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Comment on note: “measurement of solid concentration of a soluble compound in a saturated slurry”: Can. J. Chem. Eng. 65, 163‐165 (1987)

Comment on note: “measurement of solid concentration of a soluble compound in a saturated... Can. J . Chem. Eng. 65, 163-165 (1987) Dr. Sohrab Rohani Dept. of Chemical Engineering University of Saskatchewan Saskatoon, Saskatchewan, Canada S7N OW0 Reply to Rohani The technique proposed is a differential technique. Firstly, the concentration of solute in the crystal slurry is reconstructed from the temperature of the crystal slurry while secondly the concentration of the dissolved sample is estimated from its saturation temperature after dissolution. The difference in both values gives the solid concentration in the original slurry. A general disadvantage of such a differential technique is the magnification of the error in the single measurements into the final result, caused by the substraction of two large numbers. We estimated the overall accuracy from the accuracy only of the single measurements which were presented. This indeed corresponds to the error in the total KC1-concentration, which is inherent to the technique proposed. Therefore we maintain our original conclusion. If the error in the first temperature measurement is of the same order of magnitude, as Dr. Rohani suggests in his reply, the accuracy is even further reduced, which is illustrated in the following example. Example: Temperature of the crystal slurry is 40 f 1.6”C while the slurry contains 5.1 g KC1-crystals per litre. This corresponds to an increase in saturation temperature of 2°C which results in a measured temperature of 42 f 1.6”C.By substracting both numbers, a slurry concentration equivalent to 2 f 3.2”C or 5 f 7.5 g KClcrystals per litre results. This is totally unacceptable. Generally speaking, the temperature can be measured more accurately, which would increase the accuracy. However it may appear that the determination of the point at which 100% transmission occurs or the dissolution rate of the sample will then limit the accuracy. This would require further research. Editor, Can. J. Chem. Eng. Recently an instrument for measurement of solid concentrations of a soluble compound in a saturated slurry was proposed (Rohani and Paine, 1987). Solid concentration below 5 grams per litre solution are to be measured by dissolving the contained solids and monitoring the temperature at which all solids are dissolved. Experimental data were presented to illustrate the feasibility of this method. These results indicated a worst accuracy of 2°C in saturation temperature, which corresponds to an error of 1.5 % in the solute concentration of 40.6 g of KCl per 100 g water. This amounts to 6.1 grams KCl per 1000 g of water or 4.3 g KC1 per lo00 g of solution. Using the density data of Mullin (1972), this can be calculated to be 5.1 g of KC1 per litre solution. From these experimental results it appears to be unfeasible to discriminate between differences in solute concentration below 5 g per litre solution as suggested. Johan Jager Laboratory for Process Equipment Delft University of Technology Mekelweg 2 2628 CD Delft, The Netherlands Sjoerd de Wolf Laboratory of Measurement and Control Delft University of Technology Mekelweg 2 2628 CD Delft, The Netherlands http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Canadian Journal of Chemical Engineering Wiley

Comment on note: “measurement of solid concentration of a soluble compound in a saturated slurry”: Can. J. Chem. Eng. 65, 163‐165 (1987)

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References (2)

Publisher
Wiley
Copyright
Copyright © 1988 Canadian Society for Chemical Engineering
ISSN
0008-4034
eISSN
1939-019X
DOI
10.1002/cjce.5450660131
Publisher site
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Abstract

Can. J . Chem. Eng. 65, 163-165 (1987) Dr. Sohrab Rohani Dept. of Chemical Engineering University of Saskatchewan Saskatoon, Saskatchewan, Canada S7N OW0 Reply to Rohani The technique proposed is a differential technique. Firstly, the concentration of solute in the crystal slurry is reconstructed from the temperature of the crystal slurry while secondly the concentration of the dissolved sample is estimated from its saturation temperature after dissolution. The difference in both values gives the solid concentration in the original slurry. A general disadvantage of such a differential technique is the magnification of the error in the single measurements into the final result, caused by the substraction of two large numbers. We estimated the overall accuracy from the accuracy only of the single measurements which were presented. This indeed corresponds to the error in the total KC1-concentration, which is inherent to the technique proposed. Therefore we maintain our original conclusion. If the error in the first temperature measurement is of the same order of magnitude, as Dr. Rohani suggests in his reply, the accuracy is even further reduced, which is illustrated in the following example. Example: Temperature of the crystal slurry is 40 f 1.6”C while the slurry contains 5.1 g KC1-crystals per litre. This corresponds to an increase in saturation temperature of 2°C which results in a measured temperature of 42 f 1.6”C.By substracting both numbers, a slurry concentration equivalent to 2 f 3.2”C or 5 f 7.5 g KClcrystals per litre results. This is totally unacceptable. Generally speaking, the temperature can be measured more accurately, which would increase the accuracy. However it may appear that the determination of the point at which 100% transmission occurs or the dissolution rate of the sample will then limit the accuracy. This would require further research. Editor, Can. J. Chem. Eng. Recently an instrument for measurement of solid concentrations of a soluble compound in a saturated slurry was proposed (Rohani and Paine, 1987). Solid concentration below 5 grams per litre solution are to be measured by dissolving the contained solids and monitoring the temperature at which all solids are dissolved. Experimental data were presented to illustrate the feasibility of this method. These results indicated a worst accuracy of 2°C in saturation temperature, which corresponds to an error of 1.5 % in the solute concentration of 40.6 g of KCl per 100 g water. This amounts to 6.1 grams KCl per 1000 g of water or 4.3 g KC1 per lo00 g of solution. Using the density data of Mullin (1972), this can be calculated to be 5.1 g of KC1 per litre solution. From these experimental results it appears to be unfeasible to discriminate between differences in solute concentration below 5 g per litre solution as suggested. Johan Jager Laboratory for Process Equipment Delft University of Technology Mekelweg 2 2628 CD Delft, The Netherlands Sjoerd de Wolf Laboratory of Measurement and Control Delft University of Technology Mekelweg 2 2628 CD Delft, The Netherlands

Journal

The Canadian Journal of Chemical Engineering – Wiley

Published: Feb 1, 1988

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