Green methanol synthesis system for regulating and controlling reaction temperature by utilizing multi-stage fused salt energy storage

Abstract

The invention belongs to the technical field of methanol synthesis, and particularly relates to a green methanol synthesis system for regulating and controlling reaction temperature by utilizing multi-stage fused salt energy storage, which comprises a methanol synthesis tower, a low-temperature fused salt tank, a medium-temperature fused salt tank and a high-temperature fused salt tank, an upper tube plate and a lower tube plate are respectively arranged at the upper part and the lower part of the methanol synthesis tower, a plurality of reaction tubes are arrayed between the upper tube plate and the lower tube plate, and a fused salt pipeline is uniformly wound on each reaction tube; the upper ends of all the fused salt pipelines are connected with a fused salt inlet of the methanol synthesis tower through a fused salt pipeline connecting piece, and the lower ends of all the fused salt pipelines are connected with a fused salt outlet of the methanol synthesis tower through another fused salt pipeline connecting piece; an outlet of the low-temperature molten salt tank is connected with a molten salt inlet of the methanol synthesis tower, and an inlet of the medium-temperature molten salt tank is connected with a molten salt outlet of the methanol synthesis tower. The methanol synthesis reaction temperature can be reasonably controlled in a demineralized water countercurrent flow heat exchange and molten salt parallel flow heat exchange mode, so that the catalyst is in a proper active temperature range, the optimal methanol synthesis reaction state is achieved, the service life of the catalyst is prolonged to the maximum extent, and the methanol output rate is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of green methanol synthesis, and in particular relates to a green methanol synthesis system that utilizes multi-stage molten salt energy storage to regulate reaction temperature. Background Art

[0002] Methanol is an important organic chemical raw material with a wide range of uses. Methanol is required as a raw material or solvent in the production of pesticides, medicines, dyes, fragrances, coatings and three major synthetic materials. The industrial production of methanol is of great significance to other related industries and the development of the national economy. The methanol synthesis catalyst is a copper-based catalyst with a narrow activity range, low operating temperature, and short high temperature maintenance time. The operating temperature in production is generally between 240 and 290 degrees Celsius. In order to extend the service life of the methanol synthesis catalyst, the radial temperature difference of the synthesis tower is required to be small, so the requirements for the bed heat transfer of the synthesis tower are very high. In addition, the methanol synthesis reaction is carried out under variable temperature conditions. On the one hand, it is difficult to maintain isothermal because the reaction process is accompanied by a considerable thermal effect; on the other hand, the effect of isothermal operation is not good, and an optimal temperature distribution is required. The activation energy of the main and side reactions of the methanol synthesis reaction is different, and different temperatures have different effects on the rates of the main and side reactions. Therefore, temperature control of the methanol synthesis reaction is critical, but reasonable temperature control is difficult.

[0003] However, in actual production, most methanol synthesis towers have the following problems: 1) The reaction gas is introduced into the reaction tube from top to bottom for reaction. The reaction rate in the upper section of the reaction tube is faster, while the reaction rate in the lower section is slower, resulting in a higher temperature in the upper part of the reaction tube and a lower temperature in the lower part. The heat exchange medium is countercurrent heat exchanged from bottom to top, which is not conducive to the stable control of the reaction temperature. 2) Due to the reaction temperature limit, the single-function methanol synthesis system cannot produce superheated steam with a high pressure level of 10MPa, so the scope of heat recovery is limited.

[0004] In view of this, the present invention proposes a green methanol synthesis system that utilizes multi-stage molten salt energy storage to regulate the reaction temperature. Summary of the invention

[0005] In view of the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a green methanol synthesis system that uses multi-stage molten salt energy storage to control the reaction temperature. The use of desalted water countercurrent heat exchange and molten salt cocurrent heat exchange can reasonably control the methanol synthesis reaction temperature, so that the catalyst is in a suitable active temperature range, achieve the best methanol synthesis reaction state, maximize the catalyst life, and improve the methanol output rate.

