Los dispositivos de alivio de presión (PRD) se utilizan amplia y eficazmente para proteger equipos de proceso, como sistemas de tuberías, recipientes a presión, columnas de destilación y otros equipos, contra presiones que exceden la clasificación de presión de diseño en más de una cantidad fija predeterminada. El objetivo de las válvulas de alivio de presión es prevenir daños al equipo, prevenir lesiones al personal y evitar riesgos potenciales al medio ambiente.
Longitud máxima de la línea de ventilación de la válvula de alivio
The equation for the maximum length of a relief vent line is:
PAG1 = 0,25 × [(AJUSTE DE PRESIÓN × 1,1) + 14,7]
PAG2 = [(AJUSTE DE PRESIÓN × 1,1) + 14,7]
L = Longitud máxima de la línea de ventilación de alivio (pies)
D = Diámetro interior de la tubería (pulgadas)
C = Descarga mínima de aire (Lbs./Min.)
The first term in the equation, \(\frac{9 \times P_1^2 \times D^5}{C^2}\), represents the pressure drop in the relief vent line due to friction. The second term in the equation, \(\frac{9 \times P_2^2 \times D^5}{16 \times C^2}\), represents the pressure drop in the relief vent line due to the expansion of the gas as it flows through the pipe.
The equation is set equal to zero because it represents the maximum length of the relief vent line for which the pressure drop will not exceed the set pressure of the relief valve. If the length of the relief vent line is greater than the maximum length, then the pressure drop in the line will exceed the set pressure of the relief valve, and the valve will not open properly.
The equation can be used to design relief vent lines for a variety of applications, such as pressure vessels, boilers, and compressors. It is important to note that the equation is only valid for single-phase gas flow. If the fluid flowing through the relief vent line is a two-phase mixture of gas and liquid, then the equation will need to be modified.
Here is an example of how to use the equation to calculate the maximum length of a relief vent line:
The first step is to calculate the back pressure at the relief valve outlet:
P_1 = 0.25 * [(150 psig + 14.7 psia) * 1.1] + 14.7 psia = 42.6 psiaThe next step is to calculate the inside diameter of the relief vent pipe:
D = 1.5 inches - 0.133 inches (wall thickness of Schedule 40 steel pipe) = 1.367 inchesFinally, we can substitute all of the known values into the equation to calculate the maximum length of the relief vent line:
L = 9 * 42.6^2 * 1.367^5 / 100^2 = 272 feetTherefore, the maximum length of the relief vent line is 272 feet.
Dimensionamiento de la válvula de alivio
Válvulas de alivio del sistema de líquido y válvulas de alivio estilo resorte:
$$ A=\frac{G P M \times \sqrt{G}}{28.14 \times K_B \times K_V \times \sqrt{\Delta P}} $$Válvulas de alivio del sistema de líquido y válvulas de alivio operadas por piloto:
$$ A=\frac{G P M \times \sqrt{G}}{36.81 \times K_V \times \sqrt{\Delta P}} $$Válvulas de alivio del sistema de vapor:
$$ A=\frac{W}{51.5 \times K \times P \times K_{S H} \times K_N \times K_B} $$Válvulas de alivio del sistema de gas y vapor (lb/h):
$$ A=\frac{W \times \sqrt{T Z}}{C \times K \times P \times K_B \times \sqrt{M}} $$Válvulas de alivio del sistema de gas y vapor (SCFM):
$$ A=\frac{S C F M \times \sqrt{T G Z}}{1.175 \times C \times K \times P \times K_B} $$Definitions:
- A: Minimum required effective relief valve discharge area (square inches)
- GPM: Required relieving capacity at flow conditions (gallons per minute)
- W: Required relieving capacity at flow conditions (pounds per hour)
- SCFM: Required relieving capacity at flow conditions (standard cubic feet per minute)
- G: Specific gravity of liquid, gas, or vapor at flow conditions (water = 1.0 for most HVAC applications; air = 1.0)
- C: Coefficient determined from the expression of the ratio of specific heats (C = 315 if value is unknown)
- K: Effective coefficient of discharge (K = 0.975)
- KB: Capacity correction factor due to back pressure (KB = 1.0 for atmospheric discharge systems)
- KV: Flow correction factor due to viscosity (KV = 0.9 to 1.0 for most HVAC applications with water)
- KN: Capacity correction factor for dry saturated steam at set pressures above 1500 psia and up to 3200 psia (KN = 1.0 for most HVAC applications)
- KSH: Capacity correction factor due to the degree of superheat (KSH = 1.0 for saturated steam)
- Z: Compressibility factor (Z = 1.0 if value is unknown)
- P: Relieving pressure (psia) (P = set pressure (psig) + overpressure (10% psig) + atmospheric pressure (14.7 psia))
- ∆P: Differential pressure (psig) (∆P = set pressure (psig) + overpressure (10% psig) − back pressure (psig))
- T: Absolute temperature (°R = °F + 460)
- M: Molecular weight of the gas or vapor
Relief Valve Sizing Notes:
- Cuando se utilizan múltiples válvulas de alivio, una válvula se debe configurar a o por debajo de la presión de trabajo máxima permitida, y las válvulas restantes se pueden configurar hasta un 5 por ciento por encima de la presión de trabajo máxima permitida.
