Method and plant for converting plastic into oil

Abstract

A method and plant for conversion into oil is provided which can completely heat and decompose a large amount of a plastic raw material, and treat a harmful gas. The plastic raw material is dissolved in a dissolution section (31) to form an expanded plastic. The expanded plastic is sent to an inclined first-stage decomposition column (47) and a second-stage decomposition column (48) adjacent to the first-stage decomposition column, both having fixed temperature distributions, which depolymerize and decompose the plastic into a light secondarily decomposed gas. The extracted secondarily decomposed gas is cooled into oil in condensers (37, 38) and collected in oil storage tanks (42, 43).

Description

TECHNICAL FIELD

The present invention relates to a method and a plant for converting plastic into oil for collecting the oil from the plastic.

BACKGROUND ART

Various plants for collecting oil from plastic waste have been proposed, none of them, however, has sufficiently decomposed the plastic, and actually no plants are in practical operation.

The present applicants previously developed a plant for conversion into oil that has a compact and simple structure of an inverse thermal gradient type, which is disclosed in Japanese application patent laid-open publication No. 2000-16774.

There have been problems, however, with this plant for conversion into oil, including: 1) the plant can reliably convert a small amount of plastic into oil, but the plant cannot completely convert a large amount of plastic into oil, 2) the plant cannot sufficiently treat a hydrogen chloride gas that is generated in a dissolution section in dissolving PVC (polyvinyl chloride) plastic, and 3) the plant cannot sufficiently treat an off gas that has not been converted into oil.

The present invention has been mainly made in light of these problems and a primary object of the present invention is to provide a method and a plant for conversion into oil, which are able to convert a large amount of plastic into oil, to treat a hydrogen chloride gas, and to completely treat an off gas.

DISCLOSURE OF THE INVENTION

The method for conversion into oil according to the present invention comprises heating and dissolving the plastic into expanded plastic, and removing the expanded plastic, heating and depolymerizing it, and cooling it into oil. The expanded plastic may preferably be removed by being lifted at an angle, preferably at an angle of 25-30° relative to the horizontal. The expanded plastic may preferably be heated with being lifted at an angle and the expanded plastic may preferably be heated to higher temperatures at higher positions. The dissolved plastic may preferably be added with vegetable oil or animal oil or mineral oil and heated to generate expanded plastic of their mixture.

The method for conversion into oil according to the present invention may preferably comprising separating a hydrogen chloride gas generated in dissolving the plastic from other decomposed gases, then reacting the hydrogen chloride gas with hydrated lime, and collecting it as calcium chloride. An off gas not converted into oil may preferably be treated by catalytically cracking the off gas with a hot ceramic.

A plant for conversion into oil according to the present invention comprises a dissolution section for heating and dissolving the plastic into expanded plastic, and a decomposition section for removing the expanded plastic, heating and depolymerizing it, and cooling it into oil. In this plant for conversion into oil, the decomposition section may preferably comprise a removal means for removing the expanded plastic by lifting it at an angle, preferably at an angle of 25-30° relative to the horizontal. The decomposition section may preferably comprise a heating means for heating the expanded plastic with lifting it at an angle and for heating the expanded plastic to higher temperatures at higher positions. The plant may preferably comprise an oil injection means for injecting vegetable oil or animal oil or mineral oil into a connection between the dissolution section and the decomposition section. The dissolution section may preferably comprise a plurality of dissolution columns with different temperature ranges. The decomposition section may preferably comprise a plurality of tilted decomposition columns with different temperature ranges.

The plant for conversion into oil according to the present invention may preferably comprise a dechlorination system for treating a hydrogen chloride gas generated in the dissolution section. This dechlorination system may preferably comprise a separator for separating the hydrogen chloride gas from other decomposed gases, and a reactor for reacting the hydrogen chloride gas separated by the separator with hydrated lime into calcium chloride. The plant may preferably comprise an off gas treatment system for treating an off gas not converted into oil after cooling in the decomposition section by catalytically cracking the off gas with a hot ceramic.

The plant for conversion into oil according to the present invention may preferably comprise a residual collection means at the top of the final stage decomposition column of the multistage decomposition columns. The residual collection means may preferably comprise a column with its upper opening at the top of the final stage decomposition column and its lower opening in an atmosphere of an inactive gas heavier than the air.

The plant for conversion into oil according to the present invention may preferably comprise a hopper for storing and supplying the plastic into the dissolution section, and the hopper may preferably comprise a lead screw with a spiral blade. The plant may preferably comprise an unheated section formed as an unheated area of a predetermined length between the hopper and the dissolution section. The plurality of dissolution columns each may preferably comprise a lead screw with a spiral blade for carrying the plastic, and a beginning dissolution column of the plurality of dissolution columns may preferably comprise the lead screw blade with a greater pitch than the lead screws blades in other dissolution columns.

In the plant for conversion into oil according to the present invention, the dissolution section and the decomposition section each may preferably comprise: an inner column; an outer column around the inner column; a hot air space between the inner column and the outer column and through which an hot air circulates; and a temperature sensor for detecting a temperature in the dissolution section or the decomposition section, and the plant may preferably further comprise a carbon dioxide gas supplying system for supplying the carbon dioxide gas into the hot air space if the temperature sensor detects an abnormal temperature equal to or greater than a predetermined temperature.

In the plant for conversion into oil according to the present invention, the dissolution section and the decomposition section each may preferably comprise: an inner column; an outer column around the inner column; and a hot air space between the inner column and the outer column and through which an hot air circulates, and the plant may preferably further comprise: a hot air production system for generating by combustion the hot air to be supplied into the hot air space; and a drying system for drying the plastic to be supplied into the dissolution furnace, and an air in the drying system may preferably be supplied into the hot air production system to be deodorized by combustion. The air in the drying system may preferably be supplied into the off gas treatment system to be deodorized by being catalytically cracked with a hot ceramic.

