Nitric acid production process and production system

Abstract

The invention relates to the technical field of chemical engineering, and discloses a nitric acid production process and a nitric acid production system. According to the nitric acid production process, a nitric oxide supercharger is additionally arranged on the downstream of a nitric oxide compressor in a traditional four-in-one unit, the pressure of an outlet of the nitric oxide compressor can be reduced, and insufficient pressure is supplemented by the nitric oxide supercharger; in the reaction process of nitric oxide and water, the rotating speed N of a nitric oxide supercharger and / or the water supplementing amount Q of the top of the absorption tower are / is adjusted by monitoring the mass concentration C1 of nitric acid at the bottom of the absorption tower and the content C2 of NOX in tail gas at the top of the absorption tower in real time, so that the mass concentration of nitric acid is controlled to be 66% or above.

Description

A process and system for producing nitric acid Technical Field

[0001] This application relates to the field of chemical technology, specifically to a nitric acid production process and system. Background Technology

[0002] There are several production processes for dilute nitric acid, including the atmospheric pressure method, the total pressure method, the combined method, and the dual-pressure method. Among these, the dual-pressure method has become the mainstream dilute nitric acid production process in China due to its low unit consumption, low material consumption, low tail gas emissions, high product concentration, large single-unit scale, and high degree of automation. This process involves ammonia oxidation under low pressure (0.35–0.55 MPa) and nitrogen oxide (NOx) absorption under high pressure (1.0–1.5 MPa). Although this process can meet normal production needs, it still has problems such as low waste heat utilization efficiency and low product acid concentration, which require further improvement. Summary of the Invention

[0003] In view of this, this application provides a nitric acid production process and system, which aims to solve at least one of the above-mentioned problems to a certain extent.

[0004] In a first aspect, this application provides a process for producing nitric acid, comprising the following steps:

[0005] S1. Gaseous ammonia and compressed air react in an ammonia oxidation furnace to form high-temperature process gas. After heat exchange, the high-temperature process gas enters a nitrogen oxide separator for gas-liquid separation to obtain low-pressure process gas and liquid phase.

[0006] S2. The low-pressure process gas is sequentially pressurized by a nitrogen oxide compressor and a nitrogen oxide booster to become high-pressure process gas. The high-pressure process gas is then cooled to 20℃-40℃ and enters the bottom of the absorption tower, where it comes into countercurrent contact with PW water from the top of the absorption tower and reacts to produce dilute nitric acid. During this reaction, the mass concentration of nitric acid C1 at the bottom of the absorption tower and the NO content in the tail gas at the top of the absorption tower are monitored in real time. X The concentration of nitric acid is controlled to be above 66% by adjusting the speed N of the nitrogen oxide booster and / or the amount of water replenished at the top of the absorption tower.

[0007] In one alternative implementation, C2 is compared with C2*, and when C2 equals C2*, there is no need to adjust N and Q.

[0008] In one optional implementation, C2 and C2* are compared. When C2 is less than C2*, Q is adjusted, and Q is further adjusted based on the differences between ΔC1 and ΔC1* and between ΔC2 and ΔC2*, or Q is adjusted first and then N is adjusted, until ΔC1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*; or, when C2 is greater than C2*, N is adjusted first and then N or Q is adjusted, until C2 meets the emission requirements; wherein, C1* is the set value of C1, C2* is the set value of C2, ΔC1* is the set value of ΔC1, ΔC2* is the set value of ΔC2, ΔC1 is the difference between C1 before and after adjustment, and ΔC2 is the difference between C2 before and after adjustment.

[0009] In one optional implementation, when C2 is less than C2*, the controller issues a command to decrease Q at a rate of step size ΔQ1, while simultaneously collecting C1 and C2 after the Xth adjustment, and calculating Δ. X C1 and Δ X C2; if Δ X C2 is less than ΔC2* and Δ X If C1 is greater than ΔC1*, then continue to decrease Q at a rate of ΔQ1 until the adjusted ΔC2 is greater than or equal to ΔC2* or ΔC1 is less than or equal to ΔC1*; if Δ X C2 is greater than or equal to ΔC2* or Δ X If C1 is less than or equal to ΔC1*, the controller issues a command to increase N at a rate of step size ΔN1, while simultaneously collecting C1 and C2 after the Yth adjustment and calculating Δ. Y C1; if Δ Y If C1 is greater than ΔC1*, then N continues to increase at a rate of ΔN1; if Δ Y If C1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*, then the increment of N stops; where Δ X C1 is the difference between C1 before and after the Xth adjustment, where Δ X C2 is the difference between C2 before and after the Xth adjustment, where X≥1, Δ Y C1 is the difference between C1 before and after the Y-th adjustment, where Y = X + 1.

[0010] In one optional implementation, when C2 is greater than C2*, the controller issues a command to increase N by a step size ΔN2, while simultaneously collecting C1 and C2 after the Mth adjustment and calculating ΔN*. M C2, if Δ M If C2 is greater than or equal to ΔC2*, then N continues to increase at a rate of ΔN2 until C2 meets the emission requirements. M If C2 is less than ΔC2*, the controller issues a command to increase Q at a rate of step size ΔQ2 until C2 meets the emission requirements; where Δ M C2 is the difference between C2 before and after the Mth adjustment, where M≥1.

[0011] In one alternative implementation, C1* is 69%-71%.

[0012] In one alternative implementation, C2* is 150ppm-200ppm.

[0013] In one alternative implementation, ΔC1* is 0.01%-0.03%.

[0014] In one alternative implementation, ΔC2* is 5ppm-20ppm.

[0015] In one alternative implementation, ΔQ1 is 20 kg / h - 200 kg / h.

[0016] In one alternative implementation, ΔN1 is 10 rpm to 100 rpm.

[0017] In one alternative implementation, ΔQ2 is 20 kg / h to 200 kg / h.

[0018] In one alternative implementation, ΔN2 is 10 rpm to 100 rpm.

[0019] In one alternative implementation, the outlet pressure of the nitrogen oxide compressor is 0.6 MPaG-0.8 MPaG.

[0020] In one alternative implementation, the outlet pressure of the nitric oxide booster is 0.9 MPaG-1.5 MPaG.

[0021] In one optional embodiment, the high-temperature process gas formed in reaction S1 heats the saturated steam from the boiler water buffer tank into superheated steam in a steam superheater. Then, the high-temperature process gas heats the boiler water into saturated steam in a waste heat boiler. After that, the high-temperature process gas sequentially enters the first heat exchanger, the second heat exchanger, the third heat exchanger, the fourth heat exchanger, and the fifth heat exchanger to recover heat in stages. The cooled process gas enters the nitrogen oxide separator for gas-liquid separation. The process gas temperature at the outlet of the first heat exchanger is 370℃-400℃, the process gas temperature at the outlet of the second heat exchanger is 140℃-160℃, the process gas temperature at the outlet of the third heat exchanger is 85℃-95℃, the process gas temperature at the outlet of the fourth heat exchanger is 70℃-80℃, and the process gas temperature at the outlet of the fifth heat exchanger is 40℃-60℃.

[0022] In one optional embodiment, the process gas compressed by the nitric oxide compressor first enters the sixth heat exchanger to recover heat before entering the nitric oxide booster. The process gas temperature at the outlet of the sixth heat exchanger is 40°C-70°C.

[0023] In one optional embodiment, the high-pressure process gas sequentially enters the seventh, eighth, and ninth heat exchangers to recover heat before entering the bottom of the absorption tower; the process gas temperature at the outlet of the seventh heat exchanger is 70℃-80℃, the process gas temperature at the outlet of the eighth heat exchanger is 40℃-60℃, and the process gas temperature at the outlet of the ninth heat exchanger is 20℃-40℃.

[0024] In one alternative embodiment, the liquid phase separated by the nitrogen oxide separator enters the middle of the absorption tower for absorption and concentration.

[0025] In one alternative embodiment, the low-pressure process gas separated by the nitrogen oxide separator is mixed with secondary air from the bleaching tower and then compressed in the nitrogen oxide compressor.

[0026] In one alternative embodiment, PW water is cooled to 10°C-15°C by a cooler and then enters the top of the absorption tower as the absorbent.

[0027] In one alternative embodiment, the dilute nitric acid obtained at the bottom of the absorption tower enters the bleaching tower and undergoes secondary air desorption to obtain the finished dilute nitric acid.

[0028] In one optional embodiment, the absorption tower is divided into a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section from top to bottom. Each absorption section is connected to its own independent cooling water pipeline. The temperature difference between the cooling water in the first absorption section and the third absorption section is -5℃ to 5℃. The cooling water temperature in the second absorption section is 3℃ to 10℃ higher than that in the first absorption section. The cooling water temperature in the fourth absorption section is 18℃ to 28℃ higher than that in the third absorption section.

[0029] In one optional embodiment, the cooling water temperature of the first absorption section and the third absorption section is 5℃-10℃, the cooling water temperature of the second absorption section is 13℃-15℃, and the cooling water temperature of the fourth absorption section is 28℃-33℃.

[0030] In one optional embodiment, the gaseous ammonia is generated by the evaporation of liquid ammonia. The liquid ammonia is divided into two streams. The first stream of liquid ammonia enters the first ammonia evaporator and exchanges heat with cold water BR2 at 18℃-20℃. The second stream of liquid ammonia enters the second ammonia evaporator and exchanges heat with circulating water CWR at 33℃-38℃. The air is filtered, dehumidified by a refrigeration dehumidifier, and compressed by an air compressor and then divided into two streams. The secondary air heats the gaseous ammonia at the outlets of the first and second ammonia evaporators before entering the bleaching tower. The primary air mixes evenly with the heated gaseous ammonia and then enters the ammonia oxidation furnace for reaction. The cold water BR2 is converted into cold water BS2 at 13℃-15℃ after heat exchange and is used as the cooling water for the second absorption section of the absorption tower. The circulating water CWR is converted into circulating water CWS at 28℃-33℃ after heat exchange and is used as the cooling water for the fourth absorption section of the absorption tower.

[0031] In one optional embodiment, the hot water obtained by heating through the fourth heat exchanger and / or the seventh heat exchanger enters the refrigeration unit to prepare BR1 at 10°C-15°C into chilled water BS1 at 5°C-10°C, which is used as cooling water for the first and third absorption sections of the absorption tower and / or as a cold source for refrigeration dehumidifiers, coolers, and other equipment in the park.

[0032] In one optional embodiment, the high-pressure low-temperature tail gas from the absorption tower enters the ninth heat exchanger, the sixth heat exchanger and the first heat exchanger in sequence and is heated to a high-pressure high-temperature tail gas of 370°C-400°C. The high-pressure high-temperature tail gas is reduced in the nitrogen oxide reduction reactor and then enters the tail gas turbine to do work. The tail gas after doing work is directly discharged.

[0033] In one optional embodiment, a portion of the superheated steam from the steam superheater enters the first and second steam turbines to perform work. The exhaust steam after performing work is condensed and mixed with PW water, then enters the third heat exchanger to be heated to 110°C-120°C. The resulting high-temperature PW water enters the deaerator to remove dissolved oxygen. The deaerated BFW water then enters the second heat exchanger for further heating to 240°C-250°C before sequentially entering the boiler water buffer tank and the waste heat boiler. It then returns to the boiler water buffer tank for gas-liquid separation. The resulting saturated steam enters the steam superheater to be heated into superheated steam. The excess superheated steam is then sent to the park's steam network.

[0034] In one alternative implementation, the hot water from the outlet of the fifth heat exchanger and / or the eighth heat exchanger enters a heat removal device to prepare hot water, with a portion of the hot water used as tracing water and the surplus hot water used as heating water to supply the plant's office building.

[0035] In one alternative embodiment, the air compressor, exhaust gas turbine, nitrogen oxide compressor, and first steam turbine are connected by a coupling and combined into a four-in-one unit, wherein the first steam turbine and exhaust gas turbine provide the mechanical energy required for the operation of the air compressor and nitrogen oxide compressor.

[0036] In one alternative embodiment, the nitric oxide booster is coaxially connected to a second steam turbine, which provides the mechanical energy required for the operation of the nitric oxide booster.

