Fact Sheet

Direct Final Rule for Part 60, Appendix A-Test Methods:
Three New Methods for Velocity and Volumetric Flow Rate Determination in Stacks or Ducts

EPA will announce and publish in the Federal Register a Direct Final Rule for Part 60, Appendix A - Test Methods: Three New Methods for Velocity and Volumetric Flow Rate Determination in Stacks or Ducts. Today's direct final rule is made in consideration of the results of EPA field and wind tunnel studies. The primary users of the new methods will be owners and operators of utility units subject to the Acid Rain Program and certain large electric generating units and large non-electric generating units subject to the nitrogen oxides (NOx) state implementation plan (SIP) call (63 FR 57356, 1998) who must use an approved test method to periodically calibrate the flow rate monitors at these units. These three new optional test methods will allow testers to measure volumetric flow rate under a broad range of flow conditions encountered in the stacks or ducts of these units.

WHY TAKE THIS ACTION?

In 1971, EPA promulgated Method 2 "Determination of Stack Gas Velocity and Volumetric Flow Rate (Type S Pitot Tube)". At the time of its development, Method 2 was principally used with EPA Method 5 "Determination of Particulate Emissions from Stationary Sources" to help ensure appropriate sampling rates throughout a particulate sampling run.

Many EPA air quality regulations use Method 2, including Part 75. Part 75 requires affected electric utility units to install and operate continuous emission monitoring systems that provide EPA with continuous hourly measurements of sulfur dioxide, nitrogen oxides, carbon dioxide, and volumetric flow rate. Volumetric flow rate and sulfur dioxide concentration are used to calculate sulfur dioxide mass emissions at each affected source. At the end of each year, these emissions are compared to the unit's sulfur dioxide allowances to determine whether the unit held enough allowances to cover its emissions. In order to ensure the accuracy of compliance determinations, Part 75 requires owners and operators of a unit to conduct periodic performance testing of volumetric flow rate monitors by comparing flow rate data from the monitors with data reported using EPA's Method 2. Similarly, Part 96 uses Method 2 as the reference method for flow rate measurements used to calculate NOx mass emissions.

In the first three years of the Acid Rain Program, the electric utility industry raised concerns that under some flow conditions EPA's approved test method for volumetric flow rate (Method 2) could be less than optimal for measuring flow rate and thus for determining sulfur dioxide emissions and heat input. If the test method, for example, overstates flow rate, a flow rate monitor calibrated using the test method may also overstate flow rate and result in overstated sulfur dioxide emissions and heat input. To address these concerns and to provide a technical basis for potential new test methods, EPA conducted a flow study consisting of wind tunnel tests and field tests.

Method 2 does not include procedures for measuring the yaw or pitch angles of flow or wall effects in calculating stack gas velocity or volumetric flow rate. Volumetric flow rate is calculated by multiplying the average stack gas velocity by the stack cross-sectional area. Yaw and pitch characterize the extent to which gas flow is not moving straight out of a stack or duct. From the standpoint of a tester facing a vertical stack, a yaw angle is represented by flow movement to the left or right of the stack centerline. The pitch angle is represented by flow movement toward or away from the tester. The term "wall effects" refers to the drop-off of stack gas velocity near the inside wall of a stack. This velocity drop-off is caused by friction from the stack wall.

In the Acid Rain Program and in other programs requiring reporting of mass emission rates, e.g., lbs NOx /hour, a capability to measure these parameters in the calculation of volumetric flow rate could improve the reporting of pollutant emissions in some situations. The new test methods in today's rulemaking will offer new options to account for yaw and pitch components of flow and wall effects in stacks and ducts. The new test methods will also help reduce the disparity that has sometimes been reported between power plant heat rate calculated using volumetric flow rate and heat rate calculated using fuel sampling and analysis.

WHAT ARE THE MAIN COMPONENTS OF THE RULE?

Method 2F

Method 2F, "Determination of Stack Gas Velocity and Volumetric Flow Rate With Three- Dimensional Probes", is a method for measuring the yaw and pitch angle adjusted (or axial) velocity with 3-dimensional probes like the prism-shaped, five-hole probe (commonly called a DA or DAT probe) and the five-hole spherical probe.

Method 2G

Method 2G, "Determination of Stack Gas Velocity and Volumetric Flow Rate With Two-Dimensional Probes", is a variant of existing Method 2 that describes the use of yaw angle determination procedures with Type S or 3-dimensional probes to determine the yaw angle adjusted flue gas velocity in a stack or duct. Method 2G does not account for the pitch angle of flow.

Method 2H

In any stack or duct with flowing gas, the gas velocity will approach zero near the stack or duct wall. Method 2H, "Determination of Stack Gas Velocity Taking into Account Velocity Decay Near the Stack Wall", can be used in conjunction with existing Method 2 or new Methods 2F or 2G to account for the velocity drop-off near stack or duct walls when determining volumetric flow rate.

CAN I STILL USE METHOD 2 FOR PART 75 AND NOX SIP CALL REQUIREMENTS?

Yes. The three new test methods will supplement, not replace, existing Method 2.

FOR FURTHER INFORMATION

For further information about the direct final rule, call John Schakenbach at 202-564-9158 or Elliot Lieberman at (202) 564-9136.