How is the discharge volume of a safety valve determined under the following conditions
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As shown in Figure 1, nitrogen at 0.8 MPa outside the boundary area is reduced to 0.08 MPa by a self-acting valve, and a safety valve is installed. Now I want to know how to determine the discharge capacity of this safety valve under these conditions – is it based on the nitrogen supply volume to the system, or is there some formula for that? Also, should the setting pressure be 1.1 times the operating pressure, or is any adjustment necessary?
I think the discharge volume is the intake volume, or the total amount of gas used by the users downstream. The set pressure is 1.1 times the pressure after depressurization.
I have a question: for example, a normal air compressor produces 10,000 m³/h of gas, and 600 m³/h of this gas enters one of the devices. This device then reduces the pressure, and the discharge volume of the safety valve in this reduced-pressure environment should be calculated based on what? If it’s calculated based on the 600 m³/h entering the device, that is under normal operating conditions; but what if there’s a failure in the self-acting valve? Wouldn’t the flow rate increase significantly then? It also doesn’t seem appropriate to design it based on the nitrogen output, as that would result in an excessively large value
It should be considered at 600. The value of 600 is used for device 600 because it is sufficient to ensure normal and stable operation of the device under reduced pressure. As you mentioned, if the self-acting control valve fails, the flow rate in the downstream devices will increase due to the rise in pressure; however, this increase occurs only when the pressure rises. And the safety valve serves as the most timely and effective measure to prevent such pressure increases. In other words, the normal flow rate is 600; in abnormal conditions, the flow rate will be affected only up to the point where the pressure rises to 1.2 times its normal value. Therefore, the discharge capacity of the safety valve can be considered as 600×1.2=720.
Thank you. Is the coefficient of 600 multiplied by 1.2 specified by relevant standards?
Calculate the flow rate that the valve can handle when the control valve is in the fully open position, by referring to the valve’s technical data; use this value to determine the flow rate through the valve at Kvs