A synthetic ammonia feed buffer system

Abstract

The present application relates to a synthetic ammonia feed buffer system, comprising an ammonia synthesis gas buffer tank and an ammonia synthesis gas compressor, wherein the ammonia synthesis gas compressor has an inlet and an outlet, and comprises a first compressor cylinder connected to the inlet thereof and a second compressor cylinder connected to the outlet of the first compressor cylinder, wherein the first compressor cylinder is used to pressurize the input ammonia synthesis gas containing hydrogen and nitrogen to a pressure of 20-40 bar, and the second compressor cylinder is used to further pressurize the pressurized ammonia synthesis gas from the first compressor cylinder, characterized in that the outlet of the first compressor cylinder is connected to the inlet of the ammonia synthesis gas buffer tank through a first pressure reducing valve, and the outlet of the ammonia synthesis gas buffer tank is connected to the inlet of the ammonia synthesis gas compressor through a second pressure reducing valve. The synthetic ammonia feed buffer system can realize the buffering function of the ammonia synthesis raw gas in a cost-effective manner, which is conducive to maintaining the stable operation of the ammonia synthesis system.

Description

Technical Field

[0001] The present application relates to the field of synthetic ammonia, and in particular to a synthetic ammonia feed buffer system. Background Art

[0002] Ammonia (NH3) is an important chemical product, which is synthesized by hydrogen and nitrogen under the action of catalysts at a certain pressure and temperature. The raw nitrogen for synthetic ammonia is generally separated and extracted from the air through an air separation unit, while the raw hydrogen is generally produced by coal gasification or natural gas reforming, or by water electrolysis.

[0003] After the hydrogen and nitrogen are mixed, they are compressed to 130-180 bar by the synthesis gas compressor and then enter the reaction tower, where they are converted into ammonia under the combined action of the catalyst and a certain temperature and pressure. Depending on the reaction conditions, the conversion rate of ammonia is generally between 15-20%. After that, after the outlet gas of the reaction tower is cooled and separated, a part of the mixture of hydrogen and nitrogen is returned to the synthesis gas compressor as circulating gas to participate in the new reaction again. The separated ammonia is further cooled and washed and enters the product ammonia storage tank.

[0004] The inlet pressure of the syngas compressor is usually maintained between 10 and 20 bar. Too low an inlet pressure will result in: (1) the compressor pressure ratio (outlet pressure / inlet pressure) is too large, which increases the compression energy consumption; and (2) the number of compression stages of the compressor increases, the compressor volume increases, the mechanical structure becomes more complex, and the failure rate and maintenance frequency increase. At the same time, in order to make the compressor work in the high efficiency range as much as possible, the inlet pressure should not fluctuate frequently.

[0005] In ammonia synthesis plants, in order to maintain the stability of the ammonia synthesis reaction, hydrogen and nitrogen buffer tanks are usually installed before the synthesis gas compressor to ensure that the flow rate and pressure of the gas entering the synthesis gas compressor are maintained within a predetermined value or a predetermined range, or the change rate does not exceed the design limit (usually the flow rate change rate does not exceed 1% / min). In traditional coal or natural gas synthesis of ammonia, since the reaction of coal-to-hydrogen or natural gas-to-hydrogen is relatively stable, the supply of hydrogen is also relatively stable, so the capacity of the hydrogen buffer tank is usually not large.

[0006] In order to reduce carbon emissions in the ammonia synthesis process, the green ammonia synthesis plant uses renewable energy to directly couple water electrolysis to produce hydrogen. Obviously, renewable energy such as wind power and photovoltaics has a certain volatility. The flow rate of raw hydrogen produced by water electrolysis technology fluctuates frequently and rapidly, and is unpredictable. Therefore, it is necessary to configure a larger hydrogen buffer tank before the synthesis gas compressor to smooth the volatility of hydrogen supply.

[0007] The first synthetic ammonia feed buffer system is as follows Figure 1As shown, a bypass leading to a hydrogen buffer tank is arranged on the pipeline between renewable energy hydrogen production and the synthesis gas compressor. When the hydrogen production capacity is greater than the hydrogen demand for synthetic ammonia, the excess hydrogen enters the hydrogen buffer tank; conversely, hydrogen is released from the hydrogen buffer tank to supplement the hydrogen required for the synthetic ammonia reaction.

