CN220642656U - Industrial wastewater concentrated solution treatment system - Google Patents

Abstract

The utility model discloses an industrial wastewater concentrated solution treatment system, which is used for treating concentrated solution containing heavy metal ions generated after electrodialysis and comprises a concentrated solution inlet pipe, a circulating concentration mechanism, a steam generation mechanism, a condensation mechanism, a circulating descaling mechanism and a flocculation mechanism, wherein the circulating concentration mechanism, the steam generation mechanism, the condensation mechanism, the circulating descaling mechanism and the flocculation mechanism are communicated with the concentrated solution inlet pipe. Meanwhile, the utility model adopts the zero-energy-consumption condensation technology, adopts the way of introducing high-temperature steam into a fresh water tank, and achieves the condensation effect by contacting with fresh water in the form of tiny bubbles, thereby omitting the traditional condensation equipment, needing no cold water circulation pipeline, greatly saving the space occupation and energy consumption of the equipment and realizing zero-cost condensation.

Description

Industrial wastewater concentrated solution treatment system

Technical Field

The utility model relates to the technical field of environmental protection, in particular to the technical field of electrodialysis-based sewage treatment equipment, and specifically relates to an industrial wastewater concentrated solution treatment system.

Background

Electrodialysis (ED) is a method of desalting sea water using an ion exchange membrane. The ion exchange membrane is a functional membrane, and is divided into an anion exchange membrane and a cation exchange membrane, namely, a negative membrane and a positive membrane for short. The cation membrane allows only cations to pass through the anion membrane and only anions to pass through, which is the permselectivity of the ion exchange membrane. Under the action of the applied electric field, the anions and cations in the aqueous solution can move to the anode and the cathode respectively, and if an exchange membrane is added in the middle, the aim of separation and concentration can be achieved. Electrodialysis is a method that uses such principles.

Fresh water and concentrated water are generated after the wastewater is treated by electrodialysis, wherein the fresh water can be directly discharged after simple treatment, and organic matters possibly with some simple components in the fresh water can be treated by a conventional sewage treatment mode, so that the discharge standard is reached; the concentrated water contains a large amount of metal ions or heavy metal ions, and cannot be removed effectively in a simple manner. Based on this problem, many environmental protection companies have developed a great deal of technology for treating concentrated water to remove salt ions therein and achieve harmless treatment.

See publication No. CN109293086B discloses a split salt high frequency concentrated water treatment system comprising at least one compartment defined by a filter membrane and a first housing for concentrating or desalinating incoming water, wherein in case of an increase or decrease of the incoming water flow and/or the drainage flow based on the compartment such that a pressure difference is formed in the flow direction of the incoming water, the first zone and said second zone are capable of, at least based on the pressure difference, arranging the filter membrane obliquely in the second housing in such a way that the distance between the filter membranes is increased or decreased in a rotating manner around their respective hinge points, wherein the incoming water flushes the filter membrane in an oblique state in such a way that a turbulent flow is formed based on the pressure difference to suppress scaling. In order to solve the problem of concentrated water generated after electrodialysis, the above prior art has solved the treatment of concentrated water and the prevention of scaling by combining the characteristics of a membrane and the characteristics of a fluid.

Disclosure of Invention

In order to solve the problem of harmless treatment of concentrated solution generated after electrodialysis, the application provides an industrial wastewater concentrated solution treatment system for carrying out subsequent harmless treatment on industrial wastewater subjected to electrodialysis treatment, separating high-concentration ionized water, especially heavy metal ions, in a concentration and precipitation mode, thereby achieving the aim of harmless treatment emission. The treatment system that this application provided has covered the treatment of concentrate and the treatment of scale deposit in the equipment, can avoid along with concentrated water treatment's time is longer, because reasons such as scale deposit lead to throughput decline, even the problem emergence of equipment damage, the effectual operation that guarantees the system can be stable for a long time.

