Effect of Viscosity on the Moisture Content of Sediment During Filtration of Coal Slurries
Abstract Generated abstract
This study examines how liquid viscosity, varied through temperature, affects the residual moisture of filter cake during filtration of grade G coal slurries. Laboratory tests were conducted after removing fine clay particles, with filtration performed either by heating the whole pulp or by heating only the added water, and the results were fitted with parabolic temperature, moisture relationships. In both cases, cake moisture decreased as temperature increased, with minimum values near the upper tested temperature range and corresponding increases in calculated filtration efficiency. The authors conclude that reducing water viscosity is important for improving coal slurry filtration, while noting that the temperature behavior observed for magnetite concentrate at one plant does not apply to coal pulps.
Full Text
EFFECT OF VISCOSITY ON THE MOISTURE CONTENT OF THE CAKE DURING FILTRATION OF COAL PULPS
V. D. Skakun, V. M. Vityugin
(Presented by the scientific seminar of the Department of General Chemical Technology)
As is known, the filtration rate depends, other conditions being equal, on the viscosity of the medium. The viscosity of a liquid decreases with increasing temperature (for water, see curve 3 in the figure), and the curve has the form of a parabola. Obviously, the moisture content of the cake will also decrease with increasing pulp temperature, and in this case the moisture-content curve should likewise have a parabolic form.
Under laboratory conditions, the effect of the temperature of the pulp and of the water on the final moisture content of the cake was tested using grade “G” coal slurry. Fine clay particles, which exert a substantial influence on the final moisture content, were first removed from the coal slurry. The coal slurry thus prepared was mixed with water in a definite volumetric proportion, and filtration was carried out at a definite temperature.
The averaged results are given in Table 1 and in Fig. 1 (curve 1). The filtration efficiency was calculated by the formula
\[ E=\left(1-\frac{\beta_k}{\beta_p}\right)\cdot 100\%, \]
where \(\beta_k\) is the residual moisture in the dewatered cake, %;
\(\beta_p\) is the feed density, %.
Mathematical processing of the laboratory data on a computer gives the following parabolic relationship between the moisture content of the cake \((W\%)\) and the pulp temperature \((t^\circ C)\):
\[ W=19.92-0.1t+0.0005t^2,\ \% \]
with confidence coefficient \(\mu=14.4\), correlation coefficient \(r=0.775\). The root-mean-square deviation in moisture is \(\sigma=\pm 2.1\%\).
The final moisture content of the cake was also determined when only the water was heated (or cooled); after reaching a definite temperature, it was mixed with the coal slurry, and filtration was then carried out.
The averaged results are given in Table 2 and in Fig. (curve 2). Mathematical processing on a computer also gives a parabolic relationship between the moisture content of the cake \((W\%)\) and the water temperature \((t^\circ C)\):
\[ W=19.67-0.14t+0.001t^2,\ \% \]
with confidence coefficients \(\mu=10.5\), correlation \(r=0.705\), and root-mean-square deviation in moisture \(\sigma=\pm 2.26\%\). The character of the curves on
Table 1
Dependence of moisture on temperature when heating the pulp
| Filtration indices | Pulp temperature, °C | Pulp temperature, °C | Pulp temperature, °C | Pulp temperature, °C | Pulp temperature, °C | Pulp temperature, °C | Pulp temperature, °C | Pulp temperature, °C |
|---|---|---|---|---|---|---|---|---|
| 2 | 4 | 12 | 40 | 60 | 83,5 | 95 | 100 | |
| Final moisture of the sediment, % | 19,49 | 19,21 | 18,93 | 16,46 | 15,12 | 15,03 | 15,17 | 15,31 |
| Filtration efficiency, % | 9,3 | 10,7 | 12 | 23,4 | 29,7 | 30,1 | 29,5 | 28,8 |
Fig. 1. Dependence of sediment moisture on temperature.
Table 2
Dependence of moisture on temperature when heating the water
| Filtration indices | Water temperature, °C | Water temperature, °C | Water temperature, °C | Water temperature, °C | Water temperature, °C | Water temperature, °C |
|---|---|---|---|---|---|---|
| 4 | 12 | 15 | 40,5 | 76 | 80 | |
| Final moisture of the sediment, % | 19,45 | 17,8 | 16,84 | 16,6 | 15,5 | 15,5 |
| Filtration efficiency, % | 9,1 | 17,2 | 21,7 | 24,9 | 27,9 | 29,5 |
The figure shows that the moisture of the sediment, like the viscosity of water, decreases as the temperature rises; therefore, special attention should be paid to reducing the viscosity of water in the filtration of coal pulps.
Similar data were also obtained on a drum vacuum filter at the FRG [1]; moreover, simultaneously with a decrease in the moisture of the filtered cake, the specific productivity increases.
In [2] it is indicated that the moisture of the sediment decreases during filtration of finely ground magnetite concentrate; in the winter period, at a pulp temperature of 1,5—2°, the moisture content in the solid sediment is 1,5—2% lower than in the summer period, when pulp with the same characteristic is filtered, but at a temperature of 25—30°. The specific productivity, air consumption, characteristics of the filter cloth, and other filtration parameters remained constant.
The studies carried out showed that the observed decreases in moisture during filtration of magnetite concentrate at po-
...at reduced temperatures at the Ingul GOK does not occur during filtration of coal pulps.
A 4.4% reduction in cake moisture is also noted in [3] when the temperature of the filtered coal pulp is raised from 4.5 to 49°C, and in [4] by 1.5–2% when the pulp temperature is raised from 14 to 21°.
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