Dual pressure system for the production of nitric acid and method for operating the same

Abstract

This disclosure discloses a production apparatus for producing nitric acid with reduced power, the system derived from a state-of-the-art dual-pressure nitric acid plant. The system is characterized by further comprising a first device for splitting the tail gas stream into a first tail gas stream and a second tail gas stream in fluid communication with compressed air and oxygen-enriched gas, and / or a device for splitting the tail gas stream into a third tail gas stream and a fourth tail gas stream in fluid communication with compressed air and oxygen-enriched gas. The production apparatus of this disclosure allows for reduced power consumption via an air compressor. This disclosure further relates to a method for operating the system, the use of the system of this disclosure for performing the method of this disclosure, and a method for retrofitting a state-of-the-art dual-pressure nitric acid plant with the system of this disclosure.

Description

Technical Field

[0001] This disclosure relates to the field of nitric acid production in dual-pressure equipment.

[0002] introduce

[0003] Pure nitric acid is a clear, colorless liquid with a strong odor. Nitric acid is primarily produced in large quantities through the catalytic oxidation of ammonia (the Ostwald process). Ammonia is converted to nitric acid in several stages. The ammonia is first oxidized in an ammonia burner on a platinum wire mesh (commonly referred to as an ammonia converter) or cobalt balls, producing nitrogen oxides (also referred to herein as nitric oxide (NO)) and water.

[0004] 4NH3(g)+5O2(g)→4NO(g)+6H2O(g) (1)

[0005] Then, the reaction product nitrogen oxide from (1) is oxidized to nitrogen dioxide (NO2) in the oxidation zone after cooling and further oxidized to dinitrogen tetroxide (N2O4) (g):

[0006] 2NO(g) + O2(g) → 2NO2(g) (2)

[0007] 2NO2(g)→N2O4(g) (3)

[0008] The cooling of nitrogen oxide gas is first achieved by recovering the heat from the conversion of ammonia to nitrogen oxides using a waste heat recovery system. Then, it is cooled using a condenser (in which the condensed nitric acid is separated from the nitrogen oxides, nitrogen dioxide, and dinitrogen tetroxide and nitric acid gases, collectively known as NOx gases). Finally, it is heated in an absorption tower (in which NOx is absorbed). x The process is completed by releasing exhaust gas at the outlet of the gas being absorbed.

[0009] Through absorption in water, and subsequently via NO x The gas compressor compresses nitrogen dioxide and dinitrogen tetroxide, converting them into nitric acid and nitrogen oxides.

[0010] 3NO2(g)+H2O(l)→2HNO3(aq)+NO(g) (4)

[0011] 3N2O4(g)+2H2O(l)→4HNO3(aq)+2NO(g) (5)

[0012] A weak nitric acid (azeotrope) with a purity of up to 68% is obtained. Through distillation, the concentration of nitric acid can be increased to a concentrated nitric acid purity of up to 99%. The overall reaction is given by the following equation:

[0013] NH3 + 2O2 → HNO3 + H2O (6)

[0014] The main process units in nitric acid production equipment include an ammonia converter (using oxygen and a suitable catalyst to convert ammonia into nitrogen oxides), an oxidation zone (converting nitrogen oxides into nitrogen dioxide and dinitrogen tetroxide), and an absorber unit (used to absorb NO). x (Gas absorbed into water) and bleaching unit (removing unreacted dissolved gases, especially those containing NO, from nitric acid aqueous solution). x (The dissolved gases in the gas give it its typical brown color).

[0015] The production process of nitric acid can be divided into single-pressure (single pressure) and dual-pressure (partial pressure) processes.

[0016] In a dual-pressure process, the absorber unit operates at a higher pressure than the ammonia converter. Modern dual-pressure processes are characterized by the low-pressure ammonia converter typically operating at 2 to 6 bar, while the high-pressure absorber unit operates at 9 to 16 bar.

[0017] The dual-pressure process requires an air compressor to feed low-pressure air (containing approximately 21% oxygen by volume) into the converter, and also requires NO. x Gas compressor to deliver high-pressure NO x Gas is fed into the absorber unit. The air compressor operates at a pressure of 2 to 6 bar, including the endpoints, and NO... x The gas compressor operates at pressures from 9 bar to 16 bar, including the end values.

[0018] Air compressors are typically driven by exhaust turbines and steam turbines or by a power source (such as an electric motor). Therefore, the compressor unit in a dual-pressure nitric acid production system usually includes an air compressor and a NO2 compressor. x Gas compressors, exhaust turbines and steam turbines, or power sources (such as electric motors).

[0019] More specifically, referring to Figure 1, the existing dual-pressure equipment and process operate as follows: Gaseous ammonia 32, optionally preheated in a preheater unit (not shown), is mixed in a mixing device 35 with compressed air 34 pressurized to a low pressure using an air compressor 36, and the resulting ammonia / oxygen-enriched air mixture 14 is fed into an ammonia converter 37 operating at low pressure, where the ammonia is oxidized by a suitable catalyst to obtain LP NO containing water and nitrogen oxides (NO). x Gas / steam mixture 15. The heat from the mixture exiting the ammonia converter is recovered, followed by NO. x The gas / stream mixture is then cooled to the water condensation temperature in gas cooler / condenser 38, and from gaseous NO x A mixture of aqueous dilute nitric acid 17 was separated from flow 22. Gaseous NO... x Stream 22 sent to NO xA gas compressor 40 is used to increase the pressure from low to high, approximately equal to the operating pressure of the absorber unit 41. An aqueous dilute nitric acid mixture 17 is fed to the absorber unit 41, commonly referred to as an absorption tower. Pressurized NO... x Gas stream 24 is further oxidized to further convert NO into NO2 and N2O4, cooled in an auxiliary gas cooler / condenser 39, and then directed to absorber 41. Inside absorber 41, pressurized NO... x Gas stream 24 reacts with water to produce exhaust gas 5, which also contains residual NO. x A crude nitric acid stream 27 is fed into a bleaching unit 62. Residual NO in the crude nitric acid stream 27 is then vaporized using a gaseous medium 72 (such as oxygen-containing gas or air) within the bleaching unit 62, which operates at low pressure. x Gases; bleaching units typically operate at approximately the same pressures as ammonia converters. Air compressor 36 and NO x The gas compressor 40 is driven by either the exhaust gas expander 7 and the steam turbine 51 or by a power source (such as an electric motor) (not shown). Heat generated in the ammonia converter 37 is used to heat the exhaust gas 5 in an exhaust gas heat exchanger 43, which includes heat exchangers 66 and 67; therefore, an exhaust gas heater is optionally present. The exhaust gas 5 reacts with NO in the heat exchange system 43. x The gas / steam mixture 15 undergoes heat exchange and expands in the exhaust gas expander 7.

[0020] Air used for ammonia oxidation is usually referred to as primary air; air used as a stripping medium in bleaching units is usually referred to as secondary air.

[0021] According to existing technology, modifying nitric acid production equipment to increase its capacity is usually based on increasing the amount of primary air entering the reactor, which results in a proportional increase in the amount of nitric acid produced.

[0022] Increasing the amount of primary air in the reactor requires installing a new air compressor or modifying an existing one. The increase in primary air also results in a larger volume of gas subsequently being processed into NO. x In a gas compressor. This requires further modification of the NO... x The solution involves either installing a new gas compressor or modifying or replacing the exhaust gas turbine and / or steam turbine and / or electric motor. Otherwise, the NOx gas compressor will easily reach its process limits, becoming a bottleneck for the equipment.

[0023] However, the modification has obvious drawbacks. First, it requires the addition of existing equipment, namely air compressors and NOx compressors. x The costs associated with modifying or replacing the gas compressor, as well as the corresponding turbine and electric motor. Furthermore, the technical requirements for equipment modification are high, leading to extended downtime.

[0024] Another issue related to nitric acid production equipment is that operating the air compressor requires a significant amount of energy. Therefore, a large amount of energy is needed to achieve the target nitric acid production volume.

[0025] Therefore, the objective of this invention is to provide a system and a method for operating the system, which allows for a reduction or even suppression of the power required to operate the air compressor in a dinitric acid plant. Background Technology

[0026] CN110540178A (China Chengda Engineering Co., Ltd., 2019) discloses a process for producing nitric acid. A medium-pressure method for producing nitric acid is characterized by an ammonia oxidation and absorption pressure of 0.5 MPa to 0.6 MPa; the tail gas leaving the absorption tower is treated by a carbon molecular sieve temperature-switching adsorption (TSA) device to reduce the nitrogen oxide content in the tail gas to 100 mg / Nm³. 3 The process air from the air compressor is used as the regeneration desorption gas in the carbon molecular sieve temperature-switching adsorption treatment unit, and the regeneration desorption gas containing nitrogen oxides can be returned to the ammonia oxidation reactor for reuse. A layer of N2O decomposition catalyst is added to the oxidation reactor to reduce the N2O content to 50-100 PPM through the reaction. The nitric acid bleaching tower is arranged at the bottom of the absorption tower, and the two towers are integrated, thereby shortening the process flow and reducing equipment investment. However, in terms of the amount of air compressed by the air compressor, the amount of air to be compressed is the same as that without the TSA unit: in the presence of the TSA unit, the amount of compressed air is initially directly distributed between the TSA unit and the ammonia oxidation reactor, and finally, as the amount of compressed air leaving the TSA unit is also guided to the ammonia oxidation reactor, the total amount of air compressed by the air compressor is ultimately in the ammonia oxidation reactor.

[0027] In WO2018 / 162150A1 (Casale SA, September 13, 2018), a solution was proposed to overcome the modification defects. WO2018162150A1 discloses a dual-pressure apparatus for nitric acid production, comprising: a reactor providing a gaseous effluent containing nitrogen oxides; an absorber unit wherein the nitrogen oxides react with water to provide crude nitric acid, and the absorber unit operates at a pressure greater than that of the reactor; a compressor for increasing the pressure of the reactor effluent to that of the absorber unit; the apparatus further comprising a first HP bleaching unit and a second LP bleaching unit, the first HP bleaching unit stripping NO from the output stream of the absorber unit using air. x The gas provides a partially stripped nitric acid stream and a nitrogen oxide-laden air stream; the former is fed into the second LP bleaching unit, while the latter is recycled to NO. x Oxidation zone upstream of the gas compressor.

[0028] Another air compressor is also provided, which supplies air to the first HP bleach unit. Therefore, energy is required to operate the first HP bleach unit under high pressure, and then NO... x Gas recirculation to NO x Delivery side of the gas compressor.

[0029] Therefore, a process and corresponding equipment setup are still needed to minimize or even suppress operational NO. x The energy required to operate the gas compressor, and especially the air compressor, is used to avoid bottlenecks in nitric acid production associated with those compressors. Summary of the Invention

[0030] In one aspect of this disclosure, a production apparatus for producing nitric acid with reduced power consumption and reduced emissions includes:

[0031] • An air compressor that provides compressed air;

[0032] • The supply of a first oxygen-enriched gas, such as a high-pressure water electrolyzer in fluid communication with compressed air, wherein the mixing of the first oxygen-enriched gas with compressed air provides a portion of the first oxygen-containing gas;

[0033] • A mixing device for mixing the first oxygen-containing gas with an ammonia gas stream to produce an ammonia / oxygen-containing gas mixture;

[0034] • Ammonia converter, which can operate at a pressure equal to or higher than P1 and lower than P2, for oxidizing ammonia in the ammonia / oxygen-containing gas mixture to produce a NOx gas / vapor mixture containing water and nitrogen oxides;

[0035] • Devices for adjusting the ammonia concentration and / or oxygen concentration in the ammonia converter, particularly devices for controlling the flow rate of the first oxygen-enriched gas in the oxygen-containing gas and / or devices for controlling the flow rate of the ammonia gas flow, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2, particularly between 1.2 and 9.