In order to achieve the above purpose, the technical scheme adopted in the application is as follows:

the utility model provides an industrial wastewater concentrated solution treatment system which is used for treating concentrated solution containing heavy metal ions generated after electrodialysis and comprises a concentrated solution inlet pipe, a circulating concentration mechanism, a steam generation mechanism, a condensation mechanism, a circulating descaling mechanism and a flocculation mechanism, wherein the circulating concentration mechanism is communicated with a radiating pipe in the circulating concentration mechanism through a steam supply pipe and a steam return pipe respectively; the top of the circulating concentration mechanism is further provided with a steam pipe communicated with the condensation mechanism, the drainage branch pipe is further communicated with a third water pump, and the water outlet end of the third water pump is connected with a flocculation tank.

Preferably, the circulating concentration mechanism comprises a plurality of vaporization devices which are communicated with each other, the concentrated solution inlet pipe is sequentially communicated with any vaporization device through the first water pump, the water inlet branch pipe is sequentially communicated with the water inlet end of the first water pump through the liquid storage tank and the first pipeline, and the water outlet branch pipe is sequentially communicated with the water inlet end of the first water pump; the water inlet pipe is provided with a first one-way valve, and the water inlet branch pipe is provided with a second one-way valve.

Preferably, the circulating descaling mechanism comprises a second pipeline communicated with the water inlet end of the first water pump, the other end of the second pipeline is sequentially communicated with a medicament tank, the second water pump and a third pipeline, and the third pipeline is respectively communicated with any one of the vaporizing devices through the water inlet branch pipes.

Preferably, the condensing mechanism comprises a fresh water tank, a plurality of layers of fine pore grids are arranged in the fresh water tank, and a steam pipe communicated with the top of any vaporizing device, wherein the exhaust end of the steam pipe penetrates through any layer of fine pore grids and extends to the bottom position of the fresh water tank.

Preferably, the flocculation mechanism comprises a third water pump communicated with the liquid storage tank, a third one-way valve is arranged between the water inlet end of the third water pump and the liquid storage tank, the water outlet end of the third water pump is connected with a flocculation tank for flocculating concentrated liquid, and the flocculation tank is provided with a second drain pipe capable of being opened and closed.

Preferably, the steam generating mechanism further comprises a second flow pump arranged on the steam return pipe and a first flow pump for pumping water in the fresh water tank into the steam generating mechanism.

Preferably, the vaporizing device comprises a closed outer shell, the top of the outer shell is communicated with the steam pipe, a spray disc, a plurality of groups of radiating fin groups which are installed at intervals are sequentially arranged in the outer shell from top to bottom, any radiating fin group consists of a plurality of radiating fins which are installed in an inclined manner, and a containing cavity is arranged at the bottom; the spray tray is communicated with the water inlet branch pipe, and a drainage branch pipe for conveying the concentrated liquid which is not gasified into the first water pump again is arranged at the bottom of the outer shell.

Preferably, the radiating pipes in two adjacent vaporization devices are sequentially communicated, and the radiating pipe ends of two vaporization devices positioned at the ends are respectively communicated with the steam supply pipe and the steam return pipe to form a circulation pipeline.

Preferably, the radiating pipes in any one of the vaporizing devices are respectively communicated with the steam generating device to form a circulating pipeline.

The beneficial effects are that:

1. the utility model adopts the cyclic vaporization concentration to further concentrate the concentrated water, and then carries out the subsequent flocculation treatment, so that the ion quantity of wastewater subjected to primary flocculation treatment is far larger than that of conventional flocculation, and the pressure of solid-liquid separation after flocculation is greatly reduced.

2. The utility model adopts zero-energy-consumption condensation technology, adopts the way that high-temperature steam is introduced into a fresh water tank and contacts with fresh water in the form of tiny bubbles to cool down so as to achieve the effect of condensation, omits traditional condensation equipment, does not need a cold water circulation pipeline, greatly saves the space occupation and energy consumption of the equipment, and realizes zero-cost condensation.

3. The utility model also provides a circulating descaling mechanism which can remove salt scale formed in the vaporizing device at regular intervals, so that the heat dissipation efficiency of the vaporizing device is ensured, and the circulating concentration mechanism can continuously operate for a long time without efficiency reduction caused by long use time.

4. The circulating concentration mechanism can control the ion concentration of the concentrated water according to actual needs through the circulating times, meets the treatment requirements of different concentrated water, and has strong practicability and wide applicability.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive faculty for a person skilled in the art.

