JPH0673625B2 - Reactor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a novel multi-tube reactor for methanol synthesis.

[Conventional technology]

A method is well known in which a gas containing hydrocarbon as a main component is steam-reformed to obtain a mixed gas of mainly hydrogen, carbon monoxide, and carbon dioxide, and methanol is synthesized using this as a raw material.

An example of this kind of methanol synthesis is commonly used in Table 1 (Source: Catalysis Society of Japan, Catalyst Lecture NO.6 “Catalyst Reactor and its Design”, p. 294, published by Kodansha Scientific, December 1985). Figure 6 shows the equipment arrangement and pipe system of the existing methanol synthesis plant.

In FIG. 6, a synthetic raw material gas 1 mainly composed of hydrogen, carbon monoxide and carbon dioxide obtained from a hydrocarbon steam reforming system was compressed by a synthetic gas compressor 2 and then separated by a methanol separator 3. After being mixed with the circulating gas 4 and further compressed by the circulating gas compressor 5, it is heated by the heat exchanger 6 and supplied to the methanol synthesizing reactor 7 to carry out the methanol synthesizing reaction. The synthesized gas is cooled by the heat exchanger 8 and sent to the methanol separator 3, where the circulating gas 4
The unreacted gas and the crude methanol solution 9 are separated, and a part of the circulating gas 4 is released as a purge gas 10 to the outside of the system, but most of it is circulated as described above.

As the methanol synthesis reactor 7 of FIG. 6, a plurality of reaction tubes are filled with a granular solid catalyst, and a pressurized mixed gas containing hydrogen, carbon monoxide, and carbon dioxide as significant substances is flowed in the catalyst layer. Then, the catalytic reaction of 2H ₂ + CO → CH ₃ OH (1) is generated, and pressurized water under saturated conditions at a temperature lower than the appropriate reaction temperature is positioned on the outer surface of the reaction tube (1). Reactor that tries to maintain the reaction temperature within the proper range by converting the heat generated by the exothermic reaction of water into the latent heat of vaporization of water by heat transfer through the wall of the reaction tube (Japanese Patent Publication No. 56-22854). (See Japanese Laid-Open Patent Publication No. 2003-242242) and a reactor previously proposed by the present inventors, that is, a central tube is located at the center of a plurality of reaction tubes, and an annular space surrounded by the reaction tubes and the central tube is provided with a granular catalyst filling section. And the unreacted supply gas flows from below to above the central tube, and A reactor for performing an exothermic reaction in which the gas flows from the upper side to the lower side in the catalyst layer, the central tube through which the unreacted supply gas flows is connected to one or more mixing chambers installed at the upper part. And a reactor provided with a cold unreacted feed gas introduction part having a temperature lower than that of the unreacted feed gas exiting the central tube (JP-A-60-2
25632) and so on.

An outline of the above reactor is shown in FIG. This reactor is provided with a plurality of (only one is shown in the figure) reaction tubes 11, and inside the tubes 11, as shown in FIG.
And methanol is generated by a catalytic reaction while the gas moves through this catalyst layer, and the heat of reaction is transferred to the water in contact with the outside of the reaction tube 11 to obtain steam.

The gas (unreacted gas) that has been pressurized by the compressor (2 and 5 in FIG. 6) and preheated by the heat exchanger (6 in FIG. 6) is
In the figure, it is fed into a space a partitioned by an upper mirror 13 and an upper tube sheet 14. This gas disperses and flows into a plurality of reaction tubes 11 and moves in the reaction tubes 11 from top to bottom while causing the catalytic reaction of the formula (1), and is a space partitioned by a lower tube sheet 15 and a lower mirror 16. Then, it is taken out from the gas outlet nozzle provided in the lower mirror 16. Pressurized water at a saturated temperature is introduced into the space c surrounded by the upper and lower tube plates 14 and 15, the body 17, and the reaction tube 11.

The outline of the above reactor is shown in FIG. This reactor uses a gas that does not pass through a heat exchanger (6 in FIG. 6). Therefore, the temperature of the gas introduced into the reactor is 30-150.
This is different from the case of the above-mentioned reactor because the temperature is low to cause the catalytic reaction with C.

