Control method and device based on ethylene plant series connection of cracking gas compressor

Abstract

The present application relates to the technical field of cracking gas compressor control, and is a control method and device based on series cracking gas compressors of an ethylene device; after being connected in series, the first compressor is divided into three sections, the second compressor is divided into two sections, and the two sections are driven by two motors to compress the cracking gas in five sections; after receiving the main controller signal and the compression first section inlet pressure signal, the first load distribution controller controls the rotating speed of the first compressor; after receiving the main controller signal and the compression fourth section inlet pressure signal, the second load distribution controller controls the rotating speed of the second compressor. The present application uses two motor drives to replace the original turbine drive compressor, and through the cooperation of the main controller, the first load distribution controller and the second load distribution controller, the compression control of the cracking gas is realized, the carbon dioxide emission is greatly reduced, the environmental pollution and the fire explosion accidents caused by the steam material external leakage are eliminated, the adjustment is more intuitive and convenient, and the start-up and shutdown time and steps are greatly saved.

Description

Technical Field

[0001] This invention relates to the field of cracked gas compressor control technology, and is a control method and device based on a series cracked gas compressor in an ethylene plant. Background Technology

[0002] The ethylene unit employs a pre-propane removal and pre-hydrogenation process. The process involves the feedstock entering a cracking furnace for high-temperature cracking to produce cracked gas. After washing, the cracked gas enters a cracked gas compression unit, undergoing five stages of compression to 3.8-4.0 MPa before entering a separation unit to separate downstream products. Simultaneously, high-pressure boiler feedwater is used to cool the cracked gas within the cracking furnace unit, producing ultra-high-pressure steam to drive a generator set in a power station. The generated electricity, along with supplemental grid power, supplies power to the two motors of the cracked gas compressor. The existing process flow is as follows: Figure 1 As shown.

[0003] In traditional pyrolysis gas compressor drive schemes, the pyrolysis gas compressor is driven by a steam turbine. Since the pyrolysis gas compressor has a power output of up to 65,000 kW, replacing the steam turbine drive with an electric motor would be insufficient with current technology, as the power of a single motor is insufficient. Traditional turbine-driven compressors require adjusting the steam flow and temperature from the pyrolysis furnace to drive the compressor. Furthermore, the condensate rehydration system includes a rehydration pump, a vacuum valve, and a vacuum system. Operation requires adjusting various parameters and equipment operating conditions to achieve system balance. Steam adjustment is also constrained by complex factors such as the pyrolysis furnace operating status, furnace tube coking conditions, unit load, and the operator's skill and experience, often leading to mutual constraints, manpower shortages in emergencies, and difficulties in adjustment.

[0004] Patent document CN120120236A discloses a five-stage anti-surge control method for a cracked gas compressor. This method includes two anti-surge systems for hot and cold reflux control modes, consisting of a five-return, five-hot reflux valve B connected to the cracked gas compressor outlet and the cracked gas feed end, and a five-return, five-cold reflux valve A connected to the high-pressure propane dehydrogenator reflux tank outlet and the cracked gas feed end. The two compressor anti-surge control systems coordinate the reflux of the five-return, five-hot reflux valve B and the five-return, five-cold reflux valve A. The anti-surge control system for the five-return, five-cold reflux valve A includes a flow limit control for the five-stage outlet decarbonization unit and a 30% opening limit for the hot anti-surge valve. The anti-surge line for the five-return, five-cold reflux valve A is consistent with that of the five-return, five-hot reflux valve B, and is 1.2 times that of the five-return, five-hot reflux valve B. This invention can solve the technical problem of achieving more stable control of a five-stage anti-surge valve.

[0005] Patent document CN120798848A discloses a series-connected steam-driven compressor system and an automatic surge control method. The system includes a multi-stage steam-driven compressor, multiple desuperheating devices, a bypass return valve, multiple desuperheating regulating valves, and multiple orifice flow meters. By optimizing the series-connected steam-driven compressor system, it effectively solves the problems of high cost, high energy consumption, and unsatisfactory control effect in existing technologies. The series connection of the multi-stage steam-driven compressors, combined with the desuperheating devices and bypass return valves, achieves effective circulation and temperature control of the medium, reducing the cost of using a separate surge return valve in existing technologies. Simultaneously, by using vortex flow meters, pressure sensors, temperature sensors, and speed sensors, the system accurately measures the inlet flow, pressure, temperature, and speed of each stage of the compressor. Combined with theoretical surge pressure ratio calculations, it achieves early prediction and automatic control of surge risk, avoiding increased energy consumption caused by premature intervention of the bypass return valve at low speeds.

[0006] Patent document CN120830966A discloses a control method and device for a compressor unit, which can adjust the oil levels of the first and second compressors without the need for a separate oil return line. The first aspect of this application provides a control method for a compressor unit, which includes a first compressor and a second compressor connected by an air balance pipe and an oil balance pipe. The compressor unit has a regular operating step with alternating operation and an oil level adjustment step. In the oil level adjustment step, the compressor unit changes the speed of the first compressor and / or the second compressor to adjust the oil levels of the first and second compressors.

