Steel silos are widely used in the grain storage industry due to their small footprint, large reserves, and high mechanization degree.
The storage and transportation of bulk grain are the general grain circulation trend in the future, and steel grain silos will play a greater role.
Figure 1 shows the first-phase bulk grain metal silo of the Rizhao Port, there are 12 metal silos, and the single grain storage silo capacity is 12000T, the entire system was put into operation on July 12, 2005;
Figure 2 shows the third-phase expansion project of Rizhao Port’s bulk grain storage silo, there are 24 metal grain silos, 1 single grain storage silo capacity is 10,000T and the total capacity is 240,000T, is divided into 2 rows with 12 sets in each row.
Around these newly-built grain storage bin groups, loading and unloading conveyor lines, metering systems, train loading systems, automobile loading systems are constructed.
The bulk grain storage process includes:
- Train loading
- 1st and 2nd systematic train loading
Corrugated steel silo usage and management for bulk grain storage
Composition of steel grain silo
The first-phase bulk grain silo is corrugated grain bin, the silo top has 2 axial fans and 16 air outlets, the silo bottom has 4 centrifugal fans, it is equipped with air inlet ducts and ventilation network, and inside the silo, there is sweep auger installed.
There is 1 electric valve (800mm x 800mm) on the top of the grain silo and 7 valves (700mmx700m) at the bottom of the grain bin, 7 bottom valves are symmetrically distributed, the whole grain silo adopts the CGS grain condition monitor and control system.
The third-phase metal silo for bulk grains is assembled flat bottom silo, its roof sheets are all double-overlapped and have excellent sealing performance.
In each group of grain storage silos, the center axis distance between the two rows is 31m, each fan can efficiently provide the air volume and pressure required by the system for 24h.
In the case of full loading, even if the axial fan on the roof does not work, it can provide sufficient air pressure and air volume to blow through the grain pile.
The use of steel grain bin
Before material loading
All parts of the steel silo should be inspected in detail. The inspection includes:
- The opening and closing conditions of the feed inlet on the rooftop and the inspection door on the silo wall;
- Whether the temperature measuring cable is fastened;
- The position and cable plug of the sweep auger;
- Whether the iron floor flange of the ventilation network is tilted;
- The manual valve (electric valve) switch status at the bottom of the silo;
- Whether there is any debris in the silo.
After the inspection, report to the central control room.
Under normal circumstances, do not enter the silo.
If you must enter the steel grain silo, you must turn off all power supplies, use safety ropes and belts, and need someone to assist outside the steel grain bin.
Avoid entering the center of the metal silo, wear breathing equipment or dust masks correctly.
Material loading trial
When the silo is in use, it is necessary to carry out a material loading trial, and please refer to the figure below for the trial standard.
When the material loading trial is divided into 4 stages, the loading ratio of each stage is 50%, 20%, 20%, and 10%;
When the material loading trial is divided into 3 stages, the loading ratio of each stage is 60%, 30%, and 10%.
After each stage of loading is completed, the steel grain silo should be resting for a certain period of time.
After the first 2 stages of loading, the resting time is not less than 1 month;
After the final stage of loading, let it rest for no less than 2 months.
Through multi-stage loading, the uneven settlement of the foundation bottom can be reduced.
If only one stage, it may cause uneven foundation bearing pressure and uneven settlement of the silo foundation.
Before loading, confirm the target metal silo number, after closing the bottom valve and access door, open the rooftop valve, and then turn on the feeding equipment.
The material enters the grain storage silo correctly from the top valve.
During loading, the material movement direction is basically vertical, which can ensure that the material is not biased in the steel grain silo and does not rub its wall.
If the material reaches the maximum loading height, the alarm will sound.
When the material reaches the max. level, the system will automatically stop, which can prevent the grain bin from overflowing.
If the grain is loaded beyond the designed storage capacity, when the grain is full to the top of the storage, it may cause the roof to expand outward and leads to damage.
When there is too much grain in the silo, opening the manhole at the top of the silo will cause grain overflow.
During the material storage period, test the materials regularly, pay attention to the temperature in the silo timely.
