A nitrogen emission recovery device for an oxygen compressor seal

Abstract

This invention relates to a device for recovering sealed nitrogen emissions from an oxygen compressor. An additional sealed nitrogen emission recovery pipeline is added to the original oxygen compressor sealed nitrogen emission pipeline to recover and transport the sealed nitrogen emitted from the oxygen compressor to the bottom of a water cooling tower. Specifically, a sealed nitrogen emission recovery pipeline is led out from the oxygen compressor sealed nitrogen emission pipeline after the online oxygen analyzer and before the sealed nitrogen emission valve, and connected to the water cooling tower purging pipeline before the water cooling tower purging valve. A sealed nitrogen emission recovery conveying valve and a sealed nitrogen emission recovery check valve are sequentially installed on the sealed nitrogen emission recovery pipeline according to the direction of sealed nitrogen emission. This invention recovers and utilizes the sealed nitrogen from the oxygen compressor that is directly discharged into the atmosphere, achieving zero emission of sealed nitrogen and realizing the goals of energy conservation, environmental protection, carbon emission reduction, cost reduction, and efficiency improvement.

Description

Technical Field

[0001] This utility model belongs to the field of deep refrigeration air separation, and particularly relates to the sealed nitrogen system of oxygen compressor in this field. Background Technology

[0002] Deep refrigeration air separation equipment (hereinafter referred to as air separation equipment) uses the principle of low temperature distillation to simultaneously produce oxygen and nitrogen. The principle of low temperature distillation is to input the raw material air into the low temperature distillation column, and in the low temperature distillation column, through heat and mass exchange of rising vapor and reflux liquid, the oxygen and nitrogen in the raw material air are separated by taking advantage of the different boiling points of oxygen and nitrogen in the raw material air, and low temperature gaseous and liquid oxygen and nitrogen products are extracted.

[0003] The air separation unit consists of a product production system, an ambient temperature gas product compression and conveying system, and a cryogenic liquid product storage and vaporization system. The product production system consists of an air compressor, an air pre-cooling and purification device, a refrigeration device, a heat exchange device, and a distillation device. The air pre-cooling and purification device consists of an air cooling tower, a water cooling tower, and a process water pump. The ambient temperature gas product compression and conveying system consists of an oxygen compressor and a nitrogen compressor. The cryogenic liquid product storage and vaporization system consists of a liquid oxygen and liquid nitrogen storage tank and a liquid oxygen and liquid nitrogen vaporization device.

[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, and then loaded into liquid oxygen and liquid nitrogen tank trucks for sale. Alternatively, they are filled into liquid oxygen and liquid nitrogen vaporization devices, pressurized by low-temperature liquid oxygen pumps and liquid nitrogen pumps, vaporized and heated to room temperature in water bath or air bath vaporizers, and then delivered to the user's oxygen and nitrogen pipeline network.

[0005] The oxygen compressor consists of a rotor, stator, sealing gas, lubricating oil, and cooling system (see [link]). Figure 1 The oxygen compressor shaft seal is a labyrinth seal, consisting of a sealing gas chamber, a mixing gas chamber, and an oxygen chamber. The pressure in each chamber decreases in stages, creating a stepped differential pressure. Sealing gas enters the sealing gas chamber of the labyrinth seal, where the pressure is higher than that of the oxygen chamber, forming a gas seal to prevent oxygen leakage and isolate external air or lubricating oil from seeping in. Simultaneously, sealing gas enters the mixing gas chamber of the labyrinth seal for safe venting to the atmosphere. Sealing gas is also introduced into the oxygen compressor bearing housing, isolating lubricating oil vapor from oxygen, and then safely venting to the atmosphere through the isolation chamber.

[0006] Existing oxygen compressor sealing nitrogen venting processes all involve venting to the atmosphere, regulated by a control valve, to release the sealing nitrogen entering the oxygen compressor shaft seal and bearing housing into the atmosphere (see...). Figure 2Directly discharging pollutants into the atmosphere presents the following problems that need to be addressed:

[0007] 1. Under stable operating conditions, the oxygen compressor discharges sealed nitrogen gas with low oxygen content, typically less than 1%, without grease, and with a low dew point. Direct discharge wastes a lot of energy.