In the plant for conversion into oil according to the present invention, an extendable column which is extendably formed may preferably be used in a part of the dissolution column includes, and the extendable column may preferably comprise: an inner column; a bellows around the inner column which has one end fixed on the inner column and an other end slidable relative to the inner column; and an outer column which is fixed on the other end of the bellows and slidably contains the inner column.

In the plant for conversion into oil according to the present invention, the dissolution section may preferably comprise: an inner column; an outer column around the inner column; and a heating medium space between the inner column and the outer column and through which a liquid heating medium circulates, and the plant further may preferably comprise a heating medium supplying system for supplying the liquid heating medium into the heating medium space.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of the basic principle of the present invention.

FIG. 2 shows a schematic diagram of an embodiment according to the basic principle of the present invention.

FIG. 3 shows a schematic perspective view of a plant of conversion into oil of an embodiment according to the present invention.

FIG. 4 shows a schematic front view of a plant of conversion into oil of an embodiment according to the present invention.

FIG. 5 shows a schematic plan view of a plant of conversion into oil of an embodiment according to the present invention.

FIG. 6 shows a schematic diagram of FIG. 5.

FIG. 7 shows a schematic diagram of FIG. 4.

FIG. 8 shows a schematic transverse cross sectional view of a dissolution column.

FIG. 9 shows a schematic transverse cross sectional view of a decomposition column.

FIG. 10 shows a schematic diagram of a dechlorination treatment section.

FIG. 11 shows a schematic diagram of an off gas treatment section.

FIG. 12 shows a schematic diagram of another embodiment.

FIG. 13 shows a schematic diagram of a connection between a dissolution section and a decomposition section.

FIG. 14 shows recovery rates for different plastics to be treated.

FIG. 15 shows a schematic illustration of how to lift expanded plastic.

FIG. 16 shows a schematic transverse cross-sectional view of a hopper.

FIG. 17 shows a schematic perspective view of an unheated section.

FIG. 18 shows a schematic diagram of a sludge tank.

FIG. 19 shows a schematic diagram of an extendable column.

FIG. 20 shows a schematic diagram of an accident avoidance system and a deodorant system.

FIG. 21 shows a schematic diagram of another embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

The embodiments of the present invention will be described below referring to the drawings.

FIG. 1 shows a conceptual diagram illustrative of the basic principle of a method for converting plastic into oil according to the present invention. Plastic raw-material is dissolved at a temperature of 200-350° C. and is stored in a storage section 1. A decomposition column 13 lifts the plastic that is dissolved (dissolved plastic) at an angle.

The decomposition column 13 includes an inner column 2, an outer column 6 which forms a hot air space 4 around the inner column 2, and a lead screw 7. The lead screw 7 includes a rotating shaft 14 and a spiral blade 8. A motor 12 rotates the lead screw 7 at a speed of 4-5 revolutions per minute. A pipe 10 supplies a hot air into the hot air space 4 to hold the temperature of the inner column 2 at 350-620° C. for gasification and depolymerization of plastic.

The lead screw 7 carries through the inner column 2 the dissolved plastic which is primarily decomposed (into the first heavy gas state that is gasified from the dissolved state) in the lower part of the decomposition column 13 to provide a primarily decomposed gas. The lead screw 7 carries the primarily decomposed gas at a low speed to the upper part of the decomposition column 13. The primarily decomposed gas is then secondarily decomposed (into a state that is depolymerized from the plastic and can be cooled into oil) in the inner column 2 which is held at 350-620° C. by the hot air supplied from a pipe 15, to provide a light secondarily decomposed gas.

One decomposition column is enough to sufficiently secondarily decompose at the upper part of the decomposition column all oil components included in the plastic raw material. Two decomposition columns may be used of which the first stage decomposition column connects to the storage section 1 and the second stage decomposition column connects to the first stage decomposition column.

An outer case 5 resides outside the storage section 1 to form a hot air space 3 into which a hot air is sent. The plastic supplied into the storage section is heated to 200-350° C. to provide dissolved plastic mp with foamed plastic (expanded plastic) f formed on its surface. This expanded plastic f is heated with being lifted at an angle by a lead screw 7 which has its tip 14a immersed in the dissolved plastic mp. This can provide a larger contact area between the expanded plastic f and the heat to ensure the decomposition (depolymerization) of the expanded plastic f into the secondarily decomposed gas. A pipe 9 collects the secondarily decomposed gas, which is then cooled into oil and stored in an oil storage tank.

The expanded plastic f is preferably lifted at a speed of 30-60 cm/min. A lower speed will give less carrying efficiency and a higher speed will give insufficient decomposition. For example, the lead screw 7 lifts spirally the expanded plastic f as shown in FIG. 15, preferably by moving it spirally at a speed of 30-60 cm/min. This speed can be adjusted by, for example, the pitch p of the lead screw 7. The expanded plastic f is thus carried at the above-described speed and heated slowly through the inner column 2 to be sufficiently decomposed (depolymerized) in the primary and secondary decomposition temperature areas. The expanded plastic f is preferably heated for about 14-15 minutes before it is completely secondarily decomposed at about 600° C.

Different kinds of plastic raw material need to be treated at different temperatures. The storage section 1 is preferably held at temperatures (200-350° C.) at which the dissolved plastic mp can be expanded. For good decomposition, it is important to have a low temperature gradient to keep the expanded condition for a long time and to have a large contact area with the heat. For this purpose, the decomposition column 13 is preferably tilted relative to the horizontal. A hot air circulates through the tilted decomposition column 13 from top to bottom with the hot air injected at the top. The temperature thus gradually increases from bottom to top. This method is referred to as the so-called inverse thermal gradient type.

To keep the good expanded plastic f for a long time, the decomposition column 27 is preferably tilted at an angle θ of 25-30° as shown in FIG. 2. For the decomposition column 27 tilted at an angle θ of less than 25°, the expanded plastic may quickly flow transversely and disappear in a short time. For the column 27 tilted at an angle θ of higher than 30°, the gravity may make it hard to lift the expanded plastic f for a long distance from the surface of the dissolved plastic mp, so that the expanded plastic f may disappear again in a short time.

