A process water treatment system for an ethylene plant

Abstract

This utility model relates to a process water treatment system for an ethylene plant, comprising: a backwash water tank; an inlet pipe and an outlet pipe; two backwash water pumps arranged in parallel, operating intermittently. An outlet valve and a first drain pipe are installed at the outlet of each pump. A drain line is located at the bottom of the backwash water tank, and a second drain pipe is also installed on the drain line. A warm-up return line is added between the first and second drain pipes. During the intermittent operation of the two backwash water pumps, the process water in the backwash water tank flows sequentially through the closed backwash water pump, the first drain pipe, and the second drain pipe to the drain line, thus ensuring that the closed backwash water pump is always in a warm-up state. The advantages are: it not only reduces energy consumption but also avoids backfilling operations, thereby extending the service life of the backwash water pump.

Description

Technical Field

[0001] This utility model relates to the field of ethylene plant technology, and in particular to a process water treatment system for ethylene plants. Background Technology

[0002] Ethylene is one of the most basic organic raw materials in the petrochemical industry. As the core of the petrochemical industry, it has a wide range of applications and is a fundamental raw material for the production of various chemical products. The scale, output, and technological level of ethylene production represent the development level of a country's petrochemical industry.

[0003] The process water from the quench system of the ethylene plant in the applicant's plant undergoes a series of complex treatment processes to remove oil, impurities, and particles. After the water quality meets certain requirements, it enters the process water stripping unit and then the dilution steam generation system. Two backwash water pumps with a rated power of 110kW are installed in parallel in the quench zone. Since commissioning, these two backwash water pumps have generally maintained a circulation flow rate above minimum, only opening the outlet regulating valve during backwashing to supply water externally. Under this operating condition, the power consumption is relatively high. The applicant has considered changing the two parallel reverse pumps to an intermittent start-up mode. However, during intermittent start-up, especially in winter, frequent empty-filling pump operations (for freeze protection, as pumps without emptying and internal water flow are prone to freezing and cracking) and high temperature differences between the pumped medium before and after pump start-up significantly increase the probability of pump and mechanical seal damage.

[0004] Therefore, the existing process water treatment system of ethylene plants still needs further improvement. Utility Model Content

[0005] The technical problem to be solved by this utility model is to provide an ethylene plant process water treatment system that not only reduces power consumption but also avoids backwash pump operation, thereby improving the service life of the backwash water pump, in light of the current state of the technology.

[0006] The technical solution adopted by this utility model to solve the above-mentioned technical problems is: a process water treatment system for an ethylene plant, comprising:

[0007] Backwash water tank;

[0008] The water inlet pipe is connected to the water inlet of the backwash water tank, and the water outlet pipe is connected to the water outlet of the backwash water tank.

[0009] A backwash water pump is installed in the outlet pipeline;

[0010] The backwash water pumps are arranged in parallel and operate intermittently. An outlet valve and a first drain pipe are installed at the outlet of each pump. A drain line is located at the bottom of the backwash water tank, and a second drain pipe is also installed on the drain line. A warm-up return line is added between the first and second drain pipes. During the intermittent operation of the two backwash water pumps, the process water in the backwash water tank flows sequentially through the closed backwash water pump, the first drain pipe, and the second drain pipe to the drain line, thus ensuring that the closed backwash water pump is always in a warm-up state.

[0011] The two backwash water pumps mentioned above are operated in an "intermittent start mode". This means that the two backwash water pumps do not run continuously at the same time, but are started and operated intermittently in a different manner according to actual process requirements (mainly when backwashing is required).

[0012] The aforementioned "pump warm-up state" can be understood as the pump being shut down being filled with process medium (in this case, process water) at a temperature close to (or the same as) its operating temperature, and the medium is in a state of slow flow or maintaining a relatively constant temperature. The core purpose of this is to eliminate the significant temperature difference between the medium inside the shut-down pump and the operating medium, thus preventing severe thermal shock / stress from the high-temperature medium on the cold pump body and mechanical seal when the pump is restarted, and preventing equipment damage. Pump warm-up is a crucial measure to ensure the safe start-up and shutdown of pumps carrying hot media.

