How it works
A bunker, silo, or hopper holds a mass of bulk solids and releases it on demand. Physically nothing is transformed — the particles are just stored — but the bunker plays a crucial dynamic role in a process: it decouples upstream and downstream units, absorbs flow fluctuations, and provides residence time. Material flows in at one rate and out at another, and the holdup rises or falls accordingly (dm/dt = ṁ_in − ṁ_out).
In reality the way solids flow out of a vessel is a rich subject — mass flow vs. funnel flow, bridging, rat-holing, and segregation all depend on hopper geometry, wall friction, and powder cohesion. A simulation-level buffer model abstracts that away and focuses on the holdup dynamics and mixing: how the stored mass and its averaged properties evolve over time as a buffer in the flowsheet.
The model
The solids bunker performs ideal-mixed accumulation of the solid phase (other phases are bypassed), solving dm/dt = ṁ_in − ṁ_out. It maintains time-dependent norms of the stream properties and distributions to represent the mixing dynamics correctly; a non-mixing (plug-flow) variant gives first-in-first-out behavior.
- Adaptive — The user sets a target holdup mass; the outflow is adjusted toward it depending on the inflow and current mass.
- Constant — The user specifies the requested outflow at timepoints; the bunker delivers it when enough material is present, otherwise passes the inflow through (with a smoothing function for solver stability).
Equipment this model can represent
Any vessel that stores and buffers bulk solids between connected unit operations.
Silos and storage bins
Large-volume bulk storage between process stages.
Hoppers
Converging vessels feeding a downstream unit at a controlled rate.
Surge / buffer bins
Small day-bins that decouple continuous units.
Stirred slurry tanks
Agitated vessels keeping suspensions homogeneous (the “tank” analogue).
Typical engineering studies
What teams investigate with the bunker model.
Buffer / surge capacity
Add buffer capacity to a dynamic flowsheet and damp feed fluctuations.
Residence-time studies
Study residence time and how a buffer smooths disturbances reaching downstream units.
Batch/continuous decoupling
Decouple batch and continuous sections, or stabilize a recycle loop.
Buffer sizing
Size a buffer (target mass) so downstream units see a steady feed under upstream upsets.
Upset scenarios
Investigate startup/shutdown and feed-interruption scenarios dynamically.
Technical FAQ
Why does powder stop flowing from a bunker?
Flow stops from arching/bridging or rat-holing — a granular-flow failure tied to hopper geometry and powder cohesion. DyssolPro doesn’t model that mechanism; it represents the bunker as a buffer, so it predicts holdup and discharge dynamics assuming flow is maintained, while the no-flow cause is a hopper-design matter (e.g. Jenike analysis).
How can I prevent bridging and rat-holing in a silo or bunker?
Prevention is geometric — steep enough, smooth enough hoppers sized from the powder’s flow function. This is outside the simulation’s scope; DyssolPro covers the holdup/buffering behavior once reliable flow is ensured, not the arching mechanics.
What hopper angle is needed for reliable powder discharge?
The required half-angle for mass flow comes from wall friction and the powder’s flow properties (Jenike method) — a mechanical-design calculation. DyssolPro doesn’t compute hopper geometry; it models the resulting flow as a buffer in the process.
How do I design a tank for slurry suspension without settling?
Keeping solids suspended needs an agitator sized to exceed the just-suspended speed — a mixing-hardware calculation. DyssolPro models the tank as an ideally mixed holdup and tracks the buffered stream, but it doesn’t design the agitator or predict settling.
How can I avoid segregation during storage of granular material?
Segregation (by size/density during filling and discharge) is a granular-mechanics effect the model doesn’t resolve. DyssolPro assumes ideal mixing; it predicts the buffered average properties, so it can’t reproduce segregation but flags where ideal-mixing is an approximation.
What causes caking in powder storage tanks?
Caking comes from moisture migration, time consolidation, and humidity — physico-chemical effects outside the buffer model. DyssolPro tracks the stored mass and its averaged state, not the caking chemistry; upstream moisture can be studied in the connected flowsheet.
How do I calculate residence time distribution in a bunker?
RTD follows from the holdup and the flow pattern — ideal-mixing gives a known exponential-type RTD, plug flow a delay. DyssolPro models the ideal-mixed (and plug-flow variant) holdup dynamically, so you obtain the residence behavior directly and see how it buffers disturbances.
What level measurement technology works best for dusty powders?
Level sensing (radar, capacitance, weigh cells) is an instrumentation choice, not a process-model output. DyssolPro predicts the holdup mass over time, which is the quantity such a sensor measures, providing a model baseline rather than selecting hardware.
How can I prevent moisture pickup in a powder storage tank?
Moisture pickup is controlled by sealing, dry purge, and ambient control — outside the model. DyssolPro doesn’t simulate moisture ingress, but you can model the upstream and downstream moisture states in the flowsheet to bound the exposure.
How do I size a buffer tank between continuous unit operations?
Buffer size is set by how much fluctuation you must absorb and the residence you need. This is exactly a DyssolPro use case: set the target holdup mass and simulate upstream upsets to see how well the buffer steadies the downstream feed, sizing it against the disturbance.
How can I improve mass flow in a powder bunker?
Mass flow (whole-contents-moving) is achieved by hopper geometry and liner friction — a design choice. DyssolPro models the discharge as a buffer and doesn’t distinguish mass from funnel flow mechanically; that distinction is a hopper-design matter.
Why does my silo discharge unevenly?
Uneven discharge points to funnel flow or partial rat-holing — granular mechanics. DyssolPro represents a controlled outflow (adaptive or requested) and doesn’t reproduce uneven flow, which is diagnosed against the model’s assumed steady discharge.
How do I choose between mass flow and funnel flow bunker design?
The choice trades cost against flow reliability and segregation, decided from the powder’s flow function and product needs. DyssolPro doesn’t perform that mechanical design; it models the buffering once the flow regime is chosen.
How can I avoid dead zones in a storage tank?
Dead zones (stagnant material) come from funnel flow or poor agitation — geometry and mixing hardware. The ideal-mixed model has no dead zones by assumption; DyssolPro therefore can’t predict them, and the fix is an equipment-design matter.
What causes powder segregation during filling of a bunker?
Fill segregation arises from size/density differences during heap formation — a granular effect not in the model. DyssolPro assumes ideal mixing, so it represents a homogenized holdup rather than the segregated reality.
How do I design an agitator for a slurry tank?
Agitator design (impeller type, speed, power) is a mixing-hardware calculation. DyssolPro models the tank as an ideally mixed buffer and doesn’t size the agitator; it assumes the mixing the agitator is meant to deliver.
How can I prevent sedimentation in a suspension tank?
Sedimentation is prevented by sufficient agitation relative to particle settling — a hardware/operation matter. DyssolPro’s ideal-mixed assumption presumes no settling; it buffers the suspension stream but doesn’t predict settling onset.
What is the best way to empty sticky powders from a tank?
Sticky-powder discharge needs flow aids (vibration, air pads, steep liners) — equipment solutions. DyssolPro models the holdup/discharge dynamics assuming flow is achieved, not the cohesion that impedes it.
How does wall friction affect bunker discharge?
Wall friction sets the mass-vs-funnel-flow boundary and the hopper angle needed — central to flow mechanics but outside the model. DyssolPro represents the discharge as a controlled outflow and doesn’t include wall friction, which is handled in mechanical hopper design.
How can I model residence time in a storage vessel?
This is squarely in scope: DyssolPro models the bunker as an ideally mixed (or plug-flow) holdup, so you obtain residence time and the RTD directly and study how the buffer smooths disturbances across the flowsheet.