[0008] 2. When the oxygen compressor is operating stably, sealed nitrogen is discharged into the atmosphere. The area around the sealed nitrogen discharge port has low oxygen content and high noise, posing safety hazards for operators during equipment inspections.

[0009] Measurements showed that the oxygen content in the atmosphere surrounding the sealed nitrogen emission port area of ​​the oxygen compressor C70 was less than 19.8% and the noise level was greater than 95 decibels. Prolonged stays in such areas may affect personnel safety and health. Utility Model Content

[0010] (a) Technical problems to be solved

[0011] To address the shortcomings of existing technologies, this utility model provides a solution for recovering and utilizing sealed nitrogen from oxygen compressors that are directly discharged into the atmosphere, thereby achieving zero emissions of sealed nitrogen and realizing the goals of energy conservation, environmental protection, carbon emission reduction, cost reduction, and efficiency improvement.

[0012] (II) Technical Solution

[0013] To achieve the above objectives, this utility model provides the following technical solution:

[0014] This utility model discloses a sealed nitrogen emission recovery device for an oxygen compressor. The device includes an oxygen compressor, a sealed nitrogen inlet manifold, and a sealed nitrogen inlet valve installed thereon. The outlet of the sealed nitrogen inlet valve is connected to the oxygen compressor. It also includes a sealed nitrogen emission pipeline for the oxygen compressor, and a sealed nitrogen online oxygen analyzer and a sealed nitrogen emission valve sequentially arranged in the nitrogen emission direction. The sealed nitrogen emission valve is followed by atmospheric air. Furthermore, it includes a water-cooled tower for an air separation unit, a water-cooled tower purge pipe connected to the side of the water-cooled tower, and a purge valve installed thereon. The purge valve is followed by atmospheric air. This utility model adds a sealed nitrogen emission recovery pipeline to the original sealed nitrogen emission pipeline of the oxygen compressor, recovering and transporting the sealed nitrogen emitted by the oxygen compressor to the bottom of the water-cooled tower. Through heat exchange between the sealed nitrogen and the sensible and latent heat of the circulating cooling water, the temperature of the circulating cooling water is reduced.

[0015] This utility model device extends a sealed nitrogen emission recovery pipeline from the sealed nitrogen emission pipeline of the oxygen compressor after the sealed nitrogen online oxygen analyzer and before the sealed nitrogen emission valve. The sealed nitrogen emission recovery pipeline is connected to the water cooling tower purging pipeline before the water cooling tower purging valve. A sealed nitrogen emission recovery delivery valve and a sealed nitrogen emission recovery check valve are sequentially installed on the sealed nitrogen emission recovery pipeline according to the sealed nitrogen emission direction.

[0016] A further technical solution of this utility model is that the sealed nitrogen emission recovery and delivery valve is an air-opening, room-temperature, single-seat regulating valve, and the sealed nitrogen emission recovery one-way valve is a spring-loaded check valve.

[0017] A further technical solution of this utility model is to add a sealed nitrogen emission recovery and delivery valve to the air separation equipment DCS control system, which is linked with the sealed nitrogen emission valve and the sealed nitrogen online oxygen analyzer to automatically adjust the start-up, operation and shutdown of the sealed nitrogen emission recovery device.

[0018] The design principle of this utility model is as follows: The water cooling tower for air separation equipment (hereinafter referred to as the water cooling tower) is a cylindrical tower structure with a water-gas separator at the top, connecting it to the atmosphere. The water cooling tower contains either random or structured packing. Atmospheric temperature circulating water is sprayed down from the top of the tower, while 10-15 kPa waste nitrogen gas extracted from the cold box of the air separation equipment enters from the bottom of the tower, forming a counter-current contact on the surface of the packing. Due to its unsaturated nature, the waste nitrogen gas absorbs moisture, exchanging heat through sensible and latent heat. The temperature of the atmospheric temperature circulating water drops to a low-temperature cooling water level of no more than 15°C. This low-temperature cooling water is then pressurized by a low-temperature cooling water pump and transported to the air cooling tower to cool the raw material air. After passing through the water-gas separator at the top of the tower, some water droplets in the waste nitrogen gas are recovered and discharged into the atmosphere.

[0019] Under stable operating conditions, measurements taken using an online dew point analyzer, an online oxygen analyzer, an online pressure transmitter, and an offline grease analyzer in the sealed nitrogen discharge pipeline show that the nitrogen-oxygen content in the sealed nitrogen discharge pipeline is less than 2%, the dew point is less than -85℃, the pressure is 20-25 kPa, and there is no grease.

