A reaction device for producing hydrogen by pyrolysis of biomass and a method of using the same

Abstract

The present invention discloses a biomass pyrolysis hydrogen production reaction device and a method of use, and belongs to the technical field of biomass pyrolysis hydrogen production. A biomass pyrolysis hydrogen production reaction device includes: a tank body and a mixed catalytic mechanism; the inside of the tank body is provided with a second fixed cylinder, a guide cylinder, a fixed cylinder, a connecting cylinder and a first fixed cylinder from bottom to top; the side wall of the second fixed cylinder is provided with an air inlet pipe, the inside of the second fixed cylinder is provided with a dust particle catalyst, the top of the first fixed cylinder is provided with an air outlet pipe, and the end of the air outlet pipe away from the first fixed cylinder passes through the top of the tank body; the mixed catalytic mechanism is arranged inside the second fixed cylinder, the fixed cylinder and the first fixed cylinder, and is used to make the high-temperature flue gas fully contact with the dust particle catalyst. The present invention fully mixes the dust particle catalyst with small particle size and easy to fly with the high-temperature flue gas through the mixed catalytic mechanism, improves the contact degree between the catalyst and the high-temperature flue gas, and thus effectively improves the efficiency of hydrogen production by cracking the high-temperature flue gas.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass pyrolysis hydrogen production, and in particular to a biomass pyrolysis hydrogen production reaction device and a use method thereof. Background Art

[0002] With the development and application of green and efficient fuel cell technology, hydrogen as a fuel has a huge market demand. In addition to fossil fuel hydrogen production, the existing hydrogen production method can also use biomass pyrolysis to produce hydrogen.

[0003] For example, publication number CN113736499A discloses a biomass pyrolysis hydrogen production reaction device, in which when the catalyst rolls along the second spiral plate onto the tray, the high-temperature flue gas guided by the first spiral plate is more likely to contact the catalyst on the second spiral plate, which is beneficial to increase the reaction speed and make the high-temperature pyrolysis gas catalytically produce hydrogen. In addition, the rotation direction of the side of the second spiral plate is opposite to the direction of the high-temperature flue gas flowing upward along the first spiral plate, which is beneficial to further allow the high-temperature flue gas to fully react with the catalyst and improve the reaction efficiency.

[0004] However, the above invention still has shortcomings. Since the catalyst is only arranged on the second spiral plate and the tray, the contact area between the high-temperature flue gas and the catalyst is low, which affects the catalysis of the high-temperature flue gas by the catalyst. The efficiency of high-temperature flue gas catalytic production of hydrogen is low, which is inconvenient for users to use. Summary of the invention

[0005] The object of the present invention is to provide a biomass pyrolysis hydrogen production reaction device and a use method to solve the problem of low efficiency of existing high-temperature flue gas cracking hydrogen production.

[0006] The technical solution of the present invention to solve the above technical problems is as follows:

[0007] A device for producing hydrogen from biomass by pyrolysis, comprising: a tank body and a mixed catalytic mechanism; the inside of the tank body is provided with a second fixed cylinder, a guide cylinder, a fixed cylinder, a connecting cylinder and a first fixed cylinder in sequence from bottom to top; the side walls of the first fixed cylinder and the second fixed cylinder are respectively connected to the inner wall of the tank body through connecting plates; the side wall of the second fixed cylinder is provided with an air inlet pipe for conveying high-temperature flue gas to the inside of the second fixed cylinder, a dust particle catalyst is placed inside the second fixed cylinder, an air outlet pipe for outputting gas is provided on the top of the first fixed cylinder, and one end of the air outlet pipe away from the first fixed cylinder passes through the top of the tank body; the mixed catalytic mechanism is arranged inside the second fixed cylinder, the fixed cylinder and the first fixed cylinder, and is used to make the high-temperature flue gas fully contact with the dust particle catalyst.

