Apparatus for thermochemical conversion of polymers

Abstract

The apparatus of the invention comprises a cylindrical inner chamber (4) and a cylindrical outer chamber (5), coaxial with one another, the inner chamber (4) housing an auger (6) which is intended to move polymeric material continuously inside the inner chamber (4) and which has a helix (8) around the screw shaft. The apparatus also includes gas outlets (17) and solids outlets (18). The outer chamber (5) is fed with hot gases for thermochemical conversion in the inner chamber (4). The apparatus also has at least one deflector (19) arranged in the upper portion between the upper chamber (5) and the lower chamber (4), to produce a pressure loss in the hot gases so as to force said hot gases to flow predominantly or exclusively through the lower part of the outer chamber (5). It allows greater energy efficiency and durability.

Description

[0001] DESCRIPTION

[0002] APPARATUS FOR THERMOCHEMICAL CONVERSION OF POLYMERS

[0003] Technical field of the invention

[0004] The present invention relates to the circular economy, in particular to the transformation of waste into energy and industrial products. More specifically, the invention relates to a reactor for carrying out a thermochemical conversion through a continuous process, to transform various polymeric materials into recovery products, such as synthesis gas, pyrolytic oil, and recovered carbon black, especially when using rubber from end-of-life tires (ELTs) as raw material.

[0005] Background of the invention

[0006] The applicant of the present invention is also co-holder of the Spanish patent ES2388959B1 , relating to a process and apparatus for thermolysis of waste polymers. The holders of the aforementioned patent have implemented in Zaragoza (Spain), an experimental pilot scale plant for thermochemical transformation, based on a continuous processing pyrolysis reactor, auger type, of rubber materials, from end-of-life tires (ENDTs), without generating waste, into products of industrial interest, such as: 1) synthesis gas, which is used to feed the thermal energy needs of the reactor, making the plant self-sufficient and its surpluses being used for other uses, including the production of electricity for the rest of the plant;2) high-energy pyrolytic oil (TPO), which can be mixed with diesel or bunker fuel and used as a fuel, due to its aromatic hydrocarbon content, in the refining and petrochemical industries, for incorporation into new distilled products or plastics, or for distillation into limonene, light aromatics, alkyl aromatics and other linear and branched hydrocarbons; and 3) recovered carbon black (rCB), which can be used as a reinforcement in the production of tyres and rubber-containing products in general, such as hoses, rubber or plastics.

[0007] Based on the experience gained in the operation of the aforementioned pilot plant, needs for improvement have been detected in various aspects of the plant, which are resolved by means of the present invention, as explained below. Brief description of the invention

[0008] The present invention solves the aforementioned drawbacks by means of an apparatus, such as a reactor, for the thermochemical transformation by continuous pyrolysis of waste polymers and rubber, such as end-of-life tires, according to independent claim 1. The dependent claims describe preferred embodiments.

[0009] The new device features structural optimization to adapt to the thermo-mechanical loads generated during pyrolysis, improving the fatigue life of the device itself, as well as increasing its thermal efficiency.

[0010] By using the apparatus of the present invention, higher quality is obtained in the preferred conversion products, since a higher proportion of light aromatics (benzene, toluene, xylene, gum monomers, limonene) is achieved in the synthesis gas, due to the thermal efficiency allowing sufficiently high process temperatures to be reached that favor aromatization reactions, as well as greater stability, to have product consistency over time. Likewise, the high temperatures reached allow obtaining recovered carbon black in accordance with current market demands, in terms of volatile content less than 1% and ASTM D1618 Toluene extraction test above 80%.

[0011] The device produces pyrolytic oil with a high calorific capacity, which can be used in various industrial applications as an input in the production of environmentally friendly plastics with a carbon footprint up to 80% lower than that of traditional plastics.

