Conveyor System Analysis for Bulk Solids

Overview Conveying Systems

Various conveying systems are available for the transport of bulk solids, each with specific advantages and disadvantages:

Mechanical Conveying

• Screw Conveyors: Robust, low-maintenance systems for short to medium distances. Suitable for a wide range of materials, from free-flowing to cohesive.
• Belt Conveyors: High throughput rates, good for long distances, but only for free-flowing materials.
• Chain Conveyors: Suitable for heavy and abrasive materials.

Pneumatic Conveying

• Dilute Phase Conveying: High velocities (15-30 m/s), particles in suspension. Suitable for free-flowing, non-abrasive materials.
• Dense Phase Conveying: Low velocities (1-5 m/s), higher material concentrations. Gentler transport, suitable for abrasive and sensitive materials.

The choice of the appropriate system depends significantly on the material properties, conveying distance, required throughput, and process requirements.

Screw Conveyors

Screw conveyors are mechanical conveying systems that transport bulk material by means of a rotating helix in a pipe or trough. They are characterized by their robustness and versatility.

Operating Principle

The material is moved along the conveying direction by the rotation of the screw. The conveying capacity depends on the rotational speed, screw diameter, pitch, and material properties.

Critical Factors

• Bridging: Cohesive materials can form bridges between the screw flights and block material flow. The risk increases with increasing cohesion and decreasing pressure ratio.
• Wall Friction: High wall friction increases power requirements and can lead to material compaction.
• Inclination Angle: With inclined conveying, power requirements increase significantly.
• Material Compaction: The pressure of subsequent material layers can lead to increasing compaction.

Calculation

Our analysis evaluates:

• Bridging risk based on φ_i, cohesion, and geometry
• Required drive power considering friction, inclination, and throughput
• Conveying capacity and torque
• Risk assessment for different screw geometries (on request)

Pneumatic Conveying

In pneumatic conveying, the bulk material is transported through an air or gas stream in a pipeline. A distinction is made between dilute phase and dense phase conveying.

Dilute Phase Conveying

Particles are transported dispersed through the pipeline at high velocity (15-30 m/s). The gas velocity must be above the settling velocity of the particles to ensure a homogeneous suspension.

Advantages:

• Simple design
• Flexible pipe routing
• Low investment costs

Disadvantages:

• High energy consumption
• Particle attrition with abrasive materials
• Pipe wear

Critical Factors:

• Blockage Risk: At too low velocity or in pipe bends, deposits can form
• Minimum Velocity: Dependent on particle density, size, and shape
• Pressure Drop: Increases with length, bends, and material concentration

Dense Phase Conveying

Transport in plugs or continuous material layers at lower velocities (1-5 m/s). Higher material loading, gentler and more energy-efficient transport.

Advantages:

• Lower energy consumption
• Minimal particle attrition
• Reduced pipe wear
• Suitable for abrasive materials

Disadvantages:

• More complex control
• Higher system pressure required
• Not suitable for all materials

Critical Factors:

• Plug Stability: Cohesion and internal friction influence plug formation and stability
• System Pressure: Sufficient pressure required to overcome material friction
• Material Properties: Flowability, cohesion, and density are crucial

Relevant Material Properties

For a reliable conveyor system analysis, the following material properties are required:

From Yield Locus Measurements (Shear Test):

• Angle of Internal Friction (φ_i): Describes the internal friction of the material. High values (>40°) indicate free-flowing materials, low values (<30°) cohesive ones.
• Cohesion (τ_c): Cohesion of particles. High cohesion increases blockage risk in screw conveyors and is critical for dilute phase conveying.
• Unconfined Compressive Strength (σ_c): Resistance to compaction. Relevant for plug formation in dense phase conveying.
• Flowability (ffc): Classification from "non-flowing" to "free-flowing". Significantly influences the choice of conveying system.

From Wall Friction Measurements:

• Wall Friction Angle (φ_w): Friction between material and conveying pipe/trough. Directly influences power requirements for screw conveyors and pressure drop in pneumatic conveying.

From Density Measurements:

• Bulk Density (ρ_b): Loosely poured density. Influences conveying capacity and power requirements.
• Compression Density: Density under load. Important for calculating pressure drops and compaction effects.

Conveyor System Analysis

Our conveyor system analysis includes a systematic evaluation of various conveying systems for your specific material:

1. Screw Conveyor Analysis

• Bridging Risk Score (0-100): Assessment based on cohesion, φ_i, and geometry
• Power Calculation: Required drive power considering:
  • Material weight and throughput
  • Wall friction
  • Inclination angle
  • Conveying length
• Conveying Capacity: Calculation of throughput (kg/h) for given geometry
• Assessment: Traffic light system (suitable/critical/unsuitable) for material properties

2. Pneumatic Dilute Phase Analysis

• Blockage Risk Score (0-100): Assessment based on flowability and cohesion
• Minimum Velocity: Calculation of required transport velocity
• Pressure Drop Calculation: Influence of length, bends, height differences
• Assessment: Traffic light system (suitable/critical/unsuitable) for material properties

3. Pneumatic Dense Phase Analysis

• Plug Stability Score (0-100): Assessment of suitability for dense phase conveying
• Conveying Velocity: Recommended velocity for stable plug transport
• System Pressure Requirement: Estimation of required air pressure
• Assessment: Traffic light system (suitable/critical/unsuitable) for material properties

Comparative Assessment

All three systems are comparatively evaluated regarding:

• Suitability for the specific material (risk scores)
• Energy requirements and operating costs
• Maintenance effort
• Investment costs (qualitative)
• Process reliability

Required Measurements

For a meaningful conveyor system analysis, the following measurements are required:

Recommended Additional Measurements:

• Time Consolidation: Material behavior during longer storage or standstill
• Angle of Repose: Additional information on flow behavior

Measurement Process:

1. Sample Submission: Representative material sample (approx. 5-10 kg)
2. Measurements: Execution of all relevant tests in the laboratory
3. Analysis: Calculation and evaluation for all three conveying systems
4. Report: Comprehensive analysis report with recommendations
5. Consultation: Discussion of results and recommendations

Conclusion

The choice of the appropriate conveying system and its optimal design require precise knowledge of material properties. Only through experimental measurements can reliable statements be made about blockage risks, power requirements, and optimal operating parameters.

Our conveyor system analysis offers you:

• Objective evaluation of various conveying systems
• Early identification of potential problems
• Optimization of operating parameters
• Cost reduction through correct system selection
• Increased process reliability