What particle size range is suitable for a rotary drum dryer?

Rotary drum dryers work best with particles in the range of 2–50 mm. The lower limit (2 mm) is set by dust carryover in the exhaust gas — very fine material is entrained in the gas stream and lost. The upper limit depends on flight design and drum size; with custom-designed flights, particles up to 100 mm can be processed. For particles below 1–2 mm requiring uniform drying, a fluidized bed dryer is more appropriate. For powders and filter cakes below 500 µm, a flash dryer is the better choice.

How much energy does a rotary dryer consume per kilogram of water evaporated?

A well-designed rotary dryer consumes 800–1,400 kcal (3.3–5.8 MJ) per kg of water evaporated, depending on inlet moisture, operating temperature, insulation quality and whether exhaust gas heat is recovered. The theoretical minimum for water evaporation is ~600 kcal/kg. The gap above theoretical is mainly heat lost in the exhaust gas. Installing a heat recovery system (HRSG) on the exhaust gas can reduce net energy consumption by 15–30%. Electrical consumption for drive, fans and auxiliary systems typically adds 15–25 kWh per tonne of dry product.

Can a rotary dryer handle materials with explosion risk (dust or solvent)?

Rotary dryers can be designed for dust-explosive or solvent-containing materials, but require ATEX-compliant design: inert gas operation (nitrogen purge), explosion-relief venting, spark detection, interlocked temperature and oxygen monitoring, and ATEX-rated motors and instrumentation. For materials with very high explosion sensitivity (Kst > 200 bar·m/s), alternative equipment (paddle dryer with indirect heating) may be preferable. All Ermak Proses dryers are designed to EU Machinery Directive standards; ATEX configuration is specified at order stage.

What is the typical delivery time for a rotary dryer?

Delivery time depends on drum size and configuration. Standard single-pass units in the range of 1.5–2.5 m diameter: 12–20 weeks from order confirmation. Large units (3 m+ diameter, custom flights): 20–32 weeks. Combined dryer-cooler or triple-pass units: add 4–8 weeks. Lead time includes engineering, fabrication, quality inspection and shipping from Turkey to your site. We provide detailed delivery schedules at quotation stage.

What maintenance does a rotary dryer require?

Rotary dryers have fewer wearing parts than almost any other industrial dryer. Main maintenance items: (1) Tyre and riding ring wear — inspected every 6–12 months, replacement every 5–15 years depending on material and operating hours. (2) Trunnion roller adjustment — quarterly check of drum alignment. (3) Drive chain/girth gear — monthly lubrication, annual inspection. (4) Refractory lining (if fitted) — inspection after every 3,000 hours. (5) Flight replacement — every 3–10 years depending on abrasion. Planned maintenance shutdown: typically 2–5 days per year.

How do I choose between a rotary dryer and a fluidized bed dryer?

The core question is particle size and required drying uniformity. Use a rotary dryer when: particle size > 3 mm, feed is sticky or variable, throughput > 30 t/h, high inlet moisture (>15%), or operating temperature > 350°C. Use a fluidized bed dryer when: particle size is 50 µm–5 mm, uniform product moisture is critical, simultaneous drying and cooling in one unit is needed, or gentle handling is required to preserve crystal structure. For the same throughput, fluidized beds have lower energy consumption for fine particles but higher capital cost. Rotary dryers have lower capex at large scale. When in doubt, send us your process data and we will recommend the right solution.

Can the dryer be used for calcination, not just drying?

Yes. At temperatures above 800–900°C with refractory-lined drums, rotary equipment transitions from drying to calcination service. The drum design and refractory specification change significantly for calcination duty. Ermak Proses manufactures both drying-grade and calcination-grade rotary units. Typical calcination applications: lime (CaCO₃ → CaO), dolomite, bauxite, kaolin activation and catalyst regeneration. If your application involves both drying and calcination in sequence, we can design a two-zone drum with a transition section.

drying systems

Rotary (Drum) Dryer & Cooler

The workhorse of bulk solid drying — robust, high-capacity, high-temperature.

Rotary drum dryers are the most widely deployed industrial dryer type for coarse bulk solids. Their robust construction tolerates wide fluctuations in feed moisture, particle size and throughput — making them the first choice for minerals processing, biomass energy, fertilizer production and aggregate drying where throughput matters more than precision.