Due to the thin wall and good thermal conductivity of the steel silo, the grain close to steel wall is affected by the external temperature, and the temperature in the silo easily rises in summer.
If the temperature is too high, material hardening and coking will occur, this requires ventilating the metal grain silo.
In the case that the temperature in the silo cannot drop, the material should be taken out.
Incorrect unloading methods will cause damage to the overall structure of the metal grain silo and collapse it.
Only the central outlet is allowed to unload material first.
After the material in the metal grain silo is completely unloaded from the central outlet, the rest of the non-central outlet can be opened.
During the process of unloading from the center outlet, the non-center outlet must be closed.
When unloading, first turn on the conveyor under the metal grain silo, and then open the gate under the metal grain silo.
According to the outgoing delivery volume, determine the opening amount of the manual flap valve under the metal grain bin.
If the opening amount is too large, the conveyor under the silo may be blocked.
If it is a multi-point unloading, the other outlets can be opened only when the center outlet in the silo is completely empty, and two symmetrical outlets must be opened at the same time, basically ensuring their flow rate is the same.
- Natural unload stage
When the material is being unloaded, first generate a standard unloading process, and then open the electric valve at the bottom of the silo as needed.
After the process is started, the opening amount of the manual valve gradually increases.
If the opening is too large at the beginning, it will cause blockage of the belt.
In the case of a large amount of material, first, open the third group of outlets for unloading.
If the flow rate does not meet the requirements, open the second group and the first group in turn, and finally open the center outlet.
- Clearance stage
The 1st, 2nd, and 3rd group of outlets must be closed before the sweep auger is opened, and only the center outlet is opened when clearing.
As the sweep auger can’t clear completely, personnel are required to assist the clearing.
The clearing personnel stand behind the moving direction of the sweep auger, wear a seat belt, and use a steel lift and a large broom to clear the metal grain bin.
The sweep auger operator should keep in touch with the personnel in the steel grain bin, ensures that the sweep auger is not overloaded and does not slip, which can improve the clearance efficiency.
The clearance flow of the sweep auger is designed to be 250t/h.
- The metal silo shall be inspected and processed after clearing
Close the valve on the top/bottom of the metal silo, collect the cable plug of the sweep auger, fasten the temperature measurement cable, check whether the ventilation network and iron floor flange are warped and damaged, check for debris, close the access door and manhole.
Material compaction in steel silos for grain storage
When the steel silo stores grain goods, the grain goods are prone to compaction due to high moisture and temperature.
During the clearance process, manpower is required to cooperate with the clearance operation.
- After the materials are unloaded, they should clean in the silo, and the silo should be hygienic, which is conducive to the next use, especially since the first unloading must be empty.
During the daily use of the silo, do not load and unload the grain at the same time.
Loading and unloading grain at the same time will cause the grain flow in the silo to be extremely complicated and leads to overloading, which will greatly reduce steel silo life and increase the structural damage risk.
It is strictly forbidden to unload grain through the access door or open holes in the sidewall.
This will cause uneven pressure on the distribution of the grain load in the galvanized grain bin, which will result in damage to the galvanized grain bin.
When dealing with grain compaction in the corrugated grain bin, the person in charge of the site should carefully observe the compaction degree of the materials in it.
When the compaction of the materials in the silo needs to be manually processed, close the lower gate of the silo first and stop the equipment under the silo.
Reliable safety measures must be taken to prevent accidents such as material collapse and personal injury.
- When compaction occurs in the silo, the person in charge of the site should contact the central control room to confirm the weight of the remaining materials in the silo.
If the remaining material weight is 1500-2000t, it is considered to be mildly compacted, formulate a rational clearance plan.
If the remaining material exceeds 2000t, and it is unable to unload, it is considered to be severely compacted.
When the vertical height of material compaction exceeds 3m, the clearance personnel are strictly prohibited
First, use bamboo poles and other stabbing tools to reduce the height of the compaction section, so that the material accumulation angle is controlled within 45°, and then clear the lower part of the compaction.
If the material accumulation angle is greater than 45°, the clearance personnel must wear safety belts and safety ropes to reduce height.
