FI59036B - FOER FARAND FOER AOTERVINNING AV PAPPERSFIBRER UR SAMHAELLSAVFALL - Google Patents

Description

RSSr ^ l [B] (11) ANNOUNCEMENT C Q Γ) T * JWA lJ 1 V UTLÄGGN I NGSSKRIFT ^ 7 U O 0 C Patent extended 10 06 1931

Patent c? i '^ 1 ^ t ^ (51) Kv.lk?/IncCI.3 β 03 B 9/06 SUOMI — FINLAND t *> Pitanttl takamus— PatantanaBknlng 322/73 (22) Hakamlspllv · - Anattknlnpdig 02.02.73 ^ (23 ) AlkupVvl — GlMghatsdsg 02.02.73 (41) Interpreters | ulklMk »l - Bllvlt offantllg 10.08.73

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Patent · och registerstyrelaen '' Ansakin uttagd och uti. * Krift * n publkarad 27.02.8l (32) (33) (31) privilege —Begird prlorltat 09.02.72 USA (US) 22I + 815 (71) Black Clawson Fibreclaim, Inc. ., 200 Park Avenue, New York, New York 10017, USA (72) Paul G. Marsh, Middletown, Ohio, David E. Chupka, Middletown, Ohio, USA (7 * 0 Berggren Oy Ab ( 5 * 0 Method for recovering paper fibers from municipal waste -Förfarande för ätervinning av pappersfibrer ur samhällsavfall

Finnish Patent No. 5 * 4,936 describes a system and method for treating solid waste materials for recovering recyclable paper fibers. Typical wastes to be treated according to this explanation are household, commercial and industrial wastes, all of which are included in the term "municipal waste" as used below. Municipal waste usually contains substances of a very different nature, such as glass, metals, animal and food waste, vegetation, land, plastic, mostly paper and board, and other fibrous and fibrous substances such as textiles made of natural and man-made fibers.

The system and method described in the aforementioned patent, which is also summarized below, generally succeeds in separating the paper fiber component of municipal waste from water-soluble contaminants, and also in removing inorganic solids and organic solids significantly higher than fibers, which can be easily performed by gravity or by centrifugal cleaning in a liquid cyclone or 2,59036 similar cleaner. However, there is one type of contaminant that has proven difficult to effectively separate from fibers, namely organic substances that have substantially the same specific gravity as paper fibers, or have a higher specific gravity but behave hydrodynamically as if they had a significantly lower specific gravity than it does.

One type of substance in this category which poses a considerable problem is fat, a vegetable, animal or mineral fat which is always present in both household and industrial waste and which, in addition to being in itself a contaminant of paper fibers, is therefore harmful, that it tends to adhere to other light weight contaminants such as earth, ink and asphalt particles and the like and causes them to adhere to the fibers. Another type of contaminant that behaves in much the same way as fat involves waxes that are common in waste papers. Both of these types of pollutants are sometimes sometimes grouped together as a group of "solvent-soluble" pollutants, and they form a surprisingly large proportion of the solids in municipal waste, namely approximately 5%. Another type of contamination that causes similar separation problems as fat involves fine particles of non-fibrous matter, especially those such as vegetable and meat particles. The most common examples of substances that behave hydrodynamically as if they had a specific gravity less than that are particles (hair), man-made fibers, yarns and vegetable waste such as grass clippings and leaf pieces. For convenience, the phrase "light substances" is used below for all the types of pollution outlined above.

All of these light substances are present in municipal waste in considerable quantities, mainly as parts of household and institutional waste. They constitute a difficult barrier to the production of high quality paper fibers from waste contaminated by household waste, mainly because when sludge in which they and paper fibers are essential solids is treated by normal cleaning or screening methods, their hydrodynamic behavior and physical properties are not similar to those of paper. get separated.

According to the present invention, solid wastes, especially municipal waste, which typically comprises a wide variety of fibrous materials as well as other organic and inorganic solid particles, are treated to form an aqueous slurry having mainly fibrous solids and other 5 59036 lightweight materials as outlined above. -particles with a specific gravity substantially greater than 1.0. For example, municipal waste can be initially treated as described in the aforementioned Finnish patent 5 ^ 936 by mixing an aqueous medium in a treatment vessel in which the formed sludge is subjected to mechanical and hydraulic shear forces to reduce the relatively fragile portions of solid particles to a predetermined maximum particle size. A device found to be particularly suitable for this purpose is described in U.S. Patent No. 3,595-888, and the pumpable slurry obtained from this device is screened and / or otherwise purified to the extent that the remaining inorganic particles are substantially removed.