[0020] Under stable operating conditions, the online dew point analyzer, online oxygen analyzer, and offline grease analyzer measure the waste nitrogen gas extracted from the cold box of the air separation unit. The waste nitrogen gas has an oxygen content of less than 2%, a dew point of less than -85℃, and no grease.

[0021] Therefore, based on the existing technology of the structure and process characteristics of the water-cooled tower equipment in air separation equipment, and a comparison of the technical parameters of waste nitrogen and sealed nitrogen, it was determined that the sealed nitrogen of the oxygen compressor can be completely recovered and reused, and the recovered nitrogen is fed into the water-cooled tower to cool the ambient temperature circulating water.

[0022] In the DCS control system of the air separation unit, design the control logic for the automatic start-up and shutdown of the nitrogen emission recovery device for the oxygen compressor seal.

[0023] Firstly, the automatic operation control logic. When the oxygen compressor starts, the inlet valve of the sealed nitrogen inlet main opens, and simultaneously the delivery valve on the sealed nitrogen exhaust and recovery pipeline automatically opens, while the exhaust valve on the sealed nitrogen exhaust pipeline automatically closes, and the water-cooled tower purge valve remains fully closed. During oxygen compressor operation, if the sealed nitrogen online oxygen analyzer AI1 indicates an oxygen content exceeding 2%, the delivery valve on the sealed nitrogen exhaust and recovery pipeline closes, and the exhaust valve opens.

[0024] Secondly, the automatic shutdown control logic. When the oxygen compressor stops, the delivery valve on the sealed nitrogen emission and recovery pipeline automatically closes after one hour of the oxygen compressor motor shutdown feedback timer.

[0025] This utility model provides a solution for recovering and utilizing sealed nitrogen from oxygen compressors that are directly discharged into the atmosphere, achieving zero emissions of sealed nitrogen and realizing the goals of energy conservation, environmental protection, carbon emission reduction, cost reduction and efficiency improvement. It can be applied to similar processes in the air separation industry. This solution has low investment costs, is easy to implement, and has significant application effects. Attached Figure Description

[0026] Figure 1 Schematic diagram of the nitrogen labyrinth seal structure of the centrifugal oxygen compressor in an air separation unit.

[0027] Figure 2 Schematic diagram of the C70 sealed nitrogen system of the oxygen compressor in the 35000m3 / h air separation unit of Maanshan Iron & Steel.

[0028] Figure 3 This utility model provides a schematic diagram of a nitrogen emission recovery device for an oxygen compressor seal.

[0029] Figure 4 This utility model provides a simplified diagram of the automatic start-up and adjustment logic control for an oxygen compressor sealing nitrogen emission recovery device.

[0030] Figure 5 A simplified diagram of the automatic shutdown logic control applied to the exhaust process in this embodiment of the utility model.

[0031] Figure 1 Explanation of symbols in the attached diagram: Y1, centrifugal oxygen compressor impeller; M2, labyrinth seal oxygen chamber; M3, labyrinth seal mixed gas chamber; M4, labyrinth seal sealed gas chamber; V1, sealed nitrogen inlet valve; V2, sealed nitrogen exhaust valve; M5, isolation chamber; Z6, bearing housing.

[0032] Figure 2Explanation of symbols in the attached diagram: C70, oxygen compressor; C60, nitrogen compressor; AI2, online nitrogen dew point analyzer; V820, nitrogen compressor C60 check valve; V809, medium-pressure nitrogen pipeline delivery valve; V810, medium-pressure nitrogen pipeline check valve; V819, nitrogen delivery valve; V801, sealed nitrogen pressure reducing valve; V802, sealed nitrogen main inlet valve; AI1, sealed nitrogen online oxygen analyzer; V803, sealed nitrogen exhaust valve.

[0033] Figure 3 Explanation of symbols in the attached diagram: B06, water-cooled tower; C70, oxygen compressor; L4, sealed nitrogen discharge pipeline of oxygen compressor; AI1, sealed nitrogen online oxygen analyzer; V803, sealed nitrogen discharge valve; L5, sealed nitrogen inlet main of oxygen compressor; V802, inlet valve of sealed nitrogen inlet main; L7, water-cooled tower purging pipeline; V815, water-cooled tower purging valve; L8, sealed nitrogen discharge and recovery pipeline; V813, sealed nitrogen discharge and recovery conveying valve; V814, sealed nitrogen discharge and recovery check valve.