[0007] In summary, the existence of cracked gas compressors driven by steam turbines results in several problems: (1) the maintenance and repair of cracked gas compressors consumes a large amount of manpower and resources; (2) the start-up, shutdown, speed increase, and loading of cracked gas compressors waste a large amount of steam and raw materials, leading to resource waste. If electric drive is used, a single motor may not be able to meet the power requirements of the cracked gas compressor; although two motors driving two cracked gas compressors can meet the power requirements of the cracked gas compressors, there is a problem of how to match the load, speed, and pressure of the two cracked gas compressors well. Summary of the Invention

[0008] This invention provides a control method and apparatus for a series-connected cracked gas compressor in an ethylene plant, overcoming the shortcomings of the prior art. It effectively solves the problems in traditional cracked gas compressor drive schemes, where the cracked gas compressor is driven by a steam turbine, which can no longer meet the requirements for green and low-carbon operation; if electrically driven, a single motor cannot meet the power requirements of the cracked gas compressor; and although two motors driving two cracked gas compressors can meet the power requirements of the cracked gas compressors, there is a problem of how to match the load, speed, and pressure of the two cracked gas compressors well.

[0009] One of the technical solutions of this invention is achieved through the following measures: a control method based on a series-connected cracked gas compressor of an ethylene plant, which is carried out as follows: the first compressor is connected in series in three stages and the second compressor is connected in series in two stages, and is driven by two motors to perform five-stage compression of the cracked gas. The first compressor includes a compression stage 1, a compression stage 2 and a compression stage 3, and the second compressor includes a compression stage 4 and a compression stage 5. When the first compressor and the second compressor are connected in series, after receiving the main controller signal and the inlet pressure signal of the cracked gas compression stage 1, the first load distribution controller controls the speed of the first compressor. After receiving the main controller signal and the inlet pressure signal of the cracked gas compression stage 4, the second load distribution controller controls the speed of the second compressor, thereby controlling the load of the cracked gas compression system.

[0010] The following are further optimizations and / or improvements to one of the above-mentioned technical solutions:

[0011] After receiving the inlet pressure of the cracked gas compression section and the anti-surge control valve signal, the main controller feeds back the signals to the first load distribution controller and the second load distribution controller, respectively.

[0012] The first, second, and third stages of compression of the pyrolysis gas are sequentially compressed by the first stage of compression of the first compressor, the second stage of compression of the first compressor, and the third stage of compression of the first compressor. The fourth and fifth stages of compression of the pyrolysis gas are sequentially compressed by the fourth stage of compression of the second compressor and the fifth stage of compression of the second compressor.

[0013] The first compressor and the second compressor are respectively equipped with motors; and / or the power of the first compressor is from 28238 kW to 39420 kW, and the power of the second compressor is from 27942 kW to 34535 kW.

[0014] The aforementioned pyrolysis gas compression system includes a first-stage intake tank, a second-stage intake tank, a third-stage intake tank, a fourth-stage intake tank, a fifth-stage intake tank, an alkaline scrubbing tower, a dryer feed separator, a dryer, a high-pressure propane removal tower, a C2 hydrogenation reactor, and a high-pressure propane removal reflux tank. The pyrolysis gas enters the first stage of compression of the first compressor through the first-stage intake tank for first-stage compression. After first-stage compression, the pyrolysis gas enters the second stage of compression of the first compressor through the second-stage intake tank for second-stage compression. After second-stage compression, the pyrolysis gas enters the third stage of compression of the first compressor through the third-stage intake tank for third-stage compression. After third-stage compression, the pyrolysis gas enters the fourth stage of compression of the second compressor through the fourth-stage intake tank for fourth-stage compression. After fourth-stage compression, the pyrolysis gas sequentially passes through the fifth-stage intake tank, the alkaline scrubbing tower, the dryer feed separator, the dryer, and the high-pressure propane removal tower, and then enters the fifth stage of compression of the second compressor for fifth-stage compression. After fifth-stage compression, it sequentially passes through the C2 hydrogenation reactor and the high-pressure propane removal reflux tank before entering the next separation process.

[0015] An anti-surge control valve is installed on the pipeline between the outlet of the first-stage suction tank and the outlet of the fourth-stage suction tank; or / and an anti-surge control valve is installed on the pipeline between the inlet of the fourth stage of the second compressor and the outlet of the feed separator tank of the dryer.

[0016] The second technical solution of the present invention is achieved through the following measures: a device based on a series cracked gas compressor of an ethylene plant, comprising a first compressor, a second compressor, a first-stage suction tank, a second-stage suction tank, a third-stage suction tank, a fourth-stage suction tank, a fifth-stage suction tank, an alkaline scrubbing tower, a dryer feed separator, a dryer, and a high-pressure propane removal tower. Motors are respectively installed on the first compressor and the second compressor. The first compressor includes a first-stage compression, a second-stage compression, and a third-stage compression. The first-stage suction tank, the first-stage compression, the second-stage suction tank, the second-stage compression, the third-stage compression, the fourth-stage compression, the fifth-stage compression, the alkaline scrubbing tower, the dryer feed separator, the dryer, the high-pressure propane removal tower, and the fifth-stage compression are connected together from left to right by pipelines.

[0017] The following are further optimizations and / or improvements to the second technical solution of the above invention:

[0018] The above also includes a C2 hydrogenation reactor and a high-pressure propane desulfurization reflux tank. The outlet of the fifth compression stage and the inlet of the C2 hydrogenation reactor are connected together by pipelines. The outlet of the C2 hydrogenation reactor and the inlet of the high-pressure propane desulfurization reflux tank are connected together by pipelines. An outlet pipe is connected to the outlet of the high-pressure propane desulfurization reflux tank, and an inlet pipe is connected to the inlet of the first-stage suction tank.

