When filling and discharging bulk solids storage silos, several risks that may arise such as overfilling, overpressure and combustable dust explosion. By processing the signals coming from several sensors and taking necessary safety measures, silo control system automatically protects the silo from these risks. Health of critical components are monitored continuously and plant operators are warned if there exist any malfunctuining equipment. System provides a complete silo protection solution for safety of silo, workers and plant.
Silo Overpressure Protection
When bulk material storage silos are being filled by bulk tanker trucks or pneumatic conveying systems, pressurized air is used to fill the silos and it is vented from the top of the silo through jet filters (also named as dust collectors or silo vent filters). If the pressurized air entering the silo is not vented adequately, delivery in this manner may result in pressure build up and consequent rupture of the silo or connected equipment such as filter systems.
Potential Sources of Silo Over Pressurization are:
– Inadequate flow through the silo top jet filter due to wrong filter selection
– Inadequate flow through the silo top jet filter due to clogged filter elements
– Failure of pressure relief valve to vent excessive air inside the silo
– Sudden increase in air flow rate at the end of bulk tanker discharge
– Uncontrolled discharge of residual air from the bulk truck
– Inadequate maintenance of silo protection and safety equipment
Silo overpressure protection systems are used to ensure that storage silos and silo equipment have adequate safety measures to prevent over pressurization. In case of any lack of protection, these systems prevent filling the material to silos. This is achieved by making self tests for the silo equipment before filling and continuous monitoring of silo pressure during filling. Following safety systems are available in silo protection units:
– Silo inner pressure monitoring
– Jet filter clogging monitoring
– Pressure relief valve self test
– Jet filter self test
– Automatic closing of silo inlet in case of over pressure
– Cutting power of bulk truck or cutting signal of pneumatic conveying system in case of over pressure
Silo Underpressure Protection
During silo emptying, powdered material moves downwards and density of air above the material decreases as the empty volume increases if there is no air entrance from outside. This leads to a decrease in pressure and creates vacuum. If the vacuum level is high enough, the silo may collapse inside (implosion).
Main reason of a silo implosion is discharing material in the silo rapidly wihout providing adequate air ventilation.
Silo underpressure protection systems monitor pressure inside the silo and discharge speed of material. If the underpressure safety limit is exceeded, system automatically closes the silo discharge valve or stops the discharging conveyor.
Silo Overfilling Protection
Silo overfilling protection systems are suitable for preventing overfilling of silos and consequential damages or losses. Monitoring the product level continuosly inside the storage silos is the key for successful protection. Silo loading can be done by pneumatic or mechanical conveying systems. Rotating paddle sensors and radar sensors are widely used in storage silos to detect level of powdered and granular bulk solids. Main functions of silo overfilling protection system are as follows:
– Does not allow to start silo filling if it is already full.
– Gives alarm when it becomes full.
– Stops silo filling when it becomes full.
– Operates silo top jet filter (dust collector) during silo loading.
Explosion Protection for Ex-Hazardous Areas
If the handled material has a risk of explosion due to static charge build or the area is an Ex-hazardous area, grounding the truck is imperative. Electrostatic grounding testers are used to check whether the truck is grounded properly or not. Silo protection systems have a signal connection to truck grounding and bonding testers. Silo filling can only start if the safety permission signal is received from grounding and bonding tester.
Explosion vent panels are used to protect the silo, ensure worker and plant safety during handling of combustible dusts such as starch, sugar, coal and chemicals. An explosion vent or rupture panel is a safety device against excessive internal, explosion-incurred pressures, by means of pressure relief. It is designed to open at a predetermined pressure, to allow the fireball and explosive pressure to vent to a safe area. Burst sensors are used to detect if the explosion panels are ruptured due to an internal explosion. The sensors signal the opening of the bursting disc or panel so that equipment such as fans, screw feeders or rotary valves can be switched off and inform the plant operators to take relevant safety measures.
Operator Safety Warning System For Adverse Weather Conditions
Cold weather poses hazards to anybody working outdoors, but the conditions become more intense at higher places in the plants. Workers on the silo top facing different hazards than workers on the ground. What seems like a normal winter day on the ground could be high winds and extreme temperatures at heights. Companies and their workforces must understand what they could encounter to properly prepare for winter conditions.
Air temperature, humidity and wind speeds are measured by sensors at the top of the silo to give warning to workers before climbing to top, preventing any health problems or accidents caused by slippery surfaces, high winds, extreme cold and hot weathers.