Field Service Bulletin - Home - Agility Fuel Solutions · Personal injury or death will occur if...

Field Service Bulletin

Depressurize or Defuel?

Safely Working on LNG Fuel Systems

ENP-462

Rev. B: December 11, 2017

ENP-462: Safely Working on LNG Systems (Printed Copy is Not Controlled) 2 of 17

1. Introduction

Figure 1. Dual tank LNG fuel system major components. (1) LNG tank, (2) heat exchanger, (3) fuel level sender/ECU, (4) solenoid valve, (5) over-pressure

regulator, (6) engine fuel filters, (7) vent tube.

This bulletin summarizes the rules and procedures for safe maintenance and repair of LNG fuel systems. Note, this is not a reference for fire-fighting or fire response. Refer to the First Responder Guide, ENP-084, for fire fighter response guidelines.

Liquefied natural gas (LNG) fuel systems consist of a sealed and insulated cryogenic container (tank) for fuel storage as shown in Figure 1. When the ignition switch is turned on, a solenoid valve opens, allowing fuel to flow through the fuel conditioning components to the engine.

As the fuel warms, it changes into a gaseous state and expands. The expanding gas pressurizes the system and pushes fuel into the system for consumption by the vehicle engine.

Refer to Figure 1. Cryogenic liquid fuel from the tanks (1) flows into the heat exchanger (2) where the fuel warms and turns into a gas. Inside the tank, a level sensor changes electrical capacitance as the fuel level changes. The capacitance signal from the tank is interpreted by the ECU and/or the fuel level sender (3). The level sender signal goes to the

1 3, 4, 5

6

2

7

7

1


dashboard fuel gauge. A solenoid valve (4), is actuated by the vehicle ignition switch, controlling fuel flow. The regulator (5) ensures proper fuel pressure for the engine. In the engine bay, natural gas fuel filters (6) remove impurities and delivers fuel to the engine. Excess pressure due to normal LNG expansion is vented out of the system via the vent tubes (7).

A handy, one-page summary of the “LNG Safety Zones” appears at the end of this bulletin.

Warning Statements Used in this Document

Personal injury or death will occur if procedures are not followed.

Personal injury or death may occur if procedures are not followed.

Damage to equipment, fuel system or vehicle is possible if instructions are not followed.

This bulletin is a supplement to training in operation and maintenance of LNG fuel systems. It cannot replace LNG fuel system training or experience. Attempting to operate or maintain any LNG fuel system without proper training is dangerous.

2. Liquefied Natural Gas (LNG) Properties

Understanding the characteristics of LNG and how the vehicle fuel system works will help prevent personal, property and vehicle damage.

Natural gas (methane) is flammable; however, it only burns within a narrow range when mixed with air in a ratio of between 5 and 15 percent. Natural gas must be cooled to a cryogenic temperature (-260°F/-162°C) to become a liquid for storage.

Always wear gloves and eye protection when working with LNG. The extreme cold may cause frostbite to unprotected skin.


LNG has no odor, so methane detectors must be used where LNG systems are in operation or serviced.

LNG is non-toxic – but can displace oxygen in a confined space (danger of asphyxiation).

If spilled in large quantities, LNG is heavier than air and will pool on the ground for a few seconds before dissipating into the atmosphere.

Don’t allow sparks, flames or heated particles to come within six feet (2m) of the vehicle.

LNG inside the tank will not ignite or explode – because there is no oxygen.

The difference between LNG and compressed natural gas (CNG) is the way the fuel is stored: LNG is very cold (-260°F/-162°C) but under relatively low pressure (approx. 200

psi) CNG is under high pressure (3600 psi), but relatively warm (ambient

temperatures)

Figure 2. LNG “saturation curve” showing the relationship between temperature and pressure. Remember, Green or Saturated LNG is required for Agility Fuel

Solutions standard LNG installations.

Important: LNG pressure is dependent upon fuel temperature, not the amount of fuel in the system tank.