The solid particles remaining in the slurry that underwent the wedding steps consist essentially of fibrous materials and the various types of light organic contaminants described above. According to the present invention, it has been found that these light substances can be effectively removed by a centrifugal treatment which is somewhat different from normal centrifugal separation and which may be appropriately referred to as "centrifugal flotation". More specifically, this slurry is fed down a tangential feed nozzle to a conical vessel. the tangential inlet current creates a turbulent flow pattern around the centerline of the vessel, causing the solid particles in the vessel to separate into two main fractions.

The conical vessel in which this separation is performed differs in structure and operation from conventional centrifugal cleaners, in which the outlet at the base of the cone is usually approximately the same size as the inlet, but the outlet at the tip of the cone is so small that the outlet is limited to less than 5%. ) from the feed stream, which distribution is completely satisfactory when the purpose is to remove hard, granular contaminants from otherwise relatively clean paper fibers. However, for the purpose of the present invention, such a flow pattern would not give useful results because most of both the paper fibers and the light materials would exit one of the outlets at the base of the cone.

According to the present invention, the outlet at the tip of the cone is considerably larger than in a conventional cleaner, and the inlet pressure and inlet flow are kept so large that the outlet from both outlets remains quite large with a pressure drop equal to or significantly greater than that used in conventional cleaning. Under these conditions, most of the paper fibers exit through the tip opening with the outer fraction separated from the slurry inside the vessel, while the light substances exit with the inner fraction through the opening in the vessel base which is the acceptance opening in conventional centrifugal cleaners.

Although the invention is primarily directed to the separation of light contaminants from paper fibers, other processing steps may be combined with the centrifugal flotation process used for this purpose. For example, the slurry may be treated to remove the fat component from the paper fibers prior to the middle exfoliation step, and this may be done chemically by treatment with a dispersant or degreaser such as soap or detergent, or mechanically with equipment such as a disc mill or the like.

Because the slurry fraction containing the paper fibers is treated as a heavier fraction in centrifugal flotation, all of the hard, granular soot particles remain with the paper fibers. They can be easily removed in a second cleaning step, which is carried out in the usual way in centrifugal sorters. Other treatments that can be performed on paper fibers to improve their quality include e.g. dissolution and bleaching after flotation and other purification steps.

The invention also offers additional advantages in the form of by-products which it provides in addition to the recovered fibers. In particular, the reject fraction obtained from the central centrifugal flotation unit contains solvent-soluble fat and wax to such an extent that it is worthwhile to separate this component from the rest of the reject. In addition, the remaining reject material is so largely organic in nature that it is suitable as a raw material for the production of fuel, whether or not the fat and wax have first been removed.

Figure 1 schematically shows a complete system for carrying out the method according to the invention, and Figures 2 and 3 are partial views showing a modification of the system according to Figure 1.

The system of Figure 1 includes a waste treatment tank 10 into which solid waste can be fed by any suitable means, e.g. a conveyor 12. A scrap metal removal device 13 communicates with the pool 10 to remove fragile materials therefrom, and an aqueous medium such as water can be fed to the tank. through wire up to 14.

All of the above equipment may be of the type described in more detail in U.S. Patent No. 3,549,092, with the properties of the pulp being preferably as set forth in U.S. Patent No. 3,595-88. As described in detail in these patents, the basin 10 has a rotor 15 which provides a vortex flow pattern and exposes the solid waste material in the basin to severe hydraulic and mechanical shear forces, thereby reducing the relatively fragile solids to a predetermined size to be removed at the bottom of the basin. 16 through with holes of 12-25 mm.

A slurry consisting of a portion of an aqueous medium and relatively fragile solid wastes reduced to pass small enough to pass through the base plate 16 is removed along line 18 and pumped by pump 19 to a relatively large centrifugal cleaner, i.e. liquid cyclone 20, of relatively large size and performance. some of the hard, granular inorganic material exits through the tip of the cleaner as indicated by arrow 22.

