JPH0513683B2 - - Google Patents

Description

[Detailed description of the invention]

FIELD OF THE INVENTION The present invention relates to a method for concentrating and removing water from colloidal suspensions, fine solids in sludge, or particulate slurries in water using a combination of electric and acoustic (sonic or ultrasonic) fields. be. These sludges and slurries are generated during coal washing slime, ore processing, coal transportation by pipeline, and ceramic manufacturing. The method of the present invention uses the combined energy of an electric field and an acoustic field to remove a given amount of water from a suspension to remove the same amount of water from the same amount of slurry. The amount of energy required can be lower than that required when using ultrasonic (ultrasonic) fields alone or sequentially. The present invention provides the above-mentioned coal-washed slime,
Useful for removing water from ore processing sludge or coal slurry. BACKGROUND OF THE INVENTION Conventional methods for separating water from suspensions, sludges, and slurries to improve solids concentration include
(a) Mechanical dehydration methods such as centrifugation, vacuum filtration, and vibrating sieves, (b) thermal drying methods, (c) sedimentation methods, (d) ultrasonic dehydration methods,
(e) and dehydration methods using electric fields (electrophoresis or electroosmosis). However, for certain materials mixed with water, conventional dewatering methods are not preferred because particulates can clog the filter and significantly reduce overrate. Furthermore, dehydration of a suspension of colloidal microparticles is difficult with conventional solid-liquid separation methods such as vacuum filtration and centrifugation. These suspensions and slurries can also be dried with heat, but the energy consumption is very high and dust problems arise. Furthermore, natural settling due to standing still requires a large land area such as a pond. Due to high energy costs, efforts are being made to review all of the above methods and reduce their required costs. The use of electric and acoustic fields to separate water from suspended particles has also been investigated, as discussed below. When colloidal particles, such as microclays, are suspended in water, they become electrically charged and move toward one electrode when exposed to an electric field. This charge varies depending on the type of suspension or slurry; for example, some types of clay are positively charged, while most coals are negatively charged. Therefore,
In order to move the particles away from the water-permeable electrode and towards the water-impermeable electrode, the polarity of the electrode needs to be selected appropriately. Application of an electric field neutralizes the charge and causes the particles to aggregate, dehydrate the solid by electroosmosis, or move the particles as described above. The charged collection plate attracts all moving particles, such as negatively or positively charged particles, but does not collect electrically homogeneous particles. For example, proteins are charged by ionization of (COO ^- ) and (NH ₃ ⁺ ) ions.
The total or net charge of the protein is determined by the number of these groups, dissociation constant, pH, temperature, etc. However, experience has shown that most colloidal proteins are negatively charged under normal conditions in water. In addition to this, there is an electroosmotic phenomenon. Electroosmosis is
It is the movement of a liquid medium along a stationary charged surface. Movement of the liquid medium occurs in the direction of the electrode charged with the same sign as the stationary surface. That is, as slurry particles gather more densely, the water between each particle is subjected to electroosmotic forces. If the particles are negatively charged, water will flow towards the negative electrode. If this electrode is made water permeable, the dehydration process will be further accelerated. An example of the use of electric fields in the dewatering of coal wash slimes is provided by Neville C. Lockhart, Fuel, entitled "Sedimentation and Electroosmotic Dewatering of Coal Wash Slime."
It is shown in the paper in Volume 60, October issue, pages 919-923. The method that uses only ultrasonic waves to dehydrate coal is H.
IEEE Trans.on Sonics and UItrasonics, entitled “Acoustic Dehydration of Coal” by V. Fairbank et al.
SU-Volume 14, No. 4 (October 1967), pp. 175-177, and the title "Acoustic drying of ultra-fine coal"
Ultrasonics, Volume 8, No. 3 (July 1970), No.
It is known as shown on pages 165-167. Sonic or ultrasonic energy is a form of mechanical vibrational energy. Sound waves or ultrasound waves are