[0006] To achieve the above object, the present invention adopts the following technical solution: A green methanol synthesis system utilizing multi-stage molten salt energy storage to control reaction temperature, characterized in that it comprises a methanol synthesis tower, a low-temperature molten salt tank, a medium-temperature molten salt tank, and a high-temperature molten salt tank; The upper and lower parts of the methanol synthesis tower are respectively provided with an upper tube plate and a lower tube plate, a plurality of reaction tubes are arrayed between the upper tube plate and the lower tube plate, and a molten salt pipe is evenly wound around each reaction tube; the upper ends of all the molten salt pipes are connected to the molten salt inlet of the methanol synthesis tower through a molten salt pipe connector, and the lower ends of all the molten salt pipes are connected to the molten salt outlet of the methanol synthesis tower through another molten salt pipe connector; the outlet of the low-temperature molten salt tank is connected to the molten salt inlet of the methanol synthesis tower, and the inlet of the medium-temperature molten salt tank is connected to the molten salt outlet of the methanol synthesis tower; the desalted water is countercurrently exchanged from bottom to top in the methanol synthesis tower, and the molten salt is concurrently exchanged from top to bottom in the molten salt pipe.

[0007] Furthermore, the system also includes an electric heater, a deaerator, a preheater, a first steam drum, an evaporator, a superheater and a second steam drum; the inlet of the electric heater is connected to the outlet of the medium-temperature molten salt tank, the outlet of the electric heater is connected to the inlet of the high-temperature molten salt tank, the molten salt inlet of the superheater is connected to the outlet of the high-temperature molten salt tank, the molten salt outlet of the superheater is connected to the molten salt inlet of the evaporator, the steam inlet of the superheater is connected to the steam outlet of the first steam drum, the saturated water inlet of the first steam drum is connected to the saturated water outlet of the preheater, the molten salt outlet of the evaporator is connected to the molten salt inlet of the preheater, the saturated water inlet of the evaporator is connected to the saturated water outlet of the first steam drum, the saturated steam outlet of the evaporator is connected to the saturated steam inlet of the first steam drum, the molten salt outlet of the preheater is connected to the inlet of the low-temperature molten salt tank, the deoxygenated water inlet of the preheater is connected to the deoxygenated water outlet of the deaerator, the deoxygenated steam inlet of the deaerator is connected to the steam outlet of the second steam drum, and the steam inlet of the second steam drum is connected to the steam outlet of the methanol synthesis tower.

[0008] Furthermore, the molten salt pipe connector includes a mother pipe and a circular ring pipe, and a plurality of circular ring pipes are arranged in a cocentric array. Each molten salt pipe passes through the molten salt pipe hole of the upper tube plate or the lower tube plate and is connected to the corresponding circular ring pipe. One end of the mother pipe is respectively connected to each circular ring pipe, and the other end is connected to the molten salt inlet or the molten salt outlet of the methanol synthesis tower.

[0009] Furthermore, when the reaction temperature is lower than the optimal reaction temperature, the reaction temperature is increased by reducing the flow rate of desalted water in the methanol synthesis tower or reducing the transmission rate of low-temperature molten salt; when the reaction temperature is higher than the optimal reaction temperature, the reaction temperature is lowered by increasing the flow rate of desalted water in the methanol synthesis tower or increasing the transmission rate of low-temperature molten salt.

[0010] Compared with the prior art, the present invention has the following beneficial effects: 1. The temperature of the methanol synthesis reaction needs to be controlled between 250 and 260 degrees Celsius. Too high or too low a temperature will affect the synthesis yield of methanol. Since the reaction gas is passed into the reaction tube from top to bottom, the reaction rate of the upper section of the reaction tube is faster and the temperature is higher, while the reaction rate of the lower section is slower and the temperature is lower. However, the heat exchange medium (deionized water) is countercurrent heat exchange from bottom to top, which is not conducive to the control of the reaction temperature. Therefore, the present invention wraps a molten salt pipeline around each reaction tube, and the low-temperature molten salt flows from top to bottom in the molten salt pipeline, and exchanges heat with the reaction gas in parallel, so that the low-temperature molten salt with a lower temperature first exchanges heat with the upper part of the reaction tube with a higher temperature, which is conducive to controlling the reaction temperature not to be super-high, and the high-temperature molten salt exchanges heat with the lower part of the reaction tube, ensuring that the temperature of the lower part of the reaction tube is not too low, while improving the reaction rate and the methanol synthesis rate while improving the heat recovery utilization rate.

