gas purification device from dust

When they talk aboutgas purification device from dust, many immediately imagine a standard cyclone or bag filter. But in reality, especially at mining and processing plants, everything often comes down to details that are not written in catalogs. For example, the abrasiveness of dust or its tendency to caking. This is what we have to constantly struggle with.

The main types of devices and where they stumble

Cyclones, of course, are classics. Cheap, reliable, for initial rough cleaning - just what you need. But I have seen more than one installation where they were installed at the final stage for fine dust, and then they wondered why the emission standards were not met. It is important to understand here: the cyclone works well on fractions larger than 10-15 microns. If it’s smaller, the efficiency drops catastrophically.

Electrostatic precipitators are a powerful tool. But their capriciousness is often underestimated. Gas humidity, temperature, chemical composition of dust - everything affects corona and deposition efficiency. I remember an incident at one of the processing plants: they installed an electric precipitator after the drying drum, but did not take into account the periodic emissions of waterlogged material. The result is constant sticking of the electrodes, frequent shutdowns and downtime.

Bag filters, in my opinion, are now one of the most flexible options for fine cleaning. But even here there are plenty of pitfalls. Sleeve material is a science in itself. Polyester, PTFE, fiberglass - the choice depends not only on temperature, but also on chemical resistance. There was a story when, due to acid vapors in gas, ordinary polyester hoses became unusable over the course of a season, although everything was ok in terms of temperature.

Experience with magnetic separators and dust collection

In the context of mining equipment, I would like to touch on a topic that is not always immediately associated with gas cleaning. When it comes to processing iron ores, the dust is often magnetic. This can be used. CompanyLONGI Corporation, for example, is known for its magnetic separators. And here’s what’s interesting: in some aspiration schemes at the exit from crushers or screens, we tried installing low-current magnetic traps in the air ducts in front of the main filter. The idea was to pre-screen out the magnetic fraction, reducing the load on the maingas purification apparatus. This slightly increased the complexity of the system, but extended the service life of the hoses in areas with high dust levels.

By the way, aboutLONGI Corporation. They are based in Fushun and their experience in developing mining equipment since 1993 speaks volumes. On their websiteljmagnet.ruyou can see that the scale of production is serious - 4000 units of equipment per year. This is not a artisanal workshop. And when such an enterprise designs a production line, the issues of aspiration and dust collection are laid down at the design stage, and are not resolved after the fact, when everything is already standing and gathering dust. This is the right approach.

Returning to magnetic dust separation. Not everything is so smooth. The main problem is precisely the organization of the flow. In order for the particle to react to the magnetic field, the gas velocity in the air duct must be sufficiently low, and this leads to an increase in the cross-section of the duct. This is not always possible in the context of reconstruction of existing workshops. More often, this technique works on new objects, where everything is calculated from scratch.

Practical nuances of operation

Any, even the most advanced device, will run into operational issues. The most common one is access for maintenance. How many times have I seen filters pressed close to a wall or ceiling, where the hatch for replacing the hoses cannot be approached without an autogen. Designers, be human!

The regeneration system in bag filters is the heart of the device. Pulsing with compressed air seems simple, but timing and pressure are important. Too frequent pulses - excessive air consumption and fabric wear. Too rare - increased resistance, fan overload. Setting up is often done by trial and error right on the spot, for specific dust. There are no universal recipes.

Another point is the removal of captured dust from the bunker. It seems that an auger or rotary valve will solve everything. But if the dust is hygroscopic or tends to arch, it forms arches in the bunker. You have to install vibrators or aeration grilles. And these are additional points of potential air leakage, which disrupts the operation of the suction system.

When theory diverges from practice: a case of abrasive dust

I want to share one unsuccessful but instructive experience. There was an object - crushing quartzite. The dust is abrasive, like sandpaper. According to calculations, a bag filter with pulse regeneration was ideal for the required degree of purification. We selected sleeves from a material with increased wear resistance. Launched. Three months later - a sharp increase in pressure drop. They opened it up - the inner surface of the sleeves in the upper part, where the compressed air pulse hits, was badly worn out. It turned out that the regeneration itself, with a sharp blow of air, causes dust particles to move intensively inside the sleeve, causing abrasive wear of the fibers. For such dust, a system with reverse blowing and less local load on the fabric, or pre-cooling and humidification of the gas to reduce abrasiveness, would be better suited. I had to redo it.

This case shows well that the choicegas purification apparatus- these are not only tables and graphs of efficiency. This is an understanding of the physics of the process and the dynamic behavior of specific dust. Laboratory dust samples are good, but they do not always reflect its behavior in a real, continuously operating unit.

After this incident, when working with abrasive materials, we always provide an additional margin for filtration speed and insist on testing the hose material on a stand with real customer dust, if the scope of the project allows. This is more expensive at the start, but saves you from multimillion-dollar losses on repairs and downtime later.

Integration into process technology and economics

Gas cleaning is not a separate story. This is part of the technological chain. The efficiency of the device directly depends on the stability of the previous equipment. If there is a crusher in front of the filter, which produces periodic bursts of dust during loading, the filter should be designed for this peak load, and not for the average one. Otherwise, he will constantly “choke”.

Nowadays there is a lot of talk about energy efficiency. And here there is room for optimization. For example, installing frequency converters on fans of an aspiration system. They allow you to adjust the performance to the actual operating mode of the main equipment, rather than constantly driving air at full power. The energy savings are significant, and the payback period for a frequency generator can be less than two years at a large facility.

In conclusion, I will say that there is no ideal device for all cases. Each projectcleaning gases from dustis a search for a balance between efficiency, reliability, cost and ease of use. And this balance is not found in catalogues, but in production, in dialogue with technologists and repairmen who will live with this system. The main thing is not to consider the dust collection system as an annoying expense, but as an integral part of the technological process, on which the environment, human health, and, ultimately, the uninterrupted operation of the entire production depend.