A FILTRATION APPARATUS

Abstract: The filtration apparatus of the invention is of the type having one or more of upright tubular filter elements with the surface coated with a pre-coat layer of a filter aid through which a liquid is filtered. Different from conventional apparatuses, the filter element in the inventive apparatus is provided with a gas exhaust tube or liquid drain tube connected to the upper or lower part of the element. By virtue of this means, the liquid used for forming the pre-coat layer as the suspension medium can be completely discharged out of the apparatus prior to intro­ duction of the liquid to be filtered so that the liquid in the apparatus can be switched from the pre-coat forming liquid to the filtered liquid without producing a mixture thereof causing no defects in the pre-coat layer.

Description: BACKGROUND OF THE INVENTION The present invention relates to a filtration apparatus or, more particularly, to an improvement of a filtration apparatus in which a so-called pre-coat layer of a filter aid is formed on the surface of a filter element or filter medium and the liquid is filtered through the thus formed pre-coat layer. Filtration apparatuses of this type are widely used in the manufacturing process of alcoholic drinks such as beer, wine, Japanese sake and the like, seasonings such as soy sauce, vinegar, sugar, cooking oil and the like, other beverages such as fruit-based drinks, carbonated drinks, mineral water, Oolong tea and the like, pharmaceuticals and so on. As is known, a type of filtration procedures utilizes a pre-coat layer which is formed of a filter aid such as diatomaceous earth, perlite, cellulosic powder, active carbon and the like on the surface of filter elements in a substantial thickness and through which the liquid is filtered. The most conventional material as the filter element, on which the pre-coat layer is formed, includes filter cloth, filter net, filter paper and the like although several more rigid materials are sometimes used including punched metal tubes spirally wound with a wire, corrugated rectangular tubes (or tubes having an undulate polygonal cross section) spirally wound with a wire, ceramic-made cylindrical elements and so on. Different types of the filter elements may be used either alone or as a combination of two types or more. Various types of filtration apparatuses utilize one or more of cylindrical or polygonally tubular filter elements provided with a pre-coat layer in an upright disposition. These filtration apparatuses are classified into two classes depending on the position at which the filtrate is taken out of the filter element. Namely, the filtrate may be discharged at an upper part or at a lower part of the filter element. A problem in each of these filtration apparatuses is that, since the pre-coat layer is formed on a vertical surface at any rate, the pre-coat layer sometimes falls off the surface of the filter element not only in the course of the works for the formation of the pre-coat layer of a filter aid but also during the filtering works through the thus formed pre-coat layer, especially, when the liquid flow through the pre-coat layer is interrupted. In connection with the works for forming the pre-coat layer of a filter aid on the surface of a filter element, it is a possible way that the dispersion of the filter aid, from which the filter aid should be deposited to form the pre-coat layer on the surface of the filter element, is prepared by use of a liquid which is the liquid to be filtered therethrough. This method, in which the filter element and the filter aid are contacted from the very beginning by the liquid to be filtered, sometimes causes problems when the amount of certain soluble materials dis­ solved out from the filter aid and entering the filtrate must be limited or when microbiological contamination of the filtration system must be avoided. It is a usual practice in such cases that the pre-coat layer is formed using a dispersion of the filter aid in a liquid which is not the same one as the liquid to be filtered, such as cold or hot water, and thereafter the liquid passing through the pre-­ coat layer is gradually switched to the liquid to be filtered without interrupting the liquid flow therethrough. When a process of filtration is started with formation of a pre-coat layer in the above described manner, it is an unavoidable consequence that a considerably large portion of the liquid coming out of the filter element in the course of the above mentioned liquid switching is a mixture of the first liquid used as the dispersing medium of the filter aid to form the pre-coat layer and the second liquid which is the liquid to be subjected to the filtration treatment. Such a fraction of liquid mixture naturally contains the desired filtrate constituent only in a low concentration so that it is discarded as a waste or stored in a separate reservoir from which it is returned bit by bit to the preceding step of the process. The above mentioned way of discarding the transitive filtrate is undesirable when the filtered liquid is very expensive or when certain detriment is anticipated by dis­ carding the liquid while the alternative way of collecting the transitive filtrate in a separate reservoir before disposal or recycling is economically disadvantageous in respect of the investment for the facilities and consumption of large manpower and time. In order to solve the above mentioned