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ASME B133.9-1994 — Measurement of Exhaust Emissions from Stationary Gas Turbine Engines
🌫️ ASME B133.9-1994 is the standard in the B133 gas turbine procurement series that governs the measurement of exhaust emissions from stationary gas turbines during emissions performance testing (source testing). Source testing is required to meet federal, state, and local environmental regulations, and this Standard provides the measurement methods and procedures for that purpose. It applies to engines operating on natural gas and liquid distillate fuels; much of the Standard also applies to engines on special fuels such as alcohol, coal gas, residual oil, or process gas or liquid, though those methods may require modification or supplementation for exhaust components resulting from the special fuel.
💡 Emissions declaration and verification are prerequisites for environmental permitting and commercial operation of a gas turbine project. B133.9 provides consistent sampling, analysis, and calculation practices so comparisons between measured emissions and regulatory limits are founded on a traceable technical basis.
1. Scope and Overall Framework 📌
Section 1 states that the Standard provides guidance in the measurement of exhaust emissions for the emissions performance testing (source testing) of stationary gas turbines. Source testing is required to meet federal, state, and local environmental regulations. The Standard is not intended for use in continuous emissions monitoring (CEM), although many of the on-line measurement methods defined may be used in both applications.
The body has ten sections: Scope; Definitions; Exhaust Emissions from Gas Turbines; Responsibilities of the Manufacturer and User; Application Data; Measurement of Gaseous Exhaust Components; Smoke Measurement; Particulate Measurement; Fuel Analysis; and Calculations and Conversions. Section 6 is the largest core section, dealing method by method with the principal gaseous pollutants; Section 10 provides the calculation procedures for exhaust flow and emission rates (the USEPA F Factor method and the ICAO (SAE) method).
⚠️ CEM and source testing are different disciplines: B133.9 addresses source testing, emphasizing single-campaign accuracy and representativeness; for on-line continuous monitoring, follow CEM regulations such as EPA 40 CFR Part 60, though the analytical methods defined here may be reused.
2. Key Definitions and Basic Data 📖
Section 2 defines terms on which the outcome of a test depends:
- Accuracy: the closeness with which a measurement approaches the true value established independently.
- Calibration drift: the difference in the measurement system output readings from the known concentration of the calibration gas after a stated period of operation without unscheduled maintenance, repair, or adjustment.
- Calibration error: the difference between the gas concentration indicated by the measurement system and the known concentration of the calibration gas.
- Calibration gas: a mixture of gases of known concentration used for calibration.
- Air toxics: compounds admitted to the air that are determined to be toxic — defined in the United States by the USEPA, which has stipulated 189 such compounds; other jurisdictions have different lists.
Dry air composition is a fundamental assumption in emission calculations; the Standard adopts the composition of ISO 2533 (see Appendix C):
| Component | Volume Percent | Note |
|---|---|---|
| Nitrogen N₂ | 78.084% | Major component |
| Oxygen O₂ | 20.948% | Combustion oxidant |
| Argon Ar | 0.934% | Inert |
| Carbon dioxide CO₂ | 0.034% | Trace (reference air) |
| Total | 100.000% | Remaining trace components neglected |
3. Measurement of Gaseous Exhaust Components 🔬
Section 6 specifies the measured components, measurement system, sampling, and analytical instrumentation. The system covers sampling, sample transfer and conditioning, analytical instruments, testing, analysis, and reporting; probe positioning must ensure representativeness, and the transfer train must prevent component loss or condensation.
| Component | Typical Analytical Method | Measurement Key Points |
|---|---|---|
| Oxides of nitrogen (NOx) | Chemiluminescence | Watch NO₂ conversion efficiency and quenching |
| Carbon monoxide CO / carbon dioxide CO₂ | Non-dispersive infrared (NDIR) | Remove water vapor and cross-interference |
| Sulfur dioxide SO₂ | UV fluorescence or electrochemical | Avoid condensation absorbing SO₂ in the sample |
| Sulfuric acid mist H₂SO₄ | Condensation/filtration then titration | Keep sampling temperature above the dew point |
| Total hydrocarbons HC / NMHC / VOC | Flame ionization detection (FID) | Measure methane and other hydrocarbons separately |
| Ammonia NH₃ (after SCR) | Wet chemistry or chemiluminescence conversion | Evaluate ammonia slip; avoid line adsorption losses |
| Oxygen O₂ | Paramagnetic or electrochemical | Used for dilution correction and excess-air calculation |
| Water vapor H₂O | Condensation or humidity sensor | Used for dry/wet basis conversion |
Section 6.4 covers quality provisions: the system shall be calibrated per the Standard, calibration drift and calibration error verified, and recommended measurement accuracies given, with special requirements for high-humidity, high-temperature, or highly corrosive flue gases. These quality clauses are decisive for data admissible in environmental compliance reporting.
🚨 Sample transfer and conditioning are the “silent killers” of data quality: condensation in the line dissolves SO₂ and NH₃, adsorption lowers low-concentration readings, and temperature change introduces volumetric errors. The Standard requires heated, dew-point-safe, inert-material sample trains with periodic calibration — one neglected link and the measured values become invalid.
