DE4224648A1 - Dewatering of liq.-solid mixtures using pressure and heat - by forming vapour phase above mixt. and forcing filtrate through underlying filter surface in mainly liq. form - Google Patents

Abstract

In a new procedure for de-watering a liq./solid mixt. (5) which is resting on a filter medium surface (2), the mixt. is heated and pressed at the same time. The feature is that heat and the pressure are applied in such a way that a vapour phase (8) is formed, and under the effect of the pressure of this vapour, combined with the pressing pressure, the greater part of the mixt. is forced through the filter medium in a liq. form. Also claimed is an appts. for carrying out this procedure, in which a device (7) serves to simultaneously heat the mixture to a suitable temp. for the formation of a vapour phase and to exert a pressing pressure on the mixt.. USE/ADVANTAGE - Used in de-watering liq./solid mixtures. Filtrate is recovered in liq. form and does not need to undergo a subsequent liq./gas sepn. process; a higher degree of de-watering is achieved in a shorter time and energy consumption is reduced.

Description

The invention relates to a method for dehumidifying a solid applied to a filter medium / Liquid mixture, the mixture being heated and is pressed simultaneously, and a device for Application of this procedure.

Methods and devices of this type are used, for. B. for Drainage of filtered filter cake, bulk goods, piles or sludges, or also from already partially dewatered fiber suspensions, e.g. B.  in the press section of a paper machine. The Drainage can be done in batches, cycles or done continuously.

Such a method is e.g. B. from EP-A-2 63 197 known. Dewatering and drying take place here of mixtures of liquids and disper therein giert solid particles by simultaneous Kompri Mation and action of the pressure of the steam, which in the Inside of the material to be dewatered is generated. Here, the liquid phase and the gas phase together under vacuum through porous partitions sucked in and separated from the solid phase.

The disadvantage of this method is that there are none forms even dehumidification front, so that with increasing dehumidification of the filter cake Gas throughput increases due to gas breakthroughs, which through cracking and increasing porosity of the Filter cake is favored. An essential part of the The liquid phase becomes with considerable energy consumption evaporates and expelled as a gas phase. Out economic reasons must therefore be achieved dehumidification at a certain gas flow rate be canceled. Although with this known Process the dehumidification energy balance already is better than with older procedures that only working through gas flow is dewatering performance by no means optimal.

From DE-A-38 29 936 is a method for Dehumidification of a filter cake through gas throughput  known in which the filter cake under reduction its porosity is compressed so that a predetermined gas passage through the filter cake is not exceeded. This previously known method however, requires a lot of energy. The The dehumidification process takes a long time Claim, and the residual moisture cannot be arbitrarily small be made.

The object of the invention is the above led to avoid disadvantages of the prior art and in particular a method and an apparatus of the to improve the type specified in such a way that a better degree of dehumidification of a solid / liquid mixture with less energy consumption in shorter time is possible.

In the method according to the invention, this task solved in that the heating and the pressing pressure vorgenonmen of the solid / liquid mixture is that a vapor phase is formed from this, by their vapor pressure and the pressure exerted at the same time Press pressure the liquid phase of the mixture at least for the most part in liquid form through the Filter medium is expelled.

The heating and compression of the Mixture and thus the formation of the vapor phase by means of one on the side opposite the filter medium of the mixture provided heatable pressure surface.  

The invention apparently only makes up to now insufficiently taken into account knowledge that instead of using the liquid phase energy intensive gas throughput or evaporation improved dehumidification can be achieved that only on the opposite of the filter medium A vapor phase is generated by the heating, which forms a closed dehumidification front, which removes the liquid phase from the filter cake in the manner of of a liquid plug towards the Drives filter medium into the filtrate space. While this vapor pressure dehumidification becomes gas breakthroughs through the filter cake due to cracking and Shrinkage of the cake due to compression as a result mechanical repressing of the filter cake largely prevented so that essentially or at least predominantly the liquid phase through the filter medium passes through and only a small portion evaporates and is expelled in gaseous form. This can essential lower residual moisture levels with significantly less energy consumption within shorter times can be achieved. To air or gas as a Ver pressure medium has steam in cooperation with the mechanical pressure the advantage that the steam with the liquid phase is in equilibrium and so can form an efficient crowding-out front.