Fig. 1 is an isometric view of the structure of the present utility model.

Fig. 2 is an isometric view of the structure of fig. 1 in reverse vision.

Fig. 3 is a schematic view of the internal structure of the vaporizing device.

In the figure: 1-a concentrated solution inlet pipe; 2-a first one-way valve; 3-a first water pump; 4-a water inlet branch pipe; 5-a second one-way valve; 6-a vaporization device; 7-steam pipe; 8-a fresh water tank; 9-a fine pore grid; 10-a first drain pipe; 11-a first flow pump; 12-a steam generating device; 13-a second flow pump; 14-a steam return pipe; 15-a steam supply pipe; 16-a drain branch pipe; 17-a liquid storage tank; 18-a first line; 19-a second line; 20-a medicament canister; 21-a second water pump; 22-a third pipeline; 23-a third one-way valve; 24-a third water pump; 25-flocculation tank; 26-a second drain pipe.

Detailed Description

For the purposes of making the objects, technical solutions and advantages of the embodiments of the present application more clear, the technical solutions of the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is apparent that the described embodiments are some embodiments of the present application, but not all embodiments. The components of the embodiments of the present application, which are generally described and illustrated in the figures herein, may be arranged and designed in a wide variety of different configurations.

Thus, the following detailed description of the embodiments of the present application, as provided in the accompanying drawings, is not intended to limit the scope of the application, as claimed, but is merely representative of selected embodiments of the application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.

It should be noted that: like reference numerals and letters denote like items in the following figures, and thus once an item is defined in one figure, no further definition or explanation thereof is necessary in the following figures.

In the description of the present application, it should be noted that, if the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like indicate an azimuth or a positional relationship based on that shown in the drawings, or an azimuth or a positional relationship that a product of the application conventionally puts in use, it is merely for convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element to be referred to must have a specific azimuth, be configured and operated in a specific azimuth, and thus should not be construed as limiting the present application. Furthermore, the terms "first," "second," and the like in the description of the present application, if any, are used for distinguishing between the descriptions and not necessarily for indicating or implying a relative importance.

Furthermore, the terms "horizontal," "vertical," and the like in the description of the present application, if any, do not denote a requirement that the component be absolutely horizontal or overhang, but rather may be slightly inclined. As "horizontal" merely means that its direction is more horizontal than "vertical", and does not mean that the structure must be perfectly horizontal, but may be slightly inclined.

In the description of the present application, it should also be noted that, unless explicitly stated and limited otherwise, the terms "disposed," "mounted," "connected," and "connected" should be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the terms in this application will be understood by those of ordinary skill in the art in a specific context.

Example 1:

referring to fig. 1-2 of the specification, the industrial wastewater concentrate treatment system provided by the utility model is used for treating concentrate containing heavy metal ions generated after electrodialysis, and comprises a concentrate inlet pipe 1, a circulating concentration mechanism communicated with the concentrate inlet pipe 1, a steam generation mechanism, a condensation mechanism, a circulating descaling mechanism and a flocculation mechanism, wherein the steam generation mechanism is respectively communicated with a radiating pipe in the circulating concentration mechanism through a steam supply pipe 15 and a steam return pipe 14, the circulating concentration mechanism comprises a plurality of vaporization devices 6, the top of any vaporization device 6 is provided with the concentrate inlet pipe 1, the bottom is provided with a drainage branch pipe 16 for removing redundant concentrate, and the drainage branch pipe 16 is communicated with the concentrate inlet pipe 1 through a first water pump 3; the top of the circulating concentration mechanism is further provided with a steam pipe 7 communicated with the condensation mechanism, the water discharge branch pipe 16 is further communicated with a third water pump 24, and the water outlet end of the third water pump 24 is connected with a flocculation tank 25.

