System for providing cooling capacity for deep cooling air separation system

Abstract

The utility model discloses a system for providing cooling capacity for a deep cooling air separation system, which comprises a main heat exchanger, a rectifying tower system and an expansion supercharger, and further comprises a liquid level sensor for monitoring the liquid level height in the rectifying tower system, a freezing liquid controller, a freezing liquid control valve and a freezing liquid source, and a rotating shaft for connecting the expansion end and the pressurization end of the expansion supercharger is not braked by oil. The liquid level sensor monitors the height of the liquid level in the rectifying tower system and transmits a measurement result to the freezing liquid controller, and when the height of the liquid level is lower than a set value, the freezing liquid controller increases the opening degree of the freezing liquid control valve, so that the freezing liquid flows into the rectifying tower system from the freezing liquid source.

Description

Technical Field

[0001] This utility model relates to a system for providing cooling capacity to a cryogenic air separation system, and more specifically to a system that does not use oil braking in the expansion compressor of a cryogenic air separation system. Background Technology

[0002] Cryogenic air separation is a primary method for obtaining large quantities of nitrogen, oxygen, and certain inert gases in industry. Ambient temperature feed air is compressed, pre-cooled, and purified, then liquefied in the main heat exchanger and fed into a distillation column system in liquid form. After distillation, nitrogen is obtained at the top of the column, and oxygen-enriched liquid air with increased oxygen content is obtained at the bottom. Due to heat exchange with the external environment, the cryogenic air separation system inevitably experiences cooling losses during operation. To compensate for these losses, those skilled in the art often use expanders for refrigeration. The work generated by the expander can be used to drive a motor or air compressor. An expander-boost compressor is a typical device that uses the work done by expansion at the expansion end to drive the boosting end via a rotating shaft. If energy losses during friction are disregarded, according to the principle of energy conservation, the cooling and heating introduced into the cryogenic air separation unit by the cooling stream after expansion and the heating stream after boosting cancel each other out. Therefore, other measures must be used to remove the work done by the expander from the cryogenic air separation unit to achieve the effect of supplementing the cooling capacity with the expander.

[0003] In expander compressors, hydraulic braking of the rotating shaft connecting the expansion and pressurization ends is a common method for dissipating the work done by the expander. US 2023 / 0341181A1 discloses a nitrogen generator that uses hydraulic braking of the expander compressor's rotating shaft, including a rotary control box for controlling the shaft's rotational speed. It also includes a pressure measuring unit for measuring the internal pressure of the distillation column and an optimized rotational speed calculation instruction unit for receiving the pressure measurement results. This optimized rotational speed calculation instruction unit applies the calculated optimal rotational speed to the rotating shaft via the rotary control box, ensuring that the rotary compressor maintains high operating efficiency regardless of pressure changes in the nitrogen products from the distillation column.

[0004] Taking the above-mentioned example, existing hydraulic braking technology requires a relatively complex set of equipment, resulting in high investment and operating costs. Industry professionals urgently need a new method to ensure sufficient cooling for cryogenic air separation equipment, especially distillation column systems, when using expander compressors. Utility Model Content

[0005] The purpose of this invention is to improve upon the existing technology of using oil braking to dissipate the work done by the expander, and to provide cooling capacity to cryogenic air separation systems that use expander boosters in a simpler and more economical way.

[0006] On one hand, the cryogenic air separation system includes a main heat exchanger, a distillation column system and an expansion booster, as well as a level sensor for monitoring the liquid level in the distillation column system, a cryogenic liquid controller, a cryogenic liquid control valve and a cryogenic liquid source; the rotating shaft connecting the expansion end and the booster end of the expansion booster does not use oil braking.

[0007] Furthermore, the level sensor monitors the height of the liquid level in the distillation column system and transmits the measurement results to the refrigeration liquid controller. When the liquid level is lower than a set value, the refrigeration liquid controller increases the opening of the refrigeration liquid control valve, so that the refrigeration liquid flows from the refrigeration liquid source into the distillation column system.

[0008] Furthermore, the cryogenic liquid includes liquid nitrogen, and the cryogenic liquid source includes piping networks and / or storage tanks; or, the cryogenic liquid includes liquefied air.

[0009] Furthermore, the rotating shaft of the expander compressor is oil-lubricated. Preferably, oil lubrication is provided through an oil lubrication tank, a lubricating oil supply unit, and a lubricating oil reservoir.

