CN107055570B - Low-pressure ammonia synthesis equipment and low-pressure ammonia synthesis method - Google Patents
Low-pressure ammonia synthesis equipment and low-pressure ammonia synthesis method Download PDFInfo
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- CN107055570B CN107055570B CN201710169736.5A CN201710169736A CN107055570B CN 107055570 B CN107055570 B CN 107055570B CN 201710169736 A CN201710169736 A CN 201710169736A CN 107055570 B CN107055570 B CN 107055570B
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01C—AMMONIA; CYANOGEN; COMPOUNDS THEREOF
- C01C1/00—Ammonia; Compounds thereof
- C01C1/02—Preparation, purification or separation of ammonia
- C01C1/04—Preparation of ammonia by synthesis in the gas phase
- C01C1/0405—Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst
- C01C1/0417—Preparation of ammonia by synthesis in the gas phase from N2 and H2 in presence of a catalyst characterised by the synthesis reactor, e.g. arrangement of catalyst beds and heat exchangers in the reactor
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/10—Process efficiency
- Y02P20/129—Energy recovery, e.g. by cogeneration, H2recovery or pressure recovery turbines
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Abstract
The invention relates to the technical field, in particular to low-pressure ammonia synthesis equipment and a low-pressure ammonia synthesis method. The apparatus includes: a synthesis ammonia reactor; a gas compression device for compressing the reaction gas and/or the recycle gas; a heat exchanger for heat exchange of the gas, which is connected to the synthesis ammonia reactor and the gas compression device, respectively; and an ammonia cooling separator connected to the heat exchanger. The ammonia synthesis reactor in the low-pressure synthesis ammonia equipment is divided into a plurality of reaction areas, and the reaction gas is subjected to heat exchange cooling treatment before entering the inlet of the next reaction area from the outlet of the previous reaction area, so that the efficiency of synthesizing ammonia is improved; the equipment is easy to manufacture, simple in construction, easy to operate, compact in device arrangement and capable of reducing the occupied area; the device provided by the invention has reasonable design, can reduce the number of pipelines and reduce the cost.
Description
Technical Field
The invention relates to the technical field, in particular to low-pressure ammonia synthesis equipment and a low-pressure ammonia synthesis method.
Background
The ammonia synthesis is a chemical production device with high energy consumption, according to incomplete statistics, the device does not comprise a construction device, 650 traditional ammonia synthesis plants are arranged nationwide, the operation pressure of the traditional ammonia synthesis device is 12.0MPa g-32.0 MPa g, the activity temperature of the traditional iron-based catalyst is generally above 400 ℃, the activity temperature is limited by factors such as equipment materials, structural design and the like, the outlet temperature of an ammonia synthesis reactor is generally controlled within 450 ℃, and the upstream purified H is generally controlled 2 /N 2 =3, ammonia is generated on an iron catalyst, the main chemical reactions of which are as follows:
H 2 +N 2 ===NH 3 -46.11 kJ/mol。
the ammonia synthesis reaction is exothermic, the temperature of the reaction zone is reduced to facilitate the ammonia synthesis reaction to the right, a catalyst bed layer is generally adopted to be divided into a plurality of reaction zones, and the scheme of arranging heat exchangers in the zones is adopted to remove the reaction heat. However, the activation temperature of the catalyst is generally 350 ℃ or higher, the catalyst activity is fully excited to 400 ℃ or higher, and the reaction speed is slow as the ammonia concentration increases as the reaction proceeds. The first reaction zone has a larger temperature rise space because of lower inlet ammonia concentration, so the inlet temperature of the first reaction zone is set to be about 350 ℃, and the inlet gas temperature of other reaction zones is preferably controlled to be 390-400 ℃.
In view of the above, it is an urgent need in the art to provide a new low-pressure ammonia synthesis apparatus and a low-pressure ammonia synthesis method.
Disclosure of Invention
The present invention aims to address the above-mentioned drawbacks of the prior art by providing a low pressure ammonia plant and a low pressure ammonia synthesis process.