[0036] • The first gas cooler / condenser downstream of the ammonia converter produces an aqueous dilute nitric acid mixture and gaseous NO. x flow;

[0037] • A NOx gas compressor, used to compress the gaseous NOx stream to produce compressed NO at a pressure of P2. x Gas flow;

[0038] • Absorption tower, which is used to extract compressed NO from water x The NO is absorbed in the gas stream xGas, to produce gas containing residual NO x crude nitric acid gas stream and NO x The exhaust gas of the gas, including the exhaust gas outlet of the absorption tower used to vent the exhaust gas;

[0039] • A heat exchange system located upstream of the gas cooler / condenser, which utilizes the NO from the ammonia converter x The heat from the gas / vapor mixture heats the exhaust gas stream;

[0040] • Second gas cooler / condenser, which is used to cool the compressed NO x The gas stream is separated from and condensed into vapor before being supplied to the absorption tower;

[0041] • A second oxygen-containing gas, which has:

[0042] a) A pressure equal to or higher than P1 and up to P2, used downstream of the ammonia converter and the NO x The gas compressor is supplied with oxygen upstream; or

[0043] b) A pressure higher than P2 is used to supply the compressed NO x The gas flow supplies oxygen;

[0044] • A device for controlling the flow rate of the second oxygen-containing gas so that the exhaust gas contains at least 0.5% oxygen by volume; and

[0045] • A first pressure relief device, located downstream of the heat exchange system, is used to expand the exhaust gas flow to generate a first expanded exhaust gas with a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device can at least partially supply the NO. x The gas compressor and / or the air compressor provides power.

[0046] The production equipment is characterized in that it further includes:

[0047] • First and / or second means for splitting a gas stream, wherein

[0048] (i) The first diversion device is a device for diverting the exhaust gas into a first exhaust gas and a second exhaust gas, wherein the first exhaust gas has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with the first oxygen-enriched gas and compressed air, and wherein the mixture of compressed air, the first oxygen-enriched gas and the first exhaust gas provides the first oxygen-enriched gas.

[0049] (ii) The second diversion device is used to divert the exhaust gas into a third exhaust gas and a fourth exhaust gas, wherein the third exhaust gas has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixture of the third exhaust gas, compressed air and the first oxygen-enriched gas provides a second oxygen-containing gas, and wherein the second oxygen-containing gas is downstream of the ammonia converter and the NO x Upstream supply of gas compressors;

[0050] or

[0051] The second diversion device is used to split the exhaust gas flow into a third exhaust gas flow and a fourth gas flow, wherein the third exhaust gas flow is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixing of the third exhaust gas, compressed air and the first oxygen-enriched gas, and the pressurization of the mixed third exhaust gas, compressed air and the first oxygen-enriched gas in the pressurization device provide the second oxygen-containing gas at a pressure higher than P2, and wherein the second oxygen-containing gas in the NO x The gas is supplied downstream of the gas compressor and upstream of the absorption tower.

[0052] In one embodiment of the production equipment according to the present disclosure, the production equipment further includes means for controlling the flow rate of the first tail gas flow and / or the third tail gas flow.

[0053] The inventors have discovered that, instead of supplying only primary and secondary air as compressed air provided by an air compressor, the first tail gas stream and / or the third tail gas stream provided by the first and second diversion devices, respectively, can be recirculated. Oxygen-enriched gas and second oxygen-containing gas respectively supply oxygen to the ammonia converter and the absorption tower, such that even with a reduction in the amount of compressed air supplied by the air compressor, the oxygen concentration in the ammonia converter and the absorption tower is at least equal to the oxygen concentration in a state-of-the-art dual-pressure nitric acid plant.

[0054] Therefore, exhaust gas, especially oxygen-controlled exhaust gas, can be recycled as both primary and secondary air. This reduces the amount of compressed air required and lowers the power demand on the air compressor. Simultaneously, the size of the air compressor and conventional gas expander (where the exhaust gas expands in a state-of-the-art single-pressure nitric acid unit) is reduced, resulting in a smaller equipment footprint. Furthermore, it reduces NO leaving the production equipment. x Emissions. Therefore, the size required to treat these NO emissions is reduced compared to the corresponding state-of-the-art single-pressure nitric acid equipment. x The size of the emissions treatment unit. Furthermore, a separate supply of pressurized or oxygen-enriched gas ensures optimal conversion of ammonia to nitrogen oxides.

[0055] In one embodiment of the production equipment according to this disclosure, the production equipment further includes one or more of the following:

[0056] • A steam turbine, wherein the steam turbine can at least partially power the NO. x The gas compressor and / or the air compressor provides power;

[0057] • A heat exchanger for exchanging heat between the first expanded exhaust gas and the exhaust gas stream, particularly the cooler exhaust gas stream, wherein the first expanded exhaust gas exits the heat exchanger at a temperature below 300°C, wherein:

[0058] The first expanded exhaust gas, after heat exchange with the exhaust gas, is further supplied to the first diversion device, particularly downstream of the heat exchanger, where the first expanded exhaust gas is in direct fluid communication with the first diversion device; and / or

[0059] • The exhaust gas at the outlet of the absorption tower is split into a third exhaust gas stream and a fourth exhaust gas stream, especially the exhaust gas stream that is colder than the first expanded exhaust gas stream is split into a third exhaust gas stream and a fourth exhaust gas stream.

[0060] ·Removing NO x Processing unit; and

[0061] • A second pressure relief device for expanding the second exhaust gas to atmospheric pressure to generate a second expanded exhaust gas.

[0062] In one embodiment of the production equipment according to the present disclosure, the production equipment further includes a bleaching unit for bleaching the material containing residual NO. x A crude nitric acid stream is supplied to provide a bleached nitric acid stream. The bleacher has an inlet and an exhaust outlet. The inlet is in fluid communication with a high-pressure water electrolyzer supplying oxygen-enriched bleaching gas. If the bleacher operates at a pressure equal to or higher than P1 and up to or equal to P2, the exhaust outlet is downstream of the ammonia converter and the NO... x Any gas flow upstream of the gas compressor is in fluid communication, or if the bleacher operates at a pressure higher than P2, the exhaust outlet is connected to the NO. x The gas compressor downstream and the absorption tower upstream are in fluid communication, such that the supply of the second oxygen-containing gas is at least partially derived from the exhaust gas.

[0063] In one embodiment of the production apparatus according to the present disclosure, the production apparatus further includes a second oxygen-enriched gas flow in direct fluid communication with any exhaust gas flow, particularly a pressurized oxygen-enriched gas flow in direct fluid communication with any exhaust gas flow upstream of the first pressure relief device.

[0064] In one embodiment of the production apparatus according to the present disclosure, the production apparatus further includes a first oxygen-enriched gas, a second oxygen-enriched gas, a second oxygen-containing gas, an oxygen-enriched bleaching gas, and an exhaust gas, all of which are provided at least in part by a high-pressure water electrolyzer.

[0065] In one aspect of this disclosure, a method is disclosed for producing nitric acid in a production apparatus according to the present disclosure with reduced power consumption and reduced emissions. The method includes the following steps:

[0066] a) Compressing air in the air compressor to provide compressed air;

[0067] b) Supply the compressed air obtained in step a) to the mixing device;

[0068] c) Supply the ammonia gas stream to the mixing device to generate the ammonia / oxygen-containing gas mixture;

[0069] d) At a pressure equal to or higher than P1 and lower than P2, the ammonia in the ammonia / oxygen-containing gas mixture is oxidized in the ammonia converter to produce gaseous NO containing water and nitrogen oxides. x Gas / vapor mixture;

[0070] e) Cooling the gaseous NO in the heat exchange system and the gas / cooler condenser x The NO in the gas / vapor mixture x This produces a mixture of aqueous dilute nitric acid and gaseous NO. x flow;

[0071] f) In the NO x The gaseous NO is compressed in the gas compressor. x The flow thus provides the pressurized NO with pressure P2. x Compressed gas flow;

[0072] g) Absorb the pressurized gaseous NO in this absorption tower. x The flow thus provides the residual NO x crude nitric acid gas stream and NO x The exhaust gas;

[0073] h) Using the NO from the ammonia converter x The heat from the gas / steam mixture heats the exhaust gas in the heat exchange system, particularly to a temperature in the range of 150°C to 650°C;

[0074] i) Cool the compressed NO in an auxiliary gas cooler / condenser x The gas flow, particularly the compressed NO supplied at temperatures ranging from 20°C to 60°C, xGas flow; and

[0075] j) Expand at least a portion of the exhaust gas obtained in step h) in the first pressure relief device to provide the first expanded exhaust gas.

[0076] The method is characterized by further including the following steps:

[0077] k) Use a first diversion device to divert the exhaust gas flow, especially the exhaust gas flow downstream of the absorber, into a first exhaust gas flow and a second exhaust gas flow, and / or use a second diversion device to divert the exhaust gas flow into a third exhaust gas flow and a fourth exhaust gas flow.

[0078] l) Mix the first exhaust gas stream with the first oxygen-enriched gas and compressed air to provide the first oxygen-containing gas, and / or mix the third exhaust gas stream with compressed air and the first oxygen-enriched gas to provide the second oxygen-containing gas;

[0079] m) Adjust the flow rate of the first oxygen-enriched gas or the flow rate of the ammonia gas in step l) to maintain the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2, particularly between 1.2 and 9.

[0080] n) Supply the first oxygen-containing gas to the mixing unit;

[0081] o) Adjust the flow rate of the second oxygen-containing gas so that the exhaust gas, particularly the exhaust gas downstream of the absorber, contains at least 0.5% oxygen by volume; and

[0082] p) Under pressure equal to or higher than P1 and up to P2, downstream of the ammonia converter and the NO x Upstream of the gas compressor, or at a pressure higher than P2 in the NO x The second oxygen-containing gas is supplied downstream of the gas compressor and upstream of the absorption tower.

[0083] In one embodiment of the method according to this disclosure, the method further includes the following steps:

[0084] q) Adjust the flow rate of the first tail gas flow and / or the third tail gas flow.

[0085] In one embodiment of the method according to this disclosure, the first exhaust gas is mixed in step l), and the first expanded exhaust gas is split in step k), and the method further includes the following steps:

[0086] r) Before step h), the exhaust gas obtained in step g) and the first expanded exhaust gas obtained in step j) are heated in a heat exchanger, especially the exhaust gas that is colder than the first expanded exhaust gas is heated in the heat exchanger and the first expanded exhaust gas obtained in step j) so that the exhaust gas to be mixed in step l) reaches a temperature below 300°C.

[0087] s) Processing before step h) and after step r) in NO removal x The exhaust gas obtained in the treatment unit, especially the exhaust gas flow heated in step r) is treated in the NOx removal unit;

[0088] t) In the second pressure relief device, the second exhaust gas is expanded to provide a second expanded exhaust gas;

[0089] as well as

[0090] u) Recover at least a portion of the heat energy generated in the ammonia converter in a steam turbine.

[0091] In one embodiment of the method according to the present disclosure, the third exhaust gas is mixed in step l), and the exhaust gas obtained in step g) is split into a third exhaust gas and a fourth exhaust gas in step k).

[0092] In one embodiment of the method according to this disclosure, the method further includes the following steps:

[0093] v) The residue containing NO obtained by bleaching step g) in a bleacher x The crude nitric acid stream of gas is converted into a bleached nitric acid stream.

[0094] In one embodiment of the method according to this disclosure, the method further includes the following steps:

[0095] w) A second oxygen-enriched gas flow, particularly as a pressurized oxygen-enriched gas flow, is supplied to the tail gas flow, especially upstream of the first pressure relief device.

[0096] In one embodiment of the method according to this disclosure, the method further includes the following steps:

[0097] x) Operating a high-pressure water electrolyzer to produce pressurized oxygen; and

[0098] y) The oxygen generated by the water electrolysis cell in step x) provides at least a portion of the first oxygen-enriched gas, the second oxygen-containing gas, the second oxygen-enriched gas, the oxygen-enriched bleaching gas, and the oxygen-enriched waste gas.

[0099] In one aspect of this disclosure, the use of the production equipment disclosed herein for performing the methods of this disclosure is disclosed.

