Char collector

Abstract

The present invention provides a char collector (1) for a pyrolysis system (2), the pyrolysis system (2) featuring a pyrolysis reactor (17) comprising a hot char outlet (3), the char collector comprises a container (4) and a longitudinal char conveyor unit (5), and the container (4) comprises a chamber (6), a first inlet (7) connectable to the hot char outlet (3) and a first outlet (8), wherein the first inlet (7) is arranged in an upper portion of the chamber (6) and the first outlet (8) is arranged in a lower portion of the chamber (6); and the char conveyor unit (5) comprises a first end section (9) connected to the first outlet (8), a second end section (10) featuring a second outlet (11) for cooled char and a conveying mechanism (12) configured to transport char from the first end section (9) to the second outlet (11) during use; wherein the second outlet (11) is at a level above the first outlet (8), such that a gas trap is formed between the first inlet (7) and the second outlet (11) when the chamber (6) is filled with water up to a level above the first outlet (8) during use.

Claims

1. A char collector for a pyrolysis system, the pyrolysis system featuring a pyrolysis reactor comprising a hot char outlet, the char collector comprises a container and a longitudinal char conveyor unit, and the container comprises a chamber, a first inlet connectable to the hot char outlet and a first outlet, wherein the first inlet is arranged in an upper portion of the chamber and the first outlet is arranged in a lower portion of the chamber; and the char conveyor unit comprises a first end section connected to the first outlet, a second end section featuring a second outlet for cooled char and a conveying mechanism configured to transport char from the first end section to the second outlet during use; wherein the second outlet is at a level above the first outlet, such that a gas trap is formed between the first inlet and the second outlet when the chamber is filled with water up to a level above the first outlet during use.

2. A char collector according to claim 1, wherein the second outlet is at a level above a mid-level of the chamber.

3. A char collector according to claim 1, wherein the container comprises a controllable water inlet for providing water into the chamber and a water level sensor for measuring a water level inside the chamber, the water level sensor connected to the controllable water inlet, such that water is added to the chamber when the water level falls below a predetermined level.

4. A char collector according to claim 1, wherein the char conveyor unit comprises a longitudinal hollow element in which at least a lower section of the conveying mechanism is arranged.

5. A char collector according to claim 4, wherein the conveying mechanism is a helical screw and the longitudinal hollow element is a tube element.

6. A char collector according to claim 1, wherein the char conveyor unit comprises a third outlet positioned between the first outlet and the second outlet, and a lowest level of the third outlet is above a highest level of the first outlet.

7. A char collector according to claim 1, comprising at least one blade arranged to rotate inside the chamber.

8. A char collector according to claim 7, wherein the blade is connected to a rotary shaft arranged to allow rotation of the blade between a first position and a second position, wherein the blade is at a higher level in the first position than in the second position.

9. A char collector according to claim 6, wherein the longitudinal char conveyor unit comprises an air inlet arranged at a level above the third outlet.

10. A char collector according to claim 9, comprising sensors for measuring temperature, moisture and/or air flow, arranged at the second outlet, the third outlet and/or the air inlet.

11. A pyrolysis system comprising a pyrolysis reactor and a char collector according to claim 1, wherein the pyrolysis reactor comprises a hot char outlet connected to the first inlet of the char collector.

12. A method of collecting char from a pyrolysis reactor having a hot char outlet connected to the first inlet of a char collector according to claim 1, the method comprising the steps of: providing water into the chamber to obtain a water level above the highest level of the first outlet; transferring char from the hot char outlet to the chamber; cooling the char by mixing with the water in the chamber; transferring the char from the chamber to the second outlet via the first outlet and the char conveyor unit; and collecting the char from the second outlet.

13. A method according to claim 13, wherein the step of collecting the char from the second outlet comprises loading the char into a fluid tight bag which is subsequently sealed.

14. A method of controlling the moisture content of char collected from a pyrolysis reactor having a hot char outlet connected to the first inlet of a char collector according to claim 1, the method comprising the steps of: introducing a relatively dry and cold air via the air inlet; extracting a relatively moist and hot air via the third outlet; determining the temperature and moisture of the char exiting the second outlet; and increasing the flow of air into the air inlet if the char has a moisture content above a predetermined level; or decreasing the flow of air into the air inlet if the char has a moisture content below a predetermined level.

Description

SHORT DESCRIPTION OF THE DRAWINGS

[0066] The present invention is described in detail by reference to the following drawings:

[0067] FIG. 1 is a schematic drawing of a pyrolysis system according to the invention.

[0068] FIG. 2 is a cross-sectional side view of an exemplary char collector according to the invention.

[0069] FIG. 3 is a side view and a perspective view of the container of the char collector in FIG. 2.

[0070] FIG. 4 is a side view of the char collector in FIG. 2.

[0071] FIG. 5 is a cross-sectional front view of the char collector in FIG. 2.