This unreacted gas is the lower mirror 16 and the partition plate in FIG.
It flows into the space e surrounded by 18. After that, the plurality of (only one is shown in the figure) dispersion flows into the central tube 19 located in the reaction tubes 11, flows in the central tube 19 from bottom to top, and the upper mirror 13 and the upper tube sheet. It flows into the space partitioned by 14. This gas transfers heat of contact reaction to the wall of the tube as it rises in the central tube 19.
Given by heat transfer via 19 (heated and heated),
That is, in this process, the gas is preheated to an appropriate temperature and prevents the catalytic reaction temperature from rising excessively. In this way, the central tube 19 functions as a heat exchanger, and the unreacted gas has a role as a refrigerant.

The unreacted gas flowing into the space flows from the top to the bottom of the catalyst 12 layer filled in the annular columnar space between the reaction tube 11 and the central tube 19 to cause a catalytic reaction, and the lower tube sheet. 15 and dividers
It flows out into a space composed of 18 and then taken out from a gas outlet nozzle.

The heat generated in the process of causing the contact reaction while the gas moves in the annular columnar space is given to the gas in the central tube 19 and the reaction tube 11 is in contact with the pressurized water at the saturation temperature outside the reaction tube 11. It is provided by the heat transfer through the tube wall of and prevents the reaction temperature from rising excessively. The heat given to water is taken out as water vapor and used for power and other purposes.

By the way, as the catalyst used in the methanol synthesis reactor as described above, the most excellent copper-based catalyst at present is a proper reaction temperature range of 220 to 280 ° C., and the activity of the catalyst decreases when the temperature is higher than this temperature. There is a drawback that the equilibrium methanol concentration is lowered and undesirable side reaction products are increased. This temperature control is a major factor that controls the quality of the structure of the reactor for methanol synthesis. In particular, as the reaction rate increases with the improvement of the catalyst, the amount of heat generated also increases, which causes a serious problem in the temperature control technique. Unless this point is solved, the space velocity cannot be reduced.

If this space velocity can be made small, the gas flow resistance when the gas moves through the catalyst layer, that is, the pressure loss becomes small, and the driving energy (power cost) of the circulating gas compressor can be made small. The catalytic reaction time is long and the amount of methanol produced in the reactor can be large (close to the equilibrium concentration), which is an industrial advantage.

However, in the above structure, the amount of heat transfer through the tube wall of the reaction tube is limited, and the performance of the reactor is limited. That is, the heat transfer coefficient α on the water side when water transfers while generating steam bubbles on the metal wall surface is about 10,000 kcal / m ²
It is h · ° C, and it is impossible to increase it significantly. On the other hand, the heat transfer coefficient between the gas in the reaction tube and the metal wall surface is α = 1,000 to 3,000 kcal / m ² · h · ° C, although it fluctuates slightly depending on the pressure, gas composition, and flow rate, and this is greatly increased. It is impossible to let them do it.

Therefore, the heat transfer to water brought into contact with the outer surface of the reaction tube is not sufficient as a high-performance reactor in the future, and the inventors have positioned the central tube in the center of the reaction tube and He proposed the above-mentioned reactor functioning as a heat transfer tube, that is, a heat exchanger.

Incidentally, in FIG. 6, the composition of the gas 4 separated by the methanol separator 3 has a small CO, CO ₂ / H ₂ ratio as is clear from the purge gas composition of Table 1, and is about 0.05 at the point H in FIG. Is. On the other hand, the gas 1 supplied from the steam reforming system is CO, CO ₂ / H as shown in the gas composition at the inlet of the synthesis gas compressor in Table 1.
_{The 2} ratio is large and is about 0.30 at point G in FIG. This is an example, and the composition of the natural gas supplied to the steam reformer
It depends on the C / H ratio and the performance of the methanol synthesis reactor. However, there is a large difference in the CO, CO ₂ / H ₂ ratio between the outlet gas 4 of the methanol separator 3 and the makeup gas 1 from the steam reforming system, although there are some fluctuations in the concrete values. .

For the inlet gas of the methanol synthesis reactor 7 in Table 1, the outlet gas of the methanol separator is mixed at a ratio of 3.75 with respect to the supplementary gas 1 from the steam reforming system. As a result, CO, CO ₂
The / H ₂ ratio of about 0.09 is fed into the reactor 7 and brought into contact with the catalyst.

