Features of Pilotech Counter-Current Spray Dryer
- Better thermal efficiency via opposite air-liquid contact
- SUS316L two-fluid nozzle with 1- 25 µm particle range
- Minimal 10 ml sample volume for high-cost R&D testing
- Optional inert loop system
- Full IQ/OQ validation protocols and FDA 21 CFR Part 11 compliant
Your Trusted Counter-Current Spray Dryer Manufacturer
Counter-current is a type of spray dryer’s airflow configuration. In the counter-current spray dryer’s chamber, small liquid droplets come into contact with the hot airflow in opposite directions. This results in a longer residence time and a lower final moisture content in the powder.
With 21 years of experience in the R&D and production of spray dryers, Pilotech holds more than 50 patents and 5 software copyrights. We offer a wide range of counter-current spray drying equipment, including lab spray dryers, pilot-scale spray dryers, and various atomizer configurations, providing you with a rich and flexible selection. We also operate a process validation laboratory capable of providing comprehensive spray drying validation services for a variety of materials. Please feel free to contact us with any inquiries.
Compact equipment for laboratory-scale spray drying, helping save space and reduce the cost of experimental materials. Suitable for formulation screening, powder research, particle characterization, and small-batch process development.
Designed for pilot trials and scale-up studies, providing larger processing capacity for a seamless transition to industrial-scale production. Suitable for optimizing drying parameters and powder properties.
Uses shear force generated by compressed gas to atomize the feed liquid into fine droplets, achieving submicron particle sizes. Suitable for pharmaceutical, chemical, and food ingredient applications.
High-pressure liquid feed passes through a small nozzle to generate spray without separate atomizing gas, offering extremely uniform particle size distribution. Suitable for low-viscosity, low-solids-content slurries.
A high-speed rotating atomizer distributes feed into droplets through centrifugal force, supporting continuous operation and broad feed-rate adjustment. Suitable for handling high-viscosity slurries and powders requiring controlled particle size and bulk density.
Counter-Current Spray Dryer Specifications
The parameters in the table below cover various spray dryer models. Specifications vary by model and configuration.
| Parameter | Specification |
| Equipment Type | Laboratory / Pilot-Scale Counter-Current Spray Dryer |
| Application | R&D, formulation development, process optimization, powder engineering, scale-up studies |
| Feed Capacity | 1.5–5 L/h, depending on model |
| Minimum Sample Volume | 30–100 mL, depending on model and solids content |
| Drying Air | Heated air; inert gas available for solvent-based applications |
| Airflow Rate | Approx. 1.5–3 m³/min |
| Inlet Air Temperature | Up to 250–280°C for laboratory models; up to 260°C for inert-loop pilot models |
| Outlet Air Temperature | Adjustable according to feed properties and drying conditions |
| Temperature Precision | ±1°C for laboratory models; ±2°C for pilot-scale models |
| Atomization Method | Two-Fluid Nozzle / Customized |
| Standard Nozzle Diameter | 1.0–2.0 mm, depending on model |
| Optional Nozzle Diameter | 0.5 / 0.8 / 1.0 / 1.5 / 2.0 mm |
| Possible Particle Size | Approx. 1–100 μm, depending on feed and operating conditions |
| Mean Residence Time | Approx. 3.0–6.0 s for laboratory-scale configurations |
| Drying Chamber | Borosilicate glass or SUS304 stainless steel, depending on model |
| Cyclone Separator | Borosilicate glass or SUS304 stainless steel |
| Powder Collection | Cyclone separator + receiving vessel |
| Feed System | Peristaltic pump |
| Control System | PLC + 7-inch LCD touchscreen |
| Air Pressure | Approx. 0.2–2 bar for laboratory two-fluid nozzle systems |
| Compressed Air Consumption | Approx. 32 L/min for laboratory models |
| Body Material | SUS304 stainless steel |
| Atomizer Material | SUS316 stainless steel |
| Over-temperature Protection | Automatic thermal protection; blower continues until temperature falls below preset safety level |
| Automatic Needle Jet | Automatic |
| Inert Loop | Optional for organic solvents |
| Typical Scale | Laboratory research, pilot testing, process development and scale-up |
How Does a Counter-Current Spray Dryer Work?