LNG is available in two forms: “Green” or “Saturated” – Dispensed at 100 psi or greater and at -200°F/-129°C or

higher


“Blue” or “Cold” – Dispensed at 100 psi or lower and at -200°F/-129°C or lower

Green LNG is required for standard LNG systems by Agility Fuel Solutions

3. Personal Protective Equipment (PPE) for Servicing LNG Systems

Eye protection

Insulated gloves

Long pants

Long sleeve shirt

Proper footwear

Other PPE as the task requires

4. Depressurize or Defuel?

Refer to Figures 3 and 4. Depending on where work must be performed, the fuel system must be either depressurized or defueled.

Figure 3. Dual tank LNG system overview.

4.1 Depressurize to Isolate Components

When working on the system downstream from the liquid (red handle) valve, system fuel pressure can be isolated by closing the manual cylinder valve and depressurizing the system.


Figure 4. Depressurize the system when working on these components: (1) Heat exchanger, (2) solenoid valve, (3) over-pressure regulator and gauge, (4) engine fuel filters. Item (5) is the fuel level sender, an electrical component (no need to

depressurize the system.)

Depressurize the LNG System

To depressurize an LNG system, perform the following steps.

1. Turn the vehicle off.

2. Close the red handle shutoff valve (turn handle fully clockwise) on each tank. See Figure 5.

Figure 5. The liquid or fuel valve (red handle) controls fuel flow from the tank. Close this valve, start and run the engine until it stalls to depressurize the system.

3. Start and run the engine until it stalls.

4. Check the gauges on the tank and dashboard to ensure all the pressure is relieved (gauges read zero psi) as shown in Figure 6

4

1

2 3

5


5. Turn the vehicle off and follow vehicle lockout/tag out procedures. (Remove the ignition key and tag out the system, see Figure 7).

Figure 6. The LNG fuel gauge is located after the fuel regulator. This gauge should read zero psi after performing the depressurizing procedure.

Figure 7. Lockout and tagout the system before performing work. In this example, the main battery switch is the lockout point.

6. The system pressure and fuel are now isolated and contained in the fuel tank or tanks. Repair work can begin. Remember, there may be pressure remaining downstream of the solenoid valve. Be careful when loosening fittings for the first time because a small amount of gas may leak out of any fitting downstream of the solenoid lock-off valve, which is normal. When work is completed, the system can be repressurized.


5. Repressurizing the System

After work is completed on a depressurized system, the system may be re-pressurized.

1. Open the red handle shutoff valves

2. Close the gray handle vent valves

3. Remove the vehicle lock out devices and tags.

4. Start the engine and watch the fuel gauges to indicate proper pressure.

5. Perform a leak test on all components. Fix any leaks.

6. The system and vehicle is now re-pressurized and ready for service.

6. Defueling When Components Cannot be Isolated

Figure 8. Tank and components connected directly to the tank cannot be isolated so all fuel in the system must be removed before performing work.

The LNG tanks must be defueled before performing work on any tanks or components connected directly to the tanks. The following parts cannot be isolated using the red handle liquid valve:

1. Tanks

2. Tank to tank crossover plumbing

3. Fill receptacle


4. Liquid valve (red handle)

5. Vapor shutoff valve (gray handle)

6. Economizer

7. Primary relief valve

8. Secondary relief valve

9. Tank knuckle

10. 2 psi in-line check valve

11. Pressure gauge

Defueling an LNG fuel system requires careful planning for three reasons:

1. The vehicle must be towed, rather than driven to be moved*. It is usually best to drive the vehicle to near-empty to minimize the amount of fuel to be vented to the atmosphere and the time it takes to empty the system.

2. Once the system is defueled, LNG tanks become “hot.” This is the same condition as a new tank, without fuel inside. A defueled tank must be conditioned before the vehicle can be returned to normal operation.

3. The tank plumbing must be temporarily modified and a nitrogen purge is needed.

*NOTE

An Agility Fuel Solutions Pony Tank may be used to supply fuel a vehicle temporarily so it may be driven. See References section.

6.1 Defueling Preparation – Facilities and Equipment

A typical venting facility diagram is shown in Figure 9 and an example of a defueling post is shown in Figure 10.