- Al dimensionar varias válvulas de alivio, el área total requerida se calcula con una sobrepresión del 16 por ciento o 4 Psi, lo que sea mayor.
- Para vapor sobrecalentado, se pueden utilizar los valores del factor de corrección que se enumeran a continuación:
Superheat Calculator
Selected Superheat: 0 °F
Correction Factor: 0.97
Valor de sobrecalentamiento | Factor de corrección |
Sobrecalentar hasta 400 °F | 0,97 (rango 0,979–0,998) |
Sobrecalentar hasta 450 °F | 0,95 (rango 0,957–0,977) |
Sobrecalentar hasta 500 °F | 0,93 (rango 0,930–0,968) |
Sobrecalentar hasta 550 °F | 0,90 (rango 0,905–0,974) |
Sobrecalentar hasta 600 °F | 0,88 (rango 0,882–0,993) |
Sobrecalentar hasta 650 °F | 0,86 (rango 0,861–0,988) |
Sobrecalentar hasta 700 °F | 0,84 (rango 0,841–0,963) |
Sobrecalentar hasta 750 °F | 0,82 (rango 0,823–0,903) |
Sobrecalentar hasta 800 °F | 0,80 (rango 0,805–0,863) |
Sobrecalentar hasta 850 °F | 0,78 (rango 0,786–0,836) |
Sobrecalentar hasta 900 °F | 0,75 (rango 0,753–0,813) |
Sobrecalentar hasta 950 °F | 0,72 (rango 0,726–0,792) |
Sobrecalentar hasta 1000 °F | 0,70 (rango 0,704–0,774) |
Material Properties
Properties:
Molecular Weight:
Ratio of Specific Heats:
Coefficient C:
Specific Gravity:
You may use table instead of calculator
GAS O VAPOR | PESO MOLECULAR | RELACIÓN DE CALOR ESPECÍFICO | COEFICIENTE C | GRAVEDAD ESPECÍFICA |
Acetileno | 26.04 | 1.25 | 342 | 0.899 |
Aire | 28.97 | 1.40 | 356 | 1.000 |
Amoníaco (R-717) | 17.03 | 1.30 | 347 | 0.588 |
Argón | 39.94 | 1.66 | 377 | 1.379 |
Benceno | 78.11 | 1.12 | 329 | 2.696 |
N-butano | 58.12 | 1.18 | 335 | 2.006 |
isobutano | 58.12 | 1.19 | 336 | 2.006 |
Dióxido de carbono | 44.01 | 1.29 | 346 | 1.519 |
disulfuro de carbono | 76.13 | 1.21 | 338 | 2.628 |
Monóxido de carbono | 28.01 | 1.40 | 356 | 0.967 |
Cloro | 70.90 | 1.35 | 352 | 2.447 |
ciclohexano | 84.16 | 1.08 | 325 | 2.905 |
etano | 30.07 | 1.19 | 336 | 1.038 |
Alcohol etílico | 46.07 | 1.13 | 330 | 1.590 |
Cloruro de etilo | 64.52 | 1.19 | 336 | 2.227 |
Etileno | 28.03 | 1.24 | 341 | 0.968 |
Helio | 4.02 | 1.66 | 377 | 0.139 |
N-heptano | 100.20 | 1.05 | 321 | 3.459 |
hexano | 86.17 | 1.06 | 322 | 2.974 |
Ácido clorhídrico | 36.47 | 1.41 | 357 | 1.259 |
Hidrógeno | 2.02 | 1.41 | 357 | 0.070 |
Cloruro de hidrogeno | 36.47 | 1.41 | 357 | 1.259 |
Sulfuro de hidrógeno | 34.08 | 1.32 | 349 | 1.176 |
Metano | 16.04 | 1.31 | 348 | 0.554 |
Alcohol metílico | 32.04 | 1.20 | 337 | 1.106 |
Metilbutano | 72.15 | 1.08 | 325 | 2.491 |
Cloruro de metilo | 50.49 | 1.20 | 337 | 1.743 |
Gas natural | 19.00 | 1.27 | 344 | 0.656 |
Óxido nítrico | 30.00 | 1.40 | 356 | 1.036 |
Nitrógeno | 28.02 | 1.40 | 356 | 0.967 |
Óxido nitroso | 44.02 | 1.31 | 348 | 1.520 |
N-octano | 114.22 | 1.05 | 321 | 3.943 |
Oxígeno | 32.00 | 1.40 | 356 | 1.105 |
N-Pentano | 72.15 | 1.08 | 325 | 2.491 |
iso-pentano | 72.15 | 1.08 | 325 | 2.491 |
Propano | 44.09 | 1.13 | 330 | 1.522 |
R-11 | 137.37 | 1.14 | 331 | 4.742 |
R-12 | 120.92 | 1.14 | 331 | 4.174 |
R-22 | 86.48 | 1.18 | 335 | 2.985 |
R-114 | 170.93 | 1.09 | 326 | 5.900 |
R-123 | 152.93 | 1.10 | 327 | 5.279 |
R-134a | 102.03 | 1.20 | 337 | 3.522 |
Dióxido de azufre | 64.04 | 1.27 | 344 | 2.211 |
tolueno | 92.13 | 1.09 | 326 | 3.180 |