[0008] Furthermore, the above-mentioned mixed catalytic mechanism includes a vertically arranged rotating rod, the bottom end of which passes through the second fixed cylinder and is connected to a motor, the motor is arranged at the bottom of the tank body, and the rotating rod is provided with a fan blade located in the second fixed cylinder, which is used to mix the dust particle catalyst and the high-temperature flue gas and transport them upward;

[0009] The inner wall of the fixed cylinder is provided with a spiral blade, the spiral blade and the fixed cylinder form a spiral channel, and the rotating rod passes through the spiral blade and rotates with the spiral blade;

[0010] A filter screen for filtering dust particle catalyst is provided inside the first fixed cylinder, and a collecting assembly for collecting the filtered dust particle catalyst is provided inside the first fixed cylinder. The top end of the rotating rod is connected to the first fixed cylinder through the collecting assembly.

[0011] Furthermore, the above-mentioned collecting component includes a reduction gearbox arranged in the first fixed cylinder through a support rod and a fixed block arranged on the output shaft of the reduction gearbox; the reduction gearbox is connected to the top end of the rotating rod; the fixed block is provided with a scraper plate in contact with the bottom end of the filter screen, and the scraper plate is provided with a collecting frame for collecting dust particle catalysts on one side along the rotation direction, and the end of the scraper plate and the collecting frame away from the fixed block is provided with a rotating cylinder rotating along the inner wall of the first fixed cylinder; a conveying component for conveying the dust particle catalyst collected by the collecting frame to the inside of the second fixed cylinder is provided on the side walls of the first fixed cylinder and the second fixed cylinder.

[0012] Furthermore, the top of the collecting frame and the end away from the fixed block are open structures; the conveying assembly includes a plurality of circulation pipes, the top of the circulation pipes are connected to the first fixed cylinder, and the connecting position corresponds to the end of the collecting frame away from the fixed block, the bottom of the circulation pipes are connected to the second fixed cylinder, and the guide cylinder is provided with a block for separating the position where the fan blades and the circulation pipes are connected to the second fixed cylinder, and there is a gap between the bottom of the block and the bottom of the second fixed cylinder, so that the collected dust particle catalyst passes through the gap for circulation.

[0013] Furthermore, the first fixed cylinder is provided with a support ring along the circumferential direction for supporting the rotating cylinder, so that the rotating cylinder rotates along the support ring.

[0014] Furthermore, a guide ring is provided at the bottom of the second fixed tube along the circumferential direction, and the guide ring is located at the bottom of the stopper and has a gap with the stopper.

[0015] Furthermore, an inclined plate is provided at the bottom of the collecting frame to facilitate the movement of the dust particle catalyst to the circulation pipeline.

[0016] Furthermore, the side walls of the support rods are provided with reinforcing ribs.

[0017] A method for using the above-mentioned biomass pyrolysis hydrogen production reaction device comprises the following steps:

[0018] S1: transporting an appropriate amount of high-temperature flue gas from the air intake pipe to the interior of the second fixed cylinder;

[0019] S2: The mixed catalytic mechanism fully mixes the high-temperature flue gas and the dust particle catalyst to react for a period of time to complete the cracking and hydrogen production;

[0020] S3: The generated hydrogen-containing gas is discharged from the gas outlet pipe;

[0021] S4: Add or replace the dust particle catalyst in the second fixed cylinder, and repeat steps S1 to S3 to achieve repeated hydrogen production.

[0022] Furthermore, in the above step S2, when the high-temperature flue gas is transported, the motor is started synchronously, and the rotating rod drives the fan blades to rotate. The fan blades fully mix the high-temperature flue gas and the dust particle catalyst for reaction. The reaction time is 3-4 hours. At the same time, the rotating rod drives the scraper plate to rotate, and the dust particle catalyst attached to the bottom of the filter is scraped off, so that the dust particle catalyst is recovered into the second fixed cylinder for continuous circulation;

[0023] In step S3, the motor keeps working to discharge the hydrogen-containing gas to the outside. At this time, air or hydrogen is introduced from the air intake pipe simultaneously, and the scraper scrapes off the dust particle catalyst attached to the bottom of the filter, so that the dust particle catalyst is recovered into the second fixed cylinder for continuous circulation.

[0024] The present invention has the following beneficial effects:

[0025] (1) The present invention uses fan blades to fully mix the dust particle catalyst with small particle size and easy to fly with the high-temperature flue gas, thereby improving the contact degree between the catalyst and the high-temperature flue gas, thereby effectively improving the efficiency of hydrogen production by cracking the high-temperature flue gas.