[0037] In one optional embodiment, the temperature of the superheated steam is 440°C-480°C and the pressure is 3.5 MPaG-5 MPaG.

[0038] In one alternative embodiment, the temperature of the gaseous ammonia at the outlet of the ammonia vapor superheater is 160°C-180°C.

[0039] In one optional embodiment, the mass concentration of the finished dilute nitric acid is 69% or higher.

[0040] In one optional embodiment, the mass concentration of the finished dilute nitric acid is 69%-71%.

[0041] Secondly, this application also provides a nitric acid production system, comprising an ammonia oxidation furnace, a first heat exchange unit, a nitrogen oxide separator, a nitrogen oxide compressor, a second heat exchange unit, and an absorption tower connected in sequence; the nitric acid production system further includes:

[0042] The nitrogen oxide booster is located between the nitrogen oxide compressor and the absorption tower;

[0043] The control unit is used to measure the real-time nitric acid mass concentration C1 at the bottom of the absorber and the NO concentration in the tail gas at the top of the absorber. X To control the nitric acid concentration, adjust the nitrogen oxide booster speed N and / or the top water supply Q to a level of C2, ensuring the nitric acid concentration is above 66%, preferably above 69%.

[0044] In one optional implementation, C2 and C2* are compared. When C2 is less than C2*, Q is adjusted, and Q is further adjusted based on the differences between ΔC1 and ΔC1* and between ΔC2 and ΔC2*, or Q is adjusted first and then N is adjusted, until ΔC1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*; or, when C2 is greater than C2*, N is adjusted first and then N or Q is adjusted, until C2 meets the emission requirements; wherein, C1* is the set value of C1, C2* is the set value of C2, ΔC1* is the set value of ΔC1, ΔC2* is the set value of ΔC2, ΔC1 is the difference between C1 before and after adjustment, and ΔC2 is the difference between C2 before and after adjustment.

[0045] In one optional embodiment, the first heat exchange unit includes a first heat exchanger, a second heat exchanger, a third heat exchanger, a fourth heat exchanger, and a fifth heat exchanger connected in sequence. The process gas inlet of the first heat exchanger is connected to the ammonia oxidation furnace, and the process gas outlet of the fifth heat exchanger is connected to the nitrogen oxide separator.

[0046] In one alternative embodiment, the gas phase outlet of the nitrogen oxide separator is connected to a nitrogen oxide compressor, and the liquid phase outlet of the nitrogen oxide separator is connected to the central inlet of the absorption tower.

[0047] In one optional embodiment, the second heat exchange unit includes a sixth heat exchanger, a seventh heat exchanger, an eighth heat exchanger, and a ninth heat exchanger. The sixth heat exchanger is disposed between the nitric oxide compressor and the nitric oxide booster, and the seventh, eighth, and ninth heat exchangers are sequentially connected between the nitric oxide booster and the absorption tower.

[0048] In one optional embodiment, the absorption tower is divided into a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section from top to bottom. Each absorption section is connected to its own independent cooling water pipeline. The temperature difference between the cooling water in the first absorption section and the third absorption section is -5℃ to 5℃. The cooling water temperature in the second absorption section is 3℃ to 10℃ higher than that in the first absorption section. The cooling water temperature in the fourth absorption section is 18℃ to 28℃ higher than that in the third absorption section.

[0049] In one optional embodiment, the cooling water temperature of the first absorption section and the third absorption section is 5℃-10℃, the cooling water temperature of the second absorption section is 13℃-15℃, and the cooling water temperature of the fourth absorption section is 28℃-33℃.

[0050] In one optional embodiment, the nitric acid production system further includes at least one of ammonia gas production unit, air treatment unit, steam generation unit, tail gas treatment unit, nitric acid purification unit, refrigeration unit, and heat removal unit.

[0051] In one optional embodiment, the ammonia production unit includes at least one ammonia evaporator, an ammonia vapor superheater, and an ammonia-air mixer. The outlet of the ammonia evaporator is connected to the ammonia inlet of the ammonia vapor superheater, and the inlet of the ammonia-air mixer is connected to the ammonia outlet of the ammonia vapor superheater.

[0052] In one optional embodiment, the air handling unit includes an air filter, a refrigerated dehumidifier, and an air compressor connected in sequence. The outlet of the air compressor is connected to the heat source inlet of the ammonia vapor superheater and the inlet of the ammonia-air mixer. The heat source outlet of the ammonia vapor superheater is connected to the air inlet of the bleaching tower.

[0053] In one optional embodiment, the steam generating unit includes a steam superheater, a waste heat boiler, a boiler water buffer tank, a deaerator, and a first steam turbine. The steam outlet of the steam superheater is connected to the gas inlet of the first steam turbine. The exhaust steam outlet of the first steam turbine is connected via a condenser to the refrigerant inlet of a third condenser. The refrigerant outlet of the third condenser is connected to the inlet of the deaerator. The outlet of the deaerator is connected to the refrigerant inlet of a second condenser. The refrigerant outlet of the second condenser is connected to the first inlet of the boiler water buffer tank. The first outlet of the boiler water buffer tank is connected to the inlet of the waste heat boiler. The outlet of the waste heat boiler is connected to the second inlet of the boiler water buffer tank. The second outlet of the boiler water buffer tank is connected to the steam inlet of the steam superheater. The process gas inlet of the steam superheater is connected to the process gas outlet of the oxidizer. The process gas outlet of the steam superheater is connected to the process gas inlet of the waste heat boiler. The process gas outlet of the waste heat boiler is connected to the first heat exchanger.

[0054] In one optional embodiment, the exhaust gas treatment unit includes a nitrogen oxide reduction reactor and an exhaust gas turbine connected to each other. The inlet of the nitrogen oxide reduction reactor is sequentially connected to the refrigerant outlets of a first heat exchanger, a sixth heat exchanger, and a ninth heat exchanger. The refrigerant inlet of the ninth heat exchanger is connected to the exhaust gas outlet of the absorption tower.

[0055] In one optional embodiment, the nitric acid purification unit includes a bleaching tower and a nitric acid storage tank. The bleaching tower has a liquid inlet, an air inlet, a liquid outlet, and an exhaust outlet. The liquid inlet of the bleaching tower is connected to the liquid outlet of the absorption tower, the liquid outlet of the bleaching tower is connected to the nitric acid storage tank, and the exhaust outlet of the bleaching tower is connected to the inlet of the nitrogen oxide compressor.

[0056] In one optional embodiment, the refrigeration unit includes a refrigeration unit, the first inlet of which is connected to the refrigerant outlet of the fourth heat exchanger and / or the seventh heat exchanger, and the first outlet of which is connected to the refrigerant inlet of the fourth heat exchanger and / or the seventh heat exchanger.

[0057] In one optional embodiment, the heat removal unit includes a heat removal device, the inlet of which is connected to the refrigerant outlet of the fifth heat exchanger and / or the eighth heat exchanger, and the first outlet of which is connected to the refrigerant inlet of the fifth heat exchanger and / or the eighth heat exchanger.

[0058] In one alternative implementation, the air compressor, nitrogen oxide compressor, first steam turbine, and exhaust gas turbine are connected by a coupling and combined into a four-in-one unit.

[0059] In one optional embodiment, the nitric acid production system further includes a second steam turbine, which is coaxially connected to a nitrogen oxide booster. The steam outlet of the steam superheater is connected to the gas inlet of the second steam turbine, and the exhaust steam outlet of the second steam turbine is connected to the refrigerant inlet of a third condenser via a condenser.

[0060] The technical solution of this application has the following advantages:

[0061] The nitric acid production process provided in this application adds a nitric oxide booster downstream of the nitric oxide compressor in a traditional four-in-one unit. This reduces the outlet pressure of the nitric oxide compressor, and the insufficient pressure is supplemented by the nitric oxide booster. Furthermore, during the reaction of nitric oxide with water, the nitric acid mass concentration C1 at the bottom of the absorption tower and the NO content in the tail gas at the top of the absorption tower are monitored in real time. X The concentration of nitric acid is controlled at above 66% by adjusting the speed N of the nitrogen oxide booster and / or the amount of water replenished at the top of the absorption tower.

[0062] Additional aspects and advantages of the embodiments of this application will be described and shown in part in the following description, or illustrated by practice of the embodiments of this application. Attached Figure Description

[0063] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0064] Figure 1 is a process flow diagram of one embodiment of this application.

[0065] Figure 2 is a process flow diagram of Comparative Example 1.

[0066] The reference numerals in the attached figures are explained as follows:

[0067] 1-First ammonia evaporator; 2-Second ammonia evaporator; 3-Ammonia vapor superheater; 4-Air filter; 5-Refrigeration dehumidifier; 6-Air compressor; 7-Ammonia-air mixer; 8-Ammonia oxidation furnace; 9-Steam superheater; 10-Waste heat boiler; 11-First heat exchanger; 12-Second heat exchanger; 13-Third heat exchanger; 14-Fourth heat exchanger; 15-Fifth heat exchanger; 16-Nitrogen oxide separator; 17-Nitrogen oxide compressor; 18-Sixth heat exchanger; 9-Nitrogen oxide booster; 20-Seventh heat exchanger; 21-Eighth heat exchanger; 22-Ninth heat exchanger; 23-Absorption tower; 24-Bleaching tower; 25-Cooler; 26-Nitrogen oxide reduction reactor; 27-Tail gas turbine; 28-Deaerator; 29-Boiler water buffer tank; 30-First boiler water pump; 31-Second boiler water pump; 32-First steam turbine; 33-Second steam turbine; 34-Refrigeration unit; 35-Heat removal equipment; 36-Controller.

[0068] 1'-Ammonia evaporator; 2'-Ammonia steam superheater; 3'-Air filter; 4'-Air refrigeration dehumidifier; 5'-Air compressor; 6'-Ammonia-air mixer; 7'-Ammonia oxidation furnace; 8'-Steam superheater; 9'-Waste heat boiler; 10'-First heat exchanger; 11'-Second heat exchanger; 12'-Third heat exchanger; 13'-Nitrogen oxide separator; 14'-Nitrogen oxide compressor; 15'-Fourth heat exchanger; 16'-Fifth heat exchanger; 17'-Absorption tower; 18'-Bleaching tower; 19'-Cooler; 20'-Sixth heat exchanger; 21'-Nitrogen oxide reduction reactor; 22'-Tail gas turbine; 23'-Deaerator; 24'-First boiler water pump; 25'-Boiler water buffer tank; 26'-Second boiler water pump; 27'-Steam turbine. Detailed Implementation

[0069] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0070] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion.

[0071] In the description of the embodiments of this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. It should be noted that, unless otherwise expressly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0072] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0073] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0074] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0075] The related technology, which uses a double-pressure method to produce nitric acid, still has the following problems that need to be improved:

[0076] 1. Low product acid concentration. The absorption efficiency of the nitric acid absorption tower largely determines the concentration of the product acid. Absorption temperature, absorption pressure, and the amount of PW makeup water at the top of the tower are the main factors affecting the absorption efficiency. In the dual-pressure nitric acid production unit, the temperature control of nitric acid absorption is not strict enough. First, the process gas entering the absorption tower is usually cooled by circulating water. The temperature of the circulating water is greatly affected by the season. In summer, the temperature of the circulating water is generally higher, resulting in a higher temperature of the process gas entering the absorption tower. Second, the heat removal on the absorption tower plates is usually done by circulating water, which has a poor cooling effect and is not conducive to the absorption reaction. In addition, the dual-pressure nitric acid production unit usually uses a four-in-one unit, using a steam turbine and a tail gas turbine to drive an air compressor and a nitrogen oxide compressor. Because the equipment is coaxially connected, it is impossible to achieve real-time and precise control and adjustment of the operating pressure of the nitric acid absorption tower, resulting in poor absorption efficiency. Furthermore, the amount of PW makeup water at the top of the nitric acid absorption tower is related to the mass concentration of nitric acid and the NO content in the tail gas. XThe most direct influencing factor is that the amount of PW makeup water cannot be accurately controlled in existing processes, resulting in low nitric acid concentration or unqualified tail gas content.