In FIG. 2, the storage section 29 for the dissolved plastic mp is formed at a connection that connects a supplying column 28 and the decomposition column 27 in V shape. The supplying column 28 includes an inner column 20 and an outer column 21. A hot air is supplied between those components via a pipe 22 to keep the temperature inside the inner column 20 at 200-350° C.

The decomposition column 27 includes an inner column 25, an outer column 17, and a lead screw 24. The lead screw 24 is provided in the decomposition column 27 such that the bottom of its shaft is rotatably supported at the bottom wall of the storage section 29. A hot air producer supplies a heated air of 450-620° C. into between the inner column 25 and the outer column 17 via a pipe 26c. This heated air then circulates through the decomposition column 27 by flowing down and exiting out of the pipe 26b in the lower part of the decomposition column 27 and flowing into the pipe 26a in the upper part. The hot air that thus circulates through the decomposition column 27 from top to bottom is able to increase the temperature in the decomposition column 27 from bottom to top. The lower part of the decomposition column 27 is held at 300-450° C. for the primary decomposition. The upper-part of the decomposition column 27 is heated to about 600° C. for the secondary decomposition.

The expanded plastic f occurs in the storage section 29. This expanded plastic f is then carried up in a good condition through the tilted decomposition column 27 and heated on the way to provide the decomposed gas. The decomposition column 27 and a supplying section 28 are connected in V shape and the dissolved plastic mp completely plugs the storage section 29. The decomposed gas can thus safely prevent any backflow from the decomposition column 27 to the supplying column 28. It is also prevented that an external air flows through the storage section 29 into the decomposition column 29, thereby eliminating any danger of explosion.

The plant for conversion into oil using the above described method for converting plastic into oil will be described below.

In FIGS. 3-7, the plant for conversion into oil 30 according to the present invention includes, for example, a dissolution section 31, a decomposition section 32 for primarily and secondarily decomposing the plastic dissolved in the dissolution section 31, a dechlorination treatment section 33 for dechlorination in the treatment of the chlorine-including PVC, an off gas treatment section 34 for treating an off gas generated in the dissolution and decomposition of the plastic, and the first and second hot air producers 35, 36 for generating a hot air which is a heat source for the dissolution and decomposition.

As shown in FIG. 6, the dissolution section 31 includes the first dissolution column 31a which connects via an unheated section 410 to a hopper 41 into which plastic raw material drops, the second dissolution column 31b which has its back end connected under the front end of the first dissolution column 31a and intersects the first dissolution column 31a at right angles, the third dissolution column 31c which has its back end connected under the front end of the second dissolution column 31b and intersects the second dissolution column 31b at right angles, and the fourth dissolution column 31d which has its back end connected under the front end of the third dissolution column 31 and intersects the third dissolution column 31c at right angles. The first to forth dissolution columns 31a, 31b, . . . , 31d are thus arranged totally in a rectangle. The dissolved plastic is dropped and sent from the front end of the previous decomposition column to the back end of the next dissolution column serially. These dissolution columns 31a-31d may also be connected horizontally.

As shown in FIG. 16, the hopper 41 includes a funnel-shaped casing 411, a cover 412 covering the top surface of the casing 411, a motor 413 centered on-the cover 412, and a lead screw 414 including a rotating shaft 414a which connects to the motor 413 and extends through the cover 412 into the casing 411 and a spiral blade 414b attached to the rotating shaft 414a. The spiral blade 414b of the lead screw 414 is totally funnel shaped to the form of the casing 414. A distance W of about 2 to 5 cm intervenes between the inner wall of the casing 414 and the periphery of the spiral blade 414b. The motor 413 rotates the lead screw 414 at a predetermined speed to prevent the light plastic from blocking the hopper 41. The heavy plastic drops through the distance W between the inner wall of the casing 414 and the periphery of the spiral blade 414b. The lead screw 414 can reliably send the light plastic chips into the unheated section 410.

The unheated section 410 is column shaped and connected under the hopper 41 (see FIG. 17). A motor 42 connects to the end of the unheated section 410. This motor 42 connects to a lead screw 137 common to a lead screw 137 in the dissolution column 31a as described below. The motor 42 rotates the lead screw 137 to slowly forward the plastic chips sent from the hopper 41 and supply them into the dissolution column 31a. A hot air does not heat the unheated section 410, unlike the dissolution column 31 as described below. The attaching portion of the hopper 41 and the dissolution column 31 are therefore separated. This can prevent the plastic from starting to dissolve near the attaching portion of the hopper 41 or the viscous resistance of the dissolved plastic from stopping the rotation of the lead screw 137. Specifically, spacing the dissolved portion of the plastic apart from the attaching portion of the hopper 41 is able to provide a longer undissolved portion of the plastic that presses forward the dissolved plastic.

The dissolution column 31 includes a rectangular outer case 136, and an inner column 131 in the outer case 136 (see FIG. 8). The inner column 131 contains a lead screw including a rotating shaft 133 and a spiral blade 132 around the rotating shaft 133. The first dissolution column 31a includes a lead screw with a greater pitch than the lead screws 137 in the other dissolution columns 31b, 31c, and 31d. This is to provide a lower retention density of the plastic to give a lower resistance because of the first dissolution column 31a having a lower set temperature than the other dissolution columns as described below. A motor rotates the lead screw 137. For example, a motor 42 rotates the first dissolution column 31a (see FIGS. 4 and 5), and a motor 55 rotates the second dissolution column 31b.

A plurality of heatsink blades 134 reside around the inner. column 131. A hot air space 135 intervenes between the inner column 131 and the outer case 136. The first dissolution column 31a is controlled to 190-200° C., the second dissolution column 31b is controlled to 210-230° C., the third dissolution column 31c is controlled to 230-260° C., and the fourth dissolution column 31d is controlled to 300-340° C. These four dissolution columns 31a, 31b, . . . , 31d are thus arranged in a rectangle with the temperature increasing with each dissolution column. This is (a) to ensure a sufficient retention time (e.g., 20 minutes) to reliably dechlorinate the chlorine including plastic such as polyvinyl chloride, (b) to provide a moderate temperature distribution over multistage columns to help the temperature control, (c) to reduce the temperature in the first dissolution column 31a to prevent the adhesion of the plastic to the rotating shaft 133 near the hopper 41, and (d) to provide a shorter installation length of the entire plant.

