CN108072234A - The control method of air-separating plant - Google Patents

Abstract

The invention provides a control method for an air separation device. The air separation device includes a cold box, a fractionation tower system located in the cold box, an insulating material filled in the cold box, a compressor, and a compressor connected between the compressor and the fractionation tower system. The molecular sieve adsorber between the fractionation tower system includes an upper tower, a lower tower and a main condensation evaporator connected between the upper tower and the lower tower and communicated with the upper tower. The control method of the air separation device includes: air separation device When shutting down, the compressor and molecular sieve adsorber are controlled to be closed, and the fractionation tower system is not heated so that the temperature of the fractionation tower system is not higher than the temperature of the insulation material. The control method of the air separation device provided by the present invention does not heat the fractionation tower system when it is shut down, so that the fractionation tower system exchanges heat with the thermal insulation material to increase the temperature of the fractionation tower system, avoiding the pressure reduction in the fractionation tower system. negative suction phenomenon.

Description

Control method of air separation plant

technical field

The invention relates to the technical field of air separation, and more specifically, relates to a control method of an air separation device.

Background technique

Air separation plant (air separation plant) is a kind of high energy consumption equipment, and the energy consumption of air separation plant is very large. The energy consumption in the operation of the air separation plant accounts for more than 80% of its total cost, and the raw material air compressor (compressor) is the "large energy consumer" of the air separation plant.

At present, the low-temperature cryogenic air separation equipment adopts molecular sieve front-end adsorption to remove moisture, carbon dioxide, and hydrocarbons in the raw air. This process does not have a separate heating flow path (dryer + Roots blower + heater = heating temperature pipeline), but directly use the dry positive flow feed air from the molecular sieve adsorber to heat the fractionation tower system in the cold box (main heat exchanger, upper and lower towers, subcooler, crude argon I tower, crude argon II tower, Refined argon towers, pipelines, and even krypton-xenon-neon-helium rare gas separation towers, etc.), so many air separation equipment are heated by the raw material air compressor.

The traditional operation regulations stipulate that the cryogenic liquid in the fractionation tower should be drained when the cryogenic air separation plant is shut down for more than 48 hours, and the air separation plant needs to be systematically heated before shutting down or (and) starting up. The heating of the system is to heat the equipment in the cold box to 5-10°C and then stop it. The time varies from process to process. Generally, the three-high process of oxygen, nitrogen and argon takes about 24 hours.

The traditional heating method consumes a lot of energy, and it is easy to cause negative suction of external air into the fractionation tower system. When the air separation device is turned on again, it must be thoroughly heated to dry it, which further increases energy consumption.

Contents of the invention

The present invention aims to solve at least one of the technical problems existing in the prior art.

Therefore, the object of the present invention is to provide a control method for an air separation device.

In order to achieve the above object, an embodiment of the present invention provides a control method for an air separation device, the air separation device includes a cold box, a fractionation column system located in the cold box, and a thermal insulation unit filled in the cold box Material, compressor and the molecular sieve adsorber connected between the compressor and the fractionation tower system, the fractionation tower system includes an upper tower, a lower tower and connecting between the upper tower and the lower tower, And the main condensing evaporator that is communicated with the upper tower, the control method of the air separation device includes: when the air separation device is shut down, the compressor and the molecular sieve adsorber are controlled to be closed, and the fractionation tower system is not activated. The heating treatment is carried out so that the temperature of the fractionation column system is not higher than the temperature of the insulation material.

In the control method of the air separation device provided by the above-mentioned embodiments of the present invention, when shutting down, the compressor and the molecular sieve adsorber are turned off, and the fractionation tower system is not heated, so that the temperature of the fractionation tower system is not higher than the temperature of the insulation material, wherein The temperature of the fractionation tower system 1 refers to the average temperature of the fractionation tower system 1, and the temperature of the insulation material refers to the average temperature of the insulation material everywhere, so that when the temperature of the fractionation tower system is lower than the temperature of the insulation material, the fractionation The temperature of the tower system can be raised by exchanging heat with the insulation material, so that the pressure in the fractionation tower system is not lower than atmospheric pressure. When the temperature of the fractionation tower system is equal to the temperature of the insulation material, the fractionation tower system and the insulation material are exchanged with the outside world heat, so that the temperature of the fractionation tower system rises, and also makes the pressure in the fractionation tower system not lower than atmospheric pressure, which will not cause negative suction, and then the outside humid air cannot enter the fractionation tower system, so that when the air separation device is turned on again to heat up, there is no need Thorough heating and purging for a longer period of time reduces energy consumption, and compared with the related technology, heating is performed once when shutting down and starting up, and no heating is required when shutting down, which reduces the number of heating operations and further reduces the energy consumption.

