Pressure Relief
Relief Valve – Relief Header Design
The relief header is a system of piping connecting the outlets of all the relief valves into a common pipe or header that goes to the relief scrubber and then out the vent as shown in Figure 13-11. There are some general rules of thumb useful for sizing relief piping. The goal is to make [...]
25Sep2009 | admin | Comments Off | ContinuedRelief Valve – Vent or Flare Tip
A pipe that releases gas to disperse into the atmosphere is called a vent. If the gas is burned at the tip, it is called a flare. In its simplest form, a vent or flare tip is a pipe. Sometimes the pipe diameter is reduced for the last 5 ft or so to increase exit [...]
25Sep2009 | admin | Comments Off | ContinuedRelief Valve – Vent Scrubber
A vent scrubber is a two-phase separator designed to remove the liquid from the relieving fluids before the gas is flared or vented. The liquid is returned to the process. Design of vent scrubbers is covered in two-phase separators. A vent scrubber is sized as a standard two-phase separator with a liquid droplet size in [...]
25Sep2009 | admin | Comments Off | ContinuedRelief Valve – Installation
Each relief valve should be equipped with inlet piping no smaller than the valve inlet flange size, and inlet piping should be as short as practical. Inlet piping should be designed so that the pressure drop from the source to the relief valve inlet flange will not exceed 3% of the valve set pressure. Pressure [...]
25Sep2009 | admin | Comments Off | ContinuedRelief Valve Sizing – Two-Phase Flow, Standard Sizes
Two-Phase Flow
There are no precise formulas for calculating orifice area for twophase flow. The common convention is to calculate the area required for the gas flow as if there were no liquid present and the area required for
the liquid flow as if there were no gas present. The two areas are then added to approximate [...]
Relief Valve Sizing – Flow Rate for Liquids
Conventional Valve, Balanced-Bellows Valve, or Pilot-Operated Valve
The corresponding equations for liquid flow are the following:
Note that a preliminary orifice size must be determined in order to calculate Reynolds number. If the viscosity correction is significant, it may be necessary to iterate to get a final size.
25Sep2009 | admin | Comments Off | ContinuedRelief Valve Sizing – Flow Rate for Gas
The flow rate for gas through a given orifice area or the area required for a given flow rate is obtained by:
25Sep2009 | admin | Comments Off | Continued