Propagates as waves at a constant velocity through all materials, including solids, liquids, and gases. The speed of this wave is determined by the elastic and internal properties of the medium. As these waves propagate through the medium, extremely large internal and elastic forces are generated due to the extremely high frequency of these waves. The amplitude of particle motion in sonic and ultrasonic media ranges from a few micron inches to 5 milliinches (0.127 mm) (depending on power level). A 0.001 inch (0.0254 mm) ultrasound wave at 20,000 Hz produces a peak acceleration of 40,000 G (3.810×10 ⁷ mm/sec ² ) in the medium. lG (9.807×10 ³ mm/sec ² ) is the acceleration due to gravity. The force generated by the above acceleration is extremely large. Due to the above-mentioned large inertial forces generated by acoustic waves or ultrasonic waves, all media undergo material degradation, fragmentation, and separation. The sonic or ultrasonic impedance of each material varies by a factor of 3 to 8, especially in the solid and liquid phases. When the medium is a mixture of two or more different types of materials, such as water and coal, the inertial and elastic forces between them are quite large. As the inertial and elastic forces increase, the surface tension breaks and the liquid separates from the solid. In liquids, high levels of sonic and ultrasonic energy are known to cause cavitation, a phenomenon in which microbubbles are generated due to a phase transformation into a vapor phase. The presence of solid particles increases the degree of cavitation. Microbubbles are generated on the solid surface, thereby promoting solid-liquid separation by creating a gas-liquid surface whose surface energy is lower than that of the solid-liquid surface. Cavitation generates localized shock waves and, in some cases, electrically charged free radicals. These shock waves and free radicals also promote solid-liquid separation. Applying ultrasound generates high vibrational forces in the medium. The main mechanisms of sonic and ultrasonic dehydration are believed to be high vibrational forces and ultrasonic cavitation between the solid medium and water in the mixture. Degassing, viscosity reduction, and surface tension reduction occur with ultrasonic vibrations and may be other dehydration mechanisms. A portion of the ultrasound energy is absorbed by the medium and converted into heat. Internal heat generation and the resulting temperature increase lower the viscosity and surface tension, facilitating separation. The local temperature increase also increases the cavitation effect and accelerates the rate of liquid removal. Therefore, internal heating due to partial absorption of ultrasound energy has been used to accelerate liquid removal in aqueous systems. Wallis U.S. Pat. No. 3,864,249 and
No. 4028232 Each specification uses ultrasonic pressure waves,
It is disclosed that it is combined with a separation screen to facilitate liquid separation from the material to be dried. When using electric fields or acoustic energy, each requires significant amounts of energy. The object of the present invention is to overcome the above-mentioned disadvantages by reducing the energy required for dewatering, increasing the dewatering rate over conventional methods and reducing the final moisture content of the product. . The present inventor has discovered that when an acoustic field (acoustic or ultrasonic waves) and an electric field (electrophoresis/electroosmosis) are used in combination, the following effects are less predictable than when the acoustic field acts alone or the electric field acts alone. was found to be obtained. SUMMARY OF THE INVENTION The present invention provides a method for preparing an aqueous suspension of solids;
For example, methods for separating water from solids in coal slurries and the like. The method consists of simultaneously exposing the suspension to an electric field and an acoustic field (sonic or ultrasound) to separate the water bound to the solid particles and to displace the particles and water to create a particle-depleted zone. It is something. Water is then extracted from this particle-depleted area. Effect 1 of the present invention In a combination in which these are used simultaneously, the required energy is smaller than in the case where they are used alone. 2 When these are used in combination, the dehydration rate is faster than when they are used alone. 3 The combination of these together results in a lower final moisture content of the product than when used alone or sequentially. DETAILED DESCRIPTION OF THE INVENTION The figure shows a dehydration zone or chamber 10 defined by electrodes 11 and 12 which are coupled via conductors 111 and 112 to an external DC power source 200. The electrode 11 has an opening 13 through which water can pass. If the openings 13 of this electrode 11 are not narrow enough to retain particles in suspension, a filter 14 can be used. Sound generating means 15 create an acoustic field (not shown) of acoustic waves or ultrasonic waves that propagate through the suspended objects in the dehydration zone. In operation, the suspension to be treated is transferred to the dewatering zone 10 and exposed to an acoustic field (acoustic or ultrasonic) of a frequency and amplitude such that the water separates from the particles in the suspension. At the same time, a DC voltage is applied between the electrodes 11, 12 to move the charged particles in the aqueous suspension from the water-permeable electrode 11 towards the water-impermeable electrode 12 and to move the water towards the water-permeable electrode. The sound waves or ultrasound waves serve to prevent suspended particles from solidifying and to facilitate the flow of water towards the water-permeable cathode. Once the slurry passes through the dewatering zone,