[0010] Compared with the prior art, the technical solution provided by this utility model has the following advantages:

[0011] 1. Make full use of readily available cryogenic liquid resources and replenish the required cooling capacity of the cryogenic air separation system as needed;

[0012] 2. By limiting the function of oil to lubrication, the size and investment of related equipment are reduced. Attached Figure Description

[0013] The advantages and spirit of this utility model can be further understood through the following detailed description and accompanying drawings. Those skilled in the art will know that the accompanying drawings and embodiments do not impose any limitations on this utility model.

[0014] Figure 1 This is a flowchart of Example 1;

[0015] Figure 1 In the middle: 1-Distillation column system; 2-Main heat exchanger; 3-Expansion end of expander and booster; 4-Pressure end of expander and booster; 5-Rotating shaft; 6-Oil lubrication tank; 7-Lubricating oil supply unit; 8-Lubricating oil storage tank; 9-Level sensor; 10-Refrigerated liquid controller; 11-Refrigerated liquid control valve; 12-Lubricating oil control valve; 20-Feed air; 21-Return stream. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this utility model clearer, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this utility model. Based on the embodiments of this utility model, all other implementation methods obtained by those skilled in the art without creative effort are within the protection scope of this utility model.

[0017] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly" and "connection" refer to forming a component that seals against fluids such as liquids and gases by connecting two or more parts. Assembly and connection methods include welding, flange connection, bolting, bonding, or integral molding, with bonding or integral molding being preferred. The terms "connected" and "connected" refer to a state between two or more parts where fluids such as liquids and gases can flow.

[0018] The terms "downstream" and "upstream" refer to the direction of liquid or gas flow. The process of liquid or gas flowing from the inlet to the outlet is the process of flowing from upstream to downstream.

[0019] Furthermore, qualifiers such as "one" appearing in this document do not refer to a quantity limitation, but rather describe technical features not mentioned previously. Similarly, unless a noun is modified by a specific quantifier, it should be considered in this document as including both singular and plural forms; the technical solution may include either a singular or plural number of the technical feature.

[0020] It should be understood that in this utility model, "at least one (item)" refers to one or more, and "more than one" refers to two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and A and B exist simultaneously, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one (item) of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0021] The cryogenic air separation system in the present utility model refers to the combination of all equipment that can deeply cool and liquefy the feed air at normal temperature and pressure and separate it into components such as nitrogen and / or oxygen through rectification. For example, "Principles of Refrigeration and Cryogenic Technology" (edited by Wu Xingye et al.) discloses the basic principles, common processes and equipment of cryogenic air separation. Generally speaking, the cryogenic air separation system includes, but is not limited to, the main air compressor and pre-cooling and purification system for pressurizing, pre-cooling and purifying the feed air; the main heat exchanger for cooling and liquefying the feed air and the rectification tower system for rectifying and separating the liquefied air. The rectification tower system can include either a single tower or a double tower thermally connected through a condensing evaporator. The cold stream in the main heat exchanger can be the return stream from the rectification tower.

[0022] Since the operating temperature of the cryogenic process is between -150°C and -180°C, even with a cold box, it is still inevitable to have cold loss caused by heat exchange with the external environment. Therefore, in the cryogenic process, a combination of a booster and an expander is often used to continuously supplement cold to the cryogenic air separation system. The expansion booster has an expansion end and a booster end connected by a rotating shaft. The expansion end expands and cools the gas stream and does work; this part of the work drives the booster end through the rotating shaft, and the booster end compresses and heats the gas stream. The streams after expansion or compression generally return to the main heat exchanger or the rectification tower system. In addition to the energy loss caused by mechanical friction, the work done by the expander also needs to be taken out of the cryogenic air separation system in other ways. A common way is oil braking.

[0023] Oil braking is achieved by applying oil pressure to the rotating shaft, thereby changing the rotational speed of the rotating shaft. The oil pressure can be adjusted by the flow rate of the oil. The equipment required for oil braking at least includes an oil storage tank, an oil cooler, an oil pump, an oil pressure sensor, an oil quantity controller and an oil quantity control valve, etc. These equipment occupy a large area and require a不菲 investment.

[0024] The oil lubrication system in the present utility model is equipment配套 with rotating machines. The cryogenic air separation system often includes multiple rotating machines such as a main air compressor, an air booster, an expansion compressor, a liquid pump, etc. These machines can share one or more oil lubrication systems. A set of oil lubrication system generally includes an oil lubrication tank, an oil storage tank, and an oil supply unit. The said oil supply unit further includes an oil cooler and an oil pump.