[0026] (2) The present invention separates the dust particle catalyst from the hydrogen-containing gas through a filter, and then uses a scraper to clean and collect the dust particle catalyst attached to the bottom of the filter into a collecting frame. The collecting frame transports the dust particle catalyst back to the inside of the second fixed cylinder through a circulation pipe, and circulates the dust particle catalyst. This can not only avoid the accumulation of dust particle catalyst at the filter, but also realize the circulation of dust particle catalyst, thereby improving the utilization rate of dust particle catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the external structure of the biomass pyrolysis hydrogen production reaction device of the present invention;

[0028] Figure 2 It is a schematic diagram of the internal structure of the tank body of the present invention;

[0029] Figure 3 It is a schematic diagram of the internal structure of the device for producing hydrogen by pyrolysis of biomass according to the present invention;

[0030] Figure 4 It is a schematic diagram of the arrangement of the circulation pipeline of the present invention;

[0031] Figure 5 It is a schematic diagram of the arrangement of the scraper plate and the collecting frame of the present invention.

[0032] In the figure: 1-tank body; 2-first fixed cylinder; 3-connecting cylinder; 4-fixed cylinder; 5-guide cylinder; 6-connecting plate; 7-second fixed cylinder; 8-motor; 9-inlet pipe; 10-circulation pipe; 11-outlet pipe; 12-scraper plate; 13-block; 14-guide ring; 15-fan blade; 16-rotating rod; 17-spiral blade; 18-reduction box; 19-support rod; 20-support ring; 21-rotating cylinder; 22-collection frame; 23-fixed block; 25-filter screen. DETAILED DESCRIPTION

[0033] The principles and features of the present invention are described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0034] Please refer to Figures 1 to 3 The present embodiment discloses a biomass pyrolysis hydrogen production reaction device, comprising: a tank body 1 and a mixed catalytic mechanism, wherein the inside of the tank body 1 is provided with a second fixed cylinder 7, a guide cylinder 5, a fixed cylinder 4, a connecting cylinder 3 and a first fixed cylinder 2 from bottom to top, the second fixed cylinder 7, the guide cylinder 5, the fixed cylinder 4, the connecting cylinder 3 and the first fixed cylinder 2 are connected in sequence, and the side wall of the second fixed cylinder 7 and the side wall of the second fixed cylinder 2 are respectively connected to the inner wall of the tank body 1 through a connecting plate 6. The side wall of the second fixed cylinder 7 is provided with an air inlet pipe 9 for conveying high-temperature flue gas, and the air inlet pipe 9 extends out of the tank body 1, and a dust particle catalyst is placed inside the second fixed cylinder 7. The top of the first fixed cylinder 2 is provided with an air outlet pipe 11 for outputting hydrogen-containing gas to the outside, and the air outlet pipe 11 extends out of the tank body 1. The mixed catalytic mechanism is arranged inside the second fixed cylinder 7, the fixed cylinder 4 and the first fixed cylinder 2, and is used to make the high-temperature flue gas fully contact with the dust particle catalyst.

[0035] The high-temperature flue gas is obtained by mechanically mixing the existing aluminum smelting waste slag and biomass raw materials, passing through the existing drying, pyrolysis and gasification processes, and then passing them into the combustion chamber for combustion to obtain a high-temperature flue gas of 800-1200°C. The dust particle catalyst adopts the existing carbon-aluminum composite catalytic material, which is rich in active components such as iron, magnesium, and potassium, and has a catalytic cracking effect on the high-temperature flue gas, so that the high-temperature pyrolysis gas catalytically produces hydrogen. After the high-temperature flue gas enters the second fixed tube 7 from the air inlet pipe 9, it is fully in contact with the dust particle catalyst for 3-4 hours to fully react and produce hydrogen, and then the hydrogen-containing gas is discharged from the outlet pipe 11. In order to ensure that hydrogen production can proceed smoothly, insulation equipment can be set to insulate the tank or tank body to reduce the heat dissipation of the high-temperature flue gas.

[0036] In this embodiment, the diameter of the fixed cylinder 4 is smaller than the diameters of the first fixed cylinder 2 and the second fixed cylinder 7 , so the guide cylinder 5 and the connecting cylinder 3 are transitionally connected in a cone shape.

