In the design and operation of pneumatic conveying systems, atmospheric conditions are a critical but often underestimated factor. Variations in temperature, humidity, and geographic location can significantly influence material flow, equipment longevity, and overall process stability.
Air movement is fundamental in pneumatic conveying, as it enables the transport of dry bulk materials through pipelines by suspending and propelling particles using carrier gas or conveying air. Pneumatic conveyors are versatile systems used for bulk material handling, and they are generally classified into dilute phase and dense phase systems, each suited to different material properties and process requirements.
At AZO, Inc., our engineering teams address these environmental challenges, applying deep technical expertise to ensure reliable, efficient, and safe material handling. The following provides an in-depth examination of how atmospheric conditions directly affect pneumatic conveying, along with the tested design principles, control strategies, and mitigation technologies that help ensure reliable, efficient bulk material handling even in challenging climates.
When designing a system, it’s important to determine the appropriate configuration, considering horizontal piping, elbows, vertical sections, horizontal lines, and horizontal segments, to ensure optimal performance and accommodate multiple sources and multiple destinations.
System selection and performance depend heavily on material characteristics, including bulk density, particle size, and particle size distribution, which influence the choice between dense phase systems, vacuum conveying systems, and pressure systems. A pressure system uses positive pressure to push materials through the pipeline, making it suitable for transporting heavier, denser, or abrasive materials over longer distances. The velocity at which particles are transported, as well as the gas flow rate, flow rate, and conveying rate, are critical for achieving efficient operation.
Carrier gas and conveying air play a vital role in suspending and transporting particles through the conveying pipe, with system performance affected by pressure drop, pressure drops, and frictional losses. Energy consumption is another key consideration in system design, impacting long-term operational efficiency. Understanding particle size distribution is essential for selecting the right system and ensuring reliable, safe, and cost-effective conveying operations.
Pneumatic conveying systems are generally classified into two main types: dense phase conveying and dilute phase conveying.
Dense phase conveying operates at lower velocity and higher pressures compared to dilute phase, providing gentle handling of fragile or abrasive materials, minimizing product breakage, and improving energy efficiency. This method minimizes material degradation and system wear, making it suitable for applications where product integrity is critical.
On the other hand, dilute phase conveying uses higher velocities and lower pressures to transport lighter materials over longer distances, making it a versatile choice for many industrial processes. The selection between dense phase and dilute phase systems depends on several factors, including the nature of the material, required conveying distance, and specific system components.
Atmospheric conditions, such as temperature and humidity, play a significant role in the performance of both dense phase and dilute phase pneumatic conveying systems. For example, high humidity can cause certain bulk materials to absorb moisture, leading to clumping or blockages within the conveying line, while temperature fluctuations can affect the flow characteristics of sensitive materials.
A vacuum conveying system uses negative pressure generated by vacuum pumps, positive displacement pumps or regenerative blowers to transport materials, offering advantages such as gentle handling of delicate or sensitive powders and reduced dust emissions. Compared to pressure conveying, a vacuum conveying system is particularly suitable for applications requiring the transfer of fine, fragile, or hazardous materials.
These systems are especially sensitive to changes in atmospheric conditions and require careful system design to maintain consistent performance. Understanding how environmental factors interact with system type and material properties is essential for selecting the most suitable pneumatic conveying solution and ensuring reliable, efficient operation across a range of applications.
Pneumatic conveying systems (whether vacuum conveying, pressure conveying, dilute phase systems, or dense phase conveying) are highly sensitive to ambient conditions, particularly when handling hygroscopic or temperature-sensitive materials such as sugar, milk powder, flour, salt, and various pharmaceutical salts. Many other ingredients, including cocoa powder, lactose, and sodium bicarbonate, are also prone to moisture absorption, which can lead to clumping, bridging, or flow disruptions.
Protein-based products like whey protein and milk powder are especially vulnerable, as both high humidity and elevated temperatures can compromise their quality, shelf life, and taste. Excessive heat can further degrade sensitive materials such as egg powders, spices, and vitamins, while moisture in flour creates favorable conditions for microbial growth. When exposed to these environmental fluctuations, agglomeration may disrupt material flow, block discharges, compromise dosing screws and airlocks, and create inconsistencies in weighing accuracy.
Additionally, changes in conveying velocity can exacerbate or mitigate these flow issues; for example, higher conveying velocity may help prevent clumping and blockages in some cases, but can also increase the risk of material degradation or instability for sensitive products. For example, materials containing fats or oils, such as PVC Dry Blend, can cake onto pipe walls at elevated conveying velocities, leading to blockages and decreased throughput.
Each material has a critical relative humidity (CRH) threshold beyond which it begins to absorb moisture. For example, sugar and salt typically require relative humidity levels below 50% to prevent clumping. Because CRH is temperature-dependent, managing both temperature and humidity is crucial. As air temperature rises, its moisture-holding capacity increases, causing relative humidity to drop even if absolute moisture remains unchanged.
Designing systems to manage these conditions involves detailed planning. Convey line layouts, including length, number of elbows, and elevation changes, dictate airflow requirements. AZO engineers calculate the necessary cubic feet per minute (CFM) needed for target material throughput, directly influencing dehumidification and cooling system sizing. Every aspect of the conveying system — from the routing of the conveying line to the selection of system type — can influence how well the operation manages temperature, humidity, and energy efficiency.