[0012] Furthermore, using the apparatus described in the present invention, approximately 40% of the chip's weight is recovered in the form of recovered carbon black (rCB). rCB accounts for 22% of the weight of a tire for a private vehicle. Therefore, the pyrolytic process described contributes substantially to the circular economy of tires, providing a solution for the tire industry, enabling it to access high-quality recovered carbon black due to its low volatile organic content, as well as reducing the amount of waste ultimately sent to landfill. Brief description of the figures

[0013] The above and other advantages and characteristics will be more fully understood from the following detailed description of some embodiments with reference to the attached drawings, which should be considered as illustrative and not limiting, in which:

[0014] - Figure 1 shows a side view of the apparatus of the invention.

[0015] - Figure 2 shows a detail of the apparatus in Figure 1, where the drag segments in the worm screw propeller can be seen.

[0016] - Figure 3 shows a detailed view of the lower chamber with heat sink fins.

[0017] - Figure 4 shows a detail of the device where deflectors can be seen.

[0018] - Figures 5A and 5B show two embodiments of the tree.

[0019] List of references

[0020] 1 Reactor

[0021] 2 Rubber feeding

[0022] 3 First rotary supports

[0023] 4 Inner chamber

[0024] 5 Exterior chamber

[0025] 6 Worm gear

[0026] 7 Tubular structure

[0027] 8 Helix

[0028] 9 NOT APPLICABLE

[0029] 10 Internal wall

[0030] 11 Drag segments

[0031] 12 NOT APPLICABLE

[0032] 13 Hot gas inlet

[0033] 14 Hot gas outlet

[0034] 15 NOT APPLICABLE

[0035] 16 NOT APPLICABLE

[0036] 17 Gas outlet 18 Solids outlet

[0037] 19 Deflectors

[0038] 20 Fins

[0039] 21 First expansion joints

[0040] 22 Chamber Sectors

[0041] 23 Second expansion joints

[0042] 24 Third expansion joints

[0043] 25 NOT APPLICABLE

[0044] 26 NOT APPLICABLE

[0045] 27 NOT APPLICABLE

[0046] 28 NOT APPLICABLE

[0047] 29 NOT APPLICABLE

[0048] 30 NOT APPLICABLE

[0049] 31 NOT APPLICABLE

[0050] 32 NOT APPLICABLE

[0051] 33 Drive (motor)

[0052] 34 Second rotary support

[0053] 35 Spirals

[0054] 36 First set of coils

[0055] 37 Second set of coils

[0056] 38 Tubular connecting piece

[0057] Detailed description of a preferred embodiment of the invention

[0058] Next, with the help of the aforementioned figures 1-5B, a detailed description is offered of a preferred embodiment example relating to an apparatus for thermochemical conversion of polymers, where in the example represented, it is a continuous pyrolysis reactor (1) to transform rubber from out-of-use tires, hereinafter referred to as NFUs, in accordance with the present invention.

[0059] The Auger type pyrolytic reactor is fed, through a rubber feed (2), with rubber from NFUs, preferably in the form of chips or pellets, that is, devoid of the steel and textile part of the NFUs. The reactor (1) has a cylindrical shape, with a shaft, in axial direction, as well as an inner chamber (4) and an outer chamber (5) coaxial with the axial direction of the shaft. In the inner chamber (4) pyrolysis of the rubber from the NFUs is carried out. Said inner chamber (4) houses an endless screw (6), to move the rubber along the inner chamber of said inner chamber (4), allowing continuous operation. The endless screw (6), also called “Archimedes screw” comprises a helix (8), which can be continuous or segmented, and which is coaxial with the axial direction of the shaft.

[0060] The inner chamber (4) is made of superalloy material, also known as “high performance alloys”, which are alloys capable of operating at a high fraction of their melting point, thus offering special characteristics compared to austenitic stainless steel. In this way, it is possible to withstand the high temperatures to which it is continuously exposed, between 500 °C and 900 °C and more specifically around 700 °C, preventing the reactor from being affected by the phenomenon known as “creep” (also known as “slow creep” in Saxon terminology), which constitutes a material failure mode generally defined as the tendency of a solid material to permanently deform under the product of low stress states or by its own weight.The reactor (1) preferably uses, for the inner chamber (4), nickel-based ferrous superalloys, such as nickel and chromium and, optionally, molybdenum, for example, INCONEL-625, a material that has excellent mechanical resistance characteristics at high temperatures. Other alternatives, by way of example, may be: HR-120® alloy (UNS N08120); HR-160® alloy (UNS N12160); 214® alloy (UNS N07214); 230® alloy (UNS N06230); or 242® alloy (UNS N10242). Alternatively, the inner chamber (4) may be made of stainless steel.

