JPS6346352B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control method for a reversible heat exchanger for an air separation device, and in particular, a temperature control method for a reversible heat exchanger for an air separation device, which is suitable for smooth startup of the reversible heat exchanger for an air separation device. This paper relates to a temperature control method for a reversible heat exchanger.

Generally, when an air separation device is started, the entire air separation device is at room temperature, so moisture and carbon dioxide (hereinafter referred to as impurities) contained in the feed air are not brought into the rectification column side of the air separation device. First, due to the cold generated in the expander, the reversible heat exchanger was cooled down to a state where the reversible heat exchanger could completely remove impurities contained in the feed air, so that no impurities were brought into the expander. Afterwards, the rectification column is cooled down. Thus, when starting up the air separation device,
In order to cool the reversible heat exchanger and rectification column that are at room temperature, it is necessary to increase the amount of gas processed in the expander. The amount of dry low-temperature gas (hereinafter referred to as reheated gas) flowing through the reversible heat exchanger or the amount of feed air extracted from the middle of the reversible heat exchanger (hereinafter referred to as bleed air) also increases. Excessive cooling causes the temperature balance of each part of the reversible heat exchanger to collapse, resulting in a supercooled state, which causes the reversible heat exchanger to lose its ability to sublimate and remove condensed impurities on the wall surface of the channel used for switching. If this continues for a long time, it will become impossible to drive. In order to avoid such inconveniences, the temperature of each part of the reversible heat exchanger must be
It is necessary to always control the temperature to a certain specified temperature.

Conventionally, the temperature control of each part of a reversible heat exchanger is performed by detecting the temperature of an intermediate part of the reversible heat exchanger and adjusting the amount of reheat gas or bleed air based on the detected temperature.

In this temperature control method for a reversible heat exchanger, the amount of reheat gas or bleed air is forcibly reduced so that the temperature in the middle part of the reversible heat exchanger reaches a specified temperature. There were flaws.

(1) The temperature at the inlet of the expander decreases, resulting in an abnormal state in which liquid is generated, making it impossible to utilize the full capacity of the expander, resulting in a longer start-up time.

(2) It is extremely difficult to operate the expander because it is necessary to change the operating operation of the expander each time due to a reduction in the amount of reheated gas or the amount of bleed air.

The present invention aims to eliminate the above-mentioned drawbacks, and is used by switching the flow path when starting up the air separation device, and controlling the temperature to a specified value by adjusting the amount of reheated gas or the amount of bleed air. When the temperature of the reversible heat exchanger drops below the specified temperature,
In addition, if the temperature of the combined gas on the outlet side of the expander, which adiabatically expands the combined gas of raw material air cooled by the reversible heat exchanger and reheated gas or bleed air to generate cold, is higher than the saturation temperature, In addition to reducing the amount of heated gas or bleed air, when the temperature of the combined gas at the expander outlet side drops to around the saturation temperature, it is separated from the feed air in a rectification column that separates the feed air, and the reversible heat A part of the low-temperature separation gas that cools the feed air in the exchanger is released on the upstream side of the reversible heat exchanger, which reduces the start-up time of the air separation device and facilitates the operation of the expander. The present invention provides a method for controlling the temperature of a reversible heat exchanger for an air separation device.

An embodiment of the present invention will be described with reference to the drawings.

The drawing is a partial system diagram of an air separation device in which the present invention is implemented, and raw air is supplied to a compressor (not shown) that
After being compressed to Kg/cm ² G and cooled with water, it is passed from the conduit 1 through either the switching valve 2 or 3 to either the switching A flow path 7 or the B flow path 8 in the reversible heat exchanger 6. It is cooled to near the saturation temperature of air by the low-temperature return gas and reheated gas, such as reheated air, which are separated in the rectification column 12. During this cooling stage, impurities condense on the wall surface of the switching A channel 7 or B channel 8 of the reversible heat exchanger 6 and are completely removed.

The raw air from which impurities have been removed and which has been cooled to a low temperature is mostly blown into the lower part of the lower column 12a of the rectification column 12 through the conduit 11 through the check valve 9 or 10.

The rectifying column 12 is a so-called double rectifying column in which a lower column 12a and an upper column 12b are integrated.
A so-called main condenser 13 is installed to evaporate and condense the nitrogen gas above 2a.

