Precision and accuracy of photoacoustic measurements of unburned carbon in fly ash
Precision and accuracy of photoacoustic measurements of unburned carbon in fly ash
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DOI：
10.1016/s0016-2361(01)00033-3
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发表时间：
2001-09-01
期刊：
影响因子：
7.4
通讯作者：
Brown, RC
中科院分区：
文献类型：
--
作者：
Fan, MH;Brown, RC
本研究调查了影响飞灰中未燃烧碳光声测量精度和准确度的因素。这些信息对于开发监测燃煤锅炉性能的仪器很有用。这项研究确定的重要因素包括用于测量的飞灰采样和准备协议、进行光声测量的环境条件以及激发源的波长。由于光声技术检测的飞灰数量通常很小，因此代表性采样至关重要。大多数飞灰是极其不均匀的，研磨是在光声仪器中进行测试的材料采样的重要前体。飞灰的体积特性也影响光声信号。通过统计测试评估环境温度和湿度对精度的影响。事实证明，将光声单元的温度控制在零点摄氏度以内非常重要。激发源的波长对测量精度有两个主要影响。尽管与碳相比，飞灰中的矿物质是相对较弱的辐射吸收剂，但其浓度通常很高，以至于矿物成分会产生明显的背景信号。仔细选择激发波长可以减轻这种对精度的影响。影响精度的另一个因素是信号饱和，当使用 940 nm 红外辐射作为激发源时，信号饱和会在相对较低的碳浓度下发生；通过用光学不吸收粉末稀释飞灰样品可以避免这种影响。 (C) 2001 Elsevier Science Ltd. 保留所有权利。
This research investigates factors influencing precision and accuracy of photoacoustic measurements of unburned carbon in fly ash. This information is useful for the development of instruments to monitor the performance of coal-fired boilers. Important factors identified by this research include the protocols for sampling and preparing fly ash for measurements, the ambient conditions at which photoacoustic measurements are performed, and the wavelength of the excitation source. Since the quantity of fly ash interrogated by the photoacoustic technique is usually small, representative sampling is critically important. Most fly ash is extremely heterogeneous and grinding is an important precursor to sampling material for testing in the photoacoustic apparatus. Bulk properties of the fly ash also affected the photoacoustic signal. The effects of both ambient temperature and humidity on precision were evaluated through statistical testing. Temperature control of the photoacoustic cell to within a few tenths of a degree Centigrade proved to be important. The wavelength of the excitation source has two major effects on accuracy of measurements. Although mineral matter in fly ash is a relatively weak absorber of radiation compared to carbon, its concentration is typically so high that a pronounced background signal can arise from the mineral components. Careful selection of excitation wavelength can mitigate this effect on accuracy. Another factor influencing accuracy was signal saturation, which occurred at relatively low carbon concentrations when using 940 nm infrared radiation as an excitation source; this effect was avoided by diluting fly ash samples with optically non-absorbing powders. (C) 2001 Elsevier Science Ltd. All rights reserved.