JPS59262B2 - How to recover paper fibers from municipal waste - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for recovering reusable papermaking fibers from municipal waste containing substantial amounts of kitchen sinks and other organic waste. A slurry consisting essentially of cellulose fibers, contaminated with light material such as vegetable waste, but otherwise substantially free of contaminant particles, is passed through a single slit inlet and an outlet at its apex and base. Cellulose fibers are separated from other solid materials by centrifugal flotation in a conical device, by keeping the feed flow rate and pressure to the device sufficiently high and by regulating the outlet flow rate. A process that does not involve discharging substantially equal volumetric flow rates from both estuaries under pressure drop conditions equivalent to or higher than those used in conventional centrifugal purification operations in correspondingly sized spiral wave separators. It is.

The outlet stream from the apex consists mostly of good paper-grade fibers, while the outlet stream from the base outlet consists mostly of waste, a significant proportion of which is solvent-soluble fats and/or waxes that can be recovered separately. The remainder is mostly plastic and paper fiber fines.

Japanese Patent Publication No. 51-2963 describes a system and method for treating solid waste in order to recover papermaking fibers therefrom which can be reused.

Typical examples of waste that can be disposed of according to the instructions are household, commercial and industrial waste, all of which are described below in the text [
This is included in the name of municipal waste.

Municipal waste generally includes glass, metals, animal and food waste, vegetable matter, lint, plastics, a large proportion of paper and board and other fibrous and fibrous materials such as textiles made from both natural and synthetic fibres. It consists of substances of a very miscellaneous character, including:

The method and system described in Japanese Patent Publication No. 51-2963 will be summarized below in the main text, but it is generally used when separating papermaking fiber components from municipal waste from water-soluble pollutants, or when separating papermaking fiber components from water-soluble pollutants, or Effective in removing high levels of inorganic and organic solid contaminants, they are readily accomplished by gravity or centrifugal cleaning in hydrocyclones or similar leeches.

However, there is one group of contaminants that has proven to be the most difficult to separate effectively from the fibers, and this class has a specific gravity substantially equal to, or even higher than, that of papermaking fibers. consists of an organic substance that behaves hydrodynamically as if its specific gravity were substantially lower than it should be.

One type of substance that poses a major problem in this category is fats and oils, whether of animal, vegetable or mineral origin, which are unavoidably present in industrial waste as well as kitchen waste, and which are Not only is it a contaminant in itself, it also tends to adhere to other low density contaminants such as dust, ink and asphalt particles, leaving them on the fibers. This is even more inconvenient.

Another type of contaminant that behaves very similarly to fats and oils is wax, which is common in waste paper.

Both of these types of contaminants are sometimes referred to in the text below as
Collectively in the category of "solvent soluble" contaminants, they represent a surprisingly large proportion of the solids in municipal wastes, about 5%, yet still amounting to 100 pounds per ton.

Yet another type of contaminant that, like in the case of fats and oils, causes separation problems are fine particles of non-fibrous materials, such as particles of vegetables and meat in particular.

The most frequently encountered examples of materials that hydrodynamically behave as if they are less dense than they are are hair, synthetic fibers, thread, and vegetable waste, such as grass shavings and leaf fragments.

In the following text, for convenience, the terms ``light substances'' or ``light substances'' will be used to collectively refer to some of the pollutants outlined above.

All of these light substances occur in substantial quantities in municipal wastes, primarily as part of domestic and industrial waste.

They are a major obstacle in producing good quality paper fibers from waste contaminated with kitchen garbage.

This is mainly because their hydrodynamic behavior or physical properties are too similar to that of paper fibers when processing slurries in which they and paper fibers are mostly solids, but not through normal cleaning or sieving. This is because it obstructs their separation.

In carrying out the invention, solid waste materials, in particular municipal wastes, which typically consist of various fibrous materials as well as other organic and inorganic solids, are treated so that the solids therein are An aqueous slurry is formed consisting of a partially fibrous material and a light material of the type outlined above and which is substantially free of other solid particles of specific gravity greater than 1.0.

For example, starting with municipal waste, as described in Japanese Patent Publication No. 51-2963, solid, relatively brittle slurry is mixed with an aqueous medium in a treatment device and mechanical and hydraulic shear forces are applied to the resulting slurry. Break the portion down to the planned maximum particle size.

