Method for producing steam

Abstract

This disclosure provides a method for producing steam in a carbamate condenser, comprising the steps of: a) providing a gas stream containing ammonia, carbon dioxide, and water to the carbamate condenser; b) providing an aqueous cooling solution to a cooling fluid inlet, obtaining a fluid composition containing an aqueous solution containing an ammonium salt from the carbamate condenser, and obtaining steam from the cooling fluid outlet of the carbamate condenser. In another aspect, this disclosure provides a method for producing a urea-containing composition.

Description

Technical Field

[0001] This disclosure relates to the field of chemical engineering, particularly urea production. Background Technology

[0002] Global urea production (chemical formula H2NCONH2) is estimated at approximately 180 million metric tons. It is primarily used as a fertilizer to provide nitrogen to plants, but it can also be used in other production processes or as an additive in diesel-powered vehicles to reduce greenhouse gas emissions.

[0003] Different production technologies are currently available, but they all rely on a common design: ammonia and carbon dioxide are mixed in a synthesis reactor at high temperatures (above 150°C) and high pressures (above 10 MPa) to produce an aqueous urea solution, which is then processed to provide a urea melt with a urea concentration higher than 95%. The urea melt can be granulated into a solid particulate composition using various techniques such as granulation and pelletizing, or it can be diluted with water to provide an aqueous urea solution.

[0004] During the processing of the solution produced by the synthesis reactor, a gas stream containing ammonia, carbon dioxide, and water is generated. To improve the overall yield of the production unit, this gas stream is returned to the synthesis reactor in liquid form. The gas stream is then directed to a heat exchanger that also receives a cooling medium, such as water, to condense the gas stream into an aqueous solution containing ammonium salts.

[0005] The heated cooling medium produced by the heat exchanger becomes a waste stream in the production unit. In conventional production units, the heated cooling medium is cooled by water or ambient air in another heat exchanger, thereby releasing heat into the atmosphere, which is highly undesirable.

[0006] Therefore, there is a need to provide a method for reducing the environmental footprint of urea production facilities.

[0007] WO2023158314A1 (Stamicarbon, 2023) discloses a urea production process in which carbamate in a medium-pressure urea solution is decomposed in the tube bundle of a high-pressure carbamate condenser, and the resulting gas is condensed in an indirect heat exchange with the urea solution to be heated, and wherein the high-pressure stripper preferably operates at a relatively low stripping efficiency.

[0008] WO2023121443A1 (Stamicarbon, 2023) discloses a urea production apparatus having a hot stripper and a high-pressure carbamate condenser with a shell space, wherein gas from the stripper is condensed in the shell space. Summary of the Invention

[0009] A method has been discovered to recover heat generated during the condensation of a gas stream containing ammonia, carbon dioxide, and water in a carbamate condenser operating at pressures below 4.0 MPa, thus preventing this heat from being released into the atmosphere. The heat generated by condensation can be used to produce steam, particularly low-pressure steam, that can be reused in urea production units.

[0010] In a first aspect, this disclosure provides a method for producing steam in a carbamate condenser, the carbamate condenser including a fluid inlet, a fluid outlet, a cooling fluid inlet, and a cooling fluid outlet, the method comprising the following steps: a) Providing a gas stream containing ammonia, carbon dioxide and water to the fluid inlet, wherein the gas stream has a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa; b) Providing an aqueous cooling solution to the cooling fluid inlet, wherein the temperature range of the aqueous cooling solution is 60 to 110°C; c) Obtaining a fluid composition from the fluid outlet, the fluid composition comprising an aqueous solution containing an ammonium salt; d) Obtain steam from the cooling fluid outlet.

[0011] In another aspect, this disclosure provides a method for producing a urea-containing composition, the method comprising the following steps: a) In the synthesis section, ammonia is reacted with carbon dioxide to produce a synthetic solution containing urea, water and ammonium carbamate. b) The synthetic solution produced in step a) generates a urea melt containing urea and water, and one or more gas streams containing ammonia, carbon dioxide and water. c) Condensing at least one of the one or more gas streams in a carbamate condenser to generate steam, thereby producing a fluid composition comprising an aqueous solution containing an ammonium salt and steam; d) Process the urea melt produced in step b) into a urea-containing composition.