[0061] Between the propeller (8) of the worm screw (6) and the inner chamber (4) of the reactor (1), a clearance called “adjustment gap” is defined (not shown in the figures), in order to absorb deformations of the shaft due to the arrow effect due to its own weight, avoiding friction between the propeller (8) and an internal wall (10) also called “internal jacket” of the inner chamber (4). However, such a configuration causes an accumulation of product in the adjustment gap which, when cooled, can coke and form a layer with low thermal conductivity that reduces the material transport and energy transfer capacity.Therefore, preferably, the worm screw (6) includes drive segments (11) in radial extension from the helix (8), and manufactured in composite materials formed by metal impregnated with graphite, which forms long continuous filaments that provide the material with high ductility and resistance, as well as improved heat dissipation properties, or a high mechanical resistance graphite plate material type FU 11303, from STK (Shunk Kohlenstofftechnik, Germany), all with the purpose of allowing the helix (8) to have contact with the internal wall (10) of the inner chamber (4) at the points of greatest flexion. In this way, the adjustment gap, along the entire length of the worm screw (6), can be reduced to the minimum necessary to absorb the expansions of the material.The material or composite materials of the drag segments (11) have low coefficient of friction characteristics, which allows contact between the propeller (8) and the internal wall (10), ensuring drag of solid material produced by pyrolysis without forming layers of the aforementioned coked material of such a thickness that they could alter the optimal operating conditions of the reactor.

[0062] For its part, the outer chamber (5) of the reactor (1) surrounds the inner chamber (4) and houses combustion fumes or, in general, any other hot gas, which provide the heat necessary to the inner chamber (4) to carry out pyrolysis. Likewise, the outer chamber can be provided internally with a refractory lining, for example, two layers of Therlite 1250 + ISO-AL, in order to reduce the losses of thermal energy from the combustion fumes or from the hot gas to the outside.

[0063] The combustion fumes or hot gas can be produced in a combustion chamber (not shown), separate from the reactor (1), by means of the combustion of a fuel and air, such that ambient air, as an oxidizer, in a burner (not shown), and said combustion fumes are introduced, with temperature control, into the outer chamber (5), through a smoke or hot gas inlet (13). Preferably, the combustion fumes or hot gas circulate through the outer chamber (5) countercurrent to the direction of advance defined by the worm screw (6), that is to say, the hot gas inlet (13) is located at one end of the reactor (1) which is precisely opposite to the rubber feed (2).Preferably, before the introduction of the combustion fumes or hot gas into the outer chamber (5) of the reactor (1), the reactor is subjected to a heating ramp, during an ignition stage of the reactor (1), until a steady state of temperature is achieved, after which, the combustion fumes or hot gas are conducted, through the hot gas inlet (13), towards the inner jacket (4), at a temperature of up to 1100 ° C, preferably 800 ° C, to heat the inner chamber (4) by conduction and produce pyrolysis. After leaving the reactor (1), through a hot gas outlet (14), the combustion fumes or hot gas are recirculated towards an economizer (not shown) where their enthalpy is used to preheat the comburent, in particular, the ambient air, before entering the burner, as a means of energy saving.Pyrolysis is carried out in an inert atmosphere by continuous injection of N2 or any other non-reactive gas with the hydrocarbons generated through an inert gas feed (not shown). The rubber from the NFLIs remains in the auger (6) for a residence time that can be between 4 and 40 minutes, preferably between 8 and 20 minutes and more specifically for 15 minutes, which is controlled by the rotation speed of the auger (6) itself, configured remotely by an operator from a control room.

