What are the core material characteristics for centrifugal spray dryers?

The core material properties of centrifugal spray dryers serve as the key basis for equipment selection and process design, directly impacting equipment performance, product quality, and production efficiency. The following provides a detailed analysis across three dimensions: physical, chemical, and process adaptability:

I. Physical Properties: Determining Atomization and Drying Behavior

Viscosity Range

Low-viscosity materials (e.g., water, dilute solutions):

Excellent flowability, easily pumped to atomizers, suitable for centrifugal atomizers (rotation speed 10,000–50,000 rpm).

Examples: Milk, juice concentrates (viscosity <100 mPa·s). Produces uniform droplets with high drying efficiency.

High-viscosity materials (e.g., colloids, polymer solutions):

Requires dilution or specialized atomizers (e.g., pressure-type or centrifugal atomizers with anti-adhesion coatings).

Examples: Honey, starch slurry (viscosity 500–2000 mPa·s). Requires increased atomization pressure or reduced feed rate to prevent clogging.

Solid Content

Low-solid-content materials (e.g., herbal extracts, emulsions):

High water content (>80%), requiring large hot air volume for rapid evaporation, prone to fine powder generation.

Example: Chinese herbal extracts (10%-20% solids), necessitating cyclone separators + baghouse dust collectors to enhance recovery rates.

High-solids materials (e.g., suspensions, slurries):

Solid particles readily settle, requiring agitation or circulation systems to prevent agglomeration.

Example: Ceramic slurry (40%-60% solids content) requires wear-resistant atomizing discs (e.g., tungsten carbide).

Surface Tension

Low surface tension materials (e.g., solutions containing surfactants):

Form fine droplets (d50 < 30μm) but prone to foaming, necessitating defoamers.

Example: Detergent raw material solution; atomized droplets can be controlled below 20μm diameter.

High Surface Tension Materials (e.g., pure water, sugar solutions):

Larger droplets (d50 > 50μm); atomization pressure or rotational speed must be increased to refine particles.

Example: Glucose solution; increasing centrifugal disc speed to 30,000 rpm reduces particle size to 40μm.

II. Chemical Properties: Impact on Equipment Materials and Safety

Corrosivity

Acidic materials (e.g., citric acid, hydrochloric acid solutions):

Require 316L stainless steel or Hastelloy to prevent corrosion of ordinary carbon steel.

Example: In food additive production, using 316L for contact parts extends service life by 3 times.

Alkaline materials (e.g., sodium hydroxide solutions):

Require anti-alkali embrittlement treatment, such as PTFE (polytetrafluoroethylene) lining.

Example: In paper mill waste liquid treatment, PTFE-lined tower interiors reduced corrosion rates by 90%.

Flammability and Explosiveness

Materials containing organic solvents (e.g., ethanol, acetone):

Must use closed-loop models equipped with nitrogen purging, explosion-proof motors, and oxygen content monitoring (≤3%). .

Example: Pharmaceutical industry drying ethanol solutions using ATEX-certified OKAD explosion-proof models.

Dust explosion risk materials (e.g., starch, powdered sugar):

Requires wet dust collectors or inert gas protection to prevent excessive oxygen concentration in drying chambers.

Example: Flour mill adopting QFN-BL models with nitrogen displacement eliminates explosion risk.

Heat-sensitive

Active ingredient materials (e.g., enzymes, probiotics, vitamins):

Requires low-temperature drying (inlet air temperature <100°C) to prevent high-temperature inactivation.

Example: A biopharmaceutical company drying proteases using the QFN-DW-5 low-temperature model with 80°C inlet air temperature achieved 98% activity retention.

Color-sensitive materials (e.g., natural pigments, flavorings):

Requires controlled hot air temperature and residence time to prevent oxidation discoloration.

Example: During paprika drying, gradient temperature control (120°C → 80°C → 60°C) reduced color value loss by 50%.

III. Process Adaptability: Aligning with Production Goals

Particle Size and Distribution

Fine powder requirements (e.g., milk powder, catalysts):

Centrifugal atomizers produce uniform particles with d50=20-60μm, suitable for inhalation-grade products.

Example: For infant formula drying, the QFN-L series achieves particle size distribution CV <15%.

Coarse particle requirements (e.g., instant coffee, granular fertilizers):

Pressure atomizers generate particles with d50=100-300μm, offering superior flowability.

Example: In instant coffee production, adjusting nozzle orifice size (0.5-2.0mm) controls particle size around 150μm.

Moisture Control

Low moisture content requirements (e.g., desiccants, inorganic salts):

Requires extended drying time or elevated hot air temperature, while avoiding product overheating.

Example: Molecular sieve drying achieves final moisture content below 0.1% using a two-stage drying process.

Tolerance for high moisture content (e.g., feed, fertilizer):

Final moisture content can be appropriately relaxed (3%-5%) to reduce energy consumption.

Example: In fish meal production, a single-stage drying process suffices when final moisture is controlled at 5%.