[0019] A vent pipe is connected to the pipeline near the inlet of the fourth-stage suction tank. A first reflux line is connected between the pipelines at the outlets of the first-stage suction tank and the fourth-stage suction tank. A three-reverse-one anti-surge control valve is installed on the first reflux line. A second reflux line is connected between the pipeline at the inlet of the fourth stage of the second compressor and the outlet of the feed separator of the dryer. A four-reverse-four anti-surge control valve is installed on the second reflux line. A connecting pipe is connected between the pipeline at the outlet of the high-pressure propane dehydrogenator and the inlet of the C2 hydrogenation reactor. A third reflux line is connected between the connecting pipe and the outlet pipe. A five-reverse-four hot-wire anti-surge control valve is installed on the connecting pipe. A five-reverse-four cold-wire anti-surge control valve is installed on the third reflux line. Valves are installed on the inlet pipe, vent pipe, and outlet pipe, respectively.

[0020] The above also includes a main controller, a first load distribution controller, and a second load distribution controller. A first pressure sensor is installed at the inlet of the first compressor's compression stage 1, and a second pressure sensor is installed at the inlet of the second compressor's compression stage 4. The signal output terminals of the first pressure sensor, the three-stage anti-surge control valve, and the four-stage anti-surge control valve are electrically connected to the signal input terminal of the main controller. The signal output terminals of the first pressure sensor and the main controller are electrically connected to the signal input terminal of the first load distribution controller. The signal output terminal of the first load distribution controller is electrically connected to the signal input terminal of the first compressor. The signal output terminals of the second pressure sensor and the main controller are electrically connected to the signal input terminal of the second load distribution controller. The signal output terminal of the second load distribution controller is electrically connected to the signal input terminal of the second compressor.

[0021] This invention replaces the original turbine-driven compressor with a series-driven first and second compressor. Through the coordinated use of the main controller, the first load distribution controller, and the second load distribution controller, the compression control of the cracked gas is achieved. This invention can significantly reduce carbon dioxide emissions, eliminate the risk of environmental pollution and fire / explosion accidents caused by steam material leakage, reduce resource waste, and avoid the harm to human health caused by toxic and harmful substances in steam emissions. At the same time, the compression adjustment of cracked gas is no longer limited by steam quality and other systems, and the adjustment is more intuitive and convenient, greatly saving start-up and shutdown time and steps, and significantly reducing costs. Attached Figure Description

[0022] Appendix Figure 1 This is a flowchart of the existing process.

[0023] Appendix Figure 2 This is the control flowchart of the present invention.

[0024] Appendix Figure 3 This is a process flow diagram of the present invention.

[0025] Appendix Figure 4 This is a speed-up curve diagram of the first compressor or the second compressor of the present invention.

[0026] The codes in the attached diagram are as follows: 1 for the first compressor, 2 for the second compressor, 3 for the first stage of compression, 4 for the second stage of compression, 5 for the third stage of compression, 6 for the fourth stage of compression, 7 for the fifth stage of compression, 8 for the first stage suction tank, 9 for the second stage suction tank, 10 for the third stage suction tank, 11 for the fourth stage suction tank, 12 for the fifth stage suction tank, 13 for the alkaline washing tower, 14 for the dryer feed separator, 15 for the dryer, 16 for the high-pressure propane removal tower, 17 for the C2 hydrogenation reactor, 18 for the high-pressure propane removal reflux tank, 19 for the outlet pipe, 20 for the inlet pipe, 21 for the vent pipe, 22 for the first reflux line, 23 for the third reactor and first anti-surge control valve, 24 for the second reflux line, 25 for the fourth reactor and fourth anti-surge control valve, 26 for the connecting pipe, 27 for the third reflux line, 28 for the fifth reactor and fourth hot line anti-surge control valve, and 29 for the fifth reactor and fourth cold line anti-surge control valve. Detailed Implementation

[0027] The present invention is not limited to the following embodiments, and the specific implementation can be determined according to the technical solution of the present invention and the actual situation.

[0028] In this invention, for ease of description, the description of the relative positions of the components is based on the appendix to the specification. Figure 3 The layout is described using a diagrammatic method, such as the positional relationships of front, back, top, bottom, left, and right, which are based on the instructions attached. Figure 3 The orientation of the layout is determined by the direction of the map.

[0029] The present invention will be further described below with reference to embodiments and accompanying drawings:

[0030] Example 1, as shown in the attached document Figure 2 , 3 As shown, the control method based on the series-connected cracked gas compressor of the ethylene plant is carried out as follows: the first compressor 1 is divided into three sections and the second compressor 2 is divided into two sections, which are connected in series and driven by two motors to compress the cracked gas in five stages. The first compressor 1 includes a first compression stage 3, a second compression stage 4, and a third compression stage 5. The second compressor 2 includes a fourth compression stage 6 and a fifth compression stage 7. When the first compressor 1 and the second compressor 2 are connected in series, after receiving the main controller signal and the inlet pressure signal of the first compression stage 3 of the cracked gas, the first load distribution controller controls the speed of the first compressor 1. After receiving the main controller signal and the inlet pressure signal of the fourth compression stage 6 of the cracked gas, the second load distribution controller controls the speed of the second compressor 2, thereby controlling the load of the cracked gas compression system.

[0031] The above embodiment 1 can be further optimized and / or improved according to actual needs:

[0032] As attached Figure 2As shown, after receiving the inlet pressure of the first stage of cracked gas compression and the anti-surge control valve signal, the main controller feeds back the signals to the first load distribution controller and the second load distribution controller, respectively.

[0033] As attached Figure 3 As shown, the pyrolysis gas enters the next process after five stages of compression. The first, second and third stages of compression of the pyrolysis gas are successively compressed by the first stage 3 of the first compressor 1, the second stage 4 of the first compressor 1 and the third stage 5 of the first compressor 1. The fourth and fifth stages of compression of the pyrolysis gas are successively compressed by the fourth stage 6 of the second compressor 2 and the fifth stage 7 of the second compressor 2.