[0008] In the first synthetic ammonia feed buffer system, since there is no intermediate pressurizing equipment on the pipeline from renewable energy hydrogen production to the synthesis gas compressor, in order to meet the pressure requirements of the synthesis gas compressor inlet, water electrolysis hydrogen production must use high-pressure equipment, and the outlet pressure is usually 15-20 bar. The hydrogen production outlet pressure, the pressure in the hydrogen buffer tank, and the synthesis gas compressor inlet pressure should meet the following relationship:

[0009]

[0010] Therefore, the first synthetic ammonia feed buffer system has the following defects:

[0011] (1) Renewable energy hydrogen production equipment must use high-pressure equipment, which limits the equipment selection. The outlet pressure of atmospheric pressure electrolysis hydrogen production equipment is about 1 bar, which does not meet the inlet pressure requirements of the synthesis gas compressor;

[0012] (2) The pressure of the gas in the hydrogen buffer tank is limited by the hydrogen production outlet pressure and cannot be further increased, resulting in the capacity of the hydrogen storage tank being limited under the same volume (in other words, a larger hydrogen buffer tank is required under the same hydrogen storage capacity); and

[0013] (3) During the process of releasing hydrogen from the buffer tank, as the gas in the tank decreases, the pressure decreases, causing the inlet pressure of the synthesis gas compressor to decrease, which is not conducive to the stable and efficient operation of the compressor.

[0014] The second synthetic ammonia feed buffer system is as follows Figure 2 As shown in the figure, a hydrogen compressor is added between the hydrogen production equipment and the hydrogen buffer tank. Due to the addition of the hydrogen compressor, the selection range of hydrogen production equipment is wider, and both high-pressure and low-pressure types can be used. As long as the outlet pressure of the hydrogen is given, the hydrogen compressor can be adaptively designed to meet the outlet pressure requirements.

[0015] In addition, the hydrogen compressor can also increase the hydrogen storage capacity of the buffer tank. For example, in the first synthetic ammonia feed buffer system, assuming that the hydrogen production outlet pressure is 15 bar, the maximum pressure in the hydrogen buffer tank can only reach 15 bar (cannot exceed the hydrogen production outlet pressure). Assume that the minimum inlet pressure of the synthesis gas compressor is 10 bar. In other words, the hydrogen storage tank can only release hydrogen with a pressure difference of 5 bar. Assuming that the volume of the hydrogen storage tank is 500 m 3 , then the hydrogen release capacity is 2500 Nm 3After adding a hydrogen compressor, the pressure of the hydrogen production outlet can be increased from 15 bar to 20 bar, so the maximum pressure in the hydrogen storage tank can be increased to 20 bar, and hydrogen with a pressure difference of 10 bar can be released. 3 The release capacity of the hydrogen storage tank can be increased to 5000Nm 3 .

[0016] However, the second synthetic ammonia feed buffer system also has the following defects:

[0017] (1) The use of hydrogen compressor increases system energy consumption;

[0018] (2) Hydrogen has a small molecular weight and is not easy to compress. The boost pressure of a single-stage compression is relatively low, resulting in a large number of hydrogen compressor stages and a large investment; and

[0019] (3) The system adds a moving device, which increases the risk of failure and the frequency of inspection and maintenance.

[0020] Therefore, there is still a need for a synthetic ammonia feed buffer system, which can buffer the ammonia synthesis raw gas in a more cost-effective manner and maintain the stable operation of the ammonia synthesis system. Summary of the invention

[0021] The purpose of the present application is to provide a synthetic ammonia feed buffer system, which can achieve the buffering function of ammonia synthesis raw gas in a cost-effective manner, and can be used in combination with a renewable energy hydrogen production device to adapt to the hydrogen flow fluctuations of renewable energy hydrogen production.

[0022] In order to achieve the above-mentioned objectives, on the one hand, the present application provides a synthetic ammonia feed buffer system, including an ammonia synthesis gas buffer tank and an ammonia synthesis gas compressor (hereinafter also referred to as a synthesis gas compressor), the ammonia synthesis gas compressor having an inlet and an outlet, and including a first compressor cylinder connected to its inlet and a second compressor cylinder connected to the outlet of the first compressor cylinder, the outlet of the second compressor cylinder being connected to the outlet of the ammonia synthesis gas compressor, the first compressor cylinder being used to pressurize the input ammonia synthesis gas containing hydrogen and nitrogen to a pressure of 20-40 bar, and the second compressor cylinder being used to further pressurize the pressurized ammonia synthesis gas from the first compressor cylinder, characterized in that the outlet of the first compressor cylinder is connected to the inlet of the ammonia synthesis gas buffer tank through a first pressure reducing valve, and the outlet of the ammonia synthesis gas buffer tank is connected to the inlet of the ammonia synthesis gas compressor through a second pressure reducing valve.

[0023] On the other hand, the present application provides a synthetic ammonia feed system, comprising a hydrogen source, a nitrogen source and a synthetic ammonia feed buffer system according to the present application, wherein the hydrogen source and the nitrogen source are connected to the inlet of the ammonia synthesis gas compressor, and the outlet of the ammonia synthesis gas compressor is connected to an ammonia synthesis device.