To prevent the steam from escaping sideways, it is advantageous to insert the filter cake laterally close, so that the vapor phase only in the direction can spread to the filter medium. This can be done through the Chamber walls or the frame of the filter press,  or in the case of continuous filters by the other Edges of heat-insulated filter cake itself.

The method according to the invention can be used with advantage in suitably modified plate filter presses, Membrane filter presses, in chamber and frame filters press, in press filter machines, in vacuum belt filters, in vacuum / pressure drum filters, in belt presses, or apply the like.

The invention is based on the Darge in the figures provided embodiments of devices for Dehumidification of solid / liquid mixtures closer explained. Show it:

Fig. 1a-d four variants of plane filters,

Fig. 2 is a drum filter,

Fig. 3 shows a variant of a drum filter,

Fig. 4 is a quasi-continuous band filter,

Fig. 5 is a continuous vacuum belt filter,

FIGS. 6a and b show two variants rubber band in cross section,

Fig. 7 a belt press, and

Fig. 8 is a press belt filter.

The plan filter shown in Fig. 1a for batchwise dewatering of a suspension consists of a housing 1 , on the lower part of which a filter medium 2 is provided. The filtrate collecting space 3 with a filtrate outlet 4 is located below it. The suspension 5 to be dewatered is filled into the housing 1 . Part of the liquid phase is first driven through the filter medium 2 into the filtrate space 3 under its own weight or by means of a vacuum. A partially dehumidified filter cake is formed on the filter medium 2 . Then a press plate 6 with a lower pressure surface 7 is placed on top of the suspension 5 in the housing 1 . By exerting a certain pressing force, a further part of the liquid phase is pressed out of the suspension 5 through the filter medium 2 . For further dehumidification, the press plate 6 is heated to such a temperature with a suitable heating device that a thin vapor layer 8 forms on the pressure surface 7 from the liquid phase of the suspension. This vapor layer 8 now exerts a pressure on the filter cake 9 lying thereunder, which still contains the liquid portion as a liquid phase. The pressure in the vapor phase is increased until the substance-specific capillary pressure of the filter cake is reached. In this way, a further part of the liquid phase is expelled from the filter cake 9 through the filter medium 2 into the filtrate 3 . With increasing drainage, the pressing force exerted on the pressure plate 6 is continuously increased, in such a way that the filter cake 5 is compressed so that no capillaries or cracks can arise in the still liquid part 9 of the filter cake, through which the vapor phase 8 towards the filter medium 3 could break through. The liquid phase is now pushed through the filter medium by the vapor pressure along a dehumidification front 10 between the vapor phase 8 and the liquid phase 9 as a largely closed plug. Formation of capillaries or cracks is prevented by pressing the heating surface. Until the dehumidification front 10 has reached the filter medium 2 , up to 80% of the liquid can generally be squeezed out with this combined vapor pressure / compression drainage, without an excessive amount of energy being required to evaporate the liquid.

Dehumidification time, heating output, Press pressure history and time controlled or so regulated that optimal dehumidification with minimal Energy expenditure is achieved. For example, the Operation to be stopped when the steam flow is on unwanted dimension exceeds. Only that one remaining liquid can pass through if necessary further heating evaporated and from the filter cake be removed if this is not in a post following dryer happens.

Compared to previously known processes in which the Dehumidification through gas flow, d. H. Blow out or by evaporation of the liquid can be done by the use of a combined vapor pressure / Press drainage with a closed uniform dehumidification front between the  Liquid phase on the filter medium and the vapor phase on the heated pressure surface with significantly less Energy consumption very low residual liquid contents be achieved efficiently.

Figure 1b -. 1d show further variants of plate and membrane filter presses.

The plate packs of the filter presses will alternate way by heating and filter elements H, F gebil det. The solid / liquid mixture is in the Pump chambers C pumped. The pump pressure will Partial dewatered solid / liquid mixture. When a certain pump pressure is reached, the Feed into the filter chambers interrupted. Both The pre-drainage can also be used for membrane filter plates Lich also done by repressing the membranes.