The aim of the invention can be achieved by the following technical measures:
a low pressure synthesis ammonia plant, which differs from the prior art in that it comprises:
a synthetic ammonia reactor having an inlet and an outlet, comprising a plurality of reaction zones arranged at intervals in sequence in a longitudinal direction between the inlet and the outlet, each reaction zone having a reaction zone inlet and a reaction zone outlet, respectively, and performing heat exchange cooling treatment on reaction gas before entering the next reaction zone inlet from the outlet of the previous reaction zone, wherein the first reaction zone at the top is filled with an iron-based catalyst, and the other reaction zones are filled with ruthenium-based catalysts;
a gas compression device for compressing the reaction gas and/or the recycle gas;
a heat exchanger for heat-exchanging gas, which is connected to the synthesis ammonia reactor and the gas compression device, respectively; and
and an ammonia cooling and separating device connected with the heat exchanger.
Preferably, a waste heat recovery device is further arranged between the outlet of the synthetic ammonia reactor and the heat exchanger.
Preferably, the ammonia synthesis reactor sequentially comprises a first reaction zone, a second reaction zone, a third reaction zone and a fourth reaction zone which are arranged at intervals between an inlet and an outlet, the ammonia synthesis reactor further comprises a central pipe which penetrates through the outlet from the top of the first reaction zone to the outlet of the third reaction zone, and a central gas collecting pipe from the fourth reaction zone to the outlet of the reactor.
Preferably, the heat exchanger is connected to the ammonia synthesis reactor by a conduit means comprising a first conduit disposed between the heat exchanger and the bottom of the ammonia synthesis reactor, a second conduit disposed between the heat exchanger and the inlet of the second reaction zone, a third conduit disposed between the heat exchanger and the outlet of the second reaction zone, and a fourth conduit disposed between the heat exchanger and the outlet of the third reaction zone.
Preferably, the ammonia cooling separation device comprises:
a water cooler connected with the heat exchanger;
a cold exchanger connected to both the water cooler and the gas compression device;
a first ammonia condenser connected to the cold exchanger;
a second ammonia condenser connected to the first ammonia condenser;
a first ammonia separator connected to both the second ammonia condenser and the cold exchanger;
a second ammonia separator connected to both the first ammonia separator and the gas compression device; and
and a product ammonia heat exchanger connected to both the first ammonia condenser and the second ammonia separator.
Preferably, a fifth pipeline is arranged between the heat exchanger and the outlet of the waste heat recovery device.
The invention also provides a method for synthesizing ammonia at low pressure, which comprises the following steps:
compressing synthesis gas composed of nitrogen and hydrogen;
a step of heating the compressed synthesis gas;
synthesizing ammonia from the heated synthesis gas under the catalysis of an iron-based catalyst and a ruthenium-based catalyst in sequence;
recovering waste heat of ammonia gas;
and cooling and separating the ammonia gas.
Preferably, the ammonia synthesis step comprises four ammonia synthesis stages which are sequentially carried out, and heat exchange is carried out on the reacted gas between two adjacent stages to reduce the gas temperature.
Preferably, the synthesis gas is compressed to 9.0 to 10.0MPa (G).
Preferably, the reaction temperature of each stage is 310 to 430 ℃.
The ammonia synthesis reactor in the low-pressure synthesis ammonia equipment is divided into a plurality of reaction areas, and the reaction gas is subjected to heat exchange cooling treatment before entering the inlet of the next reaction area from the outlet of the previous reaction area, so that the efficiency of synthesizing ammonia is improved; the equipment is easy to manufacture, simple in construction, easy to operate, compact in device arrangement and capable of reducing the occupied area; the device provided by the invention has reasonable design, can reduce the number of pipelines and reduce the cost.
Drawings
FIG. 1 is a schematic view showing the construction of a low pressure ammonia synthesizing apparatus according to a preferred embodiment of the present invention.
FIG. 2 is a schematic diagram showing the structure of a synthesis ammonia reactor in a low pressure synthesis ammonia plant according to a preferred embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.
