A heating system and method for rapid start of an air separation plant

Abstract

The application discloses a heating system and method for quick start of an air separation device, and belongs to the technical field of air separation. A first heating gas inlet pipeline is connected to the inlet of a booster. An expanded air flow channel is provided with an expanded flow channel gas outlet after passing through a main heat exchanger. A high-pressure air flow channel is provided with a high-pressure flow channel gas outlet after passing through the main heat exchanger. An oxygen flow channel is connected with a second heating gas inlet pipeline at the oxygen outlet of a rectifying tower. The oxygen flow channel is provided with an oxygen flow channel gas outlet after passing through the main heat exchanger. The first heating gas inlet pipeline and the second heating gas inlet pipeline are connected with a heating gas source. By adding the heating gas inlet pipeline at the inlet of the booster and the liquid oxygen pump, the heating blowing stage in the air separation start process is moved forward to before the formal start of the air separation, that is, the heating blowing work is completed before the start of the air compressor, the cold start time of the air separation is reduced, and the air separation start cost is reduced.

Description

Technical Field

[0001] This invention belongs to the field of air separation technology and relates to a heating system and method for rapid start-up of air separation units. Background Technology

[0002] Air separation involves separating effective gases from the air, with oxygen and nitrogen being the primary gaseous products. Cryogenic separation is the most common method, using air as feedstock. Through compression, purification, and heat exchange, the air is liquefied into liquid air, which is mainly a mixture of liquid oxygen and liquid nitrogen. Utilizing the difference in boiling points between liquid oxygen and liquid nitrogen, they are separated through distillation to obtain oxygen and nitrogen. The air liquefaction temperature is very low; the distillation column and main heat exchanger are installed in a white cold box. The space between the equipment and the cold box panels is filled with perlite for insulation. The lowest temperature of the medium in the cold box reaches -194℃. Air separation startup is divided into hot-state startup and cold-state startup. Hot-state startup refers to startup with the distillation column at room temperature, and the main processes include heating and purging, cooling the column, liquid accumulation, purification, and product delivery. Cold-state startup refers to startup with a low-temperature liquid inside the distillation column, and the main processes include heating and purging, purification, and product delivery. After a short-term shutdown, the air separation unit is started up using a cold start method. Because there is a low-temperature liquid in the distillation column, the cold start time is shorter than the hot start time. The main time of the cold start is spent in the heating and purging stage, which lasts for about 8 hours. In the existing technology, the heating and purging stage is started after the air compressor is turned on. This stage consumes too much time and increases the start-up cost of the air separation unit. Summary of the Invention

[0003] The purpose of this invention is to solve the technical problem in the prior art that the heating and blowing stage only begins after the air compressor is turned on during cold start, resulting in excessively long cold start time and high start-up costs. The invention provides a heating system and method for rapid start-up of air separation units.

[0004] To achieve the above objectives, the present invention employs the following technical solution:

[0005] In a first aspect, the present invention provides a heating system for rapid start-up of an air separation unit, comprising an air compressor, an air-cooled tower, a molecular sieve, a booster compressor, and a distillation column connected in sequence; the molecular sieve is directly connected to the distillation column via a low-pressure air channel; the booster compressor is connected to the distillation column via two pipes, a high-pressure air channel and an expansion air channel; an expander is installed on the expansion air channel; the air compressor is connected to an air source; the low-pressure air channel, the high-pressure air channel, and the expansion air channel all pass through a main heat exchanger, so that the fluids therein exchange heat in the main heat exchanger before entering the distillation column; oxygen obtained by distillation separation in the distillation column is sent out through an oxygen channel, and nitrogen is sent out through a nitrogen channel; the oxygen channel and the nitrogen channel both pass through the main heat exchanger, so that the fluids therein exchange heat in the main heat exchanger after flowing out of the distillation column;

[0006] The inlet of the booster is connected to a first heating gas inlet pipe; the expansion air channel passes through the main heat exchanger and is provided with an expansion channel gas outlet, and the high-pressure air channel passes through the main heat exchanger and is provided with a high-pressure channel gas outlet; the oxygen channel is connected to a second heating gas inlet pipe at the oxygen outlet of the distillation column, and the oxygen channel passes through the main heat exchanger and is provided with an oxygen channel gas outlet; the first heating gas inlet pipe and the second heating gas inlet pipe are connected to a heating gas source.