A device which has been found to be particularly suitable for this purpose is disclosed in U.S. Pat.
The pulpable slurry extracted from the apparatus is subjected to sufficient screening and/or washing to substantially remove any remaining inorganic particles.

The solids remaining in the slurry after this step will consist essentially of fibrous material and the various types of light organic contaminants mentioned above.

In accordance with the present invention, it has been discovered that such light substances can be effectively removed by a centrifugal process that is somewhat different from conventional centrifugation.

It would be appropriate to call this treatment the "centrifugal flotation method."

More specifically, this slurry is fed into the conical device through the cutting line inlet.

The device still has outlets at its top and base like a regular centrifuge.

The tangential feed flow creates a swirl pattern around the axis of the device, which has the effect of separating the solids within the device into two main parts.

In the inner part, the solids will consist mainly of the light fraction of contaminants, while the other part will contain the majority of papermaking fibers.

The cone-shaped device that performs this separation differs in construction and mode of operation from ordinary centrifugal cleaners; the outlet from the base of the cone is usually about the same size as the inlet, whereas the outlet from the apex of the cone is usually approximately the same size as the inlet. It is narrowed so that the discharge therefrom is limited to a relatively small volume fraction (less than 5%) of the inlet flow, and the two divisions of the outlet flow transfer contaminants such as gravel to relatively clean paper fibers. This is quite satisfactory for the purpose of removing it from the public.

However, for the purposes of the present invention, such a division of the flow rate may not yield any useful results.

This is because the majority of the paper fibers and light substances will be discharged together from the base outlet.

In accordance with the present invention, the apex outlet is of substantially larger dimensions than in conventional cleaners, and the inlet pressure and flow rate are kept sufficiently high so that the discharge from both estuaries is in substantially equal volumetric proportions. The sag and pressure drop are similar to or substantially higher than those used in normal operations.

Under these conditions, most of the papermaking fibers are discharged from the apex, along with the outer portion where the slurry is separated in the equipment, while the light materials are discharged along with the inner portion of the equipment, which in normal centrifugal cleaning operations would be the beneficiary portion of the equipment. It will be expelled from the mouth at the base.

Although the invention primarily relates to the separation of light contaminants from papermaking fibers, the centrifugal flotation method for this purpose can be combined with other processing steps.

For example, the slurry may be treated to remove oil and fat components from the paper fibers prior to the centrifugal flotation step, and this may be done chemically by treatment with a dispersant or a degreaser such as a soap or detergent. well or disc refiner
Alternatively, it can be performed mechanically using a device such as a deflaker.

For centrifugal flotation purposes, the portion of the slurry containing paper fibers is treated as a heavy portion, so that any contaminating particles of material such as sand will remain with the paper fibers.

If so, they can be easily removed by a subsequent cleaning step of a conventional nature in a centrifugal cleaner.

Other treatments that can be applied to paper fibers to improve their quality include flotation and other cleaning steps followed by cooking and bleaching. bring benefits.

In particular, waste from centrifugal flotation devices has a very high content of solvent-soluble oils and waxes, to the extent that it becomes practical to separate these components from the rest of the waste.

In addition, the remaining waste material is mostly organic and therefore is suitable as a feedstock for conversion into fuel, whether or not the fats and waxes are removed first.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.

The system shown in FIG. 1 includes a waste treatment tank 10 to which solid waste material is fed by some suitable device, such as a conveyor 12.

A clot displacer 13 communicates with the vessel 10 to remove relatively non-friable materials therefrom, and an aqueous medium, such as water, is then fed by line 14 from the clot displacer 13 into the vessel.

All of the above devices are of the type described in detail in U.S. Pat. No. 3,549,092, preferably with a pulper having the characteristics shown in U.S. Pat. No. 3,595,488 Good too.

Rotor 15 as detailed in these patents
is located in tank 10 and creates a swirling flow pattern that exerts intense hydraulic and mechanical shear forces on the solid waste material in the tank, thereby breaking the relatively brittle portions of the solids to a predetermined size and diameter. Allows for extraction from the bed plate 16 at the bottom of the tank, which has pores in the range of 1 inch to 1 inch.
A pump 19 removes by line 18 a slurry consisting of a portion of the aqueous medium and relatively friable solid waste material crushed to a size sufficient to pass through the bed plate 16.
to a centrifugal cleaner or hydrocyclone 20 of relatively large size and volume.