[0100] In one aspect of this disclosure, existing production equipment for producing nitric acid is disclosed, wherein the existing production equipment includes:

[0101] • An air compressor, used to provide a flow of compressed air;

[0102] • A mixing device for mixing a compressed air stream with an ammonia stream to produce an ammonia / oxygen-containing gas mixture;

[0103] • An ammonia converter, which operates at a pressure equal to or higher than P1 and lower than P2, is used to oxidize ammonia in the ammonia / oxygen-containing gas mixture to produce NO containing water and nitrogen oxides. x Gas / vapor mixture;

[0104] • The first gas cooler / condenser downstream of the ammonia converter produces an aqueous dilute nitric acid mixture and gaseous NO. x flow;

[0105] • A NOx gas compressor, which is used to compress the gaseous NOx stream to produce a compressed NOx gas stream at a pressure of P2;

[0106] • Absorption tower, which is used to extract compressed NO from water x The NO is absorbed in the gas stream x Gas, to produce gas containing residual NO x crude nitric acid gas stream and NO x The exhaust gas of the gas, including the exhaust gas outlet of the absorption tower used to vent the exhaust gas;

[0107] • A heat exchange system for utilizing NO from the ammonia converter x The heat from the gas / vapor mixture heats the exhaust gas stream;

[0108] • A second gas cooler / condenser, used to cool the compressed NOx gas stream before it is absorbed in the absorption tower. x Separation and condensation of vapor in gas streams; and

[0109] • A first pressure relief device, used to expand the exhaust gas flow to generate a first expanded exhaust gas with a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device can at least partially supply the NO. x The gas compressor provides the power;

[0110] A method for modifying production equipment according to this disclosure. The modification method includes the following steps:

[0111] • Introduce a supply of a first oxygen-enriched gas in fluid communication with compressed air, such as a high-pressure water electrolyzer;

[0112] • Introduce devices for adjusting the ammonia concentration and / or oxygen concentration in the ammonia converter, particularly devices for controlling the flow rate of the first oxygen-enriched gas in the oxygen-containing gas and / or devices for controlling the flow rate of the ammonia gas flow, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2, particularly between 1.2 and 9.

[0113] • Introducing a supply of a second oxygen-containing gas, which has:

[0114] (a) A pressure equal to or higher than P1 and up to P2, used in NO x The gas compressor is supplied with oxygen upstream; or

[0115] (b) A pressure higher than P2, used to supply compressed NO x The gas flow supplies oxygen.

[0116] This ensures that the exhaust gas contains at least 0.5% oxygen by volume;

[0117] • Introduce a first device for diverting the tail gas flow and / or a second device for diverting the tail gas flow downstream of the absorption tower, wherein

[0118] (i) The first diversion device is a device for diverting the exhaust gas into a first exhaust gas and a second exhaust gas, wherein the first exhaust gas has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with the first oxygen-enriched gas and compressed air, and wherein the mixture of compressed air, the first oxygen-enriched gas and the first exhaust gas provides the first oxygen-enriched gas.

[0119] (ii) The second diversion device is used to divert the exhaust gas into a third exhaust gas and a fourth exhaust gas, wherein the third exhaust gas has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixture of the third exhaust gas, compressed air and the first oxygen-enriched gas provides the second oxygen-containing gas, and wherein the second oxygen-containing gas is downstream of the ammonia converter and the NO x Upstream supply of gas compressors;

[0120] or

[0121] The second diversion device is used to split the exhaust gas flow into a third exhaust gas flow and a fourth gas flow, wherein the third exhaust gas flow is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixing of the third exhaust gas, compressed air and the first oxygen-enriched gas, and the pressurization of the mixed third exhaust gas, compressed air and the first oxygen-enriched gas in the pressurization device provide the second oxygen-containing gas at a pressure higher than P2, and wherein the second oxygen-containing gas in the NO x The gas is supplied downstream of the gas compressor and upstream of the absorption tower. Attached Figure Description

[0122] Figure 1: A nitric acid plant according to the prior art, comprising an ammonia converter (37) operating at a pressure equal to or higher than P1 and lower than the operating pressure (P2) of the absorber (41).

[0123] Figure 2A According to the nitric acid equipment disclosed herein, it includes an oxygen-containing gas (67) with a pressure equal to or higher than the operating pressure of the ammonia converter (37) and lower than the operating temperature of the absorber (41).

[0124] Figure 2B According to the nitric acid equipment disclosed herein, it contains oxygen-containing gas (67) at a pressure higher than the operating temperature of the absorption tower (41).

[0125] Figure 3A According to the nitric acid equipment disclosed herein, it includes a bleacher (62) that operates at a pressure equal to or higher than the operating pressure of the ammonia converter (37) and lower than the operating temperature of the absorber (41).

[0126] Figure 3b: Nitric acid equipment according to this disclosure, which includes a bleacher (62) operating at a pressure equal to or higher than the operating temperature of the absorber tower (41).

[0127] Table of reference numerals

[0128]

[0129]

[0130] Detailed Implementation

[0131] Throughout the description and claims of this application, the word "comprising" and its variations mean "including but not limited to," and are not intended (and do not) exclude other parts, additions, components, integrals, or steps. Throughout the description and claims of this disclosure, unless the context requires otherwise, the singular reference includes the plural. In particular, where the indefinite article is used, unless the context requires otherwise, this disclosure will be understood to consider both the plural and the singular.

[0132] The features, wholes, properties, compounds, chemical parts, or groups described together in conjunction with specific aspects, embodiments, or examples of this disclosure shall be understood to be applicable to any other aspect, embodiment, or example described herein, unless incompatible therewith. All features of the features disclosed in this disclosure (including the description, claims, abstract, and drawings) and / or all steps of any method or process disclosed herein may be combined in any combination, except for combinations in which at least some of the features and / or steps are mutually exclusive. This disclosure is not limited to the details of any of the foregoing embodiments. This disclosure extends to any novel feature or any combination of novel features disclosed in the features disclosed in this disclosure (including the description, claims, abstract, and drawings), or to any novel step or any combination of novel steps of any method or process disclosed herein.

[0133] The numerical values ​​listed with the aid of the accompanying figures include all values ​​and fractions within these ranges, as well as the referenced endpoint values. The terms “from…to…”, “within…to…”, or “up to…” used when referring to a range of measurable values ​​(such as parameters, quantities, time periods, and similar values) are intended to include limitations associated with the disclosed range.

[0134] When the term “about” is applied to a particular value or range, that value or range is interpreted as being as accurate as the method used to measure it.

[0135] This disclosure generally relates to a system and method for producing nitric acid, particularly in a dual-pressure production facility, offering significant advantages over conventional systems and methods, wherein conventional primary and / or secondary air, consisting of pressurized air, is partially replaced by a combination of: (i) oxygen or oxygen-enriched gas, particularly pressurized oxygen or oxygen-enriched gas, such as that generated by a high-pressure water electrolyzer as further discussed herein; and (ii) a recirculated tail gas stream. In other words, in the system and method for producing nitric acid according to this disclosure:

[0136] (i) Oxygen or oxygen-enriched gas, particularly pressurized oxygen or oxygen-enriched gas, such as gas produced by a high-pressure water electrolyzer, is mixed with compressed air, particularly with a portion of the exhaust gas stream, to provide a first oxygen-containing gas stream, which is mixed with an ammonia stream and subsequently supplied to an ammonia converter, and (b) for providing a second oxygen-containing gas stream downstream of the ammonia converter, such as a second oxygen-containing gas stream, which is mixed with a NOx-containing gas stream downstream of the ammonia converter (e.g., in the oxidation section and / or upstream of the absorber), and / or used as stripping gas in a bleacher, particularly wherein the oxygen-containing bleacher exhaust gas is subsequently mixed with a NOx-containing gas stream downstream of the ammonia converter and upstream of the absorber; and

[0137] (ii) The exhaust gas leaving the absorber is split into a first exhaust gas stream and a second exhaust gas stream and / or a third exhaust gas stream and a fourth exhaust gas stream, wherein the first exhaust gas stream is mixed with oxygen or oxygen-enriched gas, particularly pressurized oxygen or oxygen-enriched gas (e.g., generated by a high-pressure water electrolyzer), and mixed with pressurized air to provide a first oxygen-containing gas stream; and / or wherein a portion of the exhaust gas leaving the absorber, particularly the third exhaust gas stream, may also be mixed with oxygen or oxygen-enriched gas, particularly pressurized oxygen or oxygen-enriched gas (e.g., generated by a high-pressure water electrolyzer) to provide a second oxygen-containing gas stream.

[0138] Dual-pressure production equipment for producing nitric acid

[0139] refer to Figure 2A , Figure 2B , Figure 3A and Figure 3B .

[0140] In one aspect of this disclosure, a production apparatus for producing nitric acid with reduced power consumption and emissions includes: an air compressor 36 that provides compressed air 34; a supply of a first oxygen-enriched gas 50 in fluid communication with the compressed air 34, wherein mixing of the first oxygen-enriched gas 50 with the compressed air 34 provides a portion of a first oxygen-containing gas 56; a mixing device 35 for mixing the first oxygen-containing gas 56 with an ammonia stream 32 to produce an ammonia / oxygen-containing gas mixture 14; and an ammonia converter 37, operable at a pressure equal to or higher than P1 and lower than P2, for oxidizing the ammonia in the ammonia / oxygen-containing gas mixture 14 to produce NO containing water and nitrogen oxides. x Gas / vapor mixture 15; means (not shown) for regulating the ammonia concentration and / or oxygen concentration in the ammonia converter 37, particularly for controlling the flow rate of the first oxygen-enriched gas 50 in the oxygen-containing gas 56 and / or for controlling the flow rate of the ammonia gas stream 32, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter 37 at a ratio of at least 1.2, particularly between 1.2 and 9; a first gas cooler / condenser 38 downstream of the ammonia converter 37 to produce an aqueous dilute nitric acid mixture 17 and gaseous NO. x stream 22;NO x Gas compressor 40, used to compress gaseous NO x Flow 22, to generate compressed NO at a pressure of P2 x Gas stream 24; Absorber 41, which is used to extract compressed NO from water x The NO is absorbed in gas stream 24 x Gas, to produce gas containing residual NO x Crude nitric acid stream 27 and containing NO xThe exhaust gas 5 includes an absorber exhaust gas outlet 6 for venting the exhaust gas 5; and a heat exchange system 43 located upstream of the gas cooler / condenser 38, which is used to utilize NO from the ammonia converter 37. x The heat from the gas / vapor mixture 15 heats the exhaust gas stream; a second gas cooler / condenser 39 is used to cool the compressed NO... x Gas stream 24 is supplied to absorber 41 from which vapor is separated and condensed; second oxygen-containing gases 68, 72, 77, having a pressure equal to or higher than P1 and up to P2, are used downstream of ammonia converter 37 and NO x Gas compressor 40 supplies oxygen upstream ( Figure 2A and Figure 3A (a) or (b) a pressure higher than P2, used to supply compressed NO x Gas flow 24 supplies oxygen ( Figure 2B and Figure 3B The device is used to control the flow rates of the second oxygen-containing gases 68, 72, and 77 so that the exhaust gases 5, 10, 64, 69, 80, 83, 84, and 85 contain at least 0.5% oxygen by volume; and a first pressure relief device 7, located downstream of the heat exchange system 43, for expanding the exhaust gases to generate a first expanded exhaust gas 64 with a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device 7 may at least partially contain NO. x The gas compressor 40 provides power.

[0141] The production equipment is characterized in that it further includes first and / or second devices 55, 82 for splitting gas streams, wherein (i) the first splitting device 55 is for splitting the exhaust gas stream into a first exhaust gas stream 10 and a second exhaust gas stream 80, wherein the first exhaust gas stream 10 has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with a first oxygen-enriched gas 50 and compressed air 34, and wherein the mixture of compressed air 34, the first oxygen-enriched gas 50 and the first exhaust gas stream 10 provides a first oxygen-containing gas 56, and (ii) the second splitting device 82 is for splitting the exhaust gas stream into a third exhaust gas stream 83 and a fourth exhaust gas stream 85, wherein the third exhaust gas stream 83 has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with compressed air 34 and the first oxygen-enriched gas 50, and wherein the mixture of the third exhaust gas 83, the compressed air 34 and the first oxygen-enriched gas 50 provides a second oxygen-containing gas 68, 72, 77, and wherein the second oxygen-containing gases 68, 72, 77 are downstream of the ammonia converter 37 and NO xThe gas compressor 40 is supplied upstream; or the second diverter 82 is a device for diverting the exhaust gas flow into a third exhaust gas flow 84 and a fourth gas flow 85, wherein the third exhaust gas flow 84 is in fluid communication with compressed air 34 and a first oxygen-enriched gas 50, and wherein the mixing of the third exhaust gas 83, compressed air 34 and the first oxygen-enriched gas 50, and the pressurization of the mixed third exhaust gas 83, compressed air 34 and first oxygen-enriched gas 50 in the pressurization device 78 provides a second oxygen-containing gas 68, 72, 77 with a pressure higher than P2, and wherein the second oxygen-containing gas 68, 72, 77 is in NO x Gas compressor 40 is supplied downstream and absorption tower 41 is supplied upstream.

