Читать книгу Continuous Emission Monitoring - James A. Jahnke - Страница 111

The entire extractive system sampling system and gas analysis system must be capable of being calibrated as a unit. In the design of the system, calibration gases should be able to be injected as close as possible at the probe – a recommendation made in fact by the EPA in its Appendix F quality assurance requirements and a requirement for cylinder gas audits and linearity checks. This is necessary to check for leaks or other operational problems in the system. In calibrating source‐level‐extractive systems, the analyzer should be calibrated at the same gas flow rate, pressure, temperature, and operating procedures that are used in monitoring the stack gas. In calibrating dilution systems, the calibration gas must enter the system before the critical orifice. Flooding the coarse filter or dilution probe with calibration gas at the inlet or using a check valve that allows calibration gas injection directly behind the coarse filter are the best methods for performing this check (Reynolds 1989). If the system is not pressurized by the calibration gas, this method can be used to determine if leaks, blockage, or gas adsorption are occurring in the system.

The system should also be capable of checking the calibration directly at the analyzer. A comparison between instrument readings from a probe calibration check and an analyzer calibration check is frequently useful in system troubleshooting.

The calibration gases are usually injected automatically every 24 hours although some operators prefer to perform calibration checks manually so that the system can be watched more closely.