Many aspects of the invention will be better understood hereinafter with reference to the drawings. The components in the drawings are not necessarily to scale. Instead, emphasis is placed upon clearly illustrating the components of the present invention. Furthermore, like reference numerals designate corresponding parts throughout the several views of the drawings.
The words "exemplary" or "illustrative" as used herein mean serving as an example, instance, or illustration. Any embodiment described herein as "exemplary" or "illustrative" is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described below are exemplary embodiments provided to enable one skilled in the art to make and use examples of the present disclosure and are not intended to limit the scope of the present disclosure, which is defined by the claims. In other instances, well-known features and methods have not been described in detail so as not to obscure the invention. For purposes of this description, the terms "upper," "lower," "left," "right," "front," "rear," "vertical," "horizontal," and derivatives thereof shall relate to the invention as oriented in FIG. 1. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary or the following detailed description. It is also to be understood that the specific devices and processes illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the inventive concepts defined in the appended claims. Thus, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting, unless the claims expressly state otherwise.
Fig. 1 shows a low pressure ammonia plant comprising: a synthesis ammonia reactor 10, a gas compression device 20, a heat exchanger 30, a waste heat recovery device 40 and an ammonia cooling separation device 50.
Wherein the ammonia synthesis reactor 10 has an inlet and an outlet. The gas compression device 20 is used to compress the reactant gas and/or the recycle gas. The heat exchangers 30 are connected to the synthesis ammonia reactor 10 and the gas compression device 20, respectively, for heat exchange of the gas. An ammonia cooling separation device 50 is connected to the heat exchanger 30. The waste heat recovery device 40 is provided between the outlet of the synthesis ammonia reactor 10 and the heat exchanger 30. The low pressure ammonia plant also includes a start-up furnace 60 in communication with the inlet of the ammonia synthesis reactor 10.
The ammonia synthesis reactor 10 includes a plurality of reaction zones disposed at intervals in the longitudinal direction in sequence between an inlet and an outlet, each reaction zone having a reaction zone inlet and a reaction zone outlet, respectively, and the reaction gas is subjected to heat exchange cooling treatment before entering the next reaction zone inlet from the outlet of the previous reaction zone. Specifically, in a preferred embodiment, the ammonia synthesis reactor 10 comprises a first reaction zone 101, a second reaction zone 102, a third reaction zone 103 and a fourth reaction zone 104 arranged at intervals in this order between an inlet and an outlet, and the ammonia synthesis reactor 10 further comprises a central tube 108 arranged to extend from the top of the first reaction zone 101 to the outlet of the third reaction zone 103. The first reaction zone 101 has an inlet 101a and an outlet 101b, the second reaction zone 102 has an inlet 102a and an outlet 102b, the third reaction zone 103 has an inlet 103a and an outlet 103b, and the fourth reaction zone 104 has an inlet 104a and an outlet 104b, wherein the first reaction zone 101 is filled with an iron-based catalyst, and the second reaction zone 102, the third reaction zone 103, and the fourth reaction zone 104 are each filled with a ruthenium-based catalyst.
