Multi-stage membrane permeation purification integrated device for electronic-grade sulfuric acid

Abstract

The application relates to a multi-stage membrane permeation purification integrated device for electronic-grade sulfuric acid, and relates to the technical field of sulfuric acid concentration, which comprises a first permeation barrel, a second permeation barrel, a third permeation barrel and a pulse type backflush assembly. The first permeation barrel, the second permeation barrel and the third permeation barrel are arranged, in the first permeation barrel, a PPES membrane can preliminarily filter out most impurities and preliminarily reduce turbidity, the DHMBA polyester membrane in the second permeation barrel is horizontally arranged, liquid can fully contact the membrane surface when passing through, medium-aperture metal ions and small-molecule organic matters can be removed, and ion purity is improved, so that deeper purification is realized, through the sulfonated ceramic membrane in the third permeation barrel, nanoscale apertures can deeply remove residual ions, and final fine filtration can be carried out, through three-stage membrane combination covering the filtration spectrum, the finished sulfuric acid can reach the electronic-grade standard, and the problem that trace metal ions and other impurities cannot be completely removed is solved.

Description

Technical Field

[0001] This application relates to sulfuric acid concentration, and more particularly to an integrated equipment for multi-stage membrane permeation purification of electronic-grade sulfuric acid. Background Technology

[0002] Waste sulfuric acid is generated in industrial production. my country is a major producer and consumer of sulfuric acid. With the continuous growth of sulfuric acid consumption, the amount of industrial waste sulfuric acid in China is also increasing year by year. The recycling and utilization of waste sulfuric acid is receiving more and more attention. In industrial production, waste acid may be generated in processes such as nitration, esterification, sulfonation, alkylation, catalysis and gas drying of organic matter, or in processes such as titanium dioxide production, steel pickling and gas drying. Its treatment methods can be roughly divided into waste sulfuric acid concentration, high temperature cracking, chemical oxidation, extraction, crystallization, fertilizer production and neutralization treatment. Among them, waste sulfuric acid can be reused after concentration.

[0003] Existing sulfuric acid purification equipment mostly uses single-stage reverse osmosis membranes. In the production process, it is difficult to achieve the purity of sulfuric acid to meet electronic grade standards, and trace metal ions and other impurities cannot be completely removed. In order to solve the above problems, an integrated electronic grade sulfuric acid multi-stage membrane permeation purification equipment has been proposed. Utility Model Content

[0004] The purpose of this application is to provide an integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device, which has the advantages of multi-stage membrane permeation purification function, and solves the problem that the purity of sulfuric acid is difficult to reach the electronic grade standard in the production process, and that trace metal ions and other impurities cannot be completely removed.

[0005] This solves the problems of existing continuous hydrochloric acid concentration equipment that uses single-stage reverse osmosis or evaporation processes, resulting in high energy consumption, easy volatilization and loss of hydrochloric acid, lack of pretreatment and membrane fouling control functions, and easy clogging of membrane pores by colloidal impurities.

[0006] The electronic-grade sulfuric acid multi-stage membrane permeation purification integrated equipment provided in this application adopts the following technical solution: it includes a first permeation tank, a second permeation tank, a third permeation tank, and a pulse backflushing assembly. The first permeation tank, the second permeation tank, and the third permeation tank are respectively equipped with PPES membrane, DHMBA polyester membrane, and sulfonated ceramic membrane.

[0007] A first connecting pipe is fixedly connected to the bottom side of the first permeation tank, and a power pump is installed on the first connecting pipe. The output end of the first connecting pipe is located on the bottom side of the second permeation tank. A second connecting pipe is located on the top side of the second permeation tank, and the output end of the second connecting pipe is located on the top of the third permeation tank. A storage bin is located at the top of the third permeation tank, and multiple discharge pipes are located at the bottom of the storage bin. A first top cover is located on the top of the first permeation tank, and an inlet pipe is located on the top of the first top cover. An outlet pipe is located at the bottom of the third permeation tank, and the output end of the inlet pipe is located at the bottom of the first top cover and is fixedly connected to a flow divider. The PPES membrane is perpendicular to the position of the first top cover. The two outlets of the flow divider are respectively located on opposite sides of the PPES membrane. The DHMBA polyester membrane is horizontally located in the middle of the second permeation tank, and the sulfonated ceramic membrane is horizontally located in the middle of the third permeation tank. The pulse backwash assembly includes a water pump.

