Multi Point Water Quenched Prove for Spatially Averaged Hot Gas Sampling in Industrial Combustors

Paper from the AFRC 2015 conference titled Multi Point Water Quenched Prove for Spatially Averaged Hot Gas Sampling in Industrial Combustors

Extracting gas samples through intrusive probes remains the most common and simple means of gas com-; position analysis. After extraction, the probe delivers the gas sample to an online or oine gas analysis; unit; these devices operate on many dierent principles but ultimately measure the composition of the gas; at the sampling unit. This procedure works well when the measured species are homogeneous in space and; when the gas temperature is low enough to freeze any chemical reactions prior to extraction. In industrial; combustors, these conditions are typically only met when the sample is taken from the exhaust stream;; where heat exchangers and other devices mix the gas and remove heat prior to sampling. When these; conditions are not met, such as when sampling from an industrial heater or gas turbine transition piece,; special design considerations are needed to ensure reliability in the measurement. In particular, the probe; must be able to quench reactions in situ to avoid subsequent oxidation and spatially average the sample.; This paper describes the design procedure for a new multi point gas sampling probe that incorporates these; considerations. A chemical kinetics analysis was performed to nd the required cooling rate to quench the; chemical reactions. With the required quenching rate known, a one-dimensional single-point probe was; designed using a heat transfer model that delivered the required cooling rate. Next, a series of these single; point probes were combined in a sample rake designed to spatially average the gas sample. The rake's; quenching rate was validated with a two-dimensional heat transfer model using ANSYS. The new multi; point probe is shown to have sucient spatial averaging and quenching rate characteristics suggesting that; it is an appropriate design for species measurement within typical industrial combustors.