Water is removed through the permeable electrode 11 and the dehydrated suspension emerges from the other end of the dewatering zone 10. Dewatering through the permeable electrode 11 can be enhanced by reinforcing means 16, which reduce the pressure outside the permeable electrode, increase the pressure within the dewatering zone, or a combination of both. The process according to the invention can be operated without this reinforcing means. However, it is preferred to use this reinforcing means. The means used to reduce the pressure on the external surface of the permeable electrode or to increase the pressure in the dewatering zone are those conventionally used to reduce or increase pressure in forced overflows. The dewatering zone 10 can be delimited by two walls (not shown) connecting between the two electrodes 11, 12 to accommodate the slurry in this zone 10. The walls in this case are made of insulating material (not shown)
The wall can also be insulated from the electrode using an electrically non-conducting material. In this embodiment, an electric field and an acoustic wave are applied simultaneously while the suspension flows through the dewatering zone 10. In other embodiments, the electric field and acoustic energy parameters may be varied to remove additional water from the suspension by flowing the suspension through additional equipment of the type shown in FIG. . In yet other embodiments, the suspension may be separately pre-treated or post-treated with acoustic energy or electric fields prior to exposure to the simultaneous method of the present invention. The operating frequency of sonic/ultrasonic generators is from approx. 5000
100,000 hertz, but preferably about 20,000 to 40,000 hertz to minimize audible noise effects in the work environment and maintain high efficiency levels.
The amplitude of the acoustic or ultrasonic waves can be any amplitude sufficient to separate water bound to particles, but approximately
A range of 0.002 mm to 0.01 mm is preferred. The applied voltage is such that a sufficient electric field is created and a current flows to cause the charged particles and water to migrate so as to improve the dehydration process by reducing the total energy requirement in the above methods used separately. Can be any voltage. The method of the present invention can be applied to aqueous coal slurry produced when loading coal using a pipeline, coal washing slime when separating coal from impurities after coal mining, ilmenite ore processing slurry, sludge or hematite ore processing slurry, It can be used in sludge and clay suspensions produced during ceramic manufacturing. Although the following specific experimental example shows only the case of coal slurry, it is clear that the present invention is generally applicable to the above-mentioned sludges and slurries. Furthermore, the dewatering capacity can also be improved by adding small amounts of surface modifiers, such as detergents or surfactants. Examples of this surface modifier include polyacrylamide gel, polystyrene sulfonate, and the like. The amount can be easily determined by one skilled in the art of dehydration. These surfactants are added before the simultaneous application of the electric and acoustic fields. Surfactants can be nonionic, anionic or cationic. Surfactants, due to their hydrophobic properties, adhere to the coal surface and release water. Certain materials, such as clay and coal, do not exhibit sufficient electrical conductivity when mixed with water to allow adequate current to flow when an electric field is applied. In this case, salts and conductivity improvers such as NaCl, KCl,
It is necessary to increase the conductivity of the mixture by adding Na ₂ SO ₄ , NaOH, KOH, NH ₄ Cl, etc. Similarly
The same effect can be achieved by changing the pH appropriately. Correct current and particle movement is thereby achieved. The method of the invention can be used to dehydrate mixtures of particles of any size and water. Preferred particle sizes range from about 10 microns to 100 microns. In the method of the invention it is important to apply sound or ultrasound waves and an electric field to the mixture so that they penetrate throughout the mixture. Separation of water from solids will not be effective unless sound waves or ultrasound waves penetrate into the mixture to be dehydrated. Although the above description and the following experimental examples combine ultrasonic and electric field dehydration with vacuum force, the use of vacuum force is not essential and other methods may be used to increase the capacity of the dehydration method of the present invention. Means 16 can also be used. Further, the following examples are merely illustrative, and the present invention is not limited thereto. All ratios are by weight unless otherwise specified. A coal slurry with coal particles having a Tyler sieve mesh size of 200 was prepared and used throughout all tests. This slurry has a 1:1 ratio of coal to water, so 50% by weight of the slurry is water. Approximately 0.1 g of NaCl was added to all samples. The particles were mixed with water using a magnetic stirrer to form a homogeneous suspension. Example 1 (Comparative Example) This is a comparative example showing how much water is removed by conventional vacuum filtration.