[0008] By adopting the above technical solutions, the purification efficiency and quality of electronic-grade sulfuric acid can be improved. In the first permeation tank, the PPES membrane can initially filter out most impurities and reduce turbidity. Its vertical arrangement helps to increase the filtration area and efficiency. Under the action of the distributor, the feed can be evenly distributed to both sides of the PPES membrane, further optimizing the uniformity of liquid distribution. Through the horizontal arrangement of the DHMBA polyester membrane in the second permeation tank, the liquid can fully contact the membrane surface when passing through, removing medium-sized metal ions and small molecule organic matter, improving ion purity, and thus achieving deeper purification. Through the sulfonated ceramic membrane in the third permeation tank, the nano-sized pores can deeply remove residual ions, enabling final fine filtration. Its horizontal installation, combined with the design of the storage tank and feed pipe, ensures that the treated liquid has higher purity and stability.

[0009] Preferably, the water pump input end is connected to a pure water supply system, the water pump output end is fixedly connected to a backwash pipe, three vertical connecting pipes are fixedly connected to the surface of the backwash pipe, a pulse control valve is provided on the surface of the vertical connecting pipe, multiple first backwash connecting pipes are provided inside the first permeation tank, a second top cover is provided on the top of the second permeation tank, multiple connecting rods are provided at the bottom of the second top cover, a second backwash connecting pipe is fixedly connected to the bottom end of the connecting rod, and a third backwash connecting pipe is provided on the bottom side of the third permeation tank;

[0010] By adopting the above technical solution, and by setting up vertical connecting pipes that are interconnected with the backwash connecting pipes inside each permeation tank, it can be ensured that the backwash medium can be evenly distributed in each permeation tank, and the overall operating efficiency of the system can be optimized. Then, by adjusting the pulse control valve, precise backwashing operation can be performed.

[0011] Preferably, a plurality of first backflush connecting pipes are symmetrically arranged on both sides of the PPES membrane, a plurality of first nozzles are provided on the surface of the first backflush connecting pipes, and the input ends of the plurality of first backflush connecting pipes are all provided on the surface of the first permeation tank and are fixedly connected to a U-shaped connecting pipe.

[0012] By adopting the above technical solution and setting multiple first nozzles, a uniform water flow distribution can be formed, which can cover every area of ​​the PPES membrane surface and avoid cleaning dead corners. At the same time, the symmetrically arranged first backwash connection pipes can balance the water pressure distribution during backwashing, reduce the impact on the membrane module, and thus better protect the integrity of the membrane material.

[0013] Preferably, the bottom of the second backflush connecting pipe is provided with a plurality of second nozzles, the second nozzles are located on the top of the DHMBA polyester film, and the input end of the second backflush connecting pipe is located on the top of the second top cover;

[0014] By adopting the above technical solution and setting multiple second nozzles, the top area of ​​the DHMBA polyester membrane can be covered, ensuring that the cleaning liquid is distributed evenly across the entire membrane surface with uniform flow and pressure. At the same time, it can reduce direct impact on the membrane surface, prevent the membrane material from being damaged due to over-cleaning, and enable the equipment to achieve higher cleaning efficiency and longer membrane module service life during operation.

[0015] Preferably, the output end of the third backflushing connection pipe is located on the inner side of the third permeation tank and at the bottom of the sulfonated ceramic membrane;

[0016] By adopting the above technical solution and setting a third backflushing connection pipe, it is possible to accurately correspond to the bottom area of ​​the sulfonated ceramic membrane, ensuring that the cleaning liquid forms a uniform coverage when flowing from bottom to top. This arrangement makes full use of the natural flow characteristics of the liquid, making the cleaning process more efficient and improving the overall cleaning effect, thereby extending the service life of the sulfonated ceramic membrane.

[0017] Preferably, the three vertical connecting pipe output ends are respectively fixedly connected to the top of the U-shaped connecting pipe, the input end of the second backflushing connecting pipe, and the input end of the third backflushing connecting pipe. A waste liquid pipe is fixedly connected to the top side of the third permeation tank, and a control valve is installed inside the waste liquid pipe.

