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3.5.12

3.5.12. Reducing Cargo Tank Vapor Pressure Using a Plant Compressor. In order to use compressor to unload transports and recover the vapor left in the cargo tank, it is important to understand the process of reducing vapor pressure. In this module you will identify:

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3.5.12

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  1. 3.5.12 Reducing Cargo Tank Vapor Pressure Using a Plant Compressor In order to use compressor to unload transports and recover the vapor left in the cargo tank, it is important to understand the process of reducing vapor pressure. • In this module you will identify: • U.S. DOT regulations pertaining to unloading operations and attendance requirements • Reasons for reducing cargo tank pressure • Procedures for recovering propane vapor using the bulk plant compressor

  2. U.S. Department of Transportation regulations require that qualified persons be “in attendance” throughout the process of loading a cargo tank motor vehicle. • The person who is responsible for loading the cargo tank is also responsible for ensuring that it is so attended. • A person is “qualified” if he/she • has been made aware of the nature of the hazardous material • has been instructed on the procedures to be followed in emergencies • is authorized to move the cargo tank • has the means to do so . DOT Regulations Pertaining to Unloading Operations

  3. DOT Regulations Pertaining to Unloading Operations • The qualified person attending the unloading operation must remain within 25 feet of the cargo tank when the internal self-closing stop valve is open. • The qualified person attending the unloading operation must have an unobstructed view of the cargo tank and delivery hose to the maximum extent practicable, except during short periods when it is necessary to activate controls or monitor the receiving container. • When unloading the transport cargo tank using the plant compressor, the vehicle engine must not be running during the unloading operation.

  4. DOT Regulations Pertaining to Unloading Operations • The cargo tank must be equipped with a passive emergency discharge control system no later than the cargo tank’s first pressure test scheduled after July 1, 2001. After that date it must have a means to automatically shut off the flow of product without the need for human intervention within 20 seconds of an unintentional release caused by a complete separation of a liquid delivery hose (passive shut-down capability).

  5. Reasons for Reducing Cargo Tank Pressure Figure 1. Vapor Left in a Railroad Tank Car or Transport Cargo Tank Expressed in Gallons of Liquid LP-Gas

  6. Reasons for Reducing Cargo Tank Pressure Figure 2. Propane Evacuation Time for a 33,000 Water Gallon Tank Car

  7. Reasons for Reducing Cargo Tank Pressure It is not economical, however, to operate the compressor for the time required to recover the maximum possible amount of propane. To do so requires expense of unloading attendant time, electricity, and wear and tear on the compressor. More than half of economically recoverable vapor is removed in the first hour of compressor operation. For that reason, many common carriers and propane marketers who operate company-owned transports, limit the vapor recovery time.

  8. Vapor Recovery Procedures Plant vapor compressors are used in unloading operations for the following reasons: • It saves time and eliminates the hazards associated with using the transport unloading pump. • It allows for recovery of some of the propane that remains in cargo tanks after the liquid has been unloaded. • It prepares the cargo tank for inspections, maintenance, or repairs.

  9. Vapor Recovery Procedures

  10. Vapor Recovery Procedures Figure 3. Typical Plant Compressor

  11. Vapor Recovery Procedures Figure 4. 4-Way Valve Vapor Flow—Position One

  12. Vapor Recovery Procedures Figure 5. Compressor and Bulk Plant Connections and Valves

  13. Vapor Recovery Procedures Figures 6 & 7. 4-Way Valve & Piping Valve Positions

  14. Vapor Recovery Procedures

  15. Vapor Recovery Procedures

  16. Vapor Recovery Procedures

  17. If for any reason the transfer operation is interrupted, or the attendant must leave the area, the compressor must be shutdown and transfer hoses disconnected as outlined in step 13. DO NOT leave transfer hoses connected to a cargo tank while unattended by a qualified person. Vapor Recovery Procedures

  18. Time to See If You Got the Key Points of This Module… • Complete the Review on page 9 & 10. • See if you are ready for the Certification Exam by checking off the performance criteria on page 11 & 12.

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