Emergency depressurization (EDP)
Emergency depressurization, or blowdown, is an important system for safeguarding process plant in the event of an emergency. Equipment such as pressure vessels exposed to fire could undergo catastrophic failure leading to an uncontrolled loss of containment. Depressurization reduces potential failure by removing inventory from the plant thereby decreasing the internal mechanical stresses and extending the plant’s integrity at elevated temperatures. [4]
As described above a process plant is typically divided into isolatable sections by emergency shutdown valves (ESDVs). Each section may be designated as belonging to a fire zone that is depressurized by a dedicated blowdown (depressurization) valve (BDV). During ESD conditions, the depressurization of only specific isolatable sections is undertaken. However, during more widespread emergency circumstances, the whole facility may be depressurized. [4]
In a typical depressurization system, the goal is to reduce the pressure in the plant to less than 50% of the design pressure within 15 minutes, or to reduce the internal pressure to 7 barg from the design pressure in 15 minutes. [4]
In certain circumstances, flare systems may not have the capacity to handle the entire plant's depressurization load. The blowdown of certain plant may be delayed until after the peak of the depressurization flow has passed.
A depressurization system comprises an actuated valve and a restriction orifice. The BDV valve is normally held in the closed position but opens on demand or on failure of the actuator. An orifice (RO) downstream of the BDV is sized to achieve the blowdown rate described above. A locked open valve may be located downstream of the orifice. The valve, in the closed position, allows the functionality of the BDV to be tested without depressurizing that section of the plant. [5]
Safety engineering is an engineering discipline which assures that engineered systems provide acceptable levels of safety. It is strongly related to industrial engineering/systems engineering, and the subset system safety engineering. Safety engineering assures that a life-critical system behaves as needed, even when components fail.
A nuclear meltdown is a severe nuclear reactor accident that results in core damage from overheating. The term nuclear meltdown is not officially defined by the International Atomic Energy Agency or by the United States Nuclear Regulatory Commission. It has been defined to mean the accidental melting of the core of a nuclear reactor, however, and is in common usage a reference to the core's either complete or partial collapse.
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A safety-critical system or life-critical system is a system whose failure or malfunction may result in one of the following outcomes:
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A gas flare, alternatively known as a flare stack,flare boom, ground flare, or flare pit is a gas combustion device used in places such as petroleum refineries, chemical plants and natural gas processing plants, oil or gas extraction sites having oil wells, gas wells, offshore oil and gas rigs and landfills.
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