红外吸收法准确测量低硫煤中硫元素含量

Determination of the Content of Sulfur of Coal by the Infrared Absorption Method with High Acccuracy

采用同步热分析-红外光谱联用仪测定煤样在程序升温条件下的差示扫描量热-热重曲线和红外吸收光谱,并通过红外吸收光谱定性鉴别燃烧气体产物。重点研究了高温燃烧-红外吸收法,即通过测量煤燃烧气体产物中二氧化硫的浓度,间接地测量煤中硫含量。该方法方便快速,重复性较好。研究发现,用不同的含硫化合物和不同的煤标准物质校准仪器,同一个煤样的硫含量结果偏差很大,即标准物质和煤样中硫元素化学形态的差别导致系统误差。采用时间-红外吸收强度曲线分析煤中高温硫和低温硫的组成,然后选择与被测煤样硫元素组成接近的煤标准物质校准仪器,因而,消除了标准物质和样品间硫元素化学形态差别导致的系统误差。另一个方面,传统的高温燃烧-红外吸收法使用多点校准方法,即通过测定多个质量的标准物质,绘制硫质量-仪器响应信号强度的工作曲线;采用单点校准方法,调节标准物质和煤样的质量,使得两者释放的硫元素质量相近,然后间隔测量煤标准物质和煤样,因而消除了红外吸收池的漂移的影响,提高了煤样硫含量结果重复性。以上述优化的方法测量一种低硫无烟煤和一种低硫烟煤,硫含量测量结果及标准偏差分别为0.345%(0.004%)和0.372%(0.008%)。经过评定,两种煤样的硫含量结果的不确定度(U,k=2)分别为0.019%和0.021%。两个主要创新在于用高温硫和低温硫组成相近的煤标准物质校准仪器,以及采用测量和校准交替进行的单点校准方法。改进后的测量方法,准确性明显好于ASTM D5106的规定值,具有一定的应用推广价值。

The present paper reported the differential scanning calorimetry-thermogravimetry curves and the infrared （IR） ab-sorption spectrometry under the temperature program analyzed by the combined simultaneous thermal analysis-IR spectrometer . The gas products of coal were identified by the IR spectrometry .This paper emphasized on the combustion at high temperature-IR absorption method ,a convenient and accurate method ,which measures the content of sulfur in coal indirectly through the de-termination of the content of sulfur dioxide in the mixed gas products by IR absorption .It was demonstrated ,when the instru-ment was calibrated by varied pure compounds containing sulfur and certified reference materials （CRMs） for coal ,that there was a large deviation in the measured sulfur contents .It indicates that the difference in chemical speciations of sulfur between CRMs and the analyte results in a systematic error .The time-IR absorption curve was utilized to analyze the composition of sul-fur at low temperatures and high temperatures and then the sulfur content of coal sample was determined by using a CRM for coal with a close composition of sulfur .Therefore ,the systematic error due to the difference in chemical speciations of sulfur be-tween the CRM and analyte was eliminated .On the other hand ,in this combustion at high temperature-IR absorption method , the mass of CRM and analyte were adjusted to assure the sulfur mass equal and then the CRM and the analyte were measured al-ternately .This single-point calibration method reduced the effect of the drift of the IR detector and improved the repeatability of results ,compared with the conventional multi-point calibration method using the calibration curves of signal intensity vs sulfur mass .The sulfur content results and their standard deviations of an anthracite coal and a bituminous coal with a low sulfur con-tent determined by this modified method were 0.345% （0.004% ） and 0.372% （0.008% ） ,respectively .The uncertainty （U ,k=2） of sulfur contents of two coal samples was evaluated to be 0.019% and 0.021% ,respectively .Two main modifications , namely the calibration using the coal CRM with a similar composition of low-temperature sulfur and high temperature sulfur ,and the single-point calibration alternating CRM and analyte ,endow the combustion at high temperature-IR absorption method with an accuracy obviously better than that of the ASTM method .Therefore ,this modified method has a well potential in the analysis of sulfur content .