General Design Practices in Reducing Risk in Grain Handling Facilities

Transcription

1 General Design Practices in Reducing Risk in Grain Handling Facilities 1

2 2 Facility Risks Welding Bearing failure Tramp metal Head pulley slippage Static electricity Electrical arcs Slippage in belt drives in confined areas Belt and pulley static electric build up Belt tracking Improper dust collection operation Nuisance sensor faults

3 3 Explosion Prevention PLC instrumentation and hazardous monitoring Reduction of fugitive dust in confined work areas Dust collection to lower the explosion level of dust ( grams/cu.m) inside of equipment. Designing transfer points outside of enclosed areas Relief vents Explosion suppression/isolation

4 4 PLC Operational Abilities - Hazard Monitoring - Equipment Control - Remote Control Trippers - Bin Temperatures - Belt Tensioning Monitoring - Vibration Monitoring - Magnehelic Auto Logging / Alarming - Alarm notification - Remote Troubleshooting - Counting Functions - Explosion Suppression Monitoring

5 5 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

6 Centralized Control Station 6

7 7 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.

8 Installations Proper spacing of rub blocks in the equipment being monitored is very important Scheduled inspections of rub blocks is necessary 8

9 Sensor Placement 9

10 Bucket Elevator Boot Rub Blocks 10

11 Conveyor Hazardous Monitoring 11

12 12 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 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.

14 14 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.

15 Pneumatic Dust Blower 15

16 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.

17 Friction from belt slippage 17

18 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.

19 Outside Equipment 19

20 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 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 22 Tramp Metal Suspended rare earth magnets over belts Ceramic lined plate magnets in direct contact applications Grate Magnets Catch bars

23 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.

24 Reactive Explosion Prevention 24

25 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 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

27 Suppression or Isolation? 27

28 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.

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31 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.

32 Questions? 32