Specifically, in the related art, when the system is shut down, the fractionation tower system is heated. Since the insulation material in the cold box is still at a low temperature after the air separation unit has been in operation for a long time, if the system is heated, the fractionation tower before and after heating will The temperature change trend in the system is "low-high-low-high", that is, the temperature of the fractionation tower system in the cold box rises first when heating, and after the heating stops, the equipment absorbs the cooling capacity in the insulation material Afterwards, the temperature drops. If the shutdown continues for a long time, when the temperature of the thermal insulation material and the fractionation tower system reaches equilibrium, the temperature of the fractionation tower system and the thermal insulation material will exchange heat with the outside again, and the temperature will rise. 6500m ³ /h air separation unit is heated to 5°C as an example. After the heating stops, the fractionation tower system absorbs the cooling capacity of the insulation material in the cold box, the temperature of the main tower drops to -40°C, and the temperature of the crude argon tower reaches Below -60°C, when the temperature of the fractionation tower system drops, the volume of the gas in the original fractionation tower shrinks, causing the outside air to enter through a "negative suction". The calculation is as follows: the total volume of the fractionating tower system is R, and the gas in the fractionating tower system is regarded as an ideal gas. At the end of heating, the temperature is T1=5°C=278K, and the pressure is P1. Passed to the fractionation tower system, the average temperature of the fractionation tower system in the cold box drops to T2=-40°C=233K, P2=P1×T2/T1=233/278=0.84, then the volume will shrink to 84% of the original, the tower If the internal pressure drops, a negative pressure will be formed instead, which will lead to negative suction of wet air. In the pressure-time curve, the volume of the original gas will decrease during the shutdown stage, and the pressure will be lower than the atmospheric pressure P0 (dotted line in Figure 2); When the air enters, it must be heated thoroughly to make it dry, and the heating twice before and after increases the energy consumption.

In this application, there is no heating after shutdown, regardless of the heat exchange between the fractionation tower system and the insulation material or the heat exchange between the fractionation tower system and the insulation material and the outside world, the temperature of the entire fractionation tower system is always in the process of rising. >T0, then the pressure P=(T/T0)P0>1, where P0 is atmospheric pressure, so the fractionation column system is always under positive pressure, which will not cause negative suction.

In addition, the control method of the air separation device provided by the above-mentioned embodiments of the present invention also has the following additional technical features:

In the above technical solution, preferably, before the shutdown of the air separation device, the air separation device is controlled to discharge part of the liquid in the upper tower and discharge the liquid in the lower tower.

In the above-mentioned embodiment, before the shutdown of the air separation unit, the liquid is drained under pressure, the liquid is drained from the lower tower, and the liquid is not drained from the upper tower. Since the upper tower is connected with the main condensing evaporator, the liquid remaining in the upper tower into the main condensing evaporator. The liquid evaporates naturally with the heat exchange between the cold box and the outside world. When it starts to evaporate, a positive pressure is formed in the tower. Even after the liquid evaporates completely, there is no positive pressure in the tower. In heat exchange with the outside world, the temperature of the fractionation tower system and insulation materials will rise naturally, and there will be no temperature drop, and will not cause the volume of the gas in the tower to shrink to form a negative pressure, so that the outside humid air cannot enter the fractionation tower system.

In the above technical solution, preferably, the liquid remaining in the upper tower accounts for less than or equal to 25% of the normal liquid level of the main condensation evaporator, to avoid The amount of liquid left is too high, causing the liquid to evaporate too long.

In the above technical solution, preferably, the liquid level in the main condensation evaporator of the liquid remaining in the upper column is equal to 15% of the normal liquid level of the main condensation evaporator.

In the above technical solution, preferably, a product output pipeline is connected to the upper tower, and a control valve is arranged on the product output pipeline, and the control method of the air separation device further includes: Before the liquid is completely evaporated, control and adjust the opening of the control valve so that the pressure in the fractionation column system is not less than atmospheric pressure.