[Problems to be solved by the invention]

Figure 9 shows the temperature distribution along the length of the reaction tube when a methanol synthesis reaction is performed using the reactor with the above structure [Source: Nozawa et al. "Methanol" Chemical Engineering Vol.46 NO.9
(1982) 512]. FIG. 9 (A) shows the same reactor as that of FIG. 7, and FIG. 9 (B) shows the temperature distribution at the corresponding position in FIG. 9 (A).

As shown in FIGS. 9A and 9B, the temperature rises at the catalyst layer inlet: (1) The methanol concentration of the inflowing gas is substantially zero, and the difference from the reaction equilibrium concentration is large. (2) This is because the reaction rate is large (the amount of heat generated per unit tube length, that is, the unit heat transfer area is large) because the unreacted CO and CO ₂ concentrations are high. It should be even more prominent.

Note that FIG. 9 also includes the factor of temperature increase-reaction rate increase.

Further, the temperature gradually decreases as it goes downward from the catalyst layer inlet, that is, from the upper region of the reaction tube in FIG. 9 (A), which means that the gas in contact with the granular solid catalyst contains a significant concentration of methanol, This is because, although there is a difference with the reaction equilibrium concentration, the reaction rate is small because the unreacted CO and CO ₂ concentrations, which are not as high as those in (1) above, are lower than in (2) above.

In other words, the reactor shown in FIG. 9 has a problem that the reaction load distribution in the tube length direction is greatly different and the load in the vicinity of the catalyst layer inlet is extremely large (too large).

On the other hand, the above-mentioned reactor proposed by the present inventors shows a behavior similar to that of FIG. 9 although there is a great improvement from that of FIG. 9 due to heat transfer through the central tube.

As described above, this increase in temperature is not preferable in terms of deactivation of the catalyst and undesired increase of side reaction products, and becomes an obstacle in reducing the space velocity.

The present invention proposes a reactor without the above drawbacks.

[Means for solving problems]

According to the present invention, a plurality of reaction tubes positioned in the vertical direction are fixed to upper and lower tube plates, a central tube is positioned in the center of the reaction tubes, and a granular space is formed in an annular space composed of the reaction tube and the central tube. Saturation temperature at which a solid catalyst is filled and a pressurized mixed gas containing hydrogen, carbon monoxide, and carbon dioxide as significant substances is brought into contact with the catalyst to carry out a methanol synthesis reaction, and the reaction heat is located outside the reaction tube. In the reactor that is converted to pressurized water to obtain water vapor, the gas separated by gas-liquid separation is pressurized by a circulating gas compressor from the upper end of the annular space filled with the granular solid catalyst in each reaction tube and flows in. As well as
Make-up gas produced by means such as steam reforming is allowed to flow into each central tube, and a plurality of gas inflows through the tube wall of the central tube from any position in the longitudinal direction of the central tube. The present invention relates to a reactor characterized in that the above-mentioned supplementary gas is allowed to flow into a catalyst layer in which a catalytic reaction is occurring from a hole to prevent an excessive rise in the catalytic reaction temperature.

As shown in FIG. 1 (A), one example of the reactor of the present invention is a central tube at the center of a plurality of reaction tubes [only one is shown in FIG. Position 19. However, the central tube 19 does not have to be provided over the entire length of the reaction tube 11, but may be up to an intermediate position of the length of the reaction tube 11 as shown in FIG. 1 (A), and as shown in FIG. 1 (B). As shown, a gas outlet hole 20 is provided at an arbitrary position of the center tube 19.
The plurality of reaction tubes 11 are attached to the upper and lower tube plates 14 and 15. Each center tube 19 has its upper end attached to the partition plate 18 and its lower end closed by an end cover 21. The reaction tube 11 is filled with a granular solid catalyst 12. The catalyst 12 in the reaction tube 11 is in a packed form as shown in FIGS. Note that FIG. 1 (C) is a sectional view at the point of FIG. 1 (A), and FIG. 1 (D) is a sectional view at the point of FIG. 1 (A).

