Pressure Relief Valves

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PRESSURE RELIEF VALVES Chemical Engineering Lab I Question: Discuss the importance of Relief Valves in the unit operations in detail, and give the design criteria/ parameters/ models available equations in the literature. Support your work by giving a typical example from the literature. INTRODUCTION Since the inception of pressurized systems to produce and transmit energy, it has been a constant goal to find safe, dependable means of relieving pressure. The simple, inexpensive, spring loaded relief valves has been manufactured for over a hundred and fifty years, performing its job with varying degrees of reliability over that time period. In the Unites States alone, boiler explosions caused a significant loss of life reaching a peak with 400 such explosions in 1904. With the adoption of the ASME Pressure and Vessel Code in 1911, boiler explosions declined to where, after 1973 they are non-existent. Over the same period, operating pressures for most systems were increased, in the case of boiler pressures increases were from 200 to 3000 psi and above. Pressure relief valves are used to safely contain pressurized gases and liquids. Throughout the years there has been an increased demand for safety in industrial and other related operating practices. These valves are one of the many devices that have been created in conjunction with standardized design and operating practices, for the provision of this very protection. In the past, vessels that now would obviously require relief valves were heated often resulting in drastic increase in pressure within the vessel. This resulted in an extremely dangerous outcome physically for all the parties involved. Pressure valves may be classified into two main categories namely reclosing and non-reclosing. Reclosing devices are the more common of these two groups. They are designed in such a manner that they reclose securely once safe pressure levels have been restored. The second type, the non-reclosing pressure valve, does not reclose nor vent all the fluid built up, for example fusible plugs. Pressure relief valves are relatively simple pieces of equipment. The operation of these devices involves a spring-loaded disk resting on a seat. When the pressure is low the force on the disk is less than the spring force on the disk and the valve remains closed. The pressure force increases causing a drop in the force that seals the disk on the seat. Once the valve is raised a larger disk area is available for the fluid to flow through providing a lifting force which is directly correlated.
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