On the Flocculation and Filtration of Coal Slimes
Abstract Generated abstract
This study examines how selected additives affect both settling and filtration in the dewatering of coal slurries, treating flocculation and filtration as linked stages of a single process. Using slurry from the Chertinskaya coal-preparation plant, the authors tested carboxymethyl cellulose, polyacrylamide, Separan, and calcium hydroxide in parallel settling and vacuum filtration experiments. All tested additives shortened filtration time compared with untreated slurry, with Separan giving the fastest filtration, while the lowest final moisture values were obtained with Separan and polyacrylamide at specific dosages. The results indicate that Separan, polyacrylamide, and lime can improve clarification under certain conditions, and the authors suggest further attention to polyacrylamide and lime because of their combined dewatering effect and availability.
Full Text
On Flocculation and Filtration of Coal Slurries
S. A. Babenko, V. A. Butkevich, V. G. Korpacheva,
Z. M. Grigorieva, E. B. Misalite
(Presented by the scientific seminar of the Department of General Chemical Technology)
At coal-preparation plants, filtration of slurries is widely used. To intensify this process, it is proposed to add various substances [1, 2]. A large number of different substances have been proposed for accelerating the settling of coal slurries by means of their flocculation [3, 4]. Settling of slurries and their filtration constitute a single process of coal dewatering. The use of additives in the settling cycle leads to their entry into the filtration cycle, and vice versa. In this connection it was of interest to trace how the same substances would affect the flocculation and filtration of slurry. For this purpose, using coal from the Chertinskaya CPP as an example, the flocculation and filtration of slurry were investigated as a function of additions of certain substances.
For the experiments, coal slurry was taken containing more than 62% of the \(-0.20 +0\) mm size class (Table 1). Before the experiments the slurry was soaked for a week
Table 1
Particle-size composition of the slurry
| Size classes, mm | +0.63 | −0.63 +0.40 | −0.40 +0.315 | −0.315 +0.28 | −0.28 +0.20 | −0.20 +0.14 | −0.14 +0 |
|---|---|---|---|---|---|---|---|
| Yield, % | 5.64 | 7.25 | 9.43 | 1.03 | 16.07 | 17.73 | 44.85 |
in water. The following were tested as flocculants: carboxymethyl cellulose (CMC), 0.1% concentration; polyacrylamide (PAA), 0.1% concentration; separam—0.05% concentration; \(Ca(OH)_2\)—2% concentration. The flocculation and filtration experiments were carried out in parallel. Settling of the slurries was observed in a cylinder of 250 ml capacity, into which slurry containing 50 g/l of solids was charged. After addition of the calculated amount of flocculant, the percentage of clarification was recorded after a definite interval of time. Clarification was taken as 100% when the slurry had settled and occupied a volume of 27 ml (this is the volume occupied by the slurry without flocculant after a week of standing).
For filtration, pulp with an S:L ratio of 1:1 was thoroughly mixed with the calculated amount of flocculant and placed on a laboratory funnel with a cloth filter under a vacuum of 250–300 mm Hg. The filtration time was recorded by the appearance of the first dry islands of slurry. After this, air drying was continued for 30 sec. The dewatered coal was weighed and its moisture content calculated. The water in all experiments
Table 2
Effect of additions of a number of substances on the flocculation and filtration of coal slurries
| Name of additive | Consumption, g/t | Clarification percentage after 10 min | Filtration time, sec | Slurry moisture content, % |
|---|---|---|---|---|
| — | — | — | 52 | 29 |
| Separan | 25 | 96 | 12 | 25 |
| Separan | 50 | 97 | 10 | 22 |
| Separan | 100 | 98 | 7 | 28 |
| PAA | 50 | 96 | 8 | 27 |
| PAA | 100 | 95 | 17 | 22 |
| PAA | 200 | 95 | 10 | 27 |
| CMC | 50 | no | 16 | 23 |
| CMC | 100 | no | 12 | 26 |
| CMC | 200 | no | 22 | 26 |
| Ca(OH)₂ | 1000 | 5 | 20 | 25 |
| Ca(OH)₂ | 2000 | 12 | 18 | 27 |
| Ca(OH)₂ | 5000 | 97 | 17 | 28 |
had a temperature of 18–20°C. The results of the experiments are summarized in Table 2, from which it is evident that all the flocculants tested reduce the filtration time from 52 sec (without flocculants) to 7 sec (Separan, consumption 100 g/t), 22 sec (CMC, consumption 200 g/t). The minimum slurry moisture content (22%) was obtained at a Separan consumption of 50 g/t and PAA—100 g/t. The coal slurry settles well after the addition of Separan—25 g/t, PAA—50 g/t, Ca(OH)₂—5 kg/t. Taking into account the overall dewatering effect and the availability of the flocculants, in further studies attention should be focused on PAA and lime.
LITERATURE
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V. S. Kaminskii, M. S. Sokolova. Use of surface-active substances to intensify the dewatering of flotation concentrate. Coke and Chemistry, 12, 1958.
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G. F. Voznyi, P. I. Tankovskii, N. I. Burda, A. Ya. Vladovskaya, N. I. Samylin. Industrial tests of microadditives for reducing the moisture content of flotation concentrate on vacuum filters. Coke and Chemistry, 4, 1959.
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V. Ya. Toporkov. Use of coagulants for the clarification of slurry waters. Coke and Chemistry, 16, 1956.
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T. G. Fomenko, I. S. Blagov, A. M. Kotkin. Flocculation of Slurries. Gosgortekhizdat, 1962.