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 stored mass rises or falls with the difference between them.
How much the contents mix while they pass through matters just as much as how much is stored. At one extreme the whole vessel is well stirred, so what leaves has the averaged composition of everything inside; at the other, material moves through in the order it arrived, so a change at the inlet reappears at the outlet only after the stored material ahead of it has left. Real vessels sit between these, depending on geometry and flow pattern.
The model
Dyssol Pro models the bunker as a dynamic solids holdup: the stored mass rises or falls with the difference between the inflow and the outflow, and the unit maintains time-dependent norms of the stream properties and distributions so the buffering dynamics are represented correctly at every time point of the flowsheet. Only the solid phase is accumulated; other phases pass through.
Two mixing behaviors are available. An ideally-mixed bunker treats the whole contents as one well-stirred holdup, so the outflow always carries the homogenized, averaged composition of everything inside. A non-mixing bunker instead keeps a queue of internal compartments — inflow fills the newest while outflow is drawn from the oldest — so material leaves in roughly the order it entered, and the chosen compartment size sets how far the behavior sits between perfect mixing and first-in-first-out plug flow.
In either case the discharge is controlled: the outflow can be held to a requested rate whenever enough material is present, or simply follow the inflow, and the ideally-mixed bunker can additionally steer its holdup toward a target mass. On this basis Dyssol Pro represents any solids buffer between connected units — silos, hoppers, surge bins, or stirred tanks — so the holdup and its averaged properties are tracked, upstream disturbances are damped, and buffer capacity is sized inside the dynamic flowsheet.
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 — a stable bridge over the outlet — or rat-holing — a stable vertical channel — both from cohesive powder in an outlet or hopper that is too small or too shallow. It is cured by sizing the outlet above the powder’s critical arching dimension and making the hopper steep and smooth enough for mass flow, using the measured flow function.
How can I prevent bridging and rat-holing in a silo or bunker?
Prevention is geometric: a large enough outlet and a hopper steep and smooth enough for mass flow, both sized from the powder’s measured flow function and wall friction. Where geometry alone is not enough, discharge aids such as vibration, air pads, or an activated hopper section restore reliable flow.
What hopper angle is needed for reliable powder discharge?
The hopper half-angle for mass flow follows from the wall-friction angle between the powder and the wall material and the powder’s internal flow properties, measured in a shear tester. Steeper, smoother walls give mass flow; a rough guide is 15 to 30 degrees from vertical, but the value must be set from the measured properties for the actual powder and wall.
How do I design a tank for slurry suspension without settling?
Keeping solids suspended needs an agitator sized so its speed exceeds the just-suspended condition for the coarsest, densest particles, which depends on particle size and density, solids loading, and liquid viscosity. The impeller type, diameter, and speed are chosen to reach that condition with margin for the heaviest expected feed.
How can I avoid segregation during storage of granular material?
Segregation during storage comes from size and density differences as material forms a heap on filling and drains on discharge. It is limited by mass-flow hopper design that keeps first-in-first-out flow, central loading to reduce rolling on the pile, lower drop heights, and a narrower feed size distribution.
What causes caking in powder storage tanks?
Caking comes from moisture migration, time consolidation under the material’s own weight, and humidity cycling that bonds particles into a solid mass. It is limited by drying the feed, sealing against humid air, and avoiding long static storage. Dyssol Pro tracks the stored mass and the composition of the buffered stream, so you can study how upstream moisture reaches the store 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. Dyssol Pro 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 for dusty powders uses radar, guided-wave, capacitance, or weigh cells, chosen for the dust, dielectric, and vessel geometry. Dyssol Pro predicts the holdup mass over time, which is exactly the quantity such a sensor tracks, giving a model baseline to compare live readings against.
How can I prevent moisture pickup in a powder storage tank?
Moisture pickup is controlled by sealing the vessel, applying a dry-gas purge or blanket, and controlling the ambient humidity around the store. Dyssol Pro tracks the moisture state of the streams entering and leaving the store, so you can bound the exposure across the connected flowsheet.
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 Dyssol Pro 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, where the whole contents move together, is achieved by making the hopper steep and smooth enough and the outlet large enough, set from the powder’s wall friction and flow function. Low-friction liners, the right wall angle, and an adequately sized outlet are the main levers, with discharge aids where geometry alone falls short.
Why does my silo discharge unevenly?
Uneven or pulsing discharge usually means funnel flow or partial rat-holing, where only a central core moves while material at the walls stays put. It is corrected by steepening and smoothing the hopper toward mass flow, enlarging the outlet, or fitting a flow-promoting insert or discharge aid.
How do I choose between mass flow and funnel flow bunker design?
Mass flow gives first-in-first-out movement, no dead zones, and minimal segregation but needs steeper, taller hoppers and costs more; funnel flow is cheaper and more compact but risks rat-holing, dead zones, and segregation. The choice is made from the powder’s flow function, its cohesion and segregation tendency, and whether the product tolerates uneven residence time.
How can I avoid dead zones in a storage tank?
Dead zones — stagnant material at the walls or corners — come from funnel flow in a hopper or poor agitation in a tank. They are avoided by mass-flow hopper geometry with steep, smooth walls and a large outlet, or, in a stirred vessel, by an impeller and baffling that sweep the full volume.
What causes powder segregation during filling of a bunker?
Fill segregation arises as particles form a heap: coarse or dense particles roll to the walls while fines stay near the centre, and dust can be carried off by air currents. It is limited by central loading, reducing the drop height, using a distributor or fill pipe, and narrowing the feed size distribution.
How do I design an agitator for a slurry tank?
Agitator design starts from the duty — solids suspension, blending, or heat transfer — then selects an impeller type and diameter and the speed and power that meet it. For suspension the speed is set above the just-suspended condition for the coarsest, densest particles, with the motor sized from the power number, the fluid density, and the resulting torque.
How can I prevent sedimentation in a suspension tank?
Sedimentation is prevented by keeping the agitation above the level at which the coarsest, densest particles settle, which depends on particle size and density, solids loading, and liquid viscosity. Adequate impeller speed and placement, and sometimes a draft tube or a set off-bottom clearance, keep the solids suspended.
What is the best way to empty sticky powders from a tank?
Sticky, cohesive powders discharge best from a mass-flow hopper with steep, low-friction walls and a generously sized outlet, backed by flow aids where needed — vibration, air pads or fluidizing cones, or a mechanical activator. Keeping the powder dry and avoiding long static storage that lets it consolidate also helps it release.
How does wall friction affect bunker discharge?
Wall friction — the friction angle between the powder and the wall material — sets whether a hopper runs in mass flow or funnel flow and the wall angle needed for mass flow. Higher wall friction demands a steeper hopper; lower friction, from a polished or lined wall, allows a shallower one and more reliable flow.
How can I model residence time in a storage vessel?
This is squarely in scope: Dyssol Pro 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.