[0034] As needed, motors are installed on the first compressor 1 and the second compressor 2 respectively; and / or the power of the first compressor 1 is from 28238 kW to 39420 kW, and the power of the second compressor 2 is from 27942 kW to 34535 kW.

[0035] As attached Figure 3 As shown, the pyrolysis gas compression system includes a first-stage intake tank 8, a second-stage intake tank 9, a third-stage intake tank 10, a fourth-stage intake tank 11, a fifth-stage intake tank 12, an alkaline scrubbing tower 13, a dryer feed separator 14, a dryer 15, a high-pressure propane degassing tower 16, a C2 hydrogenation reactor 17, and a high-pressure propane degassing reflux tank 18. The pyrolysis gas enters the first stage 3 of the first compressor 1 via the first-stage intake tank 8 for first-stage compression. After first-stage compression, the pyrolysis gas enters the second stage 4 of the first compressor 1 via the second-stage intake tank 9 for second-stage compression. After second-stage compression, the pyrolysis gas... The three-stage intake tank 10 feeds the pyrolysis gas into the compression stage 5 of the first compressor 1 for three-stage compression. After three-stage compression, the pyrolysis gas enters the compression stage 6 of the second compressor 2 via the four-stage intake tank 11 for four-stage compression. After four-stage compression, the pyrolysis gas sequentially passes through the five-stage intake tank 12, the alkaline scrubbing tower 13, the dryer feed separator 14, the dryer 15, and the high-pressure propane removal tower 16, and then enters the compression stage 7 of the second compressor 2 for five-stage compression. After five-stage compression, it sequentially passes through the C2 hydrogenation reactor 17 and the high-pressure propane removal reflux tank 18 before entering the next separation process. The first-stage intake tank 8, the second-stage intake tank 9, the third-stage intake tank 10, the fourth-stage intake tank 11, the fifth-stage intake tank 12, the alkaline scrubbing tower 13, the dryer feed separator 14, the dryer 15, the high-pressure propane removal tower 16, the C2 hydrogenation reactor 17, and the high-pressure propane removal reflux tank 18 are all existing, publicly known, and commonly used components.

[0036] As needed, an anti-surge control valve is installed on the pipeline between the outlet of the first-stage suction tank 8 and the outlet of the fourth-stage suction tank 11; or / and, an anti-surge control valve is installed on the pipeline between the inlet of the fourth-stage compression tank 6 of the second compressor 2 and the outlet of the dryer feed separator tank 14.

[0037] Example 2, as shown in the attached document Figure 3 As shown, the device based on the series cracked gas compressor of the ethylene plant includes a first compressor 1, a second compressor 2, a first-stage suction tank 8, a second-stage suction tank 9, a third-stage suction tank 10, a fourth-stage suction tank 11, a fifth-stage suction tank 12, an alkaline scrubbing tower 13, a dryer feed separator 14, a dryer 15, and a high-pressure depropanizer tower 16. Motors are installed on the first compressor 1 and the second compressor 2 respectively. The first compressor 1 includes a first-stage compression 3, a second-stage compression 4, and a third-stage compression 5. The second compressor 2 includes a fourth-stage compression 6 and a fifth-stage compression 7. The first-stage suction tank 8, the first-stage compression 3, the second-stage suction tank 9, the second-stage compression 4, the third-stage suction tank 10, the third-stage compression 5, the fourth-stage suction tank 11, the fourth-stage compression 6, the fifth-stage suction tank 12, the alkaline scrubbing tower 13, the dryer feed separator 14, the dryer 15, the high-pressure depropanizer tower 16, and the fifth-stage compression 7 are connected together from left to right by pipelines.

[0038] The above embodiment 2 can be further optimized and / or improved according to actual needs:

[0039] As attached Figure 3 As shown, it also includes a C2 hydrogenation reactor 17 and a high-pressure propane desulfurization reflux tank 18. The outlet of the five-stage compression section 7 and the inlet of the C2 hydrogenation reactor 17 are connected together by pipelines. The outlet of the C2 hydrogenation reactor 17 and the inlet of the high-pressure propane desulfurization reflux tank 18 are connected together by pipelines. An outlet pipe 19 is connected to the outlet of the high-pressure propane desulfurization reflux tank 18, and an inlet pipe 20 is connected to the inlet of the first-stage intake tank 8. The cracked gas enters the first-stage intake tank 8 through the inlet pipe 20, undergoes five stages of compression and treatment, and finally enters the next process through the outlet pipe 19.

[0040] As attached Figure 3As shown, a vent pipe 21 is connected to the pipeline near the inlet of the four-stage suction tank 11. A first reflux line 22 is connected between the pipeline at the outlet of the first-stage suction tank 8 and the outlet of the four-stage suction tank 11. A three-stage anti-surge control valve 23 is installed on the first reflux line 22. A second reflux line 24 is connected between the pipeline at the inlet of the fourth-stage compression section 6 of the second compressor 2 and the outlet of the dryer feed separator 14. A four-stage anti-surge control valve 25 is installed on the second reflux line 24. A connecting pipe 26 is connected between the pipeline at the outlet of the high-pressure propane dehydrogenator 16 and the inlet of the C2 hydrogenation reactor 17. A third reflux line 27 is connected between the connecting pipe 26 and the outlet pipe 19. A five-stage anti-surge control valve 28 is installed on the connecting pipe 26. A five-stage anti-surge control valve 29 is installed on the third reflux line 27. Valves are installed on the inlet pipe 20, the vent pipe 21, and the outlet pipe 19, respectively. The three-reverse-one anti-surge control valve 23, the four-reverse-four anti-surge control valve 25, the five-reverse-four hot-line anti-surge control valve 28, and the five-reverse-four cold-line anti-surge control valve 29 are all existing, publicly known, and commonly used valves. The three-reverse-one anti-surge control valve 23 and the four-reverse-four anti-surge control valve 25 are the anti-surge control valves mentioned in Example 1. In Example 1, an anti-surge control valve is installed on the pipeline between the outlet of the first-stage suction tank 8 and the outlet of the fourth-stage suction tank 11. This anti-surge control valve specifically corresponds to the three-reverse-one anti-surge control valve 23 in Example 2. In Example 1, an anti-surge control valve is installed on the pipeline between the inlet of the fourth-stage compression section 6 of the second compressor 2 and the outlet of the dryer feed separator tank 14. This anti-surge control valve specifically corresponds to the four-reverse-four anti-surge control valve 25 in Example 2.