This slurry is fed into the cleaner 20 from the cutting line direction, and most of the sand-like inorganic matter is removed from the top of the cleaner as shown by arrow 22.

The remainder of the slurry, comprising approximately 99% of the total volume fed to the cleaner 20 and approximately 85% of the solids, exits the top of the cleaner by line 24 to a suitable screening device 25.
, preferably to a relatively coarse separator, such as one having an inch diameter screen.

The waste removed from the slurry in the secondary clean 25 is removed via line 26, and the refined material is sent via line 27 to a relatively fine screen 30 for further screening.
For example, the diameter is 1 I.

Pass through the eyes of inches. Selected material from fine screen 30 is shown being fed by pump 31 to another cleaning device shown as centrifugal cleaner 33, while waste from screen 30 is routed from line 34 to waste disposal line 35. The waste from cleaner 33 is likewise directed by line 36 to line 35 .

Since in most cases the raw material from the cleaner 33 will still contain a significant amount of fine particles of organic dust, it is preferable to subject it to a further cleaning operation in this state.

It is represented by a pump 39 and a centrifugal cleaner 40.

Preferably, cleaner 40 is diluted to provide a more precise cleaning than cleaner 33, for example to a concentration on the order of 0.3% compared to 0.7% for cleaner 33, and/or a 6-inch cleaner. It is operated by using a 33 and 3 inch cleaner 40.

Selected raw material from cleaner 40 is passed through line 41 to fines remover 42 .

The fines remover is illustrated as a tilted screen type from which waste fines are fed by line 43 to the main waste line 35.

The solids in the fines from the fines remover 42 consist primarily of paper fibers contaminated with solvent soluble oils and waxes and other fibrous materials.

Removal of these contaminants presents the most difficult cleaning problem, and the present invention, as described herein, solves this problem.

Pump 44 and line 45 transport the selected material from fines remover 42 to centrifugal flotation device 50 .

The device is shown somewhat diagrammatically in the form of a truncated cone;
It has a cutting line inlet 51, an apex outlet 52, a stem and a base or upper outlet 53.

The apparatus 50 is specially constructed and operated to effectively separate the incoming slurry into an outer portion containing a majority of cellulosic fibrous material and an inner portion containing light pollutants, including a majority of oils and other synthetic fibers. It is a style centrifugal cleaner.

Furthermore, the apparatus 50 is operated in such a way that the outer portion is discharged as refined material through the top outlet 52, while the portion containing light contaminants is discharged as waste through the upper outlet 53.

These operating conditions and results are such that the two portions exiting each port 52 and 53 are of approximately equal volume, yet each port has a pressure drop substantially greater than that of a conventional centrifugal cleaner. A harmonized still is obtained by adjusting the feed rate and pressure.

Next, an example will be given.

EXAMPLE 1 A 3-inch diameter volute prototype cleaner is used as the device 50, with the inlet 51 and top outlet 53 each having a diameter of z inches as usual, but the apex outlet 52 having a diameter of It is satisfactory to practice the present invention when the diameter is Z 6 inches, compared to 2 inches, through which a relatively small proportion of the total volumetric flow passes (less than 5% and typically closer to 1%). The desired results were obtained.

That is, when the diameters of the inlet 51 and the top outlet 53 are 1 inch, the diameter of the apex outlet 52 - inch, the raw material supply rate is 22 gallons per minute, and the volumetric flow rates of the top outlet and the top outlet are equal. Each condition is as shown in Table 1 below.

Pressure drop was in the range of 60-80 psig.

The above tests showed that the component discharged from the apex outlet consisted of fibers of good recycled quality, containing up to 80-90% of the solids content originally contained in the slurry.

The recommended pressure drop for a 3-inch cleaner for regular centrifugal cleaning purposes is 335-335 mm with a throughflow of 22 gallons per minute.
45 psi. In contrast, in the practice of the present invention, the feed pressure and the feed flow rate are high enough to produce flow at approximately equal volumetric flow rates from both outlets 52 and 53, and the pressure drop is normal. Preferred results have been obtained when the pressure is at least equal to, but preferably somewhat higher than, that of operation, e.g. 660-80 psi.

