A synthetic ammonia process and a synthetic ammonia system

Abstract

The present invention provides a synthetic ammonia process and a synthetic ammonia system, the method is: hydrogen and nitrogen are mixed and compressed, water-cooled, and heat-exchanged with ammonia-separated gas D to obtain hydrogen-nitrogen mixed gas; the hydrogen-nitrogen mixed gas is mixed with liquid ammonia discharged from an ammonia separator to generate a low-temperature gas-liquid mixture A; the low-temperature gas-liquid mixture A is heated and flash-evaporated to obtain a liquid ammonia product and a mixed ammonia raw gas; the mixed ammonia raw gas is compressed and mixed with the synthesis gas of an ammonia synthesis tower, water-cooled to generate an ammonia-rich gas-liquid mixture C1; the low-temperature gas-liquid mixture A, the ammonia-separated gas B and the ammonia-rich gas-liquid mixture C1 are heat-exchanged to obtain an ammonia-rich low-temperature gas-liquid mixture C2, which enters an ammonia separator for separation; the low-temperature gas-liquid mixture A is heated as described above; the heated ammonia-separated gas D and the ammonia-separated gas B enter the ammonia synthesis tower for ammonia synthesis reaction. The system is suitable for the method, does not need to set up a separate ice machine system, has a simple process flow, low energy consumption, and can save equipment investment.

Description

Technical Field

[0001] The invention belongs to the technical field of synthetic ammonia, and in particular relates to a synthetic ammonia process method and a synthetic ammonia system. Background Art

[0002] In the existing synthetic ammonia production process, Figure 1 As shown, the outlet gas of the ammonia synthesis tower is cooled to about 30℃-40℃ by a water cooler, and part of the synthesis gas that has completed the ammonia synthesis reaction in the ammonia synthesis tower is condensed, and the liquid ammonia is separated in the ammonia separator. In order to reduce the inert gas content, the circulating gas is partially vented in the ammonia separator, and most of the circulating gas is recycled and mixed with the raw mixed gas pressurized by the raw gas compressor unit and then enters the ammonia cooler, where it is cooled to about -10℃, so that most of the ammonia in the gas is condensed. The low-temperature circulating gas separated into liquid ammonia cools the synthesis gas through a heat exchanger and enters the ammonia separator, and is heated to 10~30℃ to enter the ammonia synthesis tower to complete the circulation process. In order to recover ammonia in the circulating gas in this synthetic ammonia process, a separate ice machine system must be set up to provide cooling capacity for the ammonia cooler, that is, there are problems such as complex process flow, high equipment investment cost and high operating energy consumption. Summary of the invention

[0003] In view of the deficiencies in the above-mentioned prior art, the present invention provides a synthetic ammonia process method and a synthetic ammonia system. The method and system mix the low-temperature liquid ammonia separated by synthesis with the compressed and pre-cooled hydrogen-nitrogen mixed gas. During the mixing process, due to the low ammonia partial pressure in the gas, part of the liquid ammonia evaporates and gasifies, absorbing heat, thereby generating a lower-temperature low-temperature gas-liquid mixture A. The low-temperature gas-liquid mixture A is used as the main cold source, and the gas B after ammonia separation is used as a supplementary cold source to exchange heat with the ammonia-rich gas-liquid mixture C1, so that the ammonia-rich gas-liquid mixture C1 is condensed to separate most of the ammonia. In the process, both cold exchange and ammonia cooling are achieved. The method and system do not need to set up a separate ice machine system, and the process flow is simple, the energy consumption is low, and equipment investment can be saved.

[0004] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0005] A process for synthesizing ammonia, comprising the following steps:

[0006] S1, compressing the mixed gas of hydrogen and nitrogen, water-cooling it, and then pre-cooling it by heat exchange with the ammonia-separated gas D discharged from the upper part of the ammonia separator to obtain a cooled hydrogen-nitrogen mixed gas;

[0007] S2, the hydrogen-nitrogen mixed gas is mixed with the liquid ammonia discharged from the lower part of the ammonia separator to generate a low-temperature gas-liquid mixture A;

[0008] S3, heating and flashing the low-temperature gas-liquid mixture A to obtain a liquid ammonia product and a mixed ammonia raw gas;

