Dewatering of slurry with poor filterability in basket centrifuge: discharge of supernatant using bypass filter medium

When centrifugal dewatering in basket centrifuge involves the sedimentation of particles in feed slurry, the slurry separates into two phases: supernatant and cake. The dewatering proceeds as the supernatant permeates through the cake. However, if the cake formed has poor permeability, it takes longer time to reach the desired moisture content. In this study , a new method is proposed to dewater slurry which forms cake with poor permeability and a comparison was made with the conventional design. In the proposed design, the filter media is placed not only on the circuit, but also at the bottom of the filter chamber. Thus, even though the cake formed has a high hydrodynamic resistance, the supernatant could be discharged because the filter medium at the bottom has less hydrodynamic resistance than the cake and therefore works as a bypass. It is known from the previous study that when the supernatant is totally discharged, the cake will undergo a consolidation process, which will make the cake more compact. Therefore, it is postulated that the bypass filter medium would improve the dewatering efficiency drastically. The results obtained is that the supernatant still remained in the filter chamber even after 300 s of dewatering when the conventional design was used, while the supernatant was completely discharged within 150 s when the new design was used. Thus, it can be concluded that the filter medium at the bottom of the filter chamber worked as a bypass and improved the dewatering performance

Analysis of stepwise expression of sake fermentation broth

In the sake brewing, expression is used for the separation of liquid from the fermentation broth. Although the period of expression has to be as short as possible in order to prevent the sake from losing flavour, practically it takes much time to complete expression because of the highly compressible materials (e.g. proteins and starch) in the broth. For the expression of highly compressible materials, it is known empirically that the applied pressure should be low at the beginning of the expression and increased stepwise as the expression proceeds. In this study, we propose a method for the analysis of stepwise expression of highly compressible materials. The fermentation broth of sake was used as the experimental material. The experimental apparatus of constant pressure expression utilised in this study essentially consists of a vertical cylinder with a movable piston. The change in thickness of the material in the cylinder with the time was measured by a dial gauge. The mechanism of liquid removal is filtration at the beginning of expression, followed by consolidation. The filtration rate can be obtained by applying Ruth’s constant pressure filtration theory. In the consolidation period (i.e. after the end of the filtration), the deliquoring rate is calculated by the numerical analysis of the basic consolidation equation. However, because the formula expressing the distribution of solid compressive pressure pS of a filter cake with highly compressible materials has not been established well, the consolidation equation cannot be solved analytically. We therefore propose a new empirical equation representing the pS-distribution of a filter cake with highly compressible materials. The equation proposed in this study makes it possible to analyse the stepwise expression of highly compressible materials

Enhancement of slurry dewatering in basket centrifuge using bypass filter medium

When centrifugal dewatering in basket centrifuge involves the sedimentation of particles in feed slurry, the slurry separates into two phases: supernatant and cake. The process of dewatering proceeds as the supernatant permeates through the cake. In the situation where the cake formed has poor permeability, it takes longer time to completely discharge the supernatant. It is known from the previous study [1] that once the supernatant is totally discharged, the cake will undergo a consolidation process, resulting in a less moist cake. Therefore, the discharge of the supernatant is important for an efficient dewatering. According to the current practice, the supernatant is discharged by either suction using a skimming pipe from the inner side of the basket or by increasing the rotational speed. However, these methods are not the perfect solutions because the skimming pipe method requires some distance to be kept between the pipe and the cake, and it is very inefficient to dewater highly compressible materials under high rotational speed

Improving slurry dewatering performance of basket centrifuge: discharge of supernatant using bypass filter medium

In order to improve the performance of the centrifuge, a new design of dewatering of slurry which forms less permeable cake is proposed. In the proposed design, the filter media is placed not only on the circuit, but also at the bottom of the filter chamber. The additional bottom filter medium is expected to work as a bypass. The comparison of the conventional and new designs is made in this study. The supernatant is completely discharged in much shorter time when the new method is used; hence the filter medium at the bottom of the filter chamber works as a bypass and improved the dewatering performance