[0077] 2. Low waste heat utilization efficiency. The existing dual-pressure nitric acid production unit fails to fully recover the heat of ammonia oxidation, the heat of NO oxidation, and the high-temperature heat from the nitrogen oxide compressor outlet, taking into account the unit's energy balance characteristics. It only utilizes the steam generated from the waste boiler in the ammonia oxidation furnace and the heat from the high-temperature section of the recycled nitrogen oxide process stream to heat the tail gas. The recovered energy can only meet the compression energy consumption of the four-in-one unit, and even requires the introduction of steam from the outside to achieve steam balance. The heat in the medium and low temperature sections of the process gas from the ammonia oxidation furnace and the process gas from the nitrogen oxide compressor is directly water-cooled, resulting in a large amount of energy waste. In addition, the cold water required within the unit must be prepared using electricity or steam.

[0078] To address the problems existing in the aforementioned related technologies, according to a first aspect of this application, as shown in FIG1, a nitric acid production process is provided, comprising the following steps:

[0079] S1. Gaseous ammonia and compressed air react in ammonia oxidation furnace 8 to form high-temperature process gas. After heat exchange, the high-temperature process gas enters nitrogen oxide separator 16 for gas-liquid separation to obtain low-pressure process gas and liquid phase.

[0080] S2. The low-pressure process gas is sequentially pressurized by the nitrogen oxide compressor 17 and the nitrogen oxide booster 19 to become high-pressure process gas. The high-pressure process gas is cooled to 20℃-40℃ and then enters the bottom of the absorption tower 23, where it comes into countercurrent contact with PW water from the top of the absorption tower 23 and reacts to produce dilute nitric acid. During this reaction process, the mass concentration C1 of nitric acid at the bottom of the absorption tower and the NO in the tail gas at the top of the absorption tower are monitored in real time. X The content of C2 is adjusted by adjusting the speed N of the nitrogen oxide booster and / or the amount of water replenished at the top of the absorption tower Q, so as to control the nitric acid mass concentration to be above 66%, preferably above 69%.

[0081] The nitric acid production process provided in this application adds a nitric oxide booster downstream of the nitric oxide compressor in a traditional four-in-one unit. This reduces the outlet pressure of the nitric oxide compressor, and the insufficient pressure is supplemented by the nitric oxide booster. Furthermore, during the reaction of nitric oxide with water, the nitric acid mass concentration C1 at the bottom of the absorption tower and the NO content in the tail gas at the top of the absorption tower are monitored in real time. X The concentration of nitric acid is controlled at above 66% by adjusting the speed N of the nitrogen oxide booster and / or the amount of water replenished at the top of the absorption tower.

[0082] Specifically, by comparing the values ​​of C2 and C2*, the speed N of the nitrogen oxide booster and / or the water supply Q at the top of the absorber are precisely adjusted. When C2 equals C2*, it indicates that the composition of the exhaust gas at the top of the absorber meets the standards, and no adjustment of N and Q is required. When C2 is less than C2*, Q is adjusted, and Q is further adjusted based on the values ​​between ΔC1 and ΔC1*, and between ΔC2 and ΔC2*, or Q is adjusted first and then N is adjusted, until ΔC1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*; or, when C2 is greater than C2*, N is adjusted first and then N or Q is adjusted, until C2 meets the emission requirements. Wherein, C1* is the set value of C1, C2* is the set value of C2, ΔC1* is the set value of ΔC1, ΔC2* is the set value of ΔC2, ΔC1 is the difference between C1 before and after adjustment, and ΔC2 is the difference between C2 before and after adjustment. In some implementations, as an example, C1* can be 69-71 wt%, C2* can be 150-200 ppm, ΔC1* can be 0.01-0.3 wt%, and ΔC2* can be 5-20 ppm, which can be adjusted according to actual process conditions.

[0083] Furthermore, this study found that the amount of water replenished at the top of the absorber affects the nitric acid concentration and the NO content in the tail gas. X The content of NOx has a relatively large impact. Therefore, when the NOx content in the exhaust gas is detected to be lower than the set value, the water replenishment is usually reduced first. This increases the nitric acid concentration at the bottom of the absorber, while the NOx concentration at the top of the absorber increases. X The concentration also increases accordingly. If the increase in nitric acid mass concentration is less than the set value or the NO in the tail gas... X If the increase in concentration exceeds the set value, it indicates that the increase in nitric acid concentration slows down after reducing the makeup water amount, or that NO in the tail gas... X If the concentration increases rapidly, it is necessary to stop reducing the water supply and increase the absorption pressure, i.e., increase the speed of the nitrogen oxide booster. At this time, the NO in the exhaust gas will... X The concentration will decrease, and the nitric acid mass concentration will increase until the increase in nitric acid mass concentration is less than the set value or the nitric acid mass concentration reaches its set value. At this point, the speed of the nitrogen oxide booster compressor will stop increasing, because further increasing the absorption pressure will have little effect on the nitric acid mass concentration. That is, when C2 is less than C2*, the controller issues a command to decrease Q at a rate of step size ΔQ1, while simultaneously collecting C1 and C2 after the Xth adjustment, and calculating Δ... X C1 and Δ X C2; if Δ X C2 is less than ΔC2* and Δ X If C1 is greater than ΔC1*, then continue to decrease Q at a rate of ΔQ1 until the adjusted ΔC2 is greater than or equal to ΔC2* or ΔC1 is less than or equal to ΔC1*; if Δ X C2 is greater than or equal to ΔC2* or Δ XIf C1 is less than or equal to ΔC1*, the controller issues a command to increase N at a rate of step size ΔN1, while simultaneously collecting C1 and C2 after the Yth adjustment and calculating Δ. Y C1; if Δ Y If C1 is greater than ΔC1*, then N continues to increase at a rate of ΔN1; if Δ Y If C1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*, then the increment of N stops; where Δ X C1 is the difference between C1 before and after the Xth adjustment, where Δ X C2 is the difference between C2 before and after the Xth adjustment, Δ Y C1 is the difference between C1 before and after the Y-th adjustment, where Y = X + 1. In some implementations, as an example, ΔQ1 can be 20-200 kg / h, and ΔN1 can be 10-100 rpm, which can be adjusted according to the actual process conditions.

[0084] When the NOx content in the exhaust gas is detected to be higher than the set value, it should be considered to reduce the NOx content in the exhaust gas by increasing the absorption pressure (equivalent to increasing the speed of the nitric acid booster) without reducing the nitric acid concentration. If the NOx concentration in the exhaust gas decreases rapidly, it indicates that increasing the speed of the nitric acid booster is effective in reducing the NOx content. In this case, the speed of the nitric acid booster should be increased until the NOx content in the exhaust gas meets the emission requirements. If the NOx concentration in the exhaust gas decreases slowly, the speed of the nitric acid booster should be stopped, and the water replenishment should be increased until the NOx content in the exhaust gas meets the standard. That is, when C2 is greater than C2*, the controller issues a command to increase N at a step size ΔN2, while collecting C1 and C2 after the Mth adjustment, and calculating ΔN*. M C2, if Δ M If C2 is greater than or equal to ΔC2*, then N continues to increase at a rate of ΔN2 until C2 meets the emission requirements. M If C2 is less than ΔC2*, the controller issues a command to increase Q at a rate of step size ΔQ2 until C2 meets the emission requirements; where Δ M C2 is the difference between C2 before and after the Mth adjustment, where M≥1. In some implementations, as an example, ΔQ2 can be 20-200 kg / h, and ΔN2 can be 10-100 rpm, which can be adjusted according to actual process conditions.

[0085] This application enables real-time and precise control of the absorption pressure of the nitric acid absorption tower by adjusting the speed of the nitrogen oxide booster, and can improve the nitric acid absorption effect by optimizing and adjusting the PW water supply at the top of the absorption tower in real time.

[0086] As shown in Figure 1, liquid ammonia is divided into two streams. The first stream of liquid ammonia enters the first ammonia evaporator 1 and exchanges heat with cold water BR2 at 18℃-20℃. The second stream of liquid ammonia enters the second ammonia evaporator 2 and exchanges heat with circulating water CWR at 33℃-38℃. After heat exchange, the cold water BR2 is transformed into cold water BS2 at 13℃-15℃, which is used as cooling water for the second absorption section of absorber 23. The circulating water CWR is transformed into circulating water CWS at 28℃-33℃ after heat exchange, which is used as cooling water for the fourth absorption section of absorber 23. This fully utilizes the cooling capacity of liquid ammonia to prepare cooling water for heat removal from the absorber trays, thereby allowing for precise control of the cooling water temperature and improving the absorption effect.

[0087] The air is sequentially filtered, dehumidified by a refrigerated dehumidifier 5, and compressed by an air compressor 6, then split into two streams. The secondary air, after heating the ammonia gas exiting the first and second ammonia evaporators 1 and 2 in an ammonia vapor superheater 3, enters the bleaching tower 24. The primary air mixes evenly with the heated ammonia gas before entering the ammonia oxidation furnace 8 for reaction. The ammonia gas temperature at the outlet of the ammonia vapor superheater 3 is 160℃-180℃. Using a refrigerated dehumidifier to condense and remove moisture from the air reduces the water content in the raw materials, which is beneficial for increasing the concentration of the finished nitric acid. It also lowers the inlet temperature of the air compressor, thus reducing its energy consumption. The high-temperature secondary air from the air compressor enters the ammonia vapor superheater before entering the bleaching tower to recover heat and superheat the low-temperature ammonia gas. This increases the rate of the ammonia oxidation reaction and lowers the inlet temperature of the nitrogen oxide compressor, reducing its energy consumption.

[0088] The high-temperature process gas formed in reaction S1 heats the saturated steam from boiler water buffer tank 29 into superheated steam in steam superheater 9. Then, the high-temperature process gas heats the boiler water into saturated steam in waste heat boiler 10. After that, the high-temperature process gas sequentially enters the first heat exchanger 11, the second heat exchanger 12, the third heat exchanger 13, the fourth heat exchanger 14, and the fifth heat exchanger 15 to recover heat in stages. The cooled process gas enters the nitrogen oxide separator 16 for gas-liquid separation. The process gas temperature at the outlet of the first heat exchanger 11 is 370℃-400℃, the process gas temperature at the outlet of the second heat exchanger 12 is 140℃-160℃, the process gas temperature at the outlet of the third heat exchanger 13 is 85℃-95℃, the process gas temperature at the outlet of the fourth heat exchanger 14 is 70℃-80℃, and the process gas temperature at the outlet of the fifth heat exchanger 15 is 40℃-60℃. The high-temperature process gas generated by the ammonia oxidation reaction heats the saturated steam into superheated steam. This allows for the recovery of high-temperature reaction heat while simultaneously generating superheated steam, avoiding condensation losses and water hammer during the transport of saturated steam. A portion of the superheated steam is used to drive the first and second steam turbines in the four-in-one unit, while surplus superheated steam is piped to other users in the industrial park for use by other equipment, reducing the production load of the thermal power boiler.

[0089] The liquid phase separated by the nitrogen oxide separator 16 enters the middle of the absorption tower 23 for absorption and concentration. The low-pressure process gas separated by the nitrogen oxide separator 16 is mixed with the secondary air from the bleaching tower 24 and then compressed in the nitrogen oxide compressor 17. Since the secondary air from the bleaching tower is pressurized and contains nitrogen oxides that cannot be directly discharged, and the low-pressure process gas from the nitrogen oxide separator also contains incompletely oxidized NO, mixing the secondary air from the bleaching tower with the low-pressure process gas allows the air in this secondary air to make the NO oxidation reaction more complete.

[0090] The process gas compressed by the nitric oxide compressor 17 first enters the sixth heat exchanger 18 to recover heat before entering the nitric oxide booster compressor 19. The outlet pressure of the nitric oxide compressor 17 is 0.6 MPaG-0.8 MPaG, the outlet pressure of the nitric oxide booster compressor 19 is 0.9 MPaG-1.5 MPaG, and the outlet temperature of the process gas from the sixth heat exchanger 18 is 40℃-70℃. By recovering the heat from the high-temperature, high-pressure process gas at the outlet of the nitric oxide compressor and the heat of NO oxidation reaction, the gas temperature at the inlet of the nitric oxide booster compressor is reduced, thereby reducing the energy consumption of the nitric oxide booster compressor.