The remainder of the slurry, comprising approximately 99% of the total volume and about 25% of the solids fed to the purifier 20, exits the top end of the condenser down line 24 and is passed through a suitable screen 25, preferably relatively coarse, e.g., about 3 mm perforated. The reject is removed from the screen 25 along line 26 and the acceptor is passed down line 27 to a fine screen 30 for re-screening through, for example, 1.6 mm holes.

Acceptance from the fine screen 30 is pumped, as shown, by a pump 31 to a cleaning device represented by a biscuit exhaust cleaner 33, and the reject from the screen 30 is led down line 34 to reject line 35, and reject from cleaner 33 is also directed to line 35 up line 36. Since in most cases the accept from the purifier 33 still contains a significant amount of small particles of organic contaminants, it is preferably subjected to a second purification operation at this stage, represented by pump 39 and centrifugal purifier 40. Purifier 40 is preferably finer than purifier 33, for example by diluting the pulp slurry to about 0. Instead of a consistency in the cleaner 33 of about 0.7%, and / or using a 152 mm cleaner at 33 and a 76 mm cleaner at 40. The axote from the choke 40 is led down the line '41 to the zero fraction remover 42, which in the figure is represented by a sloping sieve, from which the zero fraction as a line is led down the line 43 to the shroud line 35.

The solid in the accent from the zero fraction remover 43 consists of paper fibers contaminated mainly with solvent-soluble fats and waxes and other fibrous substances. It is the removal of these contaminants that is the most difficult cleaning problem, and this problem has been solved according to the present invention as will be explained below.

The acceptance of the zero fraction remover 42 is pumped by the pump 44 along the line 45 to the centrifugal flotation unit 50, which is schematically shown in the drawing as a truncated cone provided with a tangential inlet 51, a tip outlet 52 and a base orifice 50 itself. a central exhaust cleaner, the special shape and mode of operation of which causes the incoming sludge to be divided into an outer fraction containing most of the cellulosic fiber and an internal fraction containing most of the fat and other light contaminants, including man-made fibers. The unit 50 is further driven in such a way that the external fraction leaves the tip outlet 5? as an accept while the fraction containing light contaminants is removed from the upper outlet 53 as a reject.

These operating conditions and results are achieved by proportioning the sizes of the various orifices so as to adjust the feed flow and pressure so that the two fractions exiting through the orifices 52 and 53 are approximately equal in volume and the pressure drop is substantially greater than in a conventional centrifugal cleaner. As a specific example, satisfactory results in the use of the invention have been obtained by using as a unit 50 a 76 mm diameter vortex cleaner with a diameter of 12.7 mm for both the inlet 51 and the upper outlet 53, which is conventional but 14 for the tip outlet 52. 3 mm instead of 8.5 mm, which would be the normal size of this orifice, which would allow a correspondingly smaller proportion (less than 5% and usually about 1%) of the total volume flow through.

For a pressure drop of 76 mm for a conventional centrifugal cleaner, a pressure drop of 2.5 to 3 * 2 aty at a flow rate of 84 7 59036 1 / min is recommended. On the other hand, good results in the use of the present invention have been obtained by keeping the supply pressure and supply flow so much higher that approximately equal volume flows through both outlets 52 and 53 have been obtained, the pressure drop being at least equal and preferably slightly higher than in conventional practice, e.g. - 5.6 aty.

The results of the experiments performed with the system described above show that the flow from the tip outlet 52 contains up to 80-90% of the solids originally present in the feed slurry, and that this solids consists mainly of reusable fibers and only small amounts of contaminants, mainly organic particulates and other particulate matter. -like substances. The second stream exiting the unit 50 through the top opening 53 contains only 10-20% of the original solids, but this solids consists mainly of zero fibers, hairs, man-made fibers and other non-uniform particles, and also most of the fat and wax contained in the feed slurry. Further processing of this reject from orifice 53 is explained below.

The above values in connection with the use of the unit 50 represent typical suitable operating conditions for the use of the invention, but there is some variation in these values, and it should also be noted that the consistency of the slurry fed to the unit 50 is an important factor. Thus, experiments show that the lower the consistency, the more efficient the desired separation, and the best results are obtained with consistencies at the lower end of the range of 0.3-0.7%.

