It is recognized that dusts, above all those arising from silo filling, pose a potential risk to employees and environment. When processing dry bulk material, as e.g. powders, a dusty and explosive mixture often develops inside storage containers, which entails a particular risk potential. If, for example, a tanker blows the product into a silo by means of compressed air, overpressure will build up inside along with a cloud of very fine dust, which can make the container burst. A pressure compensation valve releases the pressure into the atmosphere, however the dusty air as well. In order to avoid that, the silo filters have proven their worth.
For many decades, the SILOTOP R03 from WAM has been one of the preferred dust collectors for concrete and construction material plants. In 2018, the company decided to replace the R03 by two versions of the SILOTOP® Zero, the newly developed successor. Despite the small size of the filter media, the SILAB 14 version (14 m² filter area) with 1600 Nm³/h can take up the almost identical amount of air as the R03 (24.5 m² filter area), while the Silotop Zero with 24.5 m² (SILAB 24) provides peak values of over 2000 Nm³/h. This development progress is thanks to the new filter media. Equipped with the new filter fleece “NANO”, the SILOTOP® ZERO renders concrete and construction material plants more environmentally friendly by reducing dust emission to below 1 mg/Nm³. The old R03 model, in comparison, achieved little less than 10 mg/Nm³. In its current version, the TA Luft already required less than 20 mg/Nm³ for this kind of dusts and the values shall be modified to less than 10 mg/Nm³. In this respect, the SILOTOP® Zero exceeds the legal requirements and creates investment security, at least regarding the residual dust content.
In order to prevent the filter elements from blocking, the dust needs to be removed in regular cleaning cycles. Only in this way, the functionality of the filter elements is ensured. This can be achieved mechanically by vibrations or, as in the case of the SILOTOPs, pneumatically by injection of compressed air jets into the filter elements. The particles removed from the filter elements drop back into the storage container. The special construction of the air-jet cleaning system integrated inside the hinged weather protection cover of the SILOTOP® Zero, operates with low air consumption of only 1.8 nm³/h. This enables savings in annual operating costs of up to 50 % due to reduced compressed air consumption – savings also to the benefit of the environment.
In case the silo is finally expanded by further elements, such as a pressure compensation valve or a pressure switch, plant safety can be further increased. WAM relies on its comprehensive overfill prevention system KCS, which contains many of these compatible safety components. As most of the damages to silos or their accessories are likely to happen during the filling process, the system monitors pressure changes inside the silo and prevents overfilling.
Looking at the state of the art, there are already two good possibilities to prepare silos for the increasing future demands regarding safety of man and environment. Operators who need to plan or expand a plant or need to replace components are well advised to tune in to these demands already today in order to avoid unnecessary replacement investments.