[0012] In another aspect, this disclosure provides the use of a carbamate condenser for producing steam, wherein the carbamate condenser receives a gas stream containing ammonia, carbon dioxide and water to a fluid inlet, the gas stream having a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa. Attached Figure Description

[0013] The following description of the accompanying drawings of specific embodiments of the system according to this disclosure is given by way of example only and is not intended to limit this description, its application, or use. In the drawings, the same reference numerals refer to the same or similar parts and features.

[0014] Figure 1 A carbamate condenser capable of performing the methods described in this application is shown.

[0015] Figure 2 A schematic diagram of a urea production apparatus is shown, in which the methods described in this disclosure can be performed.

[0016] Figure 3 A schematic diagram of another urea production apparatus suitable for producing urea according to the method disclosed herein is shown. Detailed Implementation

[0017] Unless otherwise defined, all terms used in disclosing this invention (including technical and scientific terms) have the meanings commonly understood by one of ordinary skill in the art to which this invention pertains. For further guidance, terminology definitions are included herein to better understand the teachings of this invention.

[0018] All references cited in this specification are incorporated herein by reference in their entirety.

[0019] As used herein, the following terms have the following meanings: As used herein, “a”, “an”, and “the” refer to both the singular and plural indicators, unless the context clearly specifies otherwise. For example, “a device” refers to one or more devices.

[0020] As used herein, when referring to measurable values ​​such as parameters, quantities, durations, etc., "about" is intended to include variations of + / -20% or less, particularly + / -10% or less, more particularly + / -5% or less, even more particularly + / -1% or less, and even more particularly + / -0.1% or less, as well as variations deviating from the specified value by + / -20% or less, particularly + / -10% or less, more particularly + / -5% or less, even more particularly + / -1% or less, and even more particularly + / -0.1% or less, provided such variations are suitable for implementation in the disclosed invention. However, it should be understood that the values ​​referred to by the modifier "about" are themselves specifically disclosed.

[0021] As used herein, the terms “comprise,” “comprising,” and “comprises,” as well as “comprised of,” are synonymous with “include,” “including,” “includes,” or “contain,” “containing,” and are inclusive or open-ended terms that indicate the presence of the following (e.g., ingredients) without excluding or preventing the presence of additional, unlisted ingredients, features, elements, members, or steps known in or disclosed in the art.

[0022] The range of values ​​listed by endpoints includes all numbers and fractions contained within that range, as well as the listed endpoints.

[0023] Unless otherwise defined, the terms “percentage by weight,” “wt%” or “weight%” used throughout this document and instructions refer to the relative weight of each component based on the total weight of the formulation.

[0024] In a first aspect, this disclosure provides a method for producing steam in a carbamate condenser, the carbamate condenser including a fluid inlet, a fluid outlet, a cooling fluid inlet, and a cooling fluid outlet, the method comprising the following steps: a) Providing a gas stream containing ammonia, carbon dioxide and water to the fluid inlet, wherein the gas stream has a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa; b) Providing an aqueous cooling solution to the cooling fluid inlet, wherein the temperature range of the aqueous cooling solution is 60 to 110°C; c) Obtaining a fluid composition from the fluid outlet, the fluid composition comprising an aqueous solution containing an ammonium salt; d) Obtain steam from the cooling fluid outlet.

[0025] The condensation of a gas stream containing ammonia, carbon dioxide, and water produces an aqueous solution containing ammonium salts (e.g., ammonium carbonate, ammonium bicarbonate, and ammonium carbamate), releasing energy as heat, particularly from the enthalpy of condensation of gaseous water and the heat of reaction of ammonia with carbon dioxide to form ammonium salts. When a high-pressure (at least 4.0 MPa) and / or high-temperature gas stream containing ammonia, carbon dioxide, and water is condensed in a heat exchanger (e.g., a shell-and-tube heat exchanger), steam at a pressure of at least 0.3 MPa can be produced. In urea production plants, such heat exchangers are commonly referred to as high-pressure carbamate condensers. This steam can be directed to other equipment in the urea production plant that requires steam to operate, such as carbamate decomposers. By recovering the enthalpy of condensation and the enthalpy of heat from the steam, the production plant reduces its overall energy consumption by decreasing its steam output.

[0026] However, urea production units also generate gas streams containing ammonia, carbon dioxide, and water at pressures below 4.0 MPa and / or temperatures below 140°C. Conventionally, these gas streams are condensed in a carbamate condenser (e.g., a shell-and-tube carbamate condenser) using cooling water, resulting in heated cooling water. This heated cooling water needs to be cooled for reuse in the production unit. This is conventionally done using chilled water in a cooling tower (which is subsequently discharged into the environment) or using air as the cooling medium in an air cooler. This cooling ultimately results in heat release into the environment, which contributes to climate change and is undesirable.