[0091] The high-pressure process gas from the outlet of the nitric oxide booster 19 sequentially enters the seventh heat exchanger 20, the eighth heat exchanger 21, and the ninth heat exchanger 22 to recover heat before entering the bottom of the absorption tower 23. This process recovers heat from the high-pressure process gas and lowers its temperature, thus improving the absorption efficiency in the absorption tower. The process gas temperature at the outlet of the seventh heat exchanger 20 is 70℃-80℃, the process gas temperature at the outlet of the eighth heat exchanger 21 is 40℃-60℃, and the process gas temperature at the outlet of the ninth heat exchanger 22 is 20℃-40℃.

[0092] PW water, cooled to 10℃-15℃ by cooler 25, enters the top of absorption tower 23 as the absorbent. Lowering the PW water temperature improves absorption efficiency. The absorption tower 23 is divided into four absorption sections from top to bottom: a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section. Each absorption section is connected to its own independent cooling water pipeline. The temperature difference between the cooling water in the first and third absorption sections is -5℃ to 5℃. The cooling water temperature in the second absorption section is 3℃-10℃ higher than that in the first absorption section, and the cooling water temperature in the fourth absorption section is 18℃-28℃ higher than that in the third absorption section. Specifically, in some embodiments, the cooling water temperature in the first and third absorption sections is 5℃-10℃, the cooling water temperature in the second absorption section is 13℃-15℃, and the cooling water temperature in the fourth absorption section is 28℃-33℃. By precisely controlling the cooling water temperature in each absorption section of the absorption tower and the temperature of the high-pressure process gas entering the absorption tower, a low absorption temperature can be ensured. The dilute nitric acid obtained at the bottom of the absorption tower 23 enters the bleaching tower 24 and undergoes secondary air desorption to obtain a finished dilute nitric acid with a mass concentration of 66% or higher, especially 69% or higher, for example, a mass concentration of 69%-71%.

[0093] In some embodiments, as shown in Figure 1, the hot water obtained by heating through the fourth heat exchanger 14 and / or the seventh heat exchanger 20 enters the refrigeration unit 34 to prepare BR1 at 10°C-15°C into cold water BS1 at 5°C-10°C. This cold water is used as cooling water for the first and third absorption sections of the absorption tower 23 and / or as a cold source for the refrigeration dehumidifier 5, cooler 25, and other devices in the park. The cold source is heated to BR1 at 10°C-15°C and then enters the refrigeration unit 34 to be prepared into cold water BS1 again for recycling.

[0094] The high-pressure, low-temperature tail gas from the absorption tower 23 enters the ninth heat exchanger 22, the sixth heat exchanger 18 and the first heat exchanger 11 in sequence and is heated to a high-pressure, high-temperature tail gas of 370℃-400℃. The high-pressure, high-temperature tail gas is reduced in the nitrogen oxide reduction reactor 26 and then enters the tail gas turbine 27 to do work. The tail gas after doing work is directly discharged.

[0095] The superheated steam from the superheater 9 enters the first steam turbine 32 and the second steam turbine 33 to perform work. The exhaust steam after work is condensed and mixed with PW water, then enters the third heat exchanger 13 to be heated to 110℃-120℃. The resulting high-temperature PW water enters the deaerator 28 to remove dissolved oxygen. The deaerated BFW water is pressurized by the first boiler water pump 30 and then enters the second heat exchanger 12 for further heating to 240℃-250℃. It then sequentially returns to the boiler water buffer tank 29 and the waste heat boiler 10, and then returns to the boiler water buffer tank 29 for gas-liquid separation. The resulting saturated steam enters the superheater 9 to be heated into superheated steam. The excess superheated steam is sent to the park's steam network. In some embodiments, the temperature of the superheated steam is 440℃-480℃ and the pressure is 3.5MPaG-5MPaG.

[0096] The hot water from the outlet of the fifth heat exchanger 15 and / or the eighth heat exchanger 21 enters the heat removal equipment 35 to prepare hot water. Part of the hot water is used as tracing water, and the surplus hot water is used as heating water to supply the factory office building.

[0097] In summary, in this application, the steam superheater 9, waste heat boiler 10, second heat exchanger 12, third heat exchanger 13, deaerator 28, boiler water buffer tank 29, first boiler water pump 30, second boiler water pump 31, first steam turbine 32, and second steam turbine 33 constitute a high-temperature heat recovery system. This system utilizes the high-temperature reaction heat of ammonia oxidation and the reaction heat of NO oxidation to produce superheated steam. A portion of this steam is used by the unit itself, while the surplus can be supplied to other units within the industrial park. The fourth heat exchanger 14, seventh heat exchanger 20, and refrigeration unit 34 constitute a medium-temperature heat recovery system. This system recovers heat from the intermediate temperature range of low-pressure and high-pressure process gases to produce hot water, which is then used by the refrigeration unit to produce chilled water BS1 for the unit's own use and for supplying other units within the industrial park. The fifth heat exchanger 15, eighth heat exchanger 21, and heat removal equipment 35 constitute a low-temperature heat recovery system. This system recovers heat from the low-temperature range of low-pressure and high-pressure nitrogen oxides to produce hot water for the unit's pipelines and equipment. The surplus is supplied to the plant's office building as heating water. The ninth heat exchanger 22, the sixth heat exchanger 18, and the first heat exchanger 11 constitute a tail gas heat recovery system. The high-pressure, low-temperature tail gas exiting from the top of the absorption tower 23 exchanges heat with the high-pressure process gas in the ninth heat exchanger 22, lowering the temperature of the high-pressure process gas and improving the absorption effect in the absorption tower. The tail gas then enters the sixth heat exchanger 18 and the first heat exchanger 11 to recover the heat from the high-temperature, high-pressure process gas at the outlet of the nitrogen oxide compressor 17 and the high-temperature reaction heat of ammonia oxidation, thus lowering the temperature of the gas entering the nitrogen oxide booster compressor 19 and reducing the energy consumption of the nitrogen oxide booster compressor 19. Therefore, this application can fully utilize the energy balance characteristics of the dual-pressure nitric acid production unit. By setting up a high-temperature heat recovery system, a tail gas heat recovery system, a medium-temperature heat recovery system, and a low-temperature heat recovery system, it can recover and utilize the heat of ammonia oxidation, the heat of NO oxidation, and the high-temperature heat at the outlet of the nitrogen oxide compressor in a graded manner. This not only meets the heat and cooling needs of the unit but also provides additional energy to the industrial park.

[0098] Air compressor 6, exhaust gas turbine 27, nitrogen oxide compressor 17, and first steam turbine 32 are connected by couplings and combined into a four-in-one unit. First steam turbine 32 and exhaust gas turbine 27 provide the mechanical energy required for the operation of air compressor 6 and nitrogen oxide compressor 17. Nitrogen oxide booster 19 is coaxially connected to second steam turbine 33, which provides the mechanical energy required for the operation of nitrogen oxide booster 19. Therefore, the entire process can operate smoothly without additional power supply. Thus, the nitric acid production process of this application has the advantages of low energy consumption and high product acid concentration.

[0099] According to a second aspect of this application, a nitric acid production system is provided, comprising an ammonia oxidation furnace 8, a first heat exchange unit, a nitrogen oxide separator 16, a nitrogen oxide compressor 17, a second heat exchange unit, and an absorption tower 23, which are sequentially connected; the nitric acid production system further includes:

[0100] Nitrogen oxide booster 19 is located between nitrogen oxide compressor 17 and absorption tower 23;

[0101] The control unit is used to measure the real-time nitric acid mass concentration C1 at the bottom of the absorber and the NO concentration in the tail gas at the top of the absorber. X Adjust the nitrogen oxide booster speed N and / or the top water supply Q of the absorption tower to control the nitric acid mass concentration above 66%.

[0102] The nitric acid production system provided in this application adds a nitric oxide booster downstream of the nitric oxide compressor in a traditional four-in-one unit. This reduces the outlet pressure of the nitric oxide compressor, and the insufficient pressure is supplemented by the nitric oxide booster. Furthermore, during the reaction process of nitric oxide and water, a control unit is installed to monitor in real time the nitric acid mass concentration C1 at the bottom of the absorption tower and the NO content in the tail gas at the top of the absorption tower. X The concentration of nitric acid is controlled at above 66% by adjusting the speed N of the nitrogen oxide booster and / or the amount of water replenished at the top of the absorption tower.

[0103] In one optional embodiment, the first heat exchange unit includes a first heat exchanger 11, a second heat exchanger 12, a third heat exchanger 13, a fourth heat exchanger 14, and a fifth heat exchanger 15 connected in sequence. The process gas inlet of the first heat exchanger 11 is connected to the ammonia oxidation furnace 8, and the process gas outlet of the fifth heat exchanger 15 is connected to the nitrogen oxide separator 16. The gas phase outlet of the nitrogen oxide separator 16 is connected to the nitrogen oxide compressor 17, and the liquid phase outlet of the nitrogen oxide separator 16 is connected to the middle inlet of the absorption tower 23. The second heat exchange unit includes a sixth heat exchanger 18, a seventh heat exchanger 20, an eighth heat exchanger 21, and a ninth heat exchanger 22. The sixth heat exchanger 18 is disposed between the nitrogen oxide compressor 17 and the nitrogen oxide booster 19, and the seventh heat exchanger 20, the eighth heat exchanger 21, and the ninth heat exchanger 22 are connected in sequence between the nitrogen oxide booster 19 and the absorption tower 23.

[0104] In one optional embodiment, the absorber tower 23 is internally divided into a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section from top to bottom. Each absorption section is connected to its own independent cooling water pipeline. The temperature difference between the cooling water in the first and third absorption sections is -5℃ to 5℃. The cooling water temperature in the second absorption section is 3℃ to 10℃ higher than that in the first absorption section, and the cooling water temperature in the fourth absorption section is 18℃ to 28℃ higher than that in the third absorption section. By precisely controlling the cooling water temperature of each absorption section of the absorber tower and the temperature of the high-pressure process gas entering the absorber tower, a low absorption temperature can be ensured. In some embodiments, the cooling water temperature of the first and third absorption sections is 5℃ to 10℃, the cooling water temperature of the second absorption section is 13℃ to 15℃, and the cooling water temperature of the fourth absorption section is 28℃ to 33℃.

[0105] The nitric acid production system further includes at least one of the following: a gaseous ammonia production unit, an air treatment unit, a steam generation unit, a tail gas treatment unit, a nitric acid purification unit, a refrigeration unit, and a heat removal unit; wherein...

[0106] The ammonia production unit includes at least one ammonia evaporator, an ammonia vapor superheater 3, and an ammonia-air mixer 7. The outlet of the ammonia evaporator is connected to the ammonia inlet of the ammonia vapor superheater 3, and the inlet of the ammonia-air mixer 7 is connected to the ammonia outlet of the ammonia vapor superheater 3.

[0107] The air handling unit includes an air filter 4, a refrigerated dehumidifier 5, and an air compressor 6 connected in sequence. The outlet of the air compressor 6 is connected to the heat source inlet of the ammonia vapor superheater 3 and the inlet of the ammonia-air mixer 7. The heat source outlet of the ammonia vapor superheater 3 is connected to the air inlet of the bleaching tower 24.

[0108] The steam generating unit includes a steam superheater 9, a waste heat boiler 10, a boiler water buffer tank 29, a deaerator 28, and a first steam turbine 32. The steam outlet of the steam superheater 9 is connected to the gas inlet of the first steam turbine 32. The exhaust steam outlet of the first steam turbine 32 is connected to the refrigerant inlet of the third condenser 13 via a condenser. The refrigerant outlet of the third condenser 13 is connected to the inlet of the deaerator 28. The outlet of the deaerator 28 is connected to the refrigerant inlet of the second condenser 12. The refrigerant outlet of the second condenser 12 is connected to the first inlet of the boiler water buffer tank 29. The first outlet of the boiler water buffer tank 29 is connected to the inlet of the waste heat boiler 10. The outlet of the waste heat boiler 10 is connected to the second inlet of the boiler water buffer tank 29. The second outlet of the boiler water buffer tank 29 is connected to the steam inlet of the steam superheater 9. The process gas inlet of the steam superheater 9 is connected to the process gas outlet of the oxidizer 8. The process gas outlet of the steam superheater 9 is connected to the process gas inlet of the waste heat boiler 10. The process gas outlet of the waste heat boiler 10 is connected to the first heat exchanger 11.

