Sizing Pressure Regulators & Control Valves

Transcription

1 Sizing Pressure Regulators & Control Valves

2 ( ( Sizing the Pressure Regulators Sizing of regulators is usually made on the basis of Cg valve and KG sizing coefficients. Flow rates at fully open position and various operating conditions are related by the following formulae where: = flow rate in Stm 3 /h Pu = inlet pressure in bar (abs) Pd = outlet pressure in bar (abs). A > When the Cg and KG values of the regulator are known, as well as Pu and Pd, the flow rate can be calculated as follows: A-1 in sub critical conditions: (Pu<2xPd) = KG x Pd x ( Pu - Pd ) A-2 in critical conditions: (Pu 2xPd) = x Cg x Pu x sin K 1 x ( Pu - Pu Pd = KG 2 x Pu = x Cg x Pu B > Vice versa, when the values of Pu, Pd and are known,the Cg or KG values, and hence the regulator size, may be calculated using: B-1 in sub-critical conditions: (Pu<2xPd) KG = Pd x ( Pu - Pd ) Cg = x Pu x sin ( K1x Pu - Pu Pd B-2 in critical conditions (Pu 2xPd) x KG = 2 Cg = Pu 0,526 x Pu NOTE: The sin val is understood to be DEG. CAPACITY REDUCTION TABLE: REGULATOR INTEGRAL SLAM SHUT INTEGRAL MONITOR INTEGRAL SILENCER APERFLUX 851-5% -5% -5% REFLUX 819-7% -7% -5% REFLUX 819/FO -7% -7% -5% APERVAL REVAL 182 SA -10% SA -10% SB -5% SB -7% -5% -5% -7% -5% DIXI -3% Not applicable Not applicable DIVAL 600 0% Not applicable 0% NORVAL -7% Not applicable Not applicable NORVAL 608-7% Not applicable -10%

3 The above formulae are applicable to natural gas having a relative density of 0.61 w.r.t. air and a regulator inlet temperature of 15 C. For gases having a different relative density d and temperature tu in C, the value of the flow rate, calculated as above, must be multiplied by a correction factor Fc, as follows: Fc = S x ( tu ) Correction factors FC Type of gas Air Propane Butane Nitrogen Oxygen Carbon dioxide Relative density Fc Factor Lists the correction factors Fc for anumber of gases at 15 C. CAUTION: in order to get optimal performance, to avoid premature erosion phenomena and to limit noise emissions, it is recommended to check gas speed at the outlet flange does not exceed the values of the graph below. Gas pressure at the outlet flange [m/sec] Outlet pressure [bar] The gas speed at the outlet flange may be calculated by means of the following formula: V = x 2 DN 1 - x x Pd 1 + Pd where: V = = DN = Pd = gas speed in m/sec gas flow rate in Stm3/h nominal size of regulator in mm outlet pressure in barg.