[0027] It has been discovered that steam can be produced by condensing such low-pressure and / or low-temperature gas streams containing ammonia, carbon dioxide, and water. The resulting steam is reused in the urea production unit and therefore is not released into the atmosphere, thereby reducing the environmental footprint of the production unit. The produced steam is low-pressure steam.

[0028] A gas stream containing ammonia, carbon dioxide, and water is provided to the fluid inlet of a carbamate condenser. The gas stream has a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa. The gas stream is typically generated by equipment within a urea production unit, such as a carbamate decomposer. The carbamate decomposer is a device configured to receive an aqueous solution containing urea and an ammonium salt (e.g., ammonium carbamate, ammonium carbonate, and / or ammonium bicarbonate). In the carbamate decomposer, the aqueous solution is heated, for example, with steam. Heating the solution triggers the decomposition of the ammonium salt, particularly ammonium carbamate, into free ammonia and free carbon dioxide, which evaporate from the aqueous solution. The carbamate decomposer produces an ammonium-deficient aqueous urea solution and a gas stream containing ammonia, carbon dioxide, and water. The urea production unit also includes an evaporator to remove water from the aqueous urea solution. The evaporator is configured to receive the aqueous solution containing urea and water and remove a portion of the water contained in the aqueous solution. Water removal is achieved by heating the solution, which causes some of the urea in the solution to decompose into ammonia and carbon dioxide. The evaporator produces a concentrated urea solution or urea melt and a gas stream containing ammonia, carbon dioxide, and water.

[0029] An aqueous cooling solution is provided to the cooling fluid inlet, wherein the temperature range of the aqueous cooling solution is 60 to 110°C. The aqueous cooling solution may contain at least 99.0% by weight, at least 99.5% by weight, or at least 99.9% by weight of water. In some embodiments, the aqueous cooling solution is 100% water. The aqueous cooling solution is partially or completely converted into steam in the carbamate condenser, therefore it should be very pure. The aqueous cooling solution should have a temperature of at least 60°C. This temperature is required for two reasons: First, when the gas stream containing ammonia, carbon dioxide, and water condenses, an aqueous solution containing ammonium salts is formed. Some ammonium salts, such as ammonium carbamate, have poor water solubility and can crystallize at around 20°C, so maintaining the condensed liquid at a temperature of at least 60°C is important. Second, the goal of the method is to produce steam from the aqueous cooling solution. A high-temperature cooling aqueous solution promotes steam generation because less heat is wasted in heating the aqueous cooling solution to its boiling point.

[0030] The cooling fluid inlet and cooling fluid outlet are connected to each other via a cooling network.

[0031] As a gas stream containing ammonia, carbon dioxide, and water travels through the carbamate condenser, it comes into contact with a cooler surface, and the water in the gas stream begins to condense into liquid water. With the formation of liquid water, the gaseous ammonia and carbon dioxide in the gas stream transfer to the liquid phase and react together to form ammonium salts, such as ammonium carbamate, ammonium carbonate, and ammonium bicarbonate. The liquid condensate may contain one or more of these salts. The proportions of different ammonium salts depend on various factors, such as the ammonia and carbon dioxide content in the gas stream, the pressure of the condensate, and the temperature. The reaction between free ammonia and free carbon dioxide dissolved in the condensate drives the dissolution of gaseous compounds in the condensate.

[0032] When the gas stream containing ammonia, carbon dioxide, and water condenses into an aqueous solution, heat is released and absorbed by the cooling aqueous solution. If the aqueous cooling solution is at its boiling point, the water evaporates and produces steam. The steam exits the urethane condenser through the cooling fluid outlet.

[0033] In some embodiments, the pressure of the steam obtained from the cooling fluid outlet ranges from 20 to 150 kPa. This steam is considered low-pressure steam in urea production plants.

