Safety Pressure Relief Valve: Diers Method for Vent Sizing

Standard

• The Design Institute for Emergency Relief Systems (DIERS) is part of the American Institute of Chemical Engineers (AIChE). The DIERS method is outlined in the publication "Emergency Relief System Design Using DIERS Technology." Vent size is determined regarding how quickly pressure needs to be relieved when the set relief pressure is reached, causing the pressure relief valve to open.

Design Recommendations

• DIERS describes the inclusion of emergency relief vents for runaway chemical reactions within process vessels. It does not give guidelines on vent header systems. According to the "Encyclopedia of Chemical Processing and Design, Volume 61", "the major method of vent sizing for gassy systems is two-phase venting to keep the pressure constant." DIERS vent design assumes maximum gas generation rate when the relief system must be activated. If the estimated valve or venting pipe calculated is a smaller size than a standard fitting, engineers must use a larger fitting than the calculated size.

Other Recommendations

• DIERS allows for the modeling of chemical reactors to determine the ideal relief vent design when the chemical reaction is not easily estimated by existing equations. DIERS allows for the use of bench scale models to estimate worst case design testing for hybrid liquid-gas system venting. It is recommended that pressure relief systems include back-up options if the vent line is blocked.