[0009] S4, the mixed ammonia raw gas is compressed and mixed with the synthesis gas from the ammonia synthesis tower, and water-cooled to generate an ammonia-rich gas-liquid mixture C1;

[0010] S5, heat-exchanging the low-temperature gas-liquid mixture A or the low-temperature gas-liquid mixture A and the ammonia-separated gas B discharged from the upper part of the ammonia separator with the ammonia-rich gas-liquid mixture C1, so that the ammonia-rich gas-liquid mixture C1 is condensed into an ammonia-rich low-temperature gas-liquid mixture C2, and enters the ammonia separator for gas-liquid separation; at the same time, the low-temperature gas-liquid mixture A is heated in step S3, and the ammonia-separated gas B is heated;

[0011] S6. The ammonia-separated gas D heated in step S1 and the ammonia-separated gas B heated in step S5 enter the ammonia synthesis tower to undergo ammonia synthesis reaction.

[0012] In one embodiment of the present application, in step S1, the pressure of the mixed gas of hydrogen and nitrogen after compression is 3.2-3.5 MPa;

[0013] The temperature after water cooling is 30~50℃;

[0014] The temperature of the hydrogen-nitrogen mixed gas obtained after heat exchange and precooling with the ammonia-separated gas D is 0~-20°C.

[0015] In one embodiment of the present application, the temperatures of the liquid ammonia, the ammonia separated gas D and the ammonia separated gas B discharged from the ammonia separator are all -15 to -25°C;

[0016] And / or, the mass ratio of the gas B after ammonia separation to the gas D after ammonia separation is 2:1.

[0017] In one embodiment of the present application, in step S2, during the mixing of the hydrogen-nitrogen mixed gas and liquid ammonia, part of the liquid ammonia evaporates and gasifies, and the temperature of the obtained low-temperature gas-liquid mixture A is -20 to -40°C.

[0018] In one embodiment of the present application, in step S4, the mixed ammonia raw gas is compressed by a two-stage compressor, pressurized to 12 MPa, and then mixed with the synthesis gas from the ammonia synthesis tower;

[0019] After mixing, the temperature of the ammonia-rich gas-liquid mixture C1 generated by water cooling is 30-50°C.

[0020] In one embodiment of the present application, after the low-temperature gas-liquid mixture A or the low-temperature gas-liquid mixture A and the ammonia-separated gas B discharged from the upper part of the ammonia separator are heat exchanged with the ammonia-rich gas-liquid mixture C1, the low-temperature gas-liquid mixture A is heated to 20~40°C; the ammonia-rich gas-liquid mixture C1 is condensed into the ammonia-rich low-temperature gas-liquid mixture C2 at -15~-25°C.

[0021] A synthetic ammonia system, comprising:

[0022] Ammonia synthesis tower;

[0023] Ammonia separator,

[0024] A first compressor, a precooler, an ammonia cooler and a flash ammonia separation tower connected in sequence via pipelines;

[0025] The upper exhaust port of the ammonia separator is provided with a first pipeline and a second pipeline, the first pipeline is connected to the ammonia synthesis tower through the precooler; the second pipeline is connected to the ammonia synthesis tower through the ammonia cooler; the lower drain port of the ammonia separator is provided with a third pipeline, the third pipeline is connected to a fourth pipeline connecting the precooler and the ammonia cooler;

[0026] A fifth pipeline is provided at the synthesis gas outlet of the ammonia synthesis tower, and the fifth pipeline is connected to the inlet of the ammonia separator after passing through the second water cooler and the ammonia cooler in sequence;

[0027] The gas outlet of the flash ammonia separation tower is provided with a sixth pipeline connected to the fifth pipeline, and the mixed ammonia raw gas separated by flash evaporation is mixed with the synthesis gas of the ammonia synthesis tower and sent into the ammonia separator.

[0028] In one embodiment of the present application, the ammonia cooler is a three-phase flow heat exchanger, and the three-phase flow heat exchanger includes a shell side, a tube side, and an inner tube side channel arranged in sequence from the outside to the inside.

[0029] In one embodiment of the present application, the fourth pipeline is connected to the shell-side channel; the second pipeline is connected to the inner tube-side channel; and the fifth pipeline is connected to the tube-side channel.