[0034] In some embodiments, the pressure range within the cooling network is 20 to 150 kPa. It may be advantageous to supply an aqueous cooling solution to the heat exchanger at a temperature 0 to 10°C, 0 to 5°C, or 0 to 2°C lower than its boiling point. If the temperature of the aqueous cooling solution is close to its boiling point, most of the energy released by condensation is used to boil the water into steam. If the temperature of the aqueous cooling solution is much lower than its boiling point, some of the energy released by condensation is used to heat the water to its boiling point, thereby reducing the amount of steam produced. The boiling point of water depends on its pressure; therefore, it may be advantageous to regulate the pressure of the aqueous cooling solution or the pressure within the cooling network before it enters the carbamate condenser so that its temperature is very close to its boiling point (e.g., less than 10°C below its boiling point).

[0035] In some embodiments, the pressure at the cooling fluid outlet is controlled by a control valve. The control valve may be configured to maintain the pressure inside the cooling network at a level close to the boiling pressure of the cooling solution directed to the cooling fluid inlet. Because the temperature of the cooling solution may vary, the pressure inside the cooling network can be adjusted to bring the cooling solution very close to its boiling point, thereby increasing the amount of steam generated in the condenser.

[0036] In some embodiments, the fluid composition obtained in step c) is a two-phase composition comprising a liquid portion and a gaseous portion. Condensation of the gas stream containing ammonia, carbon dioxide, and water can be performed in two ways: complete condensation or partial condensation. Complete condensation describes a method in which all water vapor contained in the gas stream condenses into liquid water. In this case, the fluid composition obtained at the outlet of the carbamate condenser is a liquid. Partial condensation describes a method in which water vapor contained in the gas stream condenses only partially into liquid water. In this case, the fluid composition obtained near the outlet of the carbamate condenser is a two-phase liquid, i.e., a mixture of liquid and gas. In some embodiments, the carbamate condenser includes two fluid outlets, one for recovering the liquid portion of the fluid produced by the carbamate condenser and one for recovering the gaseous portion of the fluid produced by the carbamate condenser.

[0037] In some embodiments, the gas stream provided in step a) contains 10.0 to 50.0% by weight of ammonia. In some embodiments, the gas stream provided in step a) contains 10.0 to 40.0% by weight of carbon dioxide. The exact contents of ammonia, carbon dioxide, and water in the gas stream provided in step a) depend on a variety of factors, particularly the source of the gas stream. In some embodiments, the gas stream provided in step a) contains 10.0 to 50.0% by weight of ammonia and 10.0 to 40.0% by weight of carbon dioxide.

[0038] In some embodiments, the fluid composition obtained at the fluid outlet of the carbamate condenser in step c) contains 10.0 to 50.0% by weight of ammonia. In some embodiments, the fluid composition obtained at the fluid outlet of the carbamate condenser in step c) contains 10.0 to 40.0% by weight of carbon dioxide. The fluid composition obtained at the outlet of the carbamate condenser has the same chemical composition as the gas stream introduced into the carbamate condenser in step a), because no mass exchange occurs between the gas stream and the cooling fluid. The fluid obtained in step c) can be a pure liquid, in which case the liquid contains the same amount of ammonia and carbon dioxide as the gas stream introduced in step a). If condensation is only partial, the fluid obtained in step c) can also be a mixture of liquid and gas. In such embodiments, both the liquid phase and the gas phase may contain ammonia and carbon dioxide. In some embodiments, the fluid composition obtained in step c) contains 10.0 to 50.0% by weight of ammonia and 10.0 to 40.0% by weight of carbon dioxide.

[0039] In some embodiments, the aqueous cooling solution provided in step b) comprises 99.5 to 100% by weight water. The aqueous cooling solution is partially or completely converted into vapor during the method, therefore the aqueous cooling solution should have suitable chemical properties, particularly a very low amount of impurities that can be precipitated from the solution.

[0040] In some embodiments, the aqueous cooling solution provided in step b) comprises vapor condensate and / or demineralized water. A urea production unit includes numerous devices, including some configured to condense a stream of pure water vapor. This vapor condensate is a stream of pure water that can be used in this method.

[0041] In some embodiments, the carbamate condenser is a shell-and-tube carbamate condenser. A shell-and-tube carbamate condenser includes a body and a plurality of tubes configured to carry fluid. The shell-and-tube carbamate condenser includes two spaces in which fluid can flow without mixing with each other: the tube side, which includes all the internal space of the tubes contained within the carbamate condenser; and the shell side, which includes the volume of the carbamate condenser not contained within the tubes. In some embodiments, the carbamate condenser is a horizontal shell-and-tube heat exchanger, such as a kettle-type carbamate condenser. In some embodiments, the carbamate condenser is a vertical shell-and-tube carbamate condenser.