Another important control factor is the ratio of the flow cross-section of the feed port 51 to the flow cross-section of the tip outlet port 52. In a relatively small purifier such as the 76 mm unit described above, this ratio must be at least 1: 1 to achieve maximum yield, but need not be substantially greater than this. Thus, the diameter of the outlet 50 may be between 12.7 and 14.3 mm when the diameter of the inlet is 12.7 mm. With a larger cleaner, for example 152 mm in diameter, this ratio must be between 1: 1 and 1: 1.5.

In general, in order to achieve the maximum yield, the volume flows from both outlets must be approximately equal, but the higher the purifier, the higher the pressure drop compared to the normal operating pressures of vortex cleaners to develop similar centrifugal forces used in conventional centrifugal cleaning deliveries. For example, when a 152 mm centrifugal cleaner normally operates at a pressure difference of 2.8 aty to 8 59036 and a 76 mm centrifugal flotation unit operates at a pressure difference between 2.7 and 7 aty, a 152 mm centrifugal flotation unit requires at least 5.6 aty and preferably more, between 5.6 and 1! J aty.

The conditions outlined above have been found to be most suitable when the highest possible yield of fibers of acceptable quality is desired, but the centrifugal flotation unit 50 can also be made to operate very selectively, resulting in a smaller amount of accents containing the longest fibers present. For example, if the flow through the tip outlet 52 is reduced by 20-35 / Therefore from the feed flow, this fraction contains most of the longest fibers in the feed flow and correspondingly less zero fibers and light contaminants. Thus, if the diameter of the orifice 52 is reduced from 1.3 mm to 11.1 mm, the flow through it decreases from about 50 5S to about $ 25 and, as a rule, the amount of fiber exiting through the heel outlet 53 increases from about 12 / S to about To $ 25.

It should be noted that in the above example, the size of the outlet 52 was reduced by 8: 5, but that the effective flow cross-section of the orifice is still more than 12 times that of the tip outlet of a conventional cleaner of the same size. It is also apparent that similar results can be obtained without actually changing the size of the orifice 52, increasing the back pressure acting on it, for example by using a suitable throttle valve 56 in the line 57 from the orifice 52. In general, the best fiber yield from a centrifugal unit is obtained by increasing the pressure difference. using very low consistencies such as 0.3%, but the amount of this yield decreases correspondingly to the same extent as the amount of reject fraction increases. The most satisfactory results so far have been obtained with the 76 mm unit described above, and the above indication of the ratio of the feed opening to the tip discharge opening in terms of the 76 mm unit can be suitably reshaped to range from 1: 0.75 to 1: 1, 25 depending on the desired amount or quality of yield of acceptor fibers.

The accept of the unit 50 coming out of the tip outlet 52 usually requires additional treatment or treatments depending on the intended use for which it is ultimately subjected. Thus, it is shown in the drawing as being routed down line 56 to the additional processing stations. For example, if the accept of unit 50 still contains significant amounts of fine hard granules or fine organic dirt particles, it may be subjected to another centrifugal cleaning step, in which case station 60 represents an additional feed pump and cleaner like pump 3 and cleaner 33 used by pump 39 and cleaner 40. in addition to or instead of.

Another possible treatment is dissolution, especially if the fibrous material contains contaminants that are difficult to remove, such as grease, wax and asphalt, which can be easily dispersed by dissolution, and in any case if the fibrous material is to be bleached. Station 61 thus represents a digester, and satisfactory results can be obtained with any conventional digester using 1-15% by weight of NaOH, a pressure range of 0.7 to 7.0 aty, a temperature range of 115-170 ° C and a cooking time of 5-15 minutes. . It is clear that a suitable dewatering device capable of handling up to 45% consistency must be used before the digester, taking into account that the accept leaves the flotation unit 50 at 0.6 to 1.0% consistency, and station 62 represents the final washing and dewatering device for the dissolved mass. .

It should be noted that it is significantly more advantageous to perform the dissolution step described above after the centrifugal flotation step than before. For example, leaching tends to reduce the particle size of some light contaminants, especially man-made fibers, and thus make them more difficult to remove than larger ones. In addition, when most of the fat is removed by centrifugal flotation, the result is that fewer chemicals are needed for the subsequent dissolution step than if there were still fat left.

