Grain Dust: Characteristics, Composition, and Safe Gas Cleaning

Grain dust is a substance that is formed during production processes related to grain handling and storage. It consists of tiny particles of straw, husks, weed seeds, and grain embryos. The main cause of dust formation is the friction between grains, as well as between grains and the equipment walls. The primary danger of dust from grains is its highly combustible nature.

Grain processing facilities: elevators, mills, cereal processing plants, feed mills, silos, as well as seed production enterprises — are considered high-dust environments.

In this article, we investigated the impact of grain particles on health, causes of explosion and fire, safety measures, properties and characteristics, and most importantly, dust collection and control systems.

Grain dust exposure can pose various health risks and negatively impact respiratory health. When individuals inhale grain dust, especially in large amounts or over prolonged periods, it can cause several adverse effects in the lungs. Allergy symptoms related to air pollution from grains may include respiratory issues, such as coughing, wheezing, and shortness of breath. The dust particles can also irritate the skin, leading to the development of a rash or other allergic reactions. In certain instances, can contain toxins or contaminants that may result in poisoning if ingested or absorbed through the skin. It is important for individuals working in grain-related industries to implement necessary measures precautions to minimize exposure and maintain their respiratory health. Regular use of protective equipment, such as masks and gloves, can help reduce the risks.

This is not surprising, as these facilities were often built without considering explosion safety standards, especially in older buildings. However, even in modern large-scale grain processing plants, grain storage facilities, and baking and brewing plants, similar accidents can occur.

Currently, there are two types of technologies aimed at combating grain particles and its spread on the facility's premises. The first option is grain oiling, which helps neutralize the friction effect and reduce the likelihood of suspended particles in the air. However, the more commonly used method is aspiration. The corresponding systems collect air directly from the dust source and purify it using inertial forces or filtration. By employing this method, the dust content in the grain is considerably decreased, thereby minimizing the probability of ignition.

The principle of operation of aspiration systems involves extracting dusty air at the source of dust generation and subsequently purifying it using either inertia forces (up to 70%) or filtration elements, achieving a level of air purification of up to 99%. These systems are powered by a fan that draws air from the dust source through the filter and releases it into the atmosphere. Aspiration units can be designed to either remove dust from the production process (used in feed mills, elevators) or return it to the airflow to retain product mass (mainly applied in grain terminals).

Grain dust collection systems are vital for maintaining a safe working environment in grain processing and storage facilities. Several types of systems are commonly used:

• Cyclone separators: These systems utilize centrifugal force to separate the suspended particles from the air stream. The heavier particles are collected in a container, while the cleaned air is discharged. It consists of sleeve filters of various degrees of purification, as well as a cyclone-type inlet and air cleaning of the filter elements with a fan.

By implementing effective grain dust collectors, facilities can minimize airborne dust levels, reduce the risk of dust explosions, and promote a healthier working environment for employees.

We are a manufacturer of air purification equipment. We design and supply air cleaning systems, including the necessary collectors. Feel free to reach out to us, and we will be glad to assist you!

Grain dust control systems are implemented to effectively manage and reduce the presence of dust.

• Highly efficient removal of air pollutants.
• Reliability and long service life.
• Ease of operation and maintenance.
• High productivity.
• Safety due to the absence of moving parts.
• Wide temperature range of operation.
• Resistance to high pressure.
• Stability of hydraulic resistance.

An undeniable advantage is the ability of the equipment to maintain all functions even at high suspended particles concentrations.

Another advantage is the extensive selection of devices based on characteristics and purpose. For example, a grain cyclone separator is used to remove dust from the air. The devices are available in right and left versions with various sizes. Cyclone unloaders for grain are used to separate the conveyed material from the airflow. They also vary in technical parameters.

Grain dust suppression systems encompass various methods and practices aimed at reducing or controlling the generation and dispersal of dust. Here are some common techniques used:

1. Moisture control: Maintaining proper moisture levels in grain storage areas can help reduce the generation of air pollution. This can be achieved through appropriate grain conditioning and storage techniques.
2. Dust containment: Implementing measures such as enclosing equipment, using dust curtains or shields, and sealing openings can help contain dust within specific areas, preventing its spread.
3. Dust suppression agents: Applying dust suppressants or surfactants on grain surfaces can help reduce airborne particles formation and make the particles less prone to becoming airborne.
4. Dust extraction systems: Utilizing local exhaust ventilation systems and dust collectors near dust-emitting processes can effectively capture and remove particles that pollute at the source.
5. Regular cleaning and maintenance: Regular cleaning of equipment, machinery, and storage areas can prevent dust buildup and minimize the chances of dust becoming airborne.