[0018] By adopting the above technical solution and setting up a waste liquid pipe, the waste liquid generated during the cleaning process of the third permeation tank can be discharged. The setting of the control valve can further enhance the flexibility of operation, and the flow rate and timing of waste liquid discharge can be adjusted according to actual needs.

[0019] Preferably, the bottom of the first permeation tank, the bottom of the second permeation tank, and the third permeation tank are respectively provided with a first drain valve, a second drain valve, and a third drain valve, and the output ends of the first drain valve, the second drain valve, and the third drain valve are connected to a collection pipe;

[0020] By adopting the above technical solution and setting up collection pipes, the waste liquid discharged from each permeation tank can be collected, enabling centralized treatment of the waste liquid. By setting up three discharge valves, it is convenient to control the waste liquid discharge of each permeation tank individually, and synchronous operation can be achieved when needed, enhancing the flexibility and controllability of equipment operation.

[0021] Preferably, a feed pump is provided at the input end of the feed pipe;

[0022] By adopting the above technical solution and setting up a feed pump, the conveying capacity of the feed pipe can be effectively improved, ensuring that the raw materials enter the equipment at a stable flow rate.

[0023] In summary, this application includes at least one of the following beneficial technical effects:

[0024] This integrated multi-stage membrane permeation purification system for electronic-grade sulfuric acid utilizes a three-stage permeation tank. In the first tank, a PPES membrane initially filters out most impurities, reducing turbidity. Its vertical arrangement increases filtration area and efficiency. A distributor evenly distributes the feed to both sides of the PPES membrane, further optimizing liquid distribution uniformity. In the second tank, a horizontally arranged DHMBA polyester membrane ensures ample contact between the liquid and the membrane surface, removing medium-sized metal ions and small organic molecules, thus improving ion purity and achieving deeper purification. In the third tank, a sulfonated ceramic membrane with nano-sized pores deeply removes residual ions, enabling final fine filtration. Its horizontal installation, combined with the storage tank and feed pipe design, ensures higher purity and stability of the treated liquid. This three-stage membrane combination covers the entire filtration spectrum, enabling the finished sulfuric acid to meet electronic-grade standards, solving the problem of incomplete removal of trace metal ions and other impurities. Attached Figure Description

[0025] Figure 1 This is a frontal three-dimensional structural diagram of this application;

[0026] Figure 2 This is a schematic diagram of the structure in frontal cross-section in this application;

[0027] Figure 3 This is a structural schematic diagram of the cross-section of the first permeation tank in this application;

[0028] Figure 4 This is a structural block diagram of the operation of this application;

[0029] Figure 5 This is a structural block diagram of the pulse recoil assembly in this application.

[0030] In the picture:

[0031] 1. First permeation tank; 101. First top cover; 102. Feed pipe; 103. Diverter; 104. PPES membrane; 105. First backflushing connection pipe; 106. First nozzle; 107. U-shaped connection pipe; 108. First drain valve;

[0032] 2. Second infiltration tank; 201. Second top cover; 202. Connecting rod; 203. Second backflushing connecting pipe; 204. Second nozzle; 205. DHMBA polyester membrane; 206. Second drain valve;

[0033] 3. Third permeation tank; 301. Storage silo; 302. Feed pipe; 303. Sulfonated ceramic membrane; 304. Third drain valve; 305. Third backflushing connection pipe; 306. Discharge pipe; 307. Waste liquid pipe;

[0034] 4. Pulse-type backwash assembly; 401. Water pump; 402. Backwash pipeline; 403. Vertical connecting pipe; 404. Pulse control valve;

[0035] 5. First connecting pipe;

[0036] 6. Second connecting pipe;

[0037] 7. Power pump;

[0038] 8. Collection tube;

[0039] 9. Feed pump. Detailed Implementation

[0040] The following is in conjunction with the appendix Figure 1 -Appendix Figure 5 This application will be described in further detail below.