Table: This data is shown in Figure 2 for comparison. This initial experiment was performed with vacuum only using an aspirator attached to a typical water faucet. As is clear from Figure 2, the solid content concentration leveled off after 10 minutes and hardly changed. This is due to the formation of a cake which slows down the overspeed. Also, the solids concentration obtained due to the limiting properties exhibited by the particles is quite low. Water retained by surface tension, capillary force, etc. remains retained. The removed water is
Mainly bulk water. 50g from past experiments
There was no significant difference between the results obtained with the 35g sample and the 35g sample. The above results are presented solely for comparison purposes. Example 2 (Comparative Example) This is a comparative example using an electric field (electrophoresis and electroosmosis) (E) and a vacuum. The slurry was the same as that prepared above, and the sample amount was 35g for samples 1, 2, and 3, and 35g for sample 4.
5 and 6 are 50g.

[Table] This example performed using only an electric field and a vacuum is more efficient than using only a vacuum. This is shown in FIG. Especially example 1 using only vacuum
In this case, the moisture content after 2 minutes was only about 43%. When an electric field is applied under the same conditions, the moisture content drops to about 35%. The time and power values for samples 1, 2, and 3 were proportionally corrected for the 50 g sample using simple arithmetic calculations to allow direct comparison with the 50 g sample from other tests. It can be seen that as the dehydration process continues, the power consumption decreases rapidly. This is samples 4, 5,
3 for 6. That is, in samples 1, 2, and 3, it is assumed that the power values decrease linearly during the time used in the test. For Samples 4, 5, and 6, the required energy was determined by calculating the area under each curve on the assumption that there was a straight line between the data points. When high current (1-2 amps) is applied for a long period of time, the electrodes become hot. Therefore, the potential between the electrodes decreases and only a small amount of current can flow. Example 3 (Comparative Example) Example 3 is a comparative example in which only ultrasonic waves (U) and vacuum were used. The slurry is the same as that prepared above. The sample amount is 50g.
The frequency was 20,000 hertz.

[Table] By using ultrasound and vacuum, the overspeed is faster than with vacuum alone or with vacuum and electric field. As already mentioned, dehydration in the presence of ultrasonic energy occurs primarily through cavitation phenomena. The solids concentration achieved at 2 minutes is about 23%, compared to about 35% in the presence of the electric field in Example 2. However, it must be pointed out that as the experiment time increases, heat is generated from the horn. To reduce this effect, an external cooling coil was used. The temperature of the slurry was constantly monitored with a thermocouple. Example 4 This example was performed using a combination of electric field (electrophoresis/electroosmosis) (E), ultrasound (U), and vacuum. The slurry was prepared as described above, and the sample amount was 50 g unless otherwise specified in the table.

【table】

[Table] The results when both electric field and ultrasound are combined are:
It is shown in the table and Figures 2 and 4. The moisture concentration after 2 minutes has improved to about 18%, compared to about 23% when using ultrasound and about 35% when using an electric field. The same relationship can be seen when comparing power. For example, when an electric field and ultrasound are combined, 112.5 watts results in a liquid concentration of approximately 15%. This requires 120 watts for electric field alone and 160 watts for ultrasound. The dewatering speed for the same power value is similarly improved. FIG. 4 shows the variation of percent moisture content of a slurry or suspension versus energy consumption. To represent the degree of decrease in energy used as the dehydration process progresses, the energy values for the electric field alone and in combination are corrected.
This correction was performed using a straight line approximation. Actual and corrected values are listed in the table above. If the same amount of sample is to be dehydrated, the combination of electric field and ultrasound requires much lower values than either alone. for example,
At 4 watt hours, the percent moisture content in the presence of an electric field is about 35% and in the presence of ultrasound it is about 26%. However, combining both techniques reduces the percent moisture content to about 19%. The above tables and figures show that the dewatering rate, power consumption and final solids content are better when the combination is used than when using each technique alone. Additionally, the data above indicate that optimal separation occurs when the energy inputs from the electric and acoustic fields are approximately equal. That is, the data for samples 15, 16, 17, 18, and 19, which have a large proportion of energy input in ultrasound energy, are similar to those for samples that used ultrasound only and were gradually reduced to a combined separation level. On the other hand, other samples with approximately equal power levels for the two effects,
For example, samples 1 to 13, 20, and 21 have better results. Once one of ordinary skill in the art understands the methods and advantages of the present invention, one skilled in the art can determine the optimum power ratio to use. The vacuum degrees of Samples 2, 3, and 4 of Example 1, Samples 1 to 6 of Example 2, and Sample 8 of Example 4 are lower than the vacuum degrees of the remaining data. This is not expected to affect the experimental results, and higher vacuums than those used in the samples above would not result in faster dewatering rates or lower moisture content. Temperature was measured on several samples using thermocouples. Some of the data shown in the tables are not shown in the figures. These data indicate that the slurry temperature is high.
Their inclusion will make the moisture content results at elevated temperatures uncertain or erroneous, since water is lost through evaporation. On the other hand, as mentioned above, using a medium temperature is advantageous for dehydration, and using a high temperature is a method that combines an electric field and ultrasonic waves to dehydrate coal using a small amount of energy. This should generally be avoided as it makes it difficult to clearly show the difference. Generally, temperatures above 90°C are excessive.

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of apparatus useful in practicing the invention. FIG. 2 is a graph plotting percent moisture in a sample versus time for various methods. FIG. 3 is a graph plotting the drop in power used when an electric field is applied. FIG. 4 is a graph showing percent moisture in a sample versus power consumption. 10... Dehydration zone, 11, 12... Electrode, 13
...opening, 14...filter, 15...sound generator, 16...strengthening means.

