JPS5843148B2 - How to purify municipal waste compost - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a purification method for producing urban compost.

When municipal waste is composted through aerobic fermentation, non-compostable materials such as soft plastics, metals, and cloth contained in the municipal waste can be separated to some extent by sorting, magnetic sorting, wind sorting, etc. Brittle non-compostable materials such as glass, ceramics, and hard plastics generally have small particle sizes, and especially when they are crushed as a pretreatment, they become fine particles in the process and are difficult to separate from compostable materials.

In order to remove these brittle non-compostable materials, various attempts have been made, such as a repulsion type separation method that takes advantage of the difference in elasticity between composted materials and foreign materials, and an air separation method that takes advantage of the difference in specific gravity. Although relatively good results were obtained when the particle size of these foreign substances was large, it was virtually impossible to separate them when the particle size was small.

Therefore, these foreign substances, such as brittle non-compostable materials such as glass, ceramics, and hard plastics, not only accumulate in the soil because they do not decompose naturally, but also pose a danger to agricultural operations, so they must be virtually completely removed. In other words, removal of these foreign substances is extremely important as an essential condition for putting municipal waste compost into practical use.

In response to this, the inventors used electrostatic separation to accurately separate brittle foreign substances such as glass, ceramics, and hard plastics with relatively small particle sizes, which had previously been difficult. Through the separation process, most of the non-brittle non-compostable materials are removed, the load of electrostatic separation is reduced, the effect of electrostatic separation is enhanced, purification is made easy and reliable, and municipal waste compost becomes practical. In order to achieve this goal, a purification method was invented in which the moisture content of crushed and separated municipal waste compost raw materials was adjusted and foreign substances were removed by electrostatic separation (Japanese Patent Application No. 106955/1982), and the present invention relates to improvements thereto. Then, this moisture content is adjusted by a drying process, and as a heating source, the combustible materials among the non-brittle non-compostable materials removed by the mechanical separation process are incinerated, and the incineration heat generated at that time is used. The purpose of the present invention is to provide a method for refining municipal waste compost that can utilize more energy and reduce the amount of residue that must be disposed of in landfills.

The above-mentioned technical idea of adjusting the water content and removing foreign substances by post-electrostatic separation was created by focusing on the following findings obtained based on research and experiments conducted by the inventors. It is something that

(1) The average moisture content of municipal waste compost is generally about 40% to 5.
The moisture content is around 0%, but composted material has a high moisture content.
On the other hand, brittle foreign objects such as glass, ceramics, and hard plastics do not absorb moisture, so there is a significant electrical resistance between them. There is a difference.

According to the inventors' measurements, as shown in Figure 1, the electrical resistance value of brittle foreign materials such as glass, ceramics, hard plastics, etc. The lower limit was found to be higher than the upper limit of the electrical resistance value of the compost.

As a result, the well-known electrostatic separation method, in which two types of substances with different electrical resistances are charged and separated by the action of a high-voltage electrostatic field, has been shown to be effective even for compost consisting of a variety of substances. It was foreseen that it would be possible to separate these with high precision.

(2) Municipal waste is crushed and sieved in advance to remove non-compostable materials such as soft plastics, metals, cloth, and wood, and brittle foreign materials such as glass, ceramics, and hard plastics are mixed into compostable materials such as kitchen waste and paper. After the raw material was composted by aerobic fermentation, it was further passed through a 511t11L mesh sieve, and the moisture content of the bottom of the sieve was variously adjusted and tested using the electrostatic separation apparatus shown in FIG. 2.

In the figure, 8 is a raw material, 9 is a diaphragm, 10 is a high voltage electrode, 11 is a ground electrode, 12 is a partition, 13 is a composted material, and 14 is a non-composted material that is a brittle foreign material.

As a result, under conditions of complete dryness (moisture content 0), it was impossible to separate the composted material from the brittle foreign matter group, but when the co-average moisture content was less than 50% or more than several percent, habo lO
It has been found that it is possible to separate composted material with a purity of 0%.

FIG. 3 shows the relationship between the average moisture content and the yield of composted material (100% purity) when the applied voltage is 3 and 3.

When the average moisture content exceeds 50%, composted materials tend to adhere to foreign matter, and the apparent specific gravity of composted materials increases. Yield drops significantly.

The optimal average moisture content for electrostatic separation is generally in the range of 35% to 5%, but it is often industrially difficult to adjust the moisture content to less than 10%, so in practice it is recommended to It is preferable to adjust the amount below to 10% or more.

In terms of handling, transportation, commercial value, etc., the moisture content of the compost 9 is generally preferably 40% or less, and this condition coincides with the moisture content desired when implementing the present method.