[0030] In one embodiment of the present application, the fourth pipeline is provided with a first mixing tank, and the third pipeline is connected to the first mixing tank;

[0031] The sixth pipeline is connected to the front end of the second water cooler on the fifth pipeline after passing through the second compressor.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] 1. The synthetic ammonia process of the present invention mixes the low-temperature liquid ammonia separated by synthesis with the compressed and pre-cooled hydrogen-nitrogen mixed gas. During the mixing process, due to the low partial pressure of ammonia in the gas, part of the liquid ammonia evaporates and gasifies, absorbing heat, thereby generating a low-temperature low-temperature gas-liquid mixture A. The low-temperature gas-liquid mixture A is used as the main cold source, and the gas B after ammonia separation is used as the supplementary cold source to exchange heat with the ammonia-rich gas-liquid mixture C1, so that the ammonia-rich gas-liquid mixture C1 is condensed to separate most of the ammonia. In this process, both cold exchange and ammonia cooling are achieved. There is no need to perform refrigeration compression of ammonia separately, and the ice machine system that provides coldness for the ammonia cooler is omitted. The process flow is simple, the energy consumption is low, and the equipment investment can be saved.

[0034] 2. The low-temperature gas-liquid mixture A provides condensation and raw gas. After being heated by the ammonia cooler and separated by gas and liquid in the flash ammonia separation tower, liquid ammonia is discharged as a product. The mixed ammonia raw gas is compressed and pressurized to the pressure required for synthetic ammonia, and then mixed into the synthesis gas of the ammonia synthesis tower to achieve the recycling of uncondensed and unreacted gases, and is pressurized together with the raw gas to reduce the investment in boosting equipment.

[0035] 3. The ammonia cooler in the synthetic ammonia system adopts a three-phase flow heat exchanger to achieve simultaneous heat exchange between the main cold source low-temperature gas-liquid mixture A, the supplementary cold source ammonia separated gas B and the ammonia-rich gas-liquid mixture C1, so that most of the gaseous ammonia in the ammonia-rich gas-liquid mixture C1 is condensed into liquid ammonia. The condensation effect is stable and reliable, which can effectively improve the yield. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 The figure is a schematic diagram of the process of the existing synthetic ammonia system.

[0038] Figure 2 It is a schematic diagram of the process of the synthetic ammonia system in the present invention.

[0039] Reference numerals:

[0040] 1. Ammonia synthesis tower; 11. Second water cooler;

[0041] 2. Ammonia separation tower;

[0042] 3. The first compressor;

[0043] 5. Precooler;

[0044] 6. Ammonia cooler;

[0045] 7. Flash ammonia separation tower; 71. Second compressor;

[0046] L1, first pipeline; L2, second pipeline; L3, third pipeline; L4, fourth pipeline; L5, fifth pipeline; L6, sixth pipeline; DETAILED DESCRIPTION

[0047] In the following, only some exemplary embodiments are briefly described. As those skilled in the art will appreciate, the described embodiments may be modified in various ways without departing from the spirit or scope of the present invention. Therefore, the drawings and descriptions are considered to be exemplary and non-restrictive in nature.

[0048] In the description of the present invention, it should be understood that the terms "upper", "lower", "front", "back", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships conventionally placed when the utility model product is used, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0049] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0050] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0051] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0052] The disclosure below provides many different embodiments or examples to realize different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention.

[0053] The embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0054] The embodiment of the present invention provides an ammonia synthesis process, which comprises the following steps:

[0055] (1) A mixed gas of hydrogen and nitrogen at a certain pressure is initially compressed to 3.2-3.5 MPa by a compressor, and then cooled to 30-50°C by water cooling, preferably controlled at about 40°C by water cooling; then, the mixed gas is pre-cooled by heat exchange with the ammonia separated gas D discharged from the upper part of the ammonia separator at a temperature of about -15--25°C, preferably controlled at about -20°C, so that the gas temperature is further reduced to obtain a hydrogen-nitrogen mixed gas raw material at a temperature of about 0--20°C, preferably controlled at about -10°C; at the same time, the ammonia separated gas D is heated to about 20-40°C, preferably controlled at about 30°C.

