| Liquidus temperature of aluminium electrolyte is an important parameter in electrolysis aluminium. But there is'nt a mature way for its direct measurement till now. A global sensor based on transient thermal Analysis is regarded as a promising measurement way, which is based on the changing curve of themocouple voltage signal acquired when the sensor is inserted into the bath to estimate liquidus temperature. But the existing device (global sensor) has some defects such as meAsurement is not accurAte enough, Automatization degree is low, etc. In this paper, by improving an existing device a liquidus temperature measurement system was built up, which is composed of a sensor, an upper computer and a measuring device in hardware And communication, data processing in software. The mainly achievements are as follows:(1) Size and structure optimization design of the global sensor. Firstly, ANSYS was used to optimize the design of the size of the sensor. After several sensors made of different materials were tested, it was found that their best sizes were diffirent because of diffirent heat capabilities of diffirent materials. Based on the simulation of the measurment process with the application of ANSYS, the best sizes of the sensors corresponding to their materiaals can been determined. With this method to optimize a sensor made of stainless steel it was found that the best diameter size was 15mm which was accordant with a literature report. So this method can be used as a general way in optimizing the size of sensor. Thermal theory was used to optimize the structure design of sensor. Influence factors in the liquidus temperature measurement were gotten, and a qualitative analysis was made on how the factors affected the measurement. A series of improvement on the structure of sensor were made on the basis of above work.(2) Development of the data sampling and processing computer system. The stress was put on the development of communication program and liquidus temperature searching program. To use the existing device with a RS232 communication interface, a communication program based on RS232 protocol was developed, but then a communicationprogram based on CAN protocol was developed for two reasons that the communication based on RS232 protocol had the shortcomings of short communication distance, low communication rate, ect; the application of CAN bus in advanced control systems for aluminum smelters was becoming popular. Because the output treatment of the global sensor deeply affects the result of liquidus temperature measurement, following algorithms were researched: differencing and filtering of the signal, seeking of the max of the curve corresponding to the liquidus temperature, etc. Finally, a program for the automatic search of liquidus temperature were developed, and its correctness to search liquidus temperature was verified by test.(3) Experimental calibrating test and operating paraters optimization of the developed system. It was found that the operation parameters affected the measurement repeatability, so the following parameters were optimized: inserting depth and speed, vibrational frequency and extent. The following conclutions were drawn: inserting the sensor with a speed faster than 1 second every time, holding the sensor still after inserting, keeping the depth more than 50mm. The liquidus temperature of the electrolyte with molecule ratio from 2.4 to 2.8 was measured in lab by this measurement system, and satisfactory results were achieved. But it was found that the liquidus temperature could't be rightly determined if the molecule ratio was below 2.4. By primary inference, this problem may be caused by the material of the sensor, therefore,futural work should focus on the improvement of sensor material. |
PDF Full Text Request