dust cleaning methods

When they talk aboutdust cleaning methods, many people immediately imagine household vacuum cleaners or a rag. In industry, especially in the mining sector, where LONGIE and I have been working for decades, everything is different. The main mistake is to assume that one method is universal. Dust in a processing plant and dust in a machining shop are different enemies and require different approaches to combating them. I often see people trying to use dry mechanical cleaning at sites where aspiration with fine filters has long been needed. The result is constant relapses, equipment suffers, people breathe dirt. Let's sort it out in order, without water, like at the customer's planning meeting.

Mechanical methods: more than just a brush and dustpan

Let's start with the most seemingly simple thing. Mechanical cleaning. It is important to separate here: cleaning up already settled dust and preventing its spread. Vibrating screen systems or jetting methods are often used to remove settled dust from stationary equipment such as the separators or crushers we supply. But personal experience suggests: vibration is good for dry, non-stick dust. If there is even a little moisture in the material (and in a quarry or processing plant this is almost always the case), vibration will only compact the layer and create a crust. We had to deal with this: at one of the mining and processing plants, our magnetic separators were installed, but they ignored the recommendation for dry air blowing of the units. Six months later, maintenance personnel literally chiselled the hardened dust mass. Ineffective and dangerous.

Another aspect is the capture of dust at the moment of its formation. Here mechanical methods are primarily casings, shelters, and side suction. The principle is simple: do not let the dust fly away. But a key detail that is often overlooked in design is the airflow rate of the suction. Too low and dust is not captured, too high and it carries away useful fine-grained material. I remember a project for a quartz processing factory: the customer’s engineers insisted on powerful fans, as a result, up to 3% of the product was lost along with dust. We redesigned the system and adjusted the balance. This is about the question of whatdust cleaning methodsis always a compromise between efficiency and economics of the process.

And one more thing - manual cleaning. Yes, in the 21st century it still exists. But this should be the final method, not the main one. The use of explosion-proof industrial vacuum cleaners (for coal dust, for example) is mandatory. A common sight: workers sweep dust from equipment with ordinary brushes into the atmosphere of the workshop. Everything that was collected is back in the air. This is not cleaning, this is imitation.

Aspiration and filtration: the heart of the system

Let's move on to aspiration. This is the next level. Air duct system, fans, filters. It would seem that everything is transparent. But the devil is in the details. The first is the calculation of the aspiration network. It must be individual for each technological unit. You cannot take one powerful unit for the entire workshop - there will be an overflow at the points closest to the fan, and a lack of exhaust at the points further away. Efficiency drops catastrophically. At LONGI, when designing processing equipment complexes, we always include aspiration calculations for critical components, for example, for places where material is poured or where crusher loading occurs. On the websiteLONGI CorporationYou can see that our production is 140,000 m2 of area, and at such a scale the issues of designing dust removal systems are acute. An error in the design means constant problems in operation.

The second key element is filters. Sleeve, cartridge, electrostatic precipitators. The choice depends on the dispersion of the dust, its chemical activity, and temperature. For hot dust from drying drums, for example, bag filters made of ordinary polyester are not suitable - they sinter. You need fiberglass or special membrane coverings. But for cold stone dust for crushing - ideal. A common mistake is skimping on filters. They buy something cheaper, and then change it three times more often, and the cleaning efficiency is lower. I saw a case where, due to poor-quality bag filters, fine cement dust penetrated into the fan, causing imbalance and vibration. As a result, the entire line was stopped for a week.

And the third point is the disposal of collected dust. The filter is not a grave for dust, it collects it. If a convenient and sealed method for removing sludge is not provided (for example, a screw conveyor or a double-lock discharge system), then a secondary release will occur during filter cleaning (regeneration). All the work is in vain. At our production facilities in Fushun this issue has been worked out to the point of automation, but at many Russian enterprises I visit there are still problems with this.

