How it works
In fluidized-bed spray granulation, seed particles (nuclei) are kept fluidized by a gas stream while a liquid suspension is sprayed onto them. The liquid spreads over the particle surfaces and the solvent evaporates, leaving a thin solid shell — so each pass through the spray adds a layer and the particle grows. This layering mechanism makes growth roughly proportional to the available surface area: the more total particle surface in the bed, the thinner each layer.
The two operating modes differ in how the bed is managed. In continuous operation, fresh nuclei enter and grown product is withdrawn, so the bed reaches a steady size distribution set by the balance of spray rate, nuclei feed, and product withdrawal. In batch operation no product is withdrawn, so the whole size distribution shifts upward over time and the total solid mass in the bed increases, while total solid mass is conserved.
Not all sprayed material lands on particles — a fraction (overspray) dries in flight and leaves as dust. The practical challenge in both modes is to grow granules to target size and strength without overwetting or defluidizing the bed. In high-shear granulators — a different mechanism — growth is dominated by coalescence under impeller shear; that route is better represented by the agglomerator.
The model
Dyssol Pro models fluidized-bed layering granulation in both continuous and batch operation: it solves a population balance in which sprayed solids deposit over the total particle surface area to grow the granules, with an overspray fraction reporting to dust and a moisture balance setting the liquid leaving with the product, at every time point of the flowsheet.
Growth is coupled to surface area: the sprayed solids spread over all the particles in the bed, so the more total surface present, the thinner the layer each particle gains. In continuous operation fresh nuclei enter and product is withdrawn, so the bed settles to a steady size distribution; in batch operation nothing is withdrawn, so the whole distribution shifts upward and the bed mass grows toward the endpoint. Total solid mass is conserved, with particle size tracked as the primary property.
On this basis Dyssol Pro covers fluidized-bed layering duties from continuous and batch granulators to spouted-bed units and bottom-spray coaters, and even growth behavior beyond the standard description can be brought into the flowsheet.
Equipment this model can represent
Any fluidized-bed process that grows particles by layering sprayed suspension.
Continuous FB granulators
Steady spray-on-fluidized-bed layering with continuous product draw.
Batch FB granulators
Spray-on-fluidized-bed layering of a fixed charge.
Spouted-bed granulators
For coarse or sticky granules.
Wurster-type coaters
Bottom-spray layering for uniform shells and pellets.
Typical engineering studies
What teams investigate with the granulator model.
Product PSD prediction
Predict the steady-state product PSD (continuous) or the PSD-versus-time growth curve and endpoint (batch).
Start-up & transients
Study start-up, feed fluctuations, and the approach to steady state dynamically.
Granulation circuits
Couple with screens/mills and recycle to study size control and recycle load.
Dust quantification
Quantify dust (overspray) losses and couple a downstream cyclone/filter.
Sensitivity & scale-up
Run sensitivity/DoE on spray rate, charge, and seed PSD, then calibrate and scale up from pilot to commercial throughput.
Technical FAQ
How do I determine the endpoint of a batch granulation process?
The endpoint is when the granules reach target size (and strength), which for layering corresponds to a spray duration. Dyssol Pro models the PSD growth over time, so you can read off the spray time that reaches the target size and use that as a model-based endpoint, before refining it experimentally.
Why is my batch granulator producing inconsistent granules?
Inconsistency usually traces to variable seed PSD, spray rate, or wetting between runs. Dyssol Pro lets you vary those inputs and see how sensitively the product PSD responds, pinpointing which to control tightest for reproducibility.
How does liquid addition rate affect batch granulation?
The spray (liquid) rate sets how fast solids are deposited and how wet the bed gets — too fast risks overwetting. Dyssol Pro couples the deposited-solids growth to the spray rate, so you can study how it drives the growth trajectory and final size.
How can I avoid overwetting in batch granulation?
Overwetting is avoided by keeping spray rate below the bed’s drying capacity. Dyssol Pro tracks the solids growth and the liquid leaving via exhaust, so you can study spray rates that keep the bed within a safe wetting balance.
What causes large lumps in a high-shear granulator?
Lumps come from localized overwetting and uncontrolled coalescence under shear, so they are controlled by evening out wetting and capping the liquid input. In Dyssol Pro the coalescence-driven growth is captured with the agglomerator’s kernel model, so you can study the operating points that keep granules on-size.
How do impeller and chopper speed affect granule size?
