JPH0325718B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a path switching method for a switching main heat exchanger that is provided in an air separation device and is composed of a plurality of cores.

(Prior Art) Conventionally, as an air separation device equipped with a switching type main heat exchanger, there is one shown in FIG.
In the figure, reference numeral 1 denotes a raw material air compressor, and compressed raw material air compressed to a required pressure by this raw material air compressor 1 is precooled by an aftercooler or the like and sent to a switching type main heat exchanger 2. The switching main heat exchanger 2 cools the air to near the liquefaction point and supplies it to the lower column 3a of the double rectification column 3. In this lower column 3a, nitrogen having the lowest boiling point rises toward the top of the lower column 3a and is roughly separated.

The oxygen-enriched liquid air separated and stored at the bottom of the lower column 3a is sent to the upper column 3b of the double rectification column 3, and high-purity nitrogen gas is separated at the top of the upper column 3b using the boiling point difference. Similarly, argon-containing gas is separated in the midsection, and high-purity liquid oxygen is separated in the bottom. The argon-containing gas accumulated in the middle of the upper column 3b is supplied to the crude argon column 4, where argon is roughly separated.

On the other hand, product nitrogen and product oxygen are extracted from the top and bottom of the upper column 3b, respectively, and sent to the switching type main heat exchanger 2 where heat exchange is performed with the feed air. Further, surplus impure nitrogen is extracted from the middle part of the upper column 3b, and impure nitrogen is also extracted from the middle part of the lower column 3a. A part of the impure nitrogen from the lower column 3a is sent to the direct switching main heat exchanger 2 as reheated nitrogen, and the rest is adiabatically expanded by the expansion turbine 5 to a low temperature state, and is transferred to the upper column 3b.
It is sent to the switching main heat exchanger 2 in a reduced pressure state to about 0.03 Kg/cm ² together with impure nitrogen from the air.

This switching type main heat exchanger 2 includes a core 6 as shown in FIG. Although only one core 6 is shown in the figure, in reality many such cores are connected in parallel.

In the same figure, passage A and passage B have five
The feed air pressurized to Kg/cm ² and the impure nitrogen mentioned above are made to flow alternately by switching, and CO ₂ solidified in the passage is removed by cooling the feed air.
and H ₂ O by sublimation or melting with low pressure nitrogen,
It is designed to prevent the passageway from being blocked by CO ₂ and H ₂ O. The product oxygen is sent to the passage C, the product nitrogen is sent to the passage D, and the reheated nitrogen is sent to the passage E.

Next, the procedure for switching between the passage A and the passage B will be explained. In each core 6, a switching valve 7 is provided on the upstream side in the flow direction of the raw material air, and this switching valve 7
A damper 8 is provided on the upstream side of the core 6, and a driven valve 9 that is driven by the pressure of the flowing gas is provided on the downstream side of the core 6. As shown in FIG. 3, the switching valve 7 is provided with a solenoid valve 10, and the damper 8 is provided with a solenoid valve 11, which are connected to a switching control panel 12. This switching control panel 12 controls the solenoid valves 10 and 11.
is turned on and off, thereby opening and closing the damper 8 and opening and closing the passage A, which is caused by the switching valve 7 and the driven valve 9.
B switching is performed.

These switching valves 7 and dampers 8 are switched as follows. First, as shown by the solid line in FIG.
is located, the damper 8 is closed by operating the solenoid valve 11, and the switching spindle 13 is closed by operating the solenoid valve 10.
move. During this movement of the switching spindle 13, passage A and passage B communicate with each other, so that the pressure in passage A and the pressure in passage B are equalized. When damper 8 is opened in this state, 0.03Kg/
cm ² of impure nitrogen flows through passage B, and 5 kg/cm ² of raw material air flows through passage B, completing the switching between passages A and B.

By the way, conventionally, in each core 6, passages A and B
If the main heat exchanger 2 is equipped with, for example, 45 cores 6, a plurality of cores (for example, 5
A method is used in which the cores 6 (individuals) are considered as one block and switching is performed for each block. but,
In such block switching, the passages of a plurality of cores 6 are switched at the same time, so compared to the case where the passages are switched for each core 6, the volume of the passages that are switched in one switching is larger, and this is unavoidable. However, fluctuations in the pressure and flow rate of the raw air become large, resulting in the following disadvantages.