problem concerning the transitive filtrate which is a mixture of the liquid used for pre-coat forming and the liquid to be filtered, a method has been proposed in which the space inside the filter apparatus is pressurized with a gas such as air, carbon dioxide and the like after completion of formation of the pre-coat layer on the surface of the filter element so as to discharge the liquid used for pre-coat forming. This method also cannot provide a complete solution of the problem. For example, the pre-coat layer may fall off the surface of the filter element partly or wholly during the discharge of the liquid under pressurization or in the course of filling the filter element with the liquid to be filtered therethrough and tiny holes are sometimes formed in the pre-coat layer so that it is a difficult matter to keep the pre-coat layer in a complete defect-free condition. This problem is particularly serious in a filtration apparatus of the type in which the filtrate is taken out of the apparatus at an upper part thereof. SUMMARY OF THE INVENTION Accordingly, the present invention has an object to provide a filtration apparatus in which the liquid is filtered through a pre-coat layer formed on the surface of a filter element without the problem by the transitive filtrate which is a mixture of the liquid used in the formation of the pre-coat layer and the liquid to be filtered. Thus, the apparatus of the present invention is, ac­ cording to the first embodiment thereof, a filtration apparatus comprising a tubular filter element installed in an upright disposition having a surface on which a pre-coat layer of a filter aid is formed to filter a liquid there­ through, a gas exhaust tube being connected to the upright tubular filter element at the upper part thereof. Further, the apparatus of the present invention is, according to the second embodiment thereof, a filtration apparatus comprising a tubular filter element installed in an upright disposition having a surface on which a pre-coat layer of a filter aid is formed to filter a liquid there­ through, a liquid drain tube being connected to the upright tubular filter element at the lower part thereof. BRIEF DESCRIPTION OF THE DRAWING FIGURE l is an illustration of a flow sheet of a filtration system having a filtration apparatus according to the first embodiment of the invention built therein. FIGURE 2 schematically illustrates an axial cross sectional view of a filtration apparatus according to the first embodiment of the invention. FIGURES 3a and 3b are each a detailed illustration of a part of the filtration apparatus illustrated in FIGURE 2 showing the conjunction of the gas exhaust tube and the filter element. FIGURE 4 is an illustration of a flow sheet of a filtration system having a filtration apparatus according to the second embodiment of the invention built therein. FIGURE 5 schematically illustrates an axial cross sectional view of a filtration apparatus according to the second embodiment of the invention. FIGURE 6 is a detailed illustration of a part of the filtration apparatus illustrated in FIGURE 5 showing the conjunction of the liquid drain tube and the filter element. FIGURE 7 is a detailed illustration of a part correspond­ ing to FIGURE 6 of a filter element formed by spirally winding a wire around a tube of a punched metal or a corrugated rectangular tube showing the conjunction of the liquid drain tube and the filter element. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, the filtration apparatus of the present invention is described in more detail with reference to the accompanying drawing. In FIGURE l which is an illustration of a flow sheet of a filtration system having a filtration apparatus according to the first embodiment of the invention, the filtration apparatus l has a plural number of tubular filter elements 2 each having a circular or polygonal cross section in an upright disposition inside thereof. The upper ends of these filter elements 2 are connected to a gas exhaust tube 3 opening to the atmospheric air through a valve lle. The liquid to be filtered is introduced into the filtration apparatus l from the liquid feed line 4 through the valve llc by means of a pump l0. The pre-coat slurry contained in the pre-coat tank 9 is introduced into the filtration apparatus l through the valves llb and llc also by means of the pump l0. The filtrate coming out of the filter elements 2 is discharged through the filtrate discharge tube 5 while the liquid drain line 6 with a valve lld serves to empty the filtration apparatus l. The filtration apparatus l can be pressurized with a gas through the gas feed line 7 by opening the valve llf and the pressurizing gas can be released to the ambient atmosphere through the primary gas vent tube 8 by opening the valve llg. The system has several more valves lla, llh, lli, and llj. FIGURE 2 schematically illustrates an axial cross sectional view of another model of the filtration apparatus l and the reference numerals 2, 3 and 5 each correspond to the respective part 2, 3 or 5 in FIGURE l. Each of the filter elements 2 has an upper and a lower end member l2a and l2b by which it is held inside the housing of the filtra­ tion apparatus l provided with a pair of flanges l3 at which the covering can be disassempled from the body of the apparatus l. In the apparatus illustrated in FIGURE 2, each of the filter elements 2 is composed of three unit members made of a ceramic