Why do some devices have 3 safety valves installed, while others have only 1?
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This post was last edited by Desert Fish on 2013-1-6 at 21:47. We use the Kellogg process in the United States; the steam drum has a capacity of 100 kilograms, operates at 314 degrees, and produces 256 tons of steam. There are 3 safety valves, each with a different set pressure. Some processes also have 3 safety valves, but in those cases the pressures are higher and the flow rates are greater, yet only 1 safety valve is used. What are the standards for setting its pressure?
The number of safety valves is calculated based on the safe discharge volume, and theoretically it is independent of the operating pressure of the equipment.
This is a typical example of staged takeoff. 1. In the 100-kilogram drum you mentioned, which is used in high-pressure applications, the safety valve of the drum must be positioned in a safe location to allow for rapid release of pressure once it activates. 2. In order to allow the drum to have its pressure drop within a short period of time, if a single safety valve is chosen, it will need to be of a sufficiently large size. These two points mean that in the event of overpressure, a large amount of high-pressure steam will definitely be released after startup. Moreover, if the safety valve is too large, its return to its original position is slow, which results in the waste of a large amount of steam and causes the pressure inside the steam drum to drop rapidly. The disadvantages of this are as follows: 1. It is difficult to determine the appropriate starting pressure (if it is too low, it will lead to low pressure in the steam drum; if it is too high, there will be no protective effect). 2. Excessive loss of high-pressure steam and heat results in significant waste. 3. Excessive pressure poses certain risks when releasing large-diameter fluids. 4. The reduction in drum pressure after venting leads to unstable process operation. Given this, optimization can be achieved using a staged takeoff method like the one shown in the example, and it offers several advantages. 1. It allows for hierarchical protection: a slightly higher drum pressure can trigger the operation of safety valves with smaller diameters to release pressure. 2. After venting, once the drum pressure returns to normal, it can quickly return to its original position, thereby reducing pressure fluctuations. 3. When the differential pressure is too high, multiple safety valves activate simultaneously to facilitate efficient and substantial pressure release. The above are my own opinions. Writing is not easy; I hope it’s helpful.
What was said upstairs is very good. Installing, operating, and maintaining large-sized safety valves is more difficult compared to those of smaller size. Using multiple safety valves for the same discharge volume offers many advantages.
The book also asks: What does sealed pressure refer to? It can’t be a reset, right? For example, the drum is equipped with 3 safety valves, each with a different setting pressure; however, their sealing pressure is the same, at 11.1 MPa. The setting pressures are: 11.9----11.7-----11.5
The return pressure of a safety valve refers to the static pressure at the inlet when, after the valve has discharged, the valve disc comes into contact with the valve seat again, that is, when the opening height becomes 0. The sealing pressure of a safety valve refers to the inlet pressure during its sealing test, at which pressure the leakage rate through the sealing surface of the closing element is measured. When the set pressure is greater than 0.3 MPa, the sealing test pressure is 90% of the set pressure. When the rated pressure is greater than 5.9 MPa, the setting pressure should be selected as 1.05 times or more of the operating pressure. Therefore, the sealing pressure is only related to the operating pressure and has nothing to do with the safe launch pressure setting; hence, both are 11.1 MPa. You can check what the operating pressure of your drum is, and use the relationship mentioned above to verify the statement.