Dewatering Kinetics Research Articles

In situ synthesis of a multifunctional polymer with a stable core-shell structure for effective dewatering

A multifunctional polymer that was magnetic and had a high water absorption ability was prepared via synthesis of magnetite nanoparticles followed by surface modification and polymerization. The structure and morphology of the multifunctional polymer were characterized by X-ray diffractometer (XRD), Fourier transform infrared (FTIR), scanning electron microscope (SEM), transmission electron microscope (TEM), and energy dispersive X-ray spectroscope (EDS). The magnetite content and the magnetic property of the multifunctional polymer were analyzed by thermogravimetric analysis (TGA) and superconducting quantum interference device magnetometer (SQUID), respectively. The results suggested that the multifunctional polymer had a stable core-shell structure, a striking temperature-responsive property, and stable magnetic property. Further work was carried out to assess the performance of this multifunctional polymer at a particle size of 0.3–0.45 mm for dewatering of fine coal (<0.25 mm in size). It was found that the multifunctional polymer could give fast kinetics of dewatering and after each cycle, the polymer could be readily separated by simple magnetic separation and then regenerated and reused in next cycle while maintaining the same dewatering performance.

О влиянии флокулянтов на кинетику процессов обезвоживания и промывки красных шламов из низкокремнистых бокситов при производстве глинозема

О влиянии флокулянтов на кинетику процессов обезвоживания и промывки красных шламов из низкокремнистых бокситов при производстве глинозема

Optimization of microwave dewatering of an Indonesian lignite

Dewatering of an Indonesian lignite with microwave irradiation was optimized to increase dewatering rate and decrease energy consumption. The energy consumption of the microwave dewatering process was affected by different factors, including addition of microwave absorber, diameter-to-height ratio of lignite pile, particle size and initial moisture content of lignite. The experiment results indicated that adding absorber carbon materials (activated carbon and graphite) and metal oxides (Fe3O4, MnO2, etc.) could increase the dewatering rate and decrease the energy consumption. With increased diameter-to-height ratio of lignite pile, dewatering rate initially increased and then decreased. An optimum value exists for diameter-to-height ratio, which presents maximum dewatering rate but with minimum energy consumption. The enhancement of heat accumulation caused by larger particle size increased the dewatering rate of lignite and decreased energy consumption. The energy consumption decreased with increased lignite weight and initial moisture content. However, the energy consumption initially decreased and then increased with enhanced microwave power. Electric power consumption can be well predicted on the basis of the microwave dewatering kinetics of lignite, which can be well described by the Page model under different conditions.

Effect of Hydrodynamics During Crystallization on Mechanical Dewatering of Salicylic Acid

Mechanical cake dewatering is always desired to reduce the load on thermal dewatering (drying). Any change in the upstream process such as crystallization can have a significant influence on the filtration as well as cake dewatering characteristics. The present study deals with the effect of hydrodynamics (mixing intensity) during salicylic acid crystallization on the air dewatering characteristics in the subsequent pressure filtration. The mixing conditions during crystallization were varied by using three different types of agitators (anchor impeller [AI], curved blade turbine [CBT], and bar turbine [BT]) and by varying the speed of agitation. The effect of operating pressure and dewatering time on the final moisture content of the cake was also studied. The crystal properties (crystal size and size distribution) were found to vary with the mixing intensity, which further influenced the cake dewatering kinetics as well as the residual moisture content. An AI, which is a laminar flow impeller, produced crystals with a wide size distribution and higher mean particle size, which resulted in cake with high porosity and hence higher moisture content. The high porosity (as well as high cake permeability) caused early air breakthrough, which resulted in ineffective dewatering of cake. Therefore, in this case the residual moisture in cake was found to be higher (27%) even at higher dewatering pressure (1.5 bar gauge) and longer dewatering time (90 s). A BT creates high turbulence during mixing and produced crystals with a relatively narrow size distribution and lower mean particle size, which provided low-porosity cakes. Such cakes could be efficiently dewatered and the final cake moisture content was found to decrease to about 15%, a significant improvement in the filterability of the cake. The dewatering data were modeled according to the correlation between irreducible cake saturation and capillary number for predicting the cake dewatering characteristics (residual moisture as well as dewatering kinetics) and the results were compared with the experimental data.