FIG. 4 shows the gas composition distribution in the upper column 3b of the rectification column 3. As shown in the figure, highly pure nitrogen and oxygen are obtained at the top and bottom of the upper column 3b, respectively, and gas with the highest argon content is obtained at the middle section. When pressure fluctuations occur, the composition distribution of each gas also fluctuates, making the purity of the nitrogen and oxygen products unstable, making it difficult to obtain stable quality.

In particular, when the above-mentioned apparatus is equipped with a crude argon column 4 for separating argon, the pressure difference between the upper and lower parts of the crude argon column 4 (tower differential pressure) is smaller than that of the upper column 3b, so the above pressure The fluctuations have a large effect on the tower differential pressure, and the composition distribution of the extracted argon-containing gas fluctuates greatly. For this reason, it is not easy to set the amount of hydrogen required when deoxidizing argon-containing gas, and it is necessary to add more hydrogen than is actually required to the extracted argon-containing gas. If the amount is excessively large, the risk of explosion, etc. increases, so the amount of argon-containing gas extracted must be reduced, resulting in the problem that a sufficient amount of argon cannot be obtained.

In order to reduce pressure fluctuations in the feed air that cause such inconveniences, it is possible to perform core switching in which the passages are switched for each core, but the minimum time required to switch the passages in each core 6 is sufficient. is determined, so when switching the cores 6 one by one in this way, the time required to switch all the cores 6 is longer than when switching each block as described above, and as a result, the next This causes inconveniences such as.

Generally, during steady operation of the device, the impure nitrogen sent from the expansion turbine 5 is sufficiently cooled, so that the impure nitrogen in the air sent to the main heat exchanger 2 is
H ₂ O or CO ₂ is already solidified near the inlet (lower position in Figure 2). However, when the equipment is stopped and restarted due to maintenance or an accident, for example, the impure nitrogen sent from the expansion turbine 5 is not sufficiently cooled, so the H ₂ O or CO ₂ will not solidify near the entrance, but will solidify further in the middle.

In other words, during steady operation, there is already a
Since H ₂ O or CO ₂ solidifies, it is difficult for such solidified H ₂ O or CO ₂ to accumulate in the back of heat exchanger 2, but if the temperature of impure nitrogen is sufficiently lowered, such as at the time of restart, If not, add H ₂ O or
Since CO ₂ solidifies from the depths of the passage, it tends to solidify and accumulate one after another within the passage, causing the passage A or passage B to become clogged or a pressure loss of the raw air to occur within the passage. Furthermore, since the feed air contains a large amount of moisture upon restart, the coagulation of H ₂ O is further accelerated.

Therefore, in such cases, it is necessary to shorten the switching cycle between passages A and B and to frequently flush the passages with impure nitrogen, but there is a limit to the shortening of the switching cycle with core switching as described above. There is enough
Removal of H ₂ O or CO ₂ is difficult to perform.

(Object of the Invention) In view of the above circumstances, the present invention has been developed in a switching type main heat exchanger in an air separation device, in which there is little pressure fluctuation when switching passages, and in addition, when the impure nitrogen being sent is not sufficiently cooled. Also solidified CO ₂ and
It is an object of the present invention to provide a passage switching method that can prevent the passage from being blocked by H ₂ O.

(Structure of the Invention) The present invention provides a switching main heat exchanger installed in an air separation device, which is composed of a plurality of cores, and in each core, a passage through which raw material air flows and a passage through which impure nitrogen sent from a rectification column flows can be switched. In the exchanger, the temperature of the impure nitrogen sent to the core is detected, and if this temperature is above a predetermined value, all the cores are divided into multiple blocks and the passages are sequentially switched for each block until the temperature reaches the predetermined value. If it is less than the value, the passages are sequentially switched for each core.

(Example) FIG. 5 shows an air separation apparatus for carrying out the method of the present invention, and parts equivalent to those in FIGS. 1 to 4 above are given the same reference numerals. In this embodiment, as shown in FIG. 5, the temperature of impure nitrogen at the outlet side of the expansion turbine 5 is detected by a temperature sensor 14, and this detected value is input to the switching control device 15. In addition, in this device, the temperature on the outlet side of the expansion turbine 5 is approximately −170°C during steady operation.
Temperatures are starting to drop below ℃.

In this device, the basic switching structure of the switching main heat exchanger 2 is the same as that shown in FIGS. 2 and 3 above. Furthermore, in this embodiment, the sixth
As shown in the figure, a switching control panel 12 to which the solenoid valve 10 of each core 6 is connected includes a switching switch 16 for selecting core switching and block switching, a block switching timer 17, and a core switching timer 18. A signal is inputted to the changeover switch 16, and a signal from the changeover control device 15 is inputted to the changeover switch 16. Although not shown, each electromagnetic valve 11 is similarly connected to the switching control panel 12.

