Study on the modification and performance verification of nitrogen element analyzer for coal
To replace helium with cheaper argon,which has a thermal conductivity coefficient close to that of nitro-gen,as the carrier gas for measuring nitrogen content in coal,modifications were made to the CHN628 elemental an-alyzer and its thermal conductivity cell sensitivity was enhanced.The modified instrument employed argon as the carri-er gas with optimized parameters,including a baseline delay time of 10 s,a minimum analysis time of 120 s,a com-parison level of 1％,an equilibrium time of 30 s,a filling pressure of 150 mmHg,and an argon flow rate of 320 mL/min.Under these conditions,the nitrogen content in coal samples was measured with a smooth analytical curve.A certified coal reference material with a nitrogen content range encompassing that of routine test samples was selected to calibrate the curve,yielding a correlation coefficient(r)of 0.998,meeting the requirement for linearity.The limit of detection and limit of quantification were determined to be 0.06％and 0.15％,respective-ly,using the blank sample method,satisfying the method's requirements.A statistical comparison was conducted be-tween the two methods of using argon or helium as the carrier gas to measure nitrogen content in coal,inclu-ding measurements of the certified coal reference material GBW 11107p.F-tests and t-tests indicated that using argon as the carrier gas to measure nitrogen content in coal met the precision and accuracy requirements of the national standard GB/T 30733-2014 for intermediate precision,short-term precision,and accuracy.Therefore,the modi-fied equipment can be used to determine nitrogen content in coal.Furthermore,the adoption of argon in this method,with its stable market supply and low price,can help reduce testing costs.
nitrogen in coalthermal conductivity cellprecisionaccuracylimit of detectioncalibration curveF-testt-test
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