4 Cg and Kg valve coefficient Tables Aperflux Aperflux , , , , , , ,9 Reflux Reflux 819/FO

5 Dixi AP Dival 160 AP , ,5 Staflux 185 Staflux Aperval Aperval /

6 Cg and Kg valve coefficient Tables Reval / Terval / Terval/R / Dixi /

7 Dival Head ø / Head ø 2/TR 40 1/ Dival 700 See the capacity Table Norval / / Norval

8 ( Cg and Kg valve coefficient Tables Sizing the Control Valve Reflux Syncroflux - VLM Choise of the valve is usually on the basis of Cg valve and Cg flow rate coefficients.cg coefficient corresponds numerically to the value of air flow in SCF/H in critical conditions with full open valve operating with an upstream pressure of 1 psia at a temperature of 15 C.KG. coefficient corresponds numerically to the value of natural gas flow rate in Stm/h in critical conditions with full open valve operating with an upstream pressure of 2 bar abs at a temperature of 15 C. Flow rates at full open position and various working conditions, are bound by the following formule where: Pu = inlet pressure in bar (abs) Pd = outlet pressure in bar (abs) = flow rate in Stm/H KG, Cv, Cg = valve coefficent 1 > When the Cg and KG values of the control valve are known, as well as Pu and Pd, the flow rate can be calculated as follows: 1.1 > in non critical conditions: = K G (Pu - Pd) Pd = 16,8 x Cv x Pu x sin ( Pu - Pd Pu 1.2 > in critical conditions: Pu - Pd = 0,526 x Cg x Pu x sin ( (valid for Pu < 2 x Pd) Pu KG = x Pu = 16,8 x Cv x Pu = 0,526 x Cg x Pu (valid for Pu 2 x Pd) 2 ( 2 > Vice versa, when the values of Pu, Pd and are known, calculate the values of Cv, Cg or KG with: KG = Pd ( Pu - Pd ) Cv =.16,8xPuxsinx ( Pu - Pd (valid for Pu < 2 x Pd) 2.2 > in critical conditions: x K (valid for Pu 2 x Pd) G = 2 Cv = Cg = Pu 16,8 x Pu 0,526 x Pu A oversizing of 20% on calculated values is raccomanded. Cg formulae give flow rate values more correct while K G formulae give values 5% higher than real ones only in noncritical conditions. In the case of noise limitation level a speed at the outlet flange of 130 m/sec. it is also raccomanded. Above formulae are valid for natural gas with a relative specific gravity of 0,61 compared to air and temperature of 15 C at inlet. For gases with different relative specific gravity (S) and temperature t (in C) ), value of flow rate calculated as above, must be adjusted multiplying by: Fc = S x ( tu ) Reflux Syncroflux - VLM Pu ( Cg = 0,526. xpuxsinx ( Pu - Pd Pu ( Cv flow coefficient

9 Sizing the Control Valve Deltaflux GAS, VAPOR AND STEAM BIPHASE FLUIDS A. Subcritical conditions (when ΔP < 0.5F 2 P1) A. Subcritical conditions (when ΔP < 0.5F 2 P1) Volume flow rate (gas and vapor) = 290 Cv P Δ (P1+P2) G T Weight flow rate (gas and vapor) = 355 Cv GΔP (P1+P2) T Weight flow rate (saturated steam) W = 13,55 Cv ΔP (P1+P2) Weight flow rate (overheated steam) W = 13,55 Cv ΔP (P1+P2) (1+0,00126Δt) B. Critical conditions (when ΔP 0.5F2 P1) Volume flow rate (gas and vapor) 262 F Cv P1 = G T Constant liquid/gas mixture ratio (liquid containing non condensable gas or liquid containing high title vapor) W = 19,1 Cv ΔP (w1+w2) Variable liquid/vapor mixture ratio (liquid containing low title vapor, less then 0.5) W = 27,1 Cv W = 13,5 F Cv ΔP w1 B. Critical conditions (when ΔP 0.5F 2 P1) Constant liquid/gas mixture ratio (liquid containing non condensable gas or liquid containing high title vapor) P1 (w1+w2) Variable liquid/vapor mixture ratio (liquid containing low title vapor, less then 0.5) Weight flow rate (gas and vapor) W = 321 F Cv P1 G T W = 19,1 F Cv P1 w1 Weight flow rate (saturated steam) W = 11,73 F Cv P1 Weight flow rate (overheated steam) F Cv P1 W = 11,73 (1+0,00126 Δ t) w1 = Xg (Vg1-Vf) + Vf w2 = Xg (Vg2-Vf) + Vf

