Evaluating measurements of carbon dioxide emissions using a precision source—A natural gas burner

Figures & data

Table 1. Example of an uncertainty budget for predicted emissions measurements of CO₂

Measurement Component, xi	Value	Relative Standard Uncertainty, u(xi)/xi	Nondimensional Sensitivity Coefficient, si	Percent Contribution, %
Gas volume flow rate, (m^3/sec)	0.02983	0.0019	1.0	22.9
Gas pressure, Png (Pa)	197719	0.0016	1.0	16.3
Gas temperature, Tng (K)	290.65	0.0017	−1.0	19.0
Gas compressibility, Zng (—)	0.9958	0.0005	−1.0	1.6
Gas carbon fraction, Xc,ng (mol/mol)	1.042	0.0020	1.0	26.2
CO2 molecular weight, (g/mol)	44.0095	0.0000	1.0	0
Ideal gas constant, R (J/mol/K)	8.3144	0.0002	−1.0	0
Burner conversion efficiency, ηb (—)	1.0000	0.0015	1.0	14.0
Predicted CO2 emissions, (g/sec)	112.4	0.0040 (0.0080)	Standard (Expanded) Uncertainty

Note: The CO₂ was generated with a 2-MW fire from the natural gas burner.

Table 2. Example of an uncertainty budget for direct emissions measurements of CO₂ in the exhaust duct of the LFRL

Measurement component, xi	Value	Relative standard uncertainty, u(xi)/xi	Nondimensional sensitivity coefficient, si	Percent contribution, %
Exhaust gas mean flow velocity, Vexh (m/sec)	20.91	0.0056	1.0	9.9
Exhaust duct diameter, d (m)	1.504	0.0079	2.0	77.6
Exhaust gas mean density, ρexh (kg/m^3)	1.047	0.0034	1.0	3.6
CO2 net volume fraction—dry basis, (m^3/m^3)	0.001819	0.0053	1.0	8.9
Exhaust gas H2O volume fraction, (m^3/m^3)	0.007947	0.0031	0.05	0
Exhaust gas molecular weight, Mexh (kg/kmol)	28.7734	0.0001	−1.0	0
CO2 molecular weight, (kg/kmol)	44.0095	0.0000	1.0	0
Direct CO2 emissions, (g/sec)	107.3	0.0179 (0.0358)	Standard (Expanded) Uncertainty

Note: The CO₂ was generated using a 2-MW natural gas fire.

Figure 1. Photograph of the natural gas burner operating at a heat release of 8 MW. The 1.2-m-wide nonpremixed tube burner can deliver controlled fires from 0.1 to 8 MW.

Figure 2. Photograph of the natural gas fuel delivery system used to control and measure the mass flow rate and composition of the fuel that supplies the burner.

Figure 3. Direct emissions measurements were made in the exhaust duct that ran along the roof of the Large Fire Research Laboratory.

Figure 4. Schematic of the measurement section of the 1.5-m exhaust duct. Bulk flow was computed from a series of point velocity measurements made by traversing S probes across the duct. Gas samples flowed continuously from the sampling tee to the gas analyzers.

Figure 5. Illustration of the CO₂ mass balance as applied for the present study. The direct emissions measurements in the exhaust duct are validated by the predicted emissions measurements conducted prior to the exhaust duct.

Figure 6. The predicted emissions measurements, CO₂ output of the burner, were repeatable to within ±1.0% (shown by dashed lines).

Figure 7. Relative difference between direct and predicted emissions measurements of CO₂ for natural gas fires. Error bars represent the expanded uncertainty estimates for the direct emissions measurements, approximately ±4%. The average relative difference is shown as the dashed gray line.

Figure 8. Relative difference between direct and predicted emissions measurements of CO₂ for the case of direct emissions derived from measurements of O₂ volume fraction. Error bars represent the expanded uncertainty estimates for the direct emissions measurements, approximately ±7%. The average relative difference is shown as the gray dashed-dotted line, whereas the average from the CO₂ measurements, black dashed line, is shown for reference.

Figure 9. Data quality check of exhaust duct gas sampling measurements (direct) and fuel supply gas composition measurements (predicted). Fuel Factors computed from measurements are compared with the default value for natural gas.