NOx-concentration measuring apparatus

A NOx-concentration measuring apparatus for quantitatively analyzing the concentration of NOx contained in a sample gas, comprising:

• a sampling probe for obtaining the sample gas;
• a drain separator for condensing moisture contained in the sample gas as a condensed water and separating the condensed water from the sample gas, said drain separator having a cooling device therein for cooling the sample gas;
• an NO2 converter for converting NO2 contained in the sample gas into NO;
• a secondary cooling device for additionally cooling the sample gas;
• and
• an NO analyzer, arranged in above stated order with respect to a sample-gas line of said NOx-concentration measuring apparatus,
• wherein said drain separator is provided with a sample-gas passage serving as a part of said sample-gas line,
• a ratio of the flow rate (cm3/min) of the sample gas passing through said drain separator to the internal surface area (cm2) of said sample-gas passage is set at 15 (cm/min) or more, and
• the sample-gas line between said sampling probe and said drain separator is heated and/or thermally insulated over the entire length thereof.

A NOx-concentration measuring apparatus for quantitatively analyzing the concentration of NOx contained in a sample gas, comprising:

• a sampling probe for obtaining the sample gas;
• a drain separator for condensing moisture contained in the sample gas as a condensed water and separating the condensed water from the sample gas, said drain separator having a cooling device for cooling the sample gas;
• an NO2 converter for converting NO2 contained in the sample gas into NO;
• a secondary cooling device for additionally cooling the sample gas;
• and
• an NO analyzer, arranged in above stated order with respect to a sample-gas line of said NOx-concentration measuring apparatus,
• wherein said drain separator is operable to cool the sample gas passing through a sample-gas passage, formed therein to serve as a part of said sample-gas line, at a high flow velocity such that a ratio of the flow rate (cm3/min) of said sample gas passing through said drain separator to the internal volume (cm3) of said drain separator is set at 10 (min−1) or more, and a ratio of the flow rate (cm3/min) of said sample gas passing through said drain separator to the internal surface area (cm2) of said sample-gas passage is set at 15 (cm/min) or more, and
• the sample-gas line between said sampling probe and said drain separator is heated and/or thermally insulated over the entire length thereof.