In the above embodiment, before the liquid remaining in the upper tower evaporates, the fractionation tower system exhausts to the outside, and the opening of the control valve is adjusted. Due to the evaporation of the liquid, the pressure in the fractionation tower system is neither overpressure nor lower than atmospheric pressure. P0, to ensure that the outside humid air cannot enter the fractionation tower system. In a specific embodiment, the pressure in the fractionation column system can be neither overpressure nor less than atmospheric pressure by reducing the opening of the control valve. Certainly, the opening degree of the control valve may not be adjusted down, and at this moment, the pressure in the fractionating column system is equal to atmospheric pressure.

In the above technical solution, preferably, the product output pipeline includes an oxygen output pipeline, a nitrogen output pipeline and a dirty nitrogen output pipeline; the control valve includes an oxygen control valve arranged on the oxygen output pipeline, an oxygen control valve arranged on the nitrogen A nitrogen control valve on the output pipeline and a dirty nitrogen control valve arranged on the dirty nitrogen output line.

Before the remaining liquid in the upper tower is evaporated, all the openings of the oxygen control valve, nitrogen control valve and dirty nitrogen control valve are turned down to make the pressure in the fractionation tower system greater than atmospheric pressure. Of course, only one or two of the oxygen control valve, nitrogen control valve and dirty nitrogen control valve can be turned down, or one or both of them can be closed.

In the above technical solution, preferably, the molecular sieve adsorber is connected to the sewage nitrogen output pipeline, and on the connecting pipeline between the molecular sieve adsorber and the sewage nitrogen output pipeline, the molecular sieve adsorber and the compressor Valves are arranged on the connecting pipeline of the machine and the connecting pipeline between the molecular sieve adsorber and the fractionation tower system, and the control method of the air separation device also includes: before the liquid remaining in the upper tower is completely evaporated , to control the valve to close.

In the above embodiment, the molecular sieve adsorber is connected to the compressor through the first connecting pipeline, connected to the fractionation column system through the second connecting pipeline, and connected to the sewage nitrogen output pipeline through the third connecting pipeline, wherein, in the first connecting pipeline, the second Both the second connecting pipeline and the third connecting pipeline are equipped with valves (switching valves), wherein, controlling the on-off of the switching valves can adjust the working mode of the two molecular sieve adsorbers (air enters a molecular sieve adsorber, and is adsorbed in the molecular sieve After the adsorber is saturated, control the air to enter another molecular sieve adsorber to continue to adsorb. For the saturated molecular sieve adsorber, input high-temperature dirty nitrogen to heat the molecular sieve adsorber, and then input cold dirty nitrogen to cool down the molecular sieve adsorber, so that the molecular sieve adsorbs device to restore the adsorption capacity). Preferably, the air separation plant comprises two molecular sieve adsorbers.

Before the liquid remaining in the upper tower is completely evaporated, close the valve to prevent humid air from entering the fractionation tower system through the molecular sieve adsorber.

In the above technical solution, preferably, the control method of the air separation device further includes: after the liquid remaining in the upper column is completely evaporated, controlling the control valve to close.

After the liquid remaining in the upper tower evaporates, when the temperature of the upper tower rises slightly, close the control valve to prevent humid air from entering the fractionation tower system through the oxygen output pipeline, nitrogen output pipeline and dirty nitrogen output pipeline. Because there is no liquid evaporation in the upper tower at this time, there will be no overpressure in the fractionating tower system when the control valve is closed.

In the above embodiment, after the liquid remaining in the upper tower evaporates, the oxygen control valve, nitrogen control valve and contaminated nitrogen control valve are closed to prevent external moist air from entering the fractionation through the oxygen output pipeline, nitrogen output pipeline and contaminated nitrogen output pipeline. in the tower system.

After the liquid is completely evaporated, the fractionating tower system and the insulation material exchange heat with the outside world, the temperature rises, the gas in the fractionating tower system expands, and the pressure in the fractionating tower system may be slightly higher than atmospheric pressure, or may be equal to atmospheric pressure.

In the above technical solution, preferably, the control method of the air separation device further includes: before starting the air separation device again, controlling the compressor and the molecular sieve adsorber to be turned on, so as to boost the fractionation column system. Warm treatment.

In the above technical solution, preferably, the thermal insulation material is pearlite.