[0142] As defined herein, oxygen-enriched gas is a gas containing more than 21 vol% oxygen, more particularly more than 30 vol%, more than 35 vol%, more than 40 vol%, more than 50 vol%, more than 60 vol%, more than 70 vol%, more than 80 vol%, more than 90 vol%, more than 95 vol%, more than 98 vol%, and more than 99 vol%, more particularly 100 vol% oxygen. Oxygen-enriched gas can be provided, for example, through an air separation unit or through a water electrolyzer.

[0143] As defined in this article, an air compressor is capable of providing at least 300,000 m³ / h. 3 / h of compressed air.

[0144] As defined herein, steam is water vapor. As defined herein, the term "flow rate" refers to volumetric flow rate or mass flow rate.

[0145] Typically, the heat exchange system 43 includes at least two heat exchangers 66, 67. Those skilled in the art will recognize that the exhaust gas flow can be diverted within the heat exchange system (e.g., between heat exchangers 66 and 67). In particular, the production apparatus further includes a heat exchange system that allows gaseous NO to... x Flow 22 or via NO x The compressed gas stream 24 exchanges heat with the exhaust gas 5.

[0146] As defined herein, the exhaust gas flow is any gas flow provided downstream of the absorber tower, between the absorber tower 41 and the communication between the first exhaust gas flow 52 and the first oxygen-enriched gas 50.

[0147] As defined herein, a flow divider is any device suitable for dividing exhaust gas flow to generate, for example, a first exhaust gas flow 10 and a second exhaust gas flow 80 or a third exhaust gas flow 83, 84 and a fourth exhaust gas flow 85. In particular, a flow divider is a T-shaped connector having one inlet and two outlets, such that gas flowing through the inlet of the T-shaped connector is divided into two gas streams with the same chemical composition.

[0148] As defined herein, a pressure relief device is any suitable device for reducing the pressure of a gas flow. Specifically, a pressure relief device is a gas expander or a gas injector. Gas injectors offer the advantage of simplifying the equipment while reducing the pressure of the exhaust gas flow processed by the injector. The exhaust gas flow processed by the gas injector is a motive gas, and the second gas fed into the injector can be, for example, ambient air at a pressure lower than that of the exhaust gas flow processed by the gas injector, such as atmospheric pressure. Specifically, the exhaust gas flow is fed into the injector as a motive gas, and the second gas fed into the injector is oxygen at a pressure lower than that of the exhaust gas flow being processed by the gas injector. Feeding air or oxygen through the gas injector helps increase the concentration in the recirculated first exhaust gas flow 10 and / or the third exhaust gas flow 83, 84, thereby reducing the demand for the first oxygen-enriched gas 50. Specifically, the exhaust gas flow is fed into the injector as a motive gas, and the second gas fed into the injector is NO. x Gas / vapor mixture 15 or gaseous NO x Flow 22.

[0149] Those skilled in the art will recognize that the device for diverting the flow can be incorporated within the pressure relief device, provided that the pressure relief device includes at least two outlets for the depressurized gas flow.

[0150] As defined herein, the device for regulating ammonia and / or oxygen concentration is any device suitable for achieving a target ammonia and / or oxygen concentration. In particular, such a device is a flow control device, especially a flow control valve or orifice or guide vane, for controlling the flow rate of the first oxygen-enriched gas 50 and / or the ammonia flow 32. Specifically, this device is an integrated process control system in which the oxygen concentration is measured, thereby determining and achieving the target oxygen flow rate by controlling the flow rate of the first oxygen-enriched gas 50. The oxygen concentration can also be determined by calculation using the oxygen concentration of the first oxygen-enriched gas 50, the flow rates of the first oxygen-enriched gas 50 and the ammonia flow 32 introduced into the system, and the relative flow rate values ​​of the mixture of the first oxygen-enriched gas 50 and the ammonia flow 32.

[0151] Typically, P1 ranges from 2 bar to 6 bar, and P2 ranges from 9 bar to 16 bar. Those skilled in the art will determine the optimal oxygen concentration in the gas entering the ammonia converter 37 and the absorber 41 so that the catalytic conversion of ammonia to nitrogen oxides proceeds optimally in the ammonia converter 37 and the NO concentration in the absorber 41. x The absorption of the gas proceeds optimally. Those skilled in the art will also weigh the benefits of increasing the oxygen content in the absorption tower 41 (i.e., reducing the tower size due to improved absorption) against the disadvantages of a higher gas volume downstream of the absorption tower 41, which means that equipment (such as a larger heat exchanger) is required to heat the exhaust gas.

[0152] The inventors have discovered that, instead of supplying only primary and secondary air as compressed air 34 provided by air compressor 36, the first tail gas stream 10 and / or the third tail gas streams 83, 84 provided by the first splitter 55 and the second splitter 82, respectively, can be recirculated, particularly when controlling the oxygen content of the recirculated tail gas streams. A first oxygen-enriched gas 50 and a second oxygen-containing gas 68, each at pressure P1, supply oxygen to the ammonia converter 37 and the absorption tower 41 such that even with a reduced amount of compressed air 34 provided by air compressor 36, the oxygen concentration in the ammonia converter 37 and the absorption tower 41 is at least equal to the oxygen concentration in a state-of-the-art dual-pressure nitric acid plant. Therefore, a separate supply of high-pressure oxygen or oxygen-enriched gas ensures that the oxygen and ammonia concentrations in the ammonia converter allow for the production of commercial-grade nitric acid. Those skilled in the art will recognize that the first oxygen-enriched gas 50 can be compressed by air compressor 36 if the pressure of the first oxygen-containing gas 50 is such that the pressure of the first oxygen-containing gas 56 (considering the associated pressure drop) is lower than the operating pressure of the ammonia converter 37. Then, the fluid communication between the compressed air and the first oxygen-enriched gas 50 is introduced into the air compressor 36.

[0153] Therefore, the exhaust gas can be recycled as both primary and secondary air. This reduces the supply of compressed air 34, thus reducing the amount of compressed air required and lowering the power demand on the air compressor 34. Simultaneously, the size of the air compressor 36 and the conventional second pressure relief device 60 (where the exhaust gas 5 expands in a state-of-the-art dual-pressure nitric acid unit) is reduced, resulting in a smaller equipment footprint. Furthermore, the amount of NO leaving the production equipment is also reduced. x Emissions. Therefore, the size required to treat these NO emissions is reduced compared to the corresponding state-of-the-art dual-pressure nitric acid equipment. x The size of the emission treatment unit.

[0154] In one embodiment of the production equipment according to the present disclosure, the production equipment further includes means for controlling the flow rates of the first tail gas flow and / or the third tail gas flow 10, 83, 84.

[0155] Controlling the flow rate of the first tail gas 10 allows for further control of the pressure and temperature inside the ammonia converter 37. Similarly, controlling the flow rate of the third tail gases 83 and 84 allows for further control of the pressure and temperature inside the absorber tower 41.

[0156] In one embodiment of the production equipment according to the present disclosure, the production equipment further includes one or more of the following: a steam turbine 51, wherein the steam turbine may be at least partially an air compressor and / or NO. xGas compressor 40 provides power; heat exchanger 79 is used to exchange heat between the first expanded tail gas 64 and the tail gas flow 5, particularly the tail gas flow that is colder than the first expanded tail gas, wherein the first expanded tail gas 64 leaves the heat exchanger 79 at a temperature below 300°C, and wherein the first expanded tail gas 64 after heat exchange with the tail gas 5 is further supplied to the first diversion device 55, particularly wherein the first expanded tail gas 64 downstream of the heat exchanger 79 is in direct fluid communication with the first diversion device 55; and / or the tail gas 5 at the outlet 6 of the absorber tower 41 is diverted into a third tail gas flow 83, 84 and a fourth tail gas flow 85; NO removal x The processing unit 70; and the second pressure relief device 60, which is used to expand the second exhaust gas 80 to atmospheric pressure to generate a second expanded exhaust gas 69.

[0157] As defined herein, a device for converting steam into power is any device used to obtain power from steam. In particular, these devices are steam turbines connected to a generator.

[0158] Advantageously, the first diversion device 55 and / or the second diversion device 82 are located downstream of the heat exchange system 43. In fact, both the first tail gas stream 10 and the second tail gas stream 80 are at their optimal temperatures. This means that the first tail gas stream 10 is at a temperature below 300°C, allowing it to be fed into the ammonia converter 37 without needing to regulate the amount of ammonia fed through stream 32 to maintain the operable temperature of the ammonia converter 37. Typically, the ammonia converter operates in the temperature range of 800°C to 950°C. Furthermore, the location of the first diversion device 55 downstream of the heat exchange system 43 imparts an optimal temperature for the second tail gas stream 80 to expand, for example, to provide a temperature suitable for use at least partially for the air compressor 36 or NO. x The gas compressor 40 provides optimal energy for power.

[0159] Furthermore, the presence of the steam turbine 51 allows for the recovery of heat from the steam generated in the ammonia converter 37, and this recovered heat can be at least partially used to power the air compressor 36 or NO. x The gas compressor 40 provides power.

[0160] Specifically, the exhaust gas 5 exiting outlet 6 of absorber tower 41 is heated in heat exchanger 73, particularly first in heat exchanger 67 of heat exchange system 43, and then in heat exchanger 73, from an initial temperature in the range of 20°C to 250°C to a temperature in the range of 100°C to 450°C. Subsequently, the exhaust gas exiting heat exchanger 73 is heated in heat exchange system 43, particularly in heat exchanger 66 of heat exchange system 43, to a temperature in the range of 200°C to 550°C. The exhaust gas exiting heat exchanger 73 is then at an optimal temperature for NO removal.x The NO is processed in processing unit 70, and thus removed. x The processing unit 70 is located between the heat exchanger 73 and the exhaust gas heater 43. Those skilled in the art will have no difficulty selecting the NO removal unit. x The appropriate position of the processing unit 70 enables NO removal. x The operating temperature of the processing unit 70 is consistent with the temperature of the corresponding exhaust gas. (This is in the presence of NO removal.) x In the case of processing unit 70, NO leaves the production equipment via the second tail gas streams 69 and 80. x Emissions have been reduced.

[0161] Specifically, a portion of exhaust gas 5, namely the second exhaust gas streams 83 and 84 provided by the second diversion device 82, can be downstream of the ammonia converter 37 and NO, provided that the third exhaust gas stream 83 has a pressure equal to or higher than P1 and lower than P2. x The gas compressor 40 is recirculated upstream, or in the case of the third tail gas flow 84 having a pressure higher than P2 in NO. x The gas compressor 40 is recirculated downstream and the absorption tower 41 upstream, which reduces the load of secondary air supplied by the air compressor 36.

[0162] In one embodiment of the production apparatus according to the present disclosure, the production apparatus further includes a method for bleaching products containing residual NO. x A bleacher 62 provides a crude nitric acid stream 27 to a bleached nitric acid stream 75 via an outlet 71. The bleacher has a gas inlet 81 and a gas outlet 73 for exhaust gas 77. The gas inlet is in fluid communication with a high-pressure water electrolyzer 63 supplying the oxygen-enriched bleaching gas 72. The gas outlet is used when the bleacher 62 operates at a pressure equal to or higher than P1 and up to or equal to P2. Figure 3A In the case of downstream of ammonia converter 37 and NO x Any gas flow upstream of the gas compressor 40 is in fluid communication, or the bleacher 62 operates at a pressure higher than P2. Figure 3B In the case of NO x Any flow downstream of the gas compressor 40 and upstream of the absorption tower 41 is in communication, such that the supply of the second oxygen-containing gas 68 is at least partially derived from the exhaust gases 72 and 77.

[0163] In one embodiment of the production apparatus according to this disclosure, oxygen-enriched gas 50, second oxygen-containing gases 68, 72, and 77, oxygen-enriched bleaching gas 72, and oxygen-enriched waste gas 77 are at least partially provided by a high-pressure water electrolyzer 63. In other words, in a specific embodiment, the system of this disclosure includes a high-pressure water electrolyzer, wherein the high-pressure water electrolyzer, particularly its anode, is in fluid communication with a compressed air stream to provide an oxygen-enriched gas / compressed air stream mixture.