[0042] In another aspect, this disclosure provides a method for producing a urea-containing composition, the method comprising the following steps: a) In the synthesis section, ammonia is reacted with carbon dioxide to produce a synthetic solution containing urea, water and ammonium carbamate. b) The synthetic solution produced in step a) generates a urea melt containing urea and water, and one or more gas streams containing ammonia, carbon dioxide and water. c) Condensing at least one of the one or more gas streams in a carbamate condenser to generate steam, thereby producing a fluid composition comprising an aqueous solution containing an ammonium salt and steam; d) Process the urea melt produced in step b) into a urea-containing composition.

[0043] In particular, the method according to the first aspect is integrated into the method for producing urea according to this disclosure.

[0044] Therefore, this disclosure provides a method for producing a urea-containing composition, the method comprising the following steps: a) Ammonia is reacted with carbon dioxide in a synthesis reactor to produce a synthetic solution containing urea, water and ammonium carbamate. b) The synthetic solution produced in step a) generates a urea melt containing urea and water, and one or more gas streams containing ammonia, carbon dioxide and water. c) Condensing at least one of the one or more gas streams in a condenser, wherein the at least one of the one or more gas streams has a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa to produce steam and a fluid composition comprising an aqueous solution containing an ammonium salt, wherein the condenser receives an aqueous cooling solution with a temperature ranging from 60 to 110°C. d) Processing the urea melt produced in step b) into a urea-containing composition. In a particular embodiment, the method further includes the following steps: e) Compress the steam generated in step c) to a pressure ranging from 0.3 to 2.5 MPa.

[0045] Ammonia and carbon dioxide react together in the synthesis section of the production unit under high pressure (e.g., above 10 MPa) and high temperature (e.g., above 150°C). Under these conditions, two reactions occur: first, ammonia reacts with carbon dioxide to form ammonium carbamate (NH4O2CNH2); second, ammonium carbamate is converted into urea and water. The conversion of ammonium carbamate to urea is incomplete, and an aqueous solution containing urea, ammonium carbamate, and water is obtained. This aqueous solution produced by the reaction of ammonia and carbon dioxide is called the synthesis solution. The synthesis solution may also contain free ammonia.

[0046] In some embodiments, the method for producing a urea-containing composition is carried out in a urea production apparatus comprising a synthesis section, a decomposition section, an evaporation section, a refining section, and a condensation section. The synthesis section is configured to receive an ammonia stream and a carbon dioxide stream and produce a synthesis solution comprising urea, ammonium carbamate, free ammonia, and water. The synthesis section may include a reactor, a high-pressure stripper, and a high-pressure carbamate condenser. The decomposition section is configured to process the synthesis solution from the synthesis section into an aqueous urea solution comprising at least 60.0 wt% urea and at most 40.0 wt% water. In some embodiments, the decomposition section is configured to process the synthesis solution from the synthesis section into an aqueous urea solution comprising 60.0 to 80.0 wt% urea and 20.0 to 40.0 wt% water. The evaporation section is configured to process the aqueous urea solution from the decomposition section into a urea melt comprising at least 95.0 wt%, or 95.0 to 99.9 wt% urea and water. The refining section is configured to convert urea melt containing at least 95.0% by weight of urea into a finished urea composition, which can be in solid form such as urea pellets or urea granules, or in liquid form such as an aqueous urea solution containing 30.0 to 35.0% by weight of urea, for example, diesel exhaust fluid. The condensation section includes a condenser configured to perform the above-described method and generate vapor by condensing a gas stream containing ammonia and carbon dioxide.

[0047] In some embodiments, the urea production unit includes a hydrolyzer section, also known as a wastewater section. The hydrolyzer section is configured to receive a stream containing urea (particularly a small amount, e.g., less than 10.0% by weight) and decompose the urea into ammonia and carbon dioxide. The hydrolyzer section may be configured to generate a gas stream containing ammonia and carbon dioxide. The hydrolyzer section may be connected to a condensation section of the urea production unit, allowing the generated gas stream to be condensed into a liquid stream and recycled back to the synthesis section.

[0048] In some embodiments, the synthetic solution comprises 40.0 to 60.0% by weight of urea, 10.0 to 25.0% by weight of ammonium carbamate, 0.0 to 20.0% by weight of free ammonia and 20.0 to 30.0% by weight of water.