Effect of polyelectrolyte conditioning on the enhanced dewatering of activated sludge by application of an electric field during the expression phase

Activated sludge is known to be poorly dewaterable due to its high surface charge density and the extreme solids compressibility, even after polyelectrolyte conditioning. The application of an electric field during pressure dewatering (PDW) of sludge can enhance the dewaterability by the electroosmosis effect. A comparative study was conducted to investigate the additional effect of an electric field, applied during the expression phase, on the dewatering course of polyelectrolyte conditioned sludge, compared to mere PDW. It was found that the application of an electric field markedly improved the dewatering kinetics for all sludge samples, regardless of the conditioning treatment. Although the conditioning polyelectrolyte characteristics and dose had a major effect on the PDW of sludge, the conditioning history did not have a significant effect on the electroosmotic water transport efficiency during the sludge expression phase. By means of on-line streaming potential measurements and fractionated filtrate electrophoretic mobility measurements, it could be demonstrated that even at high polyelectrolyte doses, leading to positively charged sludge flocs, negative surface charges were still present inside the sludge matrix. During the expression of the sludge cake, when liquid is forced to move through the floc inside pores, these negative surface charges hampered PDW, but enhanced electroosmotic dewatering. Electroosmosis is therefore an appropriate technique to remove the water fraction that is associated with these negative surface charges.

Pilot-scale testing of novel fine-particle dewatering aids

Novel dewatering aids were tested on various coal samples from the United States and Canada. Both laboratory and pilot-scale filtration experiments were performed on the samples. The reagents substantially improved the dewatering kinetics and reduced the cake moistures. The cake moistures were typically reduced from the 20% to 30% (by weight) range to the 8% to 14% range using vacuum filtration. When the reagents tested were used in conjunction with a pressure filter, even higher moisture reductions were achieved. In the present work, the novel dewatering aids were tested using different types of pilot-scale vacuum filters. The pilot-scale results were consistent with those obtained in laboratory experiments.

Kinetics and mechanism during mechanical/thermal dewatering of lignite ☆

In order to increase the efficiency of lignite fired power stations the mechanical/thermal dewatering (German abbreviation: MTE, Mechanisch/Thermische Entwässerung, also used for ‘mechanical/thermal expression’) was developed at the University of Dortmund as an energy efficient process for the reduction of the water content of lignite prior to combustion [1–3], [Patentschrift DE 44 34 447 A1, 1994; Patent EP 0 784 660 B1; WO 96/10064, 1996; VDI-Berichte 1280 (1996) 165]. While a 25 t/h demonstration plant has been constructed at the Niederaußem power station of RWE in Germany and came into operation in 2001 [4], [Proceedings of the VGB/EPRI Conference, 2001] additional detailed research has been done on the process fundamentals at the University of Dortmund. Experiments for three different lignites from Germany, Greece and Australia are presented in this paper and it is shown, that the dewatering kinetics depending on time, temperature and pressure can be described by a new model derived from soil-mechanical fundamentals and rate-process-theory [5], [Mechanismen und Kinetik der Mechanisch/Thermischen Entwässerung von Braunkohle, 2001]. Due to differences in lignite composition the experimental determination of some model parameters for each coal is necessary. From the activation energy which is determined from experiments concerning dewatering kinetics it can be deduced, that even during secondary consolidation (creep) the drainage of water is the dominating process. The experiments also provide a clear distinction between the effect of the so-called ‘thermal dewatering’ due to heating of the lignite and the subsequent mechanical expression.

Reassessment of correlations for the dewatering characteristics of filter cakes

This paper presents a fundamental study on dewatering characteristics of filter cakes. Laboratory-scale batch pressure-filtration experiments were conducted on quartz, dolomite and andesite samples, having Gates–Gaudin–Schuhmann type of size distributions with different distribution parameters. The residual cake moisture and cake dewatering kinetics data were collected for filter cakes dewatered at varying applied pressure. Correlations for the entry pressure, residual saturation, pore size distribution index, and cake desaturation kinetics were studied in relation with particle size distribution characteristics. An assessment of previously recommended values of dewatering parameters and predictive correlation equations was presented with regard to their validity or limitations, and refinements were proposed for those giving poor fit.

New Rheological Test Method to Determine the Dewatering Kinetics of Suspensions

Abstract Rheology plays an important role in dewatering processes. It is therefore interesting to analyze the dewatering process and the rheological behavior of a suspension simultaneously. An exact determination of the immobilization point at the maximum of the loss factor as well as the immobilization time can be attained using an oscillatory time test with preset strain. The degree of dewatering is determined via normal force controlled gap setting. This report offers an insight into the theory of the dewatering of liquid supersaturated suspensions and shows how the kinetics of dewatering can be determined using paper coating as an example.

98/02679 The influence of surface phenomena on the dewatering of fine clean coal: Singh, B. P. Filtr. Sep., 1997, 34, (2), 159–163.

This paper presents a fundamental study on dewatering characteristics of filter cakes. Laboratory-scale batch pressure-filtration experiments were conducted on quartz, dolomite and andesite samples, having Gates–Gaudin–Schuhmann type of size distributions with different distribution parameters. The residual cake moisture and cake dewatering kinetics data were collected for filter cakes dewatered at varying applied pressure. Correlations for the entry pressure, residual saturation, pore size distribution index, and cake desaturation kinetics were studied in relation with particle size distribution characteristics. An assessment of previously recommended values of dewatering parameters and predictive correlation equations was presented with regard to their validity or limitations, and refinements were proposed for those giving poor fit.