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Rotary (Drum) Dryer & Cooler — The workhorse of bulk solid drying — robust, high-capacity, high-temperature.

How a Rotary Drum Dryer Works

A rotary drum dryer consists of a cylindrical shell, slightly inclined at 1–5°, rotating at 1–8 RPM. Wet material enters at the elevated feed end and travels through the drum by gravity and the rotation-driven conveying action of internal lifting flights.

The lifting flights — shaped steel vanes welded to the drum interior — continuously pick up the material, carry it upward, then shower it through the hot gas stream flowing along the drum axis. This cascade action maximises gas-solid contact surface and is the primary mechanism of heat and mass transfer.

Hot gas flow can be co-current (gas and material move in the same direction) or counter-current (gas flows opposite to material travel). Co-current is used for high initial moisture content, heat-sensitive materials and sticky feeds. Counter-current achieves lower final moisture levels and is used when product temperature must be elevated, or when the last percentage points of moisture are difficult to remove.

Dried product exits at the lower discharge end. Where cooling is required, the same shell can be partitioned into a drying zone and a cooling zone, or a separate cooler drum can be attached in line — the combined unit is called a rotary dryer-cooler.

Quick Reference

Feed particle size2 mm – 50 mm (up to 100 mm with modified flights)

Inlet moisture content5% – 60% (w.b.)

Outlet moisture content0.1% – 1.0% (w.b.) — product-dependent

Gas inlet temperature (co-current)300°C – 900°C

Gas inlet temperature (counter-current)200°C – 600°C

Product outlet temperature (co-current)60°C – 120°C

Drum diameter0.6 m – 4.5 m

Full specifications ↓

Technical Specifications

All parameters are indicative ranges. Final sizing is determined by process simulation based on your specific material and throughput requirements.

Standard Operating Parameters

Parameter	Value / Range	Note
Feed particle size	2 mm – 50 mm (up to 100 mm with modified flights)
Inlet moisture content	5% – 60% (w.b.)
Outlet moisture content	0.1% – 1.0% (w.b.) — product-dependent
Gas inlet temperature (co-current)	300°C – 900°C
Gas inlet temperature (counter-current)	200°C – 600°C
Product outlet temperature (co-current)	60°C – 120°C
Drum diameter	0.6 m – 4.5 m
Drum length	4 m – 30 m (L/D ratio typically 4:1 – 10:1)
Drum inclination	1° – 5° (adjustable for residence time control)
Rotation speed	1 – 8 RPM (VFD-controlled)
Evaporation capacity	0.5 – 50 t water/hour
Throughput range	1 – 200 t/h dry product (application-dependent)
Specific energy consumption	800 – 1,400 kcal/kg water evaporated (3.3 – 5.8 MJ/kg)	Lower end achievable with waste heat integration
Drum shell material	Carbon steel (S235/S355) standard; SS 304/316, Duplex on request
Heat sources accepted	Natural gas, LPG, fuel oil, biomass, waste heat / flue gas

Co-Current vs Counter-Current Configuration

Parameter	Value / Range
Flow direction	Co-current: gas → same as material \| Counter-current: gas ← opposite to material
Best for (inlet moisture)	Co-current: high moisture (>20%) \| Counter-current: lower moisture (<20%)
Achievable outlet moisture	Co-current: 0.5–2% \| Counter-current: 0.1–0.5%
Product temperature at outlet	Co-current: lower (60–100°C) \| Counter-current: higher (100–150°C)
Sensitivity to sticky feed	Co-current: handles sticky well \| Counter-current: requires drier feed
Thermal efficiency	Co-current: 50–60% \| Counter-current: 65–75%

Need a technical pre-sizing? Send us your material data sheet, moisture content, required throughput and energy source — we return a technical sizing with drum dimensions and energy balance within 2 business days.

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Material Examples & Typical Operating Conditions

Reference data from industrial installations. Actual values depend on feed consistency, particle size distribution and required product quality.