The first hot air producer 35 supplies a hot air via a pipe 70 to each dissolution column 31. The producer 35 supplies the hot air from downstream to upstream of the column 31 in the carrying direction of the plastic. Each dissolution column 31 thus has an inverse thermal gradient. Blowers 56, 57, 58 (see FIG. 4), and 60 (see FIG. 7) circulate the hot air through each dissolution column 31. A flue 59 connects to the first and second hot air producers 35, 36. The flue 59 includes branch pipes 59a, 59b, and an outlet 59c, and is inverted U shaped (see FIG. 4).

The decomposition section 32 includes the first stage decomposition column 47 controlled to 350-420° C. and the second stage decomposition column 48 adjacent to the first stage decomposition column 47 and controlled to 450-580° C. (see FIG. 7). The decomposition columns 47, 48 are tilted at 25-30° relative to the horizontal. The fourth dissolution column 31d has an end that connects into the first stage decomposition column 47. This connection forms the storage section for the dissolved plastic.

The first stage decomposition column 47 includes two unit decomposition columns 47a, 47b, which are divided by a partition 256 into two rows of left and right (see FIG. 9). The unit decomposition columns 47a, 47b each include an inner column 255, a plurality of heatsink fins 253 around the inner column 255, a lead screw 150, and a heat space 254 into which a hot air is sent. Each lead screw 150 includes a rotation shaft 251 and a spiral blade 252. Motors 51 and 52 rotate the lead screws 150 (see FIG. 5).

The second stage decomposition column 48 has almost the same structure as the first stage decomposition column 47. The second stage decomposition column 48 has unit decomposition columns 48a, 48b (see FIG. 6) which each have an inner column 148. The inner column 148 contains a lead screw 149. Motors 53, 54 (see FIGS. 5 and 7) rotate the lead screws 149 slowly (4-5 revolutions per minute).

The inner column 255 in the first stage decomposition column 47 has at its upper end a superheat 151 for heating to 580-620° C. the decomposed gas flowing through the superheat 151 (see FIG. 7). The decomposed gas that has been secondarily decomposed in the first stage decomposition column 47 exits through the superheat 151 and pipe 49, and is sent to the condenser 37 (see FIG. 5) via a scrubber 60 for alkali cleaning. The condenser 37 then cools the decomposed gas into oil, which is stored through a pipe 46 in an oil storage tank 42. Some of the oil stored in the oil storage tank 42 is supplied to the hot air producers 35, 36 via a service tank ST1.

On the way of the pipe 49 a valve 49a resides for controlling the flow rate of the decomposed gas through the pipe 49. The condenser 37 needs to receive only the light decomposed gas that has been completely secondarily decomposed in the first stage decomposition column 47. The decomposed gas derived from the pipe 49, however, may contain incompletely secondarily decomposed gas that is slightly heavy. For a smaller amount of the decomposed gas derived from the pipe 49, the incompletely decomposed gas cannot go up the rising portion of the pipe 49 and will be returned into the first stage decomposition column 47 and sent into the second stage decomposition column 48 via the falling column 120. For a larger amount of the decomposed gas derived from the pipe 49, the decomposed gas will be derived more strongly so that the incompletely decomposed gas can go up the rising portion of the pipe 49 and will be sent to the condenser 37. The valve 49a can thus adjust the amount of the decomposed gas derived from the pipe 49 to prevent the incompletely decomposed gas from being sent to the condenser 37.

The first stage decomposition column 47 is controlled to 350-420° C. as described above. The first stage decomposition column 47 is thus able to primarily and secondarily decompose the oil component corresponding to gasoline with a low decomposition temperature, and some of the oil component corresponding to coal oil and diesel oil. The superheat 151 can completely secondarily decompose the insufficiently decomposed gases. The condenser 37 can cool into oil the decomposed gases that have been secondarily decomposed as described above. The pipe 46 with a pump P can suck the gases that have been insufficiently converted into oil by the condenser 37 and store them in the oil storage tank 42 as an off gas.

The expanded plastic component that has been incompletely secondarily decomposed in the first stage decomposition column 47 is supplied to the bottom of the second stage decomposition column 48 via the falling column 120. The lead screw 149 in the second stage decomposition column 48 will then send up the expanded plastic component at an angle. The second stage decomposition column 48 is controlled to a temperature of 450-580° C. The second decomposition column 48 can thus completely secondarily decompose the residual portion of the component corresponding to coal oil and diesel oil, and the crude oil component. The residuals such as metal and dirt that have been dropped together with the plastic will be stored in a sludge tank 40 via a sludge pipe 40a.

As shown in FIG. 18, the sludge tank 40 contains water 40b. A metal gauge 40c resides in the water 40b, which collects the residuals. Taking the metal gauge 40c out of the sludge tank 40 can remove the residuals from the sludge tank 40. A cover 40d with a partial opening 40e covers the top surface of the sludge tank 40. Inactive gas 40f that is heavier than the air, such as carbon dioxide gas, fills the space above the water 40b in the sludge tank 40. The sludge pipe 40a has its bottom in the inactive gas 40f. A gas cylinder 40g connects to the sludge tank 40. The gas cylinder 40g can supply into the sludge tank 40 the inactive gas 40f, some of which overflows the opening 40e. The inactive gas 40f in which the sludge pipe 40a has its bottom can effectively prevent the air from flowing into the second stage decomposition column 48 from the sludge pipe 40a, thereby eliminating any danger of explosion. The water 40b in which the sludge pipe 40a has its bottom would float by the buoyancy the light residuals that may block the bottom of the sludge pipe 40a. The inactive gas 40f in which the sludge pipe 40a has its bottom can prevent the above described problem and allow for the smooth falling of the residuals into the water 40b.