[0024] The synthetic ammonia feed buffer system and the synthetic ammonia feed system of the present application have the following advantages:

[0025] (1) There is no restriction on the selection of water electrolysis hydrogen production equipment, either high-pressure type or low-pressure type can be used;

[0026] (2) Increase the maximum pressure of the ammonia synthesis gas buffer tank, thereby increasing the gas storage capacity under the same volume, reducing the floor space, and saving tank investment;

[0027] (3) The inlet pressure of the syngas compressor remains constant to ensure stable and efficient operation of the compressor; and

[0028] (4) No need to add hydrogen compressors, saving system energy consumption, reducing system investment, reducing the number of moving equipment, and reducing the risk of failure and the frequency of inspection and maintenance; and

[0029] (5) It can adapt to the frequent and rapid fluctuations of renewable energy and be used for dynamic synthesis of ammonia using renewable energy as the electricity source.

[0030] Other features and advantages of the present application will be described in detail in the subsequent detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The accompanying drawings are used to provide a further understanding of the present application and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present application but do not constitute a limitation to the present application. In the accompanying drawings:

[0032] Figure 1 A schematic diagram of a synthetic ammonia feed buffer system not of the present application is shown;

[0033] Figure 2 A schematic diagram showing another synthetic ammonia feed buffer system not of the present application; and

[0034] Figure 3 A schematic diagram of a synthetic ammonia feed buffer system according to the present application is shown. DETAILED DESCRIPTION

[0035] The specific implementation of the present application is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present application, and is not used to limit the present application.

[0036] Any specific numerical value disclosed herein (including the endpoint of the numerical range) is not limited to the exact value of the numerical value, but should be understood to also cover values ​​close to the exact value, such as all possible values ​​within the range of ±5% of the exact value. In addition, for the disclosed numerical range, the endpoint values ​​of the range, the endpoint values ​​and the specific point values ​​in the range, and the specific point values ​​can be arbitrarily combined to obtain one or more new numerical ranges, and these new numerical ranges should also be regarded as specifically disclosed herein.

[0037] Unless otherwise specified, the terms used herein have the same meaning as commonly understood by those skilled in the art. If a term is defined herein and its definition is different from the commonly understood meaning in the art, the definition herein shall prevail.

[0038] In the present application, the term "ammonia synthesis gas" refers to a gas mixture containing hydrogen and nitrogen suitable for synthesizing ammonia, preferably, it is essentially composed of hydrogen and nitrogen (for example, the content of other gases other than hydrogen and nitrogen is less than 10%, more preferably less than 5%, particularly preferably less than 1%, for example less than 0.5% or less than 0.1%), and wherein the molar ratio of hydrogen to nitrogen is 2:1 to 4:1, preferably 2.5:1 to 3.5:1, particularly preferably about 3:1.

[0039] In this application, except for the contents explicitly described, any matters or items not mentioned are directly applicable to those known in the art without any changes. Moreover, any embodiment described herein can be freely combined with one or more other embodiments described herein, and the technical solutions or technical ideas formed thereby are regarded as part of the original disclosure or original record of the present invention, and should not be regarded as new contents not disclosed or anticipated herein, unless a person skilled in the art considers that the combination is obviously unreasonable.

[0040] All patent and non-patent literature, including but not limited to textbooks and journal articles, mentioned herein are incorporated herein by reference in their entirety.

[0041] As described above, in the first aspect, the present application provides a synthetic ammonia feed buffer system, comprising an ammonia synthesis gas buffer tank and an ammonia synthesis gas compressor, wherein the ammonia synthesis gas compressor has an inlet and an outlet, and comprises a first compressor cylinder connected to its inlet and a second compressor cylinder connected to the outlet of the first compressor cylinder, the outlet of the second compressor cylinder being connected to the outlet of the ammonia synthesis gas compressor, the first compressor cylinder being used to pressurize the input ammonia synthesis gas containing hydrogen and nitrogen to a pressure of 20-40 bar, and the second compressor cylinder being used to further pressurize the pressurized ammonia synthesis gas from the first compressor cylinder, characterized in that the outlet of the first compressor cylinder is connected to the inlet of the ammonia synthesis gas buffer tank through a first pressure reducing valve, and the outlet of the ammonia synthesis gas buffer tank is connected to the inlet of the ammonia synthesis gas compressor through a second pressure reducing valve.