The raw material air blown into the lower column 12a is rectified and separated into liquid nitrogen in the upper part of the lower column 12a and liquid air with an oxygen concentration of about 40% in the lower part of the lower column 12a. expansion valve 1
5, the pressure is reduced to approximately 0.5Kg/cm ² G, and the conduit 1
6 to the upper part of the upper column 12b as a reflux liquid. The liquid air at the bottom of the lower column 12a is cooled by nitrogen gas from the upper column 12b through a conduit 17 to a supercooler 18, and then passed through a conduit 19 to an expansion valve 20 at a pressure of about 0.5.
The pressure is reduced to Kg/cm ² G and the upper column 12b
It is supplied to the middle part as a reflux liquid.

On the other hand, the remaining raw material air that has been cooled by the reversible heat exchanger 6 and from which impurities have been removed is sent from the conduit 11 to the branch pipe 2.
2, a part of it passes through the conduit 23 from the cold end of the reversible heat exchanger 6 through a passage without switching as reheated air of the reversible heat exchanger 6, cools the raw air, and raises the temperature of itself, until the temperature reaches approximately The air is extracted from the middle of the reversible heat exchanger 6 at -120°C, and is controlled to an appropriate amount for sublimation of carbon dioxide through the conduit 24 by the reheat air amount control valve 25, and then from the conduit 26 to the remaining conduit 27 by the control valve 2.
8. It joins with the low-temperature raw material air coming through the conduit 29 in the conduit 30, becomes uniform in temperature, undergoes adiabatic expansion in the expander 31, becomes low temperature itself, and is blown into the middle of the upper column 12b through the conduit 32. In this way, all the raw material air is sent to the upper column 12b and separated into oxygen and air by rectification, and nitrogen passes through the conduit 33 from the upper part of the upper column 12b, is heated in the supercooler 18, and is further heated to the first By liquefying a part of the air in the liquefier 34, the temperature is raised and the impurities in either the switching A flow path 7 or the B flow path 8 of the reversible heat exchanger 6 are condensed. It cools the feed air and raises its own temperature.At this time, it sublimates condensed impurities, reaches room temperature, and is discharged from the system through one of the switching valves 4 and 5 through the conduit 36.

The switching A channel 7 and the B channel 8 are periodically switched every 10 to 15 minutes and are operated continuously without being blocked by impurities.

On the other hand, the oxygen separated in the upper column 12b is stored as liquid oxygen in the main condenser 13 at the bottom of the upper column 12b, and a part of the evaporated gas is taken out from the conduit 37 and the raw air is liquefied in the second liquefier 38. The temperature of the heat is increased and the heat is guided to the cold end of the reversible heat exchanger 6 through the conduit 39.
It flows through a flow path without switching, during which time the raw material air is cooled and its own temperature is raised to a normal temperature state, and then sent out as a product oxygen gas to a separate use destination (not shown) through a conduit 40.

When the temperature of the reversible heat exchanger 6 detected by the temperature detector 41 provided at the outlet side of the reheated air of the conduit 24 falls below a specified temperature at the time of startup of such an air separation device, and If the temperature of the combined gas on the outlet side of the expander 31 detected by the temperature detector 42 provided on the conduit 32 on the outlet side of the expander 31 is higher than the saturation temperature, the temperature detectors 41, 42
In response to the signal, the automatic control device 43 is activated, and the reheat air amount control valve 25 provided on the outlet side of the reheat air of the conduit 24 is throttled. Reversible heat exchanger 6 with reduced air volume
The temperature in the middle part of is controlled to a specified temperature. In this state, when the temperature of the combined gas on the outlet side of the expander 31 detected by the temperature detector 42 drops to near saturation, the automatic control device 43 operates in response to a signal from the temperature detector 42, and the upper tower A low-temperature gas release control valve 45 provided in a conduit 44 branched from the oxygen gas conduit 39 at the lower part of the oxygen gas conduit 12b is opened by an appropriate amount. A portion of the low-temperature oxygen gas, which is the low-temperature separation gas that cools the feed air at 6, is discharged to the atmosphere upstream of the reversible heat exchanger 6 through conduit 44, low-temperature gas discharge valve 45, and conduit 46. Therefore, the amount of low-temperature oxygen gas supplied to the reversible heat exchanger 6 is reduced, and the amount of cold in the reversible heat exchanger 6 is reduced, thereby preventing overcooling of the reversible heat exchanger.

