Components of large steel silo ventilation system and related knowledge introduction

The importance of ventilation systems for large steel silo is self-evident. Not only does it play a crucial role in ensuring food safety, it also plays a crucial role in improving grain storage efficiency. The ventilation system is one of the core supporting facilities for large steel silos. Today, we will explain the components and related knowledge of large steel silo ventilation systems.

I. Main Components

The ventilation system is a complete system consisting of the following parts:

1. Power Source: Ventilation Fan

• Function: Provides air flow throughout the entire system and is the "heart" of the system.
• Types:
  • Suction Fan: Extracts humid, high-temperature air from the silo, typically used for precipitation and temperature reduction. This is the most common method.
  • Injection Fan: Blows dry, low-temperature air from the outside into the silo.
  • The fan can be either an axial flow fan (high air volume, low pressure) or a centrifugal fan (high air pressure, relatively low air volume) depending on your needs.

2. Air Distribution System: Ventilation Ducts and Floor Cages

• Function: Distributes air supplied by the fan evenly and efficiently to all parts of the material layer, avoiding dead zones.
• Structure:
  • Main Duct: The main duct connecting the fan to the internal distribution system.
  • Branch Duct/Ventilation Floor Cage: A network of ducts laid on the silo floor, typically in a circular or comb-like pattern. These ducts are perforated with numerous air holes, allowing air to evenly pass through the material. Floor cages must possess high compressive strength to withstand the weight of the material above.

3. Airflow Path: Material Porosity

• Function: The natural spaces between material particles provide passages for air to pass through the material layer. Material particle size, uniformity, and the presence of agglomeration directly impact ventilation effectiveness.

4. Protection and Filtration System: Air Inlet Screen and Silo Roof Exhaust

• Function:
  • Protective net: Installed at the fan inlet to prevent debris, insects or birds from being sucked into the bin and contaminating the materials.
  • Silo Roof Exhaust: During suction ventilation, hot, humid air is discharged through the silo roof vents. Exhaust vents are typically equipped with rain caps and insect screens to prevent the entry of rainwater and pests.

5. Control System

• Function: Modern steel silo ventilation systems are typically equipped with automatic control systems.
• Functions:
  • Automatic Timing: Set ventilation start and stop times.
  • Temperature and Humidity Sensing: Sensors installed at various locations within the silo monitor material temperature and humidity, automatically starting and stopping the fans for intelligent management (for example, automatically starting ventilation when the absolute humidity outside air is lower than inside the silo).
  • Remote Monitoring: Ventilation status can be remotely controlled and monitored via a computer or mobile app.

II. Important Functions

The ventilation system is more than just a "blowing" function; it serves many crucial and multifaceted functions:

1. Cooling Function - Ensuring Storage Safety

• Principle: Utilizes the cooler air at night or in winter to displace heat accumulated within the silo through respiration or microbial activity.
• Importance: Effectively reduces material temperature, eliminates hot spots, prevents material deterioration, caking, and fat oxidation caused by high temperatures, and most importantly, inhibits the growth of mites and mold, ensuring the safe passage of materials through the summer.

2. Humidity Control by Precipitation - Preventing Mold

• Principle: When the absolute humidity of the outside air is lower than that of the air inside the warehouse, ventilation can remove moisture from the grain.
• Importance: Maintaining the moisture content of the grain below the safe moisture level is the most fundamental measure to prevent mold and rot. For newly stored, damp grain, ventilation and precipitation are a cost-effective treatment.

3. Removing Odors and Fumigation Gases - Improving Quality and Work Safety

• Principle: Forced ventilation removes odors generated by the grain and residual fumigant (such as phosphine) gas from the warehouse.
• Importance:
  • Ensuring Quality: Eliminating odors and preserving the original flavor of the grain.
  • Ensuring Safety: Before personnel enter the warehouse to perform work, thorough ventilation must be performed to remove toxic fumigation gases and high concentrations of carbon dioxide to prevent suffocation and poisoning.

4. Maintaining Grain Temperature Balance - Preventing Condensation

• Principle: Due to fluctuations in ambient temperature and the natural respiration of the grain, temperature differences can easily form between grains at different locations within the warehouse and between the grain and the warehouse walls. When hot, humid air cools, it condenses on the cold surface, forming water known as condensation.
• Importance: Ventilation equalizes the temperature across the silo, effectively eliminating and preventing condensation. Condensation can cause a sharp increase in localized moisture, leading to severe mold and caking.

5. Maintaining Material Vitality - Especially for Seed Grains

• Principle: Provides the material with adequate oxygen to maintain its minimal respiration.
• Importance: Maintaining material viability is crucial for seeds. Good ventilation prevents loss of germination rate due to anaerobic respiration.

III. Safety Operation Specifications

1: General

• 1.1. Purpose: This specification is developed to standardize the operating procedures of ventilation systems for large steel silos, ensuring operational safety, preventing material damage, and extending equipment life.
• 1.2. Scope of Application: This specification applies to all ventilation operations for large steel silos storing bulk materials (such as grain, feed, cement, fly ash, etc.).
• 1.3. Responsibilities: Warehouse managers and operators must undergo training and be proficient in this specification before assuming their duties.