The air separation unit includes some high-purity nitrogen equipment, oxygen-nitrogen double-high equipment, oxygen-nitrogen-argon three-high equipment, rare gas partial extraction or full extraction equipment. The control method of the air separation device is that when it is shut down intermittently for a long time (generally more than 48 hours), the liquid in the fractionation tower is not drained to let it evaporate naturally to maintain a slight positive pressure, and the system does not need to be heated and thawed before shutting down or starting up It is suitable for occasions where the low-temperature air separation unit with molecular sieve adsorber at the front end is shut down for a long time but the pearlite is not removed for maintenance.

Even if the residual liquid in the tower evaporates and causes the cooling capacity to move outward, forming a certain low temperature at the outlet of the product pipe, at most only a small amount of humid air will condense on the inner wall of the outlet of the product pipe, and will not enter the equipment. The gas is blown out as it passes through.

Additional aspects and advantages of the invention will become apparent in the description which follows, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and comprehensible from the description of the embodiments in conjunction with the following drawings, wherein:

Fig. 1 is a schematic diagram of the relationship between temperature and time variation in the fractionation tower system in the related art;

Fig. 2 is a schematic diagram of the relationship between the pressure in the fractionation tower system and the change with time in the related art;

Fig. 3 is the structural representation of the air separation device described in the embodiment of the present invention;

Fig. 4 is the schematic flow chart of the control method of the air separation plant described in the embodiment of the present invention;

Fig. 5 is a schematic diagram of the relationship between temperature and time variation in the fractionation tower system described in the embodiment of the present invention;

Fig. 6 is a schematic diagram of the relationship between pressure and time variation in the fractionation column system described in the embodiment of the present invention.

Wherein, the corresponding relationship between reference numerals and component names in Fig. 3 is:

1 fractionation tower system, 2 insulation material, 3 compressor, 4 molecular sieve adsorber, 5 cold box.

Detailed ways

In order to understand the above-mentioned purpose, features and advantages of the present invention more clearly, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that, in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other.

In the following description, many specific details are set forth in order to fully understand the present invention. However, the present invention can also be implemented in other ways than described here. Therefore, the protection scope of the present invention is not limited by the specific implementation disclosed below. Example limitations.

The control method of the air separation device according to some embodiments of the present invention will be described below with reference to the accompanying drawings.

As shown in Fig. 3 and Fig. 4, according to a control method of an air separation device provided by some embodiments of the present invention, the air separation device includes a cold box 5, a fractionation column system 1 located in the cold box 5, and filled in the cold box Insulation material 2 in 5, compressor 3 and molecular sieve adsorber 4 connected between compressor 3 and fractionation tower system 1, fractionation tower system 1 includes upper tower, lower tower and between upper tower and lower tower, And the main condensing evaporator that is connected with upper tower, the control method of this air separation device comprises: when the air separation device shuts down, control compressor 3 and molecular sieve adsorber 4 to close, do not carry out heating treatment to fractionation column system 1, so that The temperature of fractionation column system 1 is not higher than the temperature of insulation material 2 .

In the control method of the air separation device provided by the above-mentioned embodiments of the present invention, when shutting down, the compressor 3 and the molecular sieve adsorber 4 are turned off, and the fractionation tower system 1 is not heated, so that the temperature of the fractionation tower system 1 is not higher than that of the thermal insulation material 2, wherein the temperature of fractionation tower system 1 refers to the average temperature of fractionation tower system 1, and the temperature of insulation material 2 refers to the average temperature of insulation material 2 everywhere, so that when the temperature of fractionation tower system 1 is low At the temperature of the insulation material 2, the temperature of the fractionation tower system 1 can be increased by exchanging heat with the insulation material 2, so that the pressure in the fractionation tower system 1 is not lower than atmospheric pressure. When the temperature of the fractionation tower system 1 is equal to that of the insulation material 2 temperature, the fractionation tower system 1 and the insulation material 2 exchange heat with the outside world, so that the temperature of the fractionation tower system 1 rises, and the pressure in the fractionation tower system 1 is also not lower than atmospheric pressure, which will not cause negative suction, and then the external humidity The air cannot enter the fractionation tower system 1, so that when the air separation device is turned on again for heating, it is not necessary to carry out a thorough heating and purging for a long time, which reduces energy consumption, and compared with the related art, when it is shut down and when it is turned on, it is carried out once. Heating, no need to heat when shutting down reduces the number of heating operations and further reduces energy consumption.

