SOP FOR GRAIN UNLOADING FROM FLAT-BOTTOM SILO

Efficient grain unloading from flat-bottom silos is essential for maintaining grain quality, ensuring smooth operations, and preventing silo system damage. Proper unloading reduces grain residue, minimizes pest infestation risks, and extends the lifespan of silo storage systems. This Standard Operating Procedure (SOP) outlines a systematic process to safely and effectively unload grain while complying with safety standards and ensuring operational efficiency.

1. Gravity Unloading

The unloading process begins with gravity unloading, which typically discharges about 85% of the grain from the silo. The grain flows out through

multiple hopper openings at the bottom of the silo, with the largest opening located at the centre and smaller openings positioned around it. Start by opening the central opening first and continue unloading until the grain stops flowing. Once the central opening stops discharging, open the other two side gates just adjacent to central gate, followed by the remaining gates in similar sequence to allow complete gravity discharge.

2. Sweep Auger Unloading

After gravity unloading, the next step is to use the sweep auger to remove the remaining grain. First, open the sidewall manhole, which is usually located on the second ring from the bottom. The manhole has two doors — an outward-opening door and an inward-opening door. Open the outward door first and then the inward door. If the inward door does not open, it may be due to a slight jam or grain obstructing it. Lightly tap the spout near the unloading gate to clear any blockage. If this does not work, the material buildup inside the silo may need to be cleared. In such cases, enter the silo from the roof manhole with proper safety gear to clear the obstruction. However, this work should always be performed under experienced supervision.

Once the manhole is open, operate the sweep auger from outside the silo and monitor its progress through the sidewall manhole. The sweep auger rotates and moves in a circular motion, sweeping grain toward the central gate. For automatic sweep augers, the auger moves through the entire silo automatically. For manual sweep augers, control the tractor movement carefully by starting with a 2/20 principle — move for 2 seconds and stop for 20 seconds — and adjust as needed. These 20 second time-period may be increased or decreased depending upon material build up in front of sweep auger. The sweep auger will leave a thin layer of 1 to 3 inches of grain, which will need to be manually swept.

3. Manual Sweeping

Once the sweep auger operation is complete and the system is electrically isolated, manual sweeping is required to remove any remaining grain. Before allowing workers inside, check for dust accumulation and turn on the roof exhaust fans to clear any dust cloud. After ensuring a safe environment, 3 to 4 workers equipped with appropriate safety gear (such as dust masks and safety shoes) can enter the silo through the side manhole to manually sweep and clean the remaining material.

4. Silo Internal Cleaning

After manual sweeping, inspect the interior of the silo thoroughly. Pay close attention to sidewalls, corners, and joints where dust and residue tend to accumulate and stick to the sidewall sheets. Ensuring that the silo is completely clean helps maintain grain quality and reduces the risk of infestation. Also, it helps to reduce the chance of sidewall sheets rusting.

5. Prophylactic Treatment

Prophylactic treatment is the most important activity after the Silo internal cleaning. Prophylactic treatment is applied to prevent pest infestation. Treat the floor, unloading hoppers, and sweep auger with an appropriate insecticide such as Malathion 50% EC or Deltamethrin 2.5% WP. Make sure the treatment is applied uniformly, following safety guidelines while handling chemicals.

6. Parking Sweep Auger

Properly parking the sweep auger after unloading ensures smooth operations in the future. Park the sweep auger close to the unloading hoppers, preferably positioning the tractor wheel near the unloading hopper that is closest to the sidewall. This placement allows easy visibility and manual operation if needed.

7. Temperature Sensing Cable Re-fixing

Once the sweep auger is parked, re-fix the temperature monitoring cables. Tie the cables to the eyelets fixed on the silo floor using fishing twine (1–2 mm thick with 20–40 kg breaking strength). The twine is designed to break when the sweep auger operates, preventing any damage. Alternatively, some manufacturers provide hammers at the cable ends to hold them in position, offering a safer and somewhat effective solution.

8. Final Closing and Sealing

After completing all unloading and cleaning activities, inspect the silo for any visible damage. Check for cracks, fractured bolt washers, and missing sealant at critical points such as the bottom, eaves, and manholes. Perform necessary repairs before sealing the silo. Once the inspection is complete, close and seal the sidewall and rooftop manholes to prepare the silo for the next filling cycle.

Following this Standard Operating Procedure ensures that the grain unloading process is carried out safely, efficiently, and without loss or contamination. Consistent adherence to these steps not only maintains grain quality but also extends the life of the silo and associated equipment.