Silo Discharge Control System

Bulk material silos have several types of discharge equipment such as screw feeders, rotary valves, butterfly valves, slide gate valves, chain conveyors, bulk truck loading bellows and pneumatic conveying systems. Depending on application, there are wide range of receiving points like bins, processing lines, weighing and batching systems, trucks, mixers etc. Silo discharge control systems provide full control over silo discharging equipment for efficient handling.

System is connected to level and pressure sensors, vibrating bin activators, discharging equipment, DCS or SCADA system and downstream equipment. Product discharge is controlled with respect to process requirements. If a truck is to be loaded, system is connected to truck loading bellow and stops when the truck is full. If a mixer is to be filled with the help of weighing unit, system stops when the desired filling amount is reached. If a pneumatic conveying system is connected to another bin, system stops when the bin is full.

Silo discharge control system also monitors the pressure inside the silo. If the silo unloading speed is high, powdered material inside the silo moves down rapidly and creates negative pressure (vacuum) above itself. If the level of negative pressure is high enough, it may cause the silo to collapse inwards. Silo control system can also monitor the silo inner pressure level and stops discharging if when the vacuum level is critical.

• A start signal comes from plant’s main electrical control unit to start silo discharging.
• Silo control system automatically checks silo for safety.
• A self test is applied on pressure relief valve (for vacuum), process air supply and silo level. If any problem is detected (low level, malfunction in jet filter), system does not allow unloading, does not send confirmation signal to main electrical control unit and keeps discharging equipment closed.
• If product level inside the silo is enough and self tests are passed, system starts operation. and sends confirmation signal.
• Silo discharging equipment is operated.
• Silo pressure is continuously measured during silo discharging.
• If the pressure inside the silo decreases below the limits (underpressure), silo pressure relief valve opens to increase the silo pressure , a signal is sent to electrical panel to stop discharging. Built in pressure sensor is also available for double protection if the pressure relief valve malfunctions. In this case the signal coming from pressure sensor is used to stop silo discharging.
• Product level in the silo is continuously measured during silo unloading.
• If the powdered product in the silo reaches low level, or a remote stop signal is received, system stops silo unloading.
• Process values are recorded for future use.

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