[0011] 2. The countercurrent heat exchange of desalted water and the parallel heat exchange of molten salt are coordinated with each other, making the reaction temperature easier to control and adjust, and the temperature distribution of the reaction tube is more reasonable. The temperature difference of the catalyst bed is small, and the reaction is basically carried out along the optimal temperature curve. Therefore, the catalyst activity is high, which can more effectively improve the product quality and the single-pass conversion rate of the reaction gas. When the reaction temperature is lower than the optimal reaction temperature, the reaction temperature is increased by increasing the steam pressure of the second drum (i.e., reducing the flow rate of desalted water in the methanol synthesis tower) or reducing the transmission rate of low-temperature molten salt; when the reaction temperature is higher than the optimal reaction temperature, the reaction temperature is reduced by reducing the steam pressure of the second drum (i.e., increasing the flow rate of desalted water in the methanol synthesis tower) or increasing the transmission rate of low-temperature molten salt; in this way, a relatively constant reaction temperature can be maintained, and the range of change is 0.1MPa, which is equivalent to 1.5 degrees Celsius. The reaction temperature is almost constant, which effectively inhibits side reactions and prolongs the service life of the catalyst.

[0012] 3. The steam produced by the methanol synthesis reaction can be reused through the molten salt temperature control system. The steam can be converted into superheated steam through the combined use of deaerator, preheater, evaporator, steam drum and superheater, and then converted into high-grade energy. Superheated steam has a wider range of applications and increases energy utilization.

[0013] 4. The synthesis tower is both a reactor and a waste heat boiler. There are multiple reaction tubes arrayed in the synthesis tower, and the reaction tubes are filled with catalysts. The heat released by the methanol synthesis reaction is quickly transferred by desalted water and molten salt. The desalted water soaks the entire reaction tube, and the latent heat of vaporization of water is large, and the heat transfer efficiency is high, so that 80% of the reaction heat can be converted into steam; the refrigerant is siphoned by heat, and no pump is required, which saves equipment costs and has high reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the overall structure of the present invention; Figure 2It is a structural schematic diagram of the molten salt pipeline connector of the present invention; Figure 3 Schematic diagram of the distribution of tube holes and through holes of the support plate of the present invention; Figure 4 It is a distribution diagram of the reaction tube, molten salt pipeline and support member of the present invention; Figure 5 It is a distribution schematic diagram of the reaction tubes of the present invention; In the figure, 1, upper head; 2, cylinder; 3, lower head; 4, reaction gas inlet; 5, reaction gas outlet; 6, desalted water inlet; 7, steam outlet; 8, molten salt inlet; 9, molten salt outlet; 10, reaction tube; 11, molten salt pipeline; 12, support plate; 13, gas distributor; 14, upper tube sheet; 15, lower tube sheet; 16, low-temperature molten salt tank; 17, medium-temperature molten salt tank; 18, high-temperature molten salt tank; 19, electric heater; 20, deaerator; 21, preheater; 22, first steam drum; 23, evaporator; 24, superheater; 25, second steam drum. DETAILED DESCRIPTION

[0015] Specific embodiments are given below in conjunction with the accompanying drawings. The specific embodiments are only used to introduce the technical solutions of the present invention in detail and are not intended to limit the protection scope of the present application.