[0072] FIG. 6 show perspective views and cross-sectional views of alternative embodiments of a blade assembly for use in the char collector in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

[0073] A schematic drawing of a pyrolysis system 2 comprising a char collector 1 according to the invention is shown in FIG. 1. The main feature of the pyrolysis system 2 is a pyrolysis reactor 17. In the pyrolysis reactor 17, materials such as waste or biomass, are pyrolyzed into products that may be divided into a solids fraction, i.e. char, and a volatile fraction. The ratio and specific contents of the fractions depend on multiple variables such as the pyrolysis temperature, time, type of material being pyrolyzed etc. However, the solids fraction is predominantly char, while the volatile fractions may be mixtures of syngas (CO,H.sub.2), tar and light hydrocarbons.

[0074] The volatile fractions are commonly further processed in a gas handling system 16 for separation, purification and/or storage of the mixture of products.

[0075] The char, i.e. the solids fractions, exits a hot char outlet 3 of the pyrolysis reactor 17 and enters a first inlet 7 of the char collector 1. The first inlet 7 is at least indirectly connected to the hot char outlet 3, such that char may be transferred from the pyrolysis reactor 17 to the first inlet 7. In some embodiments, the hot char outlet 3 may be connected to the first inlet 7 by a char transfer assembly 24 comprising e.g. a screw conveyor or similar. The hot char outlet 3 and the first inlet is always connected in a fluid tight manner, i.e. in a manner which prevents ambient air from contacting the char when transferred from the hot char outlet 3 to the first inlet 7.

[0076] The inventive char collector 1 may be used in connection with any type of pyrolysis system wherein a solids fraction of char is obtained. Examples of suitable pyrolysis systems and pyrolysis reactors are disclosed in e.g. US 2012/0043194 A1, CN103923673A and WO 2018/177997 A1.

[0077] An embodiment of a char collector 1 according to the invention is shown in FIGS. 2-5.

[0078] The char collector 1 features a container 4 and a screw conveyor 5 (i.e. a longitudinal char conveyor unit). The container 4 has a chamber 6, a first inlet 7 arranged in an upper portion of the chamber 6 and a first outlet 8 arranged in a lower portion of the chamber 6. The screw conveyor 5 features a first end section 9 connected to the first outlet 8, a second end section 10 featuring a second outlet 11 for cooled char, a tube element 13 and a helical screw 12 (i.e. a conveying mechanism) arranged within the tube element 13 and configured to transport char from the first end section 9 to the second end section 11 during use. The helical screw 12 may be driven by a motor 18. In alternative embodiments, the screw conveyor may be substituted by a belt or chain conveyor arranged within a longitudinal hollow element having a suitable cross-section, e.g. a rectangular cross-section.

[0079] The first inlet 7 is arranged such that char entering the chamber 6 may be transferred to the first outlet 8 and the first end section 9 by gravity. The first inlet 7 may be connected, directly or indirectly, to a hot char outlet 3 of any type of pyrolysis reactor or system, such that hot char may enter the chamber 6.

[0080] During use, the chamber 6 is filled with water up to a maximum level L.sub.max above a highest level of the first outlet 8, i.e. above a minimum level L.sub.min, and below the level of the first inlet 7. A lowest level of the second outlet 11 is above the highest level of the first outlet 8, and preferably above a mid-level of the chamber 6. In this manner a gas trap 23 is formed between the first inlet 7 and the second outlet 11. The gas trap 23 formed by having water up to the minimum level L.sub.min is illustrated by the hatched section in FIG. 2. The screw conveyor 5 may also feature a third outlet 14 positioned between the first outlet 8 and the second outlet 11. The third outlet 14 is arranged such that air may be introduced to the screw conveyor 12 via the second outlet 11, or an air inlet 26, and exit via the third outlet 14, e.g. arranged at an upwards facing surface of the screw conveyor 5. In this manner, a significant portion of excess moisture may be removed from the char before it is collected via the second outlet 11. In addition to the moisture removed by the introduced air, the design and length of the screw conveyor will also have a large impact on the amount of moisture/water in the char. The maximum level L.sub.max of water in the chamber 6 may be defined as a lowest level of the third outlet, see FIG. 2. A separate air inlet 26 is not a required feature but facilitates the advantageous collection of char from the second outlet as described below.

[0081] A temperature sensor 27 is arranged at the second outlet 11 to measure the temperature of the char exiting the char collector 1. To control the temperature and moisture content of the char exiting the second outlet, the char collector features temperature and moisture sensors 28,29 arranged at both the air inlet 26 and the third outlet 14. A flow meter 31 may also be arranged at the air inlet 26. Preferably, the temperature of the char exiting the second outlet 11 is within the range of 50-80 C. and the moisture content within the range of 15-25 wt %. Char having a moisture content above 15 wt % will not spontaneously combust when mixed with oxygen/air. The temperature and moisture sensors 27,28,29 and the flow meter 31 may communicate with a control system. The control system may control the flow of air to obtain char having a desired temperature and moisture content. A moisture sensor may also be arranged to measure the moisture of the char exiting the second outlet 11.