[0041] Example 1: Integrated electronic-grade multi-stage membrane permeation purification equipment for sulfuric acid, refer to Figure 1 , Figure 2 and Figure 3 It includes a first permeation tank 1, a second permeation tank 2, a third permeation tank 3 and a pulse backflushing assembly 4. The first permeation tank 1, the second permeation tank 2 and the third permeation tank 3 are respectively provided with a PPES membrane 104, a DHMBA polyester membrane 205 and a sulfonated ceramic membrane 303.

[0042] A first connecting pipe 5 is fixedly connected to the bottom side of the first permeation tank 1. A power pump 7 is installed on the first connecting pipe 5. The output end of the first connecting pipe 5 is located on the bottom side of the second permeation tank 2. A second connecting pipe 6 is installed on the top side of the second permeation tank 2. The output end of the second connecting pipe 6 is located on the top of the third permeation tank 3. A storage silo 301 is installed at the top of the third permeation tank 3. Multiple discharge pipes 302 are installed at the bottom of the storage silo 301. A first top cover 101 is installed on the top of the first permeation tank 1. A feed pipe 102 is installed on the top of the first top cover 101. The third permeation tank 3 has a discharge pipe 306 at its bottom, and the output end of the feed pipe 102 is located at the bottom of the first top cover 101 and is fixedly connected to a distributor 103. The PPES membrane 104 is perpendicular to the first top cover 101. The two outlets of the distributor 103 are respectively located on opposite sides of the PPES membrane 104. The DHMBA polyester membrane 205 is horizontally located in the middle of the second permeation tank 2, and the sulfonated ceramic membrane 303 is horizontally located in the middle of the third permeation tank 3. The pulse backwash assembly 4 includes a water pump 401, which, through the setting of the first permeation tank 3, provides a flow path for the flow path. The system comprises three permeation tanks: a first permeation tank 1, a second permeation tank 2, and a third permeation tank 3. In the first permeation tank 1, the PPES membrane 104 initially filters out most impurities and reduces turbidity. Its vertical arrangement helps improve the filtration area and efficiency. Under the action of the distributor 103, the feed can be evenly distributed to both sides of the PPES membrane 104, further optimizing the uniformity of liquid distribution. In the second permeation tank 2, the DHMBA polyester membrane 205 is horizontally arranged, allowing the liquid to fully contact the membrane surface during passage. This removes medium-sized metal ions and small organic molecules, improving ion purity and achieving deeper purification. In the third permeation tank 3, the sulfonated ceramic membrane 303, with its nano-sized pores, deeply removes residual ions, enabling final fine filtration. Its horizontal installation, combined with the design of the storage tank 301 and the feed pipe 302, ensures that the treated liquid has higher purity and stability. Through the three-stage membrane combination covering the filtration spectrum, the finished sulfuric acid can reach electronic grade standards, solving the problem of not being able to completely remove trace metal ions and other impurities.