[0041] As needed, it also includes a main controller, a first load distribution controller, and a second load distribution controller. A first pressure sensor is installed at the inlet of the first compressor 1 at the compression stage 3, and a second pressure sensor is installed at the inlet of the second compressor 2 at the compression stage 4 at the inlet. The signal output terminals of the first pressure sensor, the three-stage anti-surge control valve 23, and the four-stage anti-surge control valve 25 are electrically connected to the signal input terminal of the main controller. The signal output terminals of the first pressure sensor and the main controller are electrically connected to the signal input terminal of the first load distribution controller. The signal output terminal of the first load distribution controller is electrically connected to the signal input terminal of the first compressor 1. The signal output terminals of the second pressure sensor and the main controller are electrically connected to the signal input terminal of the second load distribution controller. The signal output terminal of the second load distribution controller is electrically connected to the signal input terminal of the second compressor 2.

[0042] Example 3, as shown in the appendix Figure 3As shown, this device is based on a series-connected cracked gas compressor in an ethylene plant. The five-stage compression is split into two compressors (first compressor 1 and second compressor 2), each equipped with a motor. The first compressor 1 has a power of approximately 39,000 kW, driving stages 1-3 of the compression, while the second compressor 2 has a power of approximately 34,000 kW, driving stages 4-5. The first compressor 1 and second compressor 2 operate in series, each with its own independent compressor control system (first load distribution controller and second load distribution controller). Both motors drive the first compressor 1 and second compressor 2 via gearboxes to achieve the series-connected cracked gas compression operation. Table 1 shows the power comparison of the turbine, the first compressor, and the second compressor.

[0043] Table 1. Power Comparison of Turbine, First Compressor, and Second Compressor

[0044] .

[0045] This invention replaces the traditional single turbine drive by electrically controlling the first compressor 1 and the second compressor 2. The electric drive control method is more stable and the adjustment is faster. Matching the two motors and two control systems during start-up, shutdown and emergency operations is also the focus and challenge of this invention.

[0046] The present invention also includes: (1) a matching control method between the main controller and the first load distribution controller and the second load distribution controller during the process of two series-connected pyrolysis gas compression; and (2) a matching and process control method between the two systems during pyrolysis gas compression start-up and shutdown, daily operation and emergency accident state.

[0047] 1. Control system: The cracked gas compressor is still set up with the traditional five-stage compression. After the electric drive is changed, the first three stages are driven by one variable frequency motor of the first compressor 1, and the fourth and fifth stages are driven by another variable frequency motor of the second compressor 2.

[0048] Main controller: The main controller controls the inlet pressure of the first compressor 1 and outputs it to two load distribution controllers (first load distribution controller and second load distribution controller).

[0049] Load distribution controller: Receives signals from the main controller, the first inlet pressure of the first pyrolysis gas compressor 1 and the fourth inlet pressure of the second pyrolysis gas compressor 2, or other required signals. The load distribution controller (first load distribution controller and second load distribution controller) outputs signals to the frequency converters of the motors on the first compressor 1 and the second compressor 2, respectively, to control the speed of the first compressor 1 and the second compressor 2, thereby realizing the control of the load of the entire pyrolysis gas compression system.

[0050] The system operates under primary performance control based on inlet pressure, with a dedicated performance load distribution controller for each motor. The primary performance control sends signals to both load distribution controllers via internal communication, which in turn control the speeds of the two motors. When the inlet pressure is too high, both motor speeds are increased simultaneously; conversely, when it is too low, both motor speeds are decreased. Simultaneously, the load distribution controllers automatically adjust the load on both compressors based on their speeds and operating points, and adjust the system pressure accordingly by adjusting the speed of the second motor.

[0051] The load distribution controller sends two frequency modulation signals to the corresponding compressor's inverter. One signal goes to the main inverter, and the other goes to the standby inverter. The standby inverter receives frequency modulation signals from two different compressors simultaneously. The controller inside the inverter determines which unit will be frequency-modulated after the standby status is switched. The switching time of the control signal inside the inverter should not be less than the overall switching time of the inverter.

[0052] Anti-surge controller: It is set up in the same way as the traditional steam-driven unit. By adjusting the three-reverse-one anti-surge control valve 23, the four-reverse-four anti-surge control valve 25, the five-reverse-four hot-line anti-surge control valve 28, and the five-reverse-four cold-line anti-surge control valve 29, the compressor (first compressor 1 and second compressor 2) is prevented from surging.

[0053] The first three compression stages can be configured with an anti-surge control valve, specifically a three-stage anti-surge control valve 23 to prevent surge in the first three stages. A low-limit inlet pressure control is also provided to prevent inlet cavitation under abnormal operating conditions. An high-limit outlet temperature control can be set to prevent outlet temperature and pressure over-limits during startup, thus preventing outlet overpressure. The four compression stages can be configured with an anti-surge control valve, specifically a four-stage anti-surge control valve 25 to prevent surge in all four stages.

