Question

In Example 4-5 the maximum flow through the nitrogen line was determined in order to size the relief device. An important concept in process safety is inherent safety. This means that the process is designed in such a fashion as to prevent hazards from resulting in an accident. Suppose that the reactor of Example 4-5 is equipped with a relief device capable of relieving nitrogen from the reactor vessel at the rate of 0.5 lbm/s. This is not enough to prevent overpressuring of the reactor in the event of a regulator failure. One inherently safer design method is to install an orifice in the nitrogen supply line to limit the flow of nitrogen. a. Calculate the orifice diameter required to reduce the flow from the nitrogen line to 0.5 lbm/s. b. What new safety or operational problems might arise as a result of installing the orifice? The example is written below

Example 4-5. The vapor space above liquid ethylene oxide (EO) in storage tanks must be purged of oxygen and then padded with 81-psig nitrogen to prevent explosion. The nitrogen in a particular facility is supplied from a 200-psig source. It is regulated to 81 psig and supplied to the storage vessel through 33 ft of new commercial steel pipe with an internal diameter of 1.049 in. In the event of a failure of the nitrogen regulator, the vessel will be exposed to the full 200-psig pressure from the nitrogen source. This will exceed the pressure rating of the storage vessel. To prevent rupture of the storage vessel, it must be equipped with a relief device to vent this nitrogen. Determine the required minimum mass flow rate of nitrogen through the relief device to prevent the pressure from rising within the tank in the event of a regulator failure.

Answer 1