[0034] Figure 4 , Figure 5 The attached diagram illustrates the following: AUTO ON means automatic start; AUTO STOP means automatic stop; PV: pressure setpoint; 0 indicates off, and 1 indicates on. Detailed Implementation

[0035] The following is in conjunction with the appendix of this utility model Figures 3-5 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.

[0036] This utility model embodiment describes a process and device for recovering sealed nitrogen emissions from the C70 oxygen compressor in a 35,000 m³ / h air separation unit. This utility model embodiment includes three aspects: the design of the C70 sealed nitrogen emission recovery process, the configuration of pipelines, valves, and instruments, and the control logic (DCS control system) and operation of the C70 sealed nitrogen system.

[0037] 1. C70 Oxygen Compressor Sealed Nitrogen Emission Recovery Process:

[0038] An additional oxygen compressor sealed nitrogen discharge recovery pipeline L8 is added to the oxygen compressor sealed nitrogen discharge pipeline L4 to recover and transport the sealed nitrogen discharged from the oxygen compressor to the bottom of the water cooling tower E06. The temperature of the circulating cooling water is reduced through heat exchange between the sealed nitrogen and the sensible and latent heat of the circulating cooling water, with the latent heat heat exchange accounting for the majority of the energy.

[0039] For example, the centrifugal oxygen compressor C70 supporting the 35,000 m3 / h air separation unit of Magang was designed and manufactured by Hangyang of China. The design pressure and flow rate of the main supply pipe L5 of the sealing nitrogen gas for the oxygen compressor C70 are 450 KPa and 500 m3 / h respectively, and the design pressure and flow rate of the sealing nitrogen gas discharge pipe L4 are 20 KPa and 500 m3 / h respectively.

[0040] The oxygen compressor C70 operates 8,500 hours per year on average. The total annual discharge of the sealing nitrogen gas is 8,500×500 m3 = 4.25 million m3, and this part of the energy consumption increases the operating cost of the oxygen of the oxygen compressor C70. The average discharge pressure and temperature at the outlet of the sealing nitrogen gas discharge pipe L4 are 20 KPa and 30 °C respectively, the dew point is -85 °C, and the relative humidity is 0%. If recycled and utilized, it can be used to absorb the latent heat of vaporization of the cooling water in the air separation process, reduce the cooling water temperature, recover energy, and reduce the operating cost of the oxygen compressor C70. Since the temperature difference between the recycled sealing nitrogen gas and the cooling water temperature is not large, the following mainly calculates the theoretical heat value of the latent heat heat exchange recovery.

[0041] Known conditions: nitrogen gas volume V = 4,250,000 m3; discharge pressure P = 20 kPa = 20,000 Pa, temperature T = 30 °C = 273.15 + 30 = 303.15 K; relative humidity 0% (dry nitrogen gas).

[0042] Calculation step 1: Calculate the mass mN2 of nitrogen gas

[0043] Use the ideal gas state equation PV = nRT, where: R = 8.314 J / (mol·K)

[0044] The molar mass of nitrogen gas MN2 = 28 g / mol = 0.028 kg / mol

[0045] n = PV / RT = 20,000×4,250,000 / 8.314×303.15 ≈ 33,700,000 mol

[0046] mN_{₂}=n×MN_{₂}=33,700,000×0.028≈943,600 kg

[0047] Calculation step two: Calculate the heat Q absorbed by nitrogen gas

[0048] Set the temperature increase of nitrogen gas ΔT = 10 °C

[0049] The specific heat capacity at constant pressure of nitrogen gas cp ≈ 1.04 kJ / (kg·K)

[0050] Q = mN_{₂}×cp×ΔT = 943,600×1.04×10 ≈ 9,810,000 kJ

[0051] The total heat Q absorbed by nitrogen gas ≈ 9,810,000 kJ

[0052] Conclusion: The theoretical average annual heat absorption capacity of the sealed nitrogen gas emitted by the oxygen compressor C70 is 9,810,000 kJ / year.