[0056] (2) Mixing the cooled hydrogen-nitrogen mixed gas with the low-temperature liquid ammonia discharged from the lower part of the ammonia separator to generate a low-temperature gas-liquid mixture A. The temperature of the liquid ammonia discharged from the lower part of the ammonia separator is about -15 to -25°C. It is preferred to control the temperature in the ammonia separator to about -20°C, even if the discharged liquid ammonia is about -20°C; mixing with the hydrogen-nitrogen mixed gas with a temperature of about 0 to -20°C. During the mixing process, part of the liquid ammonia evaporates and gasifies, absorbing heat, so that the temperature of the low-temperature gas-liquid mixture A generated after the two streams of materials are mixed is reduced to about -20 to -40°C. It is preferred to control the temperature of the generated low-temperature gas-liquid mixture A to about -30°C.

[0057] (3) The low-temperature gas-liquid mixture A is introduced into the ammonia cooler for heat exchange and heating. After the temperature rises to about 20-40°C, it enters the flash ammonia separation tower. The heating temperature is usually controlled at around 30°C. Then, the gas phase and liquid phase are separated in the flash ammonia separation tower. After flash gas-liquid separation, liquid ammonia and mixed ammonia raw gas are obtained. The obtained liquid ammonia is discharged as a liquid ammonia product for storage, and the mixed ammonia raw gas is discharged from the top of the flash ammonia separation tower.

[0058] (4) The discharged mixed ammonia raw gas is compressed by a compressor and mixed with the synthesis gas from the ammonia synthesis tower to form an ammonia-rich mixed gas. The ammonia-rich mixed gas is cooled to about 30-50°C by water cooling. Preferably, the temperature of the ammonia-rich mixed gas after water cooling is controlled at about 40°C. Part of the gaseous ammonia is condensed to generate an ammonia-rich gas-liquid mixture C1. The mixed ammonia raw gas is preferably compressed and pressurized by a two-stage compressor. After the pressure is increased to about 10-14MPa, it is mixed with the synthesis gas from the ammonia synthesis tower. The pressure after the pressure increase can usually be controlled to about 12Mpa.

[0059] (5) heat exchanging the low-temperature gas-liquid mixture A generated in step (2) with the ammonia-rich gas-liquid mixture C1; or heat exchanging the low-temperature gas-liquid mixture A and another part of the gas discharged from the upper part of the ammonia separator (i.e., the gas B after ammonia separation) with the ammonia-rich gas-liquid mixture C1; cooling and condensing the ammonia-rich gas-liquid mixture C1 to a temperature of about -15 to -25°C, and condensing most of the gaseous ammonia in the ammonia-rich gas-liquid mixture C1 into a liquid phase, and converting it into an ammonia-rich low-temperature gas-liquid mixture C2. Preferably, the temperature of the ammonia-rich low-temperature gas-liquid mixture C2 is controlled at about -20°C, and then the ammonia-rich low-temperature gas-liquid mixture C2 is sent to the ammonia separator for gas-liquid separation; at the same time, the low-temperature gas-liquid mixture A releases cold energy to achieve the temperature increase in step (3), that is, the low-temperature gas-liquid mixture A is heated from about -20 to -40°C to about 20 to 40°C; at the same time, the gas B after ammonia separation also releases cold energy to heat up.

[0060] (6) The ammonia separation gas D heated in step (1) and the ammonia separation gas B heated in step (5) are mixed and then enter the ammonia synthesis tower to perform ammonia synthesis reaction.

[0061] The ammonia-rich low-temperature gas-liquid mixture C2 is separated into gas and liquid in the ammonia separator, and the low-temperature liquid ammonia is discharged from the lower part, and the ammonia-separated gas is discharged from the upper part. The ammonia-separated gas is divided into two streams, namely, the ammonia-separated gas B and the ammonia-separated gas D; the separated liquid ammonia, the ammonia-separated gas B and the ammonia-separated gas D have a temperature of about -15~-25℃. During operation, the mass ratio of the ammonia-separated gas B and the ammonia-separated gas D should be controlled to be about 2:1, to ensure that the cold energy is fully released before entering the ammonia synthesis tower for ammonia synthesis reaction, and at the same time to ensure sufficient refrigeration of the hydrogen-nitrogen mixed gas (raw gas) and the ammonia-rich gas-liquid mixture C1.

