How it works
A fluidized-bed spray granulator combines growth and drying in one fluidized bed. Particles are kept suspended by a hot gas while a liquid suspension is sprayed onto them; the liquid spreads over the surfaces and the solvent evaporates, depositing a thin solid layer, so each pass through the spray makes the particles grow. Evaporation runs at a near-constant rate while the surface stays wet and then slows as the layer dries, which ties growth and drying together — the same heat that dries the shell limits how fast fresh liquid can be added.
The bed behaves as a spraying zone, where wetting and growth happen, and a drying zone, where particles dry between spray passes — a structure that captures real bottom- and top-spray configurations. Fine particles can be carried out by the gas (elutriation), and product is separated out at the discharge. Keeping the wetting and drying in balance is the central challenge: too wet and the bed defluidizes or over-agglomerates, too dry and growth suffers.
The model
Dyssol Pro models the spray granulator dynamically over two zones — a spraying zone where wetting and growth occur and a drying zone where particles dry between passes — coupling layering growth by population balance with the heat and mass transfer of drying, and resolving particle size, moisture, and temperature at every time point of the flowsheet.
Growth is set by the sprayed solids spreading over the available particle surface area, while a share of the spray (overspray) dries in flight and leaves as dust; convective heat and mass transfer between gas and particles drives the evaporation along a drying curve from the wet surface down to the equilibrium moisture. Fine particles can be carried out of the bed by the gas, and product is withdrawn by a chosen discharge rule — a set bed height, a constant holdup, or a classifier cut at the outlet.
On this basis Dyssol Pro covers fluidized-bed layering-with-drying duties from bottom-spray (Wurster) and top-spray granulators to spouted-bed units, and even growth or drying 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 while drying them in one vessel.
Continuous FB spray granulators
Steady layering granulation with integrated drying.
Wurster (bottom-spray) granulators
Bottom spray for uniform layer growth and coating.
Top-spray FB granulators
Spray from above the bed, common for granulation.
Spouted-bed spray granulators
For coarse, dense, or sticky granules.
Typical engineering studies
What teams investigate with the spray-granulator model.
Product size/moisture prediction
Predict product size, moisture, and temperature for given spray and gas conditions.
Wetting–drying balance
Study spray rate vs. inlet gas temperature/flow against bed moisture to stay stable.
Spray & discharge configuration
Compare bottom- vs. top-spray configurations and the three discharge modes.
Elutriation & dust recovery
Quantify elutriation/dust losses and couple a downstream cyclone/filter and a screen recycle.
Calibration & scale-up
Calibrate growth, overspray, and drying parameters to data, then scale up.
Technical FAQ
How does a fluidized bed spray granulator work?
Hot gas fluidizes the particles, a suspension is sprayed onto them, and the solvent evaporates to leave a solid layer, so particles grow while drying in the same bed. Dyssol Pro models exactly this with coupled spraying and drying zones — population-balance layering growth plus heat and mass transfer — returning size, moisture, and temperature.
How can I control granule size in fluidized bed spray granulation?
Granule size is set by the spray rate, residence, and the classifier cut at discharge. Dyssol Pro couples growth to the sprayed-solids balance and offers a zig-zag discharge cut, so you can study how spray rate and cut size shape the product PSD.
Why are granules sticking to the walls of the granulator?
Wall sticking comes from locally overwet, tacky particle surfaces. Dyssol Pro tracks surface moisture and temperature per size class, so you can study spray and drying conditions that keep particles below the tacky state.
How do spray rate and drying air temperature affect granule growth?
Spray rate adds solids (growth) and liquid (wetting); air temperature sets drying capacity. Dyssol Pro resolves both through the coupled growth and heat/mass balances, so you can map growth rate and bed moisture against spray rate and inlet temperature.
How can I avoid overwetting in a spray granulation process?
Overwetting is avoided by keeping the spray rate within the bed’s drying capacity. Dyssol Pro models that balance explicitly — sprayed liquid against evaporation — so you can find the spray-rate/temperature window that keeps the bed moisture safe.
What causes broad particle size distribution in spray granulation?