Test results obtained from operating systems such as those just described have shown that the flow from the apex outlet 52 contains up to 80-90% of the solids content originally contained in the incoming slurry. and that these solids will consist primarily of fibers of good recycled quality and will contain only small amounts of contaminants, primarily plastic fibers and particles of organic debris such as asphalt-based materials. It shows.

The other stream exiting the device 50 through the upper port 53 may contain only 10 to 20% of the original solids, but these solids are primarily composed of fines, hair, synthetic fibers, and other non-uniform materials. The particles will also consist of most of the fats and waxes that were present in the incoming feedstock.

Further handling of this waste material from line 55 is discussed below.

Although the numbers given above in connection with the use of the device 50 provide atypically preferred operating conditions in the practice of the present invention, there is some variation in these values, particularly for the device 50. 50
It should be noted that the concentration of the slurry supplied is an important factor.

In particular, test results indicate that the lower the concentration, the more effective the desired separation will be.

And the best results were obtained at concentrations at the lower end of the range 0.3-0.7%.

Another important control factor is the ratio of the flux area of the inlet 51 to the apex outlet 52.

For relatively small cleaners, such as the 3-inch unit mentioned above, this ratio should be at least 1 for maximum yield.
: It should be set to 1, but there is no need to make it large if it actually lasts.

That is, if the inlet is 5 inches in diameter, the outlet 52 may have a diameter in the range of % inches to za inches.

For larger cleaners, such as 6 inches in diameter, this ratio should be in the 1:1 to 1:1.5 range; this ratio generally requires two outlets for best yield. The volumetric flow rates through the volutes should be approximately equal; however, the larger the cleaner, the more the normal The pressure drop must be greater than the operating pressure.

For example, a 6-inch centrifugal cleaner will normally operate with a pressure drop of 40 psi, and a 3-inch centrifugal flotation device will operate with a pressure drop in the range of 40-100 psi, but a 6-inch centrifugal A floatation device requires a minimum pressure drop of 80 psi, with even higher pressure drops in the range of 80-200 psi desirable.

Although the conditions outlined above have been found to be most satisfactory for obtaining the highest yield of fibers of acceptable quality, the centrifugal flotation device 50 still provides a relatively It can also be operated with considerable selectivity to obtain small selected fractions.

For example, the flow rate from the apex outlet 52 is 20-3 of the supply flow rate.
If reduced to the 5% range, that fraction would contain the majority of the longest fibers present in the stream fed to the device and thus would contain less fines and light contaminants.

Thus, as the diameter of outlet 52 decreases from 46 inches to Z6 inches, the flow rate therethrough decreases from about 50% to about 25%, and the amount of fiber removed as waste from base outlet 53 decreases from about 12% to about 25%. It increases to about 25%.

Although in the above example the reduction in size of outlet 52 is an 8:5 ratio, the effective flux area of the outlet would still be more than 12 times that of the apex outlet of a conventional cleaner of the same size. Please be careful.

Also, by increasing the back pressure on the outlet 52 without changing its actual size, e.g.
It will be clear that a suitable throttle valve 56 in the middle of T would also achieve the same result.

In general, it can be said that the highest quality fiber yields are obtained by increasing the pressure drop from the centrifugal flotation device, reducing the selection volume, and operating at very low concentrations, e.g. 0.3%; There will be a corresponding decrease in the waste portion.

Thus, the most satisfactory results have been obtained as described above with a 3-inch device, and the above discussion regarding the ratio of inlet to apex outlet is similar to that for a 3-inch device.
Depending on the desired volume and quality of selected fibers obtained1:
A ratio in the range from 0.75 to 1:1.25 can be suitably re-indicated.

Selected material from device 50 exits at apex outlet 52 and will typically require an additional treatment or treatments depending on its end use.

It is then shown to be conveyed by line 56 to a post-processing stage.

For example, if the selected material from device 50 still contains appreciable amounts of fine particles of fine sand or organic dust, it may be subjected to another centrifugal cleaning step, in which case processing station 60 represents additional feed pumps and cleaners such as pump 31 and cleaner 33;
It can be used in addition to or instead of the pump 39 and cleaner 40.