[0109] The exhaust gas treatment unit includes a nitrogen oxide reduction reactor 26 and an exhaust gas turbine 27 connected to each other. The inlet of the nitrogen oxide reduction reactor 26 is connected in sequence to the refrigerant outlets of the first heat exchanger 11, the sixth heat exchanger 18 and the ninth heat exchanger 22. The refrigerant inlet of the ninth heat exchanger 22 is connected to the exhaust gas outlet of the absorption tower 23.

[0110] The nitric acid purification unit includes a bleaching tower 24 and a nitric acid storage tank. The bleaching tower 24 has a liquid inlet, an air inlet, a liquid outlet, and an exhaust outlet. The liquid inlet of the bleaching tower 24 is connected to the liquid outlet of the absorption tower 23, the liquid outlet of the bleaching tower 24 is connected to the nitric acid storage tank, and the exhaust outlet of the bleaching tower 24 is connected to the inlet of the nitrogen oxide compressor 17.

[0111] The refrigeration unit includes a refrigeration unit 34, the first inlet of which is connected to the refrigerant outlet of the fourth heat exchanger 14 and / or the seventh heat exchanger 20, and the first outlet of which is connected to the refrigerant inlet of the fourth heat exchanger 14 and / or the seventh heat exchanger 20.

[0112] The heat removal unit includes a heat removal device 35. The first inlet of the heat removal device 35 is connected to the refrigerant outlet of the fifth heat exchanger 15 and / or the eighth heat exchanger 21, and the first outlet of the heat removal device 35 is connected to the refrigerant inlet of the fifth heat exchanger 15 and / or the eighth heat exchanger 21.

[0113] In some embodiments, the air compressor 6, the nitrogen oxide compressor 17, the first steam turbine 32, and the exhaust gas turbine 27 are connected by a coupling and combined into a four-in-one unit. The nitric acid production system also includes a second steam turbine 33, which is coaxially connected to the nitrogen oxide booster 19. The steam outlet of the steam superheater 9 is connected to the gas inlet of the second steam turbine 33, and the exhaust steam outlet of the second steam turbine 33 is connected to the refrigerant inlet of the third condenser 13 via a condenser.

[0114] The present application will be further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application. Where specific experimental steps or conditions are not specified in the embodiments and comparative examples, they can be performed according to the conventional experimental steps or conditions described in the literature in the art. Where the manufacturers of reagents or instruments are not specified, they are all commercially available conventional reagent products. In this application, the unit % represents mass percentage.

[0115] In this application, the terms TDI represent toluene diisocyanate, MDI represent diphenylmethane diisocyanate, PW represent demineralized water, CWS represent circulating water supply, CWR represent circulating water return, and BFW represent boiler water. BS1 and BS2 both refer to chilled water supply, differing only in temperature; BR1 and BR2 both refer to chilled water return, differing only in temperature.

[0116] Example 1

[0117] A large chemical industrial park has nitric acid plants, nitrobenzene plants, aniline plants, TDI plants, MDI plants, and a thermal power boiler plant. The dilute nitric acid produced by the nitric acid plants is used as the raw material for the nitrobenzene and TDI plants. Taking the 360,000-ton-per-year nitric acid plant in the park as an example, the nitric acid production process will be explained in detail.

[0118] As shown in Figure 1, liquid ammonia at 8°C and 1.4 MPaG from the boundary area is depressurized by a regulating valve and then enters the first ammonia evaporator 1 and the second ammonia evaporator 2. It is heated by approximately 18°C ​​cold water BR2 and 35°C circulating water CWR, and evaporates into a gaseous phase at 0.56 MPaG. The gaseous ammonia then enters the ammonia vapor superheater 3 and is heated to 165°C by secondary air heating at approximately 221°C before entering the ammonia-air mixer 7.

[0119] After being filtered by air filter 4, the air enters the air-cooled dehumidifier 5 and is cooled by 5°C cold water BS1 to remove moisture. The air temperature drops from 30°C to about 20°C. Then, it enters the air compressor 6 for compression. The outlet temperature and pressure are about 221°C and 0.39 MPaG. The air at the outlet of the air compressor 6 is divided into two streams, namely primary air and secondary air. The primary air enters the ammonia-air mixer 7 and is mixed evenly with ammonia gas. The outlet temperature of the ammonia-air mixer 7 is about 218°C. The mixed gas then enters the ammonia oxidation furnace 8, where ammonia is oxidized to NO at 870°C and 0.38 MPaG, releasing a large amount of heat.

[0120] The high-temperature process gas obtained from the ammonia oxidation reaction is sequentially passed through a steam superheater 9, a waste heat boiler 10, a first heat exchanger 11, a second heat exchanger 12, a third heat exchanger 13, a fourth heat exchanger 14, and a fifth heat exchanger 15 to recover heat in stages. During this process, NO in the process gas is further oxidized to NO2, releasing heat. The process gas, cooled to 50°C, enters a nitrogen oxide separator 16 for gas-liquid separation. The separated liquid phase dilute acid is sent to the middle of the absorption tower 23 for further absorption and concentration. The separated process gas is then mixed with approximately 50°C secondary air from the bleaching tower 24. The mixed gas with a pressure of about 0.3 MPaG enters the nitrogen oxide compressor 17 for compression. The resulting process gas has a pressure of about 0.7 MPaG and a temperature of about 140°C. After recovering the heat of compression, the process gas is cooled to 50°C by the sixth heat exchanger 18 and continues to enter the nitrogen oxide booster 19 for further pressurization to 1.0 MPaG and 85°C. The high-temperature and high-pressure process gas from the nitrogen oxide booster 19 passes through the seventh heat exchanger 20, the eighth heat exchanger 21 and the ninth heat exchanger 22 in sequence to recover heat. The high-pressure process gas cooled to 20°C enters the bottom of the absorption tower 23.

[0121] In cooler 25, 4.9 t / h of 30°C PW water is cooled to 10°C using 5°C chilled water BS1. This cooled water is added from the top of nitric acid absorption tower 23. Absorption tower 23 is divided into four absorption sections from top to bottom: a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section. Each absorption section is connected to its own independent cooling water pipeline. The cooling water BS1 temperature in the first and third absorption sections is 5°C, the cooling water BS2 temperature in the second absorption section is 13°C, and the cooling water CWS temperature in the fourth absorption section is 28°C. High-pressure process gas is in full counter-current contact with the cooled PW water inside absorption tower 23 and is cooled through the first to fourth absorption sections. Approximately 69% dilute nitric acid is obtained at the bottom of absorption tower 23. The dilute nitric acid then enters bleaching tower 24, where NOx gas is removed by secondary air bleaching to obtain the finished dilute nitric acid.

[0122] It should be noted that in this implementation, the mass concentration of nitric acid C1 at the bottom of the absorption tower and the NO in the tail gas at the top of the absorption tower are monitored in real time. X To control the concentration of C2 in the finished dilute nitric acid, adjust the speed N of the nitrogen oxide booster or the amount of water replenished at the top of the absorption tower in a timely manner. The specific control methods are as follows:

[0123] The NOx content C2 in the exhaust gas exiting the top of absorber 23 was monitored online and found to be approximately 110 ppm, lower than the set value C2*. In this embodiment, C2* is 150 ppm. Controller 36 issued a command to reduce the makeup water volume Q at the top of the tower in increments of ΔQ = 100 kg / h. The changes in nitric acid mass concentration C1 at the bottom of the absorber, NOx content C2 in the exhaust gas, and the changes in nitric acid mass concentration ΔC1 and NOx content ΔC2 in the exhaust gas were monitored after the adjustment. The setting of the nitric acid mass concentration change... The setpoint for the change in NOx content in the tail gas, ΔC1*, is 0.02%, and the setpoint for ΔC2*, is 10 ppm. Calculations show that after the first adjustment, the change in nitric acid mass concentration, Δ1C1, is 0.18%, and the change in NOx content in the tail gas, Δ1C2, is 0 ppm. This satisfies the condition that Δ1C1 is greater than ΔC1* and Δ1C2 is less than ΔC2*. Therefore, the makeup water volume Q at the top of the column is further reduced in increments of ΔQ = 100 kg / h until the change in NOx content in the tail gas, ΔC2*, is reached after the 14th adjustment. 14 C2 is 11 ppm, which is greater than the set value ΔC2*, so the adjustment ΔQ is terminated. Simultaneously, controller 36 issues a command to increase the speed of the nitrogen oxide booster 19 in steps of ΔN (30 rpm), monitoring the adjusted nitric acid mass concentration C1, NOx content in the exhaust gas C2, the change in nitric acid mass concentration ΔC1, and the change in NOx content in the exhaust gas ΔC2. The set value for the change in nitric acid mass concentration ΔC1* is 0.02%, and the set value for the change in NOx content in the exhaust gas ΔC2* is 10 ppm. After the 15th adjustment, the change in nitric acid mass concentration Δ... 15 C1 is 0.08%, and the change in NOx content in the exhaust gas is Δ15 C2 is -3ppm, satisfying ΔC1 greater than ΔC1*. Continue increasing the speed of the nitrogen oxide booster 19 in steps of ΔN = 30rpm until the nitric acid mass concentration C1 is 69.02% after the 17th adjustment, which is greater than the set value C1* (69%), at which point the adjustment is terminated. The process parameters involved in the above adjustment steps are shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] After optimization and adjustment, the process gas pressure at the outlet of the nitrogen oxide booster 19 was increased to 1.1 MPaG and 95℃, the PW makeup water volume at the top of the nitric acid absorption tower was optimized to 3.5 t / h, and the mass concentration of the product dilute nitric acid can reach more than 69%, meeting the needs of downstream nitrobenzene and TDI units.

[0128] The approximately 0.9 MPaG, 10°C tail gas exiting from the top of the absorption tower 23 sequentially enters the ninth heat exchanger 22, the sixth heat exchanger 18, and the first heat exchanger 11, where it is heated to 40°C, 130°C, and 400°C, respectively. The high-temperature, high-pressure tail gas then enters the nitrogen oxide reduction reactor 26, where the nitrogen oxides are catalytically reduced to meet emission standards. After reduction treatment, the high-temperature, high-pressure tail gas enters the tail gas turbine 27 to perform work, thereby recovering the thermal and pressure energy of the tail gas. The tail gas, after performing work, is approximately 110°C and is directly discharged into the atmosphere through the chimney.

[0129] In this embodiment, the steam superheater 9, waste heat boiler 10, second heat exchanger 12, third heat exchanger 13, deaerator 28, boiler water buffer tank 29, first boiler water pump 30, second boiler water pump 31, first steam turbine 32, and second steam turbine 33 constitute a high-temperature heat recovery system. Approximately 31 t / h of exhaust steam from the outlets of the first steam turbine 32 and second steam turbine 33 is condensed to 50°C and combined with 35 t / h of waste heat from the second steam turbine. After mixing with PW water at 30°C, the mixture reaches approximately 39°C and enters the third heat exchanger 13, where it is heated to 117°C. Correspondingly, the process gas is cooled from 160°C to 89°C. The high-temperature PW water, heated by the third heat exchanger 13, enters the deaerator 28, where dissolved oxygen is removed at a pressure of 0.1 MPaG. The deaerated BFW water, at approximately 120°C, is pressurized by the first boiler water pump 30 and sent to the second heat exchanger 12 for further heating to 245°C before entering the boiler water buffer tank 29. The process gas, meanwhile, is cooled from 286°C to 160°C. Subsequently, the high-temperature BFW water... The FW water is pressurized by the second boiler water pump 31 and sent to the waste heat boiler 10 for reheating. After being converted into a gas-liquid two-phase system, it returns to the boiler water buffer tank 29 for gas-liquid separation. The resulting saturated steam of about 66 t / h enters the steam superheater 9 for further heating to 460°C to obtain superheated steam. The process gas is cooled from 870°C to 400°C. Part of the superheated steam is supplied to the first steam turbine 32 and the second steam turbine 33, and the remaining about 35 t / h is transported to the park's pipeline network to supply TDI, MDI and other units, reducing coal consumption in the thermal power boiler plant.