Grain dust is highly flammable and can instantly ignite when exposed to increased temperature or even a small spark. An explosion occurs, and rarely is it a single event. Explosions can propagate in a chain reaction to other areas and even to connected facilities through technological communication channels.

Primary explosions often occur in storage containers such as bunkers and silos. Dust that accumulates in corners is particularly hazardous. The shockwave lifts the suspended particles upward, turning it into fuel for secondary explosions.

During the initial explosion, it is possible to mitigate the pressure build-up by opening windows and doors. However, during secondary and subsequent explosions, the pressure becomes so intense that this method no longer works.

A grain dust explosion involves the instantaneous ignition of particles. In terms of destructive force, it surpasses dynamite and, in enclosed spaces, leads to the generation of excessive pressure that significantly exceeds the structural capacity of reinforced concrete.

According to grain dust explosion statistics, as reported by a source in West Lafayette, Indiana, the United States experienced a total of nine incidents in 2022, demonstrating an increase from the seven incidents reported in 2021. These figures also indicate that the average number of explosions per year over the past decade stands at 7.8. These statistics highlight the ongoing concern and need for preventive measures in the grain industry to mitigate the risks associated with grain dust explosions.

Why does grain dust explode? Agricultural dust can explode under certain conditions due to its combustible nature and the presence of an ignition source. When grain is processed or handled, fine particles of dust are generated and become suspended in the air. If the airborne particle concentration reaches a critical level and encounters an ignition source (sparks, open flames, or electrical equipment), it can cause a dust explosion. That's why grain dust is so explosive.

Note: A particle concentration of 40 g/m3 is considered an indicator of explosive potential.

Let's list the explosive properties of grain dust. Grain particles has a large surface area that enhances its combustibility. This creates a potentially explosive mixture. Oxygen is crucial for combustion, and if the suspended particles concentration reaches a critical level and encounters an ignition source, such as sparks or open flames, it can lead to a rapid and destructive explosion.

MIE (Minimum Ignition Energy) refers to the lowest amount of energy required to ignite airborne particles. Determining the MIE of grain dust is essential in assessing its potential explosibility and establishing appropriate safety measures.

Below are the MIE values of dust commonly found in grain processing facilities.

The MEC is the minimum dust concentration required for a combustible mixture. It varies for airborne particle based on factors like grain type, moisture content, particle size, and other combustible materials present.
The MEC range for suspended particles is approximately 50-150 grams per cubic meter.

The grain dust Kst, also known as the Deflagration Index, has been determined to be 89 bar m/sec based on thorough explosion testing. It indicates the rate at which a dust explosion can propagate once ignited.

Grain dust calculation is based on data regarding its quantity in 1 m3 of exhaust air from grain drying equipment. A value of 30-50 mg/m3 is considered acceptable. An alternative calculation can be made based on the concentration of the substance in the working area of the elevator.

The explosiveness is assessed based on the following factors:

• Concentration: Particles need to be in close proximity for some of them to ignite others, raising their temperature above the ignition point.
• Particle size: The particle size determines the amount of heat generated by each particle. This value depends on the grain type and dust composition. Smaller particles result in more intense contact and a stronger explosion.
• Particle composition: Typically, the composition of the particles is identical to the product present in the grain storage facility. However, each particle contains various types of molecules with different combustion heat. The chemical composition of the particles determines the minimum ignition temperature and the energy of ignition.
• Dust moisture: Moist particles first dissipate energy to increase their temperature and then expend it on converting water into steam and releasing it. Consequently, the higher the moisture content, the lower the risk ignition.
• Surrounding conditions: Air temperature and humidity play a role. In high ambient temperatures and humidity, the grain moisture content also increases. The vapor enhances heat conduction, improves heat transfer between particles, and increases atmospheric electroconductivity. Under such circumstances, the dissipation of static electricity is accelerated.

Agricultural dust detonation and ignition are possible when several factors are combined, including a mixture with air, sufficient particle concentration, the presence of an ignition source, and a minimum of 8% oxygen.

Understanding what makes grain dust explosion is crucial in ensuring safety in industries involved in grain processing and storage.

Dust poses a significant hazard, and it is crucial to follow proper aspiration and safety protocols. We have expertise in efficient dust collection.

Our company, Torch-Air, specializes in manufacturing filters for air purification, addressing all types of dust and contaminants. We offer free calculations, equipment selection, and expert consultations. With our advanced solutions, we ensure clean and safe air environments. Our team of professionals is dedicated to providing tailored recommendations and assisting you throughout the process. Experience the efficiency and reliability of our filtration systems and breathe easy with Torch-Air. Contact us today for personalized air purification solutions.