The heat exchanger 30 is connected to the ammonia synthesis reactor 10 by means of piping means comprising a first pipe 701 provided at the bottom of the heat exchanger 30 and the ammonia synthesis reactor 10 in communication with the inlet 101a of the first reaction zone 101, a second pipe 702 provided between the heat exchanger 20 and the inlet 101a of the first reaction zone 101, a third pipe 703 provided between the heat exchanger 30 and the outlet 102b of the second reaction zone 102, and a fourth pipe 704 provided between the heat exchanger 30 and the outlet 103b of the third reaction zone 103. Specifically, the whole ammonia synthesis reactor 10 is structurally divided into an inner part and an outer cylinder, wherein a catalyst used for the reaction and a heat exchanger built in the reactor are both arranged on the inner part and separated from the outer cylinder, a first pipeline 701 is a main air inlet pipeline, after air is introduced from the first pipeline 701, air enters the upper part of the reactor 10 along the inner wall of the outer cylinder, heat exchange is performed from top to bottom along a central pipe 108 at the upper part of the reactor 10, most of the air rises to the heat exchanger pipe side at the upper part of the reactor 10 after heat exchange is performed from the heat exchanger pipe side at the bottom of the reactor 10, then enters the first reaction zone 101, and then sequentially enters the second reaction zone 102, the third reaction zone 103 and the fourth reaction zone 104 in an axial direction, wherein the air can radially enter shell passes of two heat exchangers at the upper part of the reactor 10 in the axial downward movement process, and the two shell passes of the heat exchangers of the catalyst bed adopt a multi-hollow fish scale plate structure, so that the air can radially enter. Thus, no pipe interface is directly provided between the third reaction zone 103 and the fourth reaction zone 104, but the gas can reach this zone, directly entering the fourth reaction zone 104 from the axial catalyst. A fourth conduit 704 communicates to the bottom of the second reaction zone 102 and may reach the region between the second reaction zone 102 and the third reaction zone 103. A third conduit 703 communicates to the region between the first reaction zone 101 and the second reaction zone 102 and a second conduit 702 communicates into the first reaction zone 101.
The waste heat recovery device 40 comprises a medium pressure waste heat boiler 401 and a boiler feedwater preheater 402 connected to each other. A fifth pipe 705 is provided between the heat exchanger 30 and the outlet of the waste heat recovery device 40 (medium pressure waste heat boiler 401). A sixth pipe 706 is provided between the first reaction zone 101 and the start-up furnace 60 for the initial stage of the reaction.
The ammonia cooling separation device 50 includes: a water cooler 501 connected to the heat exchanger 30; a cold exchanger 502 connected to both the water cooler 501 and the gas compression device 20; a first ammonia condenser 503 coupled to the cold exchanger 502; a second ammonia condenser 504 connected to the first ammonia condenser 503; a first ammonia separator 505 connected to both the second ammonia condenser 504 and the cold exchanger 502; a second ammonia separator 506 connected to both the first ammonia separator 505 and the gas compression device 20; and a product ammonia heat exchanger 507 connected to both the first ammonia condenser 503 and the second ammonia separator 506.
The invention aims to provide a low-pressure ammonia synthesis process method of a ruthenium-based catalyst so as to meet the energy-saving and emission-reduction requirements of a domestic traditional medium-large ammonia synthesis device. The whole unit device has no exhaust emission. The process method has the characteristics of small occupied area of the production device, simple process flow, convenient operation, investment saving and the like.
Process for synthesizing ammonia at low pressure for ruthenium-based catalysts for achieving the above objects, raw material H 2 、N 2 H after purification treatment 2 /N 2 =3.0 (molecular ratio).
To achieve the above object, ruthenium-based ammonia synthesis catalysts (which are not within the scope of the present invention) are selected such that the total S is not more than 0.1ppm and the total O is not more than 20ppm (in atomic terms), and other catalyst poisons are undetectable. To meet the requirements of the novel ammonia synthesis catalyst.
To achieve the above object, the operating temperature of the ammonia synthesis reactor is controlled to be 140-430 ℃. From the viewpoints of chemical equilibrium and reaction rate, the reaction rate increases with increasing temperature, and the catalytic activity also increases. However, increasing the temperature has a serious effect on the service life of the reactor and the catalyst, and the material requirements of the required pipelines and equipment are increased, so that the investment is increased. The actual temperature of the outlet gas of each reaction zone is lower than the equilibrium temperature corresponding to the composition of the outlet gas, the difference between the two temperatures is called as an equilibrium temperature distance, and the increase of the temperature is unfavorable for the forward reaction from the aspect of chemical equilibrium; the invention is divided into 3-4 reaction areas according to the axial direction in the reactor, and in addition, the characteristics of strong toxicity resistance, high temperature resistance and wide active temperature range of the traditional iron-based catalyst are utilized, the traditional iron-based catalyst is filled in the first reaction area, and the novel ruthenium-based catalyst is filled in the other reaction areas; the equilibrium temperature distance is controlled to be 15-30 ℃; the controlled synthesis reaction operating pressure is 9.0-10.0 MPa (G). From the aspect of chemical equilibrium, increasing the pressure is beneficial to the counter-reaction, the higher the pressure is, the higher the NH3 content in the outlet gas equilibrium composition is, and the higher the pressure is, the pulverization and hardening of the catalyst bed can be caused, and the pressure drop of the reactor is increased. In order to ensure the activity and the service life of the catalyst, meet the requirement of large-scale production, reduce investment and control the operating pressure of the reactor to be within 10.0MPa (G).