[0025] The cryogenic liquid in this invention refers to a liquid stream with a temperature of approximately -120℃ to -180℃ capable of supplying cooling capacity to the distillation column system. For example, the cryogenic liquid may contain liquid nitrogen and / or liquefied air. The cryogenic liquid source may include a piping network or nearby storage tanks. A level sensor measures the liquid level in the distillation column system and transmits the measured value to the cryogenic liquid controller. When the liquid level falls below a predetermined value, it indicates that the distillation column system, i.e., the cryogenic air separation system, is experiencing insufficient cooling capacity. At this time, the cryogenic liquid controller increases the opening of the cryogenic liquid control valve, allowing more cryogenic liquid to flow into the distillation column system, thereby supplementing the insufficient cooling capacity.

[0026] Figure 1 This is a simplified schematic diagram of the cryogenic air separation process in Example 1. The distillation column system 1 is connected to the main heat exchanger 2. The feed air 20, after undergoing compression, precooling, purification, and optionally pressurization, is compressed at the pressurization end 4 of the expander and then enters the main heat exchanger 2 for cooling. The partially cooled stream leaves the main heat exchanger 2 from the middle section and then expands and cools at the expansion end 3 of the expander. The expanded stream can be directly fed back into the distillation column system 1 or after other operations. The expansion end 3 and the pressurization end 4 are connected via a rotating shaft 5. Lubricating oil in the lubricating oil storage tank 8 is connected to the lubricating oil supply unit 7. The lubricating oil supply unit 7 includes a lubricating oil cooler and a lubricating oil pump. The lubricating oil control valve 12 can be normally open or periodically open, allowing lubricating oil to enter the oil lubrication tank 6 surrounding the rotating shaft 5 and provide necessary lubrication to the rotating shaft or other components.

[0027] The liquefied air entering the distillation column system 1 is distilled to obtain a top gas and a bottom liquid. The top gas may contain sludge or nitrogen, which is returned as a return stream 21 to the main heat exchanger 2, providing cooling capacity to cool and / or liquefy the feed air 20. The liquid in the distillation column system includes both the oxygen-enriched liquid air at the bottom and the bottom liquid from each condenser / evaporator. The total amount of liquid in the distillation column system is positively correlated with the cooling capacity of the cryogenic system. The level sensor 9 measures the liquid level and transmits the data to the cryogenic liquid controller 10. When the liquid level is below a predetermined value, the cryogenic liquid controller 10 opens or increases the opening of the cryogenic liquid control valve 11, allowing more cryogenic liquid to flow from the cryogenic liquid source (not shown) into the distillation column system to supplement the cooling capacity required for producing liquid products.

[0028] The embodiments described herein are merely preferred embodiments of the present invention, and are used only to illustrate the technical solutions of the present invention and not to limit the present invention. Unless clearly indicated otherwise, each aspect or embodiment defined herein may be combined with any other one or more aspects or embodiments. In particular, any indicated preferred or advantageous feature may be combined with any other indicated preferred or advantageous feature. All technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation should be within the scope of the present invention.

Claims

1. A system for providing cooling capacity to a cryogenic air separation system, the cryogenic air separation system comprising a main heat exchanger, a distillation column system, and an expansion compressor, characterized in that, It also includes a level sensor for monitoring the liquid level in the distillation column system, a chilled liquid controller, a chilled liquid control valve, and a chilled liquid source; the rotating shaft connecting the expansion end and the pressurization end of the expander does not use oil braking.

2. The system as described in claim 1, characterized in that, The liquid level sensor monitors the height of the liquid level in the distillation column system and transmits the measurement result to the refrigeration liquid controller. When the liquid level is lower than a set value, the refrigeration liquid controller increases the opening of the refrigeration liquid control valve, so that the refrigeration liquid flows from the refrigeration liquid source into the distillation column system.

3. The system as described in claim 2, characterized in that, The cryogenic liquid includes liquid nitrogen, and the cryogenic liquid source includes a pipeline network and / or storage tanks.

4. The system as described in claim 2, characterized in that, The cryogenic liquid includes liquefied air.

5. The system as described in claim 3 or 4, characterized in that, The rotating shaft of the expander is lubricated with oil.

6. The system as described in claim 5, characterized in that, The oil lubrication is provided through an oil lubrication tank, a lubricating oil supply unit, and a lubricating oil storage tank.

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