material in a tandem arrangement by fastening with the upper and lower end members l2a and l2b. FIGURES 3a and 3b are each a detailed illustration of a part of the apparatus shown in FIGURE 2 to demonstrate the conjunction of the gas exhaust tube 3 having a gas outlet opening 3a or 3b, respectively, to the filter element 2 by means of a spindle l4 for positioning of the filter element 2, a spring l5 and a nut l6. In FIGURE 4 which is an illustration of a flow sheet of a filtration system having a filtration apparatus according to the second embodiment of the invention, the filtration apparatus l has a plural number of tubular filter elements 2 each having a circular or polygonal cross section in an upright disposition inside thereof. The lower ends of these filter elements 2 are connected to a liquid drain tube 3′ opening to the atmospheric air through a valve lle. The liquid to be filtered is introduced into the filtration apparatus l from the liquid feed line 4 through the valve llc by means of a pump l0. The pre-coat slurry contained in the pre-coat tank 9 is introduced into the filtration apparatus l through the valves llb and llc also by means of the pump l0. The filtrate coming out of the filter elements 2 is discharged through the filtrate discharge tube 5 while the liquid drain line 6 with a valve lld serves to empty the filtration apparatus l. The filtration apparatus l can be pressurized with a gas through the gas feed line 7 by opening the valve llf and the pressurizing gas can be released to the ambient atmosphere through the gas vent tube 8′ by opening the valve llg. The system has several more valves lla, llh, lli and llj. FIGURE 5 schematically illustrates an axial cross sectional view of another model of the filtration apparatus l according to the second embodiment of the invention. The reference numerals 2, 3′ and 5 each correspond to the respective part 2, 3′ or 5 in FIGURE 4. Each of the filter elements 2 has an upper and a lower end member l2a and l2b by which it is held inside the housing of the filtration apparatus l provided with a pair of flanges l3 at which the conical bottom member of the housing can be disassembled from the body of the apparatus l. Each of the filter elements 2 is a cylinder made of a ceramic material and held inside the housing of the apparatus l by means of the upper and lower end members l2a and l2b. FIGURE 6 is a detailed illustration of a part of the apparatus shown in FIGURE 5 to demonstrate the conjunction of the liquid drain tube 3′ having an opening 3′a by means of a spindle l4 for positioning of the filter element 2 and a nut l6. FIGURE 7 is a detailed illustration of a part corresponding to FIGURE 6 of a filter element formed by spirally winding a wire around a tube of a puched metal tube or a corrugated rectangular tube showing the conjunction of the liquid drain tube 3′ with a liquid drain opening 3′b and the filter element 2. Usable filter element in the inventive filtration ap­ paratus includes a variety of known tubular ones having a circular or polygonal cross section without particular limitations. Particularly preferable filter elements are ceramic-made cylindrical elements, those formed by spirally winding a wire around a punched metal tube or a corrugated rectangular. Dimensions of the filter elements such as height, wall thickness, inner diameter and the like as well as the number of the filter elements uprightly installed in the filtration apparatus of the invention are not limitative and can be suitably selected to comply with the intended filtration process. When the filtration apparatus has a plurality of the filter elements, each of the filter elements may be connected to a gas exhaust tube or liquid drain tube through a gas exhaust opening or liquid drain opening independently from the other filter elements. Alternatively, it is preferable that each of the filter elements is con­ nected at the gas exhaust or liquid drain opening to one end of a separate gas exhaust tube or liquid drain tube while the other ends of the gas exhaust tubes or liquid drain tubes are combined in a single collecting pipe through which the gas or liquid is discharged. The inner diameter of the gas exhaust opening or liquid drain opening may be sufficient when an appropriate volume of the gas or liquid can be taken out of the filter element by pressurizing or filling the filtration apparatus with the gas or liquid. According to the results of the ex­ periments undertaken by the inventors, the gas exhaust opening should preferably have an inner diameter in the range from one fifteenth to one third of the inner diameter of the filter element while the liquid drain opening should preferably have an inner diameter which is not larger than the inner diameter of the filter element but not smaller than one twentieth of the inner diameter of the filter element. When the inner diameter of the gas exhaust opening or the liquid drain opening is outside the above mentioned respective range, the gas exhaustion or liquid drain cannot be achieved with an efficiency as high as desired. The inner diameter of the gas exhaust tube or liquid drain tube adequately selected in consideration of the cross sectional area of the gas exhaust opening or the liquid drain opening, the number of the filter elements in the filtration apparatus and other parameters. The gas exhaust tube or liquid drain tube should be made preferably of a stainless steel in most cases