The invention also correspondingly provides a method for synthesizing ammonia at low pressure by using the low pressure ammonia synthesizing equipment, which comprises the following steps:
compressing synthesis gas composed of nitrogen and hydrogen;
a step of heating the compressed synthesis gas;
synthesizing ammonia from the heated synthesis gas under the catalysis of a ruthenium-based catalyst;
recovering waste heat of ammonia gas;
and cooling and separating the ammonia gas.
The ammonia synthesis step comprises four ammonia synthesis stages which are sequentially carried out, and heat exchange is carried out on the reacted gas between two adjacent stages to reduce the gas temperature. The synthesis gas is compressed to 9.0 to 10.0MPa (G). The reaction temperature of each stage is 310-430 ℃.
The low-pressure ammonia synthesis process of the ruthenium-based catalyst adopts a ruthenium-based catalyst which is different from an iron-based catalyst and has the characteristics of high activity under low temperature and low pressure conditions, the pressure of a synthesis loop is reduced to below 10.0MPa (G), the inlet air temperature of each reaction zone is controlled between 310 and 370 ℃, and the outlet temperature of the reactor is controlled between 400 and 430 ℃, so that the equipment investment and the energy consumption of an ammonia synthesis device are greatly reduced.
The process of the invention can obtain high synthetic ammonia net value more than or equal to 17% after a series of processes, and the required ammoniated product can be obtained after cooling and liquid ammonia separation.
Specifically, (1) synthetic gas compression
H from upstream device 2 、N 2 The gas is compressed to about 9.2MPa (G) by a low-pressure cylinder of a synthetic gas compressor (a gas compression device 20), mixed with circulating gas from a synthetic loop, then enters a high-pressure cylinder of the compressor, is pressurized to 10.0MPa (G) by the high-pressure cylinder, enters a heat exchanger 30 for heat exchange to 150 ℃ and then enters a reactor.
(2) Ammonia synthesis reaction zone
The synthesis gas subjected to heat exchange by the heat exchanger 30 is divided into 5 paths and sequentially conveyed through a first pipeline 701, a second pipeline 702, a third pipeline 703, a fourth pipeline 704 and a fifth pipeline 705, wherein the second path and the third path of two paths of cold gases (cold shock gases) are respectively used for adjusting the temperatures of an inlet 101a of the first reaction zone 101 and an inlet 102a of the second reaction zone 102 by directly entering the reaction zone as the cold shock gas through the second pipeline 702 and the third pipeline 703; the first and fourth gases respectively enter the middle-upper heat exchanger tube pass in the reactor 10, heat exchange is carried out on the gas reacted in the second reaction zone 102 and the gas reacted in the third reaction zone 103, the temperature is increased to 330-350 ℃, the gas rises to the top of the first reaction zone 101 along the central tube 108, and the first and fourth gases reaching the top are regulated to proper temperature by the second cooling shock gas and then enter the first reaction zone 101 for reaction. The process gas exiting the outlet 101b of the first reaction zone 101 enters the second reaction zone 102 to react along the radial direction after being regulated to a proper temperature by the third path of cold shock gas. The process gas exiting the outlet 102b of the second reaction zone 102 enters the upper interlayer heat exchanger shell pass, is subjected to temperature adjustment by cooling gas, and then enters the third reaction zone 103 from outside to inside along the radial direction. The process gas exiting the outlet 103b of the third reaction zone 103 enters the shell side of the intermediate heat exchanger, and after heat exchange by cooling gas, the process gas enters the fourth reaction zone 104 from outside to inside along the radial direction for reaction, and the process gas exiting the tower directly enters the direct-connected synthesis waste boiler 401 at the temperature of 400-410 ℃. The fifth path of synthesis gas is directly mixed with the synthesis gas at the outlet of the waste heat boiler 401 in the catalyst temperature-rising reduction stage for reducing the temperature of the gas at the outlet of the waste heat boiler by less than 300 ℃ in the reduction stage.