[0007] A further improvement of the present invention is that:

[0008] A liquid oxygen pump is installed on the oxygen flow channel before it enters the main heat exchanger.

[0009] The second heating gas inlet pipe is connected to the inlet of the liquid oxygen pump.

[0010] Valves are installed on the heating nitrogen inlet pipe and the second heating gas inlet pipe.

[0011] The gas source for heating gas input into the first heating gas inlet pipe and the second heating gas inlet pipe must be oil-free and have a dew point below -60°C.

[0012] The heating gas source is nitrogen or air.

[0013] A trace water analyzer is connected to the gas outlet of the expansion channel, the gas outlet of the high-pressure channel, and the gas outlet of the oxygen channel.

[0014] The trace water analyzer was replaced by a handheld dew point meter.

[0015] Secondly, the present invention provides a heating method for rapid start-up of an air separation unit, comprising the following steps:

[0016] Step 1: When restarting the air separation unit after a temporary shutdown for cooling, simultaneously open the valves on the first and second heating gas inlet pipes to introduce heating gas into the high-pressure air flow channel, expansion air flow channel, and oxygen flow channel to purge water of various states from the pipes.

[0017] Step 2: While performing Step 1, use a trace water analyzer or a handheld dew point meter to measure the dew point in the high-pressure air channel, expansion air channel, and oxygen channel until the dew point value is within the specified range, and the purging is complete.

[0018] Step 3: Close the valves on the first and second heating gas inlet pipes, cut off the heating gas source, start the air compressor, and proceed with the subsequent air separation process.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] This invention discloses a heating system for rapid startup of an air separation unit. By adding heated gas inlet pipes at the inlets of the booster compressor and liquid oxygen pump, the heating and purging stage during the air separation startup process is moved forward to before the formal startup of the air separation unit. That is, the heating and purging work is completed before the air compressor starts, reducing the cold start time and lowering startup costs. Air compressors have power ratings of tens of thousands of kilowatts; reducing the compressor's operating time during startup can save tens of thousands of yuan in startup costs, while also reducing the workload of personnel during the startup process. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a schematic diagram of a heating system for rapid start-up of an air separation unit according to the present invention.

[0023] Wherein: 1-Air compressor; 2-Air-cooled tower; 3-Molecular sieve; 4-Booster; 5-First heating gas inlet pipe; 6-Expander; 7-Expander channel gas outlet; 8-High pressure channel gas outlet; 9-Main heat exchanger; 10-Oxygen channel gas outlet; 11-Liquid oxygen pump; 12-Second heating gas inlet pipe; 13-Distillation column; 101-Low pressure air channel; 102-High pressure air channel; 103-Expander air channel; 104-Oxygen channel; 105-Nitrogen channel. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0025] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0026] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.

[0027] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper," "lower," "horizontal," or "inner" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of the invention is in use, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. Furthermore, terms such as "first" and "second" are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0028] Furthermore, the use of the term "horizontal" does not imply that the component must be absolutely horizontal, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0029] In the description of the embodiments of the present invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0030] The present invention will now be described in further detail with reference to the accompanying drawings:

