How is the discharge volume of the safety valve calculated in the case of a fire in the shell side of a steam heater?

When designing the safety valve for a steam heater, it is indeed necessary to take into account various operating conditions, including normal conditions, abnormal conditions, as well as potential emergency situations such as fires. This is because a fire can cause the medium in the heater to heat up rapidly and the pressure to increase, thereby leading to overpressure in the equipment. In this case, the function of the safety valve is to release pressure in order to protect the equipment from exploding or being damaged due to pressure exceeding the design limits. Regarding whether a safety valve on the shell side of a steam heater needs to account for fire conditions, it is generally necessary to follow relevant design codes and safety standards, such as those set by ASME (American Society of Mechanical Engineers) or API (American Petroleum Institute). These specifications may specify in detail under what circumstances fire conditions need to be considered. If it is necessary to calculate the discharge volume under fire conditions as required by specifications or based on engineering judgment, the following factors must be taken into account during the calculation: 1. State of the fluid in the shell side: Typically, the fluid in the shell side is assumed to be in a gaseous state under fire conditions. Because in a fire situation, even a medium that was originally in liquid form can be completely or partially vaporized due to heat. However, for media that cannot be completely vaporized, the expansion of the liquid phase may also need to be considered in the calculations. 2. Leakage rate calculation: The calculation of the safety valve’s leakage rate is based on various potential failure modes. Regarding fire scenarios, the worst-case situation is usually considered, that is, it is assumed that all the fluid in the shell side vaporizes, and appropriate formulas are used to estimate the pressure rise caused by the fire. The calculation of the discharge volume requires determining the maximum pressures and temperatures that could occur in a fire scenario, and using these values to calculate the corresponding vapor flow rate. 3. Safety valve positioning: The safety valve should be installed in an appropriate location within the shell side, to ensure that it can open quickly when the pressure exceeds the design value, thereby allowing for effective pressure release in case of a fire. In general, to ensure safety, designers need to take into account various factors such as the design parameters of the heat exchanger, the working medium, the operating environment, and relevant design standards, in order to determine whether it is necessary to install a safety valve on the shell side and to calculate the discharge volume in the event of a fire. When necessary, it is recommended to consult experienced engineers or safety experts to ensure compliance with best practices and safety standards. .