[0016] The present invention provides a green methanol synthesis system for regulating reaction temperature by using multi-stage molten salt energy storage, comprising a methanol synthesis tower, a low-temperature molten salt tank 16, a medium-temperature molten salt tank 17, a high-temperature molten salt tank 18, an electric heater 19, a deaerator 20, a preheater 21, a first steam drum 22, an evaporator 23, a superheater 24 and a second steam drum 25; The methanol synthesis tower is divided into an upper head 1, a cylinder 2 and a lower head 3 from top to bottom; a reaction gas inlet 4, a molten salt inlet 8 and a manhole (not shown in the figure) are arranged on the side wall of the upper head 1, and a gas distributor 13 is arranged at the bottom of the reaction gas inlet 4 to evenly distribute the gas flow of the reaction gas; a reaction gas outlet 5, a molten salt outlet 9 and a manhole (not shown in the figure) are arranged on the side wall of the lower head 3; a steam outlet 7 and a desalted water inlet 6 are respectively arranged at the upper and lower parts of the side wall of the cylinder 2, and the upper and lower parts of the cylinder 2 are provided with a steam outlet 7 and a desalted water inlet 6. An upper tube sheet 14 and a lower tube sheet 15 are respectively welded and fixed, and a plurality of reaction tubes 10 are arrayed between the upper tube sheet 14 and the lower tube sheet 15. A molten salt pipe 11 is evenly wound around each reaction tube 10, and the molten salt pipe 11 is welded to the reaction tube 10 through a support to play a supporting and fixing role; the upper ends of all molten salt pipes 11 are connected to the molten salt inlet 8 of the methanol synthesis tower through a molten salt pipe connector, and the lower ends of all molten salt pipes 11 are connected to the molten salt outlet 9 of the methanol synthesis tower through another molten salt pipe connector; The inlet of the medium-temperature molten salt tank 17 is connected to the molten salt outlet 9 of the methanol synthesis tower, the outlet of the medium-temperature molten salt tank 17 is connected to the inlet of the electric heater 19, the outlet of the electric heater 19 is connected to the inlet of the high-temperature molten salt tank 18, the molten salt inlet of the superheater 24 is connected to the outlet of the high-temperature molten salt tank 18, the molten salt outlet of the superheater 24 is connected to the molten salt inlet of the evaporator 23, the steam inlet of the superheater 24 is connected to the steam outlet of the first steam drum 22, the saturated water inlet of the first steam drum 22 is connected to the saturated water outlet of the preheater 21, and the molten salt outlet of the evaporator 23 is connected to the preheater 21. The molten salt inlet of the preheater 21 is connected to the deoxygenated water outlet of the deaerator 20, the deoxygenated steam inlet of the deaerator 20 is connected to the steam outlet of the second steam drum 25, and the steam inlet of the second steam drum 25 is connected to the steam outlet 7 of the methanol synthesis tower.

[0017] like Figure 2 As shown, the molten salt pipe connector includes a mother pipe and a circular pipe, and a plurality of circular pipes are arranged in a co-centric array. Each molten salt pipe 11 passes through the molten salt pipe hole of the upper tube sheet 14 or the lower tube sheet 15 and is connected to the corresponding circular pipe. One end of the mother pipe is respectively connected to each circular pipe, and the other end is connected to the molten salt inlet 8 or the molten salt outlet 9 of the methanol synthesis tower.

[0018] The upper and lower ends of the reaction tube 10 are respectively connected and fixed by welding to the corresponding tube holes of the upper tube sheet 14 and the lower tube sheet 15. A plurality of support plates 12 are evenly arranged in the height direction in the cylinder 2, and the four sides of the support plates 12 are welded and fixed to the inner wall of the cylinder 2; the support plates 12 are divided into a tube laying area and a non-tube laying area, and the tube laying area has a plurality of tube holes for the reaction tube 10 and the molten salt pipeline 11 to pass through, and the reaction tube 10, the molten salt pipeline 11 and the support plate 12 are welded and fixed together by supporting parts; there are a plurality of through holes in the non-tube laying area, and the size and spacing of the through holes are staggered with the arrangement of the tube holes, so as to increase the circulation area of ​​the heat exchange medium and make the reaction heat exchange efficient. Figure 3 As shown, for easy distinction, the tube holes on the support plate 12 are represented by hollow circles, and the through holes are represented by solid circles, and the two are arranged alternately.

[0019] like Figure 4 As shown, the four support members are tangentially welded to the reaction tube 10 and the molten salt pipeline 11 , respectively, and are welded and fixed to the support plate 12 .