NOTE: Check state and local regulations before venting a large amount of methane into the atmosphere.


Be sure to vent natural gas fuel in an open area with plenty of air circulation and no nearby sources of open flame, ignition or heat. Do not vent the system in an area where flammable gas is permitted to accumulate and potentially ignite.

Figure 9. Typical venting facilities include all of these features.

Figure 10. A portable vent post assembly used for defueling LNG and CNG vehicles.


A venting facility should include:

1. A vent pipe. This typically consists of a two-inch diameter steel pipe attached to a support structure. The pipe must extend a minimum of two feet higher than the support structure and at least 10 feet above ground level. The vent pipe must be connected to an electrical ground. There should be no ignition sources near the pipe.

2. An electrical ground connection with a minimum 3 gauge or heavier stranded copper wire attached to a ground rod, or a suitable electrical ground.

3. A high pressure electrically conductive flexible hose.

4. A hand valve to control gas flow.

5. A fire extinguisher, rated for use with natural gas. (Check with your local fire department for recommendations.)

6. Large signage indicating “NO SMOKING” and “FLAMMABLE GAS.”

6.2 Tools and Materials Needed

To defuel an LNG system, some disassembly and plumbing modification is necessary.

1. Common hand tools

2. 3/8-inch NPT elbow

3. Ground cable, minimum 3 gauge or heavier stranded copper wire

4. Ground rod and clamp

5. Length of stainless steel tubing for the discharge vent line

6. Macrotech female vent connector

7. Nitrogen gas setup

8. Fueling nozzle and nitrogen adapter

9. Nickel-Teflon tape compatible with methane gas applications

6.3 General LNG Defueling Procedure

This procedure includes a nitrogen gas purge – NEVER allow a non-inert gas – including ambient air – to enter the system. Allowing air to enter the system may create an explosive fuel/air mix in the system.

1. Depressurize the system.


2. Remove the shroud grate, then remove the 3/8-inch line from the excess flow valve to the bulkhead connector as shown in Figure 11.

Figure 11. Remove the 3/8-in. tube from the excess flow valve to the bulkhead connector.

3. Remove the excess flow valve from the red handled liquid valve as shown in Figure 12. Install a 3/8-inch NPT elbow onto the fitting at the red-handled fuel shutoff valve outlet.

Figure 12. Remove the excess flow valve and install a 3/8-in. NPT elbow in its place.


4. See Figure 13. Install an L-shaped, 1/2-inch stainless steel tubing onto the elbow to create a temporary discharge vent. The tubing should be at least six feet (or two meters) tall, to safely carry vapor away.

Figure 13. Attach an L-shaped tube to the elbow to create a temporary vent tube. This tube should be at least six foot long to route the gas up and away from the

vehicle.

5. Attach a grounding cable to the tank.

6. Now, slowly open the red shutoff valves on each tank to allow fuel to flow from the tanks to the atmosphere.

7. Do not leave the vehicle unattended while defueling.

8. When fuel stops flowing, but prior to working on the system, make sure you remove all remaining combustible gas by purging the system with nitrogen.

9. Next, close the red-handled valves.

10. Connect a pressure-regulated nitrogen purge cart to the fill receptacle and pressurize the system to 10 psi as shown in Figure 14.


Figure 14. Pressurize the fuel tanks with nitrogen to 10 psi.

11. Then disconnect the cart and replace the fill cap.

12. Open the red-handled valves, let the tank pressure bleed off to zero through the defuel tube, then close the red-handled valves.

13. Remove the defuel tube.

14. Install a Macrotech female vent connector tool to the system’s vent to station connection.

15. Open all gray-handled vent valves and allow all remaining nitrogen to vent from the Macrotech connector tool. Listen for a no-flow condition to indicate the tanks are empty.

Figure 15. Connect a Macrotech vent connector to the vent to station connection port and open the vent valves to purge the tanks.