[0062] In summary, the method mixes the synthesized and separated low-temperature liquid ammonia (about -15~ -25℃) with the compressed and pre-cooled hydrogen-nitrogen mixed gas (about 0~ -20℃). During the mixing process, due to the low ammonia partial pressure in the gas, part of the liquid ammonia evaporates and gasifies, absorbing heat, thereby generating a lower temperature low-temperature gas-liquid mixture A (about -20~ -40℃). The low-temperature gas-liquid mixture A is used as the main cold source, and the gas B after ammonia separation (about -15~ -25℃) is used as a supplementary cold source to exchange heat with the ammonia-rich gas-liquid mixture C1 (about 30~50℃), so that the ammonia-rich gas-liquid mixture C1 is condensed to separate most of the ammonia. In this process, both cold exchange and ammonia cooling are achieved. The process method does not require separate refrigeration and compression of ammonia, eliminates the ammonia refrigeration system, has a simple process flow, low operating energy consumption, and can save equipment investment.

[0063] Based on the same purpose, an embodiment of the present invention further provides an ammonia synthesis system, which is suitable for the ammonia synthesis process method described above.

[0064] like Figure 2 As shown, the synthetic ammonia system includes an ammonia synthesis tower 1, an ammonia separation tower 2, a first compressor 3, a precooler 5, an ammonia cooler 6, a flash ammonia separation tower 7 and a second water cooler 11, etc.

[0065] Among them, the first compressor 3, the precooler 5, the ammonia cooler 6 and the flash ammonia separation tower 7 are connected in series in sequence through pipelines. The raw gas (hydrogen and nitrogen) enters from the first compressor 3 and is compressed, precooled, etc. in sequence. Preferably, a first water cooler (not shown in the figure) can be arranged on the pipeline between the first compressor 3 and the precooler 5, and the first water cooler water-cools the compressed mixed gas of nitrogen and hydrogen to reduce the temperature of the mixed gas to about 30-50°C.

[0066] The exhaust port at the top of the ammonia separator 2 is provided with a branched first pipeline L1 and a second pipeline L2, the first pipeline L1 is connected to and passes through the precooler 5 and then connected to the ammonia synthesis tower 1; the second pipeline L2 is connected to and passes through the ammonia cooler 6 and then connected to the ammonia synthesis tower 1. The discharge port at the bottom of the ammonia separator 2 is provided with a third pipeline L3, and the third pipeline L3 is connected and merged with the fourth pipeline L4 connecting the precooler 5 and the ammonia cooler 6.

[0067] A fifth pipeline L5 is provided at the synthesis gas outlet of the ammonia synthesis tower 1 , and the fifth pipeline L5 is connected to and passes through the second water cooler 11 and the ammonia cooler 6 in sequence and then connected to the inlet of the ammonia separator 2 .

[0068] The liquid outlet of the flash ammonia separation tower 7 is connected to the outside through a pipeline, such as to a liquid ammonia storage tank, etc.; the gas outlet at the top of the flash ammonia separation tower 7 is provided with a sixth pipeline L6, which is connected to the fifth pipeline L5, and the mixed ammonia raw gas discharged from the flash ammonia separation tower 7 is mixed with the synthesis gas discharged from the ammonia synthesis tower 1, and then passed through the fifth pipeline L5 through the second water cooler 11 and the ammonia cooler 6 for refrigeration and then sent to the ammonia separator 2 for gas-liquid separation.

[0069] Among them, the ammonia cooler 6 is a three-phase flow heat exchanger, which includes a shell side, a tube side and an inner tube side channel which are arranged in sequence from the outside to the inside or are arranged in sequence from the outside to the inside. The fourth pipeline L4 is connected to the shell side channel of the three-phase flow heat exchanger for the circulation of the main cold source material (i.e., the low-temperature gas-liquid mixture A); the second pipeline L2 is connected to the inner tube side channel of the three-phase flow heat exchanger for the circulation of the supplementary cold source material (i.e., the gas B after ammonia separation); the fifth pipeline L5 is connected to the tube side channel of the three-phase flow heat exchanger for the circulation of the material to be refrigerated (i.e., the ammonia-rich gas-liquid mixture C1). The ammonia cooler 6 adopts a three-phase flow heat exchanger to achieve the two effects of cold exchange and ammonia cooling in the same equipment, which simplifies the process, reduces equipment investment, and can effectively reduce energy consumption.