The key feature of the counter-current spray dryer is that the feed liquid droplets come into contact with the hot gas stream in opposite directions during the drying process. This extends the residence time of the material and reduces the residual moisture in the final powder. The entire process can be broadly divided into three steps.
Atomization
It is the first step. The feed liquid is fed into the atomizer at the top, where it is atomized into small droplets.
Counter-Current Contact
At this time, hot air is introduced uniformly from the bottom of the drying tower, creating an upward airflow. Meanwhile, the atomized droplets freely settle downward from the top of the tower.
At the top, the wettest droplets first come into contact with the cooler gas, undergoing initial dehydration. As the droplets’ moisture content gradually decreases and they become increasingly difficult to dry, it continues to fall, encountering the hottest and driest inlet air entering from the bottom.
This process keeps a significant temperature and humidity difference between the material and the surrounding hot air throughout the entire descent, thereby providing continuous and efficient drying.
Particle Collection
The dried powder settles directly to the bottom and is discharged through the discharge valve. The exhaust gas is discharged from the top of the tower and enters a cyclone separator or bag filter for gas-solid separation and purification.
Key Parameters for Counter-Current Spray Drying
The counter-current spray drying process is controlled by several key process parameters. These parameters interact with each other and directly affect the quality of your final product and production efficiency.
| Key Parameters | Impact on Drying Process and Product Characteristics |
| Inlet Air Temperature
|
Affects drying rate and thermal efficiency. Higher inlet temperatures increase water evaporation capacity. However, in counter-current drying, the inlet air directly contacts the fully dried particles, so excessively high temperatures may cause thermal degradation, scorching, or melting and wall-sticking. |
| Outlet Air Temperature
|
Determines the residual moisture of the final product. The outlet temperature is jointly determined by the inlet temperature, feed rate, and solid content. A lower outlet temperature indicates insufficient evaporation and higher powder moisture. An overly high temperature wastes energy. |
| Atomization Pressure / Speed
|
Controls the droplet size distribution. Higher pressure or faster speed produces finer droplets and faster evaporation. Lower pressure results in larger droplets and faster settling, which may cause caking at the bottom or wall-sticking if not fully dried. |
| Feed Rate and Solid Content
|
Directly balances the thermal load inside the tower. Higher solid content requires less water evaporation, increasing unit capacity. Excessive feed rates lead to high local humidity, a sharp drop in outlet temperature, and severe wet powder wall-sticking. |
| Air Flow Rate and Velocity
|
Determines particle residence time and carryover rate. Excessively high upward air velocity generates strong buoyancy, carrying large amounts of wet fine powder to the top exhaust outlet. Insufficient air velocity causes particles to settle too quickly, leading to inadequate drying time. |
| Chamber Pressure
|
Ensures system safety and prevents powder leakage. A stable, slight negative pressure prevents dust from spilling into the lab or workshop while maintaining a smooth airflow field, avoiding wall deposition caused by turbulent airflow. |
Is It Difficult to Scale up Lab Counter-Current Spray Drying to Pilot Scale?
Yes. Scaling up counter-current spray drying is more difficult than that of co-current spray drying. Here are some recommendations for counter-current scale-up.
Variable Air Velocity Control
As particle mass and settling velocity change throughout the drying process, the drying chamber can use staged diameter expansion or variable air velocity control. This helps maintain sufficient particle residence time while reducing fine-powder carryover at the exhaust outlet.
Anti-Sticking Wall Configuration
To adapt to the heat and mass transfer characteristics of scale-up, you can add air hammers or continuous wall-sweep air rings in areas of the pilot-scale tower prone to wall sticking, like the cone and lower chamber walls. This helps maintain smooth operation and reduce material waste.
Optimizing Atomizer Layout
In some cases, using a single, larger nozzle is not the appropriate solution. In a pilot-scale tower, you can instead use a multi-nozzle array or custom low-angle pressure nozzles to provide staggered coverage of the spray area. This helps reduce droplet-to-droplet collisions and secondary coalescence in areas of high atomization density.
Counter-Current Spray Dryers Are Commonly Used For
Detergents and Surfactants
Products such as concentrated laundry powder require high bulk density and extremely low moisture content. This prevents caking during storage and transportation and reduces packaging volume. Counter-current drying promotes deep-layer water evaporation, enabling dense, uniform, free-flowing granules with high bulk density. It is suitable for synthetic detergent base powders, alkylbenzene sulfonate (LAS) dried powders, and similar products.