[0164] A water electrolyzer is a device used to electrolyze water, where water is broken down into oxygen and hydrogen as an electric current passes through it. This technology can be used to produce hydrogen, the main component of hydrogen fuel, as well as oxygen. A suitable high-pressure water electrolyzer may include an anode that produces oxygen according to the following reaction.

[0165] 2OH- = H2O + 1 / 2O2 + 2e-;

[0166] The cathode that produces hydrogen gas according to the following reaction,

[0167] 2H₂O + 2e⁻ = H₂ + 2OH⁻;

[0168] An electrolyte consisting of an alkaline solution (such as potassium hydroxide); and a porous membrane separating the anode and cathode to prevent hydrogen and oxygen from mixing and forming an explosive mixture. Alternatively, the anode and cathode can be separated by a solid polymer electrolyte (such as the fluoropolymer Nafion), which provides selective transport of protons from the anode to the cathode, electrical insulation between the anode and cathode, and prevents hydrogen and oxygen from mixing and forming an explosive mixture.

[0169] The anode and cathode can be made of nickel or steel, or mixtures thereof. Alternatively, to enhance the electrode reaction, the anode and cathode can contain catalysts made of iridium and platinum, respectively. The diaphragm, an electrically insulating material, is based on, for example, zirconium oxide. The diaphragm has a porosity that allows it to form a barrier against the transport of hydrogen and oxygen bubbles while containing a continuous permeable liquid electrolyte. The anode-diaphragm-cathode assembly constitutes the electrolytic cell. Electrolytic cells are stacked in series to form the core of the electrolytic cell. The hydrogen and oxygen yield for a given stack volume is directly proportional to the current density and inversely proportional to the stack distance. Regardless of the stack volume, the hydrogen and oxygen yield is directly proportional to the total current. In addition to the stack, the electrolytic cell includes auxiliary equipment such as a rectifier, a water softening unit, a water pump and cooling system, a hydrogen purification unit, and instrumentation.

[0170] The electrolyzer is operated by applying a voltage corresponding to the latest technology, plus an overpotential, to each cell. The total voltage depends on the total number of cells constituting the electrolyzer. OH- ions generated at the cathode migrate through the electrolyte in the separator to the anode, where they are consumed by the anodic reaction. Electrons travel in the opposite direction in the external circuit. The high-pressure water electrolyzer operates at a pressure higher than P1, or higher than P2, particularly higher than 2 bar, especially as a high-pressure water electrolyzer at pressures of 9 to 30 bar, more particularly 15 to 30 bar, and can operate at temperatures of 50 to 80°C or 60 to 80°C.

[0171] Therefore, high-pressure water electrolyzers produce pressurized hydrogen at the cathode and pressurized oxygen at the anode, with both gases at pressures higher than atmospheric pressure. High-pressure electrolysis requires pressurizing the water used in the process. Since pressurizing water requires less power than pressurizing gases, high-pressure water electrolyzers can produce pressurized oxygen-enriched gas with minimal power consumption.

[0172] When containing residual NO x When crude nitric acid stream 27 is bleached, NO in the nitric acid solution... x The amount of gas and nitrous acid (HNO2) is reduced. This, in turn, leads to a reduction in the brown fumes produced in the nitric acid solution. Furthermore, the nitric acid solution provided by the bleacher is of higher quality and purer. Conveniently, when containing residual NO... x When the crude nitric acid stream 27 is bleached, the supply of the second oxygen-containing gas 68 is achieved through the oxygen-enriched bleaching gas 72, and subsequently through the bleacher 62 and the exhaust gas 77.

[0173] In one embodiment of the production apparatus according to the present disclosure, the production apparatus further includes a second oxygen-enriched gas flow 74 in direct fluid communication with any exhaust gas flow, particularly a pressurized oxygen-enriched gas flow in direct fluid communication with any exhaust gas flow upstream of the first pressure relief device 7.

[0174] The feeding of the second oxygen-enriched gas flow 74 allows for a reduction in the amount of the first oxygen-enriched gas 50 that must be supplied to the mixing unit 35. In particular, the second oxygen-enriched gas flow 74 can be fed downstream of the heat exchange system 43 and upstream of the first pressure relief device 7, which allows for the output of more power from the first pressure relief device 7.

[0175] In one embodiment of the production equipment according to the present disclosure, the production equipment further includes a first oxygen-enriched gas 50, a second oxygen-containing gas 68, 72, 77, a second oxygen-enriched gas stream 74, an oxygen-enriched bleaching gas 72, and an exhaust gas 77, which are at least partially supplied by a high-pressure water electrolyzer 63.

[0176] Conveniently, the high-pressure water electrolyzer 63 supplies oxygen to all points in the production equipment that require oxygen supply. Specifically, the oxygen supply from the electrolyzer 63 is sufficient to provide oxygen for the first oxygen-enriched gas 50, the second oxygen-enriched gas 74, the second oxygen-containing gas 68, the oxygen-enriched bleaching gas 72, and the oxygen-enriched waste gas 77. In this way, the system is simplified and can include a single oxygen source from which an oxygen-containing gas flow at the desired pressure can be generated after standard pressure regulation. Furthermore, supplying additional pressurized oxygen-enriched gas upstream of the absorption tower improves the NO concentration in the absorption tower. x The absorption of the gas leads to additional nitric acid production and reduces emissions into the atmosphere. Alternatively, the size of the absorption tower can be reduced.

[0177] Another advantage of high-pressure water electrolyzers is that they produce hydrogen simultaneously with oxygen, which can be used in nitric acid production. This hydrogen is produced in a green manner, without the traditional use of natural gas, which produces the greenhouse gas carbon dioxide (CO2). The hydrogen can then be used to produce ammonia in the Haber-Bosch unit (or commonly referred to as a syngas unit). The high-pressure water electrolyzer then allows for the integration of ammonia and nitric acid production processes.

[0178] A method for producing nitric acid

[0179] In one aspect of this disclosure, a method is disclosed for producing nitric acid in a production apparatus according to the production equipment of this disclosure with reduced power consumption and reduced emissions. The method includes the following steps: a) compressing air in an air compressor 36 to provide compressed air 34; b) supplying the compressed air 34 obtained in step a) to a mixing device 35; c) supplying an ammonia stream 32 to the mixing device 35 to produce an ammonia / oxygen-containing gas mixture 14; d) oxidizing the ammonia in the ammonia / oxygen-containing gas mixture 14 in an ammonia converter 37 at a pressure equal to or higher than P1 and lower than P2 to produce gaseous NO containing water and nitrogen oxides. x Gas / vapor mixture 15; e) Cooling gaseous NO in heat exchange system 43 and gas / cooler condenser 38 x NO in gas / vapor mixture 15 x This produces a mixture of aqueous dilute nitric acid 17 and gaseous NO. x Flow 22; f) in NO x Gas compressor 40 compresses gaseous NO x Flow 22, thereby providing pressurized NO with pressure P2 x The compressed gas stream 24 (g) absorbs pressurized gaseous NO in the absorption tower 41. x Flow 24, thereby providing residual NO x Crude nitric acid stream 27 and containing NO x The tail gas of the gas 5h) uses NO from ammonia converter 37 x The heat from the gas / steam mixture 15 heats the exhaust gas 5 in the heat exchange system 43, particularly to temperatures in the range of 150°C to 650°C; i) the compressed NO is cooled in an auxiliary gas cooler / condenser 39. x Gas flow 24, particularly providing compressed NO at temperatures ranging from 20°C to 60°C. x Gas flow 24; and j) expanding at least a portion of the exhaust gas 5 obtained in step h) in the first pressure relief device 7 to provide a first expanded exhaust gas 64.

[0180] The method is characterized by further comprising the following steps: k) splitting the tail gas flow downstream of the absorber tower 41 into a first tail gas flow 10 and a second tail gas flow 80 using a first splitting device 55, and / or splitting the tail gas flow into a third tail gas flow 83, 84 and a fourth tail gas flow 85 using a second splitting device 82; l) mixing the first tail gas flow 10 with a first oxygen-enriched gas 50 and compressed air 34 to provide a first oxygen-containing gas 56, and / or mixing the third tail gas flow 83, 84 with compressed air 34 and the first oxygen-enriched gas 50 to provide a second oxygen-containing gas 68, 72, 73, 84. 7; m) Adjust the flow rate of the first oxygen-enriched gas 50 or the ammonia gas flow 32 mixed in step l) to maintain the oxygen to ammonia molar ratio inside the ammonia converter 37 at a ratio of at least 1.2, particularly between 1.2 and 9; n) Supply the first oxygen-containing gas 56 to the mixing unit 35; o) Adjust the flow rate of the second oxygen-containing gas 68 so that the tail gas flows 5, 10, 64, 69, 80, 83, 84, 85 (downstream of the absorber tower 41) contain at least 0.5% oxygen by volume; and p) At a pressure equal to or higher than P1 and up to P2, downstream of the ammonia converter 37 and NO x Gas compressor 40 is supplied with a second oxygen-containing gas 68, 72, 77 upstream, or at a pressure higher than P2 in NO. x The second oxygen-containing gas is supplied downstream of gas compressor 40 and upstream of absorption tower 41.

[0181] Typically, P1 ranges from 2 bar to 6 bar, and P2 ranges from 9 bar to 16 bar. Those skilled in the art will determine the optimal oxygen concentration in the gas entering the ammonia converter 37 and the absorber 41 so that the catalytic conversion of ammonia to nitrogen oxides proceeds optimally in the ammonia converter 37 and the NO concentration in the absorber 41. x The absorption of the gas proceeds optimally. Those skilled in the art will also weigh the benefits of increasing the oxygen content in the absorption tower 41 (i.e., reducing the tower size due to improved absorption) against the disadvantages of a higher gas volume downstream of the absorption tower 41, which means that equipment (such as a larger heat exchanger) is required to heat the exhaust gas.

[0182] The inventors have discovered that, instead of supplying only primary and secondary air as compressed air 34 provided by air compressor 36, the first tail gas stream 10 and / or the third tail gas stream 83, 84 provided by the first diverter 55 and the second diverter 82, respectively, can be recirculated. A first oxygen-enriched gas 50 and a second oxygen-containing gas 68, each at pressure P1, supply oxygen to the ammonia converter 37 and the absorption tower 41, such that even with a reduced amount of compressed air 34 provided by air compressor 36, the oxygen concentration in the ammonia converter 37 and the absorption tower 41 is at least equal to the oxygen concentration in a state-of-the-art dual-pressure nitric acid plant. Those skilled in the art will recognize that if the pressure of the first oxygen-enriched gas 50 is such that the pressure of the first oxygen-containing gas 56 (considering the associated pressure drop) is lower than the operating pressure of the ammonia converter 37, the first oxygen-enriched gas 50 can be compressed by air compressor 36. A fluid communication between the compressed air and the first oxygen-enriched gas 50 is then introduced into the air compressor 36.

[0183] Therefore, the exhaust gas can be recycled as both primary and secondary air. This reduces the supply of compressed air 34, thus reducing the amount of compressed air required and lowering the power demand on the air compressor 34. Simultaneously, the size of the air compressor 36 and the conventional second pressure relief device 60 (where the exhaust gas 5 expands in a state-of-the-art dual-pressure nitric acid unit) is reduced, resulting in a smaller equipment footprint. Furthermore, the amount of NO leaving the production equipment is also reduced. x Emissions. Therefore, the size required to treat these NO emissions is reduced compared to the corresponding state-of-the-art dual-pressure nitric acid equipment. x The size of the emission treatment unit.

[0184] In one embodiment of the method according to this disclosure, the method further includes the step of: q) adjusting the flow rates of the first tail gas 10 and / or the third tail gas 10, 83, 84. Controlling the flow rate of the first tail gas 10 enables further control over the pressure and temperature inside the ammonia converter 37. Similarly, controlling the flow rates of the third tail gases 83, 84 enables further control over the pressure and temperature inside the absorber tower 41.

