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    Noise Level Calculations: Example #1

    Uploaded by

    Susheel Wankhede
    The document describes formulas for calculating noise levels from pressure relief valves discharging gases, vapors, and steam. The key formulas calculate the sound level at 100 feet (L100) based on factors like the mass flow rate, temperature, and molecular weight. A second formula calculates the sound level (Lp) at any distance by adjusting the L100 based on the distance. An example calculation is shown for a natural gas relief valve, finding the noise level would be around 89.9 decibels at a distance of 500 feet.

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    Noise Level Calculations: Example #1

    Uploaded by

    Susheel Wankhede
    47 views2 pages
    The document describes formulas for calculating noise levels from pressure relief valves discharging gases, vapors, and steam. The key formulas calculate the sound level at 100 feet (L100) based on factors like the mass flow rate, temperature, and molecular weight. A second formula calculates the sound level (Lp) at any distance by adjusting the L100 based on the distance. An example calculation is shown for a natural gas relief valve, finding the noise level would be around 89.9 decibels at a distance of 500 feet.

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    Noise Level Calculations

    Original Title

    Noise Level Calculations

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    The document describes formulas for calculating noise levels from pressure relief valves discharging gases, vapors, and steam. The key formulas calculate the sound level at 100 feet (L100) based on factors like the mass flow rate, temperature, and molecular weight. A second formula calculates the sound level (Lp) at any distance by adjusting the L100 based on the distance. An example calculation is shown for a natural gas relief valve, finding the noise level would be around 89.9 decibels at a distance of 500 feet.

    Copyright:

    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    47 views2 pages

    Noise Level Calculations: Example #1

    Uploaded by

    Susheel Wankhede
    The document describes formulas for calculating noise levels from pressure relief valves discharging gases, vapors, and steam. The key formulas calculate the sound level at 100 feet (L100) based on factors like the mass flow rate, temperature, and molecular weight. A second formula calculates the sound level (Lp) at any distance by adjusting the L100 based on the distance. An example calculation is shown for a natural gas relief valve, finding the noise level would be around 89.9 decibels at a distance of 500 feet.

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    © All Rights Reserved
    Download as DOCX, PDF, TXT or read online from Scribd
    Download as docx, pdf, or txt
    of 2

    Noise Level Calculations

    The following formulae are used for calculating noise level


    of gases, vapors and steam as a result of the discharge of
    a pressure relief valve. The expressed formulae are
    derived from API Recommended Practice 521. Table T7-4
    on page 7-11 lists relative noise levels.
    L100 = L + 10 LOG10 (0.29354 W k T/M)
    Where:
    L100 = Sound level at 100 feet from the point of
    discharge in decibels.
    L = Noise intensity measured as the sound pressure
    level at 100 feet from the discharge.
    Reference Figure F7-7 on page 7-11.
    W = Maximum relieving capacity, pounds per hour.
    k = Ratio of specific heats of the fluid. Reference
    Table T7-7 on page 7-26.
    (For steam, k = 1.3 if unknown.)
    T = Absolute temperature of the fluid at the valve
    inlet, degrees Rankine (°F + 460).
    M= Molecular weight of the gas or vapor obtained
    from standard tables or Table T7-7 on page 7-26.
    (For steam, M = 18)
    When the noise level is required at a distance of other
    than 100 feet, the following equation shall be used:
    Lp = L100 - 20 LOG10 (r/100)
    Where:
    Lp = Sound level at a distance, r, from the point of
    discharge in decibels.
    r = Distance from the point of discharge, feet.
    Example #1
    Gas/Vapor Mass Flow (lb/hr)
    Fluid: Natural Gas
    Set Pressure: 210 psig
    Overpressure: 10%
    Back Pressure: 50 psig
    Inlet Relieving Temperature: 120F
    Molecular Weight: 19.0 (page 7-26)
    Compressibility: 1
    Selected Area: 0.503 square inches
    Noise to be calculated at: 500 feet
    Although the required capacity has been given, the noise
    level of the valve should be calculated on the total flow
    through the selected valve at the specified overpressure.
    Therefore the rated flow must first be calculated. The
    following formula is a rearrangement of the area calculation
    formula for gas and vapor in mass flow units (lb/hr).
    Reference page 5-3.
    P1 = Absolute relieving pressure
    210 + 21 + 14.7 = 245.7 psia
    Kb = 1.0
    C = 344 from Table T7-7 on page 7-26.
    K = 0.975
    W = A P1 C K Kb M / TZ
    W = (0.503)(245.7)(344)(0.975)(1)( 19)/ (580)(1)
    W = 7502 lb/hr
    T = 120F + 46F = 580R
    Pb = 50 psig
    Continuing with the noise level calculation:
    L100 = L + 10 LOG10 (0.29354 W k T/M)
    Where:
    PR = Absolute relieving pressure/absolute back
    pressure
    = P1 (Pb + 14.7) = 245.7/(50 + 14.7) = 3.8
    L = 54.5 (Figure F7-7, page 7-11.)
    k = 1.27 (Table T7-7, page 7-26.)
    W = 7502 lb/hr
    M = 19
    T = 120F + 460F = 580R
    L100=54.5+ 10 LOG10 [(0.29354)(7502)(1.27)(580)/(19)]
    L100=103.8 decibels
    At a distance of 500 feet:
    Lp = L100 - 20 LOG10 (r/100)
    Where:
    r = 500 feet
    Lp = 103.8 - 20 LOG10 (500/100)
    Lp = 89.9 decibels

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