[0042] In a preferred embodiment, the outlet pressure of the ammonia synthesis gas compressor is 130-180 bar, and the ammonia synthesis gas compressor further includes a third compressor cylinder connected to the outlet of the second compressor cylinder, which is used to further pressurize the further pressurized ammonia synthesis gas from the second compressor cylinder and the circulating gas from the ammonia synthesis process to 130-180 bar, and the outlet of the third compressor cylinder is connected to the outlet of the ammonia synthesis gas compressor.

[0043] In a preferred embodiment, the ammonia synthesis gas compressor further includes a gas mixer, which is arranged between the inlet of the ammonia synthesis gas compressor and the inlet of the first compressor cylinder, and is used to further mix the mixed gas containing hydrogen and nitrogen input from the inlet of the ammonia synthesis gas compressor to obtain the ammonia synthesis gas containing hydrogen and nitrogen input into the first compressor cylinder.

[0044] In a preferred embodiment, the ammonia synthesis gas compressor further includes a first anti-surge circuit connecting the outlet and the inlet of the first compressor cylinder, and a second anti-surge circuit connecting the outlet and the inlet of the second compressor cylinder, the first anti-surge circuit is sequentially provided with a first cooling device and a first anti-surge valve, and the second anti-surge circuit is sequentially provided with a second cooling device and a second anti-surge valve.

[0045] In a further preferred embodiment, the ammonia synthesis gas compressor comprises the gas mixer, and the first anti-surge valve of the first anti-surge circuit is connected to the inlet of the gas mixer, and the outlet of the gas mixer is in communication with the inlet of the first compressor cylinder.

[0046] In a further preferred embodiment, the outlet of the first cooling device is connected to the inlet of the first compressor cylinder through a first anti-surge valve, connected to the inlet of the ammonia synthesis gas buffer tank through a first pressure reducing valve, and connected to the inlet of the second compressor cylinder through a pipeline.

[0047] In a further preferred embodiment, the ammonia synthesis gas compressor comprises the third compressor cylinder, and the outlet of the second cooling device is connected to the inlet of the second compressor cylinder through a second anti-surge valve and to the inlet of the third compressor cylinder through a pipeline.

[0048] In a further preferred embodiment, the ammonia synthesis gas compressor further comprises a third anti-surge circuit connected to the outlet and the inlet of the third compressor cylinder, and a third cooling device and a third anti-surge valve are sequentially arranged on the third anti-surge circuit.

[0049] In a further preferred embodiment, the third compressor cylinder comprises two stages, the further pressurized ammonia synthesis gas from the second compressor cylinder enters the first stage of the third compressor cylinder, and the recycle gas from the ammonia synthesis process enters the second stage of the third compressor cylinder.

[0050] In a further preferred embodiment, the ammonia synthesis gas compressor further includes a fourth anti-surge circuit connecting the outlet of the third compressor cylinder and the inlet of the second stage of the third compressor cylinder, the fourth anti-surge circuit is provided with a fourth anti-surge valve, and the fourth anti-surge circuit shares the third cooling device with the third anti-surge circuit, or a fourth cooling device is separately provided.

[0051] In a preferred embodiment, the first pressure reducing valve and the second pressure reducing valve are controlled by a multivariable indicator control (UIC), the input signals of which are the pressure at the inlet and outlet of the ammonia synthesis gas buffer tank, the flow rate of the fresh ammonia synthesis gas and the flow rate of the inlet pipeline of the ammonia synthesis gas buffer tank. Preferably, the multivariable controller is integrated into a distributed control system (DCS) to realize automatic control and centralized monitoring.

[0052] Figure 3A schematic diagram of a preferred embodiment of a synthetic ammonia feed buffer system according to the present application is shown. As shown in the figure, the system includes an ammonia synthesis gas buffer tank and an ammonia synthesis gas compressor, wherein the ammonia synthesis gas compressor adopts a centrifugal compressor, including a first compressor cylinder (also called a low-pressure cylinder), a second compressor cylinder (also called a medium-pressure cylinder) and a third compressor cylinder (also called a high-pressure cylinder) connected in sequence, wherein the number of compressor cylinders can also be changed according to actual needs. The low-pressure cylinder, the medium-pressure cylinder and the high-pressure cylinder are respectively provided with corresponding anti-surge circuits connecting their outlets and inlets, and each anti-surge circuit is provided with a cooling device and an anti-surge valve, wherein the inlet of each cooling device is connected to the outlet of the corresponding compressor cylinder, and the outlet of each cooling device is connected to the inlet of the corresponding compressor cylinder through the anti-surge valve. In addition, the outlet of the cooling device on the anti-surge circuit of the low-pressure cylinder is also connected to the inlet of the medium-pressure cylinder through a pipeline, and the outlet of the cooling device on the anti-surge circuit of the medium-pressure cylinder is also connected to the inlet of the high-pressure cylinder through a pipeline, and the outlet of the high-pressure cylinder is also directly connected to the downstream ammonia synthesis device. The high-pressure cylinder includes two stages, wherein the ammonia synthesis gas from the medium-pressure cylinder enters the first stage of the high-pressure cylinder, and the circulating gas from the downstream ammonia synthesis process returns to the second stage of the high-pressure cylinder through a pipeline, and the outlet of the cooling device on the anti-surge circuit of the high-pressure cylinder is connected to the inlet of the first stage of the high-pressure cylinder through an anti-surge valve, and is also connected to the return pipeline of the circulating gas through another anti-surge valve, and then connected to the inlet of the second stage of the high-pressure cylinder.