[0064] Due to the pyrolysis reactions to which the rubber is subjected within the inner chamber (4), the volatile part comprising the rubber sublimates, reaching temperatures of 550 °C and higher, while the rubber travels through the auger (6) for the pre-established residence time. As a direct result of pyrolysis, two types of products are basically produced: pyrolysis gas, and a solid called “recovered carbon black” (rCB). The pyrolysis gas leaves the reactor (1) at a temperature between 200 °C and 950 °C, preferably between 400 °C and 550 °C and at a gauge pressure of between 20-800 mbar, through one or several gas outlets (17). Preferably, the reactor (1) has a single gas outlet (17), located in an upper part of the reactor (1), also preferably, in a position approximately two thirds of the length of the rubber's path within the reactor (1).For its part, the rCB leaves the reactor (1) through a solids outlet (18) located at the bottom of the reactor (1) at one end of the reactor (1) opposite to the rubber feed (2).

[0065] A segmented helix (8) is preferred, formed by turns (35), or groups of turns (35), connected along the axial direction. Even more preferably, two sets (36, 37) of turns (35) or groups of turns (35) are arranged at opposite ends of the helix (8), and oriented in opposite directions of advance. In particular, given a predetermined direction of rotation of the helix (8), for example, clockwise, a first set (36) is formed by turns (35) or groups of turns (35) located at an initial, rear end (according to the direction of advance of the rubber), and oriented to produce advance of the rubber when the helix (8) rotates in the predetermined direction of rotation, while a second set (37) is formed by turns (35), or groups of turns (35) located at the final, forward end, to produce advance in the opposite direction.The effect of arranging the second set (37) of coils (35) is to prevent the rCB formed during pyrolysis and which has not been displaced by the solids outlet (18), but has exceeded said solids outlet (18), from accumulating water below the solids outlet (18) but from being redirected towards said solids outlet (18) and removed from the inner chamber (4). By way of example, the following two embodiments are proposed for the tree:

[0066] According to a first embodiment, shown in Figures 1-4 and 5, the shaft comprises a central tubular structure (7) and two first rotating supports (3) integral with the tubular structure (7). One of the first rotating supports (3) transmits torque from a drive (33), for example a motor, to the tubular structure (7) to which it is connected. The presence of the tubular structure (7) serves to minimize self-weight bending effects. The helix (8) of the worm screw (6) is supported on the tubular structure (7), such that the tubular structure (7) provides rigidity to the helix (8), in particular to the turns (35) or sets of turns (35).

[0067] In a second embodiment, an alternative to the first embodiment and shown in Figure 5B, the tubular structure (7) of the first embodiment is omitted, so that the torque is transmitted and supported by the propeller (8), which deforms as needed. In the second embodiment, there is a single second rotating support (34), which transmits the torque from the drive (33) to the propeller (8). In the second embodiment, the turns (35), or groups of turns (35), are supported, through the drive segments (11), on the internal wall (10) of the inner chamber (4), reducing the adjustment gap to practically zero values, and causing the deformations of the inner chamber (4) - in particular, of the internal wall (10) - to be absorbed by the flexibility of the turns (35), or sets of turns (35).In the second embodiment, the turns (35) of the second type (37) are integrally connected to the turns (35) of the first type (36), for example, through a tubular connection piece (38) coaxial with the axial direction.

[0068] To optimize heat transfer, the reactor (1) has specific characteristics.

[0069] On the one hand, the reactor (1) is configured to allow exclusive, or at least substantially majority, circulation of combustion fumes or hot gases through a lower part of the outer chamber (5), which maximizes the heat transfer to the inner chamber (4) through the lower part of the reactor (1), since it is where the rubber to be transformed passes through. Preferably, the reactor (1) is configured such that the combustion fumes circulate substantially mainly through the lower part of the outer chamber (5). According to one example, in the upper part of the reactor (1), between the upper chamber (5) and the lower chamber (4), there are one or more deflectors (19), see image below, to generate pressure loss to the combustion fumes in said upper part, forcing the majority circulation of said combustion fumes through the lower part of the outer chamber (5).There may be a plurality of baffles (19), located at different positions along the axial direction.

