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Aquametry in granulate materials
2005 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

On-line aquametry, or water content measurement, is of importance to several branches of industry. In general, on-line measurements of water content are needed in order to improve the performance of different algorithms used for process control. The problem at hand might seem straightforward at first glance. However, currently there exists no standardized "of the shelf" solutions for on-line moisture measurements in granulate materials. The focus of this thesis is on-line measurements of moisture in iron ore concentrate. The moisture content of the concentrate is very important to the quality of the manufactured pellets. The water concentration within the concentrate might vary considerably compared to the water content at the surface. This makes it difficult to use remote sensing technologies such as IR, NIR etc. Hence, the long term objective of this project is to develop a low price sensor that can be embedded into the concentrate and make on-line measurements. The probe would most likely be an embedded system, preferably communicating with Radio Frequency Identification technology (RFID). However, this vision can only be realized, in conjunction with a robust measurement method. This thesis investigates two different methods that utilizes fundamentally different physical properties of the material to detect water: both of which might be suitable to incorporate into an RFID tag. The properties investigated are changes in heat conduction and changes in electrical capacitance of the system as the mositure content varies. The first method is frequently referred to in literature as the Dual-Probe Heat-Pulse or DPHP and is based on the principe how heat transfer in a granulate material. The second method is named Capacitance Probe method (CP) where a parallel plate capacitor is used to drive a clock circuit. The frequency in the resonant circuit is determined by the electrical properties of the concentrate, which in turn is dependent on the moisture content. In order to thoroughly evaluate the two methods they were first analyzed theoretically. The purpose of the theoretical study was to optimize the design of the experimental equipment. With the acquired information a measurement system was constructed. Some problems with the design did eventhough occur, the scale of the heat probes were to large, leading to very long response times an poor signal to noise ratio. To the capacitance probe, there were problems to spread the concentrate evenly between the capacitor plates. Two sets of measurements were performed. First, a number of experiments in the laboratory, with the water content kept at controlled levels, then to test the performance of the developed system in an industrial environment a second set of experiments were conducted at a concentrate silo at the LKAB pellet plant in Kiruna. The outcome of the experiments performed in laboratory showed that both methods could detect water in iron ore concentrate. The standard deviation of the measurements of the capacitance probe method was 0.35\% (mass percent) moisture. The Dual-Probe Heat-Pulse method showed random disturbances, but a clear correlation was detected. Unfortunately the capacitance probe method measurements at LKAB were inconclusive. The Dual-Probe Heat-Pulse method could, with measurements of the dry density of the material, show a correlation between water content and changes in heat conduction. One of the causes of the inconclusiveness at LKAB are discrepancies in packing density. When water is added to the material and the material is subjected to mechanical stress the particles tend to group together, the process is called agglomeration. This affects the density of the concentrate. In conclusion, both investigated methods are suitable when measuring moisture content in concentrate. Minor modifications of the sensor design would most likely improve the accuracy even more.

Place, publisher, year, edition, pages
Keyword [en]
Technology, aquametry, moisture measurements, heat transfer, capacitance, granulate material, iron ore concentrate, heat pulse
Keyword [sv]
URN: urn:nbn:se:ltu:diva-51637ISRN: LTU-EX--05/320--SELocal ID: 8d6fb895-5f07-4b80-80f2-77b323f8a7bdOAI: diva2:1025001
Subject / course
Student thesis, at least 30 credits
Educational program
Space Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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