General Design Practices in Reducing Risk in Grain ...

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General Design Practices in Reducing Risk in Grain Handling Facilities

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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

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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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“Centralized” Control Station

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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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Sensor Placement

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Bucket Elevator Boot Rub Blocks

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Conveyor Hazardous Monitoring

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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.

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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.

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Pneumatic Dust Blower

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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.

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Friction from belt slippage

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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.

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Outside Equipment

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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.

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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.

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Tramp Metal

• Suspended rare earth

magnets over belts

• Ceramic lined plate

magnets in direct contact

applications

• Grate Magnets

• Catch bars

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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.

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Reactive Explosion Prevention

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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?

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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

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Suppression or Isolation?

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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.

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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.

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Questions?