Impeller and chopper speed are high-shear variables that drive coalescence and breakage, raising collision frequency until breakage balances growth, so size peaks at an optimum. In Dyssol Pro their net effect on size is captured through calibrated growth parameters or the agglomerator’s coalescence kernel.
How can I improve reproducibility between batch granulation runs?
Reproducibility comes from controlling the critical inputs (seed, spray, endpoint). Dyssol Pro identifies which inputs most move the product PSD via sensitivity studies, so you know what to standardize to tighten run-to-run consistency.
What are critical process parameters in batch granulation?
Typically spray rate, total liquid, seed PSD, and endpoint timing. Dyssol Pro lets you rank these by their effect on the product PSD in a model-based DoE, focusing experimental effort on the truly critical ones.
How do I transfer a batch granulation recipe to larger scale?
Scale-up transfers the fitted growth behavior and matches the spray-to-surface balance at larger charge. Dyssol Pro lets you calibrate the growth parameters on lab batches and run the model at the larger charge to predict the growth curve and endpoint.
How can I model particle growth in batch granulation?
This is the unit’s purpose: a population balance with surface-area-coupled layering growth and increasing bed mass. In Dyssol Pro you set the spray and charge and it returns the PSD-versus-time growth trajectory.
How can I identify the optimal granulation endpoint using torque?
Torque-based endpoints belong to high-shear granulation, where torque tracks the wet-mass consistency as liquid is added. Dyssol Pro gives a size-based endpoint from the PSD growth curve, so you can define the endpoint from the target granule size directly.
Why does my batch granulation produce too many fines?
Excess fines mean insufficient growth or too much overspray/seed carryover. Dyssol Pro tracks the PSD growth, so you can study how spray rate and duration shift the fine fraction toward the target.
How does fill level affect batch granulator performance?
Fill (charge mass) sets the total surface area sharing the spray and therefore the per-particle growth rate. Dyssol Pro couples growth to total surface area, so you can study how charge mass changes the growth rate and time-to-endpoint.
How can I avoid overgranulation in high-shear mixing?
Overgranulation is runaway coalescence from too much liquid or massing time. In Dyssol Pro the coalescence-driven regime is captured with the agglomerator’s kernel model, so you can study the liquid input and residence time that keep growth controlled against the target size.
What causes poor binder distribution in batch granulation?
Uneven binder comes from spray pattern, droplet size, and bed mixing, and is improved with finer atomization and better fluidization. In Dyssol Pro the net growth effect of the binder is propagated through the PSD, so you can study how the overall spray rate shifts the product size.
How do I optimize wet massing time?
Wet massing is the high-shear step where the wetted mass is worked before or after liquid addition to distribute binder and densify the granules. It is optimized by balancing massing time and liquid level to reach the target granule density and size without tipping into overgranulation.
How does powder cohesiveness affect batch granulation?
Cohesion affects fluidization quality and how readily the powder wets and nucleates, so cohesive powders may need stronger fluidization or flow aids. In Dyssol Pro the resulting growth behavior is represented through calibrated parameters, so you can study how it shifts the product PSD.
How can I improve granule flowability after batch granulation?
Flowability improves with larger, rounder, less dusty granules. Dyssol Pro predicts the product PSD and dust, the main drivers of flowability, so you can target a size distribution that flows well.
How do I reduce cleaning time after batch granulation?
Cleaning time is driven by the equipment geometry and how much sticky material deposits on surfaces. It is reduced with accessible, well-draining geometries, clean-in-place design, and operating points that avoid the overwetting that leaves tacky deposits.
How can I model batch granulation using population balances?
This is exactly what the unit does: a population balance advancing the PSD by layering growth with increasing bed mass. In Dyssol Pro you parameterize the growth and run it to get the PSD trajectory, the basis for endpoint and scale-up studies.
How does continuous granulation differ from batch granulation?
In continuous operation nuclei are fed and product withdrawn so the bed runs at a steady size distribution, whereas a batch grows the whole charge over time. Dyssol Pro provides both modes of the granulator, so you can simulate the continuous steady state (and its dynamics) or the batch growth curve and compare them directly.
How can I control residence time in a continuous granulator?
Residence time is set by the bed holdup divided by the throughput, which you adjust through nuclei feed and product withdrawal. Dyssol Pro models the holdup and flows dynamically, so you can study how feed and withdrawal set residence and therefore the product size.
Why does continuous granulation produce variable particle size?