A gas produced by a steam reforming method or the like is allowed to flow into the central tube 19 as a supplementary gas 1 for the reactor 7. On the other hand, the third
As shown in the figure, the circulation gas 4 after separating the methanol (containing water and a small amount of side reaction products and solution gas) liquid in the gas-liquid separator 3 or a small amount of a new make-up gas 1
The gas added with is preheated by the heat exchanger 8 and supplied from the circulating gas nozzle of the reactor 7 so as to flow into the reaction tube 11.

As mentioned above, the gas-liquid separator 3 outlet gas 4 is CO, CO ₂ / H ₂
The ratio is small, for example, as shown in Table 1 above, in other words, the reaction significant substance concentration is small.

That is, according to the present invention, the unreacted gas with a low methanol concentration 4
Is a reactor having a structure in which CO, CO ₂ / H ₂ ratio when contacting the catalyst 12 in the reaction tube 11 can be made smaller than the conventional one shown in FIGS. 6, 7, and 8 described above. Has the first feature.

It is a matter of course that even if the difference from the reaction equilibrium concentration is large, the reaction rate cannot be high if the concentration of the reaction significant substance is small.

Further, as shown in FIG. 3, according to the present invention, after the methanol concentration in the gas moving in the catalyst 12 layer reaches a significant value, CO, CO ₂ / H ₂ ratio in the gas is large in the reactor make-up gas. The second feature is that the reactor has a structure in which 1 can be added, that is, the partial pressure of CO and CO ₂ can be increased. The reactor make-up gas 1 moves in the central tube 19 as shown in FIG. 1 (B) described above, and from the gas outflow holes 20 (plural) provided in the tube wall of the central tube 19 to the gas in the catalyst layer 12. Will be replenished.

If the methanol concentration in the gas is significant, CO, C
It goes without saying that the reaction rate cannot be too high even if the O ₂ partial pressure is increased.

Further, the present invention also includes making the gas flowing in the central tube 19 have a role as a refrigerant like the above-mentioned reactor.

The replenishment gas 1 supplied into the central tube 19 can be preheated with the gas discharged from the compressor 2 via a gas preheater (not shown), and on the other hand, 40 to 15 lower than the contact reaction temperature.
It is also possible to feed in a gas at 0 ° C. and use it for controlling the temperature of the catalytic reaction.

In the present invention, when the central tube 19 is set to a position midway between the tube lengths of the reaction tube 11 as shown in FIG. 1 (A), the filling state of the catalyst 12 is different between the position with the central pipe and the position without the central pipe. It differs as shown in FIGS. 1 (C) and (D). Therefore, when the diameter of the reaction tube 11 is the same, the space velocity is different depending on the presence or absence of the central tube 19, but this is in the region where the reaction velocity is small, that is, in the region where the concentration of methanol in the gas is increased. , The contact reaction time becomes long, so the amount of methanol produced increases (reactor 7
There are advantages that the outlet methanol concentration rises) and the gas flow resistance becomes small, so that the pressure loss becomes small. This is the third feature of the present invention.

However, there is a case as shown in FIG. 4 as an embodiment of the present invention, and in this case, the third feature is eliminated.

[Operation] [Example] In the present invention, as shown in FIG. 3, the gas discharged from the reactor 7 is cooled by the heat exchanger 8, the methanol is condensed and liquefied, and the methanol liquid is separated by the gas-liquid separator 3. To separate. The gas-liquid separator 3
After partly purging 10 of the gas 4 separated in step 1, the residual gas circulating gas compressor 5 boosts the pressure, preheats it in the heat exchanger 8, and then sends it to the reactor 7. Some amount of make-up gas 1 may be added to adjust the CO, CO ₂ / H ₂ ratio.

The new make-up gas 1 produced by means such as steam reforming (not shown) has a large CO, CO ₂ / H ₂ ratio, but the total amount (or most) of this gas does not mix with the circulating gas 4. , Sent to the reactor 7. It may be preheated by a heat exchanger (not shown) to adjust the temperature.

Note that FIG. 3 corresponds to the reactor having the structure shown in FIGS. 1 and 4, and in the reactor having the structure shown in FIG.