[0185] In one embodiment of the method according to this disclosure, the first exhaust gas 10 is mixed in step l), and wherein the expanded exhaust gas 64 is split in step k), and wherein the method further includes the following steps: r) heating the exhaust gas 5 obtained in step g) and the first expanded exhaust gas 64 obtained in step j) in a heat exchanger 79 before step h), thereby bringing the exhaust gas to be mixed in step l) to a temperature below 300°C; s) treating the NO removal process before step h) and after step r). xThe exhaust gas 5 obtained in the treatment unit 70; t) expanding the second exhaust gas stream 80 in the second pressure relief device 60 to provide a second expanded exhaust gas 69; and u) recovering at least a portion of the heat energy generated in the ammonia converter 37 in the steam turbine 51. More specifically, the first exhaust gas stream 10 is mixed in step l), and wherein the expanded exhaust gas 64 is split in step k), and wherein the method further includes the steps of: r) heating the exhaust gas stream obtained in step j) which is colder than the first expanded exhaust gas 64 in heat exchanger 79, thereby bringing the exhaust gas to be mixed in step l) to a temperature below 300°C; s) removing NO x The heated exhaust gas from step r) is processed in processing unit 70; the second exhaust gas 80 is expanded in the second pressure relief device 60 to provide a second expanded exhaust gas 69; and at least a portion of the heat energy generated in ammonia converter 37 is recovered in steam turbine 51.

[0186] Advantageously, the first diversion device 55 is located downstream of the heat exchange system 43. In fact, both the first tail gas stream 10 and the second tail gas stream 80 are at their optimal temperatures. This means that the first tail gas stream 10 is at a temperature below 300°C, allowing it to be fed into the ammonia converter 37 without needing to regulate the amount of ammonia fed through stream 32 to maintain the operable temperature of the ammonia converter 37. Typically, the ammonia converter operates in the temperature range of 800°C to 950°C. Furthermore, the location of the first diversion device 55 downstream of the heat exchange system 43 imparts an optimal temperature for the second tail gas stream 80 to expand, providing a temperature suitable for use at least partially for the air compressor 36 or NO. x The gas compressor 40 provides optimal energy for power.

[0187] Furthermore, the presence of the steam turbine 51 allows for the recovery of heat from the steam generated in the ammonia converter 37, and this recovered heat can be at least partially used to power the air compressor 36 or NO. x The gas compressor 40 provides power.

[0188] Specifically, the exhaust gas 5 exiting outlet 6 of absorber tower 41 is heated in heat exchanger 73, particularly in heat exchanger 67 of heat exchange system 43, and then heated in heat exchanger 73 from an initial temperature in the range of 20°C to 250°C to a temperature in the range of 100°C to 450°C. Subsequently, the exhaust gas exiting heat exchanger 79 is heated in heat exchange system 43, particularly in heat exchanger 66 of heat exchange system 43, to a temperature in the range of 200°C to 550°C. Then, the exhaust gas exiting heat exchanger 79 is at an optimal temperature for NO removal. x The NO is processed in processing unit 70, and thus removed. xThe processing unit 70 is located between the heat exchanger 73 and the exhaust gas heater 43. Those skilled in the art will have no difficulty selecting the NO removal unit. x The appropriate position of the processing unit 70 enables NO removal. x The operating temperature of the processing unit 70 is consistent with the temperature of the corresponding exhaust gas. (This is in the presence of NO removal.) x In the case of processing unit 70, NO leaves the production equipment via the second tail gas streams 69 and 80. x Emissions have been reduced.

[0189] Specifically, a portion of exhaust gas 5, namely the second exhaust gas streams 83 and 84 provided by the second diversion device 82, can be downstream of the ammonia converter 37 and NO, provided that the third exhaust gas stream 83 has a pressure equal to or higher than P1 and lower than P2. x The gas compressor 40 is recirculated upstream, or in the case of the third tail gas flow 84 having a pressure higher than P2 in NO. x The gas compressor 40 is recirculated downstream and the absorption tower 41 upstream, which reduces the load of secondary air supplied by the air compressor 36.

[0190] In one embodiment of the method according to this disclosure, the method further includes the following steps: v) bleaching the residue containing NO obtained in step g) in bleacher 62. x The crude nitric acid stream 27 is produced, thus generating a bleached nitric acid stream 75. When it contains residual NO... x When crude nitric acid stream 27 is bleached, NO in the nitric acid solution... x The amount of gaseous nitrous acid (HNO2) is reduced. This, in turn, leads to a reduction in the brown fumes produced in the nitric acid solution. Furthermore, the nitric acid solution provided by the bleacher is of higher quality and purer. Specifically, oxygen-enriched gas, such as that provided by a high-pressure water electrolyzer, can be supplied to the bleacher 62 as bleaching gas 72, thereby generating bleaching waste gas 77, which is then mixed with gaseous NOx streams 22 and 24. In this way, the oxygen-enriched bleaching gas is effectively utilized to increase the oxygen content in the absorption tower 41, thereby increasing the NO content in step g). x The gas is absorbed, and the corresponding air emissions are reduced. Specifically, the oxygen-enriched bleaching gas 72 is provided by a high-pressure water electrolyzer 63: since the energy required to pressurize water is less than that required to pressurize oxygen, pressurized oxygen is obtained with minimal power consumption. Conveniently, when containing residual NO... x When the crude nitric acid stream 27 is bleached, the supply of the second oxygen-containing gas 68 is achieved through the oxygen-enriched bleaching gas 72, and subsequently through the bleacher 62 and the exhaust gas 77.

[0191] In one embodiment of the method according to this disclosure, the method further includes the step of: w) supplying a second oxygen-enriched gas flow 74, particularly as a pressurized oxygen-enriched gas flow, to the exhaust gas flow, especially upstream of the first pressure relief device 7. Feeding the second oxygen-enriched gas flow 74 allows for a reduction in the amount of first oxygen-enriched gas 50 that must be supplied to the mixing unit 35. Specifically, the second oxygen-enriched gas flow 74 can be fed downstream of the heat exchange system 43 and upstream of the first pressure relief device 7, which allows for greater power output from the first pressure relief device 7.

[0192] In one embodiment of the method according to this disclosure, the method further includes the following steps: x) operating the high-pressure water electrolyzer 63, for example, at a temperature of 50°C to 80°C or 60°C to 80°C and a pressure of 9 bar to 30 bar, preferably 15 bar to 30 bar, thereby generating pressurized oxygen; and y) providing at least a portion of the first oxygen-enriched gas 50, the second oxygen-containing gases 68, 72, 77, the second oxygen-enriched gas 74, the oxygen-enriched bleaching gas 72, and the oxygen-enriched waste gas 77 by the oxygen generated by the water electrolyzer 63 in step x). In some embodiments, the pressurized oxygen or oxygen-enriched gas 50 is mixed with a compressed air stream. Conveniently, the high-pressure water electrolyzer 63 provides oxygen to all the various points in the production equipment that require oxygen feeding. In particular, the oxygen supply from the electrolyzer 63 is sufficient to provide all the oxygen for the first oxygen-enriched gas 50, the second oxygen-enriched gas 74, the second oxygen-containing gas 68, the oxygen-enriched bleaching gas 72, and the oxygen-enriched waste gas 77. In this way, the system is simplified and can include a single oxygen source from which an oxygenated gas flow at the desired pressure can be generated after standard pressure regulation.

[0193] Another advantage of high-pressure water electrolyzers is that they produce hydrogen simultaneously with oxygen, which can be used in nitric acid production. This hydrogen is produced in a green manner, without the traditional use of natural gas, which produces the greenhouse gas carbon dioxide (CO2). The hydrogen can then be used to produce ammonia in the Haber-Bosch unit (or commonly referred to as a syngas unit). The high-pressure water electrolyzer then allows for the integration of ammonia and nitric acid production processes.

[0194] The purpose of the production equipment disclosed herein

[0195] In one aspect of this disclosure, the use of the production equipment disclosed herein for performing the methods of this disclosure is disclosed.

[0196] Methods for retrofitting state-of-the-art dual-pressure nitric acid production equipment

[0197] In one aspect of this disclosure, a production apparatus for producing nitric acid is disclosed, the apparatus comprising an air compressor 36 for providing a compressed air stream 34; a mixing device 35 for mixing the compressed air stream 34 with an ammonia stream 32 to produce an ammonia / oxygen-containing gas mixture 14; and an ammonia converter 37, operable at a pressure equal to or higher than P1 and lower than P2, for oxidizing the ammonia in the ammonia / oxygen-containing gas mixture 14 to produce NO containing water and nitrogen oxides. x Gas / vapor mixture 15; a first gas cooler / condenser 38 downstream of ammonia converter 37 to produce an aqueous dilute nitric acid mixture 17 and gaseous NO. x stream 22;NO x Gas compressor 40, used to compress gaseous NO x Flow 22, to generate compressed NO at a pressure of P2 x Gas stream 24; Absorber 41, which is used to extract compressed NO from water x The NO is absorbed in gas stream 24 x Gas, to produce gas containing residual NO x Crude nitric acid stream 27 and containing NO x The exhaust gas 5 includes an absorber exhaust outlet 6 for venting the exhaust gas 5; and a heat exchange system 43 for utilizing NO from the ammonia converter 37. x The heat from the gas / vapor mixture 15 heats the exhaust gas stream; a second gas cooler / condenser 39 is used to cool the compressed NO... x Gas stream 24 is separated from and vapors are condensed before absorption in absorber 41; and a first pressure relief device 7 is used to expand the exhaust gas stream to produce a first expanded exhaust gas 64 with a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device 7 can be at least partially NO. x A gas compressor 40 and / or a pressurizing device 78 provide power; a method for converting production equipment into production equipment according to this disclosure.

[0198] The modification method includes the following steps: introducing a supply of a first oxygen-enriched gas 50 in fluid communication with compressed air 34; introducing a device (not shown) for adjusting the ammonia concentration and / or oxygen concentration in the ammonia converter 37, particularly a device for controlling the flow rate of the first oxygen-enriched gas 50 in the oxygen-containing gas 56 and / or a device for controlling the flow rate of the ammonia flow 32, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter 37 at a ratio of at least 1.2; introducing a supply of a second oxygen-containing gas 68, 72, 77, the second oxygen-containing gas having: (a) a pressure equal to or higher than P1 and up to P2, for use in NO xThe gas compressor 40 is supplied with oxygen upstream or (b) at a pressure higher than P2 for supplying compressed NO. x Gas flow 24 supplies oxygen, such that exhaust gases 5, 10, 64, 69, 80, 83, 84, 85 contain at least 0.5% oxygen by volume; a first device 55 for splitting the exhaust gases and / or a second device 82 for splitting the exhaust gases are introduced downstream of absorber tower 41, wherein (i) the first splitting device 55 is a device for splitting the exhaust gases into a first exhaust gas flow 10 and a second exhaust gas flow 80, and wherein the first exhaust gas flow 10 has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with a first oxygen-enriched gas 50 and compressed air 34, and wherein compressed air 34, The mixture of the first oxygen-enriched gas 50 and the first tail gas 10 provides a first oxygen-containing gas 56, and (ii) the second diversion device 82 is a device for diverting the tail gas into a third tail gas 83 and a fourth tail gas 85, wherein the third tail gas 83 has a pressure equal to or higher than P1 and up to P2 and is in fluid communication with compressed air 34 and the first oxygen-enriched gas 50, and wherein the mixture of the third tail gas 83, compressed air 34 and the first oxygen-enriched gas 50 provides a second oxygen-containing gas 68, 72, 77, and wherein the second oxygen-containing gases 68, 72, 77 are downstream of the ammonia converter 37 and NO x The gas compressor 40 is supplied upstream; or the second diverter 82 is a device for diverting the exhaust gas flow into a third exhaust gas flow 84 and a fourth gas flow 85, wherein the third exhaust gas flow 84 is in fluid communication with compressed air 34 and a first oxygen-enriched gas 50, and wherein the mixing of the third exhaust gas 83, compressed air 34 and the first oxygen-enriched gas 50, and the pressurization of the mixed third exhaust gas 83, compressed air 34 and first oxygen-enriched gas 50 in the pressurization device 78 provides a second oxygen-containing gas 68, 72, 77 with a pressure higher than P2, and wherein the second oxygen-containing gas 68, 72, 77 is in NO x Gas compressor 40 is supplied downstream and absorption tower 41 is supplied upstream.

[0199] As defined herein, oxygen-enriched gas is a gas containing more than 21 vol% oxygen, more particularly more than 30 vol%, more than 35 vol%, more than 40 vol%, more than 50 vol%, more than 60 vol%, more than 70 vol%, more than 80 vol%, more than 90 vol%, more than 95 vol%, more than 98 vol%, and more than 99 vol%, more particularly 100 vol% oxygen. Oxygen-enriched gas can be provided, for example, through an air separation unit or through a water electrolyzer.

[0200] As defined in this article, an air compressor is capable of providing at least 300,000 m³ / h. 3 / h of compressed air.