This main heat exchanger 2 has 45
The block switching timer 17 has five cores 6 among these cores 6.
is one block, and each block has a path A,
The operating intervals of the switching valve 7, the damper 8, and the driven valve 9 are determined so as to perform switching B, and the signals thereof are output to the switching control panel 12. For example, in Figure 7, first, the first
The passages of the cores 6 of the blocks are switched at once, then the passages of the cores 6 of the second blocks 6 to 10 are switched at once, and the passages of the cores 6 of the 45th block are switched in the same way, and then the passages of the cores 6 of the 45th blocks are switched again. The core 6 of the block is switched. On the other hand, the core switching timer 18
determines the operating intervals of the switching valve 7, damper 8, and driven valve 9 so as to sequentially switch the cores from No. 1 to No. 45 one by one in the figure, and outputs a signal.

The switching control device 15 sends a signal to select block switching with the changeover switch 16 when the detected value by the temperature sensor 14 is above a predetermined value (here -130°C), and when it is below the predetermined value is configured to send a signal indicating selection of core switching.

Generally, this predetermined value is
Based on the position where CO ₂ and H ₂ O solidify in passage A or passage B, it may be set as appropriate depending on the device. For example, during steady operation, when CO ₂ and H ₂ O in the feed air are sufficiently cooled to solidify at the inlet, the core is _switched ; Also, if the H ₂ O is cooled only to a temperature at which it enters the depths (approximately the middle part) of the passages A and B, then block switching may be performed.

In such a device, first, during steady operation, the temperature on the output side of the expansion turbine 5 has fallen sufficiently, so the core switching mode is selected by the action of the switching control device 15 and the switching switch 16.
Switching between paths A and B is performed one core at a time. At this time, for example, assuming that the minimum time required to switch the passage in each core 6 is 2 seconds, the cycle in which the passage of one core is switched (time to complete switching of all cores) is at least 2 (seconds). ×45 (core) = 90 (seconds) is required.

On the other hand, in passages A and B, _CO2 in the raw air and
H ₂ O solidifies, but since the main heat exchanger 2 is sufficiently cooled by impure nitrogen sent from the expansion turbine 5, CO 2 and H 2 O solidify at the inlet, and the CO ₂ and H ₂ O solidify at the back of the passage. Almost no accumulation. Therefore, the solidified CO ₂ and H ₂ O can be sufficiently melted or sublimed by the low pressure impure nitrogen introduced in a 90 second cycle.

On the other hand, at the time of starting use or restarting after a stop due to maintenance or failure, the output side temperature of the expansion turbine 5 has not fallen sufficiently, so the block switching mode is selected by the switching control device 15 and the switching switch 16. and aisles A and B
The switching is performed for every 5 cores. For example, if the minimum time required to switch the passage in each core 6 is 2 seconds, the minimum cycle for switching the passage in one core is 2 (seconds) x 9 (blocks) = 18 (seconds). .

On the other hand, in passages A and B, _CO2 in the raw air and
H ₂ O solidifies, but the temperature of the impure nitrogen sent from the expansion turbine 5 has not fallen sufficiently and the main heat exchanger 2 has not been sufficiently cooled, so CO ₂ and H ₂ O are removed from the inlet. It solidifies at the part where it has penetrated deep,
Try to accumulate in the aisle. However, at this time, the passages are switched by block switching, and low-pressure impure nitrogen can be introduced in a cycle of 18 seconds at the shortest, so CO ₂ and H ₂ O that solidify one after another can be quickly removed. , can prevent blockage of the passage.

As described above, in the switching method of the present invention, CO ₂ and H _{2 O} can be quickly removed by switching the passages in blocks when the temperature of impure nitrogen has not fallen sufficiently, such as when the equipment is started up. death,
Moreover, during steady operation when CO ₂ and H ₂ O accumulation is unlikely to occur, switching is performed on a core-by-core basis. Therefore, during steady operation, the volume of the passages that can be switched at one time is reduced to approximately 1/5, so that fluctuations in the pressure and flow rate of raw air due to passage switching are significantly reduced compared to the conventional method.