4. Smoke and Particulate Measurement 🌫️
Section 7 covers smoke measurement: the principal methods are visual opacity observation (current method and measurement variability), the SAE aircraft method (for aircraft-derivative engines, rating smoke number), and optical smokemeter methods; Section 7.3 lists references. Smoke measurement maps to combustion quality and black-smoke emissions, especially important for liquid-fuel machines and abnormal-combustion diagnostics.
Section 8 covers particulate measurement: recommended method, sampling train, sampling procedure, and analysis of results. Particulate sampling requires isokinetic sampling — the sampling-nozzle intake velocity must equal the stack gas velocity so the measured particulate concentration is representative. Filter media and collection devices must be dried, weighed, and handled per procedure.
5. Fuel Analysis and Emission Calculations 📐
Section 9 covers fuel analysis: recommended sampling procedures and fuel test methods. Fuel composition — especially hydrogen-to-carbon ratio, sulfur content, and impurities — directly affects theoretical air, flue-gas composition, and pollutant emission rates, so emissions testing must run in parallel with fuel sampling and analysis.
Section 10 covers calculations and conversions. On the basis of stated assumptions, symbols, and units, the engine exhaust flow rate is determined by:
- USEPA F Factor method: derives dry exhaust flow from the fuel’s heating-value F factor and measured CO₂ (or O₂) concentration — the most common method in environmental reporting.
- ICAO (SAE) method: computes exhaust flow from fuel flow and combustion stoichiometry, often used for aircraft-derivative engines.
The two methods should be cross-checked. Emission rates are reported in forms such as g/kWh, ppmvd @15% O₂, or lb/MMBtu, depending on the applicable regulation.
6. Engineering Practice Essentials 🛠️
- 📋 Test plan first: prepare a written source-test plan before the campaign — location of sampling ports and traverse points, load points, and fuel sampling schedule — and agree it with the regulator or third-party laboratory.
- 🔬 Instruments and calibration gases: use conforming analyzers, calibrate with certified reference gases, and record pre- and post-test calibrations to quantify drift and error.
- 📊 Duty recording: log load, ambient temperature and pressure, inlet/exhaust temperatures, and fuel flow to ensure the test conditions match the reported duty and support performance conversion.
- 🛠️ Special fuels: alcohol, coal gas, residual oil, and other special fuels require additional measurements (e.g., aldehydes, metals) and modified calculations reflecting actual fuel composition.
- 📄 Report archive: report measured values, corrections, calculation paths, and uncertainty per the Standard and retain them as environmental compliance records.
7. Frequently Asked Questions ❓
❓ Q: Does B133.9 apply to continuous emissions monitoring (CEM)?
A: No. B133.9 targets emissions performance testing (source testing) for regulatory compliance; however, many of the on-line measurement methods defined in the Standard may also be used in CEM applications, each following its own regulatory requirements.
A: No. B133.9 targets emissions performance testing (source testing) for regulatory compliance; however, many of the on-line measurement methods defined in the Standard may also be used in CEM applications, each following its own regulatory requirements.
❓ Q: Why must particulate sampling be isokinetic?
A: Particulate concentration depends on the sampling velocity. If the intake velocity exceeds the stack velocity, fine particles are preferentially drawn in and the result is biased high; if lower, biased low. Isokinetic sampling matches the nozzle intake velocity to the stack velocity for a representative concentration.
A: Particulate concentration depends on the sampling velocity. If the intake velocity exceeds the stack velocity, fine particles are preferentially drawn in and the result is biased high; if lower, biased low. Isokinetic sampling matches the nozzle intake velocity to the stack velocity for a representative concentration.
❓ Q: In what units are emission rates reported?
A: It depends on the applicable regulation. Common forms include mass concentration (mg/Nm³), volume concentration corrected to a reference oxygen level (e.g., ppmvd @15% O₂), or emission per unit of power or heat input (g/kWh, lb/MMBtu); the methods of Section 10 support conversion among these forms.
A: It depends on the applicable regulation. Common forms include mass concentration (mg/Nm³), volume concentration corrected to a reference oxygen level (e.g., ppmvd @15% O₂), or emission per unit of power or heat input (g/kWh, lb/MMBtu); the methods of Section 10 support conversion among these forms.
🔍 Q: What is the difference between the USEPA F Factor and ICAO (SAE) methods?
A: The F Factor method derives dry exhaust flow from fuel heating value and measured CO₂/O₂ and is the mainstream approach for environmental reporting; the ICAO (SAE) method computes flow from fuel flow and stoichiometry and is common for aircraft-derivative engines. Using both provides cross-checking and higher confidence.
A: The F Factor method derives dry exhaust flow from fuel heating value and measured CO₂/O₂ and is the mainstream approach for environmental reporting; the ICAO (SAE) method computes flow from fuel flow and stoichiometry and is common for aircraft-derivative engines. Using both provides cross-checking and higher confidence.