[0201] As defined herein, steam is water vapor. As defined herein, the term "flow rate" refers to volumetric flow rate or mass flow rate.

[0202] Typically, the heat exchange system 43 includes at least two heat exchangers 66, 67. Those skilled in the art will recognize that the exhaust gas flow can be diverted within the heat exchange system (e.g., between heat exchangers 66 and 67). In particular, the production apparatus further includes a heat exchange system that allows gaseous NO to... x Flow 22 or via NO x The compressed gas stream 24 exchanges heat with the exhaust gas 5.

[0203] As defined herein, the exhaust gas flow is any gas flow provided downstream of the absorber tower, between the absorber tower 41 and the communication between the first exhaust gas flow 52 and the first oxygen-enriched gas 50.

[0204] As defined herein, a flow divider is any device suitable for dividing exhaust gas flow to generate, for example, a first exhaust gas flow 10 and a second exhaust gas flow 80, or a third exhaust gas flow 83, 84 and a fourth exhaust gas flow 85. In particular, a flow divider is a T-shaped connector having one inlet and two outlets, such that gas flowing through the inlet of the T-shaped connector is divided into two gas streams with the same chemical composition.

[0205] As defined herein, a pressure relief device is any suitable device for reducing the pressure of a gas flow. Specifically, a pressure relief device is a gas expander or a gas injector. Gas injectors offer the advantage of simplifying the equipment while reducing the pressure of the exhaust gas flow processed by the injector. The exhaust gas flow processed by the gas injector is a motive gas, and the second gas fed into the injector can be, for example, ambient air at a pressure lower than that of the exhaust gas flow processed by the gas injector, such as atmospheric pressure. Specifically, the exhaust gas flow is fed into the injector as a motive gas, and the second gas fed into the injector is oxygen at a pressure lower than that of the exhaust gas flow being processed by the gas injector. Feeding air or oxygen through the gas injector helps increase the concentration in the recirculated first exhaust gas flow 10 and / or the third exhaust gas flow 83, 84, thereby reducing the demand for the first oxygen-enriched gas 50. Specifically, the exhaust gas flow is fed into the injector as a motive gas, and the second gas fed into the injector is NO. x Gas / vapor mixture 15 or gaseous NO x Flow 22.

[0206] Those skilled in the art will recognize that the device for diverting the flow can be incorporated within the pressure relief device, provided that the pressure relief device includes at least two outlets for the depressurized gas flow.

[0207] As defined herein, the device for regulating ammonia and / or oxygen concentration is any device suitable for achieving a target ammonia and / or oxygen concentration. In particular, such a device is a flow control device, especially a flow control valve or orifice or guide vane, for controlling the flow rate of the first oxygen-enriched gas 50 and / or the ammonia flow 32. Specifically, this device is an integrated process control system in which the oxygen concentration is measured, thereby determining and achieving the target oxygen flow rate by controlling the flow rate of the first oxygen-enriched gas 50. The oxygen concentration can also be determined by calculation using the oxygen concentration of the first oxygen-enriched gas 50, the flow rates of the first oxygen-enriched gas 50 and the ammonia flow 32 introduced into the system, and the relative flow rate values ​​of the mixture of the first oxygen-enriched gas 50 and the ammonia flow 32.

[0208] Typically, P1 ranges from 2 bar to 6 bar, and P2 ranges from 9 bar to 16 bar. Those skilled in the art will determine the optimal oxygen concentration in the gas entering the ammonia converter 37 and the absorber 41 so that the catalytic conversion of ammonia to nitrogen oxides proceeds optimally in the ammonia converter 37 and the NO concentration in the absorber 41. x The absorption of the gas proceeds optimally. Those skilled in the art will also weigh the benefits of increasing the oxygen content in the absorption tower 41 (i.e., reducing the tower size due to improved absorption) against the disadvantages of a higher gas volume downstream of the absorption tower 41, which means that equipment (such as a larger heat exchanger) is required to heat the exhaust gas.

[0209] Example

[0210] 1. 24% exhaust gas recirculation using an additional exhaust gas expander.

[0211] Reference Figure 3AAmbient air 4 is compressed in air compressor 36 to provide compressed air 34. Ammonia 32 is mixed with compressed air 34 in mixing unit 35. The oxygen to ammonia molar ratio at the inlet of the mixing unit is at least 1.2. The resulting ammonia / air mixture 14 is fed into ammonia converter 37, which operates at a temperature in the range of 800°C to 950°C and a pressure of 5.2 bar. In ammonia converter 37, ammonia is oxidized by a mixed platinum / rhodium catalyst to obtain a low-pressure NOx gas / vapor mixture 15 containing water and nitrogen oxides (NO). The heat energy of the mixture exiting the ammonia converter is recovered using a steam turbine 51 and also by heating the exhaust gas 5 as described below. The NOx gas / stream mixture is then cooled to the water condensation temperature in a water cooler / condenser 38, and an aqueous dilute nitric acid mixture 17 is separated from the gaseous NOx stream 18 and sent to absorber 41. Subsequently, the gaseous NOx stream is further oxidized to convert NO into NO2 and N2O4, providing a gaseous NOx stream 22, which is compressed to 12 bar in the NOx gas compressor 40, thereby producing a pressurized NOx gaseous stream 24. The pressurized NOx gaseous stream 24 is cooled in a cooler / condenser 39 and also sent to an absorber 41. Within the absorber unit 41, the NOx gas reacts with water to produce tail gas 5 and a crude nitric acid stream 27 containing residual NOx gas. The heat from the gaseous NOx stream 24 is used to heat the tail gas 5 to 575°C in the tail gas heater 43, thereby producing a heated tail gas. The heated tail gas is diverted through a T-tube 55. After being split in T-tube 55, 24% of the heated tail gas is expanded on tail gas expander 7 to provide expanded tail gas 64, which is then mixed with compressed air stream 34 and oxygen-enriched gas 50 at a pressure of 8 bar. The resulting compressed air 34 / oxygen-enriched gas 50 / expanded tail gas 64 is then mixed with ammonia 32 in mixing unit 35. The steps following the mixing in mixing unit 35 are repeated. The oxygen to ammonia molar ratio at the inlet of the mixing unit is at least 1.2. The remaining 76% of the heated tail gas is sent to an additional tail gas expander 60. The residual NOx gas in the crude nitric acid stream 27 is vaporized with gaseous medium 72, which is oxygen produced by water electrolyzer 63 located within bleaching unit 62, which operates at approximately the same pressure (5.2 bar) as the ammonia converter. Water electrolysis cell 63 provides oxygen-enriched gas 50 and oxygen between ammonia converter 37 and absorption tower 41, such that the oxygen concentration in exhaust gas 5 is at least 0.5% by volume. The air compressor 36 and NOx compressor 40 are both driven by exhaust gas expander 7, an additional exhaust gas expander 60, and steam turbine 51. The net power associated with air compressor 36, NOx gas compressor 40, exhaust gas expander 7, and additional exhaust gas expander 60 is 37 kW / h / t 100% HNO3. This power is generated by steam turbine 51.

[0212] 2. Comparison example: Exhaust gas is no longer recirculated.

[0213] Ambient air 4 is compressed in air compressor 36 to provide compressed air stream 34. Ammonia 32 is mixed with oxygen-enriched gas / compressed air stream mixture 53 in mixing unit 35, and the resulting ammonia / air mixture 14 is fed into ammonia converter 37 operating at 5.2 bar pressure. The oxygen to ammonia molar ratio in mixing unit 35 is at least 1.2. In ammonia converter 37, ammonia is oxidized by a mixed platinum / rhodium catalyst to obtain a low-pressure NOx gas / vapor mixture 15 containing water and nitrogen oxides (NO). The heat energy of the mixture exiting the ammonia converter is recovered using steam turbine 51. The NOx gas / stream mixture is then cooled to water condensation temperature in water cooler / condenser 38, and an aqueous dilute nitric acid mixture 17 is separated from the gaseous NOx stream 18 and sent to absorber 41. Subsequently, the gaseous NOx stream is further oxidized to convert NO into NO2 and N2O4, providing a gaseous NOx stream 22, which is compressed to 12 bar in the NOx gas compressor 40, thereby producing a pressurized NOx gaseous stream 24. The pressurized NOx gaseous stream 24 is cooled in a cooler / condenser 39 and also sent to an absorber 41. Inside the absorber 41, the high-pressure NOx gas reacts with water to produce tail gas 5 and a crude nitric acid stream 27 containing residual NOx gas. x The heat from stream 24 is used to heat exhaust gas 5 to 450°C in exhaust gas heater 43. All exhaust gas stream 5 is then sent to exhaust gas expander 7. Residual NOx gas in crude nitric acid stream 27 is then vaporized with compressed air 34 inside bleaching unit 62. Bleaching unit 62 typically operates at approximately the same pressure as the ammonia converter, i.e., 5.2 bar. The air compressor 36 and NOx compressor 40 are driven by exhaust gas expander 7 and steam turbine 51. The net power associated with air compressor 36, NOx gas compressor 40, and exhaust gas expander 7 is 75.5 kW / h / t 100% HNO3. This power is generated by steam turbine 51.

[0214] Therefore, compared to Example 1, recycling 24% of the exhaust gas can save a net power of 39 kWh / t 100% HNO3 (50%).

Claims

1. A production apparatus for producing nitric acid with reduced power consumption and emissions, comprising: • An air compressor that provides compressed air; • The supply of a first oxygen-enriched gas, wherein the mixture of the first oxygen-enriched gas and compressed air provides a portion of the first oxygen-containing gas; • A mixing device for mixing the first oxygen-containing gas with an ammonia gas stream to produce an ammonia / oxygen-containing gas mixture; • An ammonia converter configured to operate at a pressure equal to or higher than P1 and lower than P2 for oxidizing ammonia in the ammonia / oxygen-containing gas mixture to produce a NOx gas / vapor mixture containing water and nitrogen oxides; • A device for adjusting the ammonia concentration and / or oxygen concentration in the ammonia converter, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2; • A first gas cooler / condenser downstream of the ammonia converter to produce an aqueous dilute nitric acid mixture and a gaseous NOx stream; • A NOx gas compressor, used to compress the gaseous NOx stream to produce compressed NO at a pressure of P2. x Gas flow; • Absorption tower, the absorption tower being used to remove the compressed NO from water x Absorption of NO in gas stream x Gas, to produce gas containing residual NO x crude nitric acid gas stream and NO x The exhaust gas of the gas includes the exhaust gas outlet of the absorption tower used to vent the exhaust gas; • A heat exchange system located upstream of the gas cooler / condenser, the heat exchange system being used to utilize the NO from the ammonia converter x The heat from the gas / vapor mixture heats the exhaust gas stream; • A second gas cooler / condenser, the second gas cooler / condenser being used to cool the compressed NO x The gas stream is separated from the stream and the vapor is condensed before being supplied to the absorption tower; • A second oxygen-containing gas, the second oxygen-containing gas having: a) A pressure equal to or higher than P1 but not exceeding P2, used downstream of the ammonia converter and the NO x The gas compressor supplies oxygen upstream; or b) A pressure higher than P2, used to supply the compressed NO x The gas flow supplies oxygen; • A device for controlling the flow rate of the second oxygen-containing gas so that the exhaust gas contains at least 0.5% oxygen by volume; as well as A first pressure relief device, located downstream of the heat exchange system, is used to expand the exhaust gas to generate a first expanded exhaust gas with a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device is configured to at least partially supply the NO. x The gas compressor and / or the air compressor provides power; The production equipment is characterized in that it further comprises: • First and / or second means for splitting a gas stream, wherein (i) The first diversion device is a device for diverting the exhaust gas into a first exhaust gas and a second exhaust gas, wherein the first exhaust gas has a pressure equal to or higher than P1 and not exceeding P2 and is in fluid communication with the first oxygen-enriched gas and compressed air, and wherein the mixture of compressed air, the first oxygen-enriched gas and the first exhaust gas provides the first oxygen-enriched gas, and (ii) The second diversion device is used to divert the exhaust gas into a third exhaust gas and a fourth exhaust gas, wherein the third exhaust gas has a pressure equal to or higher than P1 and not exceeding P2 and is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixture of the third exhaust gas, compressed air and the first oxygen-enriched gas provides the second oxygen-containing gas, and wherein the second oxygen-containing gas is downstream of the ammonia converter and the NO x Upstream supply of gas compressors; or The second diversion device is used to split the exhaust gas flow into a third exhaust gas flow and a fourth gas flow, wherein the third exhaust gas flow is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixing of the third exhaust gas, compressed air and the first oxygen-enriched gas, and the pressurization of the mixed third exhaust gas, compressed air and the first oxygen-enriched gas in the pressurization device provide a second oxygen-containing gas with a pressure higher than P2, and wherein the second oxygen-containing gas in the NO x The gas is supplied downstream of the gas compressor and upstream of the absorption tower.