[0070] Furthermore, a first mixing tank (not shown in the figure) is further provided on the fourth pipeline L4, and the third pipeline L3 is connected to the first mixing tank. The first mixing tank is provided so that the pre-cooled raw gas and the low-temperature liquid nitrogen separated by the ammonia separator 2 are mixed in the first mixing tank, so that the liquid ammonia part is evaporated and gasified to absorb heat, and a mixture with a lower temperature (i.e., a low-temperature gas-liquid mixture A) is obtained, which provides a stable cold source supply for the subsequent ammonia cooler 6.

[0071] After the sixth pipeline L6 comes out of the gas outlet of the flash ammonia separation tower 7, it is connected to and passes through the second compressor 71, and then connected to the fifth pipeline L5; that is, the mixed ammonia raw gas separated by the flash ammonia separation tower 7 is compressed by the second compressor 71 and mixed with the synthesis gas discharged from the ammonia synthesis tower 1; the second compressor 71 is a two-stage compressor. And the connection between the sixth pipeline L6 and the fifth pipeline L5 is located at the front end of the second chiller 11, that is, water cooling is performed after mixing. Preferably, a second mixing tank (not shown in the figure) is provided at the connection between the fifth pipeline L5 and the sixth pipeline L6 to mix the two gases and provide a stable airflow for the subsequent process.

[0072] The working process of the synthetic ammonia system is as follows: the hydrogen and nitrogen mixed raw gas with a certain pressure is initially compressed to 3.2~3.5Mpa by the first compressor 3, and then cooled to about 30~50℃ by the first water cooler; then enters the precooler 5, and heat exchanges with the ammonia separated gas D from the ammonia separator 2 diverted by the first pipeline L1, and the hydrogen-nitrogen mixed gas is cooled to about 0~-20℃; at the same time, the ammonia separated gas D is heated to about 20~40℃, and sent to the ammonia synthesis tower 1 through the first pipeline L1 to participate in the synthesis. The precooled hydrogen-nitrogen mixed gas is mixed with the low-temperature liquid ammonia (about -15~-25℃) discharged from the bottom of the ammonia separator 2 in the first mixing tank to generate a low-temperature gas-liquid mixture A of about -20~-40℃; then the low-temperature gas-liquid mixture A is sent to the shell side of the ammonia cooler 6 through the fourth pipeline L4 to provide cold energy, and is heated to about 20~40℃, and finally sent to the flash ammonia separation tower 7 for separation to obtain liquid ammonia product and mixed ammonia raw gas.

[0073] The mixed ammonia raw gas is compressed and pressurized to about 12Mpa by the second compressor 71, mixed with the synthesis gas discharged from the ammonia synthesis tower 1 in the second mixing tank, and then cooled to about 30~50℃ by the second water cooler 11, and flows through the pipe channel of the ammonia cooler 6, cooled to about -15~-25℃, and then sent to the ammonia separator 2 for gas-liquid separation.

[0074] The other part of the ammonia separated gas (i.e., the ammonia separated gas B) discharged from the upper part of the ammonia separator 2 is diverted by the second pipeline L2 to pass through the inner pipe of the ammonia cooler 6 to provide a supplementary cold source for the ammonia cooler 6. At the same time, the ammonia separated gas B is heated and reheated, and is mixed with the heated and reheated ammonia separated gas D to enter the ammonia synthesis tower 1 to participate in the synthesis.

Claims

1. A process for synthesizing ammonia, characterized in that: The method comprises the following steps: S1, compressing the mixed gas of hydrogen and nitrogen, water-cooling it, and then pre-cooling it by heat exchange with the ammonia-separated gas D discharged from the upper part of the ammonia separator to obtain a cooled hydrogen-nitrogen mixed gas; S2, the hydrogen-nitrogen mixed gas is mixed with the liquid ammonia discharged from the lower part of the ammonia separator to generate a low-temperature gas-liquid mixture A; S3, heating and flashing the low-temperature gas-liquid mixture A to obtain a liquid ammonia product and a mixed ammonia raw gas; S4, the mixed ammonia raw gas is compressed and mixed with the synthesis gas from the ammonia synthesis tower, and water-cooled to generate an ammonia-rich gas-liquid mixture C1; S5, heat-exchanging the low-temperature gas-liquid mixture A or the low-temperature gas-liquid mixture A and the ammonia-separated gas B discharged from the upper part of the ammonia separator with the ammonia-rich gas-liquid mixture C1, so that the ammonia-rich gas-liquid mixture C1 is condensed into an ammonia-rich low-temperature gas-liquid mixture C2, and enters the ammonia separator for gas-liquid separation; at the same time, the low-temperature gas-liquid mixture A is heated in step S3, and the ammonia-separated gas B is heated; S6. The ammonia-separated gas D heated in step S1 and the ammonia-separated gas B heated in step S5 enter the ammonia synthesis tower to undergo ammonia synthesis reaction.

