Untitled record

(54) Name: Process for separating a fine-grained material from a liquid with which the fine-grained material is soaked

In machining details of high-speed steel and other valuable alloys, grinding operations are often used in combination with cutting oils or emulsions. In these operations, a very finely divided chip falls in oil or oil emulsion. There is currently no practical method of dealing with these chips, though. they represent a great value in the form of alloys. On the contrary, the disposal of this material presents a complicated waste and environmental problem. It is desirable to be able to melt the chip in a metallurgical furnace. This is impossible with conventional technology mainly due to three factors:

- if the chip is freely charged in the oven, oil flows into the bottom of the oven and cools and soaks it in so that cracks in the oven lining occur

- if the oil-soaked material is charged to the furnace in closed containers, the volatile constituents will evaporate, which under adverse conditions will cause combustion puffs and explosions.

- the large amount of oil gives a strong smoke development, which poses a danger to the internal and external environment.

There is therefore a great need for a practically useful method of separating nv the valuable. '! the metal particles from the liquid phase.

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Similar problems also exist in the handling of, for example, aqueous flue gas from venturi plants or aqueous acidic sludge sludge. Thus, drying of such fine-grained materials, which have the consistency of mud or sludge, has posed great problems due to the high energy consumption. Women's memory problems are also very troublesome. According to conventional technology, the first step is usually to filter or spin away as much of the liquid phase as possible. The finer the material, the greater the liquid content remaining after this step. As a second step, one usually evaporates the liquid phase. The disadvantages of this procedure are:

1st The vapor heat of the liquid is lost plus the material's specific heat absorption.

2nd The productivity of the filtration or centrifugation operation is low.

3rd The equipment is sensitive and requires careful monitoring.

4th Dissolved impurities in the liquid can precipitate.

• According to a proposed method of separating liquid from a finely divided solid phase, the liquid pulp is collected in a container in which the pulp is heated from below so that. the liquid, beginning with the lowest part of the pulp, is evaporated in a vaporization zone and drives the liquid in the overlying portions of the pulp upwards through the pulp towards the surface where it accumulates, from which the liquid is discharged from the container. The method can be said to be based on the following principles:

a) a sufficiently large gas pressure is to be produced by heating the container 25 from below in the lower parts of the pulp to press the liquid upwards at a certain desired speed. This condition can be expressed

<img file="SE409658B_D0001.tif" />

dv dt

A&gt; &amp;

dp dy (1)

In this case, dv dt = Volume flow fluid

A = Horizontal sectional area Ci = Permeability = Vertical pressure gradient

b) The grain size, or rather the seal gasket, shall be such that gas bubbles cannot substantially rise and liquid droplets cannot substantially fall down the gaps between the grains. In other words, agitation in the liquid must be prevented by the capillary forces in the atomized

7800015-5 mass. In this connection, one must assume that a gas bubble which is aiming upwards is exposed from two forces at the critical moment when it is to be impregnated, namely the upward buoyancy force and the restraining surface tension force. Conversely, a drop of liquid is also being affected, which is being laced and falling downwards. Consequently, if the channels in the pulp are less than the radius of the critical gas bubbles and droplets, the stirring of the liquid is inhibited.

Gravity F = 7Γ r³ . (liquid) - 5g^as) · 8

Surface tension force Fy = o ** · 2ZTr

At the critical minimum bubble or drip radius = Fy

The critical minimum bubble or droplet radius, r r which determines the desired, lowest sealing degree, is thus:

... ................ (2) (J&gt; liquid gas). g radius σ '= surface tension liquid - gas Q = density g = gravity acceleration

Thus, the sealing degree should be such that the minimum width of the channels between the metal particles does not exceed double critical radius

The following applies to r = bubble

(c) The gas pressure P at the bottom of the vessel shall be higher than the hydrostatic pressure of the liquid but lower than the hydrostatic pressure of the entire overlying mass. Otherwise, gas seeks up through the pulp from underlying lots. This gives the expression:

^Patm ⁺ "liquid" ^{ε (h}l ^{+ h}2&gt; &lt; ^Pgas^&lt;' ^Patm ⁺ - ^ mass ® '^ 2 ⁺ ^ liquid '® ^ 1 .............

where h ^ = the height of the liquid column accumulated on the surface and - the height of the liquid soaked pulp.

