Addressing Particulate Matter in Mineral Processing!

The reduction of particulate matter is a hot item in environmental policy worldwide. The countermeasures taken include setting up improved production processes and the installation of gas cleaning systems at emission points.
One of the industries that is intensively optimizing its production plants is mineral processing. Minerals are widely used in many different industries. Minerals, however, generate fine dust, for example, during divergent kinds of production processes or filling into (big) bags or trucks. The dust from the minerals contains very fine particulates, which, in some cases, can create a potential hazard.

Dust particles in the atmosphere arise from a wide variety of industrial activities. As well as the size and chemical composition, which can vary depending on the process. Coarse particulates can be regarded as those with a diameter bigger than 2.5 m (e.g., PM10–10 m) and fine particles less than 2.5 μm (PM2.5). Under moist conditions, particles attract water vapor and agglomerate to form small droplets. The term 'aerosol' is often used for both solid particles and droplets suspended in air.

Chemical reactions of acidic SO2 and NOx with alkaline NH3, which are emitted by the industry, also occur on the surface of existing particles. These reactions lead to substantial mixing between the different pollutants contained in particles. Hence, after a lifetime of several days in the atmosphere, an individual particle might contain both water-soluble components (e.g., sulfate, nitrate, and ammonium) and insoluble components (e.g., carbon, heavy metals, or soil).

The rates at which particles are removed from the atmosphere depend strongly on their size. Large particles deposit rapidly near their source by gravitational settling, while very fine particles also deposit relatively quickly because they are mobile. Particles in the intermediate size range (0.1–2 μm) deposit slowly and can therefore be transported over long distances between different countries and continents.

Ravebo designs wet gas scrubbers, dust scrubbers, odor scrubbers and various droplet separation systems in-house with a team of engineers. Each system is fully tailored to the specific requirements of the relevant process, in consultation with the customer. Ravebo builds both vertical columns and horizontal flow scrubbers. The systems are visualized in advance using an Inventor package, where everything is implemented in 3D presentations (Autodesk Inventor) in the customer's production installation. This method has the enormous advantage that the lead time and costs are low, and the end result is already visible at the quotation stage.

Ravebo can supply the installation as part of a total project, but it is also able to tackle the entire project turnkey. This means that not only is the scrubber delivered, but it is also installed, connected, and commissioned. The installation can be supplied with complete piping, switch cabinets, controls, pumps, fans, and all additional accessories. The scrubber can be equipped with a PLC control that is programmed by our own engineers and can be implemented on location.

Open spray systems operate based on the difference in velocity potential between liquid droplets and the incoming gas. The liquid is pumped with moderate pressure through nozzles with the objective of getting a homogeneous droplet distribution and an equal spray pattern. The droplet size is especially important, since ultrafine droplets have a particularly large surface-to-volume ratio. The exceptionally fine droplets create a fine mist, which results in an efficient capture of particles. The spray absorbers operate relatively simply, are very maintenance-friendly, and have fairly low energy costs.

Open spray absorbers have a minimal pressure loss and are virtually insensitive to contamination, which normally causes a larger pressure difference. The scrubber works according to a closed-loop pump system in which the washing liquid is pumped from the buffer.

The spray system consists of multiple removable spray lances with spray nozzles, some of which are co-current and some of which are counter-current. The positioning of these spray nozzles in the scrubber is of the utmost importance for optimal gas treatment because they absorb dust particles because of the intensive contact between the washing fluid and the process gas. The clogging-free tangential nozzles create fine droplets with a homogeneous spray pattern to capture as many dust and gas particles as possible. Optimal contact of fine liquid droplets with gases and (dust) particles will lead to a high absorption of polluting particles and gases. This type of scrubber is very suitable, among other things, for irregular concentrations (peak discharges), which will largely be absorbed by the countercurrent washing principle.

A scrubber, odor scrubber or knock-out drum can be optimally laid out when the input conditions are fully known. This is almost never the case, for various reasons. The composition of the gas can be determined relatively easily by taking samples. Particle size determination, on the other hand, is much more complicated. The same obviously applies to existing installations; however, this is about returns. A difference in mass can only be determined by taking samples before and after the scrubber. The associated particle size is also almost never known here. In order to be able to make a somewhat reliable statement about scrubbers in general, research must be carried out into the number of particles present in the gas and the particle size distribution.

The particle size determination is carried out with a so-called aerosol spectrometer. This spectrometer provides direct information regarding the number of particles and particle size distribution. Based on this data, the mass can be calculated so that a complete picture is created with regard to any (dust) particles that may be present.

The measurement is performed isokinetically, with the air acceleration at the nozzle tip being matched to the air velocity of the gas in the duct. This results in a very accurate measurement, as the particle size distribution and the number of aspirated particles correspond exactly to the conditions in the channel.

Have you ever noticed how many minerals are mined every day, and what damage this causes to Mother Earth? The demand for raw materials grows day by day, and therefore the exploration of minerals expands continuously. This means more digging, transportation, processing with high energy consumption. And more importantly, how many minerals could be recycled?

Recycling minerals is needed to save energy, money, raw materials, and natural resources. It also helps to reduce landfill use, waste incineration, and also save time required for mining of valuable minerals. As demand for minerals is increasing rapidly, it is very important to see that not a bit of minerals is wasted. Particularly with increasing industrialization the importance of mineral recycling becomes more relevant.

Minerals chain of recycling is collecting, separating, and reuse valuable materials from waste products and components to extend their useful lifetime. The core ambition of recycling minerals is to decrease the requirement for new material which is leading to rapid resource depletion.