Claims (1)

[Scope of Claims] 1. An electroosmotic dehydration method for a suspension, characterized by comprising the following (a) to (c). (a) exposing the suspension to an acoustic field of a frequency and amplitude that causes water bound to the particles in the suspension to separate; (b) at the same time to an electric field that causes the bound water to move. (c) exposing the suspension to a portion of the suspension that increases the particle concentration and the other portion of the suspension that increases the water concentration; (c) the portion of the suspension that increases the water concentration; removing the bound water from the suspension. 2. The method according to claim 1, wherein the water removal capacity is increased by applying a pressure difference to the part of the suspension where the water concentration has increased. 3. Separating the unit amount of water from the suspension with an amount of energy that is less than the amount of energy required if an acoustic field alone were used to separate the unit amount of water, Claim 1 The method described in section. 4. The unit amount of water is separated from the suspended substance using an amount of energy that is less than the amount of energy required when an electric field alone is used to separate the unit amount of water, as described in claim 1. the method of. 5. The method according to claim 1, wherein an acoustic field is added after carrying out claim 1. 6. The method according to claim 1, wherein an aqueous coal slurry is used as the aqueous suspension. 7. The method of claim 1, wherein the aqueous suspension is dehydrated by simultaneously exposing the aqueous suspension to an acoustic field and an electric field, both of which have substantially equal power levels. 8. An electroosmotic dehydration method for an aqueous suspension, characterized by comprising the following (a) to (d). (a) passing the suspension through a dehydration zone; (b) exposing the suspension to an acoustic field of an amplitude and frequency that causes separation of water bound to particles in the suspension; (c) (d) simultaneously exposing the suspension to an electric field which causes the bound water to migrate towards other parts of the zone; Removing bound water from the suspension. 9. Claim 8, wherein a pressure difference is applied to the portion of the zone through which the water moves to facilitate water removal.
The method described in section. 10. Claim 8, wherein the unit amount of water is separated from a suspended solid with an amount of energy that is less than the amount of energy required when an acoustic field alone is used to separate the unit amount of water. the method of. 11. The method according to claim 8, wherein the unit amount of water is separated from a suspended solid with an amount of energy that is less than the amount of energy that would be required if an electric field alone were used to separate the unit amount of water. Method. 12. The method of claim 8, wherein an acoustic field is added after implementing claim 8. 13. The method of claim 8, wherein an aqueous coal slurry is used as the aqueous suspension. 14. The method of claim 8, wherein the aqueous suspension is dehydrated by simultaneously exposing the aqueous suspension to an acoustic field and an electric field, the electric or power levels of which are approximately equal. 15 Electroosmotic dehydration of the aqueous suspension in a dehydration chamber having two electrodes forming mutually opposite walls of the dehydration compartment and one of which is permeable to water, and having an inlet and an outlet. A method for dehydrating an aqueous suspension, characterized by the following (a) to (e). (a) flowing the suspension into the dehydration chamber and between the two electrodes; (b) subjecting the suspension to an acoustic field of frequency and amplitude such that water bound to particles in the suspension is separated; (c) Simultaneously with step (b) above, applying an electric field between the two electrodes to move the bound water towards the water-permeable electrode; (d) Simultaneously with step (c) above. removing water from the suspension through a water-permeable electrode to remove the bound water from the suspension; (e) removing the dehydrated suspension from the dewatering compartment; 16 Claim 1, wherein a pressure difference is applied to a portion of the suspension where the water concentration has increased to promote water removal.
The method described in Section 5. 17. A method according to claim 15, wherein the unit amount of water is separated from a suspended solid with an amount of energy that is less than the amount of energy that would be required if an acoustic field alone were used to separate the unit amount of water. Method. 18. Separating said unit amount of water from a suspension with an amount of energy that is less than the amount of energy required to separate the unit amount of water using an electric field alone;
The method according to claim 15. 19. The method according to claim 15, wherein the dehydrated suspension is dehydrated by further adding an acoustic field afterwards. 20. The method of claim 15, wherein an aqueous coal slurry is used as the aqueous suspension. 21. The method according to claim 15, wherein an acoustic field and an electric field, both of which have substantially the same electric power or power, are simultaneously applied to the aqueous suspension to dehydrate the aqueous suspension. 22. The acoustic field is applied with a frequency of about 5000 to 40000 Hz and an amplitude of about 0.002 to 0.01 mm,
The method according to claim 15. 23. The method of claim 15, wherein a surface modifier is added to the slurry before or during the suspension enters the dehydration chamber.