Many of you that handle anhydrous ammonia are familiar with The Compressed Gas Association’s (CGA) 2.1, Requirements for the Storage and Handling of Anhydrous Ammonia, which is the baseline RAGAGEP for ammonia fertilizer distributor facilities. But the organization has another ammonia standard, G-2, Ammonia that is an EXCELLENT compliment to CGA 2.1. The G-2 standard is a much broader standard and is geared more towards the shipping aspect of NH3, whereas 2.1 is geared more towards a distribution/storage/end-user. They just updated G-2 and made some significant additions to the standard.
My favorite addition is the clarification of applying water to a leaking container. As I have said for years… NEVER put the water on the vessel – Put the fog pattern over the release point and let the water scrub the NH3. NH3 (just like Cl2) has a low boiling point (-28ºF) and will eventually AUTO-REFRIGERATE slowing the leak considerably; however, if we keep putting 50-70º water on the metal container we are ADDING HEAT and the auto-refrigeration may never happen or will be slowed greatly.
The standard also CONFIRMS that for use to “scrub” NH3, we need at least 1 gal (4 L) of water for every 1 lb (0.5 kg) of ammonia. But I was sad that the standard did not make it ABSOLUTELY clear that ONLY NH3 gas can be safely introduced into the water.
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9.1.2.4 Vapor leaking from an ammonia vessel can autorefrigerate the remaining liquid, which can reduce pressure and leak rate. Under these circumstances, ammonia in a container can be colder than the available water supply. At such times, water shall not be sprayed on the container walls since it can heat the ammonia and increase any If ammonia is leaking from a container, the safest practical means should be taken to stop or abate the leak. If the leak cannot be stopped, the liquid ammonia should be fed to the point of use or transferred to another suitable ammonia container and vapor ammonia captured or burned. Small quantities of ammonia from a leaking container can be absorbed by discharging into a vessel containing at least 1 gal (4 L) of water for every 1 lb (0.5 kg) of ammonia. The ammonia should be injected into the water as near the bottom of the vessel as practical. If a hose is used to inject ammonia into water, the hose shall be weighted or secured so that the end of the hose can remain near the bottom of the vessel. An approved sparging device is recommended, if available. |
Another item they addressed in this revision was the practice (CRAZY PRACTICE!) of applying “heat” to a cylinder/container to evacuate the NH3.
| Applying heat to the surface of the cylinder in an attempt to increase the flow rate of ammonia shall only be done after contacting the ammonia supplier. This is a highly hazardous practice that can result in serious personal injury and/or property damage. See 14.8.3.5 and 14.9.2.3. |
This edition also included new safety requirements when two cylinders of NH3 are manifolded together in order to meet increased flow demands. The facility should evaluate using a larger container, but if they wish to “manifold” two cylinders together, the new standard requires a DETAILED SAFETY AND TECHNICAL REVIEW using CGA P-87, Guideline for Avoiding Container Product Migration and Contamination During Use
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The practice of manifolding two or more cylinders simultaneously to increase the flow rate of liquid ammonia is potentially hazardous and should only be undertaken after a detailed safety and technical review. See CGA P-87, Guideline for Avoiding Container Product Migration and Contamination During Use [67]. Under certain … The practice of manifolding two or more cylinders simultaneously to increase the flow rate of vapor phase ammonia is potentially hazardous and should only be undertaken after a detailed safety and technical review. See CGA P-87 [67]. Under certain temperature conditions, it is possible for vapor to flow from the warmer cylinder into the cooler cylinder until it is completely filled. If the valve of the completely filled cylinder were to be closed, any rise in temperature can cause a rapid development of hydrostatic pressures in the cylinder due to expansion of the liquid ammonia. The result is a bulging and weakening of the cylinder wall with the likely sequel of rupture and potential serious personal harm and property damage. |
The standard also addresses the practice of a dual relief system where a rupture disc is used below the relief valve.
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17.4.1 Pressure relief valves 17.4.1.1 Pressure relief valves shall have direct communication with the vapor space of the container. However, if required due to special conditions, a rupture disk device may be installed between a pressure relief valve and the storage container provided:
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The standard also made it clear regarding RV maintenance and the 5-year frequency, which has come under a lot of pressure since some manufacturers have moved to a 10-year frequency. (emphasis by me)
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Each pressure relief valve shall be subjected to a periodic external visual inspection AT LEAST ONCE EACH YEAR to determine that it is suitable for continued service and is free of evidence of leakage, tampering, corrosion. foreign matter. or any damage that can impair its proper operation. No pressure relief valve is to be continued in service after the REPLACEMENT DATE MARKED ON THE DEVICE BY THE MANUFACTURER. If no date is specified, a pressure relief valve shall be replaced NO LATER THAN FIVE YEARS following the date of its manufacture or last repair, unless it has been disassembled, inspected, repaired, and tested by the manufacturer. or by a qualified repair organization in a manner such that the valve’s condition and performance after repair is certified as meeting the requirements of the original standard to which the valve was built. A qualified repair organization is one holding a valid “VR” Certificate of authorization issued by the National Board. Refer to CGA G-2.1 and to NBIC (11, 5]. |
More to come as I digest this latest revision…