[0130] The fourth heat exchanger 14, the seventh heat exchanger 20, and the refrigeration unit 34 constitute a medium-temperature heat recovery system. This system recovers 7MW and 4MW of heat from the low-pressure process gas (89℃-70℃) and high-pressure process gas (95℃-70℃) temperature ranges, respectively, to produce 85℃ hot water. This hot water then enters the refrigeration unit 34 to produce 5℃ chilled water (BS1) at 15℃ (BS1 = 8.2MW). This chilled water is then supplied to the refrigeration dehumidifier (5487kW), the cooler (25120kW), the first absorption section (489kW), and the third absorption section (4145kW) of the absorption tower 23. The remaining approximately 3MW of chilled water (BS1) is supplied to TDI, MDI, and other units through the park's chilled water network. Compared to directly using electric refrigeration, this system saves approximately 1500kW of electricity. It is understandable that, relative to the high-pressure process gas exiting the nitric oxide compressor, the high-temperature process gas obtained from the ammonia oxidation reaction can also be referred to as "low-pressure process gas" or "high-temperature low-pressure process gas" before entering the nitric oxide compressor.

[0131] The fifth heat exchanger 15, the eighth heat exchanger 21, and the heat removal equipment 35 constitute a low-temperature heat recovery system, which recovers 15MW and 3MW of heat from the low-pressure process gas temperature range of 70℃-40℃ and the high-pressure process gas temperature range of 70℃-50℃ to produce 60℃ hot water for use in the pipelines and equipment of the park. The surplus is supplied to the office building of the plant as heating water in winter.

[0132] The low-temperature cooling capacity (3.2MW) of ammonia evaporation in the first ammonia evaporator 1 is used to prepare BS2 cold water at 13℃, which is supplied to the second absorption section of the absorption tower 23 to remove heat; the remaining 1.8MW of ammonia evaporation cooling capacity is used to prepare CWS low-temperature circulating water at 33℃, which is supplied to the fourth absorption section of the nitric acid absorption tower 23 to remove heat. The insufficient CWS cooling capacity can be supplied by the park's circulating water station.

[0133] Air compressor 6, nitrogen oxide compressor 17, exhaust gas turbine 27, and first steam turbine 32 are connected by couplings and combined into a four-in-one unit. The air compressor consumes approximately 14MW of power, nitrogen oxide compressor 17 consumes 6MW, the exhaust gas turbine produces 14.5MW, and the first steam turbine 32 consumes approximately 21.3t / h of superheated steam, producing 5.5MW. The power output of the first steam turbine 32 and exhaust gas turbine 27 meets the energy consumption requirements of air compressor 6 and nitrogen oxide compressor 17. Nitrogen oxide booster 19 consumes 2.5MW of power, and the second steam turbine 33 consumes approximately 9.6t / h of superheated steam, producing 2.5MW, meeting the energy consumption requirements of nitrogen oxide booster 19.

[0134] In summary, the nitric acid production process provided in this embodiment can produce dilute nitric acid with a mass concentration of 69.02%, and can supply 35t / h of high-pressure steam, 3MW of cooling capacity and 18MW of hot water, saving 1500kW of electricity.

[0135] Example 2

[0136] This embodiment provides a nitric acid production system suitable for the process described in Embodiment 1, including a gaseous ammonia production unit, an air treatment unit, an ammonia oxidation furnace 8, a steam generation unit, a first heat exchange unit, a nitrogen oxide separator 16, a nitrogen oxide compressor 17, a second heat exchange unit, an absorption tower 23, a nitric acid purification unit, a tail gas treatment unit, a refrigeration unit, a heat removal unit, and a control unit; wherein:

[0137] The ammonia production unit includes a first ammonia evaporator 1, a first ammonia evaporator 2, an ammonia vapor superheater 3, and an ammonia-air mixer 7. The first ammonia evaporator 1 and the first ammonia evaporator 2 are connected in parallel. The outlets of the first ammonia evaporator 1 and the first ammonia evaporator 2 are both connected to the ammonia inlet of the ammonia vapor superheater 3. The inlet of the ammonia-air mixer 7 is connected to the ammonia outlet of the ammonia vapor superheater 3.

[0138] The air handling unit includes an air filter 4, a refrigerated dehumidifier 5, and an air compressor 6 connected in sequence. The outlet of the air compressor 6 is connected to the heat source inlet of the ammonia vapor superheater 3 and the inlet of the ammonia-air mixer 7.

[0139] The inlet of the ammonia oxidizer 8 is connected to the outlet of the ammonia-air mixer 7. The ammonia oxidizer 8 is integrated with the steam superheater 9 and the waste heat boiler 10. The high-temperature process gas from the ammonia oxidizer 8 will enter the steam superheater 9 and the waste heat boiler 10 in sequence. The process gas outlet of the waste heat boiler 10 is connected to the first heat exchange unit.

[0140] The steam generating unit includes a steam superheater 9, a waste heat boiler 10, a deaerator 28, a boiler water buffer tank 29, a first boiler water pump 30, a second boiler water pump 31, and a first steam turbine 32. The steam outlet of the steam superheater 9 is connected to the gas inlet of the first steam turbine 32. The exhaust steam outlet of the first steam turbine 32 is connected to the refrigerant inlet of the third condenser 13 via a condenser (not shown in Figure 1). The refrigerant outlet of the third condenser 13 is connected to the inlet of the deaerator 28. The outlet of the deaerator 28 is connected to the refrigerant inlet of the second condenser 12. The refrigerant outlet of the second condenser 12 is connected to the first inlet of the boiler water buffer tank 29. The first outlet of the boiler water buffer tank 29 is connected to the inlet of the waste heat boiler 10. The outlet of the waste heat boiler 10 is connected to the second inlet of the boiler water buffer tank 29. The second outlet of the boiler water buffer tank 29 is connected to the steam inlet of the steam superheater 9.

[0141] The first heat exchange unit includes a first heat exchanger 11, a second heat exchanger 12, a third heat exchanger 13, a fourth heat exchanger 14, and a fifth heat exchanger 15 connected in sequence. The process gas inlet of the first heat exchanger 11 is connected to the process gas outlet of the steam superheater 9, and the process gas outlet of the fifth heat exchanger 15 is connected to the nitrogen oxide separator 16. The second heat exchanger 12 and the third heat exchanger 13 can be shell-and-tube heat exchangers, which are connected in series and share a tube box.

[0142] The gas phase outlet of the nitrogen oxide separator 16 is connected to the nitrogen oxide compressor 17, and the liquid phase outlet of the nitrogen oxide separator 16 is connected to the middle inlet of the absorption tower 23.

[0143] The second heat exchange unit includes a sixth heat exchanger 18, a seventh heat exchanger 20, an eighth heat exchanger 21 and a ninth heat exchanger 22. The sixth heat exchanger 18 is located between the nitric oxide compressor 17 and the nitric oxide booster 19. The seventh heat exchanger 20, the eighth heat exchanger 21 and the ninth heat exchanger 22 are sequentially connected between the nitric oxide booster 19 and the absorption tower 23.

[0144] The bottom of the absorption tower 23 is provided with a process gas inlet, which is connected to the process gas outlet of the ninth heat exchanger 22; the top of the absorption tower 23 is provided with a PW water inlet, which is connected to the cooler 25; the inside of the absorption tower 23 is divided into a first absorption section, a second absorption section, a third absorption section and a fourth absorption section from top to bottom. Each absorption section is connected to its own independent cooling water pipeline. The cooling water temperature of the first absorption section and the third absorption section is 5℃-10℃, the cooling water temperature of the second absorption section is 13℃-15℃, and the cooling water temperature of the fourth absorption section is 28℃-33℃.

[0145] The nitric acid purification unit includes a bleaching tower 24 and a nitric acid storage tank. The bleaching tower 24 has a liquid inlet, an air inlet, a liquid outlet, and an exhaust outlet. The liquid inlet of the bleaching tower 24 is connected to the liquid outlet of the absorption tower 23, the liquid outlet of the bleaching tower 24 is connected to the nitric acid storage tank, the exhaust outlet of the bleaching tower 24 is connected to the inlet of the nitrogen oxide compressor 17, and the air inlet of the bleaching tower 24 is connected to the heat source outlet of the ammonia vapor superheater 3.

[0146] The exhaust gas treatment unit includes a nitrogen oxide reduction reactor 26 and an exhaust gas turbine 27 connected to each other. The inlet of the nitrogen oxide reduction reactor 26 is connected in sequence to the refrigerant outlets of the first heat exchanger 11, the sixth heat exchanger 18 and the ninth heat exchanger 22. The refrigerant inlet of the ninth heat exchanger 22 is connected to the exhaust gas outlet of the absorption tower 23.

[0147] Air compressor 6, nitrogen oxide compressor 17, first steam turbine 32 and exhaust turbine 27 are connected by a coupling and combined into a four-in-one unit. Nitrogen oxide booster 19 is coaxially connected to second steam turbine 33. The steam outlet of steam superheater 9 is connected to the gas inlet of second steam turbine 33. The exhaust steam outlet of second steam turbine 33 is connected to the refrigerant inlet of third condenser 13 via condenser.

[0148] The refrigeration unit includes a refrigeration unit 34. The first inlet of the refrigeration unit 34 is connected to the refrigerant outlet of the fourth heat exchanger 14 and the seventh heat exchanger 20, and the first outlet of the refrigeration unit 34 is connected to the refrigerant inlet of the fourth heat exchanger 14 and the seventh heat exchanger 20.

[0149] The heat removal unit includes a heat removal device 35. The first inlet of the heat removal device 35 is connected to the refrigerant outlet of the fifth heat exchanger 15 and the eighth heat exchanger 21, and the first outlet of the heat removal device 35 is connected to the refrigerant inlet of the fifth heat exchanger 15 and the eighth heat exchanger 21.

[0150] The control unit, including controller 36 and several monitors, can adjust the concentration of nitric acid C1 at the bottom of the absorber and the concentration of NO in the tail gas at the top of the absorber based on real-time monitoring. X Adjust the nitrogen oxide booster speed N and / or the top water supply Q of the absorption tower to control the nitric acid mass concentration above 66%.

[0151] Comparative Example 1

[0152] Taking a 360,000-ton-per-year nitric acid plant in a certain industrial park as an example, this paper provides a detailed explanation of the existing nitric acid production process.

[0153] As shown in Figure 2, liquid ammonia at 8°C and 1.4 MPaG from the boundary area is depressurized by a regulating valve and enters the ammonia evaporator 1'. It is heated by circulating water CWR at about 35°C and evaporates into a gaseous phase at 0.56 MPaG. The gaseous ammonia then enters the ammonia vapor superheater 2' and is heated to 165°C by about 1.5 t / h of steam before entering the ammonia-air mixer 6.

[0154] After being filtered by air filter 3', the air enters the air-cooled dehumidifier 4' and is cooled by 5°C cold water BS1 to remove moisture. The air temperature drops from 30°C to about 20°C. Then, it enters the air compressor 5' for compression. The outlet temperature and pressure are about 221°C and 0.39 MPaG. The air at the outlet of the air compressor 5' is divided into two streams, namely primary air and secondary air. The primary air enters the ammonia-air mixer 6' and is mixed evenly with gaseous ammonia. The outlet temperature of the ammonia-air mixer 6' is about 218°C. The mixed gas then enters the ammonia oxidation furnace 7', where ammonia is oxidized to NO at 870°C and 0.38 MPaG, releasing a large amount of heat.