[0054] The five-stage compression system can be configured with two cold and hot reflux anti-surge control valves, specifically, five-stage anti-surge control valve 28 (hot wire) and five-stage anti-surge control valve 29 (cold wire). The cold reflux anti-surge control valve has a larger safety margin than the hot reflux anti-surge control valve. Therefore, when opening the valves, open the five-stage anti-surge control valve 29 first, then the five-stage anti-surge control valve 28; when closing the valves, close the five-stage anti-surge control valve 28 first, then the five-stage anti-surge control valve 29. Simultaneously, the five-stage anti-surge control valve 29 can be set with a high-limit control for the fifth-stage outlet temperature to prevent outlet over-temperature and a high-limit control for the fifth-stage outlet pressure to prevent outlet over-pressure. A low-limit control for the outlet net flow rate can also be set to prevent low flow rate and over-temperature in the downstream separation unit.

[0055] 2. Performance Control

[0056] The controller can be equipped with built-in override control. When the inlet pressure deviation exceeds 4-5 kPa, the controller will send an override signal to open the corresponding anti-surge control valve while reducing the inverter speed to help smooth out fluctuations. When the inverter switches between main and standby modes or experiences an electrical power outage, the compressor speed will drop. The inverter will then ramp up from the control unit speed to the new speed setpoint given by the CCC (controller manufacturer) performance control. During this process, due to the speed decrease, the compressor inlet pressure increases and the intake flow decreases. The anti-surge controller will open and close the corresponding anti-surge control valve according to the compressor's operating point position to stabilize the inlet pressure.

[0057] 3. Startup Plan

[0058] Table 2 shows the controller modes and limit settings for each segment; before starting, check and confirm the controller modes and limit settings according to Table 2.

[0059] Table 2 Controller Modes and Limit Settings for Each Segment

[0060] .

[0061] Once the start-up conditions are met, the operator presses the start button for the first compressor 1. Figure 4 For the acceleration curve of either compressor 1 or compressor 2; from Figure 4 It can be seen that the first compressor 1 accelerates to (1300-1350rpm) according to the acceleration curve, pauses for 5 minutes to adjust the system pressure balance, and then accelerates to (2300-2400rpm) and pauses for 5 minutes to continue adjusting. According to the acceleration curve, it automatically accelerates to 80% of the minimum adjustable speed (3100-3200rpm) and waits for the second compressor 2 to start. During this process, each anti-surge control valve automatically closes to establish system pressure.

[0062] After the first compressor 1 starts, the operator presses the start button for the second compressor 2. The second compressor 2 automatically increases its speed to 80% of the minimum adjustable speed of 4200-4300 rpm according to the speed-up curve and waits.

[0063] After the first compressor 1 and the second compressor 2 have started, the operator presses the loading button. The three-reverse-one anti-surge control valve 23, the four-reverse-four anti-surge control valve 25, the five-reverse-four hot-wire anti-surge control valve 28, and the five-reverse-four cold-wire anti-surge control valve 29 slowly close until they are completely closed (valve closing rate 0.25% / s, valve closing rate of the five-reverse-four hot-wire anti-surge control valve 28 0.5% / s). The system pressure slowly rises to the pressure required for each segment in Table 2. When the first compressor 1 and the second compressor 2 reach the zero speed or trigger the limit control, each anti-surge control valve stops closing.

[0064] After startup, the operator manually adjusts the inlet pressure of the first compressor 1 and the second compressor 2 to adjust the speed of the first compressor 1 and the second compressor 2 to meet the process requirements in Table 2.

[0065] After the system starts feeding materials, first switch the first and second load distribution controllers to automatic mode, then switch the main controller to automatic mode. The operator adjusts the inlet pressure setpoint according to the outlet pressures of the first compressor 1 and the second compressor 2 to maintain the pressure within the preset range.

[0066] 4. Operation Control

[0067] In main control mode, the speeds of the first compressor 1 and the second compressor 2 are adjusted according to the inlet pressure of a certain segment. The speeds of the first compressor 1 and the second compressor 2 can be adjusted proportionally. The inlet pressure of the first compressor 1 is output to two independent load distribution controllers (the first load distribution controller and the second load distribution controller) through the main controller. The first load distribution controller and the second load distribution controller then coordinate the speeds of the first compressor 1 and the second compressor 2 to maintain stable system operation. At the same time, the first load distribution controller and the second load distribution controller can slowly adjust the speeds according to the speeds and operating status of the first compressor 1 and the second compressor 2 to match the operating parameters of each segment, thereby automatically adjusting the loads of the first compressor 1 and the second compressor 2.

[0068] In independent control mode, the speed of the first compressor 1 is adjusted according to the first inlet pressure of the cracked gas, and the speed of the second compressor 2 is adjusted according to the fourth inlet pressure of the cracked gas. The proportional control of the speed between the two compressors can be cancelled. In this mode, the two compressors are controlled as independent compressors to maintain stable system operation.

[0069] When the first load distribution controller and the second load distribution controller are switched to manual, the speed of the two compressors can be manually controlled.

[0070] 5. Shutdown and Troubleshooting

[0071] 5.1 During normal operation, when the second compressor 2 is interlocked and shut down

[0072] When the second compressor 2 is interlocked and shut down, it will not affect the safe operation of the first compressor 1. Therefore, the first compressor 1 will not trigger the interlock shutdown. The first compressor 1 will not stop, but will automatically unload and the speed will automatically decrease to the lowest adjustable speed. At the same time, the three-way anti-surge control valve 23 will automatically open fully, and the valve on the vent pipe 21 will automatically open to control the pressure.