Size variability comes from fluctuations in spray rate, nuclei feed, or recycle, and from the granulation dynamics amplifying them. Dyssol Pro’s population-balance model lets you impose those disturbances and see how the product PSD responds, helping you find stabilizing operating points.
How do feed rate fluctuations affect continuous granulation quality?
Feed swings shift the surface-area balance and therefore the growth rate and product size. In Dyssol Pro you apply feed-rate transients and track the PSD response, quantifying how much a given fluctuation moves the product — and how a buffer or control loop would damp it.
How can I control moisture content in continuous granulation?
Granule moisture is set by the balance of sprayed liquid against evaporation and the moisture leaving with product. Dyssol Pro carries a granule-moisture parameter and the liquid balance, so you can study how spray rate and gas conditions set the product moisture.
What sensors are useful for real-time granulation control?
Real-time control typically uses PSD (spatial filter velocimetry), bed temperature, and humidity sensors. Dyssol Pro predicts the PSD, moisture, and flows those sensors measure, giving a model basis for control design and soft sensors.
How do I start up and shut down a continuous granulation process?
Startup and shutdown are transient operations where the bed builds up or runs down toward/away from steady state. Dyssol Pro is dynamic and was validated on continuous-granulation startup, so you can simulate these transients and design the procedure and off-spec handling.
How can I prevent clogging in a continuous granulator?
Clogging from nozzle fouling and sticky deposits is tied to overwetting and stickiness. Dyssol Pro tracks the liquid balance and overspray, so you can study spray rates that avoid the overwet conditions that lead to clogging.
How do I compare twin-screw granulation and drum granulation?
Twin-screw and drum granulation use different growth mechanisms — shear-driven coalescence versus tumbling and layering — and different equipment. In Dyssol Pro each mechanism’s net effect is represented through calibrated growth parameters, so you can compare their process behavior and product PSD side by side in the flowsheet.
How can I model continuous granulation dynamics?
This is the unit’s purpose: a population balance with surface-area-coupled growth, overspray, and continuous feed/withdrawal. In Dyssol Pro you set those parameters and it returns the dynamic and steady-state PSD inside the flowsheet.
How can I stabilize product quality in continuous granulation?
Stable product comes from steady operating points and control of size via recycle/classification. Dyssol Pro lets you find stable windows and test control strategies on the dynamic model before applying them to the plant.
What causes residence time distribution broadening in a continuous granulator?
RTD broadening comes from back-mixing in the bed and recycle loops. Dyssol Pro models the bed holdup and any recycle, so you can study how mixing and recycle widen the RTD and affect product uniformity.
How do screw configuration and speed affect twin-screw granulation?
Screw configuration and speed set the conveying, mixing, and shear in a twin-screw granulator, driving coalescence and breakage and therefore granule size. In Dyssol Pro their net effect on growth and PSD is captured through calibrated growth parameters.
How can I control liquid-to-solid ratio in continuous granulation?
The liquid-to-solid ratio drives both growth and moisture, set by spray and solids feed rates. Dyssol Pro tracks both the solids growth and the liquid balance, so you can study how the ratio shifts product size and moisture.
How do I handle off-spec material during continuous granulation startup?
Off-spec product during startup is screened and often recycled. Dyssol Pro simulates the startup transient and any recycle/classification, so you can estimate the off-spec quantity and design how to rework it.
What is the best control strategy for continuous wet granulation?
Effective control targets PSD and moisture against feed and recycle disturbances. Dyssol Pro lets you test candidate strategies on the dynamic model — how the PSD and moisture respond to control moves — before commissioning.
How can I integrate drying after continuous granulation?
Granules usually need post-drying to final moisture. In Dyssol Pro you connect the granulator to a fluidized-bed dryer and study how the granule moisture evolves through the combined process.
How do I reduce waste in continuous granulation?
Waste is mainly dust (overspray) and off-spec product. Dyssol Pro quantifies the overspray-to-dust split and the off-spec fraction, so you can study operating points and recycle that minimize both.
How can I scale continuous granulation from pilot to commercial scale?
Scale-up transfers the fitted growth and overspray parameters to larger throughput and bed. Dyssol Pro lets you calibrate at pilot scale and run the model at commercial throughput inside the flowsheet to check PSD and dust before building.
How do I simulate recycle loops in continuous granulation?
Recycle of screened fines/oversize is central to granulation circuits. Dyssol Pro solves the recycle loop dynamically, so you can study how cut sizes and recycle ratios set the product PSD and the circulating load.