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Wpływ dodatku flokulantu Magnafloc 919 na przebieg filtracji wirowej podekantacyjnej zawiesiny odpadowej

Palica M., Dolina A., Gierczycki A., Kolorz S.

Rocznik Ochrona Środowiska

2009

Tom 11

1063-1075

Niniejszy artykuł jest kontynuacją cyklu prac Palicy i współpracowników dotyczących separacji fazowej zawiesin zrzutowych po wirówkach DECANTER, na których odwadnia się flotokoncentraty węgli kamiennych [1÷12]. Wiele prac w tej problematyce począwszy od lat 70-tych prowadził Piecuch i współpracownicy.

In the paper experimental results dealing with centrifugal filtration of postdecantation dump suspension after the DECANTER centrifuge and obtained in a coal mine of "Jastrzębska Spółka Węglowa". Magnaflog-919 flocculant, used by operating service, was added to suspension. The suspension is characterized by very fine grainsize increasing during subsequent cycles, what leads, in consequence, to its replacement. This is connected not only with water and deposition costs but also with the losses of solid phase which is about 81% coal. In the mentioned coal mine 30 g of dry Magnaflog-919 flocculant per 1 Mg of dry product is added to flotoconcentrate. Floccu lant is dosed in a form of 0.1% gel. Therefore it appears a question if during dewatering of dump suspension containing 7÷8% of solid phase (using e.g. centrifugal or pressure filtration) flocculant should be again added, and if an answer is positive - in what amount? As a measure of dewatering efficiency, the final moisture content in cake obtained during centrifugal filtration for defined parameters of the laboratory centrifuge (adapted to a filtration centrifuge) was assumed. The test were carried out in the range of multiplication coefficient ? = a/g = 251.3÷1786.8 and centrifugal time ? = 280÷1800 s for dump suspension containing a base flocculant dose of 30 g/1 Mg, and doses of 15 and 60 g/1 Mg. Each experimental run consists of 6 values of ? and 7 of ? (altogether 42x4 points). For each experimental run tri-parameter correlations in a form of w = f(a/g, ?) = exp[A(a/g)b ?c] + D with regression coefficient R2>0.983 were elaborated. It should be noted that however the correlations quite well describe the process they have no theoretical bases. It was stated that the Magnaflog-919 flocculant dosage in the range 15÷60 g/1 Mg of dry product, for the same a/g and ?, produced an increase of moisture content in cake after centrifugation in comparison with values obtained for dump suspension. This, rather unexpected effect, can be explained by disruption of large flocs during decantation in DECANTER centrifuges and deposition of filtrate in smaller fragments or newly created flocs, for which centrifugal forces were not sufficiently high to remove it from cake. It was proved by higher values of moisture content in cake after centrifugal filtration in comparison with pressure filtration with cake compression. It was also stated the a good usability of filter cloth PT 912 for filtration, while an additive of flocculant accelerated sedimentation. Taking these into account, it seems that dewatering of dump suspension should be carried on in two stages. In the first stage suspension (with 30 g of flocculant per 1 Mg) should be directed to a settling tank, clarified liquid from this apparatus should be used in recirculation. In the second stage post-sedimentation slurry should be directed to a mixing process unit with flotoconcentrate, situated before DECANTER centrifuges.