[0073] 5.2 During normal operation, when the first compressor 1 is interlocked and shut down

[0074] At this time, in order to prevent the risk of low pressure from the second compressor 2, the second compressor 2 will be interlocked and stopped. Under this condition, the unit will be handled and retreated as if it were shut down.

[0075] 5.3 Normal Shutdown

[0076] (1) Switch the main controller, the first load distribution controller and the second load distribution controller to manual mode, and slowly reduce the speed of the two compressors to the minimum speed.

[0077] (2) Press the normal stop button, and the inverters on the first compressor 1 and the second compressor 2 will reduce the speed according to the set speed reduction curve. The anti-surge control valves (three-anti-one anti-surge control valve 23, four-anti-four anti-surge control valve 25, five-anti-four hot-line anti-surge control valve 28 and five-anti-four cold-line anti-surge control valve 29) will automatically open fully.

[0078] 5.4 Inverter Fault Switching

[0079] Taking the device load at 100% as an example, when the inverter on the first compressor 1 fails, the inverter system can switch the inverter to the corresponding backup inverter within 200ms. During the inverter switching period, the speed of the second compressor 2 will drop rapidly to about 80% of the operating speed.

[0080] At this time, the anti-surge system detects that the unit is about to surge and sends an anti-surge control valve opening signal. 500ms later, the on-site anti-surge control valve starts to act. After another 500ms, the anti-surge control valve adjusts to the set valve position. Since the compressor speed decreases faster than the anti-surge control valve acts, the unit will experience a brief surge during inverter fault switching, which will not affect production operation.

[0081] 5.5 Power sloshing

[0082] Since power grid fluctuations are generally short-lived, the inverters used in the first compressor 1 and the second compressor 2 both have low-voltage ride-through capabilities. The speeds of the first compressor 1 and the second compressor 2 will not drop significantly, and the impact on the process system is minimal. If a power grid fluctuation or inverter switching occurs throughout the plant, the speed of the compressors (first compressor 1 and second compressor 2) will decrease much faster than that of the turbine units. After the compressor drive motors regain power, the inverters will increase the compressor speed to the target value according to the control system output. Then, the load distribution controllers (first load distribution controller and second load distribution controller) will gradually adjust and smooth out the system fluctuations. These fluctuations will have little impact on production.

[0083] Effects of the present invention

[0084] This invention describes a method for matching and controlling the main controller and load distribution controller of a pyrolysis gas compressor by using a gearbox to speed up the compressor during start-up, shutdown, daily operation, and emergency situations.

[0085] Compared to existing technologies, this invention significantly reduces carbon dioxide emissions, minimizes steam material leakage and pollution, reduces the risk of fire and explosion accidents, reduces resource waste, avoids harm to human health from toxic and harmful substances in steam emissions, and saves manpower, resources, and risks associated with routine maintenance, repairs, and adjustments required in traditional turbine-driven systems. It also frees compressor adjustments from limitations imposed by steam quality and other systems, making adjustments more intuitive and convenient. Furthermore, it significantly reduces start-up and shutdown time and procedures, saving the time and steam loss associated with warming up the system pipes and engine during traditional turbine start-up and shutdown.

[0086] (a) Economic benefits

[0087] Table 3 is a comparison table of energy consumption (turbine drive VS motor drive of the present invention); Table 4 is a table of energy consumption and electrification rate of the electric drive ethylene unit of the present invention.

[0088] Table 3 Energy Consumption Comparison (Turbine Drive VS Motor Drive of This Invention)

[0089] .

[0090] Table 4 Energy consumption and electrification rate of the electric-driven ethylene unit of this invention

[0091] .

[0092] Tables 3 and 4 compare the results with turbine-driven systems and electric motor-driven systems. The negative values ​​are due to increased energy consumption and the need for additional steam supply after electric drive. Tables 3 and 4 show that, based on calculations, the efficiency of the pyrolysis gas compressor in this invention after switching from steam-driven to electric drive is significantly improved.

[0093] 1. Electricity consumption increased by 587 million kWh / year, saving 3.77 million tons / year of ultra-high pressure steam, generating a total economic benefit of approximately 26.85 million yuan for the whole year.

[0094] 2. Reduce carbon dioxide emissions by 69,300 tons / year.

[0095] 3. The electrification rate of the ethylene plant increased from 9.66% to 29.5%.

[0096] (II) Safety and Environmental Benefits

[0097] 1. Significantly reduce carbon dioxide emissions, making the equipment operate in a green, low-carbon, low-emission, low-energy, and low-consumption manner.

[0098] 2. Reduce the risk of steam venting, material leakage, environmental pollution, and fire and explosion accidents. At the same time, reduce resource waste, avoid the harm to human health caused by toxic and harmful substances in steam venting, and minimize safety risks.

[0099] 3. Saves on the daily maintenance and repair of traditional turbine drives, which require a lot of manpower and resources and involve risks associated with adjustments and operations, as well as the need for water exchangers, water pumps and vacuum systems.

[0100] 4. Daily operation is more convenient. Compared with turbine drive, the adjustment of cracked gas compressor is more limited by the steam quality and capacity of cracking furnace. It is often necessary to adjust the operation of cracking furnace to maintain steam balance. Close cooperation between various units is required. After electric drive, the compressor adjustment is no longer limited and the adjustment is more intuitive.