2. The production equipment according to claim 1, wherein the production equipment further includes means for controlling the flow rate of the first exhaust gas flow and / or the third exhaust gas flow.

3. The production equipment according to any one of claims 1 to 2, wherein the production equipment further comprises one or more of the following: • Steam turbine, wherein the steam turbine is configured to be at least partially for the NO x The gas compressor and / or the air compressor provides power; • A heat exchanger for exchanging heat between the first expanded exhaust gas and an exhaust gas stream that is cooler than the first expanded exhaust gas, wherein the first expanded exhaust gas exits the heat exchanger at a temperature below 300°C, and wherein: - The first expanded exhaust gas downstream of the heat exchanger is in direct fluid communication with the first diversion device; and / or - The exhaust gas stream, which is colder than the first expanded exhaust gas, is split into a third exhaust gas stream and a fourth exhaust gas stream; ·Removing NO x Processing unit; and • A second pressure relief device, which is used to expand the second exhaust gas to atmospheric pressure to generate a second expanded exhaust gas.

4. The production equipment according to any one of claims 1 to 2, further comprising a bleaching unit for bleaching the material containing residual NO. x A crude nitric acid stream is provided to supply a bleached nitric acid stream. The bleacher has an inlet and an exhaust outlet. The inlet is in fluid communication with a high-pressure water electrolyzer supplying oxygen-enriched bleaching gas. If the bleacher operates at a pressure equal to or higher than P1 and not exceeding P2, the exhaust outlet is downstream of the ammonia converter and the NO... x Any gas flow upstream of the gas compressor is in fluid communication, or if the bleacher operates at a pressure higher than P2, the exhaust outlet is connected to the NO... x Any flow downstream of the gas compressor and upstream of the absorption tower is in communication, such that the supply of the second oxygen-containing gas is at least partially derived from the exhaust gas.

5. The production equipment according to any one of claims 1 to 2, further comprising a second oxygen-enriched gas flow in direct fluid communication with any exhaust gas flow.

6. The production equipment according to any one of claims 1 to 2, wherein the first oxygen-enriched gas and the second oxygen-containing gas are at least partially provided by a high-pressure water electrolyzer.

7. The production equipment according to claim 5, wherein the second oxygen-enriched gas of the second oxygen-enriched gas flow is provided at least in part by a high-pressure water electrolyzer.

8. The production equipment according to claim 4, wherein the oxygen-enriched bleaching gas and the waste gas are at least partially provided by a high-pressure water electrolyzer.

9. The production equipment according to claim 1, wherein the device for adjusting the ammonia concentration and / or oxygen concentration in the ammonia converter is a device for controlling the flow rate of the first oxygen-enriched gas in the oxygen-containing gas and / or a device for controlling the flow rate of the ammonia gas stream.

10. The production equipment according to claim 5, wherein the second oxygen-enriched gas flow is a pressurized oxygen-enriched gas flow in direct fluid communication with any exhaust gas flow upstream of the first pressure relief device.

11. A method for producing nitric acid with reduced power consumption and reduced emissions in a production apparatus according to any one of claims 1 to 10, comprising the following steps: a) Compressing air in the air compressor to provide compressed air; b) Supply the compressed air obtained in step a) to the mixing device; c) Supplying the ammonia gas stream to the mixing device to generate the ammonia / oxygen-containing gas mixture; d) Oxidizing the ammonia in the ammonia / oxygen-containing gas mixture in the ammonia converter at a pressure equal to or higher than P1 and lower than P2, thereby producing the gaseous NO containing water and nitrogen oxides. x Gas / vapor mixture; e) Cooling the gaseous NO in the heat exchange system and the gas / cooler condenser x The NO in the gas / vapor mixture x The gas, thereby producing an aqueous dilute nitric acid mixture and the gaseous NO. x flow; f) in the NO x The gaseous NO is compressed in the gas compressor x The flow thus provides pressurized NO with pressure P2. x Compressed gas flow; g) Absorb pressurized gaseous NO in the absorption tower. x The flow thus provides the substance containing residual NO x crude nitric acid gas stream and NO x The exhaust gas; h) Using the NO from the ammonia converter x The heat from the gas / steam mixture heats the exhaust gas in the heat exchange system; i) Cooling the compressed NO in an auxiliary gas cooler / condenser x Gas flow; as well as j) Expand at least a portion of the exhaust gas obtained in step h) in the first pressure relief device to provide the first expanded exhaust gas; The method is characterized by further comprising the following steps: k) The exhaust gas is split into a first exhaust gas flow and a second exhaust gas flow using a first splitting device, and / or the exhaust gas flow is split into a third exhaust gas flow and a fourth exhaust gas flow using a second splitting device; l) Mix the first exhaust gas stream with the first oxygen-enriched gas and compressed air to provide the first oxygen-containing gas, and / or mix the third exhaust gas stream with compressed air and the first oxygen-enriched gas to provide the second oxygen-containing gas; m) Adjust the flow rate of the first oxygen-enriched gas or the flow rate of the ammonia gas mixed in step l) to maintain the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.

2. n) Supply the first oxygen-containing gas to the mixing unit; o) Adjust the flow rate of the second oxygen-containing gas so that the exhaust gas contains at least 0.5% oxygen by volume; and p) Under a pressure equal to or higher than P1 but not exceeding P2, downstream of the ammonia converter and the NO x Upstream of the gas compressor, or at a pressure higher than P2 in the NO x The second oxygen-containing gas is supplied downstream of the gas compressor and upstream of the absorption tower.

12. The method of claim 11, further comprising the following steps: q) Adjust the flow rate of the first tail gas flow and / or the third tail gas flow.

13. The method according to any one of claims 11 to 12, wherein the first exhaust gas is mixed in step l), and wherein the first expanded exhaust gas is split in step k), and wherein the method further comprises the following steps: r) In the heat exchanger, the exhaust gas, which is colder than the first expanded exhaust gas, is heated together with the first expanded exhaust gas obtained in step j) so that the exhaust gas to be mixed in step l) reaches a temperature below 300°C. s) in NO removal x The exhaust gas stream heated in step r) is processed in the processing unit; t) In the second pressure relief device, the second exhaust gas is expanded to provide a second expanded exhaust gas; and u) Recover at least a portion of the heat energy generated in the ammonia converter in the steam turbine.

14. The method according to any one of claims 11 to 12, wherein the third exhaust gas is mixed in step l), and wherein the exhaust gas obtained in step g) is split into a third exhaust gas and a fourth exhaust gas in step k).

15. The method according to any one of claims 11 to 12, further comprising the following steps: v) The residue containing NO obtained in step g) by bleaching in a bleacher x The crude nitric acid stream of gas is converted into a bleached nitric acid stream.

16. The method according to any one of claims 11 to 12, further comprising the following steps: w) Supply a second oxygen-enriched gas stream to the exhaust stream.

17. The method according to any one of claims 11 to 12, further comprising the following steps: x) Operate a high-pressure water electrolysis cell to generate pressurized oxygen; as well as y) The oxygen generated by the water electrolysis cell described in step x) provides at least a portion of the first oxygen-enriched gas, the second oxygen-enriched gas, the second oxygen-containing gas, the oxygen-enriched bleaching gas, and the oxygen-enriched waste gas.

18. The method according to claim 11, wherein, In step h), the NO from the ammonia converter is used. x The heat from the gas / steam mixture heats the exhaust gas to a temperature ranging from 150°C to 650°C in the heat exchange system.

19. The method according to claim 11, wherein, In step i), the compressed NO is cooled in an additional gas cooler / condenser. x A gas flow, thereby providing the compressed NO at a temperature ranging from 20°C to 60°C. x Gas flow.

20. The method of claim 16, wherein, The second oxygen-enriched gas flow is supplied to the tail gas flow as a pressurized oxygen-enriched gas flow.

21. The method according to claim 16, wherein, A second oxygen-enriched gas flow is supplied to the exhaust gas flow upstream of the first pressure relief device.

22. Use of the production equipment according to any one of claims 1 to 10 for performing the method according to any one of claims 11 to 21.

23. A method for converting existing production equipment for nitric acid production into production equipment according to any one of claims 1 to 10, The existing production equipment mentioned above includes: • An air compressor, which provides a flow of compressed air; • A mixing device for mixing a compressed air stream with an ammonia stream to produce an ammonia / oxygen-containing gas mixture; • An ammonia converter configured to operate at a pressure equal to or higher than P1 and lower than P2 for oxidizing ammonia in the ammonia / oxygen-containing gas mixture to produce NO containing water and nitrogen oxides. x Gas / vapor mixture; • A first gas cooler / condenser downstream of the ammonia converter produces an aqueous dilute nitric acid mixture and gaseous NO. x flow; • A NOx gas compressor, wherein the NOx gas compressor is used to compress the gaseous NOx stream to produce a compressed NOx gas stream at a pressure of P2; • An absorption tower for absorbing NOx gas from the compressed NOx gas stream in water to produce a product containing residual NO. x The crude nitric acid stream and the tail gas containing NOx gas, including the tail gas outlet of the absorber tower for venting the tail gas; • A heat exchange system for using NO from the ammonia converter x The heat from the gas / vapor mixture heats the exhaust gas stream; a second gas cooler / condenser is used to cool the compressed NO. x The gas stream is separated from and condensed into vapors before absorption in the absorption tower; and • A first pressure relief device, configured to expand the exhaust gas flow to generate a first expanded exhaust gas with a pressure equal to or higher than P1 and lower than P2, wherein the first pressure relief device is configured to at least partially supply the NO. x The gas compressor provides the power; The method includes the following steps: • Introduce a supply of first oxygen-enriched gas in fluid communication with compressed air; • Introduce devices for adjusting the ammonia concentration and / or oxygen concentration in the ammonia converter, particularly devices for controlling the flow rate of the first oxygen-enriched gas in the oxygen-containing gas and / or devices for controlling the flow rate of the ammonia gas flow, for maintaining the oxygen to ammonia molar ratio inside the ammonia converter at a ratio of at least 1.2; • Introducing a supply of a second oxygen-containing gas, the second oxygen-containing gas having: (a) A pressure equal to or higher than P1 but not exceeding P2, used in the NO x The gas compressor is supplied with oxygen upstream; or (b) A pressure higher than P2, used to supply the compressed NO x The gas flow supplies oxygen. This ensures that the exhaust gas contains at least 0.5% oxygen by volume; • A first device for diverting the tail gas flow and / or a second device for diverting the tail gas flow are introduced downstream of the absorption tower, wherein (i) The first diversion device is a device for diverting the exhaust gas into a first exhaust gas and a second exhaust gas, wherein the first exhaust gas has a pressure equal to or higher than P1 and not exceeding P2 and is in fluid communication with the first oxygen-enriched gas and compressed air, and wherein the mixture of compressed air, the first oxygen-enriched gas and the first exhaust gas provides the first oxygen-enriched gas. (ii) The second diversion device is used to divert the exhaust gas into a third exhaust gas and a fourth exhaust gas, wherein the third exhaust gas has a pressure equal to or higher than P1 and not exceeding P2 and is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixture of the third exhaust gas, compressed air and the first oxygen-enriched gas provides the second oxygen-containing gas, and wherein the second oxygen-containing gas is downstream of the ammonia converter and the NO x Upstream supply of gas compressors; or The second diversion device is used to split the exhaust gas flow into a third exhaust gas flow and a fourth gas flow, wherein the third exhaust gas flow is in fluid communication with compressed air and the first oxygen-enriched gas, and wherein the mixing of the third exhaust gas, compressed air and the first oxygen-enriched gas, and the pressurization of the mixed third exhaust gas, compressed air and the first oxygen-enriched gas in the pressurization device provide a second oxygen-containing gas with a pressure higher than P2, and wherein the second oxygen-containing gas in the NO x The gas is supplied downstream of the gas compressor and upstream of the absorption tower.

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