Further, in FIG. 1 (A), the circulating gas 4 flows into the space partitioned by the partition plate 18 and the upper tube plate 14, and diffuses and flows into the upper end of each reaction tube 11 from the space, and the catalyst 12 layer is moved upward. From the bottom to the bottom while producing methanol by contact reaction. A new make-up gas 1 produced by steam reforming etc. is an upper mirror
It flows into a space partitioned by 13 and a partition plate 18, enters the upper end of each central tube 19 from the space, and diffuses and flows into the catalyst 12 layer from the outflow holes 20.

As shown in FIG. 1 (B), the central tube 19 has a partition plate [first
18] of FIG. (A) and the pipe length up to the upper end of the 12th layer of the catalyst play the role of a connecting pipe. The pipe length from the upper end of the catalyst 12 layer to the gas outflow hole 20 region is the make-up gas preheating region (role of heat exchanger). In other words, the supplementary gas 1 functions as a refrigerant and suppresses an excessive rise in the contact reaction temperature. In this section of pipe length, methanol is produced by the catalytic reaction of CO, CO ₂ and H _{2 in} the circulating gas 4.

The tube length of the central tube 19 is a region in which the supplementary gas 1 having a large CO, CO ₂ / H ₂ ratio is added to the circulating gas 4 which has reached a significant methanol concentration. This is done by a plurality of small holes (gas outflow holes) 20 provided in the tube wall of the central tube 19. There are no restrictions on the diameter, number, position, distribution, and differential pressure of the gas outflow holes 20.

The pipe length is a region where the space velocity is maintained at a high level.

There are no restrictions on the tube length of the ,,, or the diameter of the central tube 19.

In FIG. 1 (A), the gas flowing down while reacting in the catalyst 12 layer flows into the space defined by the lower tube sheet 15 and the lower mirror 16 and is taken out of the reactor 7. Upper and lower tube sheets 14 and 15 and body 17
Pressurized water at a saturation temperature is located in the space partitioned by. Of course, the temperature is maintained below the proper catalytic reaction temperature.

In FIG. 2 (A) showing another embodiment of the reactor of the present invention, the circulating gas 4 flows into the upper end of each reactor 11 from the space partitioned by the upper mirror 13 and the partition plate 18. The makeup gas 1 flows into the upper end of each central tube 19 from the space defined by the partition plate 18 and the upper tube plate 14.

The structure of FIG. 2 is different from that of FIG. 1 between the upper tube sheet 14 and the partition plate 18, and as shown in FIG. 2 (B), it is between the upper tube sheet 14 and the partition plate 18. Bend the central pipe 19 with
Position the central tube 19 through the tube wall at 22. The upper end of the connecting pipe 22 is opened to the space defined by the partition plate 18 and the upper mirror (13 in FIG. 2 (A)).

In the case of FIG. 2, there is no central pipe 19, connecting pipe 22, etc. in the space between the partition plate 18 and the upper mirror 13 in the upper part and in the space between the lower tube plate 15 and the lower mirror 16 in the lower part. In comparison with the above-mentioned reactor, it also has an advantage that the work of filling the catalyst and extracting the catalyst can be greatly facilitated.

There is also a reactor in which FIG. 2 is turned upside down, which is more advantageous in terms of catalyst filling work, in which case the gas flow in the catalyst bed is from bottom to top.

The reactor shown in FIG. 4 is obtained by extending the length of the central tube 19 of the reactor of FIG. 1 and extending it to the catalyst 12 layer lower end of the lower end of the reaction tube 11 or more, that is, the region of FIG. 1 (B). The length of the central tube is large. In this case, the catalyst 12 layer to be filled becomes an annular shape over the entire length.

The extension of the central tube 19 shown in FIG. 4 can be applied to the reactor shown in FIG.

The distribution of the contact reaction temperature in the reaction tube of the reactor of the present invention in the tube length direction is schematically shown in FIG. 5 according to the drawing procedure of FIG.

In the conventional reactor 7 shown in FIGS. 6 and 7, the make-up gas 1 is added to the circulating gas 4 and the CO, CO ₂ / H ₂ ratio is increased to be fed into the reactor 7, which is then fed to the catalyst layer. Flow into the catalyst and come into contact with the catalyst, but the methanol concentration is practically zero and C
Since the O, CO ₂ / H ₂ ratio is large, the reaction rate becomes high above the catalyst 12 layer, and the temperature rises due to the equilibrium between the heat transfer rate and the heat generation rate through the tube wall of the reaction tube 11. The reaction rate increases as the temperature rises, and the temperature reaches M. After reaching the point M, the reaction rate decreases due to the increase in methanol concentration and the decrease in CO, CO ₂ / H ₂ ratio, and the temperature also gradually decreases.