It is strictly forbidden for personnel to stand upright and work on materials that are dangerous to collapse.
- Dredge the hardened materials from the side of the manhole to internal outlets.
So that the materials form a fan-shaped surface.
- When dealing with blocked outlets, the operator cannot stand directly on the outlet.
The material accumulation angle within 2m of the outlet should not be greater than 45°, anti-sinking and non-slip wood boards should be placed.
- It is strictly forbidden to open the bottom outlets during the height reduction and smashing operations.
If it needs to be opened, it must be opened by the person in charge of the clearance operation site, and open outlets after all personnel and tools have been evacuated from the silo.
Steel grain silo usage management
Organize employees for learning and training
In order to enable employees to understand the production, safety, and technology issues of the bulk grain system, and to strengthen the education of employees on dust welding and safety knowledge, regularly organize employees to learn from other ports.
Usage and management
- Preparation before ventilation
Before ventilation, check the firmness and tightness of the connection between the fan and the air duct;
If a mobile fan is used for operation, the fan must be effectively fixed during ventilation;
The roof vent must be opened before ventilation, which can facilitate gas exchange inside and outside the silo, reduce the pressure load on the silo body during ventilation.
Before ventilating, check whether the grounding wire of the equipment is reliable, whether the wiring of the motor and the control circuit is correct, and prevent the ventilator from reversing.
- Conditions for starting and stopping the fan
If the air balance moisture value Wp≤the grain moisture value, it can be ventilated and cooled, that is, when the outdoor air is humid, do not ventilate into the silo, otherwise it will cause the moisture content in the silo to rise.
Generally, you should choose to ventilate on a clear night.
When the average temperature of the grain pile is higher than the atmospheric temperature by ≥8°C (6°C in the subtropical zone), ventilation starts, the average temperature of the grain pile can be obtained through the temperature displayed by the temperature measurement system.
Conditions for stopping the ventilator
The difference between the average grain temperature and the atmospheric temperature is ≤4℃ (subtropical zone≤3℃);
The temperature gradient of the grain pile is ≤1℃/m2 (the thickness of the grain layer);
The moisture gradient of the grain pile ≤0.3%/m2 (the thickness of the grain layer).
- Operation of the ventilation process
If the silo roof is equipped with an axial flow fan, turn on it first, and then turn on the silo bottom centrifugal fan;
When multiple fans are used at the same time, they should be started individually one by one, and the next one can be started only after the 1st one is running normally.
It is strictly forbidden to start several fans at the same time.
During ventilation, check whether the ventilator is operating normally.
If the temperature of the motor is too high or the equipment vibrates severely, it should be shut down immediately for an inspection.
The air duct sieve should be cleaned and inspected regularly.
If the sieve is found to be severely worn or not firmly fixed, it should be overhauled or replaced.
- Steel sheet temperature measurement system
For grain silos equipped with a temperature measurement system, the following requirements should be followed:
1. Observe and analyze the temperature measurement data displayed by the temperature measurement system every day.
When an abnormality is found to reach the ventilation conditions, the ventilation equipment will be activated.
2. Regularly overhaul the temperature measurement equipment.
When it is found that the temperature measurement point is faulty or does not display, it should be overhauled or the temperature measurement cable should be replaced.
3. When the ventilation is in progress, the displayed temperature is the temperature of the air flowing between the grains, not the temperature of the grains themselves.
The grain temperature can be got only after the ventilation operation is stopped for at least 15 minutes.
Galvanized grain bin safety precautions
Do a good job in safety inspections and fire drills in the galvanized grain bin area.
Regularly organize technicians, safety officers, firefighters, and team leaders to inspect the bulk grain silo, and focus the inspection on the explosion-proof and safety aspects of the galvanized grain bin area.
Metal grain bins are used to store grain, feed, and other granular, powdery materials and bulk materials, and play an irreplaceable role in various production processes of enterprises such as ports and coal mines.
It can not only shorten the material loading and unloading process, reduce operating and maintenance costs, and eliminate heavy bagging operations, but also facilitate mechanization and automation.
Therefore, it has become one of the most important granary turnover modes.