3.2.2 Student Book © 2004 Propane Education & Research CouncilPage 1 3.2.2 Performing DOT Cylinder...

3.2.2 Student Book © 2004 Propane Education & Research Council

3.2.2Performing DOT Cylinder

Evacuation and Vapor Flaring Operations

Before DOT cylinder maintenance tasks can be done—such as replacing valve or fitting or checking the tare weight of the cylinder—it may be necessary to evacuate propane liquid and flare the propane vapor.

In this module, you will learn to identify:

(1) procedures for evacuating liquid propane from cylinders

(2) procedures for conducting vapor flaring operations

3.2.2 Student Book © 2004 Propane Education & Research Council Page 1

Evacuating Liquid Propane from Cylinders

Evacuation by Gravity Transfer – Propane liquid can be removed from portable and exchange DOT cylinders by gravity transfer.

Ele va te d D o c k o r P la tfo rm

C ylin d e r In ve rte r w ithSe c u rin g Stra p s

H ig h P re ssu re LP- G a sH o se w ith E xc e ss F lo w &Sh u to ff Va lv e E a c h E n d

R e c e iv in gA SM E Ta n k

Figure 1. Evacuation of DOT Cylinder by Gravity Transfer



Evacuation by Gravity Transfer

Figure 2. Stationary Cylinder Inverter



Evacuation Using a Compressor

Figure 3. Evacuation of Receiving Tank Using a Portable Vapor Compressor



Evacuation Using a Compressor

Compressor & Scavenging Tank

Many bulk plant operators use some type of compressor system for evacuating cylinders. One of the most common methods used is the scavenging system.



Evacuation Using a Portable Compressor

Figure 4. Evacuating Vapor Service Cylinder

Inverting cylinders by hand is neither easy to do nor safe.



Evacuation Using a Portable Compressor

If the cylinder is evacuated of liquid propane for the purpose of comparing its weight to the manufacturer’s stamped tare weight as part of requalification, draining it of liquid is all that is required. It can remain pressurized with vapor for the purposes of tare weight comparison and requalification.

If however, the cylinder must be de-pressurized in preparation for valve or fitting replacement, the vapor must be reduced to near atmospheric pressure. That process may require the flaring of vapor.


Conducting Vapor Flaring Operations

Flaring is the process of burning LP-gas removed from storage containers in a controlled and safe manner.

4.3.2.3 of NFPA 58 requires that LP-gas be burned at least 25 feet from combustibles.

2001 edition

NFPA 58



Figure 5 Figure 6. Figure 7.



Figure 8a. Electronic Ignition Flare Tower

Figure 8b. Top of Flare Tower Burning Propane from Cylinder

3.2.2 Student Book © 2004 Propane Education & Research Council Pages 6 - 13


Step 1: Evacuate as much propane from the container as possible.

Step 2: Select the proper site for flaring the remaining propane in the container.

Step 3: Select the necessary equipment for flaring the remaining propane in the container.

Step 4: Assemble and connect all necessary hoses, fittings, burner, etc., to flare the remaining propane in the container.

Step 5: Pressure test the flaring assembly.



Step 6: Flare the remaining propane in the container.

Step 7: Bleed down and disconnect the flaring equipment.



Figure 9. Recommended Site for Flaring Containers (At Bulk Plant)

Although the flaring operation is simple, it does involve an open flame. As a result, certain safety precautions should be followed when selecting a site for flaring the container. These safety precautions will limit the danger

of an accidental fire while the flaring burner is operating.



NOTE: The flaring burner should be located at least 25 feet away from the container being flared, any transfer area or important building.



Flaring equipment should have these features:

1. An orifice or other gas flow controlling device

2. A built-in shutoff valve

3. Designed for vapor service

4. An approximate input rating of 500,000 BTU/hr. or less

5. Should incorporate a regulator



It is important to select a burner with both a built-in shutoff and a regulator. This allows for adjustment of the output of the burner and prevents any excessive withdrawal from the cylinder or tank being flared.

Remember, excessive withdrawal could easily cause the tank or cylinder to temporarily stop vaporizing enough gas to supply the burner. This condition may be noticed when a frost line appears on the container, yet sufficient liquid may remain to re-pressurize the container when it regains heat from surrounding air.



Figure 10. Supply Hose for Flaring Burner



Figure 11. Flaring Burner Support



During Step 6, observe the pressure gauge on the service valve (or purging adaptor). When the pressure drops below 15 psig, temporarily shut down the burner and allow the pressures in the tank or cylinder to increase. (Because of the high demand of the burner, the container may refrigerate during the flaring operation. If a frost line develops on the cylinder, temporarily shut down the burner and allow the pressure in the container to increase.)

When the vapor pressure no longer increases above 15 psig, flare the remaining vapor until the burner extinguishes.



Flaring operations should incorporate the following safety practices and recommendations:

1. Flaring operations should never be left unattended and qualified personnel should continuously monitor flaring equipment and conditions.

2. If qualified personnel must leave the flaring operation for any reason, the operation should be shut down and the valve(s) on the container being flared should be closed.

Check with your supervisor or any company-specific procedures that may apply to flaring operations.


Time to See If You Got the Key Points of This Module…

• Complete the Review on pages 14 & 15.

• See if you are ready for the Certification Exam by checking off the performance criteria on page 16.

3.2.2 Student Book © 2004 Propane Education & Research CouncilPage 1 3.2.2 Performing DOT Cylinder...

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