Material	Inlet moisture	Outlet moisture	Particle size	Gas temp.	Industry
Silica sand / Quartz sand	5–12%	<0.1%	0.5–5 mm	700–900°C	Construction / Glass
Limestone / Calcium carbonate	8–18%	<0.5%	5–25 mm	500–750°C	Cement / Chemical
Wood chips / Biomass	40–60%	8–12%	10–50 mm	300–500°C	Biomass Energy / Pellet
NPK Fertilizer granules	3–8%	<0.5%	2–6 mm	120–250°C	Fertilizer
Iron ore concentrate	8–15%	<1%	5–30 mm	600–850°C	Mining / Metallurgy
Clay / Kaolin	20–35%	<1%	5–20 mm	400–650°C	Ceramics / Chemical
Coal / Lignite	10–25%	<2%	5–30 mm	200–450°C	Energy / Mining
Phosphate rock	6–14%	<0.5%	3–25 mm	400–700°C	Fertilizer / Mining

Don't see your material? Send us your process data and we'll provide material-specific sizing.

Configurations & Variants

Single-pass co-current dryer

Standard configuration. Hot gas and material travel in the same direction. Gas enters at feed end (highest temperature), exits at discharge end. Excellent for high-moisture, heat-sensitive and sticky materials.

Best for:Wood chips, sludge cake, high-moisture minerals, sugar beet pulp

Single-pass counter-current dryer

Hot gas enters at the discharge end (where material is driest). Achieves very low residual moisture (<0.1%) and elevated product temperature. Used where complete drying is critical and product can withstand heat.

Best for:Minerals requiring ultra-low moisture, products needing elevated temperature for downstream processing

Rotary dryer-cooler (combined)

A single extended drum partitioned internally into a drying zone (hot gas) and a cooling zone (ambient or chilled air). Reduces footprint and capital cost vs two separate machines. Product exits at near-ambient temperature, ready for bagging or conveying.

Best for:Fertilizers, potash, cement clinker, chemicals requiring cool product for direct packaging

Triple-pass (multi-shell) dryer

Three concentric cylinders (or two) share a single drive. Material passes through each cylinder in sequence, achieving very high contact efficiency in a compact footprint. Suitable when installation space is limited and high evaporation rates are required.

Best for:Sludge, municipal waste, installations with tight space constraints

When to Choose a Rotary Dryer

Particle size is above 5 mm

Rotary dryers are specifically designed for coarse materials. Fluidized beds cannot fluidize particles above 5 mm efficiently.

Inlet moisture is above 20% and material is sticky

Co-current rotary dryers handle the stickiest feeds. Flash dryers require free-flowing input and fluidized beds require material that fluidizes cleanly.

Drying temperature must exceed 400°C

Only rotary dryers and flash dryers operate at these temperatures. Fluidized beds are limited to ~350°C. Rotary dryers can reach 900°C with appropriate refractory lining.

Required throughput exceeds 30 t/h dry product

At large scale, rotary dryers offer the lowest capital cost per tonne of drying capacity. Single units up to 200 t/h dry product are regularly delivered.

Feed has variable particle size distribution

Rotary dryers tolerate wide PSD without risk of channeling or uneven drying. Flash dryers and fluidized beds are sensitive to PSD variations.

When NOT to Use a Rotary Dryer

Particle size is below 1–2 mm and uniformity of drying matters

Consider instead:Fluidized Bed Dryer →

Material is a paste, suspension or liquid-solid mixture

Consider instead:Paddle Dryer →

Product is temperature-sensitive or fragile (pharmaceuticals, starch granules)

Consider instead:Belt Dryer →

Feed is a liquid that must be converted directly to powder

Consider instead:Spray Dryer →

Not sure which dryer is right for your process? We'll review your specifications and recommend the optimal solution.

Ask a technical question →

Frequently Asked Questions — Rotary Drum Dryers

In a co-current dryer, hot gas and wet material enter from the same end and travel together toward the discharge. The hottest gas contacts the wettest material, which protects heat-sensitive products and handles sticky feeds well. Outlet moisture is typically 0.5–2%. In a counter-current dryer, hot gas enters at the discharge end and flows opposite to the material. The driest material contacts the hottest gas, achieving lower outlet moisture (0.1–0.3%) and higher product temperature — useful for minerals that require very low residual moisture or elevated product temperature for downstream processing.

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Request a Quote for This Equipment

Include in your enquiry:

→Material name and composition (if relevant)
→Inlet moisture content (%) and target outlet moisture (%)
→Required throughput — dry product (t/h or kg/h)
→Particle size range (min / typical / max mm)
→Available heat source (natural gas / LPG / oil / waste heat)
→Available utilities at site (electricity voltage, steam pressure if any)
→Any special requirements (ATEX zone, temperature limits, footprint constraints)

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