cleaning dust emissions

When they talk aboutcleaning dust emissions, many immediately imagine a bag filter or a cyclone. It’s as if I installed it and the problem is solved. In fact, if everything were so simple, we would not have so many problems with complying with the maximum permissible limits in old industries. A common mistake is to consider dust as a homogeneous substance. But its fractional composition, abrasiveness, humidity, electrical properties are the foundation. If you make a mistake in the analysis, you will either get a clogged filter within a week, or a “leaky” one. a system that formally works, but does not work. I went through this myself.

From theory to "dirt" workshops

The diagrams in the books are perfect. In practice, for example, at the concentrator we worked with, the main headache was not even in the main process flow. And at those dozens of transfer points: from belt to belt, from hopper to crusher. There the emission is not constant, but pulsed, and even with a different amount of air due to suction. Putting a powerful filter on each point is golden. Don’t install it - the sanitation station will torture you. We had to combine: in some places local shelters with small cyclones, in others aspiration umbrellas combined into one network for a bag filter. And this does not take into account the fact that in winter there is condensation in the air ducts, and in summer there is overheating.

One of the key points that is often overlooked in design is how the properties of the dust change during the process. Let's say the dust at the crusher inlet is coarse and abrasive. It is logical to install a cyclone to catch the main mass and unload the main filter. But after drying or during transportation, the fine fraction can become electrified. And if you installed a standard bag filter made of non-woven material, it may begin to “hold?” this charge, the dust will be difficult to shake off, the resistance will increase sharply. You have to install filters with threads containing conductive fibers, or think about a grounding system for the hoses themselves. Trifle? On paper - yes. In reality - a simple line for a day for cleaning.

We had experience at one of the old metallurgical plants. The task is to modernizecleaning dust emissionsfrom the ferroalloy grinding area. The dust there is not only fine, it also has a tendency to stick together. We installed pulse regeneration according to the original design. Didn't work as expected. The sleeves were sticking together, backwashing did not help. We had to make changes “on the spot”: we increased the interval between pulses, but added mechanical shaking in combination with low-frequency vibration of the frames. And only after this the system reached stable parameters. The design efficiency of 99.9% was achieved, but the path was not direct.

Equipment: Choices and Tradeoffs

Now there are a lot of solutions on the market, from cheap cyclone batteries to high-tech electrostatic precipitators. But the universal “magic” no device. For coarse, dry, non-stick dust, a cyclone is all right; efficiency up to 85-90% can be achieved if you correctly calculate the diameter and speed. But when it comes to fine fractions (less than 10 microns), fine filters are indispensable. Here you can choose between bag and cartridge filters.

Sleeves are a classic. Large filtration area, relatively simple regeneration. But they require space. Cartridge ones are more compact, but more expensive to maintain, and are sensitive to humidity. I saw how at a cement plant, due to an abnormal ingress of vapor into the aspiration line, the cartridges “stood up like a stake?” per shift. I had to change it urgently. With sleeves in such a situation there would simply be a temporary increase in resistance.

Interesting experience related to the use of equipment fromLONGI Corporation. We considered their solutions for aspiration problems at a mining and processing complex. On their websitehttps://www.ljmagnet.ruyou can see that the company, established back in 1993, has serious experience in the development of mining equipment. It was important to me that they don’t just sell filters, but understand the entire technological context. For example, their engineers rightly focused on the need to accurately calculate air ducts to evenly distribute the flow across all dust collection points. Is this the same “invisible” one? work that determines the success of the entire systememissions cleaning. The area of ​​their enterprise is 140,000 m2 and the fact that they produce about 4,000 units of equipment per year indirectly speak about the scale and, possibly, a good production base for the manufacture of large-sized units, the same dust storage bins or filter sections.

Integration into the process: where the risks lie

The most advanced cleaning system can be useless if it is not integrated into the technology correctly. A classic example is dusty air sampling points. If the shelter or umbrella is not made airtight, then instead of sucking in dust, the system will drive clean air out of the workshop, and the bulk of contaminants will escape. Efficiency on paper is 99%, in fact - 40%. I have seen such situations more than once.

Another risk is changing the operating mode of the main equipment. Let's say the crusher began to work with greater productivity. Dust generation has increased. The aspiration system, designed for old volumes, cannot cope. A margin is needed for fan performance and filtration area. But there is a limit here: too powerful a fan can create such a vacuum in the shelter that it begins to suck in material along with dust, increasing its losses. We need balance.

Another nuance is the removal of trapped dust. It seems that this is a small thing: a hopper under the filter and an auger. But if the auger fails to cope or becomes clogged, the hopper becomes full, dust begins to fall back into the hoses, and the system fails. It is necessary to provide level sensors in the hopper, emergency valves, and sometimes even a pneumatic transport system for continuous removal. This complicates and increases the cost of the project, but without this reliable operation is impossible.

Economics and ecology: eternal contradictions

The customer always wants cheap and effective. The regulatory authorities are only effective. The engineer's task is to find the very point where these lines converge. Sometimes it is more profitable not to install a system with an efficiency of 99.99%, but to install two stages: a cyclone (80%) and behind it a simple bag filter (95% of the remaining). The total is the same 99%, but capital and operating costs may be lower. We need to count.

Nowadays there is a lot of talk about recovery - returning the captured product to the process. This is ideal from an economic and waste-free point of view. But again, this is not applicable for all types of dust. If the dust is mixed (for example, from different processing stages) or contaminated, its return may spoil the quality of the main product. Then it needs to be pressed and disposed of. This is a separate expense item that needs to be included at the very beginning, when calculating the payback of the entire system.cleaning dust emissions.

Here again you can turn to the experience of large equipment manufacturers. SameLONGI Corporation, judging by the information that more than 60% of their employees have higher professional education, probably employs not only designers, but also technological engineers who are able to offer not just a device, but a scheme that takes into account the further fate of the captured dust. For the mining and processing sector, which is their main profile, this is critical, as dust often represents a valuable concentrate.

Instead of a conclusion: thinking out loud

So to summarize my experience,cleaning dust emissions- it's always a system. A system tied to a specific location, material, technology and even climate. You cannot take a standard project and guarantee the result. We need preliminary measurements, dust analysis, and an understanding of the technology from the inside.

Often success or failure lies in the details: in the hose material, in the design of the unloading valve, in the logic of the regeneration control unit. There is no ideal system; there is an optimal one for given conditions. And its search is not so much a science as a craft, flavored with the experience of past mistakes and the willingness to adapt solutions to the reality of the workshop, and not to a beautiful drawing.

Therefore, when they come to me with a request “need dust cleaning?”, the first question is always: “Which one, in what process, and what to do with it next?” Without answers to these three points, any discussion of effectiveness and cost is simply wasted talk.