The second hot air producer 36 supplies a hot air via pipes 71, 71a, and 71b (see FIG. 5) to the upper parts of the first and second stage decomposition columns 47, 48. The blowers 170, 171 can circulate the hot air through the decomposition columns 47, 48 by drawing the air out of the bottoms and returning it to the tops. The decomposition columns 47, 48 thus have an inverse thermal gradient in which the temperature decreases from top to bottom. The first hot air producer 35 supplies to the dissolution section 31 a hot air that is circulated, for example, by the blower 60 through the fourth dissolution column 31d (see FIG. 7).

The inner column 148 of the second stage decomposition column 48 has at its upper end a pipe 50 that connects to a condenser 38 via a scrubber 61 for alkali cleaning (see FIG. 5). The decomposed gas that has been decomposed in the second stage decomposition column 48 goes through the pipe 50 to the scrubber 61 and into the condenser 38. The condenser 38 then cools the decomposed gas into oil, which goes through a pipe 86 to an oil storage tank 43. Some of this oil goes through a service tank ST2 to the above described first and second hot air producers 35, 36. A cooling tower CT cools the above described condensers 37, 38 (see FIG. 3).

The first and second stage decomposition columns 47, 48 include pipes 101, 102 connected thereto, both of which connect to a collecting pipe 100. The exhaust from the first and second stage decomposition columns 47, 48 goes through the pipes 101, 102 to the collecting pipe 100 into the outside. The pump P collects through the pipe 86 into the oil storage tank 43 a gas that has not been converted into oil in the condenser 38 which connects to the above described second stage decomposition column 48.

Part of the foregoing dissolution column 31 and decomposition columns 47, 48 uses an extendable column 700. The extendable column 700 includes a bellows portion 701 and a sliding portion 702 (see FIG. 19). The bellows portion 701 includes a bellows 703 and a bellows inner column 704 located in the bellows 703. The bellows inner column 704 has a longer full length than the bellows 703. The bellows 703 and bellows inner column 704 are arranged with their ends aligned on one side. The bellows inner column 704 extends beyond the other end of the bellows 703. A support column 705 resides around the extended bellows inner column 704. These bellows inner column 704 and support column 705 provide a sliding portion 702. The support column 705 has an inner diameter that is slightly larger than the outer diameter of the bellows inner column 704. The inner surface of the support column 705 and the outer surface of the bellows inner column 704 provide sliding surfaces. In FIG. 19, an inner column 706 with the same diameter as the bellows inner column 704 resides on the portion of the support 705 on which the bellows inner 704 does not reside. Formed on the butt side ends between the bellows inner column 704 and the inner column 706 are corresponding shoulders 704a, 706a. Opposite surfaces of the shoulders 704a, 706a provide sliding surfaces.

The extendable column 700 provided in a part of the dissolution column 31 and decomposition columns 47, 48 thus serves to absorb the expansion of the dissolution column 31 and decomposition columns 47, 48 that are heated and expanded. Specifically, for the first dissolution column 31a that is heated from room temperature to about 200° C. and has a longer full length due to expansion, the extendable column 700 provided in a part of the first dissolution column 31a can reduce the bellows 703 to reduce the bellows inner column 704 toward the sliding portion 702 to absorb the expansion of the first dissolution column 31a.

In the extendable column 700 shown in FIG. 19, the sliding portion 702 includes the bellows inner column 704 with its sliding area outside the bellows 701, and the support column 705 with the diameter larger than the bellows inner column 704. The bellows inner column 704 can therefore have a greater thickness without reducing the inner diameter of the bellows inner column 704. This can prevent the deformation of the extendable column 700, therefore the damage of the bellows 703 due to the deformed extendable column 700, and the fire due to the decomposed gases or the like flowing out of the damaged portion of the bellows 703.

The dechlorination treatment system 33 will now be described in detail.

Pipes 75, 76, and 77 extending from the upper surface of the dissolution columns 31a, 31b, and 31c of the dissolution section 31 connect to a pipe 78 (see FIG. 5). The pipe 78 in turn connects to the first separator 37 (see FIG. 10). The first separator 37 can separate the hydrogen chloride gas generated in the dissolution sections 31a, 31b, and 31c from the small amount of decomposed gas contained in the hydrogen chloride gas. The separator 37 includes a cooling coil 301 on the top. The hydrogen chloride gas flowing through the pipe 78 will be cooled through the cooling coil 301 and released in the lower part of the first separator 37 below the cooling coil 301. After being released, the hydrogen chloride gas goes through the cooling coil 301, the upper part of the first separator 37, and a pipe 79 into the second separator 38 that has the same structure as the first separator 37. After being separated in the second separator 38, the hydrogen chloride gas goes into the third separator 39 that has the same structure as the first and second separators 37, 38. After being completely separated from the decomposed gas in the third separator 39, the hydrogen chloride gas goes through a pipe 81 to the lower part of the reactor 300. A plurality of these separators 37, 38, and 39 can completely separate the hydrogen chloride gas from the decomposed gas.

The reactor 300 includes a stirring bar 306 with blades 308. A hydrated lime tank 83 connects to the upper part of the reactor 300. A heating column 305 resides around the hydrated lime tank 83 to dry the hydrated lime in the hydrated lime tank 83. A lead screw 303 resides at the lower part of the hydrated lime tank 83. A motor 304 rotates this lead screw 303.

