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2 2008

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Wpływ zawartości flokulantu Magnaflog 336 na przebieg filtracji ciśnieniowej kopalnianej zawiesiny zrzutowej po wirówkach BIRD'a

Palica M., Kocy G., Kurowski Ł., Pławecka A.

Rocznik Ochrona Środowiska

2008

Tom 10

301-318

Recovery of solid phase containing about 82% of coal in dry matter from mine dump suspension after the BIRD centrifuge and filtrate recirculation is important from the environmental point of view. Such phase separation is very difficult in the existing system due to the increase of concentration of the smallest solid phase fractions in liquid during a course of the process finally resulting in periodical exchange of circulating liquid. Among possible methods facilitating the separation, pressure filtration of settled in a clarifier sludge formed during sedimentation of dump suspension containing appropriate amount of Magnaflog 336 flocculant seems to be the promising one. In presented research, the usefulness of PT-912 filter cloth in the separation process (pressure and centrifugal filtration) was proved. The main goal of the investigations was the determination of optimal dosage of Magnaflog 336 flocculant in dump suspension and comparison of this value with the ones currently used in industrial practice. Tests were also performed to confirm that the separation process proceeded in agreement with the compressible cake formation model, and PT-912 filter cloth behaved according to the filtration theory. Filtration parameters measured or calculated on the base of experiments allowed one to compare experimental results with the Sorensen model (i.e. the of model of sediment filtration accompanied by filter cake compression). A full compatibility between the model and experimental results for dump suspension with and without addition of Magnaflog 336 flocculant was proved. It was stated that the dry flocculant dosage used in industrial practice equal to 3.2 g/m3 susp. (this value corresponded to 12.8 mg/4 dm3 susp. in the laboratory mixer) was overestimated with respect to the data in Fig.1. Flocculation occurred for the 40% smaller dosage than abovementioned, i.e. equal to about 1.9 g/m3 susp. The analysis of constants K' in Fig.1 proved that the addition of flocculant was necessary. Namely, flocculant dosage equal to 1.9 g/m3 susp. increased the decisive rate constant K' 2.2-3.3- folded. Flocculant addition did not change significantly moisture content in sediment after pressure filtration. For the pressure equal to about 0.2 MPa one can expect a value of the cake moisture content in the range 40.0-41.0%, while for the pressure about 1.6 MPa - 36.5-37.0%. Regardless the amount of flocculant (in the range 0.5-1.5 g/m3 susp., i.e. 2-6 g/m3 susp.) one obtained (except for one experimental result) similar values of the sediment compressibility coefficient according to Spery (s = 0.222-0.239) or Tiller and Leu (s = 0.45-0.55). In the tests performed the limiting porosity was ?0 = 0.57-0.64, while the porosity coefficient of susceptibility to pressure was in the range ß = 0.041-0.084. It was proved that the resistance of the filter medium Rk increased with the increase of flocculant amount, what was in agreement with the filtration theory. Presented in this work experimental results were compared with the earlier ones dealing with dewatering of sediment after the BIRD centrifuge. The good agreement was achieved for suspension without flocculant and with the addition of Magnaflog 336 flocculant of concentration 1 g/m3 susp. Therefore it was proved that separation of dump suspension using pressure filtration is technically possible. Post-filtration cake (after drying up) can be used for energetic purposes, filtrate (characterized by very good clarity) can be turned back to circulation, while the flocculant dosage may be decreased from about 3.2 to 2 g/m3 susp.

Periodyczna filtracja wirowa zawiesiny zrzutowej po wirówkach BIRD'a, zawierającej dodatek flokulantu Magnaflog

Palica M., Pęczek K., Kurowski Ł., Niemirowski J.

Rocznik Ochrona Środowiska

2008

Tom 10

275-288

A course of centrifugal filtration of dump suspension with and without Magnaflog 336 flocculant of concentration 1 g/m3 susp. was compared in the paper. In both cases the filter cloth PT 912 selected in batch filtration tests was used. Similarly, a flocculant dosage was chosen in additional tests in which an influence of the flocculant amount on pressure filtration was checked. It was proved that practically justifiable dosage should be slightly smaller than abovementioned (1.7 g/m3 susp.). On basis of 42 tests for suspension without flocculant and 42 tests for suspension containing flocculant, two dependencies describing dewatering intensity (final moisture content in cake) as a function of the acceleration simplex and centrifugation time were found. They are as follows w exp [A (a g)B C ] D pl = ? + where constants and exponents are given in Tab.2. The dependencies are valid with good accuracy. For most common values of (a/g) and ? used in experiments, and suspension with and without flocculant, the final moisture content of cake was in the range wpl = 37.2 - 37.6 %. Also, what was very important, filtrate was quite clear and could be turned backward to a process line. Additional experiments, such as PSD analysis and sedimentation tests, proved that the deposition of suspension and addition of flocculant favour agglomeration thus facilitating (accelerating) phase separation. Selected data of PSD analyses performed in the particle size analyser Analysette 22 of Fritsch are gathered in Tab.3. The sedimentation tests proved a decrease of the turbidity zone after 2 hours to such extent that it is possible to reduce the amount of suspension at least 5 times. Roughly calculations indicated that solid phase fraction in post-sedimentation sludge increased from about uz = 0.045 to uz = 0.173. Therefore, such sludge can be easier separated, and moreover (very important), its amount is many times smaller than the amount of inlet suspension. This implies that the initial separation of inlet suspension is strongly advisable. On the other hand, no significant differences between sedimentation with and without addition of Magnaflog 336 flocculant were observed. It seems that the turn-back of clarified liquid to circulation and a supply of sludge from a settling tank to inlet suspension, or alternatively the filtration of sludge after a settling tank should be the relatively cheaper and advisable method of dewatering