[0031] See Figure 1This invention discloses a heating system for rapid start-up of an air separation unit, comprising an air compressor 1, an air-cooled tower 2, a molecular sieve 3, a booster compressor 4, and a distillation column 13 connected in sequence; the molecular sieve 3 is directly connected to the distillation column 13 via a low-pressure air channel 101; the booster compressor 4 is connected to the distillation column 13 via two pipes, a high-pressure air channel 102 and an expansion air channel 103; an expander 6 is installed on the expansion air channel 103; the air compressor 1 is connected to an air source; the low-pressure air channel 101, high-pressure air channel 102, and expansion air channel 103 are ... the expansion air channel 103 is connected to the distillation column 13 via two pipes, a high-pressure air channel 102 and an expansion air channel 103; the expansion air channel 103 is connected to the distillation column 13 via two pipes, a high-pressure air channel 102 and an expansion air channel 103; the expansion air channel 103 is connected to the distillation column 13 via two pipes, a high-pressure air channel 102 and an expansion air channel 103; the expansion air channel 103 is connected to the distillation column 13 via two pipes, a high-pressure air channel 102 and an expansion air channel 103; the expansion air channel 102 is connected to the Both the compressed air flow channel 102 and the expanded air flow channel 103 pass through the main heat exchanger 9, allowing the fluids to exchange heat in the main heat exchanger 9 before entering the distillation column 13. The oxygen obtained by distillation separation in the distillation column 13 is sent out through the oxygen flow channel 104, and the nitrogen is sent out through the nitrogen flow channel 105. Both the oxygen flow channel 104 and the nitrogen flow channel 105 pass through the main heat exchanger 9, allowing the fluids to exchange heat in the main heat exchanger 9 after flowing out of the distillation column 13. A liquid oxygen pump 11 is installed on the oxygen flow channel 104 before entering the main heat exchanger 9.

[0032] The inlet of the booster compressor 4 is connected to a first heating gas inlet pipe 5; the expansion air channel 103 passes through the main heat exchanger 9 and has an expansion channel gas outlet 7, and the high-pressure air channel 102 passes through the main heat exchanger 9 and has a high-pressure channel gas outlet 8; the inlet of the liquid oxygen pump 11 is connected to a second heating gas inlet pipe 12, and the oxygen channel 104 passes through the main heat exchanger 9 and has an oxygen channel gas outlet 10; the first heating gas inlet pipe 5 and the second heating gas inlet pipe 12 are connected to heating gas sources. Valves are installed on the heating nitrogen inlet pipe 5 and the second heating gas inlet pipe 12. The gas source for heating gas input into the first heating gas inlet pipe 5 and the second heating gas inlet pipe 12 is required to be oil-free and have a dew point below -60°C. The heating gas source is nitrogen or air. A trace water analyzer is connected to the gas outlet 7 of the expansion channel, the gas outlet 8 of the high-pressure channel, and the gas outlet 10 of the oxygen channel, or a handheld dew point meter is used to measure the dew point in the pipes.

[0033] This invention also discloses a heating method for rapid start-up of an air separation unit, comprising the following steps:

[0034] Step 1: When restarting the air separation unit after a temporary shutdown for cooling, simultaneously open the valves on the first heating gas inlet pipe 5 and the second heating gas inlet pipe 12 to introduce heating gas into the high-pressure air channel 102, the expansion air channel 103 and the oxygen channel 104 to blow out water of various states from the pipes.

[0035] Step 2: While performing Step 1, use a trace water analyzer or a handheld dew point meter to measure the dew point in the high-pressure air channel 102, the expansion air channel 103, and the oxygen channel 104 until the dew point value is within the specified range, and the purging is completed.

[0036] Step 3: Close the valves on the first heating gas inlet pipe 5 and the second heating gas inlet pipe 12 to cut off the heating gas source, start the air compressor 1, and proceed with the subsequent air separation process.

[0037] This invention discloses a heating system for rapid startup of an air separation unit. By adding heated gas inlet pipes at the inlets of the booster compressor and liquid oxygen pump, the heating and purging stage during the air separation startup process is moved forward to before the formal startup of the air separation unit. That is, the heating and purging work is completed before the air compressor starts, reducing the cold start time and lowering startup costs. Air compressors have power ratings of tens of thousands of kilowatts; reducing the compressor's operating time during startup can save tens of thousands of yuan in startup costs, while also reducing the workload of personnel during the startup process.