[0082] A pyrolysis reaction is performed in an inert or at least oxygen free/depleted atmosphere. The gas trap is a highly advantageous feature of the char collector 1 since it removes the need for mechanical airlocks or a counterflow of expensive inert gas to prevent air/oxygen from entering the pyrolysis system and pyrolysis reactor when char is collected. Mechanical airlocks are often service intensive, vulnerable towards larger particles of non-pyrolyzed material (e.g. metal fragments and similar that may have been introduced unintentionally), char particles of larger sizes, clogging, as well as requiring control systems and actuators. The gas trap also allows for having a pressure slightly below ambient within the pyrolysis system and/or pyrolysis reactor. Below ambient pressure is present within some pyrolysis systems due to the use of suction to transfer the volatile fractions to a gas handling system.

[0083] To obtain an improved mixing of the hot char and water, as well as an improved movement of char from the first inlet 7 to the first outlet 8, the char collector 1 may feature multiple blades 9 arranged to rotate inside the chamber 6. The blades 9 are connected to a rotary shaft 19 and a motor 25 arranged to allow rotation of each blade 9 between a first position and a second position, wherein the blade 9 is at a higher level in the first position than in the second position. The rotary shaft 19 may be arranged at a centreline C of the chamber 6. The blade 9 is closer to the first inlet 7 in the first position than in the second position. In other words, during use, at least portions of the blade 9 may be above a water level in the chamber 6 when in the first position and at least portions of the blade 9 may be below the water level when in the second position. The blades 9 are not an essential part of the inventive char collector 1 but may be advantageous in particular when the throughput of char is high.

[0084] When char is transferred from the chamber 6 by the screw conveyor 5, water is gradually removed from the chamber 6, i.e. the water level is lowered. To ensure the water level is always above the minimum level L.sub.min and below the maximum level L.sub.max, the container comprises a controllable water inlet 20 for providing water into the chamber 6 and a water level sensor 21 for measuring the water level inside the chamber 6. The water level sensor 21 communicates with the controllable water inlet 20 such that water is added to the chamber when the water level falls below a predetermined level. The controllable water inlet 20 is closed when the water level sensor 21 detects a maximum water level. The predetermined water level is above the minimum level L.sub.min to avoid any risk of air entering the chamber. As a further safety precaution, a water level switch 30 is arranged to prevent the water level from falling below the minimum level L.sub.min. In an alternative embodiment of the char collector, a relatively constant water level may also be obtained in the chamber by having an overflow outlet arranged in the tube element 13. The overflow outlet may be arranged at a level corresponding to the maximum water level.

[0085] In the illustrated embodiment of the char collector, the chamber is substantially cylinder-shaped and has a horizontal centre axis. The centreline of the rotary shaft 19 coincides with the centreline C of the chamber. In this manner the distal end 22 of each blade, i.e. the end being furthest from the rotary shaft 19, may move close to the substantially circular wall of the chamber during rotation of the blade. Having the blades 9 rotating around a horizontal centreline C of a cylinder-shaped chamber 6 is advantageous in that it contributes to an efficient movement of char from an upper portion of the chamber 6 to a lower portion of the chamber 6, and further to the first outlet 8 and into the first section 9 of the screw conveyor 5. Examples of alternative embodiments of blades 9 suitable for the char collector 1 are shown in FIG. 6. Although all disclosed embodiments feature four blades 9 evenly arranged around a rotary shaft 19, an advantageous movement and wetting of char may be obtained if at least one blade 9 is present in the chamber 6.

[0086] As mentioned above, the char exiting a pyrolysis reactor has a very high temperature and a significant portion of the char is finely divided particles and fines which are highly flammable and may spontaneously combust when mixed with oxygen/air. The inventive char collector will minimize or avoid the risk of handling the produced char, since the char exiting the second outlet 11 may be controlled to have a moisture content above 15 wt % and a temperature between 50-80 C.

[0087] The inventive char collector allows for a highly advantageous method of collecting char in fluid tight bags. In the method, char exiting the second outlet 11 may be loaded into a fluid tight bag which is then sealed while the temperature of the char is still at 50-80 C. Subsequent cooling of the char loaded into the bag provides moist char in a vacuum packaging. The fluid tight bag ensures that the char is kept at a sufficient moisture level to prevent combustion and may be handled without any extensive safety procedures.

[0088] Pyrolysis systems are often used in the disposal of waste materials, wherein the obtained products, e.g. char, oil and tar, are not necessarily the main goal of the pyrolysis process. However, the obtained products, as well as the heat energy produced in the process, are valuable and it is envisioned that the pyrolysis system and char collector may be used in processes wherein the obtained products and/or the produced heat energy are the main goal. Such processes may for instance be the production of biofuel by pyrolysis of wood-based raw materials, production of char, energy production and similar. Thus, the term pyrolysis system is intended to cover systems such as waste treatment systems, biofuel production systems and power plants.