Speed Control on Belt Conveyors
In recent years, there have been repeated recommendations to control the belt speed of conveyor systems.
The level of filling of the belt trough with 100 % should serve as a basis for the control procedure.
This means that high utilisation of the average transport capacity should always be aimed for, at an adapted, reduced belt speed. This type of operation is said to reduce energy consumption and hence operating cost. This article looks at this recommendation. On the basis that the design of belt conveyors and not to establish the fictitious resistance coefficient at different belt speeds or filling levels, the limiting quantities on the motion resistance of belt conveyors are described.
Based on the dependencies of individual resistances researched, simulation calculations for a fictitious belt conveyor are used to demonstrate that the fictitious resistance coefficient of belt conveyors largely depends on the filling level and only to a small degree on the belt speed. By means of the characteristic quantity specific energy requirement it is demonstrated that speed control for the purpose of energy savings is inappropriate at traditional filling levels in the range between 60 % and 100 %.
- Introduction
Belt conveyors have proven themselves to be an excellent solution for the transport of raw mineral materials and soil.
Today, they are in most cases the most cost-effective solution for handling bulk material mass flows over short and medium conveying distances.
Despite the already advantageous costs for belt conveyor operation, there is still a desire to reduce these costs even further.
Publication sources state that, in order to balance the filling level, the belt speed should be controlled in accordance with the load. As a result, energy consumption should decrease.
Publications give the impression that a reduction of the energy consumption by up to 30 % is possible, if, by controlling the conveying speed with the nominal volume flow as a leading quantity, that is a filling level of 100 %, the belt conveyor can also be operated if the volume flow is subject to fluctuations. In this context, publication sources mention center distances of more than 1400 m.
In its summary, publication sources also suggest that more a economical operation is achieved if variable-speed drives are used for belt conveyors.
- Principle Calculation Methods to Determine the Motion Resistance of Belt Conveyors
The energy consumption of long, horizontal belt conveyor systems in stationary operating conditions is determined by the motion resistance in the loaded section of the belt and the return belt. This resistance consists of the running resistance of the rolls supporting the belt, as well as the flexure resistance of the bulk material and the belt when running across the supporting rolls. The energy required to overcome these resistances is determined by a number of operative and constructive characteristic properties.
Compared to the other resistances, overcoming differences in height requires a high amount of energy. Lifting masses to a different level here primarily determines the amount of energy required, and can therefore not be influenced. Motion resistances are all forces acting on the belt along the direction of transport, which have to be overcome during the operation of the belt conveyor.