A lead screw 309 resides at the bottom of the reactor 303. A motor 310 rotates this lead screw 309. A heating column 313 heats the surrounding area of the lead screw 309 to dry and remove the water generated during the reaction in the reactor. A calcium chloride tank 312 contains the calcium chloride generated during the reaction in the reactor 309. Temperature sensors S1, S2, and S3 reside at appropriate positions in the height direction of the reactor 300. The temperature sensors S1, S2, and S3 detect the reaction heat. These reactor heat detection signals can control the rotation of the motor 304 for the hydrated lime tank 83 and the motor 310 for the lead screw 309 for evacuating the reactor 300. Specifically, the stirring bar 306 in the reactor 300 consistently rotates, and a large amount of hydrogen chloride gas flowing into the reactor 300 can facilitate the reaction to generate a large amount of heat. The temperature sensor S3 at the highest position that detects reaction heat equal to or greater than a predetermined value will cause the lead screw 303 for the hydrated lime tank 83 to rotate to send a large amount of the hydrated lime into the reactor 300. Then the reaction proceeds to generate less reaction heat and slightly reduce the temperature. When the temperature sensor S2 at an intermediate position detects a temperature in a predetermined range, the hydrated lime is accordingly supplied. Then the reaction further proceeds to slow down. When the temperature sensor S1 at the lowest position detects a predetermined temperature, it determines that the reaction stops and rotates the lead screw 309 for evacuating the reactor 300 and collects the calcium chloride generated into the calcium chloride tank 312. After the calcium chloride generated being collected, when the reaction starts again, the temperature sensor S1 detects the starting of the reaction and causes the lead screw 303 to rotate to send the hydrated lime from the hydrated lime tank 83 into the reactor 300. As the temperature sensors S2, S3 detect the reaction heat in sequence, more hydrated lime will be supplied. As the reaction heat decreases, less hydrated lime will be supplied, and the above described procedure will be repeated.

It is said that the hydrogen chloride gas usually needs a solvent to react with a dry neutralizing agent. Here, the water generated in the reaction of the hydrogen chloride gas with the hydrated lime can provide the solvent which can facilitate the neutralization reaction. The reaction formula is as follows:
2HCl+Ca(OH)₂=CaCl₂+2H₂O

A vacuum pump 314 resides to evacuate water that is generated as vapor in this reaction and draw the hydrogen chloride gas into the reactor 300. To provide a constant suction load in the vacuum pump 314, a relief valve 315 for air inflow resides on the inlet side of the vacuum pump 314. A scrubber 317 for alkali cleaning resides to remove the hydrogen chloride gas that has been insufficiently reacted in the reactor 300.

The off gas treatment system 34 will now be described.

FIG. 11 shows a schematic diagram of the off gas treatment system 34. As shown in FIG. 11, the off gas treatment system 34 includes a casing 236. In the operation of the plant for conversion into oil, a burner 234 is consistently connected to the casing 236, which is heated to about 1200° C.

The above-described casing 236 contains a plurality of ceramic prisms 238, 238, . . . , 238. These ceramic prisms can catalytically crack an off gas in {fraction (1/100)}-{fraction (2/100)} seconds that flows in through the inlet 235 connected to the above described oil storage tanks 42, 43. The ceramic prisms can thus convert the off gas into a simple oxide such as CO₂, NO_x, and H₂O. The heat energy generated in this process goes through the outlet 237 into the first and second hot air producers 35, 36.

The off gas is an endocrine disrupter, such as acetaldehyde, which has not been converted into oil in the condensers 37, 38. In this embodiment, after once collecting the off gas, the oil storage tanks 42, 43 send it to the off gas treatment system 34. The condensers 37, 38 may directly send the off gas to the off gas treatment system 34.

The safety system in the tilted columns and the deodorant system will now be described.

As shown in FIG. 20, a number of temperature sensors S, S, . . . S reside on each dissolution column in the dissolution section 31 and each tilted column in the decomposition section 32. Each sensor S connects to a controller 511. This controller 511 can control the open/close of a valve 513 connected to a carbon dioxide gas cylinder 512. This carbon dioxide gas cylinder 512 connects to a hot air circulation path P through which the first and second hot air producers 35, 36 can send the hot air into the dissolution section 31 and decomposition section 32. The controller 511 opens the valve 513 to supply the carbon dioxide gas through the hot air circulation path Q into the dissolution section 31 and decomposition section 32, if the temperature sensor S detects an abnormal temperature due to such as accidents. This can cool the dissolution section 31 and decomposition section 32, and stop the operation of the plant for conversion into oil 30.

An accumulation facility A for the plastic to be treated has at the top a suction unit 514 with a suction fan 514a. The suction unit 514 particularly sucks an air with an odor caused by the plastic waste and sends it to the hot air producer 36 for the deodorization by combustion.

Plastic chips P crushed by a crusher 515 are dried in a drier 516 with the hot air from the hot air producer 36. The dried plastic chips P are then sent to the hopper 41. The drier 516 in which the hot air dries the plastic chips P may be filled with an odor. The air with an odor in the drier 516 is sent to the hot air producer 35 for treatment after a cyclone 517 removes fine particles mixed in the air. These systems can provide excellent deodorization.

The off gas treatment section 34 for the off gas treatment may decompose the air with an odor. The hot air producer 35, 36 or the off gas treatment section 34, therefore, may treat the air with an odor.

The embodiments described above use two stages of the decomposition columns. The dissolution section 200 may be provided as follows: the second stage decomposition column 48 may precede the third stage decomposition column 210 that has the same structure and the same tilting angle as the second stage decomposition column 48, as shown in FIG. 12. The temperature range may be of 350-400° C. in the first stage decomposition column, 400-480° C. in the second stage decomposition column, and 480-580° C. in the third stage decomposition column. Such three stages of the decomposition columns can provide a more moderate distribution of the decomposition temperature and a longer decomposition time, thereby making it possible to adapt to any change in the decomposition condition such as the plastic specific gravity, and to ensure the reliable secondary decomposition.