[0013] To avoid wasting process water, a return water line is also included to return water from the sewage line to the quench tower. This return water line is equipped with an underground tank and a submersible pump.

[0014] As an improvement, the height of the two backwash water pumps is lower than that of the backwash water tank. When the pumps are stopped and the warm-up return line is unobstructed, the static pressure (gravity flow) generated by the height difference between the backwash water tank and the pumps drives the process water to flow naturally through the stopped pumps and the warm-up return line without the need for additional power (such as a pump), ensuring a stable and reliable warm-up effect. This eliminates the need for additional pressurization equipment for the warm-up return line, simplifying the system design. Furthermore, it prevents cavitation or emptying within the pumps when they are stopped; that is, the higher position of the tank continuously provides static pressure to the lower pump, keeping the pump filled with liquid. This achieves a powerless, stable, and reliable warm-up cycle: relying on gravity drive, it is simple, reliable, and maintains the warm-up state with zero energy consumption.

[0015] As an improvement, the warm pump return pipeline is connected to the first and second drain pipes mentioned above via a detachable connection method.

[0016] The aforementioned "detachable connection method" refers to a joint type between two pipe fittings that allows for easy manual connection and separation without the need for cutting or welding. For example, a flange connection: two gasketed flanges are fastened together using bolts.

[0017] Quick-connect couplings: such as clamp quick-connect (U-joint) and threaded quick-connect, which enable quick connection and disconnection through snapping, rotation or pressing; union couplings: a type of threaded detachable pipe fitting; thus facilitating the installation, disassembly, maintenance or replacement of pipe sections.

[0018] Further improvements include a DN20 specification for the warm-up pump return line. The DN20 diameter provides the minimum continuous flow rate required to maintain the temperature of the stopped pump. The small diameter limits the diversion flow rate, avoiding significant interference with the backwash tank level and increased wastewater discharge. The use of commonly available small-diameter fittings facilitates easy procurement and installation, resulting in low cost.

[0019] As an improvement, the backwash water tank is also equipped with a level gauge and a level transmitter. The level gauge provides a local visual indication, and the level transmitter provides a remote signal (such as to the control room DCS) to control the opening of the control valve on the inlet water pipeline.

[0020] As an improvement, the inlet pipe is connected to the outlet of the upstream dual-media filter. The process water entering the backwash water tank has already been treated by the upstream dual-media filter to remove oil, impurities, and particles, meeting certain water quality standards. This ensures that the backwash water pump delivers relatively clean water, reducing wear and clogging.

[0021] Compared with existing technologies, the advantages of this invention are as follows: The two parallel backwash water pumps of this invention operate intermittently only when necessary, significantly reducing power consumption. Furthermore, the warm-up return pipeline ensures a constant, slow flow of (relatively) high-temperature process water from the backwash water tank inside the stopped pump, maintaining the pump body temperature close to the operating temperature. During startup, the temperature difference between the pump medium and the hot process water is minimal, avoiding damage to the pump body and mechanical seal caused by thermal stress. Specifically, since the stopped pump is always filled with water and in a "warm" state, there is no need for emptying or priming operations during restart; it can be started directly, effectively eliminating thermal shock during startup and shutdown, protecting the pump body and mechanical seal, reducing malfunctions and maintenance, improving equipment reliability, and extending service life. On the other hand, it simplifies or avoids frequent pump filling operations, reduces the burden on operators and the risk of misoperation, simplifies the operation process, and improves efficiency. This utility model cleverly utilizes the first drain pipe before the outlet valve and the sewage discharge pipe (second drain pipe) at the bottom of the tank in the existing structure. By adding a small return pipeline, the key function is achieved. The modification is small and the cost is low, making the energy-saving intermittent operation mode technically feasible and safe. In particular, it solves the key problem of winter operation and achieves the goal of a safe and reliable intermittent operation mode. Attached Figure Description

[0022] Figure 1 This is a flowchart of the process water treatment system of the ethylene plant according to an embodiment of the present invention. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0024] In the specification and claims of this utility model, terms indicating direction, such as "front," "rear," "upper," "lower," "left," "right," "side," "top," and "bottom," are used to describe various exemplary structural parts and elements of this utility model. However, the use of these terms is merely for the purpose of explanation and is based on the exemplary orientations shown in the accompanying drawings. Since the embodiments disclosed in this utility model can be arranged in different orientations, these terms indicating direction are for illustrative purposes only and should not be regarded as limitations. For example, "upper" and "lower" are not necessarily limited to directions opposite to or consistent with the direction of gravity.