Incidentally, when the average moisture content is high (around 50%), the yield of the composted material tends to be improved compared to the results shown in FIG. 3 by increasing the applied voltage and decreasing the particle size.

(3) To simplify the explanation, a uniform horizontal electrostatic field (voltage E
), ignoring air resistance and considering the behavior of the composted material (conductive material).If the specific gravity of the composted material is r and the particle size is d, then the horizontal electric force f1 is f1■d2・E
2. Since the gravity f2 in the vertical direction is f2ocd3·r, the angle θ that the resultant force F makes with the vertical direction as shown in FIG. 4 is θ0(tan''E-).

In order to improve the separation accuracy, it is preferable to increase θ as much as possible, that is, to increase the voltage E and decrease the particle size d and specific gravity r, but for practical purposes, the voltage is generally 40 to 50 or less. The specific gravity r is defined by the water content.

Therefore, it is preferable to make the particle size as small as possible, and in this respect, this method, which aims to separate brittle foreign substances that are easily made into fine particles, is significantly more effective than conventional repulsion methods or wind power methods. This is also one of the reasons why it is advantageous.

On the other hand, in order to increase the composting speed, it is generally preferable that the particle size of the composted material be small, and extremely small particle sizes are disadvantageous in terms of clogging of sieves, power consumption, and aeration.

Considering both the electrostatic separation accuracy and the composting conditions described above, it is desirable that the mesh size of the sieve is 15 mm or less and 5 nm or more.

As described above, the method described above not only enables highly accurate separation of brittle foreign substances in compost, which was previously difficult, but also provides the optimal adjustment conditions for moisture content and particle size when applying this method. It has basically been clarified that the conditions match well with the operating conditions for composting and the conditions for increasing commercial value.

The present invention is a method of removing non-brittle non-compostable materials such as co-soft plastics, metals and cloth through the first mechanical separation step before the composting and fermentation process of municipal waste, and then removing the remaining material group. The moisture content is adjusted to 50% or less and 5% or more, the particles are sorted through a second mechanical separation process, and then separated into compostable materials and brittle non-compostable materials such as glass, ceramics, and hard plastics through an electrostatic separation process. This is a method for refining municipal waste compost.

To explain the present invention with reference to the drawings, as shown in Fig. 5, cities where mixed collection or separate collection is carried out,
Next, through mechanical sorting process 1, soft plastics, metals,
After removing non-brittle non-compostable materials such as cloth, it enters fermentation step 2, where it is fermented and composted in a fermenter, and then undergoes a secondary mechanical separation step 3, where plastic film, which is a non-brittle non-compostable material, is processed. After the removal, the moisture content of the remaining substance group (composted material raw material) is reduced to a step 5 in which all or part of the non-brittle non-composted material removed in the primary or secondary mechanical separation steps 1 and 3 is incinerated. The waste is dried in a drying step 6 using combustion heat generated during incineration in an incinerator, then sieved to size in a sieving step 7 to remove coarse foreign matter, and then electrostatic separation step 4. This removes brittle non-compostable materials such as glass, ceramics, and hard plastics, and the remainder is collected as refined compost.

In the primary mechanical sorting step 1, after crushing, non-brittle non-compostable materials such as soft plastics, metal cloth and leather are removed by sieving.

This non-brittle non-compostable material is further magnetically sorted using a magnetic separator to remove iron, and the material that is mainly combustible is sent to an incinerator and incinerated.After passing through two sieves, the composted material is separated into glass by repulsion type separation.・Part of the ceramics, etc. is removed, and then magnetically separated by a magnetic separator to remove remaining small-sized iron pieces.

The remainder is then introduced into a fermenter for aerobic fermentation and composting.

The fermentation gas generated at this time is led to an incinerator and used as combustion air, where it is burned and deodorized.

Next, in the secondary mechanical sorting step 3, air sorting is carried out to remove the plastic film, which is sent to an incinerator and incinerated.

The composted material is then led to a drying process.

Incineration heat in an incinerator is used as a heat source for drying work, and the average moisture content is kept below 50% and above 5% (preferably 35%).
% or less and 10% or more).

The exhaust gas generated during drying is led to an incinerator and used as combustion air for combustion and deodorization.

The composted material is further subjected to a sieving operation in the sieving step 7, which is a part of the second mechanical sorting step, to remove coarse foreign matter and size the particles to about 5 to 15 particles, followed by an electrostatic sorting step. Sent to 4.

In this state, both the moisture content and particle size are adjusted to a range that allows electrostatic separation, so the electrostatic separator almost completely removes brittle non-compostable materials such as glass, ceramics, and hard plastics, resulting in purity. It is possible to separate highly purified compost.

