GUNSKIRCHEN – When planning a plant in which different raw materials in varying dosages are to be joined, mixed, and reliably provided to further processing operations, a lot of questions have to be answered in advance.
These questions are:
- Scope of demand for final products
- Mixing system to be applied, continuous or batch operation
- Number of components used
- Smallest/biggest number of each component
- Required dosing/weighing accuracy
In a first step, the number and sizes of the containers for raw materials stocking is determined starting from the known product data as well as any mixing, dosing and conveying tests that may be required. Subsequently, all conveying paths and, if required, lifts, are included on the basis of the layout concept. In the process, the optimum conveyor system, adapted to the product and the conveying path, is to be selected.
One major aspect in the conceptual design phase is explosion protection. As it has a decisive effect on layout planning, it must be considered from the outset. Especially where design-related safety measures such as bursting discs are required, the containers have to be arranged in a way that the explosion pressure can be discharged into the open air. In other cases, flameless pressure relief into the room may be applied, but even then some space has to be provided for this purpose. If explosion suppression measures are implemented, stabilizing and measuring sections of sufficient lengths have to be considered.
The figure shows the result of such a facility design. Evidently, the special challenge was to achieve a very compact plant layout. Only the three external silos were positioned independently. These 100 m³ silos accommodate the three main raw materials; moreover, there are silos with an effective volume of 5 m³ for six other raw materials. Additionally, more raw materials can be supplied from big bags and sacks.
The whole plant consists of two mixing sections which are both supplied with the same raw materials though according to different recipes, and which operate independently of each other. Each section consists of a pre-mixing unit charged with the raw materials needed in bigger quantities. Together with the other raw materials, this premix is then delivered to the main mixing unit. Subsequently, the finished mixture is conveyed to generously dimensioned feed tanks supplying the downstream units. In this plant, the products are conveyed mechanically, i.e. via trough chain conveyors and bucket conveyors.
The explosion protection concept combines several measures such as the avoidance of ignition sources, e.g. through the use of plastic components in the bucket conveyors, as well as pressure discharge facilities in the containers. To this end, the external silos are provided with bursting discs, while flameless pressure relief is used in other containers.
All in all, the plant excels through its very compact layout of the core area on a floor space of only 80m² , without the need to compromise in terms of operability and safety. And all this at a plant capacity of 3800 kg/h.