[0037] The mixed catalytic mechanism includes a vertically arranged rotating rod 16, which is located inside the second fixed cylinder 7, the guide cylinder 5, the fixed cylinder 4, the connecting cylinder 3 and the first fixed cylinder 2. The bottom end of the rotating rod 16 passes through the second fixed cylinder 2 and is connected to a motor 8. The motor 8 is fixedly mounted on the inner bottom wall of the tank body 1. The top of the rotating rod 16 is connected to the first fixed cylinder 2 through a collecting assembly. The rotating rod 16 is provided with a fan blade 15 located in the second fixed cylinder 7. When the fan blade 15 is working, an upward flowing wind is generated. When the gas flows, the high-temperature flue gas and the dust particle catalyst are stirred to make them evenly mixed, thereby improving the utilization rate of the dust particle catalyst and improving the hydrogen production efficiency.

[0038] A spiral blade 17 is provided in the fixed cylinder 4, and a spiral channel is formed between the spiral blade 17 and the inner side wall of the fixed cylinder 4. During the reaction process, the amount of dust particle catalyst entering the first fixed cylinder 2 is reduced, thereby reducing the dust particle catalyst blocking the flow channel of the hydrogen-containing gas. In this embodiment, the rotating rod 16 rotates through the middle part of the spiral blade 17 and cooperates with the middle part of the spiral blade 17.

[0039] Due to the presence of the fan blades 15, the dust particle catalyst will inevitably enter the first fixed cylinder 2. In order to prevent the dust particle catalyst from entering the exhaust pipe 11, in this embodiment, a filter net 25 for filtering the dust particle catalyst is provided inside the first fixed cylinder 2. The collecting component is located below the filter net 25 and is used to scrape and collect the dust particle catalyst at the bottom of the filter net 25.

[0040] Please refer to Figure 3 and Figure 5The collecting assembly includes a reduction box 18 arranged in the first fixed cylinder 2 through a support rod 19 and a fixed block 23 arranged on the output shaft of the reduction box 18. The input shaft of the reduction box 18 is connected to the top of the rotating rod 16, and the fixed block 23 is located between the reduction box 18 and the filter 25. The side wall of the fixed block 23 is provided with a plurality of scraper plates 12 in contact with the bottom end of the filter 25. The scraper plates 12 are provided with a collection frame 22 for collecting dust particle catalysts on one side along the rotation direction. The scraper plates 12 and the collection frame 22 are provided with a rotating cylinder 21 rotating along the inner wall of the first fixed cylinder 2 at one end away from the fixed block 23. In order to support the scraper plates 12 and the collection frame 22, in this embodiment, the first fixed cylinder 2 is provided with a support ring 20 for supporting the rotating cylinder 21 along the circumferential direction, so that the rotating cylinder 21 rotates along the support ring 20.

[0041] In order to improve the support for the reduction box 18, in this embodiment, the side walls of the support rod 19 are provided with reinforcing ribs (not shown).

[0042] Obviously, in order to facilitate the collection of dust particle catalyst, a brush can also be provided on the scraper plate 12 .

[0043] Please refer to Figure 3 and Figure 4 In order to collect the collected dust particle catalyst, in this embodiment, a conveying assembly is provided on the side walls of the first fixed cylinder 2 and the second fixed cylinder 7 for circulating the dust particle catalyst collected in the collection frame 22 into the second fixed cylinder 7.

[0044] The conveying assembly includes a plurality of circulation pipes 10, the top of which is connected to the first fixed cylinder 1, and the bottom of which is connected to the second fixed cylinder 7. The top of the collection frame 22 and the end away from the fixed block 23 are open structures, and the end of the collection frame 22 away from the fixed block 23 matches the top of the circulation pipe 10. After the collection frame 22 rotates to a certain angle, it will be connected to the circulation pipe 10, and the dust particle catalyst in the collection frame 22 can be recycled by wind. The guide cylinder 5 is provided with a stopper 13 for separating the position where the fan blade 15 and the circulation pipe 10 are connected to the second fixed cylinder 7. There is a gap between the bottom of the stopper 13 and the bottom of the second fixed cylinder 7, so that the collected dust particle catalyst passes through the gap for circulation.