[0049] To produce the urea-based composition, the synthesis solution needs to be purified and concentrated to obtain a urea melt. The urea melt is a composition comprising urea, particularly at least 90.0% by weight or 90.0 to 100% by weight urea, and 0.1 to 5.0% by weight water.

[0050] To obtain urea melt, the synthesis solution is processed in various devices, such as carbamate decomposers and evaporators. Some of these devices produce gas streams containing ammonia, carbon dioxide, and water. A carbamate decomposer is a device configured to receive an aqueous solution containing urea, ammonium carbamate, water, and optionally free ammonia. The carbamate decomposer is a heat exchanger in which the aqueous solution is heated, for example, with steam to decompose the ammonium carbamate into ammonia and carbon dioxide. The gaseous ammonia and carbon dioxide are separated from the liquid phase inside the carbamate condenser or in a liquid / gas separator located downstream of the carbamate decomposer. The carbamate decomposer produces an aqueous urea solution lacking ammonium carbamate. The aqueous urea solution produced by the carbamate decomposer may still contain ammonium carbamate.

[0051] In some embodiments, the processing step b) includes directing the synthetic solution into one or two carbamate decomposers.

[0052] In some embodiments, the processing step b) includes directing the synthetic solution into one or two carbamate decomposers, thereby producing an aqueous urea solution containing less than 5.0% by weight of ammonium carbamate and optionally free ammonia.

[0053] In some embodiments, the processing step b) includes directing the synthetic solution into one or two carbamate decomposers, thereby producing an aqueous urea solution consisting of urea and water.

[0054] In some embodiments, the processing step b) includes processing the synthetic solution into an aqueous urea solution containing urea, water, and less than 5.0% by weight of other components besides urea and water, and concentrating the aqueous urea solution into a urea melt.

[0055] Concentrating an aqueous urea solution into urea melt can be carried out in an evaporator. An evaporator is a device configured to receive an aqueous urea solution and heat it to remove water, residual ammonium carbamate, and free ammonia. The heat source can be steam.

[0056] To improve the yield of the production unit, it is important to recycle the starting materials ammonia and carbon dioxide to the synthesis section. However, it is preferable to reinject these starting materials in liquid form rather than gaseous form. Therefore, these gas streams are condensed into a liquid aqueous solution in a carbamate condenser according to the described method. In addition to generating a liquid stream that can be reinjected into the synthesis section, this condensation generates heat that can be used to produce steam, which can also be reused in the urea production unit, thereby reducing the need for steam production, which is typically carried out by burning fossil fuels, producing carbon dioxide emissions, a greenhouse gas.

[0057] In some embodiments, the method includes compressing the steam generated in step c) to a pressure ranging from 0.3 to 2.5 MPa. The steam generated in the carbamate condenser may have a pressure too low for direct reuse in the urea production unit. Many devices in the urea production unit require steam at a pressure of at least 300 kPa. Therefore, reusing the steam generated by the carbamate condenser may require first increasing the pressure of the steam, for example, using a gas compressor, to obtain steam that can be directed to the devices in the urea production unit.

[0058] In another aspect, this disclosure provides an apparatus for producing urea from urea-based compositions, comprising: - Synthesis section, configured to produce an aqueous urea solution containing urea, water and ammonium carbamate; - A decomposition section, connected to the synthesis section, the decomposition section being configured to receive an aqueous urea solution and convert the aqueous urea solution into a pure urea solution containing urea, water and less than 5.0% by weight of impurities; - An evaporation section, connected to the decomposition section, configured to remove water from a pure urea solution containing urea, water and less than 5.0% by weight of impurities to obtain a urea melt containing urea and less than 5.0% by weight of water; - Refining section, configured to receive urea melt and produce urea-containing products; - A condensation section, connected to the decomposition section and the evaporation section, wherein: - The condensation section is configured to convert the gas stream containing ammonia, carbon dioxide and water from the decomposition section and / or the evaporation section into an aqueous solution containing ammonium salts in the future; - The condensation section is also connected to the synthesis section and configured to deliver an aqueous solution containing an ammonium salt to the synthesis section; and - The condensation section includes at least one carbamate condenser configured to produce low-pressure steam by condensing a gas stream containing ammonia, carbon dioxide and water.

[0059] In some embodiments, the condensation section is configured to process an airflow containing ammonia, carbon dioxide, and water, having a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa.

