What type of safety device must be installed on a pressure vessel in an NH3 system and where should it be placed?

In ammonia (NH3) systems, it is crucial to have a safety valve installed on a pressure vessel to protect against overpressure conditions. The safety valve serves to release pressure if it exceeds a predetermined limit, preventing potential hazards such as vessel rupture or explosion.

The correct placement of the safety valve is above the liquid level. This is important because a safety valve must accurately sense the pressure of the vapor space in the vessel to function correctly. If the safety valve were placed below the liquid level, it could become submerged in liquid ammonia during normal operation. In such a scenario, the pressure relief function would be compromised, as the valve may not be able to respond to the vapor pressure effectively or could become inoperable due to liquid trapping.

By positioning the safety valve above the liquid level, it remains in contact with the vapor space, thereby ensuring that it accurately measures the pressure and can operate as intended to protect the system from excessive pressure buildup.