Specifically, the upper end of the second stage decomposition column 48 connects, via a falling column 218, to the bottom of the third stage decomposition column 210 tilted at the same angle. The second stage decomposition column 48 sends the undecomposed expanded plastic and decomposed gas that have not been extracted in the column 48 into the third stage decomposition column 210 through the falling column 218. The third stage decomposition column 210 can secondarily decompose the undecomposed expanded plastic and decomposed gas. The secondarily decomposed gas goes through a scrubber 216 for alkali cleaning into a condenser 213 which cools the decomposed gas into oil corresponding to A crude oil. This oil goes through a pipe 214 into the oil storage tank 215 where the oil is stored. A blower 221 connects to the third stage decomposition column from the top to form an inverse thermal gradient. The residuals go through a sludge pipe 219 into a sludge tank 220 filled with water where the residuals are stored. A pump P sucks the decomposed gas that has not been converted into oil in the above described condenser 213 of the third stage decomposition column 210. The pump P then sends the decomposed gas through the pipe 214 into the oil storage tank 215 where the gas is stored. The first and second stage decomposition columns 47, 48 draw the secondarily decomposed gas out of the top for conversion into oil. A superheat 151, 152 decompose the gas that has been insufficiently secondarily decomposed. The second stage decomposition column can provide the decomposed gas that corresponds to a component of diesel oil, coal oil, and some of the crude oil. The third stage decomposition column can decompose the residual component corresponding to the A crude oil. More than three stages decomposition columns may be used.

The embodiment shown in FIG. 312 uses a dissolution section 200 that is formed vertically (perpendicularly). Specifically, the first, second, and third dissolution columns 201, 202, and 203 are connected perpendicularly via connections 204, 205, respectively. The plastic from the hopper 41 goes right through the first dissolution column 201, left through the second dissolution column 202, and right through the third dissolution column 203 before being supplied to the bottom of the first stage decomposition column 47. A motor 208 rotates a lead screw 207 of the third dissolution column 203 at the lowest stage. The rotation of the motor 208 also rotates a lead screw 206 of the first dissolution column 201 via a chain 209. The rotation of the lead screw 206 in turn rotates a lead screw 212 of the second dissolution column 202 via gears G1, G2 A blower 213 circulates a hot air up through the dissolution section 200 by drawing the air out of the top at a lower temperature to the bottom at a higher temperature via a pipe 222.

In the embodiment shown in FIG. 21, a heating medium heating system 600 supplies a heating medium which heats the first to fourth dissolution columns 31a, 31b, . . . , 31d. The heating medium here refers to a liquid heating medium such as various types of thermal oil. The heating medium heating system 600 heats the heating medium to a predetermined temperature and sends the medium through a heating medium pipe 601 into a heating medium space 135′ of the dissolution column 31. The heating medium space 135 intervenes between an inner wall 131 and an outer case 136, as for the above described hot air space 135. A circulation pump 602 circulates the heating medium through the heating medium space 135 from downstream to upstream. The first dissolution column 31a is controlled to 190-200° C., the second dissolution column 31b to 210-230° C., the third dissolution column 31c to 230-260° C., and the fourth dissolution column 31d to 300-340° C., as in the above described hot air heating.

The heating medium thus used instead of the hot air can a) greatly improve the heat transfer efficiency, b) reduce the temperature drop in the dissolution column 31 when the plant stopped, because the heating medium cools less rapidly than the hot air, thereby allowing the plant to start up more quickly, and c) prevent the fire even if the inner column 131 of the dissolution column 31 is damaged.

The heating medium is used only for heating the dissolution column 31 because the heating medium generally operates at 350 #1# or less. Any other suitable heating medium, however, can be selected also to heat the decomposition columns 47, 48. Depending on the temperature at which the heating medium operates, the heating medium may only heat the dissolution columns 31 that are controlled to lower temperatures (such as first, second, and third dissolution columns 31a, 31b, and 31c).

In the embodiment shown in FIG. 13, a connection 500 connects the fourth dissolution column 31d and the lower part of the first stage decomposition column 47. Through the connection 500, the column 31d supplies the dissolved expanded plastic into the bottom of the inner column 255 in the first stage decomposition column 47. The above described connection 500 may receive vegetable or animal cooking oil or their waste oil or the like stored in a tank 502. Each dissolution column primarily and secondarily decomposes the mixture of the oil and expanded plastic. This can collect reformed oil through chemical decomposition reaction.

Generally, as shown in FIGS. 1-4, plastics such as polyethylene, polypropylene, polystyrene, ABS resin, and acrylic resin are thermally decomposed into oil (90%) that is collected as the generated oil, an off gas (7-8%) that is treated in the off gas treatment system 34, and carbide (2-3%) that is collected as the residual into the residual tank 40. Polyvinyl chloride is neutralized by calcium hydroxide into calcium chloride (about 58%), and the residual (about 42%) is thermally decomposed, but only about 30% is converted into oil and collected.

The disclosure of Japanese-patent application No. 2002-017650 (filed on Jan. 25, 2002) including the specification, claims, drawings, and abstract, and Japanese patent application No. 2002-301895 (filed on Oct. 16, 2002) including the specification, claims, drawings, and abstract are incorporated herein by reference in their entirety.

This invention is not limited to the embodiments described above. The above-described embodiments are illustrative, and any technical idea that has the substantially identical configuration and operation as the technical idea set forth in the claims of the present invention is included in the technical scope of the present invention.

Industrial Applicability

As describe above, the method and plant for converting plastic into oil according to the present invention are useful as the method and plant for converting plastic into oil for collecting the oil from the plastic waste.

Claims

1. A method for converting plastic into oil, comprising:

a dissolution step of heating and dissolving the plastic into expanded plastic; and

a decomposition step of removing the expanded plastic, heating and depolymerizing the expanded plastic, and cooling the expanded plastic into oil.

2. The method for converting plastic into oil according to claim 1,

wherein, in the decomposition step, the expanded plastic is removed by being lifted at an angle.

3. The method for converting plastic into oil according to claim 1,

wherein, in the decomposition step, the expanded plastic is removed by being lifted at an angle of 25-30° relative to the horizontal.

4. The method for converting plastic into oil according to claim 2,

wherein, in the decomposition step, the expanded plastic is heated with being lifted at an angle and the expanded plastic is heated to higher temperatures at higher positions.

5. The method for converting plastic into oil according to claim 1,

wherein, in the dissolution step, the plastic is dissolved in a dissolution section including a plurality of dissolution columns with different temperature ranges.

