The Use Of The Photoacoustic Effect Of Fly Ash Unburned Carbon Content Of The Development Of Testing Equipment

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 surroundinggas, 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.