Specifically, in the related art, when the fractionation tower system 1 is shut down, the heating operation is carried out. After the air separation device has been operated for a long time, the insulation material 2 in the cold box 5 is still in a low temperature state. Therefore, if the system is heated, as shown in the figure As shown in 1, the temperature change trend in the fractionation tower system before and after heating is the situation of "low-high-low-high", that is, the temperature of fractionation tower system 1 in the cold box 5 rises to T1 first when heating. After the heating stops, the equipment absorbs the cold in the insulation material 2 and the temperature drops to T2. If the shutdown continues for a long time, when the temperature of the insulation material 2 and the fractionation tower system 1 reaches equilibrium, the fractionation tower system 1 and the insulation material 2 It will exchange heat with the outside world again, and the temperature will rise. A1 in Figure 1 corresponds to heating when restarting. Taking the 6500m ³ /h air separation unit heated to 5°C as an example, after the heating stops, the fractionation tower system 1 absorbs the cooling capacity of the insulation material 2 in the cold box 5, and the temperature of the main tower drops to -40°C, the crude argon tower, etc. When the temperature in the fractionation tower reaches below -60°C, when the temperature of the fractionation tower system 1 drops, the volume of the gas in the original fractionation tower shrinks, resulting in the “negative suction” of outside air. The calculation is as follows: the total volume of the fractionation tower system 1 is R, the gas in the fractionation tower system 1 is regarded as an ideal gas, and the temperature at the end of heating is T1=5°C=278K, as shown in Figure 2, and the pressure is P1, Figure 2 Section A2 in the middle represents the heating process. After the heating is stopped, the thermal insulation material 2 transfers the cold energy to the fractionation tower system 1, and the average temperature of the fractionation tower system 1 in the cold box 5 drops to T2=-40°C=233K, P2=P1 ×T2/T1=233/278=0.84, then the volume will shrink to 84% of the original, and the pressure inside the tower will drop, which will instead form a negative pressure and lead to negative suction of wet air, as shown in Figure 2 in the pressure curve in the shutdown stage A3 The volume of the gas decreases, and the pressure is lower than the atmospheric pressure P0 (dotted line in Figure 2); when restarting (A4 section in Figure 2), due to the entry of humid air, it must be heated more thoroughly to dry, and the heating increases twice before and after. energy consumption.

In this application, the temperature is not heated after shutdown, regardless of the heat exchange between the fractionation tower system 1 and the insulation material 2 or the heat exchange between the fractionation tower system 1 and the insulation material 2 with the outside world, the temperature of the entire fractionation tower system 1 is always in the process of rising, as shown in the figure 5 and Figure 6, if the temperature T>T0 at any time before start-up, then the pressure P=(T/T0)P0>1, where P0 is the atmospheric pressure, so the fractionation column system is always under positive pressure and will not cause negative pressure. Suck.

Preferably, before the air separation device is shut down, the air separation device is controlled to discharge part of the liquid in the upper tower and discharge the liquid in the lower tower.

In the above-mentioned embodiment, before the shutdown of the air separation unit, the liquid is drained under pressure, the liquid is drained from the lower tower, and the liquid is not drained from the upper tower. Since the upper tower is connected with the main condensing evaporator, the liquid remaining in the upper tower into the main condensing evaporator. The liquid evaporates naturally with the heat exchange between the cold box 5 and the outside world. When it starts to evaporate, a positive pressure is formed in the tower. Even after the liquid is completely evaporated, there is no positive pressure in the tower. Although the fractionation tower system 1 and the insulation material 2 are in a low temperature state, However, with the heat exchange with the outside world, the temperature of the fractionation tower system 1 and the insulation material 2 will naturally rise, and there will be no temperature drop, and will not cause the gas volume in the tower to shrink and form a negative pressure, so that the outside humid air cannot enter the fractionation tower system. within 1.

Preferably, the liquid remaining in the upper tower accounts for less than or equal to 25% of the normal liquid level of the main condensing evaporator, so as to avoid the excessive amount of remaining liquid and cause the liquid to evaporate for too long. big.

Preferably, the liquid remaining in the upper column occupies a liquid level of the main condensing evaporator equal to 15% of the normal liquid level of the main condensing evaporator.

Preferably, the upper tower is connected with a product output pipeline, and a control valve is arranged on the product output pipeline, and the control method of the air separation device also includes: before the liquid remaining in the upper tower is completely evaporated, control and adjust the opening of the control valve to Make the pressure in the fractionation column system 1 not less than atmospheric pressure.