[0020] The reaction gas inlet 4 is arranged at an angle of 45° on the upper head 1, the reaction gas outlet 5 is arranged at the bottom of the lower head 3, the desalted water inlet 6 is arranged at the lower part of the cylinder 2, a certain distance from the lower tube sheet 15, and the steam outlet 7 is arranged at the upper part of the cylinder 2, a certain distance from the upper tube sheet 14.

[0021] like Figure 5 As shown, each reaction tube 10 is distributed on a plurality of concentric circles with the axis of the cylinder 2 as the center, and the reaction tubes 10 are spaced apart at appropriate distances along the radial and circumferential directions of the cylinder 2. Multiple temperature monitoring points are set from top to bottom in each reaction tube 10 to feedback and adjust the steam pressure and molten salt transport rate, thereby controlling the reaction temperature.

[0022] The electric heater 19 can use off-peak electricity or photovoltaic power for energy supply.

[0023] The working principle and workflow of the present invention are: The reaction gas enters the methanol synthesis tower from the reaction gas inlet 4, and is evenly distributed on the upper head 1 through the gas distributor 13, and then evenly flows into each reaction tube 10. In the reaction tube 10, the reaction gas reacts under the action of the catalyst to generate methanol and release a large amount of heat. One path of desalted water enters the methanol synthesis tower from the desalted water inlet 6 of the cylinder 2, performs countercurrent heat exchange with the reaction gas in the reaction tube 10, absorbs the heat generated by the methanol synthesis reaction and becomes steam, and is discharged from the steam outlet 7 at the upper part of the cylinder 2 and enters the second steam drum 25 for storage; the low-temperature molten salt is transported from the low-temperature molten salt tank 16 through the molten salt pump (not shown in the figure) and enters the methanol synthesis tower from the molten salt inlet 8 of the upper head 1, enters each molten salt pipeline 11 through the molten salt pipeline connector, performs parallel flow heat exchange with the reaction gas in the reaction tube 10, absorbs the heat generated by the methanol synthesis reaction and becomes medium-temperature molten salt, and the medium-temperature molten salt is discharged from the molten salt outlet 9 of the methanol synthesis tower through the molten salt pipeline connector at the lower end of the molten salt pipeline 11 and enters the medium-temperature molten salt tank 17. The medium-temperature molten salt in the medium-temperature molten salt tank 17 enters the electric heater 19 for heating and becomes high-temperature molten salt, which enters the high-temperature molten salt tank 18 for storage; thereafter, the high-temperature molten salt passes through the superheater 24, the evaporator 23, and the preheater 21 in sequence for heat exchange and becomes low-temperature molten salt, which is stored in the low-temperature molten salt tank 16. Another desalted water enters the deaerator 20 for storage, the steam in the second drum 25 enters the deaerator 20, deoxygenates the desalted water, and then the deoxygenated water enters the preheater 21 for heat exchange with the molten salt in the preheater 21, becomes saturated water and enters the first drum 22 for storage, the saturated water in the second drum 22 enters the evaporator 23, exchanges heat with the molten salt in the evaporator 23, becomes saturated steam, and returns to the second drum 22, the saturated steam in the second drum 22 enters the superheater 24 to exchange heat with the molten salt therein, and becomes superheated steam for external use.

[0024] The low-temperature molten salt tank 16, the medium-temperature molten salt tank 17, the high-temperature molten salt tank 18, the electric heater 19, the deaerator 20, the preheater 21, the second steam drum 22, the evaporator 23, the superheater 24 and the second steam drum 25 constitute a molten salt temperature control system. Since a plurality of temperature monitoring points are arranged in the reaction tube 10, the reaction temperature is monitored. When the reaction temperature is lower than the optimum reaction temperature, the reaction temperature is increased by increasing the steam pressure of the second steam drum 25 (i.e., reducing the flow rate of the desalted water in the methanol synthesis tower) or reducing the transmission rate of the low-temperature molten salt. When the reaction temperature is higher than the optimum reaction temperature, the reaction temperature is reduced by reducing the steam pressure of the second steam drum 25 (i.e., increasing the flow rate of the desalted water in the methanol synthesis tower) or increasing the transmission rate of the low-temperature molten salt. The steam pressure of the second steam drum 25 and the transmission rate of the low-temperature molten salt are coordinated and controlled according to the reaction temperature, so that the catalyst is in a suitable active temperature range, the best methanol synthesis reaction state is achieved, the methanol synthesis yield is improved, and the life of the catalyst is extended to the maximum extent.