In the plate filter press according to Fig. 1b, the steam pressure drainage is made possible by heating the plate H. During this process, the volume of the filter chamber C is reduced by pressing the plate packs. The bendable side edge seals S adapt. The liquid is pressed through the porous filter medium F and collected.

In the Menbranfilterpesse of FIG. 1c is carried out heating of the solid / liquid mixture through one of the membrane filter plate M opposing heating plate H. During the heating of the volume of the filter chamber C is reduced by repressing the membrane M. The liquid is pressed through the filter medium F attached to the membrane M and collected.

In the membrane filter press according to FIG. 1d, the solid / liquid mixture is heated by a heat transfer fluid in the membranes M. During the heating, the volume of the filter chamber C is also reduced by repressing the membrane M. The liquid is pressed through the porous filter medium F opposite the membrane heating plate M and collected.

Washing can also be carried out in all filter presses, the device shown in FIG. 1d being best suited.

The after the liquid caused by the vapor pressure displacement process in the solid still ver permanent liquid can be suitably, e.g. B. be separated under vacuum.

Described using simple flat filter presses bene procedure can be advantageous in conclusion dampening of an already formed, filtered Filter cake in continuous or cyclical working automatic filter presses of various Apply kind.

In Fig. 2, a drum filter is shown, which has a rotating filter drum 11 , which with a filter medium, for. B. is covered with a filter cloth. The interior 12 of the filter drum 11 forms the filtrate space, which is advantageously at a lower pressure than the exterior for suctioning off the filtrate. For example, the outside space can be under positive pressure, the filtrate space under atmospheric pressure or negative pressure, or the outside space can be under atmospheric pressure while there is a negative pressure in the interior 12 .

The suspension to be dehumidified is placed in a task zone 13 on the outer circumference of the filter drum 11 . The continuous rotation of the filter drum 11 results in a continuous dehumidification of the suspension applied, so that a partially dehumidified filter cake is formed there. In a closing zone 14 , this filter cake can be washed to wash out contaminants therefrom. This is followed by an intermediate dehumidification zone 15 in which the filtered filter cake can be further dehumidified.

This pre-dehumidified filter cake reaches in the lower part of the drum filter between the filter drum 11 and a steel belt 17 rotating over deflection rollers 16 . In the entrance area 18 of the steel belt 17 , the filter cake is first further dehumidified by mechanical compression, as a result of which the pore space between the solid particles is reduced. In the adjacent zone 19 , the steel strip 17 is heated. The steel strip 17 can be heated electrically, by means of gas flames, inductively or in another suitable manner. The pressure of the steel belt 17 on the filter drum 11 can be increased continuously by appropriately adjusting the deflection rollers 16 from the input zone 18 to the end zone 19 . The effect of the heating of the steel belt 17 and the increase of the contact pressure is the same as in the previous example, ie a vapor phase forms on the steel belt 17 in the dehumidification zone 19 , while on the drum filter 11 the filter cake is still in the liquid phase, whereby a largely closed dehumidification front forms between the vapor phase and the liquid phase. Due to the steadily increasing pressure of the steel belt 17 on the filter drum 11 it is achieved that almost no pores or cracks can form in the filter cake, through which the vapor phase can break through. An extremely energy-efficient dehumidification of the filter cake is also achieved here. After leaving the press zone 19 , the now largely dry filter cake reaches the take-off zone 20 , where the solids content is sucked off with a suitable suction device 21 .

It can be advantageous if the filter cake in the removal zone 20 has a certain residual moisture and residual cohesion directly on the filter medium 11 . As a rule, this still somewhat moist area of the filter cake contains the concentrated impurities, which can be removed from the filter drum 11 by a removal knife 22 .

In the variant of a drum filter shown in FIG. 3, the suspension task takes place instead by immersion in a tub 23 filled with suspension. Here too, the relative negative pressure inside the drum results in a preliminary drainage 24 , a wash 25 and an intermediate drainage 26 before the filtered filter cake reaches the area between the heated belt 27 and the filter drum 28 . The dewatering process is essentially analogous to that in the previous example, and the dehumidified solid is removed with the suction device 29 .