[0038] The working principle of this invention is as follows:

[0039] The basic air separation process is as follows: Air compressor 1 compresses atmospheric air to provide feed air and establish pressure in the lower column. The feed air enters air-cooled tower 2 for washing and preliminary cooling, and then enters molecular sieve 3 to remove harmful impurities such as water and acetylene. The clean air after molecular sieve 3 enters the main heat exchanger 9 as low-pressure air, is cooled, and then enters the distillation column 13. The other path goes to booster compressor 4. After being compressed by booster compressor 4, the air is divided into two branches. In one branch, the expanded air is cooled in the main heat exchanger 9 and then drawn out from the middle to enter the expander 6 for further cooling before entering the distillation column 13. In the other branch, the high-pressure air is liquefied after being cooled in the main heat exchanger 9 and then enters the distillation column 13. The three paths of low-temperature air or liquefied air cooled in the main heat exchanger 9 enter the distillation column 13 and are separated into liquid oxygen and nitrogen through distillation. The low-temperature nitrogen is reheated to room temperature in the main heat exchanger 9 and then sent out. The liquid oxygen is pressurized by liquid oxygen pump 11, vaporized in the main heat exchanger 9, reheated to room temperature, and then sent out.

[0040] The distillation column 13, main heat exchanger 9, partial expander 6, and liquid oxygen pump 11 are installed in their respective cold boxes. Five media exchange heat in the main heat exchanger: forward-flowing low-pressure air, expanding air, and high-pressure air, and counter-flowing nitrogen and oxygen. The upper part of the main heat exchanger 9 is at ambient temperature, while the lower part is at a low temperature. The forward-flowing medium cools down in the main heat exchanger, while the counter-flowing medium heats up. The forward-flowing and counter-flowing media exchange heat with each other.

[0041] After a temporary shutdown for cold preservation, the distillation column 13 contains low-temperature liquid and pressure, preventing humid air from entering. Therefore, a cold start after a cold preservation shutdown does not require heating to purge the distillation column. The low-pressure air channel 101 and nitrogen channel 105 of the main heat exchanger 9, which are connected to the distillation column 13 without isolation, also have pressure and do not require heating to purge. However, the high-pressure air channel 102, expansion air channel 103, and oxygen channel 104 of the main heat exchanger 9 are not directly connected to the distillation column 13 due to isolation by valves or other equipment. After shutdown, pressure cannot be established in these channels, and without positive pressure, humid air may enter. Therefore, heating to purge is necessary during startup to remove water in various forms. Otherwise, water and fumes will enter the distillation column 13, where the water will freeze at low temperatures, clogging the distillation column packing and causing the air separation unit to malfunction. Therefore, these channels must be heated to purge.

[0042] Normally, during the start-up process of the air separation unit, the main heat exchanger 9 is heated and purged with clean air from the molecular sieve 3, which requires the air compressor 1 to operate. Since the temperature at the bottom of the main heat exchanger 9 is low, the purging time is relatively long. During this process, most of the raw material air compressed by the air compressor 1 is released, resulting in waste and high cost.

