts with calcium carbonate in the slurry in the absorption tower to generate calcium sulfite, which is further oxidized to calcium sulfate (gypsum) under the action of oxidizing air.

The product is discharged through the gypsum discharge system to achieve the purpose of desulfurization.

2. Denitrification

Function: Reduce the content of nitrogen oxides (NOx) in exhaust gas and reduce its impact on the atmospheric environment and human health.

Working principle: Selective catalytic reduction (SCR) is widely used.

Under the action of the catalyst, ammonia (urea decomposition can also provide ammonia) is used as a reducing agent to reduce nitrogen oxides into nitrogen and water.

The reaction temperature is usually around 300-400℃, and it is mainly used in high-temperature exhaust gas emission links such as regeneration aluminum melting furnaces, so that the exhaust gas undergoes a denitrification reaction when passing through a reactor equipped with a catalyst.

3. Deacidification

Function: Remove acidic gases such as hydrogen chloride (HCl) and hydrogen fluoride (HF) from waste gas to avoid equipment corrosion and environmental pollution.

Working principle: Adopt the alkali solution absorption method.

Use alkaline solution such as sodium hydroxide (NaOH) or calcium hydroxide (Ca(OH)₂) as absorbent.

When the waste gas contacts the absorption liquid, the acidic gas reacts with the alkali to generate salt and water, thereby achieving deacidification.

4. Remove dioxins

Function: Dioxins are highly toxic organic pollutants, and their removal reduces significant risks to ecosystems and human health.

Working principle: Mainly activated carbon adsorption method.

Activated carbon is sprayed into the flue, and the dioxin is adsorbed in the pore structure of the activated carbon.

The activated carbon particles that adsorb the dioxin are then captured by equipment such as a bag dust collector to remove the dioxin.

5. Dust collector

Function: Reduce dust concentration in the production environment, improve air quality, and reduce dust wear on equipment and harm to operators’ health.

Working principle:

Cyclone dust collector: After the dusty gas enters the cyclone dust collector, it rotates at high speed.

The dust particles are thrown to the wall of the device under the action of centrifugal force, and then fall into the dust hopper along the wall under the action of gravity to achieve the purpose of dust removal.

Baghouse dust collector: The dusty gas passes through the filter bag of the bag dust collector, and the dust is intercepted on the surface by the filter bag.

The gas is discharged through the filter bag, and the accumulated dust is removed by the cleaning system.

Electrostatic dust collector: The dusty gas passes through the high-voltage electric field, and the dust particles move to the electrode and deposit after being charged.

The dust is collected by vibration and other methods to achieve gas purification.