[0025] Figure 1 This invention illustrates a preferred embodiment of a process water treatment system for an ethylene plant. The system includes a backwash water tank 10, an inlet pipe 30, an outlet pipe 40, and a backwash water pump 20. The inlet pipe 30 is connected to the inlet of the backwash water tank 10, and the outlet pipe 40 is connected to the outlet of the backwash water tank 10. The backwash water pump 20 is located within the outlet pipe 40.

[0026] Process water enters the backwash water tank 10 after oil and solid impurities are removed by an upstream dual-media filter. Alternatively, upstream high-pressure boiler feedwater can also flow into the inlet pipe 30 and then into the backwash water tank 10. The backwash water tank 10 is a vertical tank, with its upper part connected to the outlet of the upstream dual-media filter via the inlet pipe 30. The bottom of the backwash water tank 10 is generally equipped with a settling structure (this is existing technology and will not be elaborated further). Two level gauges 13 are installed on the side wall of the backwash water tank 10 for on-site monitoring, and a level transmitter 14 is configured to transmit the signal to the DCS system, which then controls the opening of the automatic regulating valve in the inlet pipe 30. A drain pipe 11 is located at the bottom of the backwash water tank 10, and a second drain pipe 12 is installed between the two valves on the drain pipe 11.

[0027] The outlet pipe 40 connects to the bottom outlet of the backwash water tank 10, and two backwash water pumps 20 are connected in parallel on the pipe. The mounting base of the backwash water pumps 20 is lower than the bottom of the backwash water tank 10 to form a stable gravity pressure difference. Specifically, the backwash water pumps 20 are centrifugal pumps with a rated power of 110kW. Both backwash water pumps 20 are equipped with outlet valves 41 at their outlets. The pipe section before the outlet valve is equipped with a first drain pipe 42, which can be equipped with a DN20 ball valve as standard.

[0028] In this embodiment, the two backwash water pumps 20 operate in an intermittent start-up mode. A warm-up return pipeline 50 is added between the first drain pipe 42 and the second drain pipe 12. During the intermittent start-up operation of the two backwash water pumps 20, the process water in the backwash water tank 10 flows sequentially through the closed backwash water pump 20, the first drain pipe 42, and the second drain pipe 12 to the sewage pipeline 11, thus ensuring that the closed backwash water pump 20 is always in a warm-up state. The warm-up return pipeline 50 can be made of DN20 stainless steel pipe, with both ends connected to the ball valve outlets of the first drain pipe 42 and the second drain pipe 12 respectively via threaded or clamp-type quick-connect couplings.

[0029] This embodiment also includes a return water pipeline 60 for returning water from the sewage pipeline 11 to the upstream quench tower. The return water pipeline 60 is equipped with an underground tank 61 and a submersible pump 62. The pressure of the underground tank 61 is generally 0.03 MPa.

[0030] The operation flow of the process water treatment system in the ethylene plant is as follows:

[0031] Normal backwashing operation: Start a backwash water pump 20 (e.g., pump A), open its outlet valve 41, and process water is delivered to the backwash unit via the outlet pipeline 40. At this time, backwash water pump 20 (e.g., pump B) is in a stopped state, its outlet valve 41 is closed, but the inlet valve of pump B remains open. The stopped backwash water pump 20 (pump B) forms a gravity flow loop through the following path: backwash water tank 10 → pump B pump chamber → first drain pipe 42 before pump B outlet valve 41 → warm pump return pipeline 50 → second drain pipe 12 → sewage pipeline 11 → underground tank 61. The water in the underground tank 61 is pumped back to the aforementioned quench tower (not shown in the attached diagram) by the submersible pump 62. Driven by static pressure difference, the process water in the backwash water tank 10 flows slowly through the stopped backwash water pump 20 at a relatively small flow rate, keeping the temperature of the backwash water pump 20 above the corresponding temperature and reducing the temperature difference with the operating medium. When the running backwash pump needs to be stopped, simply close its outlet valve 41 and shut down the pump. Then, start the pre-warmed standby backwash pump 20 and open its outlet valve 41 to complete the switchover; no priming is required throughout the process. Simultaneously, the recently stopped backwash pump enters "warm-up" mode.

