2. Tube Conveyor Design
The TC-3A-overland tube conveyor system connects the power plant to the truck loading station.
Conveyor running resistance is determined following the DIN 22101 standard applicable for troughed belt conveyors. Auxiliary, grade and special resistances apply nearly unchanged for the dimensioning of the tube conveyor, but additional resistance components are likewise included in the determination of the main resistance.
The form forces of the tube is determined primarily by the tube diameter and the transverse stiffness of the tube conveyor belt.
Friction resistance in the belt overlap zone results from the permanent opening and closing of the tube cross-section when passing through the idler stations. The tube belt opens by reason of its transverse stiffness, when not supported from the circularly arranged idlers. The circular cross-section is then re-established at the idler stations. This effect leads to a main resistance component not present in the troughed belt, since the overlapping belt edges cause friction resistance when the conveyor cross-section is opened and closed.
| General technical details of TC-3A | |
|---|---|
| Material | Ash and Gypsum |
| Centre Distance | C-C = 4535 m |
| Elevation | I = 24.5 m |
| Design mass flow | Im ≈ 1400 t/h |
| Max. belt speed | vmax = 4.8 m/s; |
| Max. fill ratio | ηF ≈ 0.72 |
| Steel cord tube conveyor belt | HS-Rollgurt 1500 S-K2 7T:6S Conti Extra, width 1500 mm, nominal breaking strength kN=1500 N/mm |
| Operating temperatures for the belt | -35°C ≤ T ≤ 60°C |
| Outer (idler) diameter in top strand | DT ≈ Ø 430 mm |
| Outer (idler) diameter in bottom strand | DB ≈ Ø 400 mm |
| Idler spacing in straight | pS = 2.0 m |
| Idlers spacing in curves | pC = 1.5 m |
| AC-Motors | Head TL2: 2 x 500 kW + 1 x 500 kW Tail TT1: 1 x 500 kW |
| Curves | 8 „tight“ horizontal und 7 vertical curves (min. Curve Radius Rmin = 350 m) |
| Take-up | at head TL2 |
| Belt rip protection | Sensor loops embedded (vulcanized) in the belt top cover every 200 m and two ContiProtect rip detection units with two pairs of transmitters and receivers at head and tail |
Additional change on the outer diameter of the conveyor cross-section occur if the tube belt conveyor follows a curved route. Expansion of this kind leads to a reduction in the conveyor cross-section and thus to increased friction resistance in the belt overlap zone.
Thus this additional main resistance component occurring on the tube conveyor is determined by the following parameters:
- tube diameter
- belt tension
- idler spacing
- curve radius
- transverse stiffness of the conveyor belt
- friction value between the overlapping belt edges.
The current research on conveyor running resistance in the case of tube conveyors does not yet allow for a determination of the two aforementioned main resistance components using the individual resistance method.
The standard procedure remains in place. Adapted to account for the main influential variables, namely
- belt design,
- line layout (curve layout) and
- ambient temperatures,
a fictitious friction coefficient is defined that can be used to determine the main resistance.
Belt properties determine main resistance to a much greater extent in the case of tube conveyors than in the case of troughed belts.
Various belt manufacturers supply tube belts with different belt designs and thus strongly deviating properties, particularly in terms of transverse stiffness.
It is recommended that the conveyor calculation be coordinated with the potential belt supplier before the contract is awarded. This allows for consideration of the specific features of the conveyor belt used.
The conveyor was designed in consultation with ContiTech based on a fictitious friction coefficient of DIN-f = 0.043 for the loaded conveyor in a stationary state.
Analog to the computation for the troughed belt conveyor, the belt tension values for all operating conditions, namely:
- all routes loaded at maximum running resistance
- all routes loaded at minimum running resistance
- only routes graded upward loaded
- only routes graded downward loaded
- idling
are to be determined in equilibrium, at start-up and during braking. Initial tension is determined for tube conveyors in a manner similar to that of the troughed belt. The goal is to ensure traction between the drive pulley and the belt in all operating states and to rule out unallowable belt sag and buckling.