[0053] The outlet of the cooling device corresponding to the low-pressure cylinder is also connected to the inlet of the ammonia synthesis gas buffer tank through the low-pressure cylinder exhaust pipeline, and a first pressure reducing valve is arranged on the low-pressure cylinder exhaust pipeline. The outlet of the ammonia synthesis gas buffer tank is connected to the fresh gas intake main pipeline of the synthesis gas compressor through the buffer gas pipeline, and a second pressure reducing valve is arranged on the buffer gas pipeline. The fresh gas intake main pipeline is used to deliver fresh hydrogen from the hydrogen source and fresh nitrogen from the nitrogen source to the inlet of the ammonia synthesis gas compressor.

[0054] A pressure transmitter (PI) is provided at the downstream position of the first pressure reducing valve on the low-pressure cylinder exhaust pipeline and at the downstream position of the second pressure reducing valve on the buffer gas pipeline, respectively, which can transmit the pressure signal to the UIC controller, and then output the control instruction to the first pressure reducing valve and the second pressure reducing valve through the controller, so as to form a feedback loop, so that the inlet and outlet pressures of the ammonia synthesis gas buffer tank are maintained at a predetermined value or a predetermined range. A flow indicator is provided on the fresh gas intake main pipeline of the synthesis gas compressor, and the UIC controller controls the opening of the first pressure reducing valve and the second pressure reducing valve by monitoring the intake flow of the synthesis gas compressor, so as to control the charging and discharging of the ammonia synthesis gas buffer tank. That is, when the growth rate of the fresh gas intake flow exceeds the limit value, the opening of the first pressure reducing valve is increased, the opening of the second pressure reducing valve is reduced or the second pressure reducing valve is closed, so that the ammonia synthesis gas buffer tank is in a charging state; on the contrary, when the decrease rate of the fresh gas intake flow exceeds the limit value, the opening of the second pressure reducing valve is increased, the opening of the first pressure reducing valve is reduced or the first pressure reducing valve is closed, so that the ammonia synthesis gas buffer tank is in a degassing state. In addition, a flow indicator (FI) is also provided downstream of the first pressure reducing valve on the low-pressure cylinder exhaust pipeline, which can transmit the flow signal to the UIC controller, and is used to control the flow of the low-pressure cylinder exhaust pipeline through the UIC controller so that it does not exceed 10% (generally 2-5%) of the full flow of the low-pressure cylinder outlet, to avoid excessive exhaust and triggering the anti-surge adjustment of the compressor's intermediate pressure cylinder or high pressure cylinder. The control strategy of the UIC controller is integrated into the DCS system of the synthetic ammonia plant to achieve fully automated control and centralized monitoring.

[0055] like Figure 3 As shown, fresh hydrogen from a renewable energy hydrogen production device as a hydrogen source and fresh nitrogen from an air nitrogen production device as a nitrogen source are first combined in the fresh gas inlet main pipeline of the synthesis gas compressor, and then combined with the buffer gas from the ammonia synthesis gas buffer tank, and then enter the inlet of the ammonia synthesis gas compressor, and enter the low-pressure cylinder after further mixing in the gas mixer of the ammonia synthesis gas compressor.

[0056] In a second aspect, the present application provides a synthetic ammonia feed system, comprising a hydrogen source, a nitrogen source and a synthetic ammonia feed buffer system according to the present application, wherein the hydrogen source and the nitrogen source are connected to the inlet of an ammonia synthesis gas compressor of the synthetic ammonia feed buffer system, and the outlet of the ammonia synthesis gas compressor is connected to an ammonia synthesis unit.

[0057] According to the present application, the hydrogen source can be any device suitable for providing high-purity hydrogen, and the present application has no strict restrictions on this. In some specific embodiments, the hydrogen source is a renewable energy hydrogen production device, which uses renewable energy to produce hydrogen by electrolyzing water. According to the present application, the renewable energy can be selected from wind power generation, hydropower generation and photovoltaic power generation.