Working principle:

the concentrated water produced after treatment by electrodialysis equipment, such as an electrodialysis tank, also enters the treatment system provided by the embodiment through the concentrated solution inlet pipe 1, and is concentrated by a circulating concentration mechanism, as shown in fig. 1 and 2, the concentration mode is that the water is evaporated in a vapor mode by adopting the evaporation device 6, the residual salt is continuously left in the concentrated solution, so that the salt concentration is increased, after one cycle is treated by the evaporation device 6, concentrated water and vapor with larger concentration are produced, wherein the vapor is condensed into harmless fresh water by the condensing mechanism, and the concentrated water is continuously concentrated by the next concentration process. And (3) flocculating the concentrated water with high concentration by a flocculation mechanism after the concentrated water reaches treatment expectation, and finally performing harmless treatment on the concentrated water by adopting conventional solid-liquid separation or neutralization reaction. In this embodiment, the steam generating mechanism may be a conventional electric heating steam boiler or a gas steam boiler, and of course, other existing steam generating devices may also be used.

Example 2:

on the basis of the embodiment 1, this embodiment is further optimized as a preferred embodiment of the present utility model, and as shown in fig. 1-3, the circulating concentration mechanism includes a plurality of vaporization devices 6 that are mutually communicated, the concentrate inlet pipe 1 is sequentially communicated with the first water pump 3, the water inlet branch pipe 4 and any one of the vaporization devices 6, and the water outlet branch pipe 16 is sequentially communicated with the water inlet end of the first water pump 3 through a liquid storage tank 17 and a first pipeline 18; the water inlet pipe 1 is provided with a first one-way valve 2, and the water inlet branch pipe 4 is provided with a second one-way valve 5. When concentration treatment is carried out, the concentrated solution from the concentrated solution water inlet pipe 1 sequentially passes through the water inlet branch pipe 4 under the driving action of the first water pump 3, the second one-way valve 5 enters any one of the vaporization devices 6 for vaporization concentration, the concentrated solution is divided into water vapor and high-concentration ionized water, the water vapor is sent into the condensation mechanism from the vapor pipe 7 arranged at the top, and the high-concentration ionized water is used for subsequent treatment or enters the next concentration treatment until the preset cycle number or concentration time is reached.

In this embodiment, the circulating descaling mechanism includes a second pipeline 19 that is connected to the water inlet end of the first water pump 3, the other end of the second pipeline 19 is sequentially connected to a medicament tank 20, a second water pump 21, and a third pipeline 22, and the third pipeline 22 is respectively connected to any one of the vaporizing devices 6 through the water inlet branch pipes 4. After long-time concentration and vaporization, scale can be generated in the vaporizing device 6 and attached to the internal radiating fins to cause water flow and air flow blockage, so that concentration effect is affected, at the moment, scale removal agents in the agent tank 20 sequentially pass through the third pipeline 22, the vaporizing device 6, the water discharge branch pipe 16, the liquid storage tank 17, the first pipeline 18 and the second pipeline 19 to form a closed loop after returning to the agent tank 20, salt scale attached to the inner wall of a pipeline can be completely removed after circulation scale removal, and in the circulation process, a filter screen for filtering solid salt scale is arranged in the agent tank 20, so that salt scale falling in a block shape can be timely separated, and more agents can be avoided. For example, the filter screen can be arranged at the top of the medicament tank, and the reflowed medicament is firstly sent into the filter screen at the top and then returned to the bottom of the medicament tank 20 after being filtered to participate in subsequent circulation, so that the effect of solid-liquid separation can be achieved in the circulation process.

In this embodiment, the condensing mechanism includes a fresh water tank 8, a plurality of fine pore grids 9 are installed in the fresh water tank 8, and a steam pipe 7 is communicated with the top of any vaporization device 6, and the exhaust end of the steam pipe 7 extends to the bottom position of the fresh water tank 8 through any fine pore grid 9. After the high-temperature steam is introduced into the fresh water pond 8 through the steam pipe 7, the high-temperature steam cannot escape immediately due to the blocking of the fine pore grating 9, and can only rise under the buoyancy action through the fine pores on the fine pore grating 9, and the fine pore grating 9 is provided with multiple layers, so that the steam bubbles become smaller and rise slowly, in the process, the steam is always contacted with water for cooling, and the liquefaction phenomenon becomes water drops and is fused into fresh water, so that the condensation recovery effect is achieved. In the process, natural contact cooling is adopted, a condenser is not needed, no energy is consumed, and the technology fully utilizes the zero energy consumption condensation of resources and has higher practical value compared with the existing condenser. Further, since the amount of fresh water produced by electrodialysis is much larger than the amount of concentrated water, the normal temperature fresh water in the fresh water tank 8 is sufficient for condensation of high temperature steam.