2. The process for synthesizing ammonia according to claim 1, characterized in that: In step S1, the pressure of the mixed gas of hydrogen and nitrogen after compression is 3.2-3.5 MPa; The temperature after water cooling is 30~50℃; The temperature of the hydrogen-nitrogen mixed gas obtained after heat exchange and precooling with the ammonia separated gas D is 0 to -20°C.

3. The process for synthesizing ammonia according to claim 1 or 2, characterized in that: The temperatures of the liquid ammonia, the ammonia separated gas D and the ammonia separated gas B discharged from the ammonia separator are all -15~-25℃; And / or, the mass ratio of the gas B after ammonia separation to the gas D after ammonia separation is 2:

1.

4. The process for synthesizing ammonia according to claim 3, characterized in that: In the step S2, during the mixing process of the hydrogen-nitrogen mixed gas and liquid ammonia, part of the liquid ammonia evaporates and gasifies, and the temperature of the obtained low-temperature gas-liquid mixture A is -20 to -40°C.

5. The process for synthesizing ammonia according to claim 1 or 4, characterized in that: In step S4, the mixed ammonia raw gas is compressed by a two-stage compressor, pressurized to 10-14 MPa, and then mixed with the synthesis gas from the ammonia synthesis tower; After mixing, the temperature of the ammonia-rich gas-liquid mixture C1 generated by water cooling is 30-50°C.

6. The process for synthesizing ammonia according to claim 5, characterized in that: After the low-temperature gas-liquid mixture A or the low-temperature gas-liquid mixture A and the ammonia-separated gas B discharged from the upper part of the ammonia separator are heat exchanged with the ammonia-rich gas-liquid mixture C1, the low-temperature gas-liquid mixture A is heated to 20~40°C; the ammonia-rich gas-liquid mixture C1 is condensed into the ammonia-rich low-temperature gas-liquid mixture C2 at -15~-25°C.

7. An ammonia synthesis system used in the ammonia synthesis process according to any one of claims 1 to 6, characterized in that: include: Ammonia synthesis tower; Ammonia separator, A first compressor, a precooler, an ammonia cooler and a flash ammonia separation tower connected in sequence via pipelines; Wherein, the upper exhaust port of the ammonia separator is provided with a first pipeline and a second pipeline, and the first pipeline is connected to the ammonia synthesis tower through the precooler; The second pipeline is connected to the ammonia synthesis tower through the ammonia cooler; a third pipeline is provided at the lower drain port of the ammonia separator, and the third pipeline is connected to the fourth pipeline connecting the precooler and the ammonia cooler; A fifth pipeline is provided at the synthesis gas outlet of the ammonia synthesis tower, and the fifth pipeline is connected to the inlet of the ammonia separator after passing through the second water cooler and the ammonia cooler in sequence; The gas outlet of the flash ammonia separation tower is provided with a sixth pipeline connected to the fifth pipeline, and the mixed ammonia raw gas separated by flash evaporation is mixed with the synthesis gas of the ammonia synthesis tower and sent into the ammonia separator.

8. The ammonia synthesis system according to claim 7, characterized in that: The ammonia cooler is a three-phase flow heat exchanger, which includes a shell side, a tube side and an inner tube side channel which are arranged in sequence from the outside to the inside.

9. The ammonia synthesis system according to claim 8, characterized in that: The fourth pipeline is communicated with the shell-side channel; the second pipeline is communicated with the inner tube-side channel; and the fifth pipeline is communicated with the tube-side channel.

10. The ammonia synthesis system according to claim 7, characterized in that: The fourth pipeline is provided with a first mixing tank, and the third pipeline is connected to the first mixing tank; The sixth pipeline is connected to the front end of the second water cooler on the fifth pipeline after passing through the second compressor.

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