The dehumidification method according to the invention can also be applied to a bandpass filter, as shown in FIG. 4. Here, an endless filter band 30 moves over pulleys 31 , 32 clockwise or step by step over a filter zone 33 . The stepwise movement of the belt 30 is brought about by a suitably controlled movement of part of the deflection rollers 32 . In an inlet zone 33 of the filtration zone, the suspension to be dehumidified is applied to the belt 30 and pre-dewatered with the aid of a vacuum suction box 34 . In the following step 35 , washing takes place, again a part of the filtrate being sucked off by a suction device 36 . Furthermore, a step 37 for intermediate dehumidification of the filter cake is provided, the filtrate again being sucked off with a suction device 38 , finally the filtered filter cake reaches the pressing zone 39 in the last step, where a heated punch 40 is intermittently placed under pressure on the filter cake, whereby again the heating takes place in such a way that a thin vapor phase is formed on the pressure surface of the stamp 40 , which expels the liquid phase in a largely closed dehumidification front during the step duration. The dehumidified solid 41 is removed after the last deflection roller. In this way, a quasi-continuous dehumidification of a suspension can be achieved with little energy to a low residual moisture.

By means of the band filter shown in Fig. 5, a continuous dehumidification of a solid / liquid mixture, for. B. a sediment sludge, a sewage sludge or the like. The suspension to be dehumidified is placed at the feed point 42 on an endlessly circulating filter belt 43 . The filter belt 43 may e.g. B. consist of plastic or metal. The applied solid / liquid mixture or the suspension to be dehumidified settles on the filter belt 43 in the entrance zone 44 and is washed in a multi-stage countercurrent washing device 45 . The Waschein device 45 is followed by an intermediate dehumidification zone 46 , in which the suspension is further dehumidified due to a pressure difference between the outer space and the inner filtrate space 47 . In the following dehumidification zone 48 , a steel belt 49 running parallel to the filter belt 43 is arranged, which runs at the same speed as the filter belt 43 . The steel belt 49 is heated by a Heizeinrich device 50 . The steel belt 49 is pretensioned so that it presses in the running direction with increasing pressure on the filter cake between the steel belt 49 and the filter belt 43 . Here, too, a gas phase is formed on the underside of the steel belt 49 by the combined temperature and pressure treatment of the filter cake between the steel belt 49 and the filter belt 43 , which presses the liquid phase along a closed dehumidification front through the filter belt 43 . The largely dewatered solid is removed by a removal device 51 after leaving the pressing zone 48 . The remaining on the belt filter 53 Verun cleanings are washed off by a following washing device 52 .

It is with the band filters described above important to prevent the steam from escaping at the edges of the To prevent tape. To do this, the filter cake be enclosed laterally so that the Spread the vapor phase only in the direction of the filter medium can.

Fig. 6a shows a suitable belt 53 in cross section, which is provided with edges 54 or side support belts, through which a trough is formed which receives the press belt 55 with little play.

As shown in Fig. 6b, the band 56 can also be pulled up on the edges 57 so far that it includes the filter cake 59 together with the heated press band 58 .

Another option is to edge the Thermally isolate tape so that on the edges no steam is formed, but only on average area of the tape. The liquid phase of the Filter cake itself as a seal.  

The method according to the invention can also be used in the screen belt press shown in FIG. 7. In such a belt press, a top wire 60 cooperates with a bottom wire 61 and dewatered together in the contact zone between the two wire belts a registered broke tes solid / liquid mixture. This mixture is applied to the top wire in a feed zone 62 and dewatered in a screen zone 63 before it reaches the wedge zone 64 between the two screens 60 and 61 . In the following press zone 65 , the suspension is pre-dewatered under the action of pressure. Then the pre-dewatered filter cake passes into the area of a heated press roll 66 , where in the area of the lower sieve 61 a gas phase is formed by the heated press roll 66 , which presses the liquid phase of the filter cake through the top sieve 60 , so that the filter cake follows in the shear zone 67 is already largely dehumidified before it is thrown off at the separation point 68 by the top wire and the bottom wire.