In this embodiment, the flocculation mechanism includes a third water pump 24 that is communicated with the liquid storage tank 17, a third one-way valve 23 is disposed between a water inlet end of the third water pump 24 and the liquid storage tank 17, a flocculation tank 25 for flocculating the concentrated liquid is connected to a water outlet end of the third water pump 24, and the flocculation tank 25 has a second drain pipe 26 that can be opened and closed.

In this embodiment, the steam generating means further comprises a second flow pump 13 arranged on the steam return pipe 14, and a first flow pump 11 for pumping water from the fresh water tank 8 into the steam generating means. Although the water in the steam generating mechanism is recycled, the water is always consumed in the long-time use process, and when water is needed to be replenished, the water is only needed to be added in a fade-in way through the first flow pump 11, so that the recycling of changing waste into valuable is realized.

Example 3:

on the basis of any one of the above embodiments, in this embodiment, the vaporization device 6 and the connection manner between the multiple vaporization devices 6 are refined, specifically, as shown in fig. 2 and fig. 3 in the specification, any one of the vaporization devices 6 includes a closed outer shell 61, the top of the outer shell 61 is communicated with the steam pipe 7, a spray tray 62, multiple groups of heat dissipation fin groups 63 installed at intervals are sequentially installed in the outer shell 61 from top to bottom, and each heat dissipation fin group 63 is composed of multiple heat dissipation fins installed obliquely, and a containing cavity located at the bottom; the spray tray 62 is communicated with the water inlet branch pipe 4, and the position of the outer shell 61 at the bottom is provided with a water discharge branch pipe 16 for re-feeding the non-evaporated concentrated liquid into the first water pump 3.

In this embodiment, the heat dissipation pipes in the two adjacent vaporization devices 6 are sequentially connected, and the ends of the heat dissipation pipes of the two vaporization devices 6 located at the ends are respectively connected with the steam supply pipe 15 and the steam return pipe 14 to form a circulation pipeline. The connection mode forms a series connection of the steam supply mechanism and any one of the vaporization devices 6 to form a large internal circulation, and has the advantages that the heat supply and the heat dissipation of any one of the vaporization devices 6 are equal, and the vaporization devices 6 can be operated at full load to generate the maximum concentration efficiency; the disadvantage is that when the amount of the concentrated liquid to be concentrated is not large, the part of the vaporization device 6 which is not directly closed participates in the work, and the device is fully opened when opened and fully closed when closed. To compensate for this, the present embodiment provides another alternative solution, that is, the radiating pipes in any one of the vaporizing devices 6 are respectively communicated with the steam generating device 12 to form a circulation pipeline. Therefore, the vaporization devices 6 are in parallel connection, do not interfere with each other and do not affect each other, part of the vaporization devices 6 can be selected to participate in the work or all the vaporization devices can participate in the work according to the volume of the actual concentrated liquid, the vaporization devices can be selectively closed through the valve, higher flexibility is achieved, and the investment of the controlled valve and the circulating pump equipment is increased. As another alternative, the vaporization devices 6 may be first connected in series to form a large cycle, then the vaporization devices 6 are connected in pairs through a pipeline with valves, and valves are also disposed between adjacent vaporization devices 6, so that one or part of or all of the vaporization devices 6 may be selectively implemented by opening and closing different valves to participate in the operation.