On the other hand, in the reactor of the present invention, the CO and CO ₂ / H ₂ ratios are kept small when gas flows into the catalyst 12 layer, so this temperature rise is small (point m in FIG. 5). Note that the central tube 19 is positioned so that this area becomes the area, the gas in the central tube 19 functions as a refrigerant, and the combined effect of the pressurized water of the saturated temperature located outside the reaction tube 11 and the refrigerant effect makes m The temperature rise at the point is small.

In the region from the point n to the point p where the contact reaction temperature slightly decreased after passing the point m, the supplementary gas 1 with a large CO, CO ₂ / H ₂ ratio was dispersedly supplied from the inside of the central tube 19 to generate the CO required for the contact reaction. , CO ₂ is replenished. As a result, the temperature rises again, but since it is a distributed supply, an excessive rise in temperature can be completely prevented.

In the region from the p point to the lower end of the catalyst 12 layer, the supplementary gas 1 is not supplied from the inside of the central tube 19, but is contained in the gas at the p point.
CO and CO ₂ move while reacting with H ₂ . It should be noted that, since the reaction rate becomes small due to the decrease of CO, CO ₂ concentration, the temperature also gradually decreases, but from the known fact that the lower the contact reaction temperature near the outlet of the reaction tube 11, the higher the equilibrium methanol concentration becomes. The temperature, catalyst bed height, and space velocity are important factors for reactor performance.

〔The invention's effect〕

According to the present invention, various effects can be achieved such that the reaction load can be made uniform over the entire length of the reaction tube, the temperature can be prevented from rising excessively, and the work of filling and withdrawing the catalyst can be facilitated.

[Brief description of drawings]

1 (A) to 1 (D) are views showing an embodiment of the reactor of the present invention. FIG. 1 (A) is an overall view, and FIG. 1 (B) is a partially enlarged sectional view thereof. 1 (C) is a cross-sectional view of the point of FIG. 1 (A), FIG. 1 (D) is a cross-sectional view of the point of FIG. 1 (A),
2 (A) and 2 (B) are views showing another embodiment of the reactor of the present invention. FIG. 2 (A) is an overall view, and FIG. 2 (B) is a partially enlarged sectional view thereof. FIG. 3 is a diagram showing the whole system of methanol synthesis for explaining the operation of the reactor of the present invention, FIG. 4 is a diagram showing another embodiment of the reactor of the present invention, and FIG. 5 is a diagram of the reactor of the present invention. FIG. 6 is a diagram for explaining the action and effect, FIG. 6 is a diagram showing the whole system of conventional methanol synthesis, FIGS. 7 and 8 are diagrams showing a conventional reactor, and FIGS. It is a figure for demonstrating the fault of the conventional reactor shown in a figure.

Claims (2)

[Claims] 1. A plurality of reaction tubes positioned in the vertical direction are fixed to upper and lower tube plates, and a central tube is positioned at the center of the reaction tubes to form an annular space composed of the reaction tube and the central tube. Saturation in which a granular solid catalyst is filled, a pressurized mixed gas containing hydrogen, carbon monoxide and carbon dioxide as significant substances is brought into contact with the catalyst to carry out a methanol synthesis reaction, and the reaction heat is located outside the reaction tube. In the reactor that was transferred to pressurized water at a temperature to obtain steam, the gas separated by gas-liquid separation was pressurized with a circulating gas compressor from the upper end of the annular space filled with the granular solid catalyst in each reaction tube. In addition to allowing the gas to flow in, the make-up gas produced by means such as steam reforming is allowed to flow into the pipe of each central pipe, and the pipe wall of the central pipe is removed from any position in the longitudinal direction of the central pipe. Contact from multiple gas inflow holes Reactor, characterized in that while results in response to certain catalyst layer was to prevent an excessive increase of the contact reaction temperature as above makeup gas flows. 2. The reactor according to claim 1, wherein a part of the supplementary gas is added to the gas separated by the gas-liquid separator.