[0058] According to the present application, the nitrogen source can be any device suitable for providing high-purity nitrogen, and the present application has no strict restrictions on this. In some specific embodiments, the nitrogen source is an air separation nitrogen production device.

[0059] The synthetic ammonia feed buffer system and the synthetic ammonia feed system of the present application are suitable for use in combination with a renewable energy hydrogen production device, which can adapt to the hydrogen flow fluctuations of renewable energy hydrogen production and cost-effectively achieve buffering of ammonia synthesis raw gas.

[0060] Specifically, if Figure 3 As shown, when the hydrogen flow rate of the renewable energy hydrogen production device remains stable, the first pressure reducing valve and the second pressure reducing valve of the synthetic ammonia feed buffer system of the present application are both closed, and the fresh hydrogen and fresh nitrogen are combined and directly enter the ammonia synthesis gas compressor, and then enter the low-pressure cylinder after being mixed by the gas mixer, and then mixed with the circulating gas after being compressed in two stages of the low-pressure cylinder and the medium-pressure cylinder, and then enter the ammonia synthesis process after being compressed by the high-pressure cylinder.

[0061] When the hydrogen flow rate increase rate of the renewable energy hydrogen production device exceeds the limit (for example, 1% / min), unlike the traditional solution, the fresh hydrogen and fresh nitrogen in the synthetic ammonia feed buffer system of the present application do not enter the ammonia synthesis gas buffer tank after being combined, but first enter the low-pressure cylinder of the ammonia synthesis gas compressor, and the pressure is increased to 20-40 bar through the low-pressure cylinder, and then a certain proportion (for example, 2-5% of the full flow of the low-pressure cylinder outlet) of the hydrogen / nitrogen mixed gas (i.e., ammonia synthesis gas) is extracted into the ammonia synthesis gas buffer tank through the low-pressure cylinder exhaust pipeline connected to the outlet of the cooling device on the low-pressure cylinder anti-surge circuit, so that the buffer tank is gradually filled. At this time, the second pressure reducing valve is closed, the first pressure reducing valve is opened and its opening is controlled, so that the hydrogen / nitrogen mixed gas is decompressed to a pressure not exceeding the design pressure of the buffer tank, for example, 20-40 bar.

[0062] When the hydrogen flow rate of the renewable energy hydrogen production device drops beyond the limit (e.g. 1% / min), the first pressure reducing valve is closed and the second pressure reducing valve is opened, and the buffer gas in the ammonia synthesis gas buffer tank is mixed with the fresh gas and then enters the low-pressure cylinder of the ammonia synthesis gas compressor to supplement the shortage of fresh gas. At this time, the opening of the second pressure reducing valve is controlled so that the outlet pressure of the buffer tank is always kept constant, for example, at a predetermined value between 10-30 bar, thereby stabilizing the compressor inlet pressure.

[0063] The synthetic ammonia feed buffer system and the synthetic ammonia feed system of the present application have the following advantages:

[0064] (1) Make full use of the pressurizing capacity of the low-pressure cylinder of the ammonia synthesis gas compressor, first pressurize the mixed gas of hydrogen and nitrogen to 20-40 bar, and then extract a small part of the pressurized mixed gas to the ammonia synthesis gas buffer tank, thereby increasing the storage pressure of the buffer tank. In the traditional scheme, the pressure of the buffer tank generally does not exceed 20 bar, but the present invention can increase the pressure of the buffer tank to 20-40 bar without adding additional hardware equipment, the gas storage capacity can be increased by 1-2 times, and the investment of a hydrogen compressor can be saved.

[0065] (2) The conventional solution uses a pure hydrogen buffer tank, while the ammonia synthesis gas buffer tank of the present application stores a mixture of hydrogen and nitrogen, and the hydrogen / nitrogen mixing ratio is the same as the synthesis gas mixing ratio required by the downstream ammonia synthesis unit, for example, 3:1. Since the molecular weight of the hydrogen / nitrogen mixed gas is greater than that of pure hydrogen, the energy consumption of compressing the mixed gas to the same pressure is 20-30% lower than that of compressing pure hydrogen. In other words, under the condition of the same buffer gas storage capacity, the present invention can save energy consumption by about 20-30%.

[0066] (3) By controlling the opening of the second pressure reducing valve, the feed buffer system of the present application can ensure that the inlet pressure of the ammonia synthesis gas compressor remains constant, so that the compressor always works under the most efficient working conditions. For a typical dynamic green synthetic ammonia plant, energy consumption can be saved by about 5-10%. In addition, the stable inlet pressure can also reduce the workload of the compressor and reduce the failure rate. Example

[0067] The present application is further described below in conjunction with embodiments, but the present application is not limited thereby.