In the temperature control method of a reversible heat exchanger for an air separation device as in this example, by reducing the amount of reheated air when starting up the air separation device, the temperature in the middle part of the reversible heat exchanger reaches a specified temperature. In addition, the temperature of the combined gas on the outlet side of the expander never falls below the saturation temperature, so the expander's cold generation ability can be fully utilized, and the amount of reheated air can be There is no need to change the operating operation of the expander. Previously, it was thought that releasing low-temperature separated gas into the atmosphere when starting up an air separation device would not only result in cooling loss for the entire air separation device, but would also have a negative effect on the sublimation removal of condensed impurities. However, in the present invention, since the expander's cold generation ability can be fully utilized, the amount of cold generated by the entire air separation device increases, and the amount of low-temperature separated gas released into the atmosphere is reduced. Since the amount of air is only about 1 to 5% of the total amount of air in the air separation device, there is no fear that sublimation removal of condensed impurities will be inhibited.

In this example, raw air cooled by a reversible heat exchanger was used as the reheated gas and the gas adiabatically expanded in the expander. It is obvious that the same actions and effects as described above can be obtained even if nitrogen gas from the lower column is used, and furthermore, no particular problem occurs even if bleed air is used instead of reheated gas. Regarding the release of low-temperature separation gas, in this example, the case of releasing low-temperature oxygen gas was explained, but it is also possible to release low-temperature nitrogen gas. In the case of a device for extracting pure nitrogen, a similar effect can be achieved by releasing cold gas from the inlet conduit of a reversible heat exchanger for high purity nitrogen. Furthermore, in this embodiment, an intermediate reheating type reversible heat exchanger in which reheated gas is taken out from the middle of the reversible heat exchanger was used as the reversible heat exchanger. A similar effect can be obtained by using a reversible heat exchanger of a hot end reheating type in which heat is taken out from the hot end of the exchanger. In addition, in general air separation equipment, a blow valve for heating and drying when the air separation equipment is stopped is provided, similar to the low-temperature gas release valve described in this example. When operating manually without installing an automatic control device, a blow valve may be used to release the low temperature separated gas.

As explained above, the present invention provides a method for controlling the temperature of a reversible heat exchanger for an air separation device, when the temperature of the reversible heat exchanger falls below a specified temperature, and when the combined gas on the outlet side of the expander is If the temperature is higher than the saturation temperature, the amount of reheated gas or extracted air is reduced, and when the temperature of the combined gas at the expander outlet drops to around the saturation temperature, it is separated from the raw air in the rectification column. In addition, by releasing a part of the low-temperature separated gas that cools the feed air in the reversible heat exchanger on the upstream side of the reversible heat exchanger, the temperature of the reversible heat exchanger can be controlled to a specified temperature, and Since the expander's cold generation ability can be fully utilized, it has the effect of shortening the start-up time of the air separation equipment, and changes the operating operation of the expander by reducing the amount of reheated gas or bleed air. Since this is not necessary, there is an effect that the operation of the expander can be made extremely easy.

[Brief explanation of the drawing]

The drawings illustrate one embodiment of the invention,
FIG. 1 is a partial system diagram of an air separation device implementing the present invention. 2 to 5...Switching valve, 6...Reversible heat exchanger,
9, 10...Check valve, 11, 22, 23, 24,
26, 27, 30, 32, 33, 35, 37, 3
9,44,46... Conduit, 12... Rectification tower, 18
...Supercooler, 25...Reheat air control valve, 28...
... Regulating valve, 31... Expander, 34... First liquefier, 38... Second liquefier, 41, 42... Temperature detector, 43... Automatic control device.

Claims (1)

[Claims] 1. A reversible heat exchanger that is used by switching the flow path and is controlled to a specified temperature by adjusting the amount of reheat gas or bleed air, and the raw material air cooled by the reversible heat exchanger and the reheated Temperature control at the time of startup of the reversible heat exchanger of an air separation device comprising an expander that adiabatically expands the gas or the combined gas with the bleed air to generate cold, and a rectification column that separates the raw material air. In the method, if the temperature of the reversible heat exchanger falls below the specified temperature and the temperature of the combined gas on the outlet side of the expander is higher than the saturation temperature, the amount of reheated gas or extracted gas When the amount of air is reduced and the temperature of the combined gas on the outlet side of the expander drops to around the saturation temperature, the raw air is separated from the raw material air in the rectification column and cooled in the reversible heat exchanger. 1. A temperature control method for a reversible heat exchanger for an air separation device, characterized in that a part of the low-temperature separated gas is released on the upstream side of the reversible heat exchanger.