In the above-mentioned embodiment, as shown in Figure 6, before the liquid remaining in the upper tower evaporates, the fractionation tower system 1 exhausts to the outside, and the opening of the control valve is controlled. Due to the evaporation of the liquid, the pressure in the fractionation tower system 1 Not lower than the atmospheric pressure P0, to ensure that outside humid air cannot enter the fractionation tower system 1. Of course, the opening of the control valve can also not be adjusted down. At this time, the pressure in the fractionation column system 1 is equal to the atmospheric pressure.

Preferably, the product output pipeline includes an oxygen output pipeline, a nitrogen output pipeline and a dirty nitrogen output pipeline; the control valve includes an oxygen control valve arranged on the oxygen output pipeline, a nitrogen control valve arranged on the nitrogen output pipeline and a nitrogen control valve arranged on the dirty nitrogen output Polluted nitrogen control valve on the pipeline.

Before the remaining liquid in the upper tower evaporates, the openings of the oxygen control valve, nitrogen control valve and dirty nitrogen control valve are all adjusted to a small size, so that the pressure in the fractionation tower system 1 is greater than atmospheric pressure. Of course, only one or two of the oxygen control valve, nitrogen control valve and dirty nitrogen control valve can be turned down, or one or both of them can be closed.

Preferably, as shown in Figure 3, the molecular sieve adsorber 4 is connected to the sewage nitrogen output pipeline, wherein, on the connecting pipeline between the molecular sieve adsorber 4 and the compressor 3, on the connecting pipeline between the molecular sieve adsorber 4 and the fractionation tower system 1, Valves are installed on the connecting pipeline between the molecular sieve adsorber 4 and the sewage nitrogen output pipeline, and the control method of the air separation device also includes: before the liquid remaining in the upper tower is completely evaporated, the control valve is closed. Preferably, two molecular sieve adsorbers 4 are arranged between the compressor 3 and the fractionation column system 1 .

In the above embodiment, the molecular sieve adsorber 4 is connected to the compressor 3 through the first connecting pipeline, connected to the fractionation tower system 1 through the second connecting pipeline, and connected to the sewage nitrogen output pipeline through the third connecting pipeline, wherein, in the first connecting pipeline The pipeline, the second connecting pipeline, and the third connecting pipeline are all equipped with valves (switching valves), wherein, controlling the on-off of the switching valve can adjust the working mode of the two molecular sieve adsorbers 4 (air enters a molecular sieve adsorber 4, After the molecular sieve adsorber 4 is saturated, the air is controlled to enter another molecular sieve adsorber 4 to continue to adsorb. For the saturated molecular sieve adsorber 4, input high-temperature dirty nitrogen to heat the molecular sieve adsorber 4, and then input cold dirty nitrogen to the molecular sieve The temperature of the adsorber 4 is lowered so that the molecular sieve adsorber 4 recovers its adsorption capacity).

Before the liquid remaining in the upper tower is completely evaporated, the valve is closed to prevent humid air from entering the fractionation tower system 1 through the molecular sieve adsorber 4 .

Preferably, the control method of the air separation device further includes: after the liquid remaining in the upper tower is completely evaporated, the control valve is closed.

After the liquid remaining in the upper tower evaporates, when the temperature of the upper tower rises slightly, close the control valve to prevent humid air from entering the fractionation tower system 1 through the oxygen output pipeline, nitrogen output pipeline and dirty nitrogen output pipeline. Because there is no liquid evaporation in the upper tower at this time, the situation of overpressure will not occur in the fractionating tower system 1 by closing the control valve.

In the above embodiment, after the liquid remaining in the upper tower evaporates, the oxygen control valve, nitrogen control valve and contaminated nitrogen control valve are closed to prevent external moist air from entering the fractionation through the oxygen output pipeline, nitrogen output pipeline and contaminated nitrogen output pipeline. Inside the tower system 1.

After the liquid is completely evaporated, the fractionation tower system 1 and the insulation material 2 exchange heat with the outside world, the temperature rises, the gas in the fractionation tower system 1 expands, and the pressure in the fractionation tower system 1 may be slightly higher than atmospheric pressure, or may be equal to atmospheric pressure .

Preferably, the control method of the air separation device further includes: before starting the air separation device again, controlling the opening of the compressor 3 and the molecular sieve adsorber 4 to heat the fractionation column system 1 .

In the above technical solution, preferably, the thermal insulation material 2 is pearlite.