The foregoing description is only of the preferred embodiments of the present application and is not intended to limit the same, but rather, various modifications and variations may be made by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims (9)

1. The utility model provides an industrial waste water concentrate processing system for handle the concentrate that contains heavy metal ion that produces after electrodialysis, including concentrate inlet tube (1), with the concentrated mechanism of circulation concentration of concentrate inlet tube (1) intercommunication, steam generation mechanism, condensation mechanism, circulation scale removal mechanism and flocculation mechanism, its characterized in that: the steam generation mechanism is respectively communicated with a radiating pipe in the circulating concentration mechanism through a steam supply pipe (15) and a steam return pipe (14), the circulating concentration mechanism comprises a plurality of vaporization devices (6), the top of any vaporization device (6) is provided with a concentrated solution inlet pipe (1), the bottom of any vaporization device is provided with a drainage branch pipe (16) for removing redundant concentrated solution, and the drainage branch pipe (16) is communicated with the concentrated solution inlet pipe (1) through a first water pump (3); the top of the circulating concentration mechanism is further provided with a steam pipe (7) communicated with the condensation mechanism, the water discharge branch pipe (16) is further communicated with a third water pump (24), and the water outlet end of the third water pump (24) is connected with a flocculation tank (25).

2. The industrial wastewater concentrate treatment system of claim 1 wherein: the circulating concentration mechanism comprises a plurality of vaporization devices (6) which are mutually communicated, the concentrated solution water inlet pipe (1) is sequentially communicated with any vaporization device (6) through the first water pump (3), and the water inlet branch pipe (4) is sequentially communicated with the water inlet end of the first water pump (3) through the liquid storage tank (17) and the first pipeline (18); the water inlet pipe (1) is provided with a first one-way valve (2), and the water inlet branch pipe (4) is provided with a second one-way valve (5).

3. The industrial wastewater concentrate treatment system of claim 2 wherein: the circulating descaling mechanism comprises a second pipeline (19) communicated with the water inlet end of the first water pump (3), a medicament tank (20), a second water pump (21) and a third pipeline (22) are sequentially communicated with the other end of the second pipeline (19), and the third pipeline (22) is respectively communicated with any one vaporization device (6) through the water inlet branch pipe (4).

4. The industrial wastewater concentrate treatment system of claim 2 wherein: the condensing mechanism comprises a fresh water pond (8), a plurality of layers of fine pore grids (9) are arranged in the fresh water pond (8), and a steam pipe (7) communicated with the top of any one vaporization device (6), wherein the exhaust end of the steam pipe (7) penetrates through any layer of fine pore grids (9) and extends to the bottom of the fresh water pond (8).

5. The industrial wastewater concentrate treatment system of claim 2 wherein: the flocculation mechanism comprises a third water pump (24) communicated with the liquid storage tank (17), a third one-way valve (23) is arranged between the water inlet end of the third water pump (24) and the liquid storage tank (17), the water outlet end of the third water pump (24) is connected with a flocculation tank (25) for flocculating concentrated liquid, and the flocculation tank (25) is provided with a second drain pipe (26) capable of being opened and closed.

6. The industrial wastewater concentrate processing system of claim 4 wherein: the steam generating mechanism further comprises a second flow pump (13) arranged on the steam return pipe (14), and a first flow pump (11) for pumping water in the fresh water tank (8) into the steam generating mechanism.

7. The industrial wastewater concentrate treatment system of any of claims 2-6 wherein: the vaporizing device (6) comprises a closed outer shell (61), the top of the outer shell (61) is communicated with the steam pipe (7), a spray disc (62), a plurality of groups of radiating fin groups (63) which are installed at intervals are sequentially arranged in the outer shell (61) from top to bottom, and any radiating fin group (63) consists of a plurality of radiating fins which are installed obliquely and a containing cavity which is positioned at the bottom; the spraying disc (62) is communicated with the water inlet branch pipe (4), and a water outlet branch pipe (16) for re-conveying the unvaporized concentrated liquid into the first water pump (3) is arranged at the bottom of the outer shell (61).

8. The industrial wastewater concentrate processing system of any of claims 1-6 wherein: the radiating pipes in the two adjacent vaporizing devices (6) are sequentially communicated, and the radiating pipe ends of the two vaporizing devices (6) positioned at the ends are respectively communicated with the steam supply pipe (15) and the steam return pipe (14) to form a circulating pipeline.

9. The industrial wastewater concentrate processing system of any of claims 1-6 wherein: the radiating pipes in any one of the vaporizing devices (6) are respectively communicated with the steam generating device (12) to form a circulating pipeline.