[0032] The switching cycle of the backwash water pump 20 in this embodiment is set according to the backwash requirements, and the warm-up pump flow rate can also be selected according to the actual ambient temperature.

[0033] In this embodiment, the two parallel backwash water pumps 20 operate intermittently only when necessary, significantly reducing power consumption. Furthermore, the warm-up return line 50 ensures a constant, slow flow of (relatively) high-temperature process water from the backwash water tank 10 inside the stopped pump, maintaining the pump body temperature close to the operating temperature. During startup, the temperature difference between the pump medium and the hot process water is minimal, preventing damage to the pump body and mechanical seal due to thermal stress. Specifically, since the stopped pump is always filled with water and in a "warm" state, no emptying or priming operation is required upon restarting; it can be started directly, effectively eliminating thermal shock during startup and shutdown, protecting the pump body and mechanical seal, reducing malfunctions and maintenance, improving equipment reliability, and extending service life. On the other hand, it simplifies or avoids frequent pumping operations, reduces the burden on operators and the risk of misoperation, simplifies the operation process, and improves efficiency. This utility model cleverly utilizes the first drain pipe 42 before the outlet valve 41 and the sewage pipe 11 (second drain pipe 12) at the bottom of the tank in the existing structure. By adding a small return pipe, the key function is achieved. The modification is small and the cost is low, making the energy-saving intermittent operation mode technically feasible and safe. In particular, it solves the key problem of winter operation and achieves the goal of a safe and reliable intermittent operation mode.

Claims

1. A process water treatment system for an ethylene plant, comprising: Backwash water tank (10); The inlet pipe (30) and the outlet pipe (40) are connected to the inlet of the backwash water tank (10) and the outlet pipe (40) is connected to the outlet pipe (40) of the backwash water tank (10). A backwash water pump (20) is installed in the outlet pipe (40); The backwash water pump (20) is characterized by having two pumps arranged in parallel, which operate in an intermittent start-up mode. An outlet valve (41) and a first drain pipe (42) are provided at the outlet of the two backwash water pumps (20). A sewage pipe (11) is provided at the bottom of the backwash water tank (10), and a second drain pipe (12) is also provided on the sewage pipe (11). A warm pump return pipe (50) is added between the first drain pipe (42) and the second drain pipe (12). During the intermittent start-up operation of the two backwash water pumps (20), the process water in the backwash water tank (10) can flow through the backwash water pump (20) in the closed state, the first drain pipe (42), and the second drain pipe (12) to the sewage pipe (11), thereby ensuring that the backwash water pump (20) in the closed state is always in a warm pump state.

2. The ethylene plant process water treatment system of claim 1, wherein: It also includes a return water line (60) for returning water from the sewage line (11) to the quench tower, the return water line (60) being equipped with an underground tank (61) and a submersible pump (62).

3. The ethylene plant process water treatment system of claim 1, wherein: The height of the two backwash water pumps (20) is lower than the height of the backwash water tank (10).

4. The ethylene plant process water treatment system of claim 3, wherein: The warm pump return line (50) is connected to the first drain pipe (42) and the second drain pipe (12) mentioned above by a detachable connection method.

5. The ethylene plant process water treatment system of claim 3, wherein: The specification of the warm pump return line (50) is DN20.

6. The ethylene plant process water treatment system of any one of claims 1-5, wherein: The backwash water tank (10) is also equipped with a level gauge (13) and a level transmitter (14).

7. The ethylene plant process water treatment system of any one of claims 1-5, wherein: The water inlet pipe (30) is connected to the outlet of the upstream dual-media filter.

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