[0025] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A green methanol synthesis system utilizing multi-stage molten salt energy storage to control reaction temperature, characterized in that: Including methanol synthesis tower, low-temperature molten salt tank, medium-temperature molten salt tank and high-temperature molten salt tank; The upper and lower parts of the methanol synthesis tower are respectively provided with an upper tube plate and a lower tube plate, a plurality of reaction tubes are arrayed between the upper tube plate and the lower tube plate, and a molten salt pipe is evenly wound around each reaction tube; the upper ends of all the molten salt pipes are connected to the molten salt inlet of the methanol synthesis tower through a molten salt pipe connector, and the lower ends of all the molten salt pipes are connected to the molten salt outlet of the methanol synthesis tower through another molten salt pipe connector; the outlet of the low-temperature molten salt tank is connected to the molten salt inlet of the methanol synthesis tower, and the inlet of the medium-temperature molten salt tank is connected to the molten salt outlet of the methanol synthesis tower; the desalted water is countercurrently exchanged from bottom to top in the methanol synthesis tower, and the molten salt is concurrently exchanged from top to bottom in the molten salt pipe.

2. The green methanol synthesis system for regulating reaction temperature by using multi-stage molten salt energy storage according to claim 1 is characterized in that: The system also includes an electric heater, a deaerator, a preheater, a first steam drum, an evaporator, a superheater and a second steam drum; the inlet of the electric heater is connected to the outlet of the medium-temperature molten salt tank, the outlet of the electric heater is connected to the inlet of the high-temperature molten salt tank, the molten salt inlet of the superheater is connected to the outlet of the high-temperature molten salt tank, the molten salt outlet of the superheater is connected to the molten salt inlet of the evaporator, the steam inlet of the superheater is connected to the steam outlet of the first steam drum, the saturated water inlet of the first steam drum is connected to the saturated water outlet of the preheater, the molten salt outlet of the evaporator is connected to the molten salt inlet of the preheater, the saturated water inlet of the evaporator is connected to the saturated water outlet of the first steam drum, the saturated steam outlet of the evaporator is connected to the saturated steam inlet of the first steam drum, the molten salt outlet of the preheater is connected to the inlet of the low-temperature molten salt tank, the deoxygenated water inlet of the preheater is connected to the deoxygenated water outlet of the deaerator, the deoxygenated steam inlet of the deaerator is connected to the steam outlet of the second steam drum, and the steam inlet of the second steam drum is connected to the steam outlet of the methanol synthesis tower.

3. The green methanol synthesis system for regulating reaction temperature by using multi-stage molten salt energy storage according to claim 1 or 2, characterized in that: The molten salt pipe connector includes a mother pipe and a circular pipe. A plurality of circular pipes are arranged in a co-centric array. Each molten salt pipe passes through a molten salt pipe hole of an upper tube sheet or a lower tube sheet and is connected to a corresponding circular pipe. One end of the mother pipe is respectively connected to each circular pipe, and the other end is connected to a molten salt inlet or a molten salt outlet of a methanol synthesis tower.

4. The green methanol synthesis system for regulating reaction temperature by using multi-stage molten salt energy storage according to claim 3 is characterized in that: When the reaction temperature is lower than the optimal reaction temperature, the reaction temperature is increased by reducing the flow rate of desalted water in the methanol synthesis tower or reducing the transmission rate of low-temperature molten salt; when the reaction temperature is higher than the optimal reaction temperature, the reaction temperature is lowered by increasing the flow rate of desalted water in the methanol synthesis tower or increasing the transmission rate of low-temperature molten salt.

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