As the electrostatic separator, a known composite cylindrical type having both a corona electric field and an electrostatic field as shown in FIG. 6 may be used.

That is, the composted material that has fallen into the grounded rotating cylinder 20 via the conveyor 19 passes through a corona electric field and then further passes through an electrostatic field, where it is divided into conductive composted material B and insulating brittle non-composted material 0 group. They are classified as follows.

21 is a brush, 22 is a corona discharge electrode, 23 is a compost hopper, and 24 is a foreign matter hopper.

As the electrostatic separation step 4, in addition to the above-mentioned composite cylindrical method, various known methods can be used, such as a pure electrostatic cylindrical method, a corona discharge cylindrical method, a method of dropping in a horizontal electric field, and a frictional charging method. I can do it.

If metals are removed before fermentation step 2, it is possible to prevent electric metals from eluting in fermentation step 2.

A magnetic separator or repulsion type separator may be inserted in a process after fermentation process 2, and in this case, some metal, glass, ceramics, etc. can be removed in advance to reduce the load on the electrostatic separator. .

In the above example, the steps shown in the following items are the steps corresponding to the positions of the -second mechanical sorting step 1 and the second mechanical sorting step 3 (including the sieving step 7), or a part of the steps. can also be applied.

Thus, the same process may be applied to the primary and secondary positions, or different processes may be applied to each.

(a) Mechanical sorting process (denoted as M) only (does not include crushing process).

As the mechanical sorting process M, vibrating sieving, trommel sieving, repulsion sorting, wind sorting, etc. are selected.

If the material has already been sufficiently crushed before entering the process of this embodiment, crushing does not necessarily need to be performed in this process.

Furthermore, if the first step is enough to crush the material, the second step may not be necessary.

However, sieving and grading are performed in the second stage. (b) The mechanical separation process M is accompanied by a crushing process (denoted as S), and S and M
(S+M) is a crushing/sorting process in which S and M are connected in series in the order of separate processes.

As this shredding step S, a method such as a hummer mill type, a shredder set, a trommel type, etc. is selected.

(e) The mechanical separation step M is accompanied by a crushing step S, and S and M are performed simultaneously in the same device (SM
) is an integrated process of crushing and separation.

As this device, for example, a selective crushing and sorting machine as a crushing and sieving machine as shown in FIG. 7 can be used.

This is a cylindrical screen 1 rotated by a drive device 17.
5 and a scraping plate 16 which is rotated by a drive device 18 at a speed different from that of the cylinder, and the raw material is sent in the axial direction to repeat crushing and sieving in an integrated manner. The non-brittle non-compostable materials A and (B+C) are easily coarsely selected.

Here, B is a composted material and C is a brittle non-composted material.

Although it is also possible to use a crushing/sieving machine that does not have a scraper plate 16, a crusher and sieve machine that does not have a scraper plate 16 has a better crushing effect and
Sieving action is fast and reliable.

The drying step may be placed before, after, or both of the fermentation steps.

As a form of utilizing heat from incineration of non-brittle non-compostable materials, (a)
A type in which the incinerator is equipped with a waste heat boiler and the generated steam is used as the heat source for the drying process, (→ a type in which the heat source is high-temperature air that has been heat exchanged with the incinerator waste gas, (c), or the incinerator is a partial combustion type or This is a two-chamber circulation type pyrolysis device, and there are several types that use the combustion waste gas, produced oil, produced gas, etc. as the heat source.

Fermentation gases with odors released from the fermenter in this case,
It is desirable from the viewpoint of pollution control and economics to use the dry exhaust gas etc. in the drying process as combustion air in an incinerator and deodorize it by combustion.

Since the above embodiment is configured as described above, it brings about the following effects.

(1) Since the waste heat from incineration of non-brittle non-composted materials is used to adjust the moisture content of the compost, the energy efficiency is high.

(2) It is an excellent Go□M system because it can also dispose of non-brittle non-compostable materials.

There is very little final residue that needs to be landfilled.

Only glass/ceramics and incineration ash.

(3) Fermentation gas and dry exhaust gas can be deodorized, so secondary pollution measures are perfect.

(4) A crushing and sieving process is provided before the fermentation process, and this process removes most of the non-brittle non-compostable materials (mostly soft plastics with low bulk specific gravity), so the compost is sent to the fermentation tank. The volume of the raw material becomes i~+, and the processing capacity of the equipment after the fermenter increases by 2 to 3 times.