Another possible post-treatment is cooking, especially if the fibers contain difficult-to-remove contaminants such as fats, oils, waxes and bitumen, which are easily dispersed by cooking and in any case still However, it is used when bleaching textiles.

Station 61 therefore represents a digester, any conventional digester, using NaOH as the chemical at a concentration of 1-15% by weight, and pressure and temperature conditions of 10 psi and 239 psi.
Satisfactory results are obtained at temperatures ranging from 100 psi and 338°F and times from 5 to 15 minutes.

A suitable dehydrator should be used before the digester, which will reduce the 0.6-1.0
%, yet station 62 represents the final stage of the cooking and dewatering equipment.

It should be noted that it is much more beneficial to carry out the cooking step just described after the centrifugal flotation step than before.

For example, cooking tends to reduce the particle size of certain light contaminants, particularly synthetic fibers, which make them more difficult to remove than if they were larger.

Additionally, removing most of the fat by centrifugation results in less chemicals being required in the subsequent cooking process than if the fat was still present.

Depending on the amount of oily material present in the slurry, it may be advantageous in the practice of the invention to include a preliminary step aimed at loosening the oil from the fibers prior to subjecting the slurry to centrifugal flotation.

For example, soaps, detergents or other grease dispersants may be added to the slurry.

Apart from that, the slurry may additionally be subjected to a mechanical action or a papermaking action tending to loosen the fats and oils from the fibers, for example in a disc refiner or a def soaker. The section shown here has been modified to provide such an additional processing station 65 between the fines remover 42 and the flotation device 50, which is the preferred arrangement for this refining and/or fat dispersion stage.

Another optional step, particularly useful for eliminating particles that hydrodynamically tend to behave like paper fibers, is to aerate the slurry prior to centrifugal flotation device 50. That's true.

FIG. 3 shows a portion of the system of FIG. 1, but here modified to provide a pressure tank 66 connected parallel to line 45,
It is such that a small portion, for example 20%, of the feed flow to the device 50 passes therethrough and then rejoins the main stream.

If the tank 66 is kept approximately half full with air pressurized to, for example, 90 psi, the air will dissolve into the liquid and will be released as bubbles within the device 50.

These air bubbles tend to attach themselves to the contaminant particles, acting as if they were of lower specific gravity, thereby causing them to migrate into the inner part within the device 50 and into its base outlet 53. looks like.

Although a complete system like the one described above seems preferable,
However, considerable modifications may be made within the scope of the invention.

For example, the centrifugal flotation device 50 is quite effective as a fines remover and the line 41 except for the fines remover 42 because the fines are separated into a portion that is discharged through the base outlet 53.
can be connected directly to the pump 44.

Similarly, the number of centrifugal cleaning stages 33 and 44 is primarily a matter of choice determined by the amount of fine inorganic and organic dust particles remaining after the initial treatment in cyclone 20 and sorting devices 25 and 30.

In a further variation of the system shown in FIG. 1, one or both of the screens 25 and 30 may be replaced by a centrifugal flotation device, in which the majority of the contaminants removed by sieving are large particles, low specific gravity particles, e.g. It can perform the same sorting function on plastic, wax paper, wood, corn, leaves, etc.

For example, a 6 inch centrifugal flotation device may serve satisfactorily with coarse sorter 25, followed by a 3 inch centrifugal flotation device for fine sorting, followed by a regular fine screen.

A special benefit derived from using centrifugal flotation devices for screening is that they waste a considerably lower proportion of paper fibers than ordinary screens, thus increasing the yield of fibers in the screened material. be.

After washing with one or more centrifugal cleaners 33 and 40, the selected material is fed to a centrifugal flotation device 50 as already described.

All such modified systems and conditions can also be further modified with the addition of one or both refining and fat dispersion equipment.

As already mentioned, the differences between the preferred concentrations for carrying out each step will require dilution and dehydration equipment at various locations in the system, but it is not appropriate to illustrate such equipment. This seems unnecessary to businesses.

However, it may be helpful to supplement the above explanation with preferred values for each step in terms of concentration.

3.5% for the cyclone 20 and the coarse screen 25, 1% for the fine screen 30, 0.7% for the cleaner 33, 0.5% for the cleaner 40, 0.3% for the fine powder remover 42, and 0.0% for the centrifugal flotation device 50. 5% and 35% in digester 61.

