The dust suppression system proposed by WLP aims to solve in the best way the felling problem of airborne dust in all areas in which are carried out of stone crushing, demolition of buildings in urban areas and in all environments where it is necessary to contain the emission of dust into the atmosphere.
The dust suppression system proposed by WLP is based on the principle of creating a controlled area with the aim of bringing to the ground powders purely silicon-based or otherwise rocky origin, while creating a wet layer, but without the establishment of runoff, which prevents the risk to fly up during the passage of heavy vehicles.
The obvious advantage of a dust suppression system thus conceived is twofold, involving the primary aspect of safeguarding the health of the workers engaged in the processing and of the users, but also to safeguard the mechanical efficiency of the road trucks, drastically reducing the downtime for cleaning air filters in the first place and no less important it prevents the risk of failure of transmission components, often subject to abnormal wear due to the accumulation of particulate matter in mechanically sensitive areas such as constant velocity joints and ball bearings, and hydraulic rods.
The design idea of WLP dust comes from the observation of two distinct phenomena. The first is that normally are used in the job sites systems for reduction of dust rather rudimentary (shedding of water in the liquid phase) to moisten the soil, getting only for limited periods the desired effects, however, with a very low efficiency (ratio of water used and the surface very high) and with the formation of mud really hard to be removed in some areas of the yard. The second is that nature, usually much more efficient than human solutions, manages the removal of the poor by incorporating within the rain the dust particles through two mechanisms: the first is to close within the raindrop particle , the second is linked to the fact that the water from the molecular point of view can be considered as an electric dipole which attracts towards if the finer particles of silica dust, behaving as an electrostatic filter real.
From practical point of view and physical is therefore much more efficient electrostatic-hydraulic filter instead of a cleaning with water droplets sizable.
We must make further consideration of the physical nature.
The water molecules in the free state are very unstable and have a low energy level (condition of all natural phenomena) with a trend to recombine into larger drops, however, after having incorporated the powder particle internally . This observation is easily found in nature in different phenomena. In the most polluted areas normally it rains more or more abruptly than in the less polluted, because the water particles suspended in air in the form of water vapor are used as a physical basis by the suspended dust to recombine themselves in larger drops .
This phenomenon, also defined as heterogeneous nucleation, is the effect of coalescence of small water droplets, not sufficiently heavy to overcome the air friction to start the fall path that leads to the ground. The solid particle of siliceous material or other, soluble or insoluble, acts as a condensation nucleus around which the small water drops to accumulate until reaching a mass such as to make them precipitate, thus delivering to the ground even the foreign particle.
An example of that isthe red rains rich of desert sands. In nature the system is very efficient . In nature, the removal of dust from the atmosphere takes place essentially in two ways: by dry deposition and by wet deposition. The dry deposition works intercepting the particles along the current lines by obstacles; the two main mechanisms are the deposition by gravity and the deposition by impact. In the first case it is a phenomenon that affects mainly the particles with diameter greater than 10 µm, resulting in negligible for smaller particles. The second mechanism is associated with charge air passage of solid particles through a barrier (vegetated surface or full of obstacles).
If the inertia of the particles is not large enough to allow the same to follow the change of direction of the flow lines that an obstacle, it is observed the change of trajectory following small radii of curvature, with ground deposition of the particles. The presence of water significantly increases the efficiency of the deposition processes (wet deposition). The mechanisms involving water can involve the different phases, from the vapor to the liquid phase or solid.
It is interesting to observe what happens in nature inside and outside the cloud download rain to the ground:
- Rainout: The particles act as condensation nucleus for the droplets of the cloud. Some of these droplets increase in size until they fall (sedimentation by gravity) to the surface in the form of drops of rain. The particles (condensation nucleus ) so deposited are washed from the atmosphere.
- Washout: It is the removal of particles by raindrops formed earlier. The particles are incorporated into an existing drop; the difference with the rainout is the fact that in this case has already formed a drop of sufficient size to fall.
- Sweep Out: Particles placed under the cloud may impact in a drop falling to the ground and are deposited with the drop itself. This is probably the wet deposition mechanism less efficient. Because, in fact, insects are not leached from the atmosphere when it rains? It is observed that the removal of dust in accordance with traditional watering systems and sputtering is carried out precisely on the basis of this mechanism, which in nature also appears to be the less efficient to flush the solid particles from the air.
- Occult deposition: It refers to the deposition associated with clouds that are in contact with the ground, such as the fog or the clouds orographic. It is a more complicated concept of the other three. The impact efficiency is the probability that a particle impacts in a surface that intercepts a flow, rather than being diverted around the object. It is strongly dependent on the shape, with the larger aerosols that have a higher probability of impact on a surface compared to smaller particles.
The efficiency of the impact of water droplets is greater than that of the aerosols in respect of which act as a nucleus. This increases the probability for aerosols incorporated in drops. The efficiency of "bonding" is the probability that an object that has impacted against a surface not rebounds and is not readily suspended. The efficiency of "gluing" of clouds of droplets is greater than that of the aerosol. Therefore, the clouds that come in contact with the ground can result in a better deposition rate for small aerosols.
The challenge is to copy and optimize the natural phenomenon. The principle of spraying water into the atmosphere in the form of drops may be the ideal solution. Enough in fact, through simple rain bird system, spray the area to be treated.
But it would soon realize that:
- you have a massive amount of water making a muddy area of the site in a short time and also causing considerable disturbance to the workers involved and to the movement of vehicles;
- The treated water / surface ratio would be high with poor results and little long-lasting;
- the system would not have those effects of electro-hydraulic filter indicated above;
- it is based on the treatment of air interception system particele less efficient.
The aim is therefore to create an efficient filter and it lasts for as long as possible. The first point is to get water droplets of appropriate size, indeed better to say to reduce the water to a state of suspended practically vapor; with the appropriate dimensions of the nozzles are reached size of the droplets also less than 80 µm (the mist in nature is constituted by droplets of diameter comprised between 10 and 50 µm, the rain has dimensions greater than 1 mm, up to 7 mm in the case of drops very large) to maximize the effect of the phenomena of rainout and washout, being, as stated previously, the most effective in the particulate removal capacity from the atmosphere. The second is to create a controlled area and which has the water in suspension in the form described above, which captures dust and the carry-overs to the ground without creating pools of mud and extended to prolong the effect for some tens of minutes even after system shutdown with immediate effect on reducing energy and water consumption. The presence of such small drops in the area also results in a better comfort for the workers in the case where external temperatures are particularly high. This system is easily achieved by creating a cannon which we will call "mist" able to atomize the water and to transfer the water at a considerable distance from the point of emission.