[0070] On the other hand, additionally or alternatively, from the lower part of the inner chamber (4), that is to say on the outside of the inner wall (10), heat dissipation fins (20) protrude, preferably slender, needle-shaped cylindrical fins (20) (called "studs" in Saxon terminology), located to come into contact with the hot fumes or gas and thus increase the heat transfer towards the inner chamber (4) through the inner wall (10) of the inner chamber (4). The individual and, above all, combined action of the lower circulation of the combustion fumes and the fins (20) allow a greater use of the enthalpy of the combustion fumes or hot gases.

[0071] Another distinctive advance provided by the present invention relates to incorporating one or more expansion joints (21, 23, 24) to reduce the tension level of the inner chamber (4) generated by expansions of the material of the inner wall (10) itself. The inner wall (10) is a tube that reaches temperatures of 500 °C to 700 °C along its entire length, which generates a maximum expansion in the longitudinal direction of the inner chamber (4), which can be of the order of 90 mm between the cold and hot state. The expansion joints (21, 23, 24) absorb the expansions of the inner chamber (4) in the aforementioned axial direction. The expansion joints (21, 23, 24) are made of textile material or materials, such as Nextel®, from the manufacturer 3M, to cancel the tension load on the internal wall (10) associated with the spring effect that would exist if said expansion joints (21, 23, 24) were metallic.The expansion joints (21, 22, 23) therefore perform the function of allowing free expansion of the internal wall (10) which, if not allowed, would generate high levels of tension in said internal wall (10), known as the aforementioned "spring effect". Additionally, the expansion joints (21, 23, 24) act as thermal insulation and generate a barrier to the flow and transmission of heat from the combustion fumes or hot gas circulating through the external chamber (5).

[0072] The expansion joints (21, 23, 24) comprise one or more first expansion joints (21), as explained below. Specifically, the outer chamber (5) is longitudinally divided into a plurality of consecutive contiguous chamber sectors (22), where said plural expansion joint(s) (21) are arranged around a confluence area of ​​every two contiguous chamber sectors (22), connecting said chamber sectors (22), such that each first expansion joint (21) allows a movement between said contiguous chamber sectors (22), due to contractions and expansions. The images show an example of an outer chamber (5) divided into two contiguous chamber sectors (22) and, therefore, with a single first expansion joint (21).

[0073] Optionally, similarly to that explained for the first expansion joints (21), one or several second (23) and / or third (24) expansion joints can be provided, located, respectively, at the gas outlet (17) and at the solids outlet (18). The expansion joints (21, 23, 24) ensure tightness in the outer chamber (5). In the particular case of the second (23) and third (24) expansion joints, they are connected to the corresponding chamber sector (22), with its respective gas outlet (17) and solids outlet (18).

Claims

CLAIMS 1.- Apparatus for the continuous thermochemical conversion of polymers, to transform polymeric material, the apparatus comprising: - cylindrical inner chamber (4), which defines a longitudinal axial direction; - coaxial shaft with axial direction; - worm screw (6), housed in the inner chamber (4), and which in turn comprises a helix (8) to continuously move the polymeric material along the inner chamber (4); - cylindrical outer chamber (5), to receive hot gases to heat the polymeric material of the inner chamber (4) to carry out its thermochemical conversion in the inner chamber (4), the inner chamber (4) being coaxial with the outer chamber (5) and the inner chamber (4) being housed in the outer chamber (5); - at least one gas outlet (17), to allow synthesis gases formed in the inner chamber (4) to escape during the thermochemical transformation; and - at least one solids outlet (18), to allow solids produced in the inner chamber (4) to escape during the thermochemical transformation; the reactor (1) being characterized additionally comprises at least one deflector (19) arranged superiorly between the upper chamber (5) and the lower chamber (4), to produce pressure loss of the hot gases to force a majority or exclusive circulation of said hot gases through the lower part of the outer chamber (5). 2.- Apparatus according to claim 1, wherein the at least one deflector (19) comprises a plurality of deflectors (19) arranged in different positions along the axial direction. 3.- Apparatus according to any of claims 1-2, which additionally comprises heat dissipation fins (20), preferably in the form of slender cylindrical needles, which protrude from the lower part of the inner chamber (4) towards the outer chamber (5), to come into contact with the hot gases and increase heat transfer towards the inner chamber (4). 4.- Apparatus according to any of claims 1-3, which additionally comprises one or several expansion joints (21, 23, 24), made of textile material, to absorb expansions of the internal chamber (4) in the axial direction. 5.- Apparatus according to claim 4, where the expansion joints (21, 23, 24) have a thermal insulating character to generate a barrier to the flow and transmission of heat from the hot gases that circulate through the outer chamber (5).