[0155] The high-temperature process gas obtained from the ammonia oxidation reaction is sequentially passed through a steam superheater 8', a waste heat boiler 9', a first heat exchanger 10', and a second heat exchanger 11' to recover heat in stages. The process gas exiting the second heat exchanger 11' still has a temperature of about 190°C. The process gas then enters the third heat exchanger 12' and is cooled to about 50°C by circulating water CWS. During this process, NO in the process gas is further oxidized to NO2 and heat is released. The cooled process gas enters the nitrogen oxide separator 13' for gas-liquid separation. The separated liquid phase dilute acid is sent to the middle of the absorption tower 17' for further absorption and concentration. The separated process gas is mixed with secondary air of about 50°C from the bleaching tower 18' to form a mixed gas with a pressure of about 0.3 MPaG. It enters the nitrogen oxide compressor 14' for compression. The process gas exiting has a pressure of about 0.9 MPaG and a temperature of about 125°C. The high-temperature and high-pressure process gas is sequentially passed through the fourth heat exchanger 15' and the fifth heat exchanger 16' to recover heat. The high-pressure process gas cooled to 40°C enters the bottom of the absorption tower 17'.

[0156] In cooler 19', 4.9 t / h of 30°C PW water is cooled to 10°C using 5°C chilled water BS1, and added from the top of absorber 17'. Absorber 17' is divided into four absorption sections from top to bottom: a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section. Each absorption section is connected to its own independent cooling water pipeline. The cooling water BS1 temperature for the first absorption section is 5°C, the cooling water CWS temperature for the second absorption section is 28°C, and the cooling water CWS temperature for the third and fourth absorption sections is 32°C. High-pressure process gas is in full counter-current contact with the cooled PW water in absorber 17', and is deheated through the first to fourth absorption sections. Approximately 65% ​​dilute nitric acid is obtained at the bottom of absorber 17'. The dilute nitric acid then enters bleaching tower 18', where NOx gas is removed by secondary air bleaching to obtain the finished dilute nitric acid. The approximately 0.8 MPaG, 15°C tail gas exiting from the top of the absorption tower 17' sequentially enters the fourth heat exchanger 15' and the first heat exchanger 10', where it is heated to 110°C and 410°C respectively. The high-temperature, high-pressure tail gas then enters the nitrogen oxide reduction reactor 21', where the nitrogen oxides are catalytically reduced to meet emission standards. After reduction treatment, the high-temperature, high-pressure tail gas enters the tail gas turbine 22' to perform work, thereby recovering the thermal and pressure energy of the tail gas. The tail gas, after performing work, is at approximately 110°C and is directly discharged into the atmosphere through the chimney.

[0157] In this comparative example, because the outlet pressure of the nitrogen oxide compressor 14' cannot be adjusted independently, the cooling effect of the nitric acid absorption tower 17' is limited, and the PW makeup water volume at the top of the nitric acid absorption tower is not optimized and controlled, the resulting product has a low nitric acid mass concentration of only about 65%.

[0158] In this comparative example, the air compressor 5', nitrogen oxide compressor 14', exhaust gas turbine 22', and steam turbine 27' are connected by a coupling and combined into a four-in-one unit. The air compressor 5' consumes approximately 14MW of power, the nitrogen oxide compressor 14' consumes 9MW of power, the exhaust gas turbine 22' does approximately 13MW of power, and the steam turbine 27' consumes approximately 38t / h of superheated steam and does approximately 10MW of power. The power output of the steam turbine 27' and the exhaust gas turbine 22' meets the energy consumption requirements of the air compressor 5' and the nitrogen oxide compressor 14'.

[0159] In this comparative example, the steam superheater 8', waste heat boiler 9', second heat exchanger 11', deaerator 23', boiler water buffer tank 25', first boiler water pump 24', second boiler water pump 26', and steam turbine 27' constitute a high-temperature heat recovery system with a capacity of 53 t / h. PW water at 30°C enters the second heat exchanger 11' and is heated to 120°C, while the process gas is cooled from 295°C to 190°C. The high-temperature PW water returns to the deaerator 23', where dissolved oxygen is removed under a pressure of 0.1 MPaG. The deaerated BFW water at approximately 120°C is then pressurized by the first boiler water pump 24' and sent to the boiler water buffer tank 25'. The deaerated BFW water is then pressurized by the second boiler water pump 26' and sent to the waste heat boiler 9' to recover the high-temperature reaction heat, generating approximately 53 t / h of saturated steam. The saturated steam enters the steam superheater 8' and is further heated to 460°C to obtain superheated steam, while the process gas is cooled from 870°C to 420°C. Part of the superheated steam is supplied to the steam turbine 27', part to the ammonia steam superheater 2', and the remaining approximately 11.5 t / h is transported to the park's pipeline network to supply TDI, MDI, and other units, reducing coal consumption in the thermal power boiler plant.

[0160] The third heat exchanger 12', the fifth heat exchanger 16', and the sixth heat exchanger 20' are circulating water coolers, which remove 32MW, 6MW, and 1.5MW of medium and low temperature heat respectively to cool the logistics. The circulating water is supplied by the park's circulating water station. This part of the heat is not reused and requires a large amount of circulating water.

[0161] The low-temperature cooling capacity generated by ammonia evaporation in ammonia evaporator 1' is used to prepare 28°C chilled water (CWS 5MW) to remove heat from the second absorption section of absorber 17'. The circulating water required for the third and fourth absorption sections of nitric acid absorber 17' is supplied by the park's circulating water station. The air refrigeration dehumidifier 4', cooler 19', and the first absorption section of absorber 17' require 487kW, 120kW, and 489kW of low-temperature BS1 respectively. This cooling capacity needs to be generated by an electric refrigeration unit, consuming approximately 314kW of electricity.

[0162] In summary, the existing nitric acid production process can produce dilute nitric acid with a mass concentration of 65%, can supply 11.5 t / h of high-pressure steam, and requires 314 kW of electricity.

[0163] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A process for producing nitric acid, characterized in that, The process includes the following steps: S1, ammonia gas reacts with compressed air in an ammonia oxidation furnace (8) to form a high-temperature process gas. After heat exchange, the high-temperature process gas enters a nitrogen oxide separator (16) for gas-liquid separation to obtain a low-pressure process gas and a liquid phase. S2, the low-pressure process gas is pressurized by a nitrogen oxide compressor (17) and a nitrogen oxide booster (19) to become a high-pressure process gas. The high-pressure process gas is cooled to 20℃-40℃ and then enters the bottom of the absorption tower (23), where it comes into countercurrent contact with PW water from the top of the absorption tower (23) and reacts to obtain dilute nitric acid. During this reaction, the mass concentration C1 of nitric acid at the bottom of the absorption tower and the NO in the tail gas at the top of the absorption tower are monitored in real time. X The content of C2 is adjusted by adjusting the speed N of the nitrogen oxide booster and / or the amount of water replenished at the top of the absorption tower Q, so as to control the nitric acid mass concentration to be above 66%, preferably above 69%.

2. The nitric acid production process according to claim 1, characterized in that, Compare the values ​​of C2 and C2*. When C2 equals C2*, no adjustment of N and Q is needed. Alternatively, when C2 is less than C2*, adjust Q and continue adjusting Q or first adjust Q and then N based on the values ​​between ΔC1 and ΔC1* and ΔC2 and ΔC2*, until ΔC1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*. Alternatively, when C2 is greater than C2*, adjust N first and then continue adjusting N or Q until C2 meets the emission requirements. Here, C1* is the set value of C1, C2* is the set value of C2, ΔC1* is the set value of ΔC1, ΔC2* is the set value of ΔC2, ΔC1 is the difference between C1 and C2 before and after adjustment, and ΔC2 is the difference between C2 and C2 before and after adjustment.

3. The nitric acid production process according to claim 2, characterized in that, When C2 is less than C2*, the controller (36) issues a command to reduce Q at a speed of step size ΔQ1, while collecting C1 and C2 after the Xth adjustment and calculating Δ. X C1 and Δ X C2; if Δ X C2 is less than ΔC2* and Δ X If C1 is greater than ΔC1*, then continue to decrease Q at a rate of ΔQ1 until the adjusted ΔC2 is greater than or equal to ΔC2* or ΔC1 is less than or equal to ΔC1*; if Δ X C2 is greater than or equal to ΔC2* or Δ X If C1 is less than or equal to ΔC1*, the controller (36) issues a command to increase N at a speed of step size ΔN1, and at the same time collects C1 and C2 after the Yth adjustment, and calculates Δ Y C1; if Δ Y If C1 is greater than ΔC1*, then N continues to increase at a rate of ΔN1; if Δ Y If C1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*, then the increment of N stops; where Δ X C1 is the difference between C1 before and after the Xth adjustment, where Δ X C2 is the difference between C2 before and after the Xth adjustment, where X≥1, Δ Y C1 is the difference between C1 before and after the Yth adjustment, Y = X + 1; or, when C2 is greater than C2*, the controller (36) issues an instruction to increase N at a speed of step size ΔN2, while collecting C1 and C2 after the Mth adjustment, and calculating Δ M C2, if Δ M If C2 is greater than or equal to ΔC2*, then N continues to increase at a rate of ΔN2 until C2 meets the emission requirements. M If C2 is less than ΔC2*, the controller (36) issues a command to increase Q at a rate of step size ΔQ2 until C2 meets the emission requirements; where Δ M C2 is the difference between C2 before and after the Mth adjustment, where M≥1; preferably, C1* is 69%-71%, C2* is 150ppm-200ppm, ΔC1* is 0.01%-0.03%, ΔC2* is 5ppm-20ppm, ΔQ1 is 20kg / h-200kg / h, ΔN1 is 10rpm-100rpm, ΔQ2 is 20kg / h-200kg / h, and ΔN2 is 10rpm-100rpm.