System configuration also impacts the ease of integrating environmental control technologies. For instance, straight, accessible conveying lines make it simpler to install air coolers, dehumidifiers, or monitoring sensors at critical points. Conversely, complex layouts with multiple sources and destinations may require more sophisticated control strategies to ensure consistent environmental conditions throughout the entire system.
Climate data also plays a role. Local weather patterns, even in arid regions, can bring temporary humidity spikes during rainy seasons or nighttime temperature drops. This information allows engineers to design for worst-case scenarios, not just average conditions.
Once materials are conveyed into silos, moisture management continues. Open vent filters or fill lines can allow external humidity to infiltrate, even after the conveying process. "Blanket air" systems are used to continuously purge the headspace above stored product with dry air, preventing moisture migration into the bulk material.
Ultimately, thoughtful design of the conveying line and system configuration not only optimizes material flow and minimizes system wear, but also enhances the ability to maintain stable environmental conditions. By considering these factors early in the system design process, manufacturers can ensure their pneumatic conveying systems deliver reliable, efficient, and safe performance — regardless of external climate challenges.
Effective control of atmospheric conditions requires integrated systems that address both humidity and temperature.
Desiccant dryers condition intake air before it enters the system. Regenerative dryers heat ambient air, pass it through moisture-absorbing media, and deliver extremely dry process air. Since this process raises air temperature significantly, downstream cooling becomes necessary to protect both equipment and product integrity.
AZO incorporates air-to-air heat exchangers, and air-to-liquid heat exchangers similar to automotive radiators, using chilled water or glycol to regulate process air temperatures. This is especially critical for materials like plastic additives, which may soften and become tacky at elevated temperatures, and for flour, where excessive heat can affect dough performance. Sugar milling operations, which introduce substantial heat, also benefit from dedicated sugar cooling systems to prevent downstream complications.
Continuous monitoring is essential for maintaining system integrity. Relative humidity and temperature sensors verify that conditions stay within specified parameters. Without proper controls, conveying lines can reach temperatures up to 200°F due to blower discharge or dehumidification without post cooling, necessitating protective guarding to ensure worker safety.
Failure to control these variables can result in material bridging or ratholing, blocked discharges, and inconsistent feeding into dosing screws or airlocks. As material builds up and forms stable arches inside silos and hoppers, flow interruptions occur. In an effort to restore flow, operators may attempt to manually dislodge these blockages using poles, rods, or other tools inserted through access points; a highly dangerous practice that can lead to serious safety incidents, severe injuries, or even fatalities if the material suddenly collapses.
The sudden release of trapped material not only endangers personnel but can also overwhelm downstream equipment and compromise the structural integrity of the vessel. In flour systems, excessive moisture further increases these risks by promoting mold growth, which contributes to clumping and unstable material flow.
Additionally downstream equipment needs to be protected from excessive heat that can damage seals, bearings, gaskets, and electrical devices.
AZO engineers have encountered situations where customers underestimated the risks associated with fluctuating humidity and temperature, often assuming that certain climates inherently posed minimal moisture challenges. Deserts, for instance, are frequently perceived as consistently dry environments; however, seasonal rains introduce unexpected moisture into the atmosphere increasing humidity. These conditions allow moisture to infiltrate conveying lines and storage vessels, leading to material clumping inside silos, equipment blockages, and production stoppages when adequate moisture control systems are not in place.
Pharmaceutical salts present even greater challenges. Some salts are so hygroscopic that they can liquefy upon absorbing moisture. Unlike food-grade salts, which may include flow aids to assist handling, pharmaceutical salts cannot include additives due to strict formulation requirements. These materials require continuous blanketing with dry air to prevent them from turning into a liquid state or cause clumping inside hoppers or silos.
Additionally, materials stored in silos may experience condensation when temperatures drop overnight. This creates internal moisture that can cling to sidewalls or settle within hoppers, further increasing the risk of clumping or material blockages.
For operators assessing their existing pneumatic conveying systems or planning new bulk material handling installations, AZO recommends starting with a comprehensive system assessment. This review should account for changing environmental conditions, shifts in production demands, and any facility expansions that may have introduced new temperature or humidity challenges.
From there, it’s important to thoroughly characterize the materials being handled, identifying their specific sensitivity to humidity and temperature to establish accurate operating thresholds. With this understanding in place, implementing real-time monitoring equipment allows for continuous oversight, ensuring any deviations are detected and addressed promptly.
When issues arise, targeted retrofits such as the addition of dehumidifiers or air coolers can often resolve problems without requiring major capital investments. Ultimately, partnering with experienced system specialists ensures that all these elements come together into a fully integrated, reliable solution for managing atmospheric conditions in bulk material handling.
In many cases, simple system improvements can yield significant performance gains without requiring substantial capital investment. A thoughtful review of material sensitivities, conveying system design, and environmental factors allows facilities to operate more reliably, safely, and efficiently.
Managing atmospheric conditions is not just about avoiding clumping or downtime; it's about safeguarding your product quality, protecting your equipment, and ensuring long-term operational success.
By implementing dehumidification, temperature control, and real-time monitoring, manufacturers create a stable processing environment that resists seasonal shifts and unforeseen climate challenges. At AZO, we bring decades of experience designing integrated solutions that adapt to your facility’s unique environmental demands.
Contact our team today to explore how AZO can help optimize your pneumatic conveying system for maximum reliability and performance.