Wet methods: fogging and scrubbers

Now about the wet onesdust cleaning methods. They are often either demonized (they say, only dirt and corrosion), or, on the contrary, considered a panacea. The truth, as always, is in the middle. Fogging is an excellent method for dust suppression in open areas: in places where bulk materials are reloaded, in warehouses. Principle: creation of a fine water suspension that binds dust particles and precipitates them. But! Water should be supplied in the form of a mist, not large drops. Large drops will not bind fine dust, but will only create wet dirt. The equipment for this is high-pressure nozzles, a water treatment system (so as not to clog).

Scrubbers (wet gas scrubbers) are used for cleaning gas-air emissions. Effective for sticky, fibrous or reactive dust. But the main headache here is the sludge. The result is dirty water that needs to be purified or disposed of. This is a whole additional system. At one of the ferroalloy plants, a scrubber was installed to capture dust from electric furnaces. The dust was caught, but they ended up with tons of sludge with a high content of heavy metals. Disposal turned out to be more expensive than the cleanup itself. We had to revise the technological chain.

And an important note on climate. Wet methods in the Russian winter pose a risk of icing. Supply lines, nozzles themselves, settling tanks. You need either heating or preservation for the winter with a transition to other methods. This is often not taken into account in typical designs designed for milder climates.

Special cases: explosive and toxic dust

A separate issue is explosive dust (coal, flour, sugar). Any heredust cleaning methodsmust be viewed through the lens of explosion protection. Intrinsically safe equipment, emergency pressure relief systems (explosion valves), use of antistatic materials for air ducts. The biggest mistake is to use a regular vacuum cleaner to remove coal dust. The slightest spark and disaster. Only vacuum systems with appropriate certification are needed. In the mining equipment that LONGI develops (more than 4,000 pieces of equipment per year), we always provide suitable aspiration solutions for areas with potentially explosive atmospheres, often in cooperation with specialized companies.

With toxic dust (lead compounds, beryllium, silica) the approach is even tougher. Here the system must be absolutely sealed. The highest class HEPA or ULPA filters are used. And the main thing is control. The system must have constant monitoring of dust content at the filter outlet. No “set it and forget it?”. Filters are changed according to regulations, and often earlier, when efficiency drops. Personnel must be trained and equipped with personal protective equipment even when servicing these systems. Alas, this is a problem at many old enterprises in the post-Soviet space. I saw people changing filters clogged with lead dust without respirators. This is a crime.

And one more nuance for toxic dust is disposal. Such dust cannot simply be thrown into a landfill. It is a hazardous waste. This means that the treatment system must be linked to the system of safe disposal or disposal of waste. This will increase the cost of the project several times, but there is no other way.

Process integration: the key to success

Here we come to, perhaps, the most important thing. Anyone, even the most perfectdust cleaning methodis doomed to failure if it is not integrated into the technological process, but is an “add-on”. Cleaning should be planned at the line design stage, and not installed later, when everything is already working and gathering dust. When designing, you need to take into account: points of dust formation, physical and chemical properties of dust, the required degree of air purification (according to sanitary standards), the possibility of recovering the collected material (sometimes this is a valuable product!).

ExperienceLONGI Corporation, where more than 60% of employees are college-educated engineers and technicians, shows that the most successful projects are those where the Chief Technologist and Environmental Health/Ecology departments work with the Equipment Design department from the very beginning. For example, when creating a new model of a magnetic separator, we immediately simulate the flow of material and air in order to determine the optimal points for connecting aspiration and the type of shelter. This saves the customer a lot of effort and money in the future.

And one last thing. There are no static solutions. Technology changes, raw materials can change characteristics. The cleaning system must have some performance reserve and the possibility of modernization. Regular efficiency audits, dust measurements, and analysis of the condition of filters are not bureaucracy, but a tool for decision-making. Sometimes it is easier and cheaper to change the type of filter element in a timely manner or add another suction unit than to pay fines for emissions or treat employees for occupational diseases. In general, dust cleaning is not a one-time event, but part of the production culture. Without this, everything else is half measures.