Ceramics and Inorganic Minerals
Counter-current spray drying is highly effective for processing slurries with high solid content, and the resulting particles exhibit good density and internal structure. This powder helps reduce porosity, cracking, or uneven shrinkage during subsequent high-temperature sintering. As a result, counter-current spray drying is commonly used to process alumina, zirconia ceramic powders, kaolin, and high-purity silicates.
Chemicals and Catalysts
Counter-current spray drying is a good choice for the production of barium sulfate, sodium silicate, silica gel particles, and various inorganic salts. Because these products typically have extremely stringent requirements for final moisture content. The high-temperature gas stream at the end of the counter-current spray drying can effectively remove bound water. The high thermal efficiency also significantly reduces energy costs during production.
Building Materials and Metallurgical Powders
Construction additives and metallurgical auxiliaries require the processing of raw slurries with extremely high moisture content, and the final products must exhibit excellent flowability. By incorporating a wear-resistant design into counter-current spray dryers, you can use them to process concrete admixtures, cement additives, and refractory slurries.
Counter-Current Drying vs Co-Current Spray Drying
Flow Principle
In counter-current drying, the droplets move in the opposite direction to the hot air. But in co-current drying, the droplets and hot air enter simultaneously from the top of the tower or from the same side and flow in the same direction. The gas and liquid advance together, resulting in a relatively short contact time.
Temperature Profile
In counter-current drying, the droplets initially come into contact with low-temperature gas and gradually move into a high-temperature, low-humidity zone.
In co-current drying, the temperature is highest at the top of the drying tower and lowest at the bottom. The wet droplets come into contact with the hottest air. Due to the massive evaporation of moisture, an evaporative cooling effect occurs, keeping the material’s temperature below the inlet air temperature. This airflow configuration is more suitable for handling heat-sensitive materials.
Thermal Efficiency
Counter-current spray drying maintains a high heat transfer temperature difference, enabling extremely low residual moisture content. In co-current spray drying, as the drying process progresses, the temperature difference for moisture evaporation gradually decreases. Thermal efficiency is moderate, and the final residual moisture content of the powder is higher than that achieved in counter-current spray drying.
Particle Properties
In counter-current drying, moisture evaporates relatively slowly and uniformly, making it unlikely for a hard surface to form instantly. You can use this process to produce solid, smooth-surfaced, and densely structured particles with a high bulk density.
In co-current drying, wet droplets are subjected to intense thermal shock, causing rapid crusting on the surface while moisture inside vaporizes and expands. This process often results in thin-walled, porous, or hollow particles with low bulk density.
Thermal Sensitivity
Counter-current drying is not suitable for heat-sensitive materials. Because the final product is exposed to the highest temperature during the drying process.
We recommend using a co-current spray dryer to process heat-sensitive materials, including pharmaceuticals, enzyme preparations, dairy products, and food extracts. Because the material is exposed to heat for an extremely short time and is protected by evaporative cooling, this minimizes thermal degradation.
Counter-Current Spray Dryer vs Mixed-Flow Spray Dryer
A mixed-flow spray dryer combines the physical characteristics of co-current and counter-current flow. The table below outlines the main differences between counter-current and mixed-flow spray dryers.
| Comparison Dimension | Counter-Current Spray Dryer | Mixed-Flow Spray Dryer |
| Flow Principle | Liquid is sprayed downwards while hot air flows upwards, moving in opposite directions. | The nozzle is usually located at the bottom, spraying upwards, while hot air is introduced from the top. Material moves upwards first (counter-current) and then downwards (co-current). |
| Residence Time | Long. | Extremely long. |
| Particle Size Range | Medium to coarse particles. | Coarse particles. Can produce large, dust-free powders up to 100–300 µm or more. |
| Material Suitability | Suitable for non-heat-sensitive materials that can tolerate high temperatures. | Moderately heat-sensitive to heat-resistant materials. Suitable for hard-to-dry feeds with high solid content and high viscosity. |
| Thermal Efficiency | Extremely high thermal efficiency. Lower exhaust outlet temperature and full energy utilization. | High thermal efficiency, falling between co-current and pure counter-current designs. |
| Equipment Complexity and Cost | Relatively straightforward structure with fixed ductwork design. | Complex structure. Nozzles are prone to falling material contamination, and system investment is higher. |
Factors Affecting the Price of a Counter-Current Spray Dryer
Evaporation Capacity and System Size
Water evaporation rate is the most fundamental factor determining counter-current spray dryer costs. As the evaporation rate increases, the volume of the drying tower, the power of the hot air furnace, the airflow of the induced draft fan, and the size of the gas-solid separation system all should increase, directly driving up manufacturing and material costs.