2: Pre-Ventilation Inspection and Preparation

2.1. Verify the Purpose of Ventilation:

• Cooling: Ventilate when the outside air temperature is lower than the grain temperature inside the warehouse (generally, it is recommended that the outside temperature be at least 4°C lower than the grain temperature).
• Precipitation: Ensure that the absolute humidity of the outside air is lower than that of the air inside the warehouse. Precipitation ventilation is strictly prohibited during high humidity weather such as rain, fog, and snow, or when the relative humidity is ≥85%.
• Conditioning/Odor Elimination: Select appropriate weather conditions based on specific process requirements.
• Post-Fumigation Ventilation: Ensure that the specified airtightness period has been met and wear necessary protective equipment.

2.2. Equipment Inspection:

• Electrical System: Check that the fan power cord, control cabinet, and switches are intact and free of electrical leakage hazards.
• Fan: Check that the fan blades, protective screen, and base fasteners are functioning properly, rotate smoothly, and detect any abnormal noises.
• Duct System: Confirm that the connections between the vents and the fan are properly sealed and leak-free. Check the silo roof exhaust vents for unobstructed access and the rain cap and insect screens for proper operation.
• Sensor System: Check the temperature and humidity sensors inside the silo and the data from the external weather station for accuracy and reliability.

2.3. Material Condition Assessment:

• Review the grain condition records to determine the current average temperature, moisture content, and location of the highest temperature point.
• Determine whether the material is caking, clinging to the wall, or experiencing localized lumps. If present, address these issues before ventilation. Failure to do so will result in uneven ventilation and even duct blockage.

3: Ventilation Operation Procedures

3.1. Startup:

• Based on the ventilation objectives, refer to the "Temperature and Humidity Comparison Chart" or rely on the intelligent system to confirm that ventilation conditions are met.
• Properly connect the fan to the duct, ensuring the flexible joints are secure and sealed to prevent rainwater from backflowing through the joints.
• Operational Sequence: Start the fan first, then open the vent valve (if a shut-off valve is provided). To stop the fan, close the valve first, then stop the fan. This sequence can reduce the fan startup load.

3.2. Operation Monitoring:

• Regular Recording: Record the fan operating status, current, voltage, and temperature and humidity changes inside and outside the silo at least once every four hours. Abnormal current may indicate a fan blockage or malfunction.
• Effectiveness Evaluation:
  • Cooling Ventilation: Reduce the temperature of the bottom material in the silo to the target value, avoiding over-ventilation.
  • Precipitation Ventilation: Calculate the unit ventilation rate. After ventilation, allow the material to sit for a period of time (usually 24 hours) before testing the moisture content to determine whether the target has been achieved.
• Preventing Condensation: In cold weather, if the material temperature drops too low after ventilation, contact with the warm air inside the silo should be prevented, causing condensation. Intermittent ventilation is recommended.
• Weather Monitoring: Closely monitor weather changes. If the weather becomes unsuitable for ventilation (such as rain or fog), immediately shut down the machine.

3.3. Special Operations - Ventilation After Fumigation:

A "Fumigated, No Entry" warning sign must be displayed in a conspicuous location. After ventilation for at least 24-48 hours, use a gas detector to check the residual concentration of fumigants such as phosphine on the silo roof and surrounding areas.

Once the concentration is confirmed to be below the safety threshold (e.g., 0.3 ppm), the warning signs may be removed, and personnel may enter the silo only after approval.

4: Completion of Ventilation and Subsequent Work

• 4.1. Shutdown Operations: Shut down the equipment in the correct sequence (close the valves first, then stop the fans).
• 4.2. Data Archiving: Record the start and end times, total duration, purpose, external weather conditions, and effectiveness evaluation (temperature reduction, precipitation, etc.) of each ventilation session in detail, and include this in the grain status file.
• 4.3. Equipment Maintenance: Disconnect the power supply, clean and maintain the fans, inspect the equipment, and store and properly store ventilation hoses and other equipment.

5: Safety Precautions

• 5.1. Electrical Safety: Working with live electrical equipment is strictly prohibited. All repairs and inspections must be performed with the power off.
• 5.2. Mechanical Safety: When the fan is operating, do not allow your body, clothing, or tools to come near the high-speed rotating blades and transmission components.
• 5.3. Height Work Safety: When inspecting the silo roof, wear a safety belt and follow the height work regulations.
• 5.4. Confined Space Work: Personnel are strictly prohibited from entering the silo during ventilation operations. If entry is necessary, the confined space work approval and supervision system must be strictly implemented.
• 5.5. Fumigant Safety: When handling post-fumigation ventilation, operators must wear approved gas masks and work in pairs or more, with mutual supervision.

6: Common Faults and Emergency Response

Summary:

Three Principles of Ventilation

• 1. Safety First: Always prioritize personal and equipment safety.
• 2. Scientific Judgment Principle: Ventilation is more than simply blowing air; it must be scientifically determined based on accurate temperature and humidity data.
• 3. Timely Stop Principle: Ventilation should be stopped promptly after achieving its intended purpose to avoid excessive ventilation that wastes energy or even negative effects (such as excessive water loss).

The ventilation system for a large steel silo is a sophisticated engineering process consisting of four key components: power generation, distribution, filtration, and control. Its core function is to create a cool, dry, and uniform storage environment. By reducing temperature, dehumidifying, detoxifying, and maintaining a uniform temperature, it ultimately achieves the core goals of preventing mold, ensuring material quality, minimizing storage losses, and ensuring operational safety. A scientifically designed and well-functioning ventilation system is essential for the safe and efficient operation of large steel silos.

Written by

Shandong Shelley Grain Steel Silo Co., Ltd

Editor Jin

WhatsApp : +86-18653877118

Email : shelley@cnshelley.com