[0060] In some embodiments, the synthesis section includes a reactor, a high-pressure stripper, and a high-pressure carbamate condenser.

[0061] In some embodiments, the decomposition section includes one or more heat exchangers configured to decompose ammonium carbamate contained in an aqueous solution. In some embodiments, the decomposition section includes one or more liquid-gas separators.

[0062] In some embodiments, the evaporation section includes one or more evaporators, such as two evaporators. The evaporators are configured to remove water from an aqueous solution containing urea.

[0063] In some embodiments, the refining section includes a granulator, such as a fluidized bed granulator or a granulation tower. In some embodiments, the refining section includes a mixing device for adding one or more of the following components to the urea melt: for example, urease inhibitors (such as N-n-butylthiophosphoric acid triamine), nitration inhibitors (such as 3,4-dimethylpyrazole phosphate), granulation additives (such as urea-formaldehyde), macronutrients (nitrogen, phosphorus, potassium), mesonutrients (magnesium, calcium, sulfur), or micronutrients (zinc, copper, boron, manganese, molybdenum, iron).

[0064] In some implementations, the refining section includes a scrubber for removing contaminants (such as ammonia and urea) from the airflow.

[0065] In some embodiments, the urea production apparatus includes a hydrolyzer section connected to the evaporation section and the condensation section, the hydrolyzer section being configured to remove urea from the aqueous stream and deliver a gas stream containing water, ammonia, and carbon dioxide to the condensation section.

[0066] In another aspect, this disclosure provides the use of a carbamate condenser for producing steam, wherein the carbamate condenser is configured to receive a gas stream comprising ammonia, carbon dioxide and water to a fluid inlet, the gas stream having a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa.

[0067] Figure 1 A carbamate condenser 1 suitable for performing the method according to the first aspect of this disclosure is shown. The carbamate condenser 1 is a vertical shell-and-tube heat exchanger including a fluid inlet 2, a fluid outlet 3, a cooling fluid inlet 5, and a cooling fluid outlet 4. The fluid inlet 2 is located near the top of the condenser 1, allowing condensate formed inside the carbamate condenser 1 to flow naturally to the fluid outlet 3 by gravity. The carbamate condenser 1 includes a plurality of tubes not shown in the figures. These tubes may be fluidly connected to the cooling fluid inlet 5 and the cooling fluid outlet 4, allowing cooling fluid to flow through these tubes. Alternatively, these tubes may be fluidly connected to the fluid inlet 2 and the fluid outlet 3, allowing gas flow and condensate obtained from the gas flow to flow in these tubes.

[0068] Figure 2A schematic diagram of a urea production apparatus suitable for producing urea according to the method disclosed herein is shown. The urea production apparatus includes a synthesis section 10 configured to produce an aqueous urea solution comprising urea, water, and ammonium carbamate. The synthesis section 10 is configured to receive a gaseous ammonia stream, a gaseous carbon dioxide stream, and high-pressure steam. The synthesis section 10 is connected to a decomposition section 20, configured to receive the aqueous urea solution and convert it into a pure urea solution comprising urea, water, and less than 5.0% by weight impurities. In addition to the pure urea solution, the decomposition section 20 is also configured to generate one or more gas streams comprising ammonia, carbon dioxide, and water. The decomposition section 20 is connected to an evaporation section 30 and a condensation section 50. The evaporation section 30 is configured to receive the pure urea solution from the decomposition section 20 and remove water from the pure urea solution to obtain a urea melt comprising urea and less than 5.0% by weight water. The evaporation section 30 is connected to a refining section 40, configured to receive the urea melt and produce a urea-containing product. The urea-containing product can be a solid product, such as granules or pellets, or a liquid product, such as a urea solution or a urea ammonium nitrate solution. A condensation section 50 is configured to receive a gas stream containing ammonia, carbon dioxide, and water from a decomposition section 20 and an evaporation section 30, to convert the gas stream into an aqueous solution containing an ammonium salt, such as ammonium carbamate. The condensation section 50 is connected to a synthesis section 10 and configured to deliver the aqueous solution containing the ammonium salt to the synthesis section 10. The condensation section 50 includes at least one carbamate condenser configured to produce low-pressure steam, i.e., steam with a pressure range of 20 to 150 kPa, by condensing the gas stream containing ammonia, carbon dioxide, and water, having a temperature range of 100 to 140°C and a pressure range of 0.1 to 4.0 MPa. The low-pressure steam generated by the condensation section 50 can be delivered to the synthesis section 10, decomposition section 20, and / or evaporation section 30, depending on the steam balance of the production unit and the needs of different sections. The low-pressure steam can be compressed to a higher pressure depending on the section of the production unit to which it is delivered.

