Thread Content
I. Overview: There are three main raw materials used in the production of industrial silicon: silica, low-rank coal, and wood chips. Among them, the moisture content of small seed coal and wood chips varies significantly compared to that of silica, which has a great impact on the subsequent drying process. The traditional drying method involves manual sampling for analysis in a laboratory, where the laboratory uses the national standard weight-loss drying method to determine the water content of the material. The laboratory approach is considered a more accurate method, as all the equipment and procedures involved in it have well-defined origins and standards. II. The impact of the moisture content of raw materials on subsequent processing: 1. For drying systems, the dryer is merely a device that generates power; the moisture content of the material after drying depends on its moisture content before drying. A dryer simply performs drying; the extent to which drying occurs depends on the dryer’s capacity, and only a qualitative assessment can be made. If a qualitative evaluation is required, laboratory testing is necessary, though such tests can generally only determine what has already happened. 2. The moisture content of the materials entering the reduction furnace should not be too high or too low; if the moisture level is too low after drying, it can lead to the formation of fly ash. An excessive amount of fly ash results in high dust concentrations in the workshop, posing a risk of occupational hazards to workers ； Excessively high dust concentrations in the workshop pose a risk of flash explosions, and they increase the technical requirements for equipment in other workshops, resulting in unnecessary costs. Additionally, over-drying of materials causes the dryers to operate at higher levels than necessary, leading to energy waste. 3. The impact of excessive moisture in the materials entering the reduction furnace is even greater; firstly, materials with high moisture content entering the reduction furnace will lower the temperature inside it. Secondly, the water in materials with a high water content is instantly converted into saturated steam under the high-temperature conditions in the furnace, thereby changing the pressure inside the furnace. It is well known that the pressure, temperature, and other parameters of polysilicon reduction furnaces have specific requirements, and they cannot be changed or fluctuate frequently. Excess pressure inside the furnace increases safety risks and reduces its lifespan. Therefore, keeping the moisture content of raw materials within a reasonable range is crucial for reducing occupational hazards, saving energy and protecting the environment, ensuring product quality, as well as safeguarding the safety of equipment operators. III. Advantages and disadvantages of the original moisture testing method The original testing method refers to the laboratory testing approach used to determine the moisture content of materials. The advantage of this method is its accuracy, as the precision of the drying method, once human factors are excluded, can be considered equivalent to that of a laboratory balance; however, it has no other advantages. The disadvantages can be divided into four aspects: 1. Poor timeliness and complex operation; according to the relevant procedures, manual sampling at multiple different locations is required, followed by placing the samples in an oven for 2 hours of drying. Weight measurement is then carried out immediately, and the weight difference is calculated. By the time this information is fed back to the drying system, the batch of materials may already have been placed in the reduction furnace. 2. Real-time performance: Laboratory analyses require a certain amount of time to produce results, which means that it is not possible to adjust the output of the dryer in real time; this is of little value for the overall production process. 3. Human error: Different operators handling the same batch of materials may introduce a certain degree of error. 4. Open-loop control is not conducive to the control and improvement of product quality; for example, closed-loop control of the moisture content of the materials and the operating capacity of the dryer can serve subsequent processing steps better. IV. Recommendations for online material moisture detection solutions 1. Online material moisture detection refers to the measurement of a material’s moisture content through online testing; this method offers real-time performance, the ability for remote data transmission, and high accuracy. It detects the moisture content of materials in real time; as the materials pass over the sensor surface, their moisture level can be measured quickly. This allows the data to be transmitted accurately to the system via PLC or DCS communication methods. Subsequently, a PID closed-loop control mechanism is employed, utilizing the system and the dryer’s output, to dry the materials to the moisture level specified by the process requirements. This process can be accomplished with just a microwave online moisture meter, which enables real-time collection and transmission of moisture data. 2. Why use an online microwave moisture meter? Online moisture meters have been in the Chinese market for 20 years; in the early days, they were primarily used in the military and pharmaceutical industries. Internationally, there are three principles for online moisture meters: near-infrared optical principle, high-frequency capacitance principle, and microwave principle. The infrared principle can only measure the moisture content on the surface of materials, and it is affected by dust and environmental factors; it is therefore mainly used in the tobacco industry. Both the high-frequency capacitance principle and the microwave principle can be used to measure the average moisture content within a certain thickness of material; they are widely applied in the coal chemical industry, calcium carbide production, and the metallurgical industry. In contrast, moisture meters based on the high-frequency capacitor principle need to come into contact with the material, which makes them unsuitable for measuring bulk materials and can reduce the lifespan of the sensor. Combined with the processing technology, the microwave moisture meter is better suited for measuring the moisture content of two types of materials on-site: wood chips and seed coal. 3. Comparison of the optimization effects of online moisture measurement. With the use of online moisture meters, the frequency of manual sampling can be reduced or even eliminated altogether. This allows laboratory staff to devote more time to other tasks, rather than spending it on traveling to the site or waiting for the drying oven to finish its work. The measurement data from the online moisture meter is transmitted promptly to the host computer system, which can automatically adjust the output of the dryer based on the set moisture level, thereby enabling real-time control and adjustment. For example, if the moisture content of that batch of materials is high, and the reading obtained using a moisture meter differs significantly from the target moisture level, the upper-level system will increase the frequency of operation of the dryer in order to bring the moisture content to the target level ； The moisture content of this batch of materials is relatively low; the exact moisture level is determined using a moisture meter, and this information is sent back to the main computer. The main computer then adjusts the output of the dryer accordingly, so that the materials do not become too dry, which could otherwise lead to issues related to environmental protection or occupational health due to flying dust. 4. Diagram showing the differences in the process flow for measuring moisture content using laboratory methods and online methods. (It’s difficult to send images; please imagine it on your own.) It is clear that using an online moisture meter not only helps optimize the manufacturing process but also enables the automatic generation of production reports, thus creating a closed-loop control system together with the dryer.