In facilities prepared for the receipt of bulk solids by road or railway, the dust generation process begins as soon as the trucks or wagons arrive, which, when unloading the products in the hoppers, produce a huge cloud of dust that causes a harmful environmental impact, creating unhealthy conditions and causing serious damage to health, damaging machinery and enhancing the possibility of explosions.

The unloading operation of products in road or railway hoppers can be performed through manual or mechanized processes. In the manual unloading process, operators are directly exposed to the environment taken up by the suspended powder, however, in mechanized unloading processes, due to their ease of operation, they are out of reach of the powder, as it is contained and confined in the unloading area.

In a hopper there are two stages of dust generation in any type of bulk solid product discharge. The first is at the beginning of unloading, when the hopper is empty and the truck or wagon is full. The product flows out in large quantities and at high speed, hitting the hopper bottom and thus releasing an immense amount of powder which, when detaching from the mass of the product, is vertically dragged by the volume of air that occupied the space, towards the hopper bottom grid.

It is at this stage that the lamellae placed at the bottom of the hopper come into action, functioning as a mechanical barrier to contain dust, as they automatically open and close by gravity, with the passage and with the weight of the product. At this stage, the suction system must be more intense inside the hopper, whose space has now been occupied by the product, in order to aspirate the entire volume of air and dust generated by the handling.

As the product is unloaded, the hopper is filled and the generation of dust becomes smaller until reaching the moment of the second phase, when the dust is generated by the impact of product on the product, outside the hopper, but mainly on the grid of the same. At this stage, the suction system is more intense in the upper part of the hopper and is automatically performed by the suction system itself through its strategically positioned sensors, because the static losses in the suction are very high, making the system suction more intensely through the upper sensors.

Outside the cabin, a system comprising a centrifugal fan, pipes for transporting the air and dust flow, plus a bag filter sucks in air and dust, filtering the air. When the air is clean and free of dust, it is again released into the environment. Therefore, the complete system consists of the dust suction, below and above the hopper grid, through a powerful external system that aspirates, filters and releases the filtered and clean air back into the environment.

For any of these processes, TMSA has specialized over the years and today has complete solutions for Suction Systems for Hoppers, which are suitable for both manual and mechanical unloading, providing a cleaner environment, preserving well-being and the health of the operators.

The unloading operation of bulk solid products manually, in road or railway hoppers, consists of enclosing the entire unloading area by means of a cabin equipped with closing curtains, both at the entrance and at the exit, with the function of preventing that external air belts interfere with the suction. The product is unloaded from the wagons or trucks through the existing outlets and falls, by gravity, into the hopper where a powerful suction system made up of side sensors sucks air and dust, taking them to the bag filters where the air is filtered.

To avoid the accumulation of dust generated in the fall or caused by friction between product and product, the grids are closed with lamella that open and close automatically by gravity, with the passage and with the weight of the material. Therefore, the complete system consists of the dust suction below and above the hopper grid, aided in large part by the lamella and by the suction of the lateral sensors on the hopper, which have the function of aspirating the suspended dust that is being generated in the shock with the hopper grid. The suction efficiency is significantly increased by the lamellas, as the powder is confined in the hopper, ensuring that it does not spread back into the environment.

Unloading can also be done through the dumper bucket of the truck itself, with the suction system being identical to the manual one, but with a great advantage, since the rear of the truck is inside the cabin, preventing the dust from spreading outside.

Among all the types and unloading systems available, the best set of solutions to the problem is the one equipped with mechanical dumpers. The truck is parked on a longitudinal platform that tilts up to an angle of 45 degrees, causing the material to flow by gravity into the hopper. With regard to the ease of operation and protection of the health of operators, this is the process with the most efficient set, as the suction system is only performed in the unloading area, which provides operators with several resources, and also allows they are at a safe distance and out of the flow of suspended powder.

Depending on the hopper design, there is a very usual layout where filters can be incorporated on the sides of the cabin/unloading area, working in the same way as described in the previous systems, however, sucking and discharging the powder directly into the hopper, not being necessary for the installation of air and dust transport pipes, as well as dust return ducts, as shown in the photo below. In this case, the fans can be installed inside or outside the building, depending on layout or option.

All suction systems are made up of side sensors, which aspirate both at the top and inside the hopper, and are equipped with bags with individual adjustments. A network of piping connects the sensors to the bag filter, which in turn connects to the centrifugal fan that releases the filtered, dust-free air into the atmosphere.

It is important to point out that the use of environmental control systems in processes is essential for the success of the operation of any industry, as it guarantees safety measures against fire and explosions, including the conservation of the manufacturing plant and machinery, the preservation of the health of operators and the conservation of the environment in which it operates.