[0069] Figure 3 A schematic diagram of another urea production apparatus suitable for producing urea according to the method disclosed herein is shown. This urea production apparatus includes... Figure 2The production unit shown includes the following identical sections: synthesis section 10, decomposition section 20, evaporation section 30, refining section 40, and condensation section 50. This urea production unit also includes a hydrolyzer section 60, configured to handle the liquid stream containing urea; this section may be referred to as the wastewater section. Some sections of the production unit, such as evaporation section 30, may generate a waste stream (liquid or gaseous) containing a small amount of urea. This gas stream can be condensed into a liquid stream containing urea in evaporation section 30 or hydrolyzer section 60. In hydrolyzer section 60, the liquid stream containing urea is heated, causing the urea to decompose back into ammonia and carbon dioxide in the gas phase. This gas stream is then directed to condensation section 50 for recycling back to synthesis section 10. Condensation section 50 may be configured to combine the gas streams in condensation section 30 and hydrolyzer section 60 before condensation. The condensation section 50 includes at least one carbamate condenser configured to produce low-pressure steam, i.e., steam with a pressure range of 20 to 150 kPa, by condensing a gas stream containing ammonia, carbon dioxide and water, the gas stream having a temperature range of 100 to 140°C and a pressure range of 0.1 to 4.0 MPa.

Claims

1. A method for producing steam in a carbamate condenser, the carbamate condenser comprising a fluid inlet, a fluid outlet, a cooling fluid inlet, and a cooling fluid outlet, the method comprising the following steps: a) Providing a gas stream containing ammonia, carbon dioxide and water to the fluid inlet, wherein the gas stream has a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa; b) Providing an aqueous cooling solution to the cooling fluid inlet, wherein the temperature range of the aqueous cooling solution is 60 to 110°C; c) Obtaining a fluid composition from the fluid outlet, the fluid composition comprising an aqueous solution containing an ammonium salt; d) Obtain steam from the cooling fluid outlet.

2. The method of claim 1, wherein the pressure of the steam obtained from the cooling fluid outlet is in the range of 20 to 150 kPa.

3. The method according to any one of claims 1 to 2, wherein the pressure range of the aqueous cooling solution provided in step b) is 20 to 150 kPa.

4. The method according to any one of claims 1 to 3, wherein the fluid composition obtained in step c) is a biphase composition comprising a liquid portion and a gas portion.

5. The method according to any one of claims 1 to 4, wherein the gas flow provided in step a) comprises 10.0 to 50.0% by weight of ammonia.

6. The method according to any one of claims 1 to 5, wherein the gas flow provided in step a) comprises 10.0 to 40.0% by weight of carbon dioxide.

7. The method according to any one of claims 1 to 6, wherein the aqueous cooling solution provided in step b) comprises 99.5 to 100% by weight water.

8. The method according to any one of claims 1 to 7, wherein the aqueous cooling solution provided in step b) comprises vapor condensate and / or demineralized water.

9. A method for producing a urea-containing composition, the method comprising the following steps: a) Ammonia is reacted with carbon dioxide in a synthesis reactor to produce a synthetic solution containing urea, water and ammonium carbamate. b) The synthetic solution produced in step a) generates a urea melt containing urea and water, and one or more gas streams containing ammonia, carbon dioxide and water. c) Condensing at least one of the one or more gas streams in a condenser, wherein the at least one of the one or more gas streams has a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa to produce steam and a fluid composition comprising an aqueous solution containing an ammonium salt, wherein the condenser receives an aqueous cooling solution with a temperature ranging from 60 to 110°C. d) Process the urea melt produced in step b) into a urea-containing composition.

10. The method of claim 9, wherein the method further comprises the following steps: e) Compress the steam generated in step c) to a pressure ranging from 0.3 to 2.5 MPa.

11. A carbamate condenser for the production of steam, wherein the carbamate condenser receives a gas stream containing ammonia, carbon dioxide and water to a fluid inlet, the gas stream having a temperature ranging from 100 to 140°C and a pressure ranging from 0.1 to 4.0 MPa.

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