10 Cg and Kg valve coefficient Deltaflux LIUIDS A. Subcritical conditions (when ΔP < F 2 ΔPc) Volume flow rate f = Cv ΔP 1.17 Gf Weight flow rate W = 855 Cv GfΔP B. Critical conditions (when ΔP F 2 ΔPc) Volume flow rate f = F Cv ΔPc 1.17 Gf Weight flow rate W = 855 F Cv Gf ΔPc ΔPc = P1-Pc Pv Pc = Pv (0,96-0,28 ) Pk ΔPk = Kc (P1-Pv) Note: For values of ΔP ΔPk the valve works under cavitation conditions. Glossary Cv ΔP ΔPc ΔPk Δt F G Gf Kc Xg P1 P2 = valve flow rate coefficient: US gpm of water with P = 1 psi = valve pressure drop P1-P2: bar = maximum dimensioning differential pressure: bar = cavitation differential pressure: bar = overheating temperature delta t1 - ts: C = valve recovery factor: non dimensional = gas relative density (air=1): non dimensional = liquid relative density at operating temperature (water at 15 C=1) = valve incipient cavitation factor: non dimensional = weight percentage of gas or vapor in the mixture at upstream pressure: % = valve upstream pressure: bar abs = valve downstream pressure: bar abs Pc Pk Pv T t1 ts f W W1 W2 Vf Vg1 Vg2 = vena contracta critical pressure: bar abs = thermodynamic critical point pressure: bar abs = vapor pressure at operating temperature: bar abs = upstream gas absolute temperature (273+ C): K = overheated steam upstream temperature: C = saturated steam temperature at upstream pressure: C = volume flow rate at 15 C and bar abs: Sm3/h = volume flow rate: m3/h = weight flow rate: Kg/h = upstream mixture density: kg/m3 = downstream mixture density: kg/m3 = specific volume of liquid: m3/kg = specific volume of gas or vapor at upstream pressure: m3/kg = specific volume of gas or vapor at downstream pressure: m3/kg

11 Cv coefficient Deltaflux Deltaflux Liquid control application Dn " 2 Cv coefficient at % opening Liquid trim Deltaflux Gas control application Dn " 2 Cv coefficient at % opening Gas trim Note: To verify the dimensioning and, in detail, for the dimensioning of Deltaflux control valves bigger than 24, always refer to Pietro Fiorentini S.p.A.

12 Sizing the Slam Shut Valves Calculation of the pressure drop The following formula can be used to calculate pressure losses of the slam shut valve in fully open position: Δp = KG x Pu - (KG2 x Pu 2 ) x KG Δp = pressure loss in bar Pu = absolute inlet pressure in bar = flow rate Stm3/h KG = flow coefficient Pressure loss calculated as above is referred to natural gas with specific gravity of 0.61 (air=1) temperature of 15 C at valve inlet, for gases with different specific gravity S and temperatures t C, pressure loss can still be calculated with the above formula, replacing the value of the flow coefficent in the table with: KG1 = KG x S x ( t)

13 SBC / SCN / / / HBC Dilock /

14 Sizing the Safety Relief Valves Calculation of the pressure regulator The flow rate is calculated by the following formulae: M q = (0.9 Kc) (394.9 x C) P1 A = Z1 T1 q M q = maximum flow rate to be discharged, in Kg/h = maximum flow rate (Stm3/h) A = minimum area (cm 2 ) (see table) Kc = outflow coefficient P 1 = setting pressure plus a 10% overpressure (bar abs) T 1 = temperature in K of the fluid at the valve inlet during the discarge, reported by user or by designer. 0,9 = safety coefficient M = molecular mass of the fluid in Kg/Kmol (see table) Z1 = compressibiliti factor of the fluid under the P1 conditions to be considered approximately equal to one if the actual values is not known. Cp exponent of equation of the isentropic expansion k= Cv under the P1 and T1 conditions. Cp = specific heat at consistant pressure Cv = specific heat at consistant volume 2 C = coefficient of expansion = C = k ( ) (see table) k+1 k+1 k-1

15 PVS 782 Calculation area (cm2) Outflow coefficient K 4,71 0,56 20,03 0,56 43,01 0,56 74,66 0, ,56 0,56 9,59 0,56 Molecular mass and expansion coeff. Relative density Carbon dioxide Hydrogen Methane Natural gas* Nitrogen Oxigen Propane * Medium value Molecular mass M 28,97 44,01 2,02 16,04 18,04 28,02 32,00 44,09 Coefficient of expansion C 0,685 0,668 0,686 0,669 0,669 0,685 0,685 0,635 Capacity table versus pressure Pressure Size 2 barg 10 barg 20 barg 30 barg 40 barg Flow rate (Kg/h)

16 Pietro Fiorentini S.p.A. via E.Fermi 8/10 I Arcugnano (VI) Italy Tel Fax The data are not binding. We reserve the right to make eventual changes without prior notice. CT-s 570-E June 10