although the material may be selected depending on the particularly intended filtration process in which the inventive filtration apparatus is used. As is described above in detail, the most characteristic feature of the invention consists in the gas exhaust tube or liquid drain tube connected to the filter element at the upper part or lower part, respectively, thereof to give a possibility of filling the filtration apparatus with the liquid to be filtered or discharging the liquid for pre-coat forming keeping the once formed pre-coat layer in a defect-­ free condition. Namely, the procedures of forming of the pre-coat layer, discharging of the liquid for pre-coat forming, interruption of the liquid flow and filling of the filtra­ tion apparatus with the liquid to be filtered can be performed without the problem of falling of the pre-coat layer. Thus, the filtration process using the inventive filtration apparatus can be performed without the disadvantage due to the mixture of the liquid for pre-coat forming and the liquid to be filtered otherwise unavoidable in the transitive stage. This is because, in the inventive filtration apparatus, different from conventional filtration apparatuses utilizing a pre-coat layer, formation of the pre-coat layer can be directly followed by complete discharge of the liquid used for the formation of the pre-coat layer out of the filtration apparatus prior to introduction of the liquid to be filtered into the apparatus without falling of the once formed pre-coat layer or formation of tiny holes therein. Absence of the liquid mixture otherwise produced in the transitive stage of switching from the liquid for pre-coat forming to the liquid to be filtered provides great ad­ vantages not only relative to the costs for the disposal or recycling treatment of such a liquid mixture but also in respect of improvements in the quality of the product produced in the process involving filtration. In the following, the filtration apparatus of the invention is described in more datail by way of examples. Example l The filtration apparatus used in this test had l9 ceramic-made cylindrical filter elements uprightly installed in the housing. Each of the filter elements was constructed of three unit elements each having a height of 500 mm, inner diameter of 70 mm and wall thickness of 25 mm in a tandem arrangement. The spindle for positioning of the filter element was provided with a gas exhaust opening of 7 mm diameter at the upper end thereof so that the gas inside the apparatus could be discharged to the outer atmo­ sphere through a gas exhaust tube connected to the opening. A filtration system was constructed using this filtration apparatus according to the flow sheet illustrated in FIGURE l. The pre-coat tank 9 was filled with an aqueous suspen­ sion of diatomaceous earth which was circulated along a path of valve llb, pump l0, valve llc, filtration apparatus l, filtrate discharge tube 5, valve llj and pre-coat tank 9 so as to form a pre-coat layer of diatomaceous earth on the outer surface of the filter elements 2. When the pre-coat layer had been completed, the valves llb and llj were closed with the pump l0 turned off and, simultaneously, carbon dioxide gas was introduced into the filtration apparatus by opening the valve llf so as to discharge the water for pre-coat forming by opening the valve lli. When the liquid surface in the filtration ap­ paratus l had reached the level of the filtrate discharge tube 5, the valve lld was opened to completely discharge the remaining water. Further, the water for pre-coat forming remaining in the piping between the valves lla and lld was discharged by opening the valves lla and lld for a short while followed by closing. Thereafter, the filtration apparatus l was filled with beer introduced therein to through the valve lla, pump l0 and valve llc. The air inside was discharged during this procedure through the secondary gas exhaust tube 3 by opening the valve lle. After completion of filling of the ap­ paratus with the beer, the beer was filtered through a path of the valve lla, pump l0, valve llc, filtration apparatus l and valve llh by simultaneously closing the valve lle and opening the valve llh. The above described filtration of beer could be performed absolutely without producing a mixture of the water for pre-­ coat forming and the beer and removal of the yeast contained in the beer was complete. No defects were found at all in the pre-coat layer during the filtration procedure such as falling of the layer and formation of tiny holes therein. Comparative Example l The filtration system and filtration apparatus were substantially the same as in Example l except that the apparatus had no secondary gas exhaust tube 3. The filtration apparatus was filled with beer under gas dis­ charge by opening the valve llg or the valve lli. The results of filtration were not satisfactory due to partial falling of the pre-coat layer and formation of tiny holes in the upper part of the pre-coat layer. Example 2 The filtration system was constructed according to the flow sheet illustrated in FIGURE l using a filtration ap­ paratus in which a single ceramic-made cylindrical filter element was installed in an upright disposition. The filter element was constructed of three unit elements each having a height of 500 mm, inner diameter of 70 mm and wall thick­ ness of 25 mm in a tandem arrangement and the upper end member l2a of the element was