(3) Waste heat recovery of ammonia synthesis loop
The reacted gas directly enters the direct-connected synthetic waste boiler 401 through a connecting forging piece with internal heat preservation at the lower part of the reactor 10, and saturated steam with the pressure of 2.5MPa is produced as a byproduct. The temperature of the process gas is reduced to 220-240 ℃ and enters a boiler feed water preheater 402 to heat boiler water, and the gas from the boiler feed water preheater 402 enters a tube side of a heat exchanger 30 at 150-165 ℃ to heat the gas entering the reactor 10 in the shell side. In view of the different initial and final activities of the catalyst in the reactor 10 (generally, the initial stage inlet tower temperature is lower and the final stage inlet tower temperature is higher), the inlet and outlet of the boiler feed water preheater 402 is provided with a bypass regulating valve in order to conveniently regulate the catalyst inlet into the reactor and the initial and final stage gas temperature.
(4) Cooling separation of product liquid ammonia
The temperature of the process gas exiting the heat exchanger is reduced to 70-75 ℃ and then enters a water cooler 501 for further cooling to 30-35 ℃. The process gas from the water cooler 501 enters the tube side of the cold exchanger 502 to exchange heat with shell side cold gas, the temperature is reduced to 21-24 ℃, then the process gas sequentially enters the first ammonia condenser 503 and the second ammonia condenser 504, the temperature is reduced to-12 ℃, then the process gas enters the first ammonia separator 505 to separate condensed liquid ammonia, and the gas after the liquid ammonia separation of the first ammonia separator 505 enters the cold exchanger 502 to recover cold energy. The process gas exiting the cold exchanger 502 enters a high-pressure cylinder of the compressor and the synthesis gas after being pressurized by the low-pressure cylinder to be mixed and compressed, and then the next cycle is performed. The liquid ammonia separated by the first ammonia separator 505 is decompressed to 3.1MPa (G), and enters the second ammonia separator 506 to separate non-condensable gas, the product liquid ammonia of the second ammonia separator 506 is sent to an ammonia warehouse after heat exchange with frozen liquid ammonia in the product ammonia heat exchanger 507, and the gas separated by the second ammonia separator 506 is mixed with fresh gas by a low-pressure cylinder inlet of a compressor.
Critical device operating parameters (example typical data):
(1) ammonia synthesis reactor
The reactor is in the form of an axial direction;
reactor inlet gas volume: 70547-10780 m3/h;
inlet hydrogen/nitrogen (mole): 2.85 to 3.05;
reactor inlet temperature: 140 ℃;
reactor outlet temperature: 420 ℃;
reactor interval heat exchanger design temperature: 550 ℃;
reactor outer barrel design temperature: 285 deg.c;
reactor outer barrel design pressure: 10.5MPa (G);
catalyst loading: 50m3 (30 m3 iron-based+20 m3 ruthenium-based);
waste heat boiler byproduct steam pressure: 2.5-4.0 MPa (G).
(2) Catalyst bed zone design
First reaction zone inlet temperature: 310 ℃;
first reaction zone outlet temperature: 459 ℃;
second reaction zone inlet temperature: 318 ℃;
second reaction zone outlet temperature: 428 deg.c;
third reaction zone inlet temperature: 342 ℃;
third reaction zone outlet temperature: 416 ℃;
fourth reaction zone inlet temperature: 375 deg.c;
fourth reaction zone outlet temperature: 406 ℃.