[0045] In order to facilitate the recovery of the dust particle catalyst, in the present embodiment, a guide ring 14 is circumferentially provided at the bottom of the second fixed cylinder 7, and the guide ring 14 is located at the bottom of the stopper 13 and has a gap with the stopper 13. At the same time, an inclined plate (not shown) is provided at the bottom of the collecting frame 22 to facilitate the movement of the dust particle catalyst to the circulation pipe 10.

[0046] This embodiment also provides a method for using the above-mentioned biomass pyrolysis hydrogen production reaction device, comprising the following steps:

[0047] S1: delivering an appropriate amount of high-temperature flue gas from the air inlet pipe 9 to the interior of the second fixed cylinder 7;

[0048] S2: When conveying high-temperature flue gas, the motor 8 is started synchronously, and the rotating rod 16 drives the fan blade 15 to rotate. The fan blade 15 fully mixes the high-temperature flue gas and the dust particle catalyst for reaction. The reaction time is 3-4 hours. At the same time, the rotating rod 16 drives the scraper plate 12 to rotate, and the dust particle catalyst attached to the bottom of the filter screen 25 is scraped off, so that the dust particle catalyst is recovered into the second fixed cylinder 7 to continue to circulate;

[0049] S3: The motor 8 keeps working to discharge the hydrogen-containing gas to the outside. At this time, air or hydrogen is introduced from the air inlet pipe 9 simultaneously. The scraper plate 12 scrapes off the dust particle catalyst attached to the bottom of the filter screen 25, so that the dust particle catalyst is recovered into the second fixed cylinder 7 for continuous circulation.

[0050] S4: Add or replace the dust particle catalyst in the second fixed cylinder 7, and repeat steps S1 to S3 to achieve repeated hydrogen production.

[0051] When the hydrogen-containing gas is discharged to the outside, or the collecting frame 22 is connected to the circulation pipe 10, the flow of gas in the first fixed cylinder 2 will clear the dust particle catalyst in the spiral channel and the collecting frame 22, and simultaneously scrape off the dust particle catalyst at the bottom of the filter screen 25 to avoid clogging the filter screen 25 and affecting the recovery of the hydrogen-containing gas.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A device for producing hydrogen by pyrolysis of biomass, characterized in that: include: A tank body (1) and a mixed catalytic mechanism; the tank body (1) is provided with a second fixed cylinder (7), a guide cylinder (5), a fixed cylinder (4), a connecting cylinder (3) and a first fixed cylinder (2) in order from bottom to top; the side walls of the first fixed cylinder (2) and the second fixed cylinder (7) are connected to the inner wall of the tank body (1) via connecting plates (6) respectively; the side wall of the second fixed cylinder (7) is provided with an air inlet pipe (9) for conveying high-temperature flue gas to the inside of the second fixed cylinder (7); a dust particle catalyst is placed inside the second fixed cylinder (7); the top of the first fixed cylinder (2) is provided with an air outlet pipe (11) for outputting gas; the end of the air outlet pipe (11) away from the first fixed cylinder (2) passes through the top of the tank body (1); the mixed catalytic mechanism is arranged inside the second fixed cylinder (7), the fixed cylinder (4) and the first fixed cylinder (2) to make the high-temperature flue gas fully contact with the dust particle catalyst; The mixed catalytic mechanism comprises a vertically arranged rotating rod (16), the bottom end of the rotating rod (16) passes through the second fixed cylinder (7) and is connected to a motor (8), the motor (8) is arranged at the bottom of the tank body (1), and the rotating rod (16) is provided with a fan blade (15) located in the second fixed cylinder (7) for mixing the dust particle catalyst and the high-temperature flue gas and conveying them upwards; The inner wall of the fixed cylinder (4) is provided with a spiral blade (17), the spiral blade (17) and the fixed cylinder (4) form a spiral channel, and the rotating rod (16) passes through the spiral blade (17) and rotates in cooperation with the spiral blade (17); A filter screen (25) for filtering dust particle catalyst is provided inside the first fixed cylinder (2), a collection assembly for collecting the filtered dust particle catalyst is provided inside the first fixed cylinder (2), and the top end of the rotating rod (16) is connected to the first fixed cylinder (2) via the collection assembly.

