Safety valve dimensioning

In the fine chemicals and pharmaceutical industries, reactors are often used for diverse processes. In such a case, it is difficult to define a scenario for the design of the pressure relief system. Nevertheless, this is required by law in many countries. Thus, a specific approach must be found to solve the problem. One possibility, that is applicable for tempered systems, consists of reversing the approach. Instead of dimensioning the safety valve or bursting disk, one can choose a practicable size and calculate its relief capacity for two-phase flow with commonly-used solvents. This relief capacity will impose a maximum heat release rate for the reaction at the temperature corresponding to the relief pressure. 

Most supercritical fluid equipment use CO2 non toxic, non flammable, it is particularly safe. However, CO2 build-up in closed rooms could lead to people asphyxia. It is the reason why all possible CO2 emissions (exit valves, safety valves, rupture disks,...) must be collected in a "over-dimensioned" vent line ensuring a good dispersion of the gas in the outside atmosphere. Moreover, it is highly recommended to install CO2 detectors in the equipment room but also in any connex room, for action on high power fans and operators information. Anyway, it is preferable not to operate an equipment in rooms located over other rooms, especially underground cellars, where CO2 that is heavier than air may accumulate. 

Example 7.1 Dimensioning of a safety valve and a bursting disc for the pressure relief of a liquid... 

Example 7.4 Dimensioning of a safety valve for pressure relief with two-phase flow—critical (choked) discharge. 

Example 7.5 Dimensioning of a safety valve for a pressure reUef with two-phase flow—subcritical (unchoked) discharge... 

Unfortunately, the transmission pressme on a munber of temperature control imits on the market today is insufficient. A safety valve is frequently built into such units, which opens a parallel circuit within the unit, once a limiting pressure has been exceeded. Unfortunately this is not always noticeable to the user. Only a fraction of the flow delivery then flows through the mould, and the temperature control suffers accordingly. Naturally, the flow resistances of the temperature eontrol circuits should be kept as low as possible. To this end, there should be sufficiently thiek hoses, as short as possible, between the temperature control unit and the mould. The temperature eontrol channels in the mould must be of suitable dimensions. 

Scope, 52 Basis, 52 Compressible Flow Vapors and Gases, 54 Factors of Safety for Design Basis, 56 Pipe, Fittings, and Valves, 56 Pipe, 56 Usual Industry Pipe Sizes and Classes Practice, 59 Total Line Pressure Drop, 64 Background Information, 64 Reynolds Number, R,. (Sometimes used Nr ), 67 Friction Factor, f, 68 Pipe—Relative Roughness, 68 Pressure Drop in Fittings, Valves, Connections Incompressible Fluid, 71 Common Denominator for Use of K Factors in a System of Varying Sizes of Internal Dimensions, 72 Validity of K Values,... 

Codes and standards relevant to safety relief valves (SRVs) can vary quite considerably in format around the world, and many are sections within codes relevant to boilers or pressure-containing vessels. Some will only oudine performance requirements, tolerances and essential constructional detail, but give no guidance on dimensions, orifice sizes and so forth. Others will be related to installation and application. It is quite common within many markets to use several codes in conjunction with one another and it is not uncommon that specifications call for sections taken from several codes, which makes compliance by manufacturers complex and uneconomical. An overview of most common worldwide codes and standards is given in Appendix M. 

Final visual Inspection overall dimensions, pad plates and vent holes, lifting lugs, safety vents/valves, provision for mpture disc, drain points, sample points, thickness of flanges and holes, gussets for nozzles, ovality check... 

V-1 American National, Canadian, and Compressed Gas Association Standard for Compressed Gas Cylinder Valve Outlet and Inlet Connections, Detailed dimensioned drawings of 65 valve outlet connections for almost 200 different products. The standard covers threaded connections, yoke outlets, and the Pin Index Safety System for flush outlet valves of the yoke type used for medical gases. (92 pages)... 

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