Discussion on whether an emergency shut-off valve is needed at the outlet of the liquid ammonia storage tank in the production facility area
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The liquid ammonia storage tank has a capacity of 100 m3 and is used for ammonia absorption refrigeration. It is regularly filled using road tankers, with flexible hoses being employed for the filling process; an emergency shut-off valve is installed at the location where the hose is connected. The pressure in the tank is 1.5 MPa. The outlet of the tank is connected to three ammonia coolers, and there is a main manual valve at the outlet. A shut-off valve is located before the inlet of each ammonia cooler. An emergency shut-off valve is also installed for draining the ammonia from the tank. The tank is equipped with a high liquid level alarm, but no interlock system is present. There is also no emergency shut-off valve at the outlet – should one be added there as well?
Emergency shut-off valves are now required to be installed in tank areas. But in the plant area, it is best to install them for safety reasons; emergency shut-off valves with two ports have already been installed, so it doesn’t matter to add another one.
Is it necessary to add an emergency shut-off valve for the ammonia tank vent? ?
An emergency shut-off valve has been added to the outlet of the ammonia tank in our facility, and it is to be controlled remotely.
This post was last edited by Hua Ge on 2016-10-28 at 20:52. Please draw a schematic diagram of the process flow, so that the analysis can be more targeted. Furthermore, according to the cold storage design specifications, there is no requirement for high liquid level alarms or emergency shut-off valves in liquid ammonia tanks, and it is specified that the amount of ammonia stored should not exceed 40 tons. The density of liquid ammonia is 0.617 grams per cubic centimeter, with a storage coefficient of 0.85; therefore, 100 cubic meters correspond to 52.445 tons. Your quantity exceeds the allowed limit.
It is also advisable to install an emergency shut-off valve at the outlet of the ammonia tank
Are there any mandatory standards?
It is based on the Interim Provisions on the Management of Major Hazard Sources, Order No. 40 issued by the State Administration of Work Safety, as well as Document No. 368 issued by the same authority (which requires the installation of emergency shut-off devices for key facilities among major hazard sources, such as toxic gases, highly toxic liquids, and flammable gases)； (In accordance with the requirements of Order No. 40), alarm systems for high and low liquid levels in the storage tank should be installed as required by the standards; automatic interlocks should be in place to shut off the feed valve to the tank when the liquid level is too high, and to stop the material transfer process when the liquid level is too low. Document No. 368 issued by the Chief Safety Supervisor)
I’m not sure whether your ammonia refrigeration system is a closed-loop system that uses an ammonia compressor for cooling. (Our current system does not have any emergency shut-off mechanism; the storage capacity is around 20 tons.) There is only an alarm for high liquid level, and when this alarm triggers, the supply of ammonia to the compressor is automatically cut off. We do not have a system for draining excess liquid; instead, when pressure becomes too high, a safety valve activates and sends the gas to a flare. Since the system is designed to control the amount of ammonia filled in, it should be impossible for the liquid level to rise excessively.
Refer to this document; it’s better to set it anyway. **General Administration of Work Safety and Ministry of Housing and Urban-Rural Development: Notice on Further Strengthening the Safety Design Management for Hazardous Chemicals Construction Projects, An Jian Zong Guan San [2013] No. 76. (22) Emergency shutoff devices that can be operated automatically or remotely manually should be installed on the pipelines for feeding and discharging materials from toxic material storage tanks, cryogenic storage tanks, and pressure spheres.
Has anyone told me what to do with the pump after the emergency shut-off valve is activated, and whether it will get damaged?