摘要
粉煤灰是燃煤火力发电厂电力生产中煤粉燃烧的排出物。一方面，由于粉煤灰中未燃烧的碳的含量直接影响粉煤灰的性质，测量粉煤灰中未燃烧的碳的含量就成为粉煤灰综合利用中的一个重要环节；另一方面，检测粉煤灰中未燃烧碳的含量是评价火力发电厂燃煤锅炉中煤的燃烧效率的重要参考指标，对于能源节约和环境保护也有着十分重要的意义。
通常，人们采用“烧失法”(LOI)和热解重量分析法(TGA)来测量粉煤灰中未燃烧的碳的含量。烧失法本身存在较大的系统误差，无法实现准确测量，而且要求高温环境，操作工作繁琐。热解重量分析法(TGA)是比较精确的检测粉煤灰中的碳含量的方法，但是检测过程操作复杂，仪器价格昂贵，不易推广使用。一直以来，人们都在寻求一种简便廉价而且有较高精度的新型碳含量检测仪器。
光声效应是一种光与物质的相互作用过程，是物质吸收光能后转换成声能的物理过程。粉煤灰光声效应的产生源于粉煤灰材料对入射调制光能量的吸收。粉煤灰吸收了入射调制辐射能量，部分能量以热能的形式传给周围气体，引起温度场的微小变化，从而产生周期性的气体热扩散。这种周期性的气体热扩散会在光声池中产生周期性的压力振动，并且在空气柱中传播。高灵敏度的微音器可以检测到产生的光声信号。
应用光声效应来检测粉煤灰中碳的含量是一种全新的碳检测技术。我们研制出一套应用光声效应的检测仪器来测量粉煤灰中未燃烧碳的含量，同时总结出一套简便实用的测量方法。
实践证明，利用光声效应检测粉煤灰中未燃烧的碳的含量是可行的，我们设计的检测仪和测量方法有着操作简便、价格低廉、可实现自动化、具有一定的精度以及受粉煤灰中其他成分影响小的优点，相信在未来有很大的发展潜力。
本论文的主要内容如下：
1．简述了光声技术的发展、特点和应用。
2．叙述了粉煤灰中光声效应的基本原理，包括粉煤灰的物理化学性质、固体中的光声效应理论等部分。重点介绍了固体中光声效应的R—G理论模型，分析了光声信号的产生与饱和机理。
3．完成了全部电路的设计和制作，包括滤波放大电路、直流稳压电源电路和激
郑州大学硕士学位论文
摘要
励源电路。
4.采用ACL8112数据采集卡采集光声信号，然后对其进行软件处理。
5.对粉煤灰中碳含量的光声效应测量进行了实验研究，包括光声实验设备的研
制、粉煤灰样品的制备、实验结果与讨论等部分
Fly ash is the discharged byproduct of coal combustion in coal-fired power industry. On the one hand, because the content of unburned carbon in fly ash directly influences the quality of fly ash, measuring the content of unburned carbon in fly ash is very important during the comprehensive utilization. On the other hand, because unburned carbon in fly ash is a major index of coal combustion efficiency, measuring the content of unburned carbon in fly ash is increasingly important due to energy conservation and environmental concerns.
Currently, the loss-on-ignition(LOI) test and thermogravimetric analysis(TGA) are used to measure the content of unburned carbon in fly ash. LOI has much systematic error, and is not an accurate indicator of unburned carbon in fly ash. What's more, it requires high temperature, and is very overloaded with details. TGA is a very accurate instrument to measure unburned carbon in fly ash, but it is too expensive and its manipulation is too complex. Consequently, a cheap and accurate instrument to test unburned carbon in fly ash is sought by the engineering and power industry.
The photoacoustic effect is the interactivity of light and matter, and is the physical process during which the optical energy is transformed into acoustic energy. The photo-acoustic effect results from the absorption of modulated light energy. When the chopped light impinges on the fly ash in an enclosed cell, fly ash will absorbs the irradiated energy. Some of the energy absorbed by fly ash is transferred as heat energy to the surrounding
gas, where it results in a minute change of temperature field. Subsequent expansion of heated gas causes a periodic pressure oscillation at the frequency of the excitation, which travels through the gas column producing acoustic wave or signal. The acoustic signals can be detected by a sensitive microphone.
It is a new method that detecting the content of carbon in fly ash by photoacoustic effect. We designed a set of instrument to measure unburned carbon in fly ash by using photoacoustic effect, and a practical and simple measuring method. By experiment, it is proved that this technique is simple , convenient and accurate during measuring the content of unburned carbon in fly ash, can realize automation easily, and is affected little by mineral matter in fly ash. So it has great potentiality in the future.
The main topics and achievements of this thesis are as follows:
1. The advancement, characteristic and application of photoacoustic technique.
2. The fundamentals of photoacoustic effect in fly ash, including the physical and chemical property of fly ash, the theory of the photoacoustic effect with solids. The R-G model of photoacoustic effect with solids, and the theory of the generation and saturation of photoacoustic signal of fly ash are described.
3. The design and accomplishment of circuit, including filter amplifier circuit, DC regulated power supply circuit, and driving source circuit.
4. The data acquisition of photoacoustic signal by ACL8112 card, and the data processing by software.
5. The experimental research of detecting the content of unburned carbon in fly ash, including the design of photoacoustic apparatus, the preparation of fly ash sample, and the conclusion and discussion.
引文
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