Vapor depressuring system

Bare pressure vessels in a process unit protected by vapor depressuring usually do not require protection by fixed water spray systems. 

In sizing depressuring valves, it should be assumed that heater burners are shut-off, reboilers are shutdown, and normal flow in the vessel has ceased. Vapor depressuring valves should be designed such that the initial, instantaneous depressuring flow rates do not exceed the capacity of the closed pressure relief system and the flare. 

At the Vapore facility located at ENEA Casacda Research Centre, testing of the Automatic Depressurization System (ADS) of AP-600 reactor coolant system is in progress. 

The Automatic Depressurization System Test is a full sized simulation of one of the two AP600 depressurization system flowpaths from the pressurizer which will duplicate or conservatively bound the operating conditions of the AP600 ADS valves, sparger, and quench tank. The ADS test is being performed at ENEA s VAPORE Test Facility in Casaccia, Italy, and will be conducted in two parts. Phase A and Phase B. 

Unit Shutdown and Depressurization This shutdown layer isolates an entire process unit, process train, or process area involved in a fire or other emergency, thus limiting the supply of fuel. This includes pumps, vessels, compressors, etc., which comprise an entire process unit up to and including plot limit boimdaries. Associated emergency depressurization systems for process vessels and equipment should be applied when it is necessary to reduce the potential of a boiling liquid expanding vapor explosion (BLBVB), or to reduce inventories of hazardous materials. 

Vapors from depressurization valves are typically routed to a pipe header and then to the flare to safely remove the vapors from the area and dispose of them without impact to the environment. A special concern when high levels of pressurized gases are released into a piping system is the possibihty of auto-refrigeration of the piping material that may cause a brittle fracture. A process engineer should verify which pipe materials and flow rates, specified for the depressurization system, are suitable for the pressures, flows, and gases under consideration. 

The second emergency system is an automatic depressurization system. In the event of an uncontrolled reaction, the reaction can be safely limited by depressurizing the reactor to the vent system. The heat of vaporization of the boiling reaction mass safely removes heat from the reactor. The emergency vent system will be sized to handle the peak venting needs of the reactor system. 

This is the release of vapors and gases from a PRV and a depressuring system to tile atmosphere. The following points must be considered before deciding on any discharge to fhe atmosphere ... 

Relieving vapors from various pressure-relief and depressuring valves in the system must be collected in individual flare headers that should be appropriately located near each process area. Subheaders must be interconnected to a main flare header which feeds to a knock- out drum and disposal system. Condensates that are carried over by vapors are separated in the knock-out drum. The vapors that exit the vessel go to the flare stack where they are burned. 

Variations in temperature, pressure, vapor composition, and possible liquid entrainment into the relieving system during the depressuring period... 

The PCA process uses supercritical fluid drying to help preserve fine microstructures in the material. Supercritical fluid drying is a technique that has been used for many years to dry biological materials and, more recently, aerogels (qv). The original solvent is replaced by exchange with a supercritical fluid, such as C02, and the system is depressurized above the critical temperature of the SCF. SCFs have no vapor—liquid interface. Thus fine microstructures are... 

The gas pressure was then reduced by a slight depressurization in the chamber until the interface just reappeared. It was established that this procedure permitted the contents to be adjusted less than 2 to 3 percent of the critical pressure. Stirring was discontinued about two minutes before sampling, to allow the system to equilibrate the vapor and liquid phases. 

The addition of the enthalpy difference Ah2 to the enthalpy of the liquid L-y at X = const. leads to point 2 which again represents a two-phase system vapor and liquid. The enthalpy of the vapor G2 is valid for P2

mass flow L is depressurized and a small mass is converted to vapor which has nearly the same enthalpy as Gj. The state of the liquid changes fromZj withxj to Z l and x, and this point I, , x is approximately the point of intersection of the straight hne G, , and the isobaric curve P2 = const. In the same way the point L 2, X2 can be found. 

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