[0043] Please see Figure 2 , Figure 3 and Figure 5The input end of water pump 401 is connected to a pure water supply system, and the output end of water pump 401 is fixedly connected to a backwash pipe 402. Three vertical connecting pipes 403 are fixedly connected to the surface of the backwash pipe 402, and pulse control valves 404 are installed on the surface of the vertical connecting pipes 403. Multiple first backwash connecting pipes 105 are installed inside the first permeation tank 1. A second top cover 201 is installed on the top of the second permeation tank 2. Multiple connecting rods 202 are installed at the bottom of the second top cover 201, and the bottom end of the connecting rods 202 is fixedly connected to the second backwash connecting pipes 203. A third backwash connecting pipe 305 is installed on the bottom side of the third permeation tank 3. The vertical connecting pipes 403 are interconnected with the backwash connecting pipes inside each permeation tank, which ensures that the backwash medium can be evenly distributed to each tank. In the permeate tank, the overall operating efficiency of the system is optimized. Precise backwashing can be performed under the control of the pulse control valve 404. Multiple first backwash connection pipes 105 are symmetrically arranged on both sides of the PPES membrane 104. Multiple first nozzles 106 are provided on the surface of each first backwash connection pipe 105. The input ends of the multiple first backwash connection pipes 105 are all located on the surface of the first permeate tank 1 and are fixedly connected to U-shaped connection pipes 107. By setting multiple first nozzles 106, a uniform water flow distribution can be formed, covering every area of ​​the PPES membrane 104 surface, avoiding cleaning dead zones. Simultaneously, the symmetrical arrangement of the first backwash connection pipes 105 can balance the water pressure distribution during backwashing, reducing the impact on the membrane module and thus better protecting the membrane. To ensure the integrity of the membrane material, multiple second nozzles 204 are installed at the bottom of the second backflushing connection pipe 203. These second nozzles 204 are positioned on top of the DHMBA polyester membrane 205. The input ends of the second backflushing connection pipe 203 are all located on top of the second top cover 201. By installing multiple second nozzles 204, the top area of ​​the DHMBA polyester membrane 205 can be covered, ensuring that the cleaning solution is evenly distributed across the entire membrane surface with uniform flow and pressure. Simultaneously, this reduces direct impact on the membrane surface, preventing damage to the membrane material due to over-cleaning. During operation, the equipment achieves higher cleaning efficiency and a longer membrane module lifespan. The output end of the third backflushing connection pipe 305 is located inside the side of the third permeate tank 3, at the bottom of the sulfonated ceramic membrane 303. By setting up a third backflushing connection pipe 305, the bottom area of ​​the sulfonated ceramic membrane 303 can be precisely aligned, ensuring a uniform coverage as the cleaning solution flows from bottom to top. This arrangement fully utilizes the natural flow characteristics of the liquid, making the cleaning process more efficient and improving the overall cleaning effect, thereby extending the service life of the sulfonated ceramic membrane 303. The output ends of the three vertical connection pipes 403 are respectively fixedly connected to the top of the U-shaped connection pipe 107, the input end of the second backflushing connection pipe 203, and the input end of the third backflushing connection pipe 305. A waste liquid pipe 307 is fixedly connected to the top side of the third permeation tank 3. A control valve is installed inside the waste liquid pipe 307. By setting up the waste liquid pipe 307, the waste liquid generated during the cleaning process of the third permeation tank 3 can be discharged. The control valve is also included.This further enhances operational flexibility, allowing for the adjustment of wastewater discharge flow rate and timing based on actual needs.

[0044] Please see Figure 1 , Figure 2 and Figure 4 The bottom of the first permeation tank 1, the bottom of the second permeation tank 2, and the third permeation tank 3 are respectively equipped with a first discharge valve 108, a second discharge valve 206, and a third discharge valve 304. The output ends of the first discharge valve 108, the second discharge valve 206, and the third discharge valve 304 are connected to a collection pipe 8. By setting the collection pipe 8, the waste liquid discharged from each permeation tank can be collected, and the waste liquid can be centrally treated. By setting three discharge valves, it is convenient to control the waste liquid discharge of each permeation tank individually, and synchronous operation can be achieved when needed, which enhances the flexibility and controllability of equipment operation. The input end of the feed pipe 102 is equipped with a feed pump 9. By setting the feed pump 9, the conveying capacity of the feed pipe 102 can be effectively improved, ensuring that the raw material enters the equipment at a stable flow rate.

[0045] The implementation principle of this application embodiment is as follows:

[0046] In use, the raw material is transported to the first permeation tank 1 by the feed pump 9. Under the action of the PPES membrane 104, most impurities can be initially filtered out, and the turbidity can be initially reduced. The pretreated clear liquid is pressurized by the power pump 7 through the first connecting pipe 5 and enters the second permeation tank 2. The DHMBA polyester membrane 205 in the second permeation tank 2 is horizontally arranged, which allows the liquid to fully contact the membrane surface when passing through, and can remove medium-sized metal ions and small molecule organic matter, thereby improving ion purity. Then the liquid enters the third permeation tank 3 through the second connecting pipe 6. The sulfonated ceramic membrane 303 in the third permeation tank 3 has a nano-sized pore size that can deeply remove residual ions, and can perform final fine filtration. At the same time, its horizontal installation method combined with the design of the storage tank 301 and the discharge pipe 302 can ensure that the treated liquid has higher purity and stability. The filtered liquid can flow into the final collection device through the discharge pipe 306.

[0047] The embodiments described in this specific implementation are preferred embodiments of this application and are not intended to limit the scope of protection of this application. Identical components are represented by the same reference numerals. Therefore, all equivalent changes made to the structure, shape, and principle of this application should be covered within the scope of protection of this application.