provided with a gas exhaust opening of 7 mm diameter to which a gas exhaust tube was connected. The procedure of filtration using the above described filtration system was substantially the same as in Example l excepting replacement of the beer with a sugar syrup and carbon dioxide gas with air. The results were that the sugar syrup could be filtered without dilution by inter­ mixing of water and removal of the yeast contained in the sugar syrup was complete. Example 3 The filtration system and filtration apparatus were substantially the same as in Example l except that the filtration apparatus had seven filter elements each formed of a corrugated rectangular tube having a height of 700 mm, inner diameter of 26 mm and wall thickness of 2 mm spirally wound with a wire. Oolong tea was filtered using this filtration apparatus in substantially the same manner as in Example l excepting replacement of the carbon dioxide gas with nitrogen. The results were that the Oolong tea could be filtered without dilution by intermixing of water and removal of the bacteria contained in the Oolong tea was complete. Example 4 The filtration apparatus had seven ceramic-made cylindrical filter elements uprightly installed in the housing. Each of the filter elements had a height of 700 mm, inner diameter of 20 mm and wall thickness of 5 mm and the spindle for positioning of the filter element was provided with a liquid drain opening of 7 mm diameter at the lower end of the element so that the liquid inside the apparatus could be discharged to the outside of the ap­ paratus through a liquid drain tube connected to the opening. A filtration system was constructed using this filtration apparatus according to the flow sheet illustrated in FIGURE 4. The pre-coat tank 9 was filled with an aqueous suspension of diatomaceous earth which was circulated along a path of valve llb, punp l0, valve llc, filtration apparatus l, filtrate discharge tube 5, valve llj and pre-coat tank 9 so as to form a pre-coat layer of diatomaceous earth on the outer surface of the filter elements 2. When the pre-coat layer had been completed, the valves llb and llj were closed with the pump l0 turned off and, simultaneously, carbon dioxide gas was introduced into the filtration apparatus l by opening the valve llf so as to discharge the water for pre-coat forming by opening the valve lle. When the liquid surface in the filtration ap­ paratus l had reached the level of the liquid drain tube 3′, the valve lld was opened to completely discharge the remaining water. Further, the water for pre-coat forming remaining in the piping between the valves lla and lld was discharged by opening the valves lla and lld for a short while followed by closing. Thereafter, the filtration apparatus l was filled with beer introduced thereinto through the valve lla, pump l0 and valve llc. The air inside was discharged during this procedure by opening the valve lli. After completion of filling of the apparatus with the beer, the beer was filtered through a path of the valve lla, pump l0, valve llc, filtration apparatus l and valve llh by simultaneously closing the valve lli and opening the valve llh. The above described filtration of beer could be performed absolutely without producing a mixture of the water for pre-coat forming and the beer and removal of the yeast contained in the beer was complete. No defects were found at all in the pre-coat layer during the filtration procedure such as falling of the layer and formation of tiny holes therein. Comparative Example 2 The system and apparatus for the filtration of beer were substantially the same as in Example 4 except that the filtration apparatus had no liquid drain tube 3′ and the water for pre-coat forming was discharged by opening the valves llc and lld and/or the valve lli. The results of filtration were not satisfactory due to partial falling of the pre-coat layer and formation of tiny holes in the pre-­ coat layer. Example 5 The filtration system and filtration apparatus were substantially the same as in Example 4 except that the filtration apparatus had seven filter elements each formed of a corrugated rectangular tube having a height of 700 mm, inner diameter of 26 mm and wall thickness of 2 mm spirally wound with a wire. Oolong tea was filtered using this filtration apparatus in substantially the same manner as in Example 4 excepting replacement of the carbon dioxide gas with nitrogen. The results were that Oolong tea could be filtered without dilution by intermixing of water and removal of the bacteria contained in the Oolong tea was complete.

Claims: 1. A filtration apparatus comprising a tubular filter element installed in an upright disposition having a surface of which a pre-coat layer of a filter aid is formed to filter a liquid therethrough which further comprises a gas exhaust tube connected to the upright tubular filter element at an upper part thereof. 2. A filtration apparatus comprising of tubular filter element installed in an upright disposition having a surface on which a pre-coat layer of a filter aid is formed to filter a liquid therethrough which further comprises a liquid drain tube connected to the upright tubular filter element at a lower part thereof.

Inventors: ICHIKAWA, SEIICHIRO, KURODA, HIROSHI, NOGUCHI, SATOSHI, OTSUKA, TOSHIO, SAHARA, HIROHISA
Applicants: SAPPORO BREWERIES LIMITED
Application year: 1987
Main classification: B01D24
IPC codes: B01D35, B01D37, B01D36, B01D29