6. The method for converting plastic into oil according to claim 1,

wherein, in the dissolution step, the dissolved plastic is added with vegetable oil or animal oil or mineral oil to generate expanded plastic of a mixture of the plastic and the vegetable oil or animal oil or mineral oil, and

in the decomposition step, the expanded plastic is removed, heated and depolymerized, and cooled into oil.

7. The method for converting plastic into oil according to claim 1,

wherein, in the decomposition step, the expanded plastic is removed and heated in a decomposition section including a plurality of decomposition columns with different temperature ranges.

8. The method for converting plastic into oil according to claim 1, further comprising

a hydrogen chloride gas treatment step of separating a hydrogen chloride gas generated in dissolving the plastic in the dissolution step from other decomposed gases, then reacting the hydrogen chloride gas with hydrated lime, and collecting the hydrogen chloride gas as calcium chloride.

9. The method for converting plastic into oil according to claim 1, further comprising

a off gas treatment step of treating an off gas not converted into oil in the decomposition step by catalytically cracking the off gas with a hot ceramic.

10. A plant for conversion into oil, comprising:

a dissolution section for heating and dissolving the plastic into expanded plastic; and

a decomposition section for removing the expanded plastic, heating and depolymerizing the expanded plastic, and cooling the expanded plastic into oil.

11. The plant for conversion into oil according to claim 10, wherein the decomposition section comprises removal means for removing the expanded plastic by lifting the expanded plastic at an angle.

12. The plant for conversion into oil according to claim 10, wherein the decomposition section comprises removal means for removing the expanded plastic by lifting the expanded plastic at an angle of 25-30° relative to the horizontal.

13. The plant for conversion into oil according to claim 11,

wherein the decomposition section comprises heating means for heating the expanded plastic with lifting the expanded plastic at an angle and for heating the expanded plastic to higher temperatures at higher positions.

14. The plant for conversion into oil according to claim 10, wherein the dissolution section comprises a plurality of dissolution columns with different temperature ranges.

15. The plant for conversion into oil according to claim 10, comprising

oil injection means for injecting vegetable oil or animal oil or mineral oil into a connection between the dissolution section and the decomposition section.

16. The plant for conversion into oil according to claim 10, wherein the decomposition section comprises a plurality of tilted decomposition columns with different temperature ranges.

17. The plant for conversion into oil according to claim 10, further comprising

a dechlorination system for treating a hydrogen chloride gas generated in the dissolution section,

wherein the dechlorination system comprises a separator for separating the hydrogen chloride gas from other decomposed gases, and a reactor for reacting the hydrogen chloride gas separated by the separator with hydrated lime into calcium chloride.

18. The plant for conversion into oil according to claim 10, further comprising

an off gas treatment system for treating an off gas not converted into oil after cooling in the decomposition section by catalytically cracking the off gas with a hot ceramic.

19. The plant for conversion into oil according to claim 16, wherein each of multistage decomposition columns depolymerizes the plastic into a decomposed gas which is cooled into oil.

20. The plant for conversion into oil according to claim 16, wherein at least part of the decomposition column comprises a superheat for further depolymerizing the depolymerized plastic.

21. The plant for conversion into oil according to claim 16, wherein the decomposition column is heated with increasing temperatures from bottom to top.

22. The plant for conversion into oil according to claim 16, comprising

residual collection means at a top of a final stage decomposition column of the multistage decomposition columns.

23. The plant for conversion into oil according to claim 22, wherein the residual collection means comprises a column with its upper opening at the top of the final stage decomposition column and its lower opening in an atmosphere of an inactive gas heavier than an air.

24. The plant for conversion into oil according to claim 10, further comprising a hopper for storing and supplying the plastic into the dissolution section,

wherein the hopper comprises a lead screw with a spiral blade.

25. The plant for conversion into oil according to claim 24, further comprising an unheated section formed as an unheated area of a predetermined length between the hopper and the dissolution section.

26. The plant for conversion into oil according to claim 14, wherein the plurality of dissolution columns each comprise a lead screw with a spiral blade for carrying the plastic,

a beginning dissolution column of the plurality of dissolution columns comprises the lead screw blade with a greater pitch than the lead screws blades in other dissolution columns.

27. The plant for conversion into oil according to claim 14,

wherein the dissolution section and the decomposition section each comprise: an inner column; an outer column around the inner column; a hot air space between the inner column and the outer column and through which an hot air circulates; and a temperature sensor for detecting a temperature in the dissolution section or the decomposition section, and

wherein the plant further comprises a carbon dioxide gas supplying system for supplying the carbon dioxide gas into the hot air space if the temperature sensor detects an abnormal temperature equal to or greater than a predetermined temperature.

28. The plant for conversion into oil according to claim 14,

wherein the dissolution section and the decomposition section each comprise: an inner column; an outer column around the inner column; and a hot air space between the inner column and the outer column and through which an hot air circulates,

wherein the plant further comprises: a hot air production system for generating by combustion the hot air to be supplied into the hot air space; and a drying system for drying the plastic to be supplied into the dissolution section, and

wherein an air in the drying system is supplied into the hot air production system to be deodorized by combustion.

29. The plant for conversion into oil according to claim 18, further comprising

a drying system for drying the plastic to be supplied into the dissolution section,

wherein an air in the drying system is supplied into the off gas treatment system to be deodorized by being catalytically cracked with a hot ceramic.

30. The plant for conversion into oil according to claim 14,

wherein an extendable column which is extendably formed is used in a part of the dissolution column includes, and

wherein the extendable column comprises: an inner column; a bellows around the inner column which has one end fixed on the inner column and an other end slidable relative to the inner column; and an outer column which is fixed on the other end of the bellows and slidably contains the inner column.

31. The plant for conversion into oil according to claim 10,

wherein the dissolution section comprises: an inner column; an outer column around the inner column; and a heating medium space between the inner column and the outer column and through which a liquid heating medium circulates, and

wherein the plant further comprises a heating medium supplying system for supplying the liquid heating medium into the heating medium space.