Claims

1. An integrated electronic-grade sulfuric acid multi-stage membrane permeation purification system, comprising a first permeation tank (1), a second permeation tank (2), a third permeation tank (3), and a pulse-type backflushing assembly (4), characterized in that: The first permeation tank (1), the second permeation tank (2) and the third permeation tank (3) are respectively equipped with PPES membrane (104), DHMBA polyester membrane (205) and sulfonated ceramic membrane (303). A first connecting pipe (5) is fixedly connected to the bottom side of the first permeation tank (1). A power pump (7) is installed on the first connecting pipe (5). The output end of the first connecting pipe (5) is located on the bottom side of the second permeation tank (2). A second connecting pipe (6) is installed on the top side of the second permeation tank (2). The output end of the second connecting pipe (6) is located on the top of the third permeation tank (3). A storage bin (301) is installed at the top inside the third permeation tank (3). Multiple discharge pipes (302) are installed at the bottom of the storage bin (301). A first top cover (101) is installed on the top of the first permeation tank (1). A power pump (7) is installed on the top of the first top cover (101). There is a feed pipe (102), and the bottom of the third permeation tank (3) is provided with a discharge pipe (306). The output end of the feed pipe (102) is located at the bottom of the first top cover (101) and is fixedly connected with a diverter (103). The PPES membrane (104) is perpendicular to the position of the first top cover (101). The two outlets of the diverter (103) are respectively located on opposite sides of the PPES membrane (104). The DHMBA polyester membrane (205) is horizontally located in the middle of the second permeation tank (2). The sulfonated ceramic membrane (303) is horizontally located in the middle of the third permeation tank (3). The pulse backwash assembly (4) includes a water pump (401).

2. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 1, characterized in that: The water pump (401) is connected to a pure water supply system at its input end. A backwash pipe (402) is fixedly connected to the output end of the water pump (401). Three vertical connecting pipes (403) are fixedly connected to the surface of the backwash pipe (402). A pulse control valve (404) is provided on the surface of the vertical connecting pipe (403). Multiple first backwash connecting pipes (105) are provided inside the first permeation tank (1). A second top cover (201) is provided on the top of the second permeation tank (2). Multiple connecting rods (202) are provided at the bottom of the second top cover (201). A second backwash connecting pipe (203) is fixedly connected to the bottom end of the connecting rod (202). A third backwash connecting pipe (305) is provided on the bottom side of the third permeation tank (3).

3. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 2, characterized in that: Multiple first backflush connecting pipes (105) are symmetrically arranged on both sides of the PPES membrane (104). Multiple first nozzles (106) are provided on the surface of the first backflush connecting pipes (105). The input ends of the multiple first backflush connecting pipes (105) are all provided on the surface of the first permeation tank (1) and are fixedly connected to a U-shaped connecting pipe (107).

4. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 2, characterized in that: The bottom of the second backflush connecting pipe (203) is provided with a plurality of second nozzles (204), the second nozzles (204) are located on top of the DHMBA polyester film (205), and the input end of the second backflush connecting pipe (203) is located on top of the second top cover (201).

5. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 2, characterized in that: The output end of the third backflushing connection pipe (305) is located on the inner side of the third permeation tank (3) and at the bottom of the sulfonated ceramic membrane (303).

6. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 2, characterized in that: The output ends of the three vertical connecting pipes (403) are respectively fixedly connected to the top of the U-shaped connecting pipe (107), the input end of the second backflushing connecting pipe (203) and the input end of the third backflushing connecting pipe (305). The top side of the third permeation tank (3) is fixedly connected to a waste liquid pipe (307), and a control valve is installed inside the waste liquid pipe (307).

7. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 1, characterized in that: The bottom of the first permeation tank (1), the bottom of the second permeation tank (2), and the third permeation tank (3) are respectively provided with a first drain valve (108), a second drain valve (206), and a third drain valve (304). The output ends of the first drain valve (108), the second drain valve (206), and the third drain valve (304) are connected to a collection pipe (8).

8. The integrated electronic-grade sulfuric acid multi-stage membrane permeation purification device according to claim 1, characterized in that: The feed pipe (102) is equipped with a feed pump (9) at its input end.

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