Flour conveying systems: safety, sizing and equipment
Flour is one of the most challenging materials to convey pneumatically. It is fine, combustible, food-grade and sensitive to heat and moisture. Getting any of those factors wrong creates safety risks, quality failures or regulatory non-compliance. This guide covers how to design a pneumatic flour conveying system that meets safety, sizing and food-grade requirements.
Efficient flour conveying
Phase selection
There are a number of reasons that make pneumatic conveying the best way to efficiently transport flour in general and wheat flour in particular. If you have the right equipment, at least. There are several things to consider to truly benefit from the many advantages pneumatic conveying has to offer.
Wheat flour is a relatively fine material (typically smaller than 0.3mm), which means it can be transported in either dilute and dense phase. Dilute phase suits lighter throughput over shorter distances, while dense phase is preferable where product degradation or pipeline wear is a concern. The right choice depends on your specific installation, throughput requirements and flour grade.
Sizing your flour conveying system
Next, you need to look at the size of your new or existing installation. Making sure you have right flow and air pressure for the type of flour you’re conveying. This will help you create a smooth and efficient conveying process. An incorrectly sized blower or compressor could lead to high energy bills, frequent blockages, and long unloading times.
Safety requirements for pneumatic flour conveying
When choosing the right equipment for your flour conveying system, quality and safety are two important matters. This includes both the physical safety of the production/processing facility as well as the issue of food safety. While flour is not deemed to be dangerous, it is a flammable material when moved in bulk and could combust. In addition, as a food, it is subject to stringent quality standards. For both reasons, wheat flour needs to be transported at a temperature not exceeding 40°C.
When conveying materials for food production, such as flour, it is also important to use oil-free blowers, compressors as the air comes into direct contact with the material. Oil-free air blowers and compressors ensure that there is no oil contamination of your product.
Flour conveying system: specification checklist
Before specifying or upgrading your flour conveying installation, confirm your system meets all of the following requirements:
- Correctly sized blower or compressor: undersized equipment causes blockages and energy waste, oversized equipment inflates capital and running costs
- Class 0 oil-free certification: mandatory for any application where conveying air contacts food-grade material directly
- Aftercooler: required to keep conveying air below 40°C and prevent combustion or flour degradation
- Water separator or dryer: removes moisture created by the cooling process to protect product quality
Designing a flour conveying system
A well-designed flour conveying system integrates correctly sized, oil-free equipment with adequate cooling and moisture removal. This allows large volumes to be moved efficiently, safely and within food-grade compliance requirements.
Oil-free air blowers and compressors for flour conveying
To make sure your installation is as efficient as it can be, you need a correctly sized blower or air compressor. Defining the right size of compressor or blower can be difficult and often requires specialized software. Even if you’re dealing with an existing installation, a one-on-one replacement of the old equipment is often not the most efficient solution. Make sure to do a sizing check before you invest in a new blower or compressor.
Class 0 certification
On top of that, make sure your compressor or blower delivers Class 0 certified or oil-free air. The Class 0 certification ensures there is no oil added to the air during the compression process.
Eliminating explosion risks
Flour dust suspended in air is combustible. In sufficient concentrations it can ignite, and in an enclosed pipeline or silo the consequences can be severe. Eliminating explosion risk requires both correct system design and properly certified equipment. A standard industrial compressor or blower is not sufficient for flour conveying environments.
Aftercoolers
In addition to a compressor or blower, you will need an aftercooler, to get the air temperature below 40°C. This to ensure the flour is not burned and that it does not combust.
To guarantee that your pneumatic conveying system for flour is safe, you should always make sure that the relevant equipment is certified according to the local guidelines. This ensures the continuous quality of your production outputs.
Integrated vs separate aftercoolers
Some compressors, feature an integrated aftercooler. In the case of a blower, however, it will have to be installed separately. If you decide to use a water-cooled aftercooler, it may also be necessary to add a chiller. It lowers the water temperature to a manageable and constant level to ensure that the aftercooler can do its job.
Water separator or dryer
Because the cooling process with an aftercooler creates moisture, the system also needs a water separator or dryer to protect the quality of the wheat flour. Most integrated aftercoolers come with an integrated water separator. For some specific cases, a dryer instead of a water separator can be used to remove the moisture from the air.
The role of fluidization for flour
Compressed air can also be used for the so-called “fluidization” process when conveying flour from a silo. Here, very low-pressure air is injected at the bottom side walls of the silo. This ensures that the flour does not stick to the sides of the silo and makes it easier to convey, which reduces energy costs. Conveying with such a low pressure usually doesn’t require any ancillaries. However, all (raw) materials used for food production need to comply to certain high quality standards. So, your fluidization system for flour does require an aftercooler and water separator or dryer to ensure the flour remains at top quality.
Compressed air in grain mills
Flour and grain milling facilities rely on compressed air and blowers across multiple processes beyond conveying. In most installations, the same compressed air system serves all of them. Understanding the full range of applications helps ensure your installation is correctly sized and specified from the outset.
- Pneumatic conveying: blowers and compressors move grain, flour and intermediate milling products between intake, processing and storage at different pressures and phases depending on the material stage.
- Silo fluidization: low-pressure air injected at the base of flour or grain silos prevents compaction and bridging, ensuring consistent discharge without mechanical intervention.
- Filter cleaning (pulse jet): baghouse and dust collector filters require periodic bursts of compressed air to dislodge accumulated flour dust. This demands clean, dry, oil-free air at consistent pressure (typically 5–7 bar).
- Instrument air: pneumatic actuators, valves and control systems throughout the mill require a stable, dry compressed air supply. Moisture or contamination in instrument air causes process instability and equipment failure.
In all of these applications, oil-free compressed air is a non-negotiable requirement. Flour dust in contact with oil-contaminated air creates both a food safety and an explosion risk.
Need help optimizing your flour conveying system?
Not sure how to replace your old compressed air system with a new one? Let us help you. The right size of installation is crucial: not only does it help you save on energy costs, it also shortens unloading times and helps you avoid blockages. Calculating the right size of installation is difficult and requires specific software and skills. We can help you identify and size the right flour powder conveying system for your application (whether dilute or dense phase).
What type of compressed air is required for flour conveying?
Oil-free compressed air is essential. Flour comes into direct contact with the conveying air, so any oil contamination creates both a food safety issue and an increased explosion risk. Class 0 oil-free certification is the industry standard for food-grade applications.
What temperature must conveying air be kept below for flour?
Conveying air must remain below 40°C. Above this threshold, flour quality degrades and the risk of combustion increases significantly. An aftercooler is required on most installations, with a water separator or dryer to remove the moisture the cooling process creates.
What is ATEX certification and why does it matter for flour conveying?
ATEX is the European standard governing equipment used in explosive atmospheres. Flour dust suspended in air is combustible. Any compressor, blower or ancillary equipment used in a flour conveying system must be certified to operate safely in these conditions. Standard industrial equipment is not sufficient.
Can both dilute and dense phase conveying be used for flour?
Yes. Wheat flour is fine enough (typically under 0.3mm particle size) to be conveyed in either phase. The choice depends on distance, throughput requirements and the sensitivity of the specific flour grade to degradation during conveying.
What causes blockages in flour conveying systems?
The most common causes are undersized equipment, incorrect air pressure for the phase being used, and moisture in the conveying air causing the flour to clump. Correct sizing, oil-free air and adequate drying equipment eliminate the majority of blockage risks.