Materials of Construction
If the material you need to process is highly corrosive, you will need to use 316L stainless steel or Hastelloy, or have the inner walls electropolished or treated with a corrosion-resistant coating. This will increase material costs by 30%–100%.
Automation System and Compliance
An automation control system based on a PLC and a touchscreen includes PID automatic temperature control, closed-loop airflow control, and safety interlocks. If used in the pharmaceutical industry or for specific research applications, adding data logging, electronic signatures, and audit trail capabilities that comply with 21 CFR Part 11 will significantly increase software and validation costs.
System Cycle and Explosion Proofing
Standard open-loop systems are less expensive.
However, if your material contains organic solvents or easily oxidizable components, you must use a closed-loop system. These systems include a nitrogen recirculation system, a condensation recovery unit, oxygen concentration monitoring, and ATEX/Ex explosion-proof certification technology. These typically increase equipment costs by more than 50%.
Auxiliary Systems
If you need to add auxiliary systems, this will also increase costs. For example, whether to install high-efficiency heat recovery systems. The exhaust gas filtration level, whether to choose a single-stage cyclone separator or a wet scrubber. Whether to integrate a Clean-in-Place (CIP) system and an automatic air hammer.
The feed rate directly determines the heat load and evaporation balance within the drying tower. In counter-current spray drying, increasing the feed rate consumes more thermal energy, causing the outlet temperature to drop. If the heat supply is insufficient, this can easily result in incomplete drying of the material or cause wall deposition. Conversely, an excessively low feed rate can cause localized overheating in the drying tower, increasing the risk of thermal degradation of the material.
Counter-current spray drying has a significant impact on particle size and microstructure. In this process, the material settles from top to bottom, moving in the opposite direction to the hot gas stream rising from the bottom, and the rising gas stream prolongs the suspension time. Moisture evaporates relatively uniformly from the droplet surface, making it less likely for rapid surface crusting or internal expansion and rupture to occur. Therefore, this process is more conducive to producing dense, solid powders with coarser particle sizes and high bulk density.
Laboratory systems may have shorter residence times, usually 3 to 6 seconds. Industrial configurations can be designed for longer residence times depending on chamber geometry and operating conditions, typically 10 to 30 seconds. As the droplets fall, they are impeded by the upward flow of hot air, causing their descent to slow. This longer residence time allows for thorough heat and mass transfer, promoting the evaporation of deeply bound water and enabling the final product to achieve an extremely low residual moisture content.
As long as a closed-loop system and explosion-proof design are in place, the counter-current spray dryer can safely process organic solvents. Our closed-loop system uses inert gases like nitrogen in place of air as the drying medium. It is equipped with online oxygen monitoring, explosion-proof rupture discs, and a solvent condensation and recovery unit. It is capable of maintaining oxygen concentrations below the explosion limit, achieving safe operation with materials containing flammable organic solvents or flammable dust.
Both our laboratory and pilot-scale counter-current spray dryers support on-the-fly parameter adjustment during operation. You can use the PLC touchscreen to fine-tune the feed pump speed, inlet air temperature, atomization pressure, and induced draft fan airflow in real time. The system’s built-in closed-loop feedback control responds instantly to adjustments, allowing you to quickly optimize the process during a single experiment.
We can provide pharmaceutical companies and high-standard R&D laboratories with comprehensive IQ (Installation Qualification) and OQ (Operational Qualification) validation documentation packages. The validation documentation includes material certificates for equipment (like 316L certificates), calibration reports for critical sensors, electrical and control system drawings, and draft standard operating procedures. Pilotech supports clients in regulatory reviews under industry standards like GMP, FDA, or 21 CFR Part 11.