How it works
A fluidized-bed spray granulator combines growth and drying in one fluidized bed. Particles are kept suspended by a hot gas; a liquid suspension is sprayed onto them, spreads over the surfaces, and the solvent evaporates, depositing a solid layer — so particles grow by layering, pass after pass. Unlike the simplified granulator, this model resolves the drying explicitly: heat from the gas evaporates the liquid (constant-rate while the surface is wet, then a falling rate as it dries), and it tracks size-dependent moisture and temperature.
The bed is split into 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 by a chosen separation mode. 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
The fluidized-bed spray granulator is a dynamic, two-zone model — a spraying zone and a drying zone, each with two ideally mixed phases (solid+liquid and gas+vapor). It couples population-balance layering growth with explicit drying, resolving particle size, moisture, and temperature.
Layering growth in the spraying zone is driven by the effective sprayed solids over the particle surface, with the overspray fraction K_os reporting to dust. Drying uses convective heat and mass transfer (Nusselt/Sherwood) with a relative-drying-rate curve between the critical and equilibrium moisture. Fines leave by elutriation (a settling-velocity grade efficiency), and product is withdrawn by one of three discharge modes. One compound of each type is supported.
Configurable options
- Spray configurationBottom- or top-spray, setting the gas routing between the spraying and drying zones.
- Discharge modeTarget bed height, constant holdup, or a zig-zag classifier cut at the product outlet.
- Drying curveCritical and equilibrium moisture defining the relative-drying-rate curve.
- Overspray fraction K_osShare of sprayed solids that bypasses growth and reports to dust.
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. DyssolPro 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. DyssolPro 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 surfaces — a stickiness effect not modelled mechanically. DyssolPro tracks surface moisture and temperature per size class, so you can study spray/drying conditions that keep particles below the tacky state, while the wall deposit itself is equipment-side.
How do spray rate and drying air temperature affect granule growth?
Spray rate adds solids (growth) and liquid (wetting); air temperature sets drying capacity. DyssolPro 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. DyssolPro 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. DyssolPro’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. DyssolPro models the bottom/top spray gas routing and layering growth, so you can compare spray configurations — droplet-scale detail enters through the growth parameters rather than explicit atomization.
How can I improve binder distribution in fluidized bed granulation?
Even binder distribution comes from spray pattern, bed mixing, and drying balance. DyssolPro doesn’t resolve in-bed spray uniformity, but it models the spray/dry 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. DyssolPro 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. DyssolPro 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 is a nozzle/feed issue (drying at the tip, solids, viscosity) outside the model. DyssolPro covers the granulation once droplets are sprayed; nozzle design and feed handling are equipment-side, though the wetting balance it predicts helps avoid the overwet conditions around the nozzle.
Why is my granulator producing hollow or weak granules?
Hollow/weak granules form from rapid drying or poor layer consolidation — morphology effects the model doesn’t predict mechanistically. DyssolPro computes the drying history (moisture, temperature) that governs them, so you can study gentler drying conditions, while strength/morphology stay experimental.
How does atomization pressure affect granule size?
Atomization pressure sets droplet size, which influences layering vs. agglomeration and the granule structure. This enters DyssolPro through the growth parameters rather than an explicit atomization model, so you study its net effect on PSD via calibration.
How can I balance drying and wetting in spray granulation?
This is the core trade-off: enough spray for growth, enough heat for drying. DyssolPro 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/sticky and particles stop fluidizing — a hydrodynamic failure not resolved by the model. DyssolPro tracks the surface moisture and temperature that precede it, so you can avoid those conditions, but the fluidization mechanics are equipment-side.
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. DyssolPro 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. DyssolPro’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 entering through the growth behavior. DyssolPro captures its net effect via calibrated growth parameters rather than a rheological sub-model.
How can I reduce batch-to-batch variation in spray granulation?
Variation comes from inconsistent seed, spray, and drying conditions. DyssolPro 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?
DyssolPro models growth by layering (with external nucleation via the nuclei inlet and overspray) in this unit; breakage/attrition is not included, and agglomeration-type growth is handled by the agglomerator. So you model nucleation and layering growth here and add breakage or agglomeration units where those mechanisms matter.