6. Apparatus according to any of claims 4-5, wherein the outer chamber (5) is longitudinally divided into at least two consecutive contiguous chamber sectors (22), where the expansion joints (21, 23, 24) comprise one or more first expansion joints (21), surrounding the outer chamber (5), connecting pairs of chamber sectors. (22) contiguous, allowing a relative displacement between said contiguous chamber sectors (22), to absorb expansions and contractions of the interior chamber (4). 7.- Apparatus according to claim 6, which additionally comprises one or several second expansion joints (23) located at the gas outlet (17) and / or one or several third expansion joints (24) located at the solids outlet (18), the second expansion joints being mounted (23) and the third (24) expansion joints, connecting their corresponding chamber sector (22) with their respective gas outlet (17) and solids outlet (18). 8.- Apparatus according to any of claims 1-7, which additionally comprises an adjustment gap between the helix (8) of the worm screw (6) and the inner chamber (4), as well as additionally comprises drag segments (11) in radial extension of the helix (8), and manufactured in composite materials with graphite, such as metal impregnated with graphite or graphite plate material, to contact the inner chamber (4) and drag solid material, product of the thermochemical conversion, adhered to the inner chamber (4) in the adjustment gap. 9.- Apparatus according to any of claims 1-8, wherein the inner chamber (4) is made of stainless steel or metal superalloy. 10.- Apparatus according to claim 9, wherein the inner chamber (4) is made of a nickel-chromium ferrous superalloy. 11.- Apparatus according to any of claims 1-10, which additionally includes an inert gas supply to feed non-reactive gas into the inner chamber (4), so that the thermochemical conversion occurs in an inert medium. 12.- Apparatus according to any of claims 1-11, comprising a single gas outlet (17), located at the top of the outer chamber (5), and located approximately two thirds of the length of the path of the polymeric material inside the reactor (1). 13.- Apparatus according to any of claims 1-11, wherein the outer chamber (5) is provided with an inner refractory lining to reduce thermal energy losses from hot gases. 14.- Apparatus according to any of claims 1-13, wherein the helix (8) is segmented into turns (35), or groups of turns (35), connected along the axial direction. 15.- Apparatus according to claim 14, which includes two sets (36, 37) of turns (35) or groups of turns (35) at opposite ends of the helix (8) and oriented in opposite directions of advance, where, for a predetermined direction of rotation of the helix (8): - a first set (36) is formed by turns (35), or groups of turns (35), located at an initial, rear end (with respect to the direction of advance considered for the polymeric material), and oriented to produce advance of said polymeric material when the helix (8) rotates in the predetermined direction of rotation; while - a second set (37) is formed by turns (35), or groups of turns (35), located at a front end, to produce advance in the opposite direction when the helix (8) rotates in the predetermined rotation direction, to redirect towards the solids outlet (18) the rCB formed during the thermochemical conversion and that has passed the solids outlet without accessing said solids outlet (18). 16.- Apparatus according to any of claims 1-15, wherein the shaft comprises a central tubular structure (7) on which the propeller (8) is supported. 17.- Apparatus according to any of claims 1-16, wherein the propeller (8) is configured to support torque without the need for a central tubular structure (7). 18.- Apparatus according to claim 17, wherein the coils (35), or groups of coils (35) are flexible to rest internally on the inner chamber (4) and absorb deformations of the inner chamber (4).

19. Apparatus according to claims 15 and 17 simultaneously, which additionally comprises a tubular connection piece (38) to solidly connect the turns (35) of the second type (37) with the turns (35) of the first type (36).

20. Apparatus according to any of claims 1-19, wherein said apparatus is a reactor (1) Auger type pyrolytic.

Images