When shutting down, only the liquid is discharged without heating, and even some liquid is left. At the beginning, the residual liquid in the upper tower evaporates to form a positive pressure. Even if the liquid evaporates, there is no positive pressure in the fractionation tower system 1, as shown in Figure 5. 1. Although the pearlite is in a low-temperature state, the temperature will rise naturally, and the temperature rise curve is also unilaterally upward, and they are always in the process of rising. It is impossible to have a process of falling from high to low, and will not cause volume shrinkage to form negative pressure. In Figure 5, B indicates that the liquid has evaporated, and C indicates that the heating is turned on again. In Figure 6, the pressure curve in the fractionation tower system 1 is divided into two sections. In the first section, the liquid vaporization pressure rises, but in fact it is still exhausting to the outside. , there is no liquid in the second section, the temperature of the gas in the tower rises with the pearlite, the volume slowly expands, and the pressure also rises, but the slope is smaller, but in fact it is still exhausting (leakage), D represents After the liquid evaporates, the actual pressure of the fractionation tower system 1 may be slightly higher than the atmospheric pressure (atmospheric pressure is shown by the dotted line a in Figure 3). At this stage, the oxygen control valve, nitrogen control valve and dirty nitrogen control valve can be closed to avoid humid air as much as possible. Enter. As shown in Figure 6, no matter it is the first stage or the second stage, the pressure is always greater than the atmospheric pressure P0, and no negative pressure will be caused.

The air separation unit includes some high-purity nitrogen equipment, oxygen-nitrogen double-high equipment, oxygen-nitrogen-argon three-high equipment, rare gas partial extraction or full extraction equipment. The control method of the air separation device is that when it is shut down intermittently for a long time (generally more than 48 hours), the liquid in the fractionation tower is not drained to let it evaporate naturally to maintain a slight positive pressure, and the system does not need to be heated and thawed before shutting down or starting up , suitable for occasions where the low-temperature air separation unit with molecular sieve adsorber 4 at the front end is shut down for a long time but the pearlite sand is not removed for maintenance.

In a specific embodiment of the present invention, for a 6500m ³ /h air separation plant, the air separation unit only drains liquid and does not heat up when it is shut down, and a small amount of liquid is left in the upper tower to allow it to evaporate naturally. After about 8 days The liquid basically evaporates to light (the temperature of fractionation tower system 1 basically does not rise after evaporation, and the temperature of fractionation tower system 1 starts to rise after evaporation, as shown in Figure 5). The evaporation of liquid also causes the temperature in the middle of the main heat exchanger to drop, and the temperature at the hot end A small amount of sweat frosting. When it was restarted after 26 days, the system was only purged for more than 0.5 hours, and all equipment was not completely heated to normal temperature. It is generally more difficult to heat up the tower), and the cooling speed of the air separation unit is also faster. After the liquid accumulation is over and one expander is stopped, the temperature in the middle of the main heat exchanger is also normal quickly, and then the air separation unit operates normally.

Only purging time of 0.5h is due to the fact that the molecular sieve adsorber 4 was completely normal during the previous operation of the molecular sieve process equipment, and the content of carbon dioxide and other substances exiting the adsorber was very low. In addition, the resistance of the main heat exchanger did not increase. As long as the system There will be no negative suction, and the wet air will not penetrate into the system; the second is that even if there is a small amount of water frozen at the mouth of the return product pipe (oxygen output pipeline, nitrogen output pipeline and dirty nitrogen output pipeline), when the purge is restarted or even After normal start-up, the backflow gas from the product pipe is dry at low pressure and reheated at normal temperature, which can remove the moisture and take it away. On the contrary, if heating is carried out after draining, it will cause negative suction and wet air will enter. When restarting, it must be heated and purged thoroughly for a long time. The experience needs to be reheated thoroughly, generally 10h~12h , but cause energy waste (a set of 6500m ³ /h air separation equipment before and after the total heating 34h power consumption is about 150,000 KWh).

Even if the residual liquid in the tower evaporates and causes the cooling capacity to move outward, forming a certain low temperature at the outlet of the product pipe, at most only a small amount of humid air will condense on the inner wall of the outlet of the product pipe, and will not enter the equipment. The gas is blown out as it passes through.