2. The device for producing hydrogen from biomass by pyrolysis according to claim 1, characterized in that: The collecting assembly comprises a reduction box (18) arranged in the first fixed cylinder (2) via a support rod (19) and a fixed block (23) arranged on the output shaft of the reduction box (18); the reduction box (18) is connected to the top end of the rotating rod (16); the fixed block (23) is provided with a scraper plate (12) in contact with the bottom end of the filter screen (25); the scraper plate (12) is provided with a collecting frame (22) for collecting dust particle catalyst on one side along the rotation direction; the scraper plate (12) and the collecting frame (22) are provided with a rotating cylinder (21) rotating along the inner wall of the first fixed cylinder (2) at one end away from the fixed block (23); and a conveying assembly for conveying the dust particle catalyst collected by the collecting frame (22) to the inside of the second fixed cylinder (7) is provided on the side walls of the first fixed cylinder (2) and the second fixed cylinder (7).

3. The device for producing hydrogen from biomass by pyrolysis according to claim 2, characterized in that: The top of the collecting frame (22) and the end away from the fixed block (23) are open structures; the conveying assembly comprises a plurality of circulation pipes (10), the top of the circulation pipe (10) is connected to the first fixed cylinder (2), and the connection position corresponds to the end of the collecting frame (22) away from the fixed block (23), the bottom of the circulation pipe (10) is connected to the second fixed cylinder (7), the guide cylinder (5) is provided with a stopper (13) for separating the fan blade (15) and the position where the circulation pipe (10) is connected to the second fixed cylinder (7), and there is a gap between the bottom of the stopper (13) and the bottom of the second fixed cylinder (7), so that the collected dust particle catalyst passes through the gap for circulation.

4. The device for producing hydrogen from biomass by pyrolysis according to claim 2, characterized in that: The first fixed cylinder (2) is provided with a support ring (20) along the circumferential direction for supporting the rotating cylinder (21), so that the rotating cylinder (21) rotates along the support ring (20).

5. The device for producing hydrogen from biomass by pyrolysis according to claim 3, characterized in that: A guide ring (14) is provided at the bottom of the second fixed cylinder (7) along the circumferential direction; the guide ring (14) is located at the bottom of the stopper (13) and has a gap with the stopper (13).

6. The device for producing hydrogen from biomass by pyrolysis according to claim 3, characterized in that: The bottom of the collecting frame (22) is provided with an inclined plate for facilitating the movement of the dust particle catalyst toward the circulation pipe (10).

7. The device for producing hydrogen from biomass by pyrolysis according to claim 2, characterized in that: The side wall of the support rod (19) is provided with reinforcement ribs.

8. A method for using the biomass pyrolysis hydrogen production reaction device according to any one of claims 1 to 7, characterized in that: The following steps are involved: S1: transporting an appropriate amount of high-temperature flue gas from the air inlet pipe (9) to the interior of the second fixed cylinder (7); S2: The mixed catalytic mechanism fully mixes the high-temperature flue gas and the dust particle catalyst to react for a period of time to complete the cracking and hydrogen production; S3: The generated hydrogen-containing gas is discharged to the outside through the gas outlet pipe (11); S4: Add or replace the dust particle catalyst into the second fixed cylinder (7), and repeat steps S1 to S3 to achieve repeated hydrogen production.

9. The method of use according to claim 8, characterized in that: In step S2, when the high-temperature flue gas is transported, the motor (8) is started synchronously, and the rotating rod (16) drives the fan blades (15) to rotate. The fan blades (15) fully mix the high-temperature flue gas and the dust particle catalyst to react. The reaction time is 3-4 hours. At the same time, the rotating rod (16) drives the scraper plate (12) to rotate, and the dust particle catalyst attached to the bottom of the filter screen (25) is scraped off, so that the dust particle catalyst is recovered into the second fixed cylinder (7) and continues to circulate; In step S3, the motor (8) continues to work to discharge the hydrogen-containing gas to the outside. At this time, air or hydrogen is simultaneously introduced from the air inlet pipe (9), and the scraper scrapes off the dust particle catalyst attached to the bottom of the filter screen (25), so that the dust particle catalyst is recovered into the second fixed cylinder (7) and continues to circulate.

Images