Depending on the amount of fat present in the slurry, it may be advantageous to include in the process of the invention a pre-step to remove fat from the fibers before centrifugal flotation of the slurry. For example, a soap, detergent or other dispersant may be added to the slurry. Alternatively or in addition, the slurry may be mechanically treated to remove grease from fibers or papermaking materials, e.g., in disc mills, etc. Figure 2 shows a portion of the system of Figure 1 modified so that such a further processing station 65 is adapted to zero divider 42 , which is the most suitable place for this grinding and / or fat dispersing station.

Another alternative step that is particularly useful in removing particles that tend to behave hydrodynamically, such as paper fibers, is to inject air into the slurry prior to the centrifugal flotation unit 50. Figure 3 shows a portion of the system of Figure 1 modified with line 45 connected in parallel. the pressure vessel 66 in such a way that a smaller portion, for example 20%, of the flow fed to the unit 50 passes through the pressure vessel 56 and then merges with the main flow. If the tank 66 is kept approximately half full of air at a pressure of e.g.

6.3 aty, air dissolves in the liquid, which is then released as bubbles inside the unit 50. It appears that these bubbles tend to adhere to the contaminant particles and make them behave as if they have a specific gravity lower than it is, and thus migrate to the inner fraction in the unit 50 and its heel outlet 53.

The whole system appears to be the most advantageous as it has been described so far, but it can be quite modified within the scope of the invention. For example, since the centrifugal flotation unit 50 is quite efficient as a zero fraction remover, whereby the zero fraction separates into the fraction leaving through the base outlet 53, it is possible to omit the zero fraction remover 42 and connect the line 41 directly to the pump 44. Similarly, the number of centrifugal cleaners depends on the amount of fine inorganic and organic contaminant particles remaining after the initial treatments in cyclone 20 and screening stations 25 and 30.

As another modification of the system of Figure 1, it is possible to replace one or both screens 25 and 30 with a center co-flotation unit capable of performing substantially the same soul properties as most of the contaminants removed by screening are large particles of light weight materials such as plastic, wax paper, corn cobs, leaves, etc. For example, a 152 mm centrifugal flotation unit satisfactorily replaces a coarse screen 25 and may be followed by a 76 mm centrifugal flotation unit for fine sorting or a conventional fine screen. A particular advantage of using centrifugal flotation units in this sorting step is that the amount of paper fiber they discard is significantly lower than that of conventional screens, resulting in an increase in the yield of accept fiber. After cleaning, in one or more centrifugal cleaners 33 and 40, the acceptor is fed to the centrifugal flotation unit 50 as previously described. All of these modified methods and kits can also be further modified by adding either a grinding or fat dispersing station or both.

As previously mentioned, although the differences between the densities suitable for performing the step require dilution or dewatering stations at various points in the system, it has been considered unnecessary to present these stations to those skilled in the art. However, it may be advantageous to supplement the above information on consistency by listing the most suitable values for each step: 3.5% with cyclone 20 and coarse sieve 25, 1% with fine sieve 30, 0.7% with purifier 33, 0.5% with purifier 40, 0 .3% with a zero fractionator 42, 0.5% with a centrifugal flotation unit 50 and 35% with a digester 61.

It should also be mentioned that both the zero fraction removal unit and the centrifugal flotation unit have a dewatering effect on the acceptor material coming from them. For example, if the slurry enters the zero fraction remover as 0.3% thick, the acceptor thickens by about 3.5%. In a centrifugal flotation unit, the consistency of the acceptor material is approximately twice that of the input consistency, while the consistency of the reject material obtained from the heel outlet is about half of the input consistency.

As already mentioned, solvent-soluble fats and waxes make up approximately 5% of the solids in municipal waste and make up an even larger proportion of the 50 rejects of the flotation unit, namely about 20-35%. in a rosin reactor or similar final disposal device, but it is also possible to recover the solvent-soluble part for other purposes, for example as a raw material for the production of soap or fuel. In fact, because the reject of unit 50 is essentially purely organic in nature, the major components other than fat and wax are of natural or synthetic origin such as vegetation or plastic, and because it is also relatively uniform in particle size and small enough to enter the accept fraction on the fine screen 30, as a whole excellent soniva to be converted into fuel by pyrolysis or hydrogenation according to Finnish patent application no. 3559/71. Station 70 in Figure 1 thus represents such processing.