In summary, the control method of the air separation device provided by the embodiment of the present invention, when shutting down, the compressor 3 and the molecular sieve adsorber 4 are turned off, so that the fractionation tower system 1 is not heated, and the fractionation tower system 1 is exchanged with pearlite. The temperature rises due to heat, so that the pressure in the fractionating tower system 1 is not lower than atmospheric pressure, which will not cause negative suction, and then the outside humid air cannot enter the fractionating tower system 1, so as to avoid heat exchange between the fractionating tower system 1 and pearlite after heating As a result, the temperature of the fractionation tower system 1 decreases, which in turn leads to negative suction in the fractionation tower system 1 .

In the description of the present invention, unless otherwise specified and limited, the term "plurality" refers to two or more; unless otherwise specified or explained, the terms "connected", "fixed", etc. should be broadly defined It is understood that, for example, "connection" may be a fixed connection, a detachable connection, or an integral connection, or an electrical connection; it may be a direct connection or an indirect connection through an intermediary. Those of ordinary skill in the art can understand the specific meanings of the above terms in the present invention according to specific situations.

In the description of this specification, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "front", "rear", "left", "right" etc. are based on the orientation shown in the drawings Or positional relationship is only for the convenience of describing the present invention and simplifying the description, but does not indicate or imply that the referred device or unit must have a specific direction, be constructed and operated in a specific orientation, and therefore, should not be construed as a limitation of the present invention.

In the description of this specification, descriptions of the terms "one embodiment", "some embodiments", "specific embodiments" and the like mean that specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in the present invention In at least one embodiment or example of . In this specification, schematic representations of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (10)

1. A control method for an air separation plant, said air separation plant comprising a cold box, a fractionation column system positioned in the cold box, an insulating material filled in the cold box, a compressor and a compressor connected to the compressor Molecular sieve adsorber between the machine and the fractionation tower system, the fractionation tower system includes an upper tower, a lower tower and a main unit connected between the upper tower and the lower tower and communicated with the upper tower The condensing evaporator is characterized in that it includes: When the air separation unit is shut down, the compressor and the molecular sieve adsorber are controlled to be closed, and the fractionation tower system is not heated, so that the temperature of the fractionation tower system is not higher than the temperature of the thermal insulation material . 2. the control method of air separation plant according to claim 1, is characterized in that, also comprises: Before the shutdown of the air separation device, control the air separation device to discharge part of the liquid in the upper tower and discharge the liquid in the lower tower. 3. The control method of the air separation plant according to claim 2, characterized in that, The liquid remaining in the upper column accounts for a liquid level of the main condensing evaporator less than or equal to 25% of the normal liquid level of the main condensing evaporator. 4. The control method of the air separation plant according to claim 3, characterized in that, The liquid remaining in the upper tower accounts for a liquid level of the main condensation evaporator equal to 15% of the normal liquid level of the main condensation evaporator. 5. The control method of the air separation plant according to any one of claims 2 to 4, characterized in that, A product output pipeline is connected to the upper tower, and a control valve is arranged on the product output pipeline. The control method of the air separation device also includes: before the liquid remaining in the upper tower is completely evaporated, control and adjust The opening of the control valve is such that the pressure in the fractionation column system is not less than atmospheric pressure. 6. The control method of the air separation plant according to claim 5, characterized in that, Described product output pipeline comprises oxygen output pipeline, nitrogen output pipeline and sewage nitrogen output pipeline; The control valve includes an oxygen control valve arranged on the oxygen output pipeline, a nitrogen control valve arranged on the nitrogen output pipeline, and a polluted nitrogen control valve arranged on the polluted nitrogen output pipeline. 7. The control method of the air separation plant according to claim 6, characterized in that, The molecular sieve adsorber is connected to the dirty nitrogen output pipeline, and the connecting pipeline between the molecular sieve adsorber and the dirty nitrogen output pipeline, the connecting pipeline between the molecular sieve adsorber and the compressor, the A valve is provided on the connecting pipeline between the molecular sieve adsorber and the fractionation tower system, and the control method of the air separation device further includes: before the liquid remaining in the upper tower is completely evaporated, controlling the valve to be closed . 8. The control method of the air separation plant according to claim 5, further comprising: After the liquid remaining in the upper tower is completely evaporated, the control valve is controlled to be closed. 9. The control method of the air separation plant according to any one of claims 1 to 4, further comprising: Before the air separation device is started up again, the compressor and the molecular sieve adsorber are controlled to be turned on, so as to heat the fractionation tower system. 10. The control method of the air separation plant according to any one of claims 1 to 4, characterized in that, The thermal insulation material is pearlite.