[0101] 5. Saves time and manpower spent on warming up pipes and the steam loss during the start-up and shutdown of traditional turbines (it takes 10-12 hours for a turbine to warm up to 500℃ at a rate of 40-50℃ / h). It can save at least 10 hours.

[0102] In summary, this invention can significantly reduce carbon dioxide emissions, reduce steam material leakage and pollution, minimize the risk of fire and explosion accidents, reduce resource waste, avoid harm to human health from toxic and harmful substances in steam emissions, and save the manpower and resources consumed in daily system maintenance and repair, as well as the risks associated with adjustment operations, that are associated with traditional turbine drives. Simultaneously, it frees compressor daily adjustments from limitations imposed by steam quality and other systems, making adjustments more intuitive and convenient; it also significantly reduces start-up and shutdown time and procedures, saving the time and steam loss associated with warming up the system pipes and the steam emissions required during traditional turbine start-up and shutdown.

[0103] The above technical features constitute the embodiments of the present invention, which have strong adaptability and implementation effect. Unnecessary technical features can be added or removed according to actual needs to meet the needs of different situations.

Claims

1. A control method for an ethylene plant based on a train of cracking gas compressors, characterized in that The method is as follows: the first compressor is divided into three sections, the second compressor is divided into two sections, and the five-section compression of the cracked gas is driven by two motors in series, the first compressor includes compression section one, compression section two and compression section three, the second compressor includes compression section four and compression section five, when the first compressor and the second compressor are operated in series, the first load distribution controller receives the main controller signal and the cracked gas compression section one inlet pressure signal, and controls the rotating speed of the first compressor, the second load distribution controller receives the main controller signal and the cracked gas compression section four inlet pressure signal, and controls the rotating speed of the second compressor, so as to control the load of the cracked gas compression system; the anti-surge control valve is installed on the pipeline between the outlet of the section one suction tank and the outlet of the section four suction tank, the anti-surge control valve is installed on the pipeline between the inlet of the compression section four of the second compressor and the outlet of the dryer feed separation tank, the main controller receives the cracked gas compression section one inlet pressure and the anti-surge control valve signal, and feeds back the signals to the first load distribution controller and the second load distribution controller respectively; the cracked gas compression system includes the section one suction tank, the section two suction tank, the section three suction tank, the section four suction tank, the section five suction tank, the caustic washing tower, the dryer feed separation tank, the dryer, the high-pressure de-propane tower, the carbon two hydrogenation reactor and the high-pressure de-propane reflux tank; the cracked gas enters the first compressor for one-section compression through the section one suction tank, enters the first compressor for two-section compression through the section two suction tank after the one-section compression, enters the first compressor for three-section compression through the section three suction tank after the two-section compression, enters the second compressor for four-section compression through the section four suction tank after the three-section compression, enters the second compressor for five-section compression through the section five suction tank after the four-section compression, and then enters the next separation process through the carbon two hydrogenation reactor and the high-pressure de-propane reflux tank after the five-section compression; the venting pipe is connected to the pipeline near the inlet of the section four suction tank, the first reflux line is connected between the outlet of the section one suction tank and the outlet of the section four suction tank, the three-reflux-one anti-surge control valve is installed on the first reflux line, the second reflux line is connected between the inlet of the compression section four of the second compressor and the outlet of the dryer feed separation tank, the four-reflux-four anti-surge control valve is installed on the second reflux line, the communication pipe is connected between the outlet of the high-pressure de-propane tower and the inlet of the carbon two hydrogenation reactor, the third reflux line is connected between the communication pipe and the outlet pipe, the five-reflux-four hot-line anti-surge control valve is installed on the communication pipe, the five-reflux-four cold-line anti-surge control valve is installed on the third reflux line, and the valves are installed on the inlet pipe, the venting pipe and the outlet pipe respectively.

2. The control method for an ethylene plant train de-ethanizer compressor as claimed in claim 1, wherein The one-section compression, the two-section compression and the three-section compression of the cracked gas are sequentially compressed through the compression section one of the first compressor, the compression section two of the first compressor and the compression section three of the first compressor, and the four-section compression and the five-section compression of the cracked gas are sequentially compressed through the compression section four of the second compressor and the compression section five of the second compressor.

3. The control method for a series ethylene plant deethanizer compressor as claimed in claim 1 or 2, characterized in that The first compressor and the second compressor are respectively provided with a motor; or / and, the power of the first compressor is 28238kw-39420kw, and the power of the second compressor is 27942kw-34535kw.

4. An apparatus for controlling a train-up gas compressor of an ethylene-based plant using the method of claim 1 or 2, wherein, The first compressor, the second compressor, a first suction tank, a second suction tank, a third suction tank, a fourth suction tank, a fifth suction tank, an alkali washing tower, a dryer feed separation tank, a dryer, a high-pressure depropanizer are sequentially connected through pipelines from left to right, the first compressor comprises a compression first stage, a compression second stage and a compression third stage, and the second compressor comprises a compression fourth stage and a compression fifth stage.

5. The apparatus for controlling a series depropanizer compressor of an ethylene-based plant as defined in claim 4, wherein The first compressor and the second compressor are respectively provided with a motor; or / and, the power of the first compressor is 28238kw-39420kw, and the power of the second compressor is 27942kw-34535kw.

6. The ethylene-based plant in-line cracking gas compressor control method-based apparatus as claimed in claim 5, wherein The first compressor and the second compressor are respectively provided with a motor; or / and, the power of the first compressor is 28238kw-39420kw, and the power of the second compressor is 27942kw-34535kw. The first compressor and the second compressor are respectively provided with a motor; or / and, the power of the first compressor is 28238kw-39420kw, and the power of the second compressor is 27942kw-34535kw.

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