As an alternative to using the reject of the flotation unit 50 entirely as the fuel source, its solvent-soluble portion can be recovered separately by conventional methods such as flotation clarification followed by distillation or a chemical recovery step using a suitable solvent. Station 70 in Figure 1 thus also represents such selective recovery stations. The residue after removal of the solvent-soluble portion consists essentially of paper zero fiber which passes through a 100 mesh screen and is thus essentially of no value for papermaking. These zero fibers are usually 60-70% of the 50 rejects of the flotation unit. Thus, it is usually most practical to dispose of this residue by burning 12,59036 rackets, except as described in the next paragraph.

If flotation units are used as screens for stations 25 and 30 in Figure 1, the reject material thereof is similar to the reject material of the flotation unit 50, in that it is also mainly organic in nature and also has a relatively small proportion of usable paper fibers. In addition, it contains a considerable amount of plastic and other organic matter, e.g. said solvent-soluble contaminants. It is thus well suited as a raw material for the production of fuel, whether or not a solvent-soluble part is first recovered from it, and if the system is adapted to treat this reject in this way, it is usually suitable to combine the flotation unit 50, especially if the solvent-soluble fraction is first removed from this fraction.

Although the method and product described above constitute preferred embodiments of the invention, it should be noted that the invention is not limited to this particular method and product, but that changes may be made therein without departing from the scope of the invention as set forth in the appended claims.

Claims (11)

13 59036 1. The method of by-products, e.g. for the recovery of paper fibers for re-use from waste containing waste paper contaminated with household waste, whereby the waste is formed into a pumpable aqueous slurry with a particle size of at most of the paper fibers and the solid consists essentially of paper fibers with greasy liquids; this slurry is fed into a conical vessel having a tangential inlet near the base of the cone and outlets at the tip and base of the cone, the flow cross-sections of the inlet and the outlet in the base being substantially equal, b) the feed flow to said inlet is kept so large cause the slurry to separate in the vessel into an outer fraction containing most of the paper fibers and an inner fraction containing most of the greasy liquids, and to leave the outer fraction and the inner fraction at the tip outlet, respectively. (c) the effluent streams through both outlets are maintained in a predetermined relationship so that the outer fraction exiting through the tip outlet contains most of the paper fibers entering the vessel; (d) the waste materials contained in the effluent outlet through the base outlet are recovered for reuse; waste materials are further processed to convert them into one or more of the following by-products: (i) fat constituents, (ii) fuel containing those fat constituents, (iii) fuel essentially free of those fat constituents. Method according to Claim 1, characterized in that the ratio of the effective flow cross-sections of the inlet to the tip outlet is between 1: 0.75 and 1: 1.25. A method according to claim 1, characterized in that the effective flow cross-section of all the openings is substantially equal and that the outlet flows from the outlet openings are substantially equal. A method according to claim 1, characterized in that the slurry is subjected to a grinding treatment before the feeding step (a) according to claim 1, in order to remove fat from the paper fibers. 14 59036 A method according to claim 1, characterized in that a fat dispersant is mixed into the slurry before the feed step (a) according to claim 1. The method of claim 1, characterized in that the vessel has a diameter of about 7.5 cm, the flow cross-section of each orifice corresponds to the area of a circle of about 1.3 cm in diameter, and the pressure drop in the vessel is at least as large as? - 4.2 at. The method of claim 1, wherein the sludge to be pumped comprises water, paper fibers, household waste, and at least one of the following contaminants: frangible and non-friable inorganic substances; vegetation waste; insoluble inorganic substances; sand and other pulp, characterized in that the sludge is purified by centrifuging most of the inorganic substances before performing steps (a), (b) and (c) according to claim 1. Method according to Claim 1 or 7, characterized in that the acceptance mass is dissolved. A method according to claim 7, characterized in that the centrifugally purified slurry is screened to remove larger particles having a specific gravity of paper fibers, after which the sorted slurry is purified by centrifugation to remove high specific gravity particles, and a substantial portion of fine fibers is separated from the sorted and centrifuged sludge. A method according to claim 9, characterized in that the waste materials obtained in the purification are combined with the waste material of step (d) of claim 1, wherein the further treatment of the waste materials comprises their conversion into fuel. A method according to claim 1 or 9, wherein the waste material contains a substantial amount of solvent-soluble fat and / or wax components, characterized in that these solvent-soluble components are separated from the rest of the waste material.