[0068] Example 1

[0069] The synthetic ammonia feed buffer system used is as follows Figure 3 As shown in the figure, the renewable energy hydrogen production device adopts the process of water electrolysis to produce hydrogen, and wind power and photovoltaic power provide green electricity. Since the output (i.e. output power) of wind power and photovoltaic power fluctuates in a wide range, the hydrogen flow rate in the hydrogen production process will also fluctuate frequently between 10-100%. The nitrogen flow rate of the air separation nitrogen production device is adjusted synchronously with the hydrogen flow rate of the electrolytic hydrogen production to ensure that the fresh gas volume of hydrogen and nitrogen is maintained at 3:1.

[0070] The outlet pressure of hydrogen and nitrogen production is 15 bar. Under normal working conditions, fresh hydrogen and fresh nitrogen are mixed and directly enter the ammonia synthesis gas compressor. The optimal inlet pressure of the compressor is also 15 bar, and the outlet pressure of the low-pressure cylinder is 40 bar. The first pressure reducing valve and the second pressure reducing valve are both closed, and the mixed gas is compressed to 150 bar by the compressor and enters the subsequent ammonia synthesis process.

[0071] When the hydrogen flow rate of electrolytic hydrogen production exceeds 1% / min, the load regulation rate of the ammonia synthesis process is limited, and the large amount of fresh gas generated rapidly cannot be consumed in a short time. At this time, the first pressure reducing valve is opened to control the flow of the low-pressure cylinder exhaust pipeline to allow 2-5% of the pressurized hydrogen / nitrogen mixture (i.e., ammonia synthesis gas) to flow back to the ammonia synthesis gas buffer tank. The maximum design pressure of the ammonia synthesis gas buffer tank is 30 bar, so the opening of the first pressure reducing valve is controlled to reduce the pressure of the reflux gas to 30 bar.

[0072] When the hydrogen flow rate of electrolytic hydrogen production drops by more than 1% / min, the ammonia synthesis process cannot quickly reduce the load in a short time. At this time, open the second pressure reducing valve to release the hydrogen / nitrogen mixed gas in the ammonia synthesis gas buffer tank so that the gas volume entering the ammonia synthesis gas compressor meets the needs of the ammonia synthesis reaction. Control the opening of the second pressure reducing valve to keep the pressure at the outlet of the buffer tank constant at 15 bar.

[0073] In this embodiment, the volume of the ammonia synthesis gas buffer tank is 500 m 3 , release pressure difference 15 bar, maximum release capacity 7500 Nm 3 In comparison, the release pressure difference of the conventional buffer system is about 5 bar, and the gas storage capacity of the present invention is increased by about 2 times compared with the conventional solution.

[0074] The outlet pressure of the ammonia synthesis gas compressor is 150 bar, the inlet pressure is 15 bar, and the compressor pressure ratio is 10. In contrast, the compressor inlet pressure of the traditional scheme fluctuates between 10-15 bar, and the maximum pressure ratio can reach 15. The present invention can reduce the compressor pressure ratio by 33% and reduce the compressor investment.

[0075] The preferred embodiments of the present application are described in detail above; however, the present application is not limited to the specific details in the above embodiments. Within the technical concept of the present application, a variety of simple modifications can be made to the technical solution of the present application, and these simple modifications all fall within the protection scope of the present application.

[0076] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, this application will not further describe various possible combinations.

[0077] In addition, the various implementation modes of the present application may be arbitrarily combined, and as long as they do not violate the concept of the present application, they should also be regarded as the content invented by the present application.

Claims

1. A synthetic ammonia feed buffer system, comprising an ammonia synthesis gas buffer tank and an ammonia synthesis gas compressor, wherein the ammonia synthesis gas compressor has an inlet and an outlet, and comprises a first compressor cylinder connected to the inlet thereof and a second compressor cylinder connected to the outlet of the first compressor cylinder, wherein the outlet of the second compressor cylinder is connected to the outlet of the ammonia synthesis gas compressor, wherein the first compressor cylinder is used to pressurize the input ammonia synthesis gas containing hydrogen and nitrogen to a pressure of 20-40 bar, and the second compressor cylinder is used to further pressurize the pressurized ammonia synthesis gas from the first compressor cylinder, wherein: The outlet of the first compressor cylinder is connected to the inlet of the ammonia synthesis gas buffer tank through a first pressure reducing valve, and the outlet of the ammonia synthesis gas buffer tank is connected to the inlet of the ammonia synthesis gas compressor through a second pressure reducing valve. The outlet pressure of the ammonia synthesis gas compressor is 130-180 bar. The ammonia synthesis gas buffer tank stores a mixed gas of hydrogen and nitrogen, and the hydrogen / nitrogen mixing ratio is the same as the synthesis gas mixing ratio required by the downstream ammonia synthesis unit.