[0043] This invention introduces heated nitrogen gas into the booster compressor 4, which enters the air separation system through the first heated gas inlet pipe 5. This heated nitrogen gas then purges the expansion air channel 103 and the high-pressure air channel 102, exiting from the expansion channel gas outlet 7 and the high-pressure channel gas outlet 8, respectively, thus removing water from the channels. Similarly, heated nitrogen gas is introduced into the liquid oxygen pump 11, entering the air separation system through the second heated gas inlet pipe 12. This heated nitrogen gas then purges the oxygen channel, exiting from the oxygen channel gas outlet 10, thus removing water from the channels. By using nitrogen gas to heat and purge the relevant channels of the main heat exchanger before the air separation system is officially started, the heating and purging process is streamlined, reducing the number of heating and purging steps and saving start-up time and costs.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A heating system for rapid start-up of an air separation unit, characterized in that, The system includes an air compressor (1), an air-cooled tower (2), a molecular sieve (3), a booster compressor (4), and a distillation column (13) connected in sequence; the molecular sieve (3) is directly connected to the distillation column (13) through a low-pressure air channel (101); the booster compressor (4) is connected to the distillation column (13) through two pipes, a high-pressure air channel (102) and an expansion air channel (103); an expander (6) is installed on the expansion air channel (103); the air compressor (1) is connected to an air source; the low-pressure air channel (101) is connected to the distillation column (13) through two pipes, a high-pressure air channel (102) and an expansion air channel (103); an expander (6) is installed on the expansion air channel (103); the air compressor (1) is connected to an air source; the low-pressure air channel (102) is connected to the distillation column (13) through two pipes, a high-pressure air channel (102) and an expansion air channel (103). 1) Both the high-pressure air flow channel (102) and the expansion air flow channel (103) pass through the main heat exchanger (9), so that the fluid in them exchanges heat in the main heat exchanger (9) before entering the distillation column (13); the oxygen obtained by distillation separation in the distillation column (13) is sent out through the oxygen flow channel (104) and the nitrogen is sent out through the nitrogen flow channel (105); both the oxygen flow channel (104) and the nitrogen flow channel (105) pass through the main heat exchanger (9), so that the fluid in them exchanges heat in the main heat exchanger (9) after flowing out of the distillation column (13); The inlet of the booster (4) is connected to a first heating gas inlet pipe (5); the expansion air channel (103) passes through the main heat exchanger (9) and is provided with an expansion channel gas outlet (7); the high pressure air channel (102) passes through the main heat exchanger (9) and is provided with a high pressure channel gas outlet (8); the oxygen channel (104) is connected to a second heating gas inlet pipe (12) at the oxygen outlet of the distillation column (13); the oxygen channel (104) passes through the main heat exchanger (9) and is provided with an oxygen channel gas outlet (10); the first heating gas inlet pipe (5) and the second heating gas inlet pipe (12) are connected to a heating gas source; A liquid oxygen pump (11) is installed on the oxygen flow channel (104) before entering the main heat exchanger (9). The second heating gas inlet pipe (12) is connected to the inlet of the liquid oxygen pump (11).

2. The heating system for rapid start-up of an air separation unit according to claim 1, characterized in that, Valves are installed on the first heating gas inlet pipe (5) and the second heating gas inlet pipe (12).

3. The heating system for rapid start-up of an air separation unit according to claim 1, characterized in that, The gas source for heating gas input into the first heating gas inlet pipe (5) and the second heating gas inlet pipe (12) is required to be oil-free and have a dew point below -60°C.

4. The heating system for rapid start-up of an air separation unit according to claim 3, characterized in that, The heating gas source is nitrogen or air.

5. The heating system for rapid start-up of an air separation unit according to claim 1, characterized in that, A trace water analyzer is connected to the gas outlet (7) of the expansion channel, the gas outlet (8) of the high-pressure channel, and the gas outlet (10) of the oxygen channel.

6. The heating system for rapid start-up of an air separation unit according to claim 5, characterized in that, The trace water analyzer was replaced by a handheld dew point meter.

7. A heating method for rapid start-up of an air separation unit based on the system described in any one of claims 1-6, characterized in that, Includes the following steps: Step 1: When restarting the air separation unit after a temporary shutdown for cooling, simultaneously open the valves on the first heating gas inlet pipe (5) and the second heating gas inlet pipe (12) to introduce heating gas into the high-pressure air flow channel (102), the expansion air flow channel (103) and the oxygen flow channel (104) to blow out water of various states in the pipes; Step 2: While performing Step 1, use a trace water analyzer or a handheld dew point meter to measure the dew point in the high-pressure air channel (102), the expansion air channel (103), and the oxygen channel (104) until the dew point value is within the specified range, and the purging is completed. Step 3: Close the valves on the first heating gas inlet pipe (5) and the second heating gas inlet pipe (12), cut off the heating gas source, start the air compressor (1), and carry out the subsequent air separation process.

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