[0053] 2. Configuration of piping, valves, and instruments for the C70 oxygen compressor sealed nitrogen emission recovery device:

[0054] Based on actual calculations and several on-site tests, the diameter, pressure, and material of the sealed nitrogen emission and recovery pipeline for the C70 oxygen compressor are 100mm, 3.1MPa, and 304 stainless steel, respectively.

[0055] A sealed nitrogen emission recovery delivery valve V813 and a sealed nitrogen emission recovery check valve V814 are installed sequentially at the inlet and outlet ends of the sealed nitrogen emission recovery pipeline of the oxygen compressor C70. The sealed nitrogen emission recovery delivery valve V813 is an air-opening diaphragm type room temperature single-seat regulating valve with a valve diameter of 100mm, and the sealed nitrogen emission recovery check valve V814 is a spring-loaded check valve with a valve diameter of 100mm.

[0056] The sealed nitrogen emission recovery and delivery valve V813, the sealed nitrogen emission recovery check valve V814, the sealed nitrogen emission valve V803, and the online oxygen analyzer AI1 are electrically connected to the air separation equipment DCS control system.

[0057] 3. Control logic of the sealed nitrogen system for the C70 oxygen compressor (DCS control system):

[0058] In the DCS control system of the 35000m3 / h air separation unit, design the control logic for the automatic start-up and shutdown of the sealed nitrogen emission recovery device of the oxygen compressor C70.

[0059] Firstly, the automatic operation control logic. When oxygen compressor C70 starts, simultaneously with the opening of inlet valve V802 on the sealed nitrogen inlet main L5, the delivery valve V813 on the sealed nitrogen exhaust recovery pipeline L8 automatically opens, and the exhaust valve V803 on the sealed nitrogen exhaust pipeline L4 automatically closes. The purge valve V815 on the water-cooled tower E06 remains fully closed. When oxygen compressor C70 is running, if the online oxygen analyzer AI1 indicates an oxygen content exceeding 2%, the delivery valve V813 on the sealed nitrogen exhaust recovery pipeline L8 closes, and the exhaust valve V803 opens.

[0060] Secondly, the automatic shutdown control logic. When oxygen compressor C70 stops, and the oxygen compressor motor shutdown feedback timer reaches 1 hour, the delivery valve V813 on the sealed nitrogen emission and recovery pipeline L8 automatically closes completely.

Claims

1. A sealed nitrogen emission recovery device for an oxygen compressor, comprising an oxygen compressor, a sealed nitrogen inlet manifold, and a sealed nitrogen inlet manifold inlet valve disposed thereon, the outlet of the sealed nitrogen inlet manifold inlet valve being connected to the oxygen compressor; further comprising a sealed nitrogen emission pipe for the oxygen compressor, and a sealed nitrogen online oxygen analyzer and a sealed nitrogen emission valve disposed thereon in sequence according to the nitrogen emission direction, the sealed nitrogen emission valve being connected to the atmosphere; additionally comprising a water-cooled tower for an air separation unit, a water-cooled tower purge pipe connected to the side of the water-cooled tower, and a purge valve disposed thereon, the purge valve being connected to the atmosphere; characterized in that: A sealed nitrogen emission recovery pipeline is led out from the sealed nitrogen emission pipeline of the oxygen compressor before the sealed nitrogen emission valve, after the sealed nitrogen online oxygen analyzer. The sealed nitrogen emission recovery pipeline is connected to the water cooling tower purging pipeline before the water cooling tower purging valve. A sealed nitrogen emission recovery delivery valve and a sealed nitrogen emission recovery check valve are sequentially installed on the sealed nitrogen emission recovery pipeline according to the sealed nitrogen emission direction.

2. The oxygen compressor sealing nitrogen emission recovery device according to claim 1, characterized in that: The sealed nitrogen emission recovery and delivery valve is an air-opening, ambient temperature, single-seat regulating valve, and the sealed nitrogen emission recovery check valve is a spring-loaded check valve.

3. The oxygen compressor sealing nitrogen emission recovery device according to claim 2, characterized in that: A sealed nitrogen emission recovery and delivery valve is added and connected to the air separation equipment DCS control system. It is linked with the sealed nitrogen emission valve and the sealed nitrogen online oxygen analyzer to automatically adjust the start-up, operation and shutdown of the sealed nitrogen emission recovery device.

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