2. The synthetic ammonia feed buffer system according to claim 1, wherein the ammonia synthesis gas compressor further comprises a third compressor cylinder connected to the outlet of the second compressor cylinder, which is used to further pressurize the further pressurized ammonia synthesis gas from the second compressor cylinder and the circulating gas from the ammonia synthesis process to 130-180 bar, and the outlet of the third compressor cylinder is connected to the outlet of the ammonia synthesis gas compressor.

3. The synthetic ammonia feed buffer system according to claim 2, wherein the ammonia synthesis gas compressor further comprises a gas mixer, which is arranged between the inlet of the ammonia synthesis gas compressor and the inlet of the first compressor cylinder, and is used to further mix the mixed gas containing hydrogen and nitrogen input from the inlet of the ammonia synthesis gas compressor to obtain the ammonia synthesis gas containing hydrogen and nitrogen input to the first compressor cylinder.

4. The synthetic ammonia feed buffer system according to any one of claims 3, wherein the ammonia synthesis gas compressor further comprises a first anti-surge circuit connected to the outlet and inlet of the first compressor cylinder, and a second anti-surge circuit connected to the outlet and inlet of the second compressor cylinder, the first anti-surge circuit is provided with a first cooling device and a first anti-surge valve in sequence, and the second anti-surge circuit is provided with a second cooling device and a second anti-surge valve in sequence.

5. A synthetic ammonia feed buffer system according to claim 4, wherein the ammonia synthesis gas compressor includes a gas mixer as defined in claim 3, and the first anti-surge valve of the first anti-surge circuit is connected to the inlet of the gas mixer, and the outlet of the gas mixer is connected to the inlet of the first compressor cylinder.

6. A synthetic ammonia feed buffer system according to claim 5, wherein the outlet of the first cooling device is connected to the inlet of the first compressor cylinder through a first anti-surge valve, connected to the inlet of the ammonia synthesis gas buffer tank through a first pressure reducing valve, and connected to the inlet of the second compressor cylinder through a pipeline.

7. A synthetic ammonia feed buffer system according to any one of claims 6, wherein the ammonia synthesis gas compressor includes the third compressor cylinder defined in claim 2, and the outlet of the second cooling device is connected to the inlet of the second compressor cylinder through a second anti-surge valve, and is connected to the inlet of the third compressor cylinder through a pipeline.

8. The synthetic ammonia feed buffer system according to claim 7, wherein the ammonia synthesis gas compressor further comprises a third anti-surge circuit connected to the outlet and inlet of the third compressor cylinder, and a third cooling device and a third anti-surge valve are sequentially arranged on the third anti-surge circuit.

9. The synthetic ammonia feed buffer system according to claim 8, wherein the third compressor cylinder comprises two stages, the further pressurized ammonia synthesis gas from the second compressor cylinder enters the first stage of the third compressor cylinder, and the recycled gas from the ammonia synthesis process enters the second stage of the third compressor cylinder.

10. According to the synthetic ammonia feed buffer system of claim 9, the ammonia synthesis gas compressor further includes a fourth anti-surge circuit connecting the outlet of the third compressor cylinder and the inlet of the second stage of the third compressor cylinder, the fourth anti-surge circuit is provided with a fourth anti-surge valve, and the fourth anti-surge circuit shares the third cooling device with the third anti-surge circuit, or a fourth cooling device is separately provided.

11. A synthetic ammonia feed buffer system according to any one of claims 1 to 10, wherein the first pressure reducing valve and the second pressure reducing valve are controlled by a multivariable controller, the input signals of the controller are the pressures at the inlet and outlet of the ammonia synthesis gas buffer tank, and the flow rate of the fresh ammonia synthesis gas and the flow rate of the ammonia synthesis gas buffer tank inlet pipeline. Preferably, the multivariable controller is integrated into a distributed control system DCS to achieve automatic control and centralized monitoring.

12. A synthetic ammonia feed system, comprising a hydrogen source, a nitrogen source and a synthetic ammonia feed buffer system according to any one of claims 1 to 11, wherein the hydrogen source and the nitrogen source are connected to the inlet of an ammonia synthesis gas compressor of the synthetic ammonia feed buffer system, and the outlet of the ammonia synthesis gas compressor is connected to an ammonia synthesis unit.

13. The synthetic ammonia feed system according to claim 12, wherein the hydrogen source is a renewable energy hydrogen production device, wherein the renewable energy is selected from wind power generation, hydropower generation and photovoltaic power generation.

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