A broad PSD comes from uneven growth, nucleation of new fines, and recycle. Dyssol Pro’s population balance resolves the full PSD and the classifier cut, so you can study which conditions broaden it and how classification tightens the product.
How do nozzle position and droplet size influence granule quality?
Nozzle position (bottom/top spray) sets where wetting and drying occur; droplet size affects layering vs. agglomeration. Dyssol Pro models the bottom/top spray gas routing and layering growth, so you can compare spray configurations, with droplet-scale detail entering through the calibrated growth parameters.
How can I improve binder distribution in fluidized bed granulation?
Even binder distribution comes from spray pattern, bed mixing, and drying balance. Dyssol Pro models the spray and drying zones and the net growth, so you can study the wetting-drying balance that supports uniform layering.
How do I prevent elutriation of fines in a spray granulator?
Elutriation falls with lower gas velocity and fewer fines. Dyssol Pro models elutriation with a size-dependent grade efficiency, so you can study how gas velocity and the fine fraction drive the loss and size a downstream cyclone/filter to recover it.
How can I scale up fluidized bed spray granulation?
Scale-up transfers the growth, overspray, and drying parameters to a larger bed and gas flow. Dyssol Pro lets you calibrate them at pilot scale and run the model at production geometry to check PSD, moisture, and dust before building.
How can I avoid spray nozzle clogging in fluidized bed granulation?
Clogging comes from suspension drying at the nozzle tip or from high solids and viscosity in the feed. It is controlled by conditioning the feed, keeping it flowing, adding nozzle purge or cooling air, and matching the nozzle bore to the suspension.
Why is my granulator producing hollow or weak granules?
Hollow or weak granules form from rapid drying or poor layer consolidation. Dyssol Pro computes the drying history — moisture and temperature — that governs them, so you can study gentler drying conditions that build denser, stronger layers.
How does atomization pressure affect granule size?
Atomization pressure sets droplet size, which influences layering vs. agglomeration and the granule structure. This enters Dyssol Pro through the calibrated growth parameters, so you can study its net effect on the product PSD.
How can I balance drying and wetting in spray granulation?
This is the core trade-off: enough spray for growth, enough heat for drying. Dyssol Pro models both explicitly in the two zones, so you can find the spray-rate/temperature/gas-flow combination that grows granules while keeping the bed in a stable moisture range.
What causes defluidization during spray granulation?
Defluidization happens when the bed gets too wet and sticky and particles stop fluidizing. Dyssol Pro tracks the surface moisture and temperature that precede it, so you can steer the spray and drying conditions that keep the bed safely fluidized.
How do seed particles affect granule growth?
Seed (nuclei) number and size set the surface area sharing the spray, hence the per-particle growth rate. Dyssol Pro takes an external-nuclei inlet and couples growth to total surface area, so you can study how seed feed and size control the product size.
How can I control layering versus agglomeration mechanisms?
Layering (smooth shell growth) dominates at good drying; agglomeration (sticking) dominates when wetter. Dyssol Pro’s granulator models the layering mechanism; for agglomeration-dominated growth the agglomerator’s kernel model is the right tool, and comparing the two helps you target the regime you want.
What is the impact of binder viscosity on spray granulation?
Binder viscosity affects droplet spreading and layer formation — a material property that enters through the growth behavior. Dyssol Pro captures its net effect via calibrated growth parameters, so you can study how it shifts the product PSD.
How can I reduce batch-to-batch variation in spray granulation?
Variation comes from inconsistent seed, spray, and drying conditions. Dyssol Pro lets you run sensitivity studies on those inputs to see which most move the product PSD and moisture, so you control the critical ones for consistency.
How do I model nucleation, growth, and breakage in fluidized bed granulation?
A full population balance for granulation growth tracks three mechanisms: nucleation forms new fine particles, layering growth deposits sprayed solids onto existing particle surfaces, and breakage fractures particles into smaller ones. Dyssol Pro’s spray granulator implements nucleation — through the external nuclei inlet and overspray — and layering growth in its population balance, while agglomeration-driven growth and breakage are represented by combining it with Dyssol Pro’s agglomerator and mill units, so you match whichever mechanisms your process actually shows.