Safety valve of liquid ammonia storage tanks and flow rate issues in ammonia pipelines
Thread Content
The safety valve inlet of the liquid ammonia storage tank is DN65, while the outlet is DN80; the diameter then changes to 65 after the outlet. In the calculations related to discharge volume provided in the tank’s design documents, the diameter of the safety valve that results from these calculations is smaller than DN65. Could this be a problem? Should it still be changed to DN50 at the inlet, and should the safety valve also be replaced with one that has a DN50 inlet and a DN65 outlet? I read in the process manual that the flow velocity in ammonia pipelines at 0.7 MPa should be below 20.2 m/s; if it reaches 40 m/s, will corrosion just increase?
Generally, a necking should not be added to the outlet of a safety valve, as this would reduce the flow rate. The inlet diameter can be made larger for safety reasons, but the discharge volume is controlled by the degree of opening
This post was last edited by seefar on 2012-12-27 13:42. It doesn’t work. GB150-2011’s B10.1. The discharge diameter shall be no smaller than the outlet diameter of the discharge device.
Section 13.0.1 of HG/T20570.2-95 also stipulates that the diameter of the pipe at the outlet of the safety valve shall be no smaller than the outlet diameter of the safety valve; the size of the safety valve should be determined based on the discharge volume. High flow rates increase resistance; moreover, they must not exceed the safe flow rate to prevent the generation of static electricity.
The high ammonia gas flow rate isn’t due to the generation of static electricity, right? It doesn’t seem like it; perhaps the high flow rate results in greater friction, which increases the risk of safety accidents.
1. The diameter of the safety valve outlet pipe must not be smaller than that of the valve’s outlet end. In addition to discharge requirements, the reason for increasing the diameter of the safety valve outlet pipe is to reduce the reactive force on the pipe. The selection of a safety valve size involves first calculating the required discharge area, and then choosing from the manufacturer’s products a safety valve whose size is the next highest above that required discharge area. Then calculate the actual discharge volume based on the selected safety valve. Therefore, the piping setup for the safety valve is determined based on the size of the safety valve selected. 2. An excessive ammonia flow rate not only increases the corrosion rate but also leads to higher pressure; when selecting the pipe diameter, it is necessary to consider whether it can meet the system’s requirements. For general Class A and B media, a recommended safe critical flow velocity exists for pipeline transportation, and this velocity must not be exceeded in the design.