It should also be noted that both the fines remover and the centrifugal flotation device have a dewatering effect on the selected feedstock therefrom.

For example, if the feedstock enters the fines remover at 0.3%, the refined feedstock will be dehydrated to about 3.5%.

In the centrifugal flotation device, the concentration of the selected raw material is approximately 2 of the input concentration.
doubling, while the concentration of waste from the base outlet is about half of the input value.

As already noted, solvent-soluble contaminants oils, fats and waxes constitute approximately 5% of the solids in municipal waste, and they represent an even greater proportion in the waste from flotation device 50.
In other words, it constitutes a range of 20-35%.

This waste can be incinerated in a fluidized bed reactor or similar final disposal equipment along with the waste from the preceding cleaning and sorting equipment, but the solvent soluble portion can also be used for other uses, e.g. It is also practical to recover it, for example as a raw material for the production of soap or fuel.

In fact, the waste from the device 50 is essentially entirely organic, so that the main components other than oils and waxes are natural or synthetic in origin, such as plastics and plants.
Also, it is relatively 1 that passed through the fine screen 30.
Due to their uniform and sufficiently small particle size, all wastes are highly suitable for conversion into fuel by calcination or hydrogenation according to JP-A-47-12713.

Therefore, the apparatus 70 of FIG. 1 also represents such processing.

An alternative to using all of the waste from flotation device 50 as a fuel source is to process the solvent-soluble portion by conventional treatment, such as an initial flotation-clarification step, followed by distillation or chemical treatment using a suitable solvent. It can be collected separately through a collection process.

Therefore, stage 70 of FIG. 1 also represents such a selective recovery stage.

The residue after removal of the solvent soluble portion consists mostly of paper fiber fines that can pass through a 100 mesh mesh and is therefore essentially worthless for papermaking purposes.

These fines typically consist of 60-7 of the waste material from the flotation device 50.

Therefore, it is generally practical to dispose of the residue by incineration, except as noted in the following text. As mentioned earlier, when floating devices are used as screens at stations 25 and 30 in Figure 1, , and the waste material from flotation devices will be similar in that it is primarily organic and still contains a relatively low proportion of recycled paper fibers.

It also contains a substantial proportion of plastics and other organic materials, including solvent-soluble contaminants.

It would then be suitable for use as a feedstock for conversion into fuel, whether or not the solvent-soluble portion is first recovered from it, and if the system is still intended to handle waste in this manner. For example, it is usually practical to combine it with the waste from flotation device 50, especially if the solvent soluble portion is first removed from the feedstock.

Although the methods and products described herein are preferred embodiments of the invention, the invention is not limited to these specific methods and products, and modifications may be made without departing from the spirit of the invention.

[Brief explanation of drawings]

FIG. 1 shows a somewhat schematic overall system for implementing the invention. 2 and 3 are fragmentary views showing a modification of the system of FIG. 1.

Claims (1)

[Scope of Claims] 1. In recovering paper fibers for reuse from waste, including waste paper contaminated with oily contaminants, the method comprises: (a) preparing an aqueous slurry that can be pumped from the waste; The solid components are of the same maximum particle size as the paper fibers and are essentially oils, fats, and other organic substances that have a lower specific gravity than the paper fibers but are hydrodynamically (b) feeding the slurry into a conical device which has a tangentially disposed inlet port adjacent to its base; It also has outlets at its apex and base, the inlet and the base outlet being of substantially the same flux area, the flux area of the apex outlet being of the same order of magnitude as the base outlet, but with substantially the same flux area. (c) is larger than the apex outlet of an ordinary centrifugal cleaner of essentially the same size as the device;
maintaining the feed flow rate sufficiently higher than that to the inlet of a conventional cleaner to cause the device to develop a pressure drop at least equivalent to that used in a conventional cleaner for a conventional centrifugal cleaning operation; thereby causing the slurry in the device to undergo a spiral separation into an outer portion containing a majority of paper fibers and an inner portion containing a majority of light contaminants, and (d) substantially reducing the discharge flow rate from both outlets thereof. Recovery of paper fibers from waste, characterized in that the amount of paper fibers is maintained at the same level as above so that the portion of the outer part discharged from the apex outlet as raw material contains the majority of the paper fibers entering the device. Hoto