Pressure Dewatering Research Articles

Dewatering Machine for Paper and Pulp

Rotary Press Filter is a rotational pressurized dewatering machine that has a unique dewatering mechanism. It was developed by CRIQ, the industrial research center in Quebec, Canada and manufactured and distributed by Fournier Industries Inc. Tomoe Engineering Co., Ltd. started its production under their license this year (2002).Feature of Rotary Press are: 1) High-dewaterability, 2) A simple structure. 3) A tight-sealed structure that prevent odor emission. 4) A small foot print. 5) Less enegy cost, 6) Easy and minimal maintenance works. It meets needs of today and future.We have already installed 14 units (including sewerage application) in Japan and installed 3 units in 2 paper making plants for their wastewater sludge treatment. Further, we are conducting dewatering tests on respective applications with our test machine and have been obtaining good results. We will introduce the Rotary Press Filter for pulp & paper industry.

Performance evaluation of electrodewatering system for sewage sludges

A laboratory-scale electrodewatering system, incorporating an electric field as an additional driving force to conventional pressure dewatering, has been developed to decrease the water content of sludges generated in wastewater treatment. Consisting of a piston-type filter press, a power supply and a data acquisition system, the electrodewatering system’s performance was evaluated as a function of applied pressure, applied voltage, sludge type and filtration time. Experiments were carried out using sewage sludges with the electric field up to 120 V/cm and pressure ranging from 98.1 to 392.4 kPa. Electrodewatering involving a combination of electric field and pressure enhances both the dewatering rate and final dewatered volume. The final water content of sewage sludges in the electrodewatering system can be reduced to 62 wt%, as compared to 78 wt% achieved with the pressure filtration alone. The electrodewatering system shows the potential to be an effective method for reducing the water content in sludges.

Improvement of filtration kinetics by pressure electrofiltration

The requirement to dewater finely dispersed products is rising world-wide. Because the flow resistance increases with decreasing particle size, the mechanical dewatering of fine particle suspensions is time-consuming. The electrofiltration potential increases with the particle surface area. Therefore the combination of mechanical and electrical filtration seems to be an effective method to enhance the filtration kinetics. Experiments at the Institute of Mechanical Process Engineering and Mechanics (MVM) at the University of Karlsruhe (TH) showed that this combination results in an acceleration of the filtration kinetics. Thus the filtration time was less than half compared to traditional pressure filtration. If an electric field is applied in addition to pressure dewatering, four additional effects occur. On the one hand, the electrokinetic effects of electroosmosis and electrophoresis benefit filtration. The electrophoresis decreases the migration velocity of the particles. The electroosmosis moves the surrounding diffusive layer of the particles and promotes the filtration flow. On the other hand, electrolysis and a decrease in thermal viscosity occur. As a result of the applied electric field, the fluid is electrolytically decomposed and electrolytic gas is generated. This gas displaces water but also increases the electric resistance between the electrodes. The electric resistance of the bulk converts electrical energy into thermal energy, resulting in a temperature rise of the suspension or filter cake. An increasing temperature causes a lower viscosity and easier dewatering. These single effects and their influence on the process have to be known in order to succeed in industrial implementation of the process. The dewatering effect of the generated electrolytic gas can be calculated by a continuity balance. The change in viscosity can be eliminated by knowledge of the temperature. Based on the root equation of cake building filtration, Yukawa developed an equation for pressure electrofiltration. The electrokinetic effects can be separated using this equation. The electroosmotic pressure and the electrophoretic coefficient can then be calculated if the filter media and bulk resistance are known. Experiments on a specially constructed pressure/electro filter showed that the acceleration of the filtration kinetics is mainly caused by electrophoresis. Electroosmosis only has a little effect. The bulk resistance, which mainly influences the filtration kinetics, will be abated by the electrophoretically reduced particle velocity.

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE1*

This paper describes the role of pressurized electroosmotic dewatering (EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters (filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied. Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness. With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying. *This article was published with incorrect figures in Drying Technology, 19(1), pp. 185–198. The complete article with correct figures is reprinted here.

PRESSURIZED ELECTROOSMOTIC DEWATERING IN A FILTER CYCLE

This paper describes the role of pressurized electroosmotic dewatering(EOD) in a filter cycle. A laboratory-scale filter-press was used to filter a highly conductive silica suspension under constant pressure, followed by washing and mechanical precompression of the filter cake and finally by pressurized EOD at constant electric current. The influence of filter cycle parameters(filtration and washing pressure and duration, mechanical pressure, and electric field intensity) on the final cake dryness and energy consumption was studied.Electrodes of different materials, forms, and surfaces were used. The optimal conditions of each filter cycle operation were found to minimize the energy consumption during EOD and maximize the cake dryness.With mechanical pressure and electric field intensity increasing, the total energy consumption increased, but the specific energy consumption (per kg of expressed water) decreased, and the final filter cake was dryer. The pressurized EOD also used less energy than thermal drying.

Wastepaper Fibers in Cementitious Composites

The use of cellulose fibers, reclaimed from wastewater from paper recycling, as reinforcement in cementitious building products is discussed. An experimental program is based on the development of a material composed of Portland Cement mixed with sludge produced by the treatment of wastewater from a paper recycling plant. This sludge is composed primarily of cellulose fibers and Kaolinitic clay. The primary obstacle in the development of a mixing process is the problem of achieving an intimate mixing of the fibers and the cement, as the fibers tend to coalesce and form soft inclusions in the hardened mass. This problem is overcome by introducing the cement into the sludge prior to chemical or mechanical dewatering, followed by vibratory and pressure dewatering of the cement/sludge slurry. Optical and Electron microscope photographs clearly indicate the differences between mixing techniques. Physical properties of the resulting mass are measured as a function of varying mix proportions and mixing techniques. Compressive strength on the order of 10.3 MPa (1,500 psi), and tensile strength on the order of 2.8 MPa (400 psi) have been obtained.