Gentle Dense Phase Conveying for Fragile Products

Conveying performance, product condition and equipment life depend on the interaction between the material, gas, pipeline and operating sequence. A generic technology label is not enough to approve the duty.

A stable transfer that reaches the required capacity while keeping breakage, surface abrasion and fines generation within a measured product acceptance limit.

Fragile granules, pellets and agglomerates can lose value when conveying creates chips, fines or a changed particle size distribution. The damage can affect appearance, dissolution, flow, dust generation and the performance of the next process step.

Why lower velocity can help

Particle damage in pneumatic conveying is strongly connected to collision energy. Published experimental and modelling work shows that particle impacts, especially at bends, are important degradation mechanisms. Dense phase operation often lowers gas and particle velocity, which can reduce severe impacts.

That advantage has limits. Dense phase material may move as plugs, slugs or a moving bed. Sliding contact can create surface attrition, while an unstable plug can produce pressure fluctuations, sudden acceleration or blockage. The engineering question is therefore not whether dense phase is gentle in general. It is whether the selected flow mode is gentle for the actual product and route.

Characterize the product before selecting equipment

Record the initial particle size distribution, shape, bulk density, moisture and mechanical strength. State which property must be protected and how it will be measured. A verbal requirement such as minimal damage cannot be used as an acceptance criterion.

Material state matters. Storage time, temperature, moisture and prior handling can change strength or flow behavior. Test samples should represent normal production variation rather than an ideal laboratory sample.

Evaluate whether dense phase flow is feasible

Research on pneumatic conveying behavior shows that particle size distribution, permeability and air retention influence the flow modes a material can support. Some free flowing materials can form plugs or slugs. Fine materials with suitable air retention may move as a fluidized dense bed. Other materials may not support stable dense phase transport.

A conveying trial should identify the stable operating region. Record mass flow, pressure behavior, gas use, restart performance and material condition. A single successful transfer does not define a complete operating envelope.

Design the route around product protection

Minimize unnecessary bends and sudden changes in direction. Review feed points, boosters, valves and the final approach to the receiver because local acceleration can defeat the benefit of a low average velocity. Bend radius and geometry should be part of the product protection review.

The receiving stage also matters. A gentle pipeline can still damage product through a high speed entry, a hard target surface or an unsuitable discharge device. Follow the particles from source to final destination.

Write a measurable acceptance test

Take controlled inlet and outlet samples across repeated cycles. Compare the agreed quality measures and record the system settings. Include normal startup, steady operation, a controlled stop and restart. If segregation matters, sample at more than one point in the receiving batch.

The accepted configuration should identify material condition, route, pipe size, pressure, air settings, feed rate and bend arrangement. Future changes can then be reviewed against a known baseline.

Control the complete velocity and impact history

Low nominal conveying velocity does not by itself prove gentle handling. Product can still experience severe acceleration at the vessel outlet, air-injection points, restrictions and the final receiver. Map each change in direction and cross-section, and review startup, normal transfer, line clearing and turndown separately. Stable plugs or dunes should reach the destination without repeated collapse and re-acceleration.

Design measurable protection and recovery criteria

Define product damage with a method suited to the material: particle-size change, whole-piece retention, fines generation, visual defects or a downstream performance measure. Sample feed and conveyed product with methods that do not create their own breakage bias. A blocked line requires a pressure-safe isolation and clearing sequence; simply increasing gas or repeating starts can create the highest damage event in the cycle.

Include safety, inspection and cleaning

Review combustible-dust data, ignition sources, connected volumes and propagation paths for the actual material. Provide access to bends, injection points and receiver internals where retained fragments or wear can accumulate. Commission across the proposed rate range and include a controlled stop and restart. Preserve pressure profiles, cycle timing and product results so a change in route, batch size, particle condition or control recipe can be assessed against evidence.

Particle size distribution, particle strength, shape, bulk density, permeability, air retention, moisture, required rate, route, lift, bend geometry, feed arrangement, receiving vessel and the permitted change in product quality.