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2
Facility Risks
• Welding
• Bearing failure
• Tramp metal
• Head pulley slippage
• Static electricity
• Electrical arcs
• Nuisance sensor faults
• Slippage in belt drives in
confined areas
• Belt and pulley static
electric build up
• Belt tracking
• Improper dust collection
operation
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Explosion Prevention
• PLC instrumentation and hazardous monitoring
• Reduction of fugitive dust in confined work areas
• Dust collection to lower the explosion level of
dust (25-500 grams/cu.m) inside of equipment.
• Designing transfer points outside of enclosed
areas
• Relief vents
• Explosion suppression/isolation
4
PLC Operational Abilities
- Hazard Monitoring
- Equipment Control
- Remote Control Trippers
- Bin Temperatures
- Belt Tensioning Monitoring
- Vibration Monitoring
- Magnehelic Auto Logging / Alarming
- Email Alarm notification
- Remote Troubleshooting
- Counting Functions
- Explosion Suppression Monitoring
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PLC
•Instrumentation -Allows the operators to be at a safe area controlling the
process.
-Allows the entire system to be centralized.
-Allows one operator to have Total Process Control.
•Functionality -Provides detailed information to track and trend
-Many equipment operations can be monitored and
tracked for increased operation intelligence
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Hazardous Monitoring Installations
•Needs to follow NEC code •Conduit runs need to be well planned
•Water has been a big problem for most older Hazard Monitoring systems due to poor installation practices.
•Condensation from outside going into new building requires duct seal and rated drain plugs should keep any water out of conduit.
•Installation must be monitored to ensure of proper sensor placement.
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Installations
•Proper spacing of rub blocks in the equipment
being monitored is very important
•Scheduled inspections of rub blocks is
necessary
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Wireless/Battery Hazardous Monitoring
• Wireless Hazardous Monitoring system that can
monitor moving systems.
• 3 year battery life that reports changes of states
and updates the PLC system
• Alarms if out of range
• Equipment meets Class 2, Division 1, Group G.
13
Dust Control Design
• Centralized or Decentralized Dust System?
- Centralized:
One large dust collector picks up from a host of
different pieces of equipment resulting in
interconnecting a large amount of critical equipment.
- Decentralized:
Multiple smaller collectors providing dust control on
individual pieces of equipment.
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Dust Control Design
• Main function is to reduce the amount of dust
concentration in equipment.
• Baghouse have high levels of dust concentration
and must be adequately protected.
• Dust control modifications after installation can
result in loss of transport velocity and build up of
dust in ducting.
• Magnehelic gauges must be monitored to make
sure that a loss in transport velocity does not
occur.
16
Bucket Elevator Considerations
• Dangerous grain handling equipment due to high
concentration of dust within the casings.
• Available outside with pressure venting?
• Belt take up
- Screw take ups can be troublesome on large legs
• Head pulley slippage
- Intense heat generation from head pulley spinning.
18
Concrete Silos
• Intervented vs. Individual vented.
- Intervented silos are vented among a cluster of silos
to allow air transfer during filling and unloading
operation. Interconnects multiple silos.
- Individual vented silos are not individually connected
and have their own venting system.
• In a belt tripper system poor dust control can
lead to over pressurization of bins during filling
and can lead to a high concentration of dust
emissions inside the gallery.
20
Electrical Installations
• Defining area classifications
• Electrical wiring, grounding, bonding and conduit
be rated for area classification.
• Ensure routing of conduit is away from walkways
or areas that may get damaged during
maintenance.
• Electrical distribution equipment are rated for
proper interrupting rating based on transformer
and power company ratings.
21
Electrical Motors in Class II, Div.1 Group G areas
• Motor must be dust ignition proof: “enclosed in a
manner that excludes dust and does not permit
arcs, sparks or heat otherwise generated
…inside of an enclosure”
• protected with thermostats rated below the
minimum ignition point of dust.
• Motors must be carefully selected when using
VFD’s and additional ventilation may be needed
when operating at lower speeds.
22
Tramp Metal
• Suspended rare earth
magnets over belts
• Ceramic lined plate
magnets in direct contact
applications
• Grate Magnets
• Catch bars
23
Other Design Considerations
• Pressurization of MCC rooms
• Pressurization of tunnels
• Grounding of pneumatic systems and structures
• Containment equipment to make equipment dust
tight and self cleaning
• Hot work permits during modifications of
equipment must be monitored by qualified
individuals.
25
Explosion Suppression Design Criteria
• Ensure the explosion suppression system has
correct KST (maximum pressure rise in
containment of a specific dust) value
- Most grains are rated a class 1
• Pred (reduced maximum deflagration pressure in
a vented enclosure)
• Is the unit outside and have proper NFPA 68
venting?
• Can the unit be suppressed or isolated?
26
Explosion Suppression/Isolation
• Chemical:
- Sodium Bicarbonate
- Dupont FE-25
• Mechanical Gates:
- Variety of gates on the market that are installed inline.
- Limitation of sizes
• Flameless Venting if equipment is inside
28
Installation of Suppresion/Isolation Systems
• Ensure that the canisters installed have no
obstructions in front of discharge
• Ensure pressure sensors and are not in line with
product flow.
• Mounting needs to be able to withstand pressure
and weight of canister
• Maintenance access
• Engineering support when retro-fitting older
equipment.
31
Conclusion
• Review NFPA Codes and Standards for
applicable recommendations prior to
installations.
• Use instrumentation within your plant to reduce
risk and gain better knowledge of the health of
your system.
• A well designed system is only as strong as the
installation.