摘要:

It is shown that the settling rates of thickened slurries can be greatly enhanced by application of D.C. voltages. It is demonstrated that the settling rates increase remarkably with increasing electric field intensity. The basic differential equation for gravitational settling of thick slurries is derived and this is extended to electroforced sedimentation. The theoretical' settling rates and the porosity distributions in settling sediments of both gravitatinal and electroforced settling compare favorably with experimental observations. In addition, it is shown that the compression-permeability characteristics in the low compressive pressure region can be closely determined analytically by using batch sedimentation data.

ISSN:0737-3937    

DOI:10.1080/07373938808916389

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

This paper deals with electroosmotic dewatering that can be very effective for sludge which is difficult to dewater by conventional mechanical techniques. First, the dewatering mechanism of sludge due to electroosmosis is analyzed theoretically based on an electroosmotic flow through a compressible packed bed of particles, and then its processes under the conditions of both constant electric current and constant voltage are discussed both theoretically and experimentally. Further theoretical expressions for the dewatering rate and the electric power consumption are proposed using a simple model in which the sludge bed consists of two parts: a dewatering bed and a dewatered bed. The equations obtained theoretically are demonstrated to be applicable to the design of electroosmotic dewatering equipment.

ISSN:0737-3937    

DOI:10.1080/07373938808916390

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

An important factor in the dewatering of fine suspensions by electro-osmosis is efficient mechanical collection and removal of water that is electrically generated. The mechanical collection can be the rate-determining step,controlling the overall dewatering. When the water is not efficiently removed, on-off power regimes appear to give as good results as continuous power application. This is not the case when water removal is highly efficient. A true test of the effect of different power regimes is possible with a thin bed of the suspension in a vacuum-assisted electrofilter, which provides a strong driving force to collect the water. Under these conditions, the rate of dewatering for full-wave or continuous power is always about double that for half-wave or on-off power regimes. These results suggest that recurring claims in the literature of the advantages of current interruptions or reversals in electro-osmotic dewatering may be erroneous or only partially correct.

ISSN:0737-3937    

DOI:10.1080/07373938808916391

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A cell for the electrokinetic dewatering of ball clay is described. By combining the electroosmotic and electrophoretic processes it has been demonstrated that the electrokinetic cell can be operated on a continuous basis.The electroosmotic and electrophoretic processes are found to be directly proportional to the applied current as predicted by electrokinetic theory.Ball clay was found to deposit in the range 60-70% solids with an accompanying energy requirement of 100-170Wh/Kg, based on a dry weight basis. The corresponding deposition rate was 50kg/m2/hr at a current density of 145/m2. The parallel electroosmotic water removal process was found to occur at a rate of 120dm3/hr/m2 for a specific energy consumption of 55Wh/dm3.

ISSN:0737-3937    

DOI:10.1080/07373938808916392

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Investigations were carried out on the effect of the ultrasonic field and some selected chemical compounds on the process of preparing sludges to be dewatered by mechanical devices.

ISSN:0737-3937    

DOI:10.1080/07373938808916393

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Interesting results have been observed in applying acoustic energy to dewatering and drying materials. However, drying by acoustic energy alone is expensive, energy intensive, and at best can be justified only in applications where rapid drying is necessary to preserve a product, the product is heat sensitive and its value justified the cost. However, synergistic effects have been observed when acoustic energy has been used with electrophoresis and electro-osmosis to dewater materials. An electroacoustic dewatering (EAD) technology has been developed in recent years that indicates good economic potential and an effectiveness that exceeds most conventional methods of dewatering. Very good results have been obtained from laboratory studies using the techniques with fine coal slurries, food products, municipal sewage sludges, and many other products.

ISSN:0737-3937    

DOI:10.1080/07373938808916394

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The influence of acoustic energy in drying of high ash coal in association with thermal energy is studied. The variables used in the experiments are air temperatures 70°C and 120°C, acoustic intensities 120, 135 and 145 dB for different grain sizes ranging from 44 to 1000 microns (µm). It is established that the drying process in coal is feasible above a critical sound pressure level given by P=125+10 log f (f is the acoustic frequency in KHz). Removal of moisture in coal is enhanced with time, intensity of sound and air temperature. The drying rate is more pronounced for coal with particle size range 149 to 297 microns.

ISSN:0737-3937    

DOI:10.1080/07373938808916395

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The use of low frequency vibration in combination with compression has been studied in the laboratory as a technique for improving the dewatering of compressible filter cakes. Experiments have been done with a variety of solids-water cakes over a wide range of squeeze pressures. Two types of apparatus were used: double membrane filter presses operating at 0.7 to 2.8 MN/m2 and a vacuum filter operating at 0.07 MN/m2. Frequencies of vibration were in the range of 0.5 to 60 cycles/min with the filter presses, and 30 to 120 cycles/min with the vacuum filter. Amplitudes of vibration were in the range of 4% to 10% of the unsupported filter cake span in both types of apparatus. Substantial improvements in compression dewatering were obtained in all the tests, and the power required to vibrate the filter cakes was low at just over 1 kWh/t dry solids. The thermal saving, equivalent to the additional water removal caused by vibration, ranged from 130 to 400 kWh/t dry solids.

ISSN:0737-3937    

DOI:10.1080/07373938808916396

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Separation of liquids from a fine particle suspension plays an important role in many industrial processes. In the last few years, a number of technologies have been developed for the separation of slurries with coarse particle suspensions and intermediate particle sizes. However, separation of fine particles from these suspensions can be difficult and prohibitively costly.Battelle has developed a solid-liquid separation technology that utilizes difference in electrokinetic/acoustic properties to enhance the conventional solid-liquid separation techniques such as vacuum filters and presses. The present paper describes the application of this electroacoustic dewatering technology to Hamburg dredged material.

ISSN:0737-3937    

DOI:10.1080/07373938808916397

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Dewatering, or limited thickening, of dilute suspensions can be achieved using microfiltration, but is accompanied by the undesirable permeate flux decline. Experimental data showing this effect are presented, and data indicating some alleviation of the problem using electrical fields are shown. Various models claimed to interpret flux decline are overviewed and discussed. Although some reflect the shape of the flux curve, all must be critized on the basis that they do not provide any insight as to the causes of the phenomenon.

ISSN:0737-3937    

DOI:10.1080/07373938808916398

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor