Intake device for oxygen compressor start-up nitrogen operation phase

Abstract

The utility model discloses an oxygen compressor starting nitrogen gas running stage's air inlet device, the device according to oxygen pressure machine air inlet pressure, flow design value, design air separation device liquid nitrogen gasification equipment output's normal temperature nitrogen gas as oxygen pressure machine starting nitrogen gas running stage's nitrogen gas source, utilize liquid nitrogen pump frequency changer, nitrogen gas pneumatic conveying valve's adjusting function, change liquid nitrogen pump speed, adjust pneumatic nitrogen gas conveying valve opening degree, will liquid nitrogen gasifier export normal temperature nitrogen gas pressure, flow value adjust to oxygen pressure machine air inlet pressure, flow design value, convey to oxygen pressure machine air inlet pipeline, the utility model solves oxygen pressure machine starting nitrogen gas running stage because of using low pressure nitrogen gas, medium pressure nitrogen gas's air inlet technology and produces nitrogen gas air inlet pressure value and oxygen pressure machine air inlet pressure design value do not tally, lead to oxygen pressure machine operating condition deviates problem, has improved oxygen pressure machine starting nitrogen gas running stage's safety stability significantly.

Description

Technical Field

[0001] This utility model belongs to the field of deep refrigeration air separation, and in particular relates to the air intake process and device for the nitrogen operation stage of oxygen compressor startup in this field. Background Technology

[0002] Deep cooling air separation unit, also known as air separation unit, uses the principle of low temperature distillation. The raw material air is fed into a low temperature distillation column, where heat and mass exchange occurs through rising vapor and reflux liquid. Taking advantage of the different boiling points of oxygen and nitrogen in the raw material air, oxygen and nitrogen are separated from the air, and low temperature gaseous and liquid oxygen and nitrogen products are extracted.

[0003] The ambient temperature gas product compression and conveying system of the air separation unit consists of an oxygen compressor and a nitrogen compressor. The cryogenic liquid product storage and vaporization system of the air separation unit consists of liquid oxygen and liquid nitrogen storage tanks and liquid oxygen and liquid nitrogen vaporization equipment.

[0004] Low-temperature gaseous oxygen and nitrogen products are heated to room temperature via the main heat exchanger and then compressed and pressurized by the oxygen compressor (hereinafter referred to as "oxygen compressor") and nitrogen compressor (hereinafter referred to as "nitrogen compressor") outside the cold box before being delivered to the user's oxygen and nitrogen pipeline network. Low-temperature liquid oxygen and nitrogen products are stored in liquid oxygen storage tanks and liquid nitrogen storage tanks, respectively. Some liquid oxygen and liquid nitrogen are filled into liquid oxygen and liquid nitrogen vaporization equipment, pressurized by the low-temperature liquid oxygen pump and liquid nitrogen pump, and vaporized and heated to room temperature in a water bath or air bath vaporizer before being delivered to the user's oxygen and nitrogen pipeline network.

[0005] Domestic and international existing technologies for starting up oxygen compressors involve two stages: nitrogen operation and oxygen operation. The nitrogen operation stage lasts 3 to 30 minutes. During the nitrogen operation stage, compressed nitrogen is used to purge the oxygen compressor rotor, diffuser, bends, reflux vent, interstage cooler, gas filter, valves, and pipelines of any flammable or combustible substances. This ensures that combustion and explosion are prevented during the oxygen operation stage, guaranteeing safe start-up and operation of the oxygen compressor.

[0006] In the current technology, during the nitrogen start-up phase of oxygen compressors, the nitrogen used is either low-pressure nitrogen or medium-pressure nitrogen. For oxygen compressor start-up nitrogen operation, low-pressure nitrogen is used, specifically designed to be low-pressure nitrogen produced at the top of the air separation unit's upper column, with a pressure of 10–15 kPa. For medium-pressure nitrogen, it is designed to be medium-pressure nitrogen from the user's nitrogen pipeline network, with a pressure regulation design value of 500–600 kPa.

[0007] The following issues exist in the current oxygen compressor startup nitrogen operation phase and need to be improved.

[0008] The design value of the oxygen compressor inlet pressure is based on the pressure of the low-pressure oxygen product extracted from the lower part of the upper column of the air separation unit. In the oxygen compressor process design, low alarm value, high alarm value, low interlock shutdown value, and high interlock shutdown value of the oxygen compressor inlet pressure are set to ensure the safe start-up and operation of the oxygen compressor.

[0009] During the nitrogen operation phase of the oxygen compressor startup, the design and use of low-pressure and medium-pressure nitrogen inlet processes result in different pressures between the low-pressure and medium-pressure nitrogen and the low-pressure oxygen product pressure. The large difference between the nitrogen inlet pressure and the oxygen compressor design value causes the oxygen compressor's operating conditions to deviate, which has a significant impact on the safe and stable operation of the oxygen compressor during startup.

[0010] Firstly, the process of introducing low-pressure nitrogen during the nitrogen operation phase of the oxygen compressor startup.

[0011] In the process design of the air separation unit, low-pressure nitrogen and low-pressure oxygen products are produced from the top and bottom of the upper column of the air separation unit, respectively. Therefore, the design pressure value of the low-pressure nitrogen product is less than the design pressure value of the low-pressure oxygen product.

[0012] During the nitrogen start-up phase of the oxygen compressor, low-pressure nitrogen is used. The oxygen compressor inlet pressure is lower than the design value. To prevent the oxygen compressor inlet pressure from dropping to the low alarm value or the low interlock shutdown value, the oxygen compressor reflux valve is opened. The nitrogen that has been pressurized at the oxygen compressor outlet is throttled and depressurized through the reflux valve and input into the oxygen compressor inlet pipeline, increasing the oxygen compressor inlet pressure. This increases the actual nitrogen compression flow rate of the oxygen compressor, raises the current value of the oxygen compressor main motor, and results in poor operating stability of the oxygen compressor.

[0013] Secondly, the process of introducing high-pressure nitrogen during the nitrogen operation phase of the oxygen compressor startup.

[0014] In conventional industrial equipment, the operating pressure of medium-pressure nitrogen is 1000–2000 kPa. After being regulated to the oxygen compressor inlet pressure by a pressure regulating valve, the pressure difference drops significantly, resulting in large fluctuations in both the nitrogen flow rate at the regulator valve outlet and the nitrogen flow rate at the oxygen compressor inlet. The medium-pressure nitrogen network in conventional industrial equipment, especially in steel mills, experiences significant pressure fluctuations. Consequently, the large fluctuations in the medium-pressure nitrogen at the regulator valve outlet lead to large fluctuations in the nitrogen flow rate at the oxygen compressor inlet. Therefore, domestic and international oxygen compressor manufacturers and operators design the medium-pressure nitrogen regulation value to be 500–600 kPa to maintain a stable nitrogen flow rate at both the regulator valve outlet and the oxygen compressor inlet.

[0015] During the nitrogen operation phase of the oxygen compressor startup, the design value for medium-pressure nitrogen is 500-600 kPa. When input to the oxygen compressor inlet, the design value for medium-pressure nitrogen is greater than the pressure value of the low-pressure oxygen product produced in the lower part of the upper column of the air separation unit.

[0016] When the oxygen compressor is started and operates with medium-pressure nitrogen, the inlet pressure of the oxygen compressor is greater than the design value. To prevent the inlet pressure of the oxygen compressor from increasing to the high alarm value or the high interlock shutdown value, the reflux valve of the oxygen compressor is fully closed, the opening of the inlet guide vane of the oxygen compressor is reduced, the inlet pressure value of the oxygen compressor is decreased, the actual compressed flow rate of the nitrogen at the inlet of the oxygen compressor is reduced, the operating characteristic curve of the oxygen compressor enters the unstable region, the oxygen compressor experiences a surge failure and shuts down, and the operating safety of the oxygen compressor is poor.

[0017] The following is an example illustration of the problems existing in the prior art:

[0018] I. Taking the centrifugal oxygen compressor II C40 supporting the 35000 m3 / h air separation unit as an example, see the attached drawing for illustration Figure 1 , the low-pressure nitrogen is produced from the top of the upper column of the rectification tower K01 of the air separation unit. The liquid oxygen (abbreviation: LOX) produced from the lower part of the upper column of the rectification tower K01 of the air separation unit is successively input into the liquid oxygen booster pump P01 and the liquid oxygen evaporator E04, and the low-pressure oxygen product is output. The low-pressure nitrogen and the low-pressure oxygen are heat-exchanged through the main heat exchanger E01. The low-pressure nitrogen enters the nitrogen compressor C60 through the nitrogen compressor inlet guide vane V7108, and the output medium-pressure nitrogen enters the nitrogen pipeline network. At the same time, the low-pressure oxygen enters the inlet guide vane V3302 of the oxygen compressor through the low-pressure oxygen inlet valve and is input into the oxygen compressor II C40, and the output medium-pressure oxygen enters the oxygen pipeline network; during the startup stage of the oxygen compressor II C40, it is designed to operate with low-pressure nitrogen. A branch pipe of low-pressure nitrogen is led out from the low-pressure nitrogen pipeline at the input end of the nitrogen compressor inlet guide vane V7108 and connected to the low-pressure oxygen pipeline at the input end of the inlet guide vane V3301 of the oxygen compressor. The oxygen compressor low-pressure nitrogen inlet valve V7158 and the oxygen compressor nitrogen isolation valve V7188 are successively arranged on the branch pipe from the nitrogen input direction.

[0019] The design value, low alarm value, and low interlock shutdown value of the inlet pressure of the oxygen compressor II C40 are 95 KPa, 50 KPa, and 30 KPa respectively, and the design value of the low-pressure nitrogen pressure is 10 KPa; the design value and overcurrent shutdown value of the main motor current of the oxygen compressor II C40 are 355.6 A and 385 A respectively.

[0020] The inlet pressure of the oxygen compressor II C40 is 10 KPa, which is less than the low interlock shutdown value of 30 KPa. To prevent the inlet pressure of the oxygen compressor II C40 from dropping to the low interlock shutdown value and shutting down, the opening of the reflux valve is opened to 100%, the inlet pressure value of the oxygen compressor II C40 is increased to 40 KPa, and the main motor current value of the oxygen compressor II C40 rises to 379 A, exceeding the current design value of 355.6 A, resulting in poor stability of the low-pressure nitrogen operation.

[0021] II. Taking the centrifugal oxygen compressor I C70 supporting the 35000 m3 / h air separation unit as an example, see the attached drawing for illustration Figure 2During the start-up phase of the oxygen compressor IC70, it is designed to operate using medium-pressure nitrogen. A medium-pressure nitrogen branch pipe is led out from the medium-pressure nitrogen pipeline at the outlet end of the nitrogen compressor C60 and connected to the low-pressure oxygen pipeline at the inlet guide vane V3301 of the oxygen compressor. The branch pipe is equipped with the oxygen compressor medium-pressure nitrogen inlet valve V7178 and the oxygen compressor nitrogen isolation valve V7188 in sequence from the nitrogen input direction.

[0022] The design values, high alarm values, and high interlock shutdown values ​​for the inlet pressure of oxygen compressor ICO70 are determined by the pneumatic nitrogen delivery valve. The design value for medium-pressure nitrogen regulation is 500 kPa. The inlet pressure of oxygen compressor ICO70 exceeds the high interlock shutdown value by 150 kPa. Therefore, by fully closing the oxygen compressor ICO70 reflux valve, reducing the opening of the oxygen compressor ICO70 inlet guide vane to 25%, the oxygen compressor ICO70 inlet pressure is reduced to 108 kPa, and the nitrogen flow rate of oxygen compressor ICO70 is reduced to 11000 m3 / h, causing the operating characteristic curve to enter the unstable region. To avoid surge failure and interlock shutdown during nitrogen operation of oxygen compressor ICO70, the opening of the oxygen compressor ICO70 vent valve is increased to 28%, increasing the nitrogen flow rate of oxygen compressor ICO70 to 30000 m3 / h. However, the safety of medium-pressure nitrogen operation during the startup of oxygen compressor ICO70 is poor. Utility Model Content

[0023] (a) Technical problems to be solved

[0024] To address the shortcomings of existing technologies and to solve the problem of significant deviations between the nitrogen inlet pressure and the design value of the oxygen compressor inlet pressure caused by the use of low-pressure and medium-pressure nitrogen in the nitrogen inlet process during the start-up nitrogen operation phase of the oxygen compressor, resulting in deviations from the operating conditions of the oxygen compressor, this utility model aims to ensure that the nitrogen inlet pressure reaches the design value of the oxygen compressor during the start-up nitrogen operation phase, so that the oxygen compressor operates under its design conditions during the nitrogen operation phase. At the same time, it achieves fully automatic control, ensuring the safe and stable operation of the oxygen compressor during the start-up phase.

[0025] (II) Technical Solution

[0026] To achieve the above objectives, this utility model provides the following technical solution:

[0027] This utility model discloses an air intake device for the nitrogen operation phase of an oxygen compressor startup. Based on the design values ​​of the oxygen compressor's air intake pressure and flow rate, the room-temperature nitrogen output from the liquid nitrogen vaporization equipment of the air separation unit is designed as the nitrogen source for the nitrogen operation phase of the oxygen compressor startup. By utilizing the frequency converter of the liquid nitrogen pump and the adjustment function of the pneumatic nitrogen delivery valve, the speed of the liquid nitrogen pump is changed, and the room-temperature nitrogen pressure and flow rate at the outlet of the liquid nitrogen vaporizer are adjusted to the design values ​​of the oxygen compressor's air intake pressure and flow rate and kept constant. The nitrogen is then delivered to the oxygen compressor's air intake pipeline, ensuring that the oxygen compressor operates stably under its design conditions during the nitrogen operation phase of the oxygen compressor startup.

[0028] The device of this utility model includes a room-temperature nitrogen pipeline connecting the liquid nitrogen storage tank of an air separation unit to the nitrogen pipeline network, as described in the prior art. The pipeline is sequentially connected to the liquid nitrogen storage tank, liquid nitrogen pump, liquid nitrogen vaporizer, pressure transmitter, and flow meter, as well as a nitrogen pipeline network delivery valve and a check valve on the pipeline. The technical solution of this utility model is to lead a nitrogen delivery branch pipe from the outlet end of the liquid nitrogen vaporizer of the room-temperature nitrogen pipeline, after the pressure transmitter and flow meter, and connect it to the oxygen inlet pipeline at the inlet guide vane inlet end of the oxygen compressor, replacing the original nitrogen delivery pipeline. The nitrogen delivery branch pipe is equipped with a nitrogen delivery valve and a nitrogen check valve sequentially from the nitrogen input direction, or the nitrogen isolation valve on the original nitrogen delivery pipeline is retained after the nitrogen check valve.

[0029] The liquid nitrogen vaporization equipment of the air separation unit consists of a liquid nitrogen storage tank, a liquid nitrogen pump, and a water bath or air bath vaporizer. The liquid nitrogen pump consists of a pump body and a frequency converter. The load of the liquid nitrogen pump frequency converter can be adjusted in the range of 0 to 100%. The outlet pressure and flow rate of the liquid nitrogen vaporization equipment can be adjusted to the design value range of the oxygen compressor inlet.

[0030] The diameter and pressure rating of the nitrogen delivery branch pipe for starting nitrogen operation of the oxygen compressor are the same as the diameter and pressure rating of the ambient temperature nitrogen pipeline at the outlet end of the liquid nitrogen vaporizer of the liquid nitrogen vaporization equipment.

[0031] The process of this utility model can be summarized as follows: during the nitrogen operation stage of the oxygen compressor startup, the liquid nitrogen vaporization equipment is put into operation, the liquid nitrogen pump is started, the frequency of the liquid nitrogen pump frequency converter is increased, the liquid nitrogen vaporizer is put into operation simultaneously, the low-temperature nitrogen is pressurized and vaporized to the set pressure and flow rate, the nitrogen delivery valve of the oxygen compressor is opened, and the opening degree of the nitrogen delivery valve of the oxygen compressor is finely adjusted according to the set flow rate value, so as to deliver room temperature nitrogen with constant pressure and flow rate to the oxygen compressor inlet pipe at the front end of the oxygen compressor inlet guide vane.

[0032] The nitrogen delivery valve is pneumatic. The liquid nitrogen pump frequency converter, pressure transmitter, flow meter on the ambient temperature nitrogen pipeline and the pneumatic nitrogen delivery valve on the nitrogen delivery branch pipe are electrically connected to the air separation unit DCS control system. The pressure transmitter pressure value is set to be the same as the oxygen compressor inlet pressure design value, and the flow meter setting value is the same as the oxygen compressor inlet flow design value. The frequency of the liquid nitrogen pump frequency converter is automatically adjusted according to the pressure setting value. The opening of the pneumatic nitrogen delivery valve can be finely adjusted according to the flow meter setting value to keep the nitrogen inlet pressure and flow rate in a stable state during the nitrogen operation phase of the oxygen compressor startup.

[0033] A further technical solution of this utility model is to enhance safety, by leading a nitrogen venting pipeline from the nitrogen inlet side pipeline of the nitrogen delivery branch pipe. The venting pipeline is sequentially equipped with a nitrogen venting valve and a venting silencer from the nitrogen input direction, and the nitrogen in the venting pipeline is directly discharged to the atmosphere. The nitrogen venting valve is a pneumatic venting valve. The pneumatic venting valve, pressure transmitter and air separation unit DCS control system are electrically connected, and a high pressure alarm value is set. During the nitrogen operation phase of the oxygen compressor startup, when the nitrogen pressure in the ambient temperature nitrogen pipeline reaches the high alarm value, the pneumatic nitrogen venting valve automatically opens.

[0034] This utility model provides a nitrogen intake device for the nitrogen operation phase of an oxygen compressor startup. It is designed to use constant pressure and constant flow ambient temperature nitrogen from a liquid nitrogen vaporization equipment and a variable frequency liquid nitrogen pump for boosting, and the nitrogen from the liquid nitrogen vaporizer for vaporization as the nitrogen intake source for the oxygen compressor startup. During the nitrogen operation phase of the oxygen compressor startup, it solves the problem of the oxygen compressor intake pressure not matching the design value. At the same time, DCS technology is designed as the system control technology, and the liquid nitrogen pump frequency converter is designed for automatic adjustment. The nitrogen delivery valve and vent valve are pneumatic valves for automatic adjustment, realizing fully automatic operation.

[0035] The application of this utility model significantly improves the safety and stability of the oxygen compressor during the nitrogen operation phase of startup. This utility model's technical solution can be applied to various types of oxygen compressors in different industries. Attached Figure Description

[0036] Figure 1 A schematic diagram of the low-pressure nitrogen inlet process and equipment during the start-up and nitrogen operation phase of the oxygen compressor in a 35,000 m³ / h air separation unit.

[0037] Figure 2 A schematic diagram of the medium-pressure nitrogen inlet process and equipment during the start-up and nitrogen operation phase of the oxygen compressor in a 35,000 m³ / h air separation unit.

[0038] Figure 3 This utility model provides a schematic diagram of the nitrogen intake process and device during the nitrogen operation phase of an oxygen compressor startup.

[0039] Figure 4 A schematic diagram of the control system of this utility model embodiment.

[0040] Explanation of symbols in the attached diagram: K01, distillation column; P01, liquid oxygen booster pump; E04, liquid oxygen evaporator; E01, main heat exchanger; C60, nitrogen compressor; V7168, medium-pressure nitrogen delivery valve; V7108, nitrogen compressor C60 inlet guide vane; V7158, oxygen compressor low-pressure nitrogen inlet valve; V7178, oxygen compressor medium-pressure nitrogen inlet valve; V7128, oxygen compressor low-pressure oxygen inlet valve; V7188, oxygen compressor nitrogen isolation valve; B50, liquid nitrogen storage tank; P50, liquid nitrogen pump. And its frequency converter; E50, liquid nitrogen vaporizer; P1, pressure transmitter; F1, flow meter; V7220, nitrogen pipeline delivery valve; V7221, check valve; V7222, oxygen compressor nitrogen delivery valve; V7223, oxygen compressor nitrogen check valve; W01, venting silencer; V3301, oxygen compressor I C70 inlet guide vane; C70, oxygen compressor I; C40, oxygen compressor II; V3302, oxygen compressor II C40 inlet guide vane; V7224, oxygen compressor nitrogen venting valve. Detailed Implementation

[0041] The following is in conjunction with the appendix of this utility model Figures 3-4 The technical solutions of the embodiments of this utility model will be clearly and completely described; obviously, the described embodiments are only some embodiments of this utility model, and not all embodiments.

[0042] This utility model embodiment provides a technical solution for the nitrogen intake process and device during the nitrogen operation phase of an oxygen compressor startup, specifically implemented in the nitrogen operation phase of the oxygen compressor IC70 in a 35000m3 / h air separation unit. This embodiment includes four aspects: gas source selection, pipeline and valve design and configuration, design of nitrogen intake process control logic (DCS control system) for oxygen compressor operation, and operation.

[0043] I. Gas Source Selection

[0044] The design process of this utility model embodiment is as follows: during the nitrogen start-up and nitrogen operation phase of the oxygen compressor ICO70, the nitrogen source is ambient temperature nitrogen supplied by the liquid nitrogen vaporization equipment of the 35000 m³ / h air separation unit. The liquid nitrogen vaporization equipment includes a liquid nitrogen storage tank B50, a liquid nitrogen pump and its frequency converter P50, and a liquid nitrogen vaporizer E50. Under normal operating conditions of the air separation unit, the nitrogen vaporization equipment is connected to the nitrogen pipeline network through an ambient temperature nitrogen pipeline. The ambient temperature nitrogen pipeline for liquid nitrogen vaporization is opened or closed according to production needs; the oxygen compressor ICO70 starts up with nitrogen... During operation, the liquid nitrogen in the liquid nitrogen storage tank B50 of the 35000m3 / h air separation unit is pressurized to the design pressure of 110KPa of the oxygen compressor IC70 by the frequency converter of the liquid nitrogen pump P50. It then enters the liquid nitrogen vaporizer E50 and is vaporized to the design temperature. The nitrogen is then fed into the nitrogen delivery valve V7222 through the nitrogen delivery branch pipe and adjusted to the design flow rate of 35000m3 / h. The nitrogen is then fed into the inlet end of the oxygen compressor IC70 inlet guide vane V3301, so that the nitrogen inlet pressure and flow rate of the oxygen compressor IC70 are stabilized within the design range.

[0045] The liquid nitrogen storage tank B50 of the 35000m3 / h air separation unit is designed to store 1000m3 of liquid nitrogen. Calculations show that this translates to a gaseous nitrogen storage capacity of 648 × 1000m3 = 648000m3. During the nitrogen operation phase of the oxygen compressor C70 startup, the designed nitrogen flow rate is 35000m3 / h, and the operating time is 0.25 hours. Calculations show that the nitrogen consumption during the nitrogen operation phase of the oxygen compressor C70 startup is 35000 × 0.25m3 = 8750m3. The nitrogen storage capacity of the liquid nitrogen storage tank B50 can 100% meet the nitrogen consumption during the startup of the oxygen compressor C70.

[0046] II. Piping and Valve Design and Configuration

[0047] The device of this embodiment includes an oxygen compressor IC70 and an oxygen compressor inlet guide vane V3301, a nitrogen delivery pipeline connecting the inlet end of the inlet guide vane V3301 and a nitrogen isolation valve V7188 installed on the pipeline. The device includes a room temperature nitrogen pipeline connecting the liquid nitrogen storage tank B50 of the air separation unit to the nitrogen pipeline network. The pipeline sequentially connects the liquid nitrogen storage tank B50, the liquid nitrogen pump P50 and frequency converter, the liquid nitrogen vaporizer E50, the pressure transmitter P1 and the flow meter F1, as well as a nitrogen pipeline network delivery valve V7220 and a one-way valve V7221 on the pipeline, and the outlet of the liquid nitrogen vaporizer E50. At the end, a nitrogen delivery branch pipe is led out from the pipeline after the pressure transmitter P1 and the flow meter F1, and connected to the oxygen inlet pipeline at the inlet guide vane V3301 of the oxygen compressor. The branch pipe is equipped with a nitrogen delivery valve V7222, a nitrogen check valve V7223 and a nitrogen isolation valve V7188 in sequence from the nitrogen input direction. At the same time, a vent pipe is led out from the pipeline at the input end of the nitrogen delivery valve V7222 to the atmosphere. A nitrogen vent valve V7224 and a vent silencer W01 are installed in sequence along the nitrogen input direction on the vent pipe.

[0048] The liquid nitrogen pump P50 is designed as a centrifugal type with frequency converter regulation. The outlet working pressure and flow rate are 20~2000KPa and 1000~35000m3 / h, respectively. The P50 liquid nitrogen pump frequency converter automatically adjusts the outlet working pressure and flow rate.

[0049] The E50 liquid nitrogen vaporizer is designed as a water bath type, with a design working pressure and flow rate of 0~2000KPa and 0~35000m3 / h, respectively, which meets the nitrogen pressure and flow rate requirements for the start-up nitrogen operation of the oxygen compressor IC70.

[0050] The pressure transmitter P1 and flow meter F1 of the liquid nitrogen vaporization equipment are designed to be electrically connected to the DCS control system of the 35000 m³ / h air separation unit. The pressure transmitter P1 operates at a pressure of 0–2500 kPa, and the flow meter F1 operates at a flow rate of 0–40000 m³ / h, meeting the requirements for continuous online monitoring of nitrogen pressure and flow rate during nitrogen operation of the oxygen compressor C70. The design incorporates 20mA signals from the pressure transmitter P1 and flow meter F1 to the DCS control system of the 35000 m³ / h air separation unit. The flow meter F1 is designed as an orifice plate type. The nitrogen vent valve V7224 of the oxygen compressor C70 is also electrically connected to the DCS control system. When the pressure transmitter P1 reading rises to the high alarm value of 120 kPa, the nitrogen vent valve V7224 automatically opens to prevent the inlet pressure of the oxygen compressor C70 from exceeding the high alarm value during nitrogen startup.

[0051] Based on actual calculations and several field tests, the diameter, pressure, and material of the nitrogen delivery pipeline and nitrogen venting pipeline for the start-up nitrogen operation of the oxygen compressor IC70 are the same as those of the ambient temperature nitrogen pipeline at the outlet of the liquid nitrogen vaporizer E50 in the liquid nitrogen vaporization equipment, which are 300mm, 25MPa, and 304 stainless steel, respectively. The nitrogen delivery valve V7222 of the oxygen compressor IC70 is designed with the same valve diameter as the nitrogen delivery pipeline, both being 300mm, to meet the design flow regulation. The nitrogen delivery valve V7222 is selected as a pneumatic single-seat sleeve ambient temperature regulating valve with an air-to-open diaphragm actuator. The nitrogen delivery valve V7222 automatically adjusts the valve opening based on the flow meter F1 display value, maintaining the nitrogen intake flow rate of the oxygen compressor IC70 at the design value of 35000m³ / h during the start-up nitrogen operation phase. The nitrogen vent valve V7224 installed on the vent pipeline is a pneumatic multi-hole sleeve speed-controlled ambient temperature regulating valve with an air-to-close diaphragm actuator. Its valve diameter is the same as that of the nitrogen delivery valve V7222 of the oxygen compressor IC70, both being 300mm, to meet the design vent flow rate of 35000m³ / h.

[0052] 3. Design the nitrogen intake process control logic for the oxygen compressor, i.e., the DCS control system.

[0053] In the DCS control system of the 35000m3 / h air separation unit, three control logics for automatic nitrogen operation, regulation, and shutdown are added to the nitrogen operation starting of the oxygen compressor IC70.

[0054] When the oxygen compressor IC70 starts, the liquid nitrogen pump P50 will automatically start and coast at low speed when the signals of the nitrogen isolation valve V7188 being fully open and the oxygen inlet valve V7128 being fully closed are met simultaneously.

[0055] When the motor operating signal of oxygen compressor IC70 is normal, liquid nitrogen pump P50 automatically loads and nitrogen delivery valve V7222 automatically opens; simultaneously, oxygen compressor C70 inlet guide vane V3301 automatically opens, and the oxygen compressor IC70 inlet pressure and flow rate reach the set values ​​of 108KPa and 35000m3 / h, respectively.

[0056] When the signals of nitrogen isolation valve V7188 of oxygen compressor IC70 being fully closed and oxygen inlet valve V7128 being fully open are simultaneously met, liquid nitrogen pump P50 will automatically stop, and the liquid nitrogen vaporization equipment will shut down.

[0057] IV. Operating Method

[0058] First, in the DCS control system operation station of the 35000m3 / h air separation unit, put the nitrogen pipeline delivery valve V7220 into the fully closed state, and put the oxygen compressor nitrogen vent valve V7224 into the closed state.

[0059] Next, the oxygen compressor IC70 is started. The nitrogen isolation valve V7188 of the oxygen compressor IC70 automatically opens fully, the oxygen inlet valve V7128 automatically closes fully, the liquid nitrogen pump P50 starts automatically, the speed of the liquid nitrogen pump P50 increases to 100 r / min, and 20 seconds after the liquid nitrogen pump P50 starts automatically, the oxygen compressor IC70 starts automatically. After the oxygen compressor IC70 starts, the motor runs for 60 seconds, the motor running signal changes to a green normal operation signal, the liquid nitrogen pump P50 automatically loads to the design range of 3200 r / min, and the nitrogen delivery valve V7222 automatically opens to 70% of the design range.

[0060] Simultaneously, the inlet guide vane V3301 of the oxygen compressor IC70 automatically opens to 50% of the design range, maintaining the oxygen compressor IC70's inlet pressure and flow rate at the set values ​​of 108 kPa and 35,000 m³ / h.

[0061] Finally, after 900 seconds of nitrogen operation in oxygen compressor IC70, the nitrogen isolation valve V7188 of oxygen compressor IC70 automatically closes completely, the oxygen inlet valve V7128 automatically opens completely, the liquid nitrogen pump P50 automatically stops, the nitrogen delivery valve V7222 automatically closes completely, the liquid nitrogen vaporization equipment stops, the nitrogen operation phase of oxygen compressor IC70 ends, and the oxygen purification phase begins.

Claims

1. An air intake device for the nitrogen operation phase of an oxygen compressor startup, comprising an oxygen compressor and an oxygen compressor inlet guide vane, a nitrogen delivery pipeline connected to the inlet end of the oxygen compressor inlet guide vane and a nitrogen isolation valve installed on the pipeline, and further comprising a liquid nitrogen vaporization device and delivery pipeline for an air separation unit, wherein the liquid nitrogen vaporization device and delivery pipeline comprises a room temperature nitrogen pipeline connecting a liquid nitrogen storage tank to a nitrogen pipeline network, the pipeline sequentially connecting a liquid nitrogen storage tank, a liquid nitrogen pump and its frequency converter, a liquid nitrogen vaporizer, a pressure transmitter and a flow meter, and a nitrogen pipeline network delivery valve and a check valve on the pipeline, characterized in that... The device includes a nitrogen delivery branch pipe extending from the outlet end of the liquid nitrogen vaporizer of the ambient temperature nitrogen pipeline, after the pressure transmitter and flow meter, and connecting to the oxygen inlet pipeline at the inlet guide vane of the oxygen compressor, replacing the original nitrogen delivery pipeline. The nitrogen delivery branch pipe is equipped with a nitrogen delivery valve and a nitrogen check valve in sequence from the nitrogen input direction, or the nitrogen isolation valve on the original nitrogen delivery pipeline is retained after the nitrogen check valve.

2. The air intake device for the nitrogen operation phase of an oxygen compressor startup according to claim 1, characterized in that: The nitrogen delivery branch pipe leads out a nitrogen vent pipe from the nitrogen pipeline on the inlet side of the nitrogen delivery valve. The nitrogen vent pipe is equipped with a nitrogen vent valve and a vent silencer in sequence from the nitrogen input direction. The nitrogen in the vent pipe is directly discharged into the atmosphere.

3. The air intake device for the nitrogen operation phase of an oxygen compressor according to claim 1, characterized in that: The nitrogen delivery valve is pneumatic, and the liquid nitrogen pump frequency converter, pressure transmitter, flow meter on the ambient temperature nitrogen pipeline and the pneumatic nitrogen delivery valve on the nitrogen delivery branch pipe are electrically connected to the air separation unit DCS control system.

4. The air intake device for the nitrogen operation phase of an oxygen compressor according to claim 2, characterized in that: The nitrogen vent valve is a pneumatic vent valve, and the pneumatic vent valve, pressure transmitter and air separation unit DCS control system are electrically connected.

Images