The method according to the invention can also be applied to the press belt filter shown in FIG. 8. The mixture to be dehumidified is introduced at a feed point 70 between two synchronously running sieve and press belts 71 , 75 on the top and 72 , 76 on the bottom. The belts are surrounded on the back by press fluid cushions 72 and 73 , through which a pressing force is exerted on the suspension or the filter cake between the belts. The filter cake is heated on one side, for example by supplying and controlling the upper space 73 of the press fluid separately from the lower fluid space 74 , and heating it separately. Here, too, a gas phase is formed on one of the belts 75 , while the liquid phase of the filter cake is largely retained on the other belt 76 , so that the liquid phase is expelled in a closed front through the corresponding filter belt.

The method according to the invention is not based on the described applications limited, d. H. on the Dehumidification or dewatering of a filter cake, but can be used with analog advantages for the Dehumidification of solid / liquid mixtures, Suspensions and fillings in general, i. H. With various solids, e.g. B. bulk goods, heap plants or fiber suspensions, and difference use liquids. Even with membrane filters the application of the method is advantageous, the heating with one of the membrane opposite lying heating surface or by heating the membrane yourself can be done.

Claims (15)

1. A method for dehumidifying a solid / liquid mixture ( 5 ) applied to a filter medium ( 2 , 11 , 28 , 43 , 61 , 71 , F), the mixture ( 5 ) being heated and at the same time pressed, characterized in that the heating and the pressing pressure of the solid / liquid mixture ( 5 ) is carried out in such a way that a vapor phase ( 8 ) is formed therefrom, the vapor phase and the simultaneously applied pressing pressure at least for the most part in the liquid phase ( 9 ) of the mixture in liquid Form is expelled through the filter medium ( 2 ). 2. The method according to claim 1, characterized in that the vapor phase ( 8 ) in the solid / liquid mixture ( 5 ) on the filter medium ( 2 , F) opposite side (H) of the mixture ( 5 ) is formed. 3. The method according to claim 2, characterized in that the vapor phase ( 8 ) on a heatable pressure surface ( 7 ) on the filter medium ( 2 , F) opposite side (H) of the mixture ( 5 ) is formed. 4. The method according to claim 2 or 3, characterized in that during the formation of the vapor phase ( 8 ), the vapor formation at the lateral edges ( 54 , 57 , S) of the mixture ( 5 ) is prevented. 5. The method according to any one of claims 1-4, characterized in that during the expulsion of the liquid phase ( 9 ) by the gas phase ( 8 ) the pressing pressure on the solid / liquid mixture ( 5 ) is continuously increased. 6. The method according to any one of claims 1-5, characterized in that the liquid phase ( 9 ) is suctioned off under vacuum. 7. Apparatus for applying the method for dehumidifying a solid / liquid mixture ( 5 ) applied to a filter medium ( 2 , 11 , 28 , 49 , 61 , 71 , F) according to one of claims 1-6, characterized in that on of the filter medium (2) opposite side (H) means (6, 17, 27, 40, 49, 66, 73) for simultaneous heating of the mixture (15) to an amount sufficient to form a gas phase temperature and to exercise a pressing pressure on the mixture ( 5 ) is provided. 8. The device according to claim 7, characterized in that the device ( 6 ) for the simultaneous heating and application of pressure is designed as a press ram ( 6 , 40 ) with heatable pressure surface. 9. The device according to claim 8, characterized in that the filter medium ( 30 ) is a cyclically moving belt ( 30 ), and that the press ram ( 40 ) during the idle times of the belt ( 30 ) heats and compresses the mixture ( 5 ). 10.The device according to claim 7, characterized in that the filter medium has a continuously circumferential surface, in particular a drum ( 11 , 28 ) or a belt ( 43 , 61 , 72 ), and that the device for simultaneous heating and pressure application synchronously with it Moving surface, in particular a heatable press belt ( 17 , 27 , 49 , 71 ). 11. The device according to claim 10, characterized in that the filter medium and the device for heating and exerting pressure each have a synchronously running sieve belt ( 60 , 61 , 71 , 72 ), one of the sieve belts having a heatable press device ( 66 , 73 ) acts. 12. Application of the method according to one of the claims 1 - 6 for dehumidifying a filter cake. 13. Application of the method according to one of the claims 1 - 6 for dehumidifying bulk goods or piles works. 14. Application of the method according to one of the claims 1 - 6 for dehumidifying a fiber suspension. 15. Use of the device according to claim 10 or 11 in the drainage section of a paper machine.