CALCULATING THE SPEED OF SOUND IN NATURAL …

1 CALCULATING THE SPEED OF SOUND IN NATURAL GAS. USING AGA REPORT NO. 10. Jerry Paul Smith Joel Clancy JPS Measurement Consultants, Inc Colorado Engineering Experiment Station, Inc (CEESI). 13002 Walnut Lake Rd 2365 240th Street Houston TX 77065 Garner, IA 50438. Introduction AGA Report No. 10 are an extension of the infor- The SPEED of SOUND in NATURAL gas is the velocity a mation contained in AGA Report No. 8, SOUND wave travels in the gas. There are a number of Compressibility Factors of NATURAL Gas and Other gas properties that affect the SPEED of SOUND and they Related Hydrocarbon Gases and it does contain include the composition of the gas, the pressure of the excerpts from AGA Report No.

2 8. This is especially gas and the temperature of the gas. The American true since the SPEED of SOUND is related to the Gas Association Report No. 10 SPEED of SOUND in compressibility of the gas. NATURAL Gas and Other Related Hydrocarbon Gases provides an accurate method for CALCULATING the SPEED Applicable Gas Compositions of SOUND in NATURAL gas and other related hydrocarbon The calculations described in AGA Report No. 10 are fluids. only recommended for gases with characteristics within the ranges outlined in Table 1. The average Purpose of AGA Report No. 10 expected uncertainties for gases whose composition The development of ultrasonic flow meters prompted are within the normal range column will correspond to the development of AGA Report No.

3 10. The the uncertainties shown in Figure 1. When the gas ultrasonic meter determines the SPEED of SOUND in the compositions fall within the expanded range, higher gas as it calculates the flow of gas through the meter. uncertainties can be expected, especially outside of In order for one to check the accuracy of the SPEED of Region 1. It is not recommended to use AGA Repot SOUND measured by the ultrasonic meter, it was No. 10 outside of the gas composition ranges shown in necessary to have an accurate method to calculate the Table 1. SPEED of SOUND in NATURAL gas. AGA Report No. 10. was developed to do just that. The SPEED of SOUND There is not an accepted database for water, heavy calculated by the method in AGA Report No.

4 10 hydrocarbons or hydrogen sulfide in NATURAL gas for compares very favorably to the SPEED of SOUND determining the uncertainties of the calculated gas determined by the highly accurate research that was properties. Therefore the method in this document is the basis for the report. The information in AGA only for the gas phase. With that in mind the SPEED of Report No 10 is not only useful for CALCULATING the SOUND calculated by AGA Report No. 10 is limited to SPEED of SOUND in NATURAL gas but also other gas compositions where the mole percent water is thermodynamic properties of hydrocarbon fluids for below the water vapor dew point, when the mole other applications such as the compression of NATURAL percent heavy hydrocarbons is below the hydrocarbon gas and the critical flow coefficient represented by C*.

5 Dew point and for pure hydrogen sulfide. The audience for AGA Report No. 10 is measurement The application of this method for calculation of the engineers that are involved with the operation and SPEED of SOUND outside of the ranges shown in Figure startup of ultrasonic meters, sonic nozzles and others 1 should be verified by experimental tests to insure that are involved in applying the principles of NATURAL their accuracy. It is not recommended using this gas thermodynamics to production, transmission or calculation method near the critical point. For distribution systems. pipeline quality gas that is usually not a constraint because seldom do pipeline operating conditions come The methods for CALCULATING the SPEED of SOUND in close to the critical point.

6 Table 1 Range of Gas Mixture Characteristics Consistent with AGA Report No. 10. Quantity Normal Range Expanded Range Relative Density' to to Gross Heating Value 477 to 1150 Btu/scf 0 to 1800 Btu/set Gross Heating Value to MJ/m3 0 to 66 MJ/m3. Mole Percent Methane to 0 to Mole Percent Nitrogen 0 to 0 to Mole Percent Carbon Dioxide 0 to 0 to Mole Percent Ethane 0 to 0 to Mole Percent Propane 0 to 0 to Mole Percent Total Butanes 0 to 0 to Mole Percent Total Pentanes 0 to 0 to Mole Percent Hexanes Plus 0 to 0 to Dew Point Mole Percent Helium 0 to 0 to Mole Percent Hydrogen 0 to 0 to Mole Percent Carbon Monoxide 0 to 0 to Mole Percent Argon # 0 to Mole Percent Oxygen # 0 to 21.

7 0. Mole Percent Water 0 to 0 to Dew Point Mole Percent Hydrogen Sulfide 0 to 0 to * Reference Conditions: relative Density at 60 F, psia. ** Reference Conditions: Combustion at 60 F, psia; density at 60 F, psia **Reference Conditions: Combustion at 25 C, MPa; density at 0 C, MPa # The normal range is considered to be zero for these compounds 6. Calculate the real gas constant pressure heat Calculation Method capacity at the operating conditions The method used in AGA Report No 10 to calculate 7. Calculate the ratio of heat capacities, cp/cv, at the the SPEED of SOUND is the detailed characterization of operating conditions the gas composition.

8 This limits the use of this 8. Calculate the SPEED of SOUND based on the results document to the methods provided the AGA Report of the preceding steps No. 8, Detailed Characterization Method. 9. Calculate the isentropic exponent, k The equations that are shown are extremely difficult to Formulas for Calculation of the SPEED of SOUND solve without the use of a computer. They are best As one can see from the formulas on the following solved using programs that are available from various pages these calculations are for people that are expert sources. They make the job of CALCULATING the SPEED mathematicians. These equations are duplicated of SOUND a rather simple task once you have the directly from AGA Report No.

9 10. They are accurate input data outlined in the next paragraph. extremely difficult for people without a degree in mathematics to perform and then it would take a while The reliability of the calculation results is dependent if they do the calculations without the use of a on the accuracy of the determination of the computer. It is certainly something that most people composition, the flowing temperature and the flowing would not want to attempt without access to a pressure data of the NATURAL gas under consideration. computer. There are a number of commercially The flowing pressure has a lesser degree of an effect available programs that can be purchased and used for on the accuracy of the calculations than changes of the these calculations.

10 It is relatively easy to make the same amount in either of the other two inputs. In calculations using the computer programs. The inputs other words an error of 1 psi in the flowing pressure required are a complete gas analysis at least through measurement has a much less effect on the accuracy C6+ or higher, the flowing pressure and the flowing of the SPEED of SOUND calculation than an error of 1 temperature. degree in the flowing temperature measurement. Ultrasonic Meter Operation A description of the calculations that are required for An ultrasonic meter uses transducers to create SOUND determining the SPEED of SOUND follows.