4. The nitric acid production process according to any one of claims 1-3, characterized in that, The high-temperature process gas formed in reaction S1 heats the saturated steam from the boiler water buffer tank (29) into superheated steam in the steam superheater (9). Then, the high-temperature process gas heats the boiler water into saturated steam in the waste heat boiler (10). After that, the high-temperature process gas enters the first heat exchanger (11), the second heat exchanger (12), the third heat exchanger (13), the fourth heat exchanger (14), and the fifth heat exchanger (15) in sequence to recover heat step by step. The cooled process gas enters the nitrogen oxide separator (16) for gas-liquid separation. The process gas temperature at the outlet of the first heat exchanger (11) is 370℃-400℃, the process gas temperature at the outlet of the second heat exchanger (12) is 140℃-160℃, and the process gas temperature at the outlet of the third heat exchanger (13) is 85℃. ℃-95℃, the process gas temperature at the outlet of the fourth heat exchanger (14) is 70℃-80℃, and the process gas temperature at the outlet of the fifth heat exchanger (15) is 40℃-60℃; and / or, the process gas compressed by the nitrogen oxide compressor (17) first enters the sixth heat exchanger (18) to recover heat before entering the nitrogen oxide booster (19), and the process gas temperature at the outlet of the sixth heat exchanger (18) is 40℃-70℃; and / or, the high-pressure process gas sequentially enters the seventh heat exchanger (20), the eighth heat exchanger (21) and the ninth heat exchanger (22) to recover heat before entering the bottom of the absorption tower (23); the process gas temperature at the outlet of the seventh heat exchanger (20) is 70℃-80℃, the process gas temperature at the outlet of the eighth heat exchanger (21) is 40℃-60℃, and the process gas temperature at the outlet of the ninth heat exchanger (23) is 40℃-60℃. The process gas temperature at the outlet of heat exchanger (22) is 20℃-40℃; and / or, the liquid phase separated by the nitrogen oxide separator (16) enters the middle of the absorption tower (23) for absorption and concentration; and / or, the low-pressure process gas separated by the nitrogen oxide separator (16) is mixed with secondary air from the bleaching tower (24) and then compressed in the nitrogen oxide compressor (17); and / or, PW water is cooled to 10℃-15℃ by the cooler (25) and then enters the top of the absorption tower (23) as the absorbent; and / or, the dilute nitric acid obtained at the bottom of the absorption tower (23) enters the bleaching tower (24) and is desorbed by secondary air to obtain the finished dilute nitric acid; and / or, the inside of the absorption tower (23) is divided into the first absorption section, the second absorption section, the third absorption section and the fourth absorption section from top to bottom. The four absorption sections are each connected to their own independent cooling water pipelines. The temperature difference between the cooling water in the first and third absorption sections is -5℃ to 5℃. The cooling water temperature in the second absorption section is 3℃ to 10℃ higher than that in the first absorption section. The cooling water temperature in the fourth absorption section is 18℃ to 28℃ higher than that in the third absorption section. Preferably, the cooling water temperatures in the first and third absorption sections are 5℃ to 10℃, the cooling water temperature in the second absorption section is 13℃ to 15℃, and the cooling water temperature in the fourth absorption section is 28℃ to 33℃. And / or, the outlet pressure of the nitrogen oxide compressor (17) is 0.6MPaG to 0.8MPaG. And / or, the outlet pressure of the nitrogen oxide booster (19) is 0.9MPaG to 1.5MPaG。 5. The nitric acid production process according to claim 4, characterized in that, The gaseous ammonia is generated by the evaporation of liquid ammonia. The liquid ammonia is divided into two streams. The first stream of liquid ammonia enters the first ammonia evaporator (1) and exchanges heat with cold water BR2 at 18℃-20℃. The second stream of liquid ammonia enters the second ammonia evaporator (2) and exchanges heat with circulating water CWR at 33℃-38℃. The air is filtered, dehumidified by a refrigeration dehumidifier (5), and compressed by an air compressor (6) and then divided into two streams. The secondary air heats the gaseous ammonia at the outlets of the first ammonia evaporator (1) and the second ammonia evaporator (2) and then enters the bleaching tower (24). The primary air mixes evenly with the heated gaseous ammonia and then enters the ammonia oxidation furnace (8) for reaction. The cold water BR2 is transformed after heat exchange. BS2, a cold water at 13℃-15℃, is used as cooling water for the second absorption section of the absorption tower (23); CWR, after heat exchange, is converted into CWS, a circulating water at 28℃-33℃, and used as cooling water for the fourth absorption section of the absorption tower (23); and / or, hot water obtained by heating through the fourth heat exchanger (14) and / or the seventh heat exchanger (20) enters the refrigeration unit (34) to prepare BR1 at 10℃-15℃ into cold water BS1 at 5℃-10℃, which is used as cooling water for the first and third absorption sections of the absorption tower (23) and / or as a cold source for the refrigeration dehumidifier (5), cooler (25), and other equipment in the park; and / or, from the absorption tower ( The high-pressure, low-temperature tail gas of 23) enters the ninth heat exchanger (22), the sixth heat exchanger (18) and the first heat exchanger (11) in sequence and is heated to a high-pressure, high-temperature tail gas of 370℃-400℃. The high-pressure, high-temperature tail gas is reduced in the nitrogen oxide reduction reactor (26) and then enters the tail gas turbine (27) to do work. The tail gas after doing work is directly discharged; and / or, part of the superheated steam from the steam superheater (9) enters the first steam turbine (32) and the second steam turbine (33) to do work. The exhaust steam after doing work is condensed and mixed with PW water and enters the third heat exchanger (13) to be heated to 110℃-120℃, and the resulting high-temperature P W water enters the deaerator (28) to remove dissolved oxygen. The deaerated BFW water enters the second heat exchanger (12) and is heated to 240℃-250℃. It then enters the boiler water buffer tank (29) and the waste heat boiler (10) in sequence. It then returns to the boiler water buffer tank (29) for gas-liquid separation. The resulting saturated steam enters the steam superheater (9) and is heated into superheated steam. The excess superheated steam is sent to the park's steam network. And / or, the hot water from the outlet of the fifth heat exchanger (15) and / or the eighth heat exchanger (21) enters the heat removal equipment (35) to prepare hot water. Some of the hot water is used as tracing water, and the excess hot water is used as heating water to supply the plant's office building.

6. The nitric acid production process according to claim 5, characterized in that, An air compressor (6), a tail gas turbine (27), a nitrogen oxide compressor (17), and a first steam turbine (32) are connected by a coupling and combined into a four-in-one unit. The first steam turbine (32) and the tail gas turbine (27) provide the mechanical energy required for the operation of the air compressor (6) and the nitrogen oxide compressor (17); and / or, a nitrogen oxide booster (19) is coaxially connected to a second steam turbine (33), and the second steam turbine (33) provides the mechanical energy required for the operation of the nitrogen oxide booster (19); and / or, the temperature of the superheated steam is 440℃-480℃ and the pressure is 3.5MPaG-5MPaG; and / or, the temperature of the gaseous ammonia at the outlet of the ammonia steam superheater (3) is 160℃-180℃; and / or, the mass concentration of the finished dilute nitric acid is 69%-71%.

7. A nitric acid production system, comprising an ammonia oxidation furnace (8), a first heat exchange unit, a nitrogen oxide separator (16), a nitrogen oxide compressor (17), a second heat exchange unit, and an absorption tower (23) connected in sequence; characterized in that, The nitric acid production system also includes: a nitrogen oxide booster (19), located between the nitrogen oxide compressor (17) and the absorption tower (23); and a control unit, used to adjust the nitric acid mass concentration C1 at the bottom of the absorption tower and the NO concentration in the tail gas at the top of the absorption tower based on real-time monitoring. X To control the nitric acid concentration at 66% or higher, preferably 69% or higher, the following steps are taken: First, compare the values ​​of C2 and C2*. If C2 is less than C2*, adjust Q. Then, based on the values ​​of ΔC1 and ΔC1*, and ΔC2 and ΔC2*, continue adjusting Q or first adjusting Q and then N until ΔC1 is less than or equal to ΔC1* or C1 is greater than or equal to C1*. Second, if C2 is greater than C2*, first adjust N and then continue adjusting N or Q until C2 meets the emission requirements. Wherein, C1* is the set value of C1, C2* is the set value of C2, ΔC1* is the set value of ΔC1, ΔC2* is the set value of ΔC2, ΔC1 is the difference between C1 and C2 before and after adjustment, and ΔC2 is the difference between C2 and C2 before and after adjustment.

8. The nitric acid production system according to claim 7, characterized in that, The first heat exchange unit includes a first heat exchanger (11), a second heat exchanger (12), a third heat exchanger (13), a fourth heat exchanger (14), and a fifth heat exchanger (15) connected in sequence. The process gas inlet of the first heat exchanger (11) is connected to the ammonia oxidation furnace (8), and the process gas outlet of the fifth heat exchanger (15) is connected to the nitrogen oxide separator (16). Alternatively, the gas phase outlet of the nitrogen oxide separator (16) is connected to the nitrogen oxide compressor (17), and the liquid phase outlet of the nitrogen oxide separator (16) is connected to the central inlet of the absorption tower (23). The second heat exchange unit includes a sixth heat exchanger (18), a seventh heat exchanger (20), an eighth heat exchanger (21), and a ninth heat exchanger (22). The sixth heat exchanger (18) is located between the nitrogen oxide compressor (17) and the nitrogen oxide booster (19), and in the nitrogen oxide... A seventh heat exchanger (20), an eighth heat exchanger (21), and a ninth heat exchanger (22) are sequentially connected between the booster (19) and the absorption tower (23); and / or, the absorption tower (23) is divided into a first absorption section, a second absorption section, a third absorption section, and a fourth absorption section from top to bottom. Each absorption section is connected to its own independent cooling water pipeline. The temperature difference between the cooling water in the first absorption section and the third absorption section is -5℃ to 5℃. The cooling water temperature in the second absorption section is 3℃ to 10℃ higher than that in the first absorption section. The cooling water temperature in the fourth absorption section is 18℃ to 28℃ higher than that in the third absorption section. Preferably, the cooling water temperature in the first absorption section and the third absorption section is 5℃ to 10℃, the cooling water temperature in the second absorption section is 13℃ to 15℃, and the cooling water temperature in the fourth absorption section is 28℃ to 33℃.

9. The nitric acid production system according to claim 7 or 8, characterized in that, The nitric acid production system further includes at least one of the following: a gaseous ammonia production unit, an air treatment unit, a steam generation unit, a tail gas treatment unit, a nitric acid purification unit, a refrigeration unit, and a heat removal unit; the gaseous ammonia production unit includes at least one ammonia evaporator, an ammonia vapor superheater (3), and an ammonia-air mixer (7), the outlet of the ammonia evaporator being connected to the gaseous ammonia inlet of the ammonia vapor superheater (3), and the inlet of the ammonia-air mixer (7) being connected to the gaseous ammonia outlet of the ammonia vapor superheater (3); the air treatment unit includes an air filter (4), a refrigeration dehumidifier (5), and an air compressor (6) connected in sequence, the outlet of the air compressor (6) being connected to the heat source inlet of the ammonia vapor superheater (3) and the inlet of the ammonia-air mixer (7); the ammonia vapor superheater (3) The heat source outlet is connected to the air inlet of the bleaching tower (24); the steam generating unit includes a steam superheater (9), a waste heat boiler (10), a boiler water buffer tank (29), a deaerator (28), and a first steam turbine (32). The steam outlet of the steam superheater (9) is connected to the gas inlet of the first steam turbine (32). The exhaust steam outlet of the first steam turbine (32) is connected to the refrigerant inlet of the third condenser (13) via a condenser. The refrigerant outlet of the third condenser (13) is connected to the inlet of the deaerator (28). The outlet of the deaerator (28) is connected to the refrigerant inlet of the second condenser (12). The refrigerant outlet of the second condenser (12) is connected to the first inlet of the boiler water buffer tank (29). The first outlet of the boiler water buffer tank (29) is connected to the waste heat boiler. The inlet of the furnace (10) and the outlet of the waste heat boiler (10) are connected to the second inlet of the boiler water buffer tank (29), and the second outlet of the boiler water buffer tank (29) is connected to the steam inlet of the steam superheater (9); the process gas inlet of the steam superheater (9) is connected to the process gas outlet of the oxidizer (8), the process gas outlet of the steam superheater (9) is connected to the process gas inlet of the waste heat boiler (10), and the process gas outlet of the waste heat boiler (10) is connected to the first heat exchanger (11); the tail gas treatment unit includes a nitrogen oxide reduction reactor (26) and a tail gas turbine (27) connected to each other, the inlet of the nitrogen oxide reduction reactor (26) is connected in sequence to the refrigerant outlet of the first heat exchanger (11), the sixth heat exchanger (18) and the ninth heat exchanger (22), and the... The refrigerant inlet of the nine heat exchangers (22) is connected to the tail gas outlet of the absorption tower (23); the nitric acid purification unit includes a bleaching tower (24) and a nitric acid storage tank. The bleaching tower (24) has a liquid inlet, a gas inlet, a liquid outlet, and a gas outlet. The liquid inlet of the bleaching tower (24) is connected to the liquid outlet of the absorption tower (23), the liquid outlet of the bleaching tower (24) is connected to the nitric acid storage tank, and the gas outlet of the bleaching tower (24) is connected to the inlet of the nitrogen oxide compressor (17); the refrigeration unit includes a refrigeration unit (34). The first inlet of the refrigeration unit (34) is connected to the refrigerant outlet of the fourth heat exchanger (14) and / or the seventh heat exchanger (20), and the first outlet of the refrigeration unit (34) is connected to the refrigerant inlet of the fourth heat exchanger (14) and / or the seventh heat exchanger (20);The heat removal unit includes a heat removal device (35), the first inlet of which is connected to the refrigerant outlet of the fifth heat exchanger (15) and / or the eighth heat exchanger (21), and the first outlet of which is connected to the refrigerant inlet of the fifth heat exchanger (15) and / or the eighth heat exchanger (21).

10. The nitric acid production system according to claim 9, characterized in that, The air compressor (6), nitrogen oxide compressor (17), first steam turbine (32) and exhaust gas turbine (27) are connected by a coupling and combined into a four-in-one unit; and / or, the nitric acid production system further includes a second steam turbine (33), which is coaxially connected to the nitrogen oxide booster (19), the steam outlet of the steam superheater (9) is connected to the gas inlet of the second steam turbine (33), and the exhaust steam outlet of the second steam turbine (33) is connected to the refrigerant inlet of the third condenser (13) via a condenser.

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