(5) A repulsion type separation process is installed before the fermentation process to remove glass and ceramics with a relatively large diameter in advance, and the stirring action during the fermentation process makes the glass finer and reduces the burden on the electrostatic separation process. This prevents the increase in the amount of waste, so you can obtain high-quality compost.

Similarly, by installing a magnetic separator before the fermentation process, foreign substances can be removed as much as possible before exposure to the acidic atmosphere during fermentation, preventing the elution of heavy metals and producing high-quality compost.

(6) After the fermentation process and before the drying process, a wind separation process is installed to remove small pieces of plastic film.

Before the fermentation process, the moisture content of the compost raw material is 60 to 70%, and films tend to adhere to the wet raw material, and the whites of the raw material adhere to the inner wall of the equipment, resulting in poor wind separation efficiency.

Further, after the drying process, the moisture content of the compost is adjusted to 10 to 35% and the specific gravity becomes small, so the bulk specific gravity approaches that of the films and the separation efficiency decreases.

Between the fermentation process and the drying process, that is, when the moisture content of the compost is 40-5
If it is in the 0% range, the compost will not adhere to the inner wall of the device and the difference in specific gravity between the compost and the films will be maintained at an appropriate level, making it possible to effectively separate the films.

A vertical (zigzag type) wind-powered separator separates compost downwards and films upwards.

(7) Before the electrostatic separation process, a sieving process is provided as a second mechanical separation process to size the compost and foreign substances to be electrostatically separated (which may involve crushing as the case may be). This increases the electrical separation efficiency.

(8) Due to the above-mentioned effects, a revolutionary high-quality compost made from municipal waste can be obtained.

According to the present invention, a primary and a secondary mechanical separation step is provided, and the fermentation tank is required to be small because a large amount of material unsuitable for composting is removed in the primary step, and the stirring operation is performed because there are fewer foreign substances. In the second stage, large particles are removed in the first stage, so separation is easy; if only the first stage is used, grading is insufficient; If only the second stage was used, the processing capacity would be too small, but by using both the first and second stages, granulation is performed well.
It is possible to provide a method for refining municipal waste compost that can easily obtain a particle size suitable for the next electrostatic separation process and improve the electrostatic separation accuracy and separation ability, and can have extremely effective practical effects. .

[Brief explanation of the drawing]

The drawings relate to embodiments of the present invention, and Fig. 1 is a graph showing experimental results, Fig. 2 is an explanatory diagram of the experimental apparatus, and Fig. 3 is a graph showing experimental results.
The figure is a graph showing the experimental results, Figure 4 is an explanation diagram of the operation, and Figure 5 is a graph showing the experimental results.
The figure is a flow sheet of an example, FIG. 6 is an explanatory diagram of an electrostatic separator, and FIG. 7 is an explanatory diagram of a crushing and sieving machine. 1...-Second mechanical separation step, 2...Fermentation step, 3...Second mechanical separation step, 4...
...Electrostatic separation process, 5...Incineration process, 6...
... Drying process, 7... Sieving process, 8...
...Raw material, 9...Vibration plate, 10...
High voltage pole, 11... Ground pole, 12...
Partition, 13... Composted material, 14...
Non-compostable material, 15...Cylindrical screen, 16.
...Scraper, 17, 18... Drive device, 1
9...Conveyor, 20...Grounded rotating cylinder, 21...Brush, 22...Corona discharge electrode, 23...Compost hopper , 24...
...Foreign object hopper.

Claims (1)

[Claims] 1. Non-brittle non-compostable materials such as soft plastics, metals and cloth are removed from municipal waste through a first mechanical separation process, and then composted through a composting fermentation process, and then The moisture content is adjusted to 40% or less and 10% or more by a drying process, then coarse foreign matter is removed by a second mechanical separation process, and the components under the sieve are separated by an electrostatic separation process.
A method for refining municipal waste compost, which is characterized by obtaining purified compost by removing brittle non-compostable materials such as glass, ceramics, and hard plastics. 2 The second mechanical sorting step has a pore size of 5 to 151!
2. The method according to claim 1, using a mm screen. 3 Non-brittle non-compostable materials such as soft plastics, metals and cloth are removed from municipal waste through the first mechanical separation process, followed by composting through the composting fermentation process, and then the moisture content is reduced through the drying process. is adjusted to 40% or less and 10% or more, then coarse foreign matter is removed by a second mechanical separation process, and the components under the sieve are separated by an electrostatic separation process.
Purified compost is obtained by removing brittle non-compostable materials such as glass, ceramics, hard plastics, etc., and the drying step is characterized in that the drying process is performed using combustion heat generated by burning the non-brittle non-compostable materials. A method for refining municipal waste compost.