By combining condition (3) with equation (1), the maximum separation rate can be calculated.

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An object of the present invention is to further increase the maximum separation rate. According to the invention, this is done by increasing the gas pressure gradient in the vertical in the mass by amplifying the difference between the gas pressure Pg_as in the lower part of the pulp and the pressure on the solid phase in the upper surface of the pulp in addition to what is achieved by the heating. This can be achieved by applying an external pressure P 2 to the solid phase from above, for example by pressing a screen which is permeable to the liquid but not to the solid phase against the solid phase. Another way is ζ '*' vacuum suction on the top of the container, ie vacuum suction from the container space over the surface of the pulp. Both of these options can also be combined. Equation (3) can thus be extended according to (4):

P, +. g (h. + h_) P^&lt; P + P, + $ - gh + vacuum needed ^island 1 2 gas y vacuum mass 2 'liquid' S^hrsl

By either or both of these measures, the pressure difference between the gas pressure P in the evaporative zone in the lower part of the pulp and the pressure on the solid phase on the surface of the pulp increases. At the same time, the steaming temperature is affected in a favorable direction.

The invention will now be explained in more detail by describing a preferred embodiment with reference to the accompanying drawings, which schematically illustrate the principles of the invention. The figures show

Fig. 1 shows a container containing a liquid-containing mass from which the liquid phase is being separated from the solid phase, and

Fig. 2 pressure conditions in the container according to the invention and under normal conditions respectively.

Referring first to Fig. 1, a container is generally designated by the numeral 1. The container 1 may, for example, consist of a plate drum tightly sealed with a lid 2. In the container 1, a mass 3 of a particulate solid soaked in a liquid is stored. The solid material may, for example, consist of abrasive chips, metal oxides in the form of dust from flue gas purification plants, or metal compounds from bed bath residues. The liquid phase may consist, for example, of cutting oil, oil emulsion, water or pickle acid, or of mixtures of different liquids. In the illustrated situation, the liquid has been separated from the lower portions of the pulp in the container. The lower, drier part, which mainly 40 consists of comparatively dry powder, has been designated 4.

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Between the dry part 4 and the liquid soaked mass 3 there is a vaporization zone 5 formed by the contents of the container being heated from below by a number of oil burners 6. Other heating methods are also possible, such as, for example, heating with gas burners, whereby gases obtained during the process can be practically possible. is used during heating. Waste heat from other processes can also be utilized, as well as electric heating. The number 7 denotes a duct for the discharge of combustible gas from the container 1. The duct 7 is connected to an air pump 8 for providing a negative pressure in the container in the space 9 above the mass 3.

In order to increase the pressure on the solid phase in the pulp 3, i.e. on the amount of solid particles in the pulp, a piston 10 is provided which can be pressed down against the pulp 3 by means of a rod 11 which is sealedly stored in the lid 2. The pressing of the piston 10 to the pulp 3 takes place via a screen cloth 12 which can pass through liquid from the pulp 3 which is substantially impervious to the solid particles in the pulp 3. The liquid filtered through the screen cloth 12 continues to pass through openings 13 in the piston 10 and accumulates as an increasingly separated amount of liquid 14. The amount of liquid 14 is sucked out of the container 1 by replacing the conduit 7 with a liquid suction line, after the vacuum pump 8 has been disconnected. Alternatively, drainage can be effected under vacuum by means of a special liquid suction device. It is also possible to remove the amount of liquid 14 as a final operation after completion of separation of the liquid from the solid phase in the container.

Gradually, the evaporation zone 5 will migrate upwards in the pulp 3. Fig. 1 thus illustrates the situation picture when approximately half the amount of the pulp in the container has been processed. The pressure conditions in the container are schematically illustrated in the diagram in Fig. 2. The solid line thus illustrates the conditions according to the invention, where a pressure difference exists between the pressure in the dry part 4 of the pulp in the container and the gas pressure on the surface of the pulp. The dotted line in the diagram of Fig. 2 illustrates corresponding conditions in case the pressure in the space 9 in the upper part of the container 1 corresponds to atmospheric pressure and the piston 10 is not pressed against the mass 3. The pressure difference A p the pressure difference ^ p £. The process according to the invention can also be combined with continuous supply of new pulp to the upper part of the container and continuous removal of separated liquid and dried material, whereby the level of the evaporation zone is kept substantially constant in the room.

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