The device and the method of the invention have the following advantages:
1. the production device constructed by the invention has the advantages of easy manufacturing of process equipment, simple construction, easy operation, compact device arrangement, reduced occupied area and accordance with environmental protection standards;
2. the production device constructed by the invention saves about 15% of total investment compared with the equipment, pipelines and materials of other production devices with the same scale and other process technologies, and has obvious economic benefit;
3. the power consumption of the synthesis gas compressor is reduced by about 15% by using the production device constructed by the invention, and obvious market competition benefits are achieved;
4. the inlet temperature of the water cooler is reduced to be within 75 ℃, so that the consumption of circulating water is reduced.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.
Claims (10)
1. A low pressure synthesis ammonia plant, characterized in that it comprises:
a synthetic ammonia reactor having an inlet and an outlet, comprising a plurality of reaction zones arranged at intervals in sequence in a longitudinal direction between the inlet and the outlet, each reaction zone having a reaction zone inlet and a reaction zone outlet, respectively, and performing heat exchange cooling treatment on reaction gas before entering the next reaction zone inlet from the outlet of the previous reaction zone, wherein the first reaction zone at the top is filled with an iron-based catalyst, and the other reaction zones are filled with ruthenium-based catalysts;
a gas compression device for compressing the reaction gas and/or the recycle gas;
a heat exchanger for heat-exchanging gas, which is connected to the synthesis ammonia reactor and the gas compression device, respectively; and
and an ammonia cooling and separating device connected with the heat exchanger.
2. The low pressure ammonia plant of claim 1, wherein a waste heat recovery device is further provided between the outlet of the ammonia synthesis reactor and the heat exchanger.
3. The low pressure ammonia plant of claim 1, wherein the ammonia synthesis reactor comprises a first reaction zone, a second reaction zone, a third reaction zone, and a fourth reaction zone disposed in sequence and spaced apart between the inlet and the outlet, the ammonia synthesis reactor further comprising a central tube disposed therethrough from the top of the first reaction zone to the outlet of the fourth reaction zone.
4. A low pressure ammonia plant according to claim 3, wherein the heat exchanger is connected to the ammonia synthesis reactor by a conduit means comprising a first conduit arranged between the heat exchanger and the bottom of the ammonia synthesis reactor, a second conduit arranged between the heat exchanger and the inlet of the second reaction zone, a third conduit arranged between the heat exchanger and the outlet of the second reaction zone, and a fourth conduit arranged between the heat exchanger and the outlet of the third reaction zone.
5. The low pressure ammonia plant of claim 1, wherein the ammonia cooling separation device comprises:
a water cooler connected with the heat exchanger;
a cold exchanger connected to both the water cooler and the gas compression device;
a first ammonia condenser connected to the cold exchanger;
a second ammonia condenser connected to the first ammonia condenser;
a first ammonia separator connected to both the second ammonia condenser and the cold exchanger;
a second ammonia separator connected to both the first ammonia separator and the gas compression device; and
and a product ammonia heat exchanger connected to both the first ammonia condenser and the second ammonia separator.
6. The low pressure ammonia plant according to claim 2, characterized in that a fifth conduit is provided between the heat exchanger and the outlet of the waste heat recovery device.
7. A method for synthesizing ammonia at low pressure, characterized in that it employs the low pressure ammonia synthesizing apparatus according to claim 1, comprising the steps of:
compressing synthesis gas composed of nitrogen and hydrogen;
a step of heating the compressed synthesis gas;
synthesizing ammonia from the heated synthesis gas under the catalysis of an iron-based catalyst and a ruthenium-based catalyst in sequence;
recovering waste heat of ammonia gas;
and cooling and separating the ammonia gas.
8. The method of synthesizing ammonia at low pressure according to claim 7, wherein the step of synthesizing ammonia comprises four stages of synthesizing ammonia performed sequentially, and heat exchange is performed between two adjacent stages of reacted gas to reduce the temperature of the gas.
9. The method of low pressure synthesis ammonia according to claim 7, wherein the synthesis gas is compressed to 9.0 to 10.0MPa (G).
10. The method for low-pressure synthesis of ammonia according to claim 8, wherein the reaction temperature at each stage is 310 to 430 ℃.
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