安全阀计算手册.doc

Relief Valve Sizing (Single Phase) Calculation 安全阀(单相泄放)计算手册 Page 1 of 12 DESCRIPTION This document briefly describes the one phase relief valve calculation spreadsheet, which will be the standard relief valve calculation tool of LGN. The calculation method used in this spreadsheet is based on calculation methods as given in API 520 part 1 (7 th ed., 2000, page 41-56). It is strongly mended to read these pages before one starts with the calculations. All calculations are done in SI units. FORMULAS GAS AND VAPOR FLOW ? Flow through the relief valve is called critical if11 2 ??????????? k ki bkP P where: P b Maximum back pressure kPa a P Upstream relieving pressure. This is the set pressure plus the allowable overpressure plus atmospheric pressure. kPa a k i Ideal gas heat capacity ratio orC p,ig/C v,ig- C p,ig Ideal gas heat capacity at constant pressure kJ/ C v,ig Ideal gas heat capacity at constant volume kJ/ Although this equation is only valid for ideal gases, it may be used to calculate critical pressure ratio. k i can be obtained from table 7 in API 520 part 1. Otherwise, the following formula can be used:R MW c MW ck igp igpi????, , where: k i Ideal gas heat capacity ratio - C p,ig Ideal gas heat capacity at constant pressure kJ/ MW Molecular weight - R Gas constant KJ/ If the ideal gas heat capacity is not known, use the actual heat capacity in the same equation. Errors are found to be only small. Relief Valve Sizing (Single Phase) Calculation 安全阀(单相泄放)计算手册 Page 2 of 12 ? Critical Flow (Gas or Vapor): The following equation can be used to size a pressure relief device in gas or vapor service that operates at critical flow conditions. MW ZTKKPKC W A cbd??????? 160 ,13 where: A Required discharge area (for standard types see table 1) mm 2 W Required mass flow through the device. kg/hr C Coefficient determined from an expression of the ratio of the specific heats (k=C p /C v) of the gas or vapor at inlet relieving conditions. This can be obtain