16. Close the grey-handled vent valves, disconnect the Macrotech connector and replace the vent cap.

17. Remove the ground cable.

18. Once the nitrogen purge is complete, the system is safe to work on.

19. When all work is completed, don’t forget to re-install the excess flow valve and the line from the excess flow valve to the bulkhead.

a. Always clean the threads and reapply two to three wraps of nickel-impregnated Teflon tape on the threads when reusing tapered fittings.

20. Defueled tanks become “hot” and must be conditioned as described in Section 7.

7. Conditioning the Defueled Tanks

If the system tanks have been defueled, the tanks must be conditioned before returning the vehicle to service. On initial filling of a “hot” tank, the pressure inside the tank will rise rapidly as the cold LNG entering the “hot” tank is quickly vaporized (pressure increases quickly) and the filling process will stop automatically before the tank is filled.

1. Vent the tank to the atmosphere to zero psi. This removes nitrogen from the new tank. Do not vent this gas back to the station.

2. Connect the fill station hose to the vehicle and fill the tank until the station pump stops. The pressure in the tank will typically be from 200-230 psi at this point. Disconnect the station fill hose.

3. With the tank pressure at 200 psi or above, check the setting of the overpressure regulator and, if necessary, adjust it as follows. The tank must be at 200 psi or greater to do this.

a. Disconnect from the fuel station.

b. Start and run the engine at idle.

c. Loosen the jam nut on the overpressure regulator to free the adjustment T-handle. Adjust the pressure to 148 psi as measured at the overpressure regulator gauge. Then, tighten the jam nut to lock the handle and setting.

d. Once the regulator is set, stop the engine, and connect the station vent hose to the tank vent receptacle.

4. Open the grey vent valve on each tank and watch the pressure gauge drop. When tank pressure drops to 140 psi, close the grey-handled vent valves and continue filling until the station pump stops automatically.

5. The vehicle should now be disconnected from the fill station and driven for 10 to 15 minutes to slosh the LNG inside the tank and ensure the temperature in both tanks are equalized.


6. Once this short drive is completed, return the vehicle to the station.

7. If the pressure is still above 150 psi, vent the tanks to 140 psi and restart the fueling process.

8. Verify the dashboard fuel level display indicates full.

9. This completes the tank conditioning process and the vehicle can be returned to service.

8. Attachment

LNG Safety Zones

9. References

Agility Fuel Solutions, “First Responder Guide,” ENP-084

Agility Fuel Solutions, “Pony Tank Operation Manual,” ENP-005

Agility Fuel Solutions, “Pony Pallet Operation Manual,” ENP-372

Agility Fuel Solutions, “Type 2 Pony Tank Operation Manual,” ENP-249

Agility Fuel Solutions, “LNG Fuel System Operation Manual,” ENP-064

Agility Fuel Solutions, “LNG Fuel System User Manual,” ENP-334

Agility Fuel Solutions Field Service Bulletin, “Service Facility Fuel Handling Equipment,” ENP-380

Watch the Agility Fuel Solutions LNG Video Series posted on our website.

10. Warranty Statement

Does not apply.

If you have any questions, contact Agility Fuel Solutions Customer Care: +1 949 267 7745, toll free: +1 855 500 2445 or [email protected].

Proprietary Statement

The information provided within this document is proprietary and confidential. All prior versions, including updates and revisions forwarded separately, are proprietary. The information provided by Agility Fuel Solutions to its customers and clients is solely for the use of those customers and clients. No portion of this manual may be reproduced or distributed without express written consent of Agility Fuel Solutions. Agility Fuel Solutions reserves the right to utilize the intellectual property contained within this publication as content for any other publication produced by Agility Fuel Solutions.


Trademark Notice

Agility® and TUFFSHELL® are registered trademarks of Agility Fuel Solutions. Drop-N-Go™ is a trademark of Agility Fuel Solutions. Trademarks of other manufacturers are the property of their respective companies.

Agility Fuel Solutions

3335 Susan Street Suite 100

Costa Mesa, CA 92626 USA

www.agilityfuelsolutions.com

Field Service Bulletin - Home - Agility Fuel Solutions · Personal injury or death will occur if...

Documents

Transcript of Field Service Bulletin - Home - Agility Fuel Solutions · Personal injury or death will occur if...