Figures 8 to 10 show time and feed air flow rate, time and differential pressure in the upper column 3b, and time and crude argon column 4.
The relationship between the tower differential pressure is shown, respectively.
As shown in these figures, by setting the core switching mode during steady operation, it is possible to significantly suppress fluctuations in the flow rate of feed air and fluctuations in the differential pressure in each tower. Along with this, the composition distribution in the lower column 3a and upper column 3b of the rectification column 3 is stabilized, nitrogen and oxygen of stable quality can be obtained, and argon in the gas extracted from the crude argon column 4 is stabilized. Since the content rate is also stable, it is possible to increase the amount of argon produced.

Along with this, the operating range of the raw material air compressor 1 is also expanded. FIG. 11 shows the performance curve of the compressor 1, where the straight line L is the surge line, the curves C ₁ ,
For C ₂ and C ₃ , the guide valve opening degree is 33.5%, respectively.
This shows the relationship between flow rate and pressure at 69.4% and 94%. For example, if the pressure of raw air is 5Kg/cm ² G
Assuming that the maximum value of the guide valve opening is 69.4%,
The original operating range of the compressor 1 is J, but if there is a pressure fluctuation due to passage switching, the minimum flow rate must have an allowance of 1/2 of the fluctuation range. As shown in the figure, the flow rate fluctuation width H in the case of core switching is much smaller than the flow rate fluctuation width G in the case of block switching, and therefore the minimum flow rate of the compressor 1 can be set to a smaller value. Therefore, the operating range F of the compressor 1 when the core is switched is wider than that of the compressor 1 when the block is switched.

In this embodiment, the signal from the temperature sensor 14 is input to the switching control device 15 to automatically select between block switching and core switching. Alternatively, the block switching or core switching may be manually selected.

Further, in the same embodiment, the output side temperature of the expansion turbine 5, that is, the temperature of the impure nitrogen introduced, is detected, but the temperature of this impure nitrogen and the temperature in the passages A and B follow each other. However, the same effect as described above can be obtained by directly detecting the temperature in the passages A and B and selecting between block switching and core switching based on the detected temperature.

(Effects of the Invention) As described above, the present invention detects the temperature of impure nitrogen sent to each core, and when this temperature is higher than a predetermined value, divides all the cores into a plurality of blocks and divides each core into multiple blocks. The passages are sequentially switched, and if the same temperature is below a predetermined value, the passages are switched sequentially for each core, so the impure nitrogen temperature is high and CO ₂ and H ₂ O in the raw air are transferred to the deep part of the passage. In conditions where impure nitrogen is likely to solidify and accumulate, block switching quickly introduces impure nitrogen and removes CO ₂ and H ₂ O to prevent passage blockage. During steady operation, core switching It is possible to suppress fluctuations in the pressure and flow rate of raw air. This variation in pressure and flow rate can provide effects such as stabilizing the quality of product nitrogen and product oxygen, increasing the production amount of product argon, and expanding the operating range of the raw air compressor.

[Brief explanation of the drawing]

Fig. 1 is a structural diagram of a conventional air separation device, Fig. 2 is a structural diagram of a switching type main heat exchanger in the same air separation device, and Fig. 3 is a structural diagram of passage switching in the switching type main heat exchanger. Fig. 4 is a graph showing the gas composition distribution in the upper column of the rectification column of the air separation device, Fig. 5 is a structural diagram of the air separation device in which the method of the present invention is implemented, and Fig. 6 is the switching system in the same device. A structural diagram showing the switching control of the solenoid valve of the main heat exchanger, Fig. 7 is an explanatory diagram of block switching and core switching, Fig. 8 is a graph showing the relationship between time and raw air flow rate, and Fig. 9 is a graph showing the relationship between time and raw air flow rate. Figure 10 is a graph showing the relationship between time and the differential pressure in the crude argon column, and Figure 11 is a graph showing the performance curve of the raw air compressor. be. 2... Switchable main heat exchanger, 3... Rectification column, 6...
... Core, 14 ... Temperature sensor, 15 ... Switching control device, A, B ... Passage.

Claims (1)

[Claims] 1. In a switching type main heat exchanger installed in an air separation device, consisting of a plurality of cores, and in each core, a passage through which feed air flows and a passage through which impure nitrogen sent from a rectification column flows can be switched. Detects the temperature of impure nitrogen flowing through the air, and if this temperature is above a predetermined value, all cores are divided into multiple blocks and the passages are sequentially switched for each block, and when the same temperature is below a predetermined value, each core is 1. A method for switching passages in a switching type main heat exchanger in an air separation device, characterized in that the passages are sequentially switched for each passage.