Method for reducing carbon dioxide emissions in urea plants

Abstract

The present disclosure provides a urea production plant comprising: a first steam network configured to receive high pressure steam; the apparatus includes a first steam network configured to receive low pressure steam, and a second steam network configured to receive low pressure steam, where the apparatus includes a steam compressor configured to receive steam from the second steam network, convert low pressure steam to high pressure steam, and deliver the high pressure steam to the first steam network. The present disclosure provides a method for reducing carbon dioxide emissions from a urea production plant.

Description

Technical Field

[0001] The present disclosure relates to the field of urea production. Background Art

[0002] Urea (H2NCONH2) is the most commonly used nitrogen-containing fertilizer today. Global production is estimated at around 200 million tons per year. In addition to its use as a fertilizer, urea is also used in various chemical syntheses and as a solution to reduce nitrogen oxide emissions in diesel-powered vehicles.

[0003] Urea production plants can use different technologies, such as the Stamicarbon process or the Saipem process, but they all rely on the same basic principle. In the synthesis section of a urea production plant, ammonia and carbon dioxide (CO2) react at high pressure (above 130 bar) and high temperature to produce an aqueous solution containing urea, ammonium carbamate and free ammonia. The aqueous solution is then purified and concentrated to obtain a urea melt. The urea melt can be diluted to obtain an aqueous urea solution that can be used for a selective catalytic or non-catalytic reduction system (such as diesel exhaust fluid), mixed with other nutrient sources (such as ammonium nitrate) to obtain an aqueous urea ammonium nitrate solution, or solidified into a urea-containing solid (such as granules or pellets).

[0004] The production of urea requires a large amount of energy input, in particular due to the reaction equilibrium between the starting materials and the final product. In most urea plants, this energy is obtained by burning non-renewable energy sources such as natural gas or oil to heat water and produce steam. However, this energy production releases large amounts of the greenhouse gas carbon dioxide into the atmosphere, and authorities and customers are constantly demanding the reduction of carbon dioxide emissions from urea production.

[0005] EP3896031A1 (Casale, 2021) discloses a method for converting an ammonia-urea plant, wherein: the ammonia section is modernized to produce an additional amount of low-pressure steam; the condensing stage of the high-pressure urea synthesis loop is improved to use partial condensation heat of the urea stripping tower vapor to produce medium-pressure steam, which is fed to one or more steam users in the urea section, in particular for carbamate decomposition, and the low-pressure steam input to the urea section is balanced by introducing additional low-pressure steam produced in the ammonia section.

[0006] EP3656759A1 (Casale, 2020) discloses a method for synthesizing urea from CO2 and NH3, wherein a steam stream (13) produced in a condenser (3) of a high-pressure synthesis loop is compressed to increase its pressure and temperature, and the steam is then used as a heat source for downstream steps of the method. Summary of the invention

[0007] The present inventors have found a new way to reduce carbon dioxide emissions in a urea plant and have designed a urea plant with reduced carbon dioxide emissions.

[0008] In a first aspect, the present disclosure provides a urea production device, comprising: a first steam network, which is configured to receive high-pressure steam; and a second steam network, which is configured to receive low-pressure steam, wherein the device includes a steam compressor, which is configured to receive steam from the second steam network, convert the low-pressure steam into high-pressure steam, and transport the high-pressure steam to the first steam network.

[0009] On the other hand, the present disclosure provides a urea production device, which includes a first steam network, which is configured to receive high-pressure steam with a pressure of 1.5 MPa to 11 MPa; and a second steam network, which is configured to receive low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa, wherein the device includes a steam compressor, which is configured to receive steam from the second steam network, convert the low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa into high-pressure steam with a pressure of 1.5 MPa to 11 MPa, and transport the high-pressure steam to the first steam network.

[0010] In another aspect, the present disclosure provides a method for reducing carbon dioxide emissions from a urea production facility, comprising the steps of:

[0011] - providing low pressure steam from the second steam network to the steam compressor;

[0012] -Convert low-pressure steam into high-pressure steam in a steam compressor;

[0013] - directing the high pressure steam to the first steam network.

[0014] In another aspect, the present disclosure provides a method for reducing carbon dioxide emissions from a urea production facility, comprising the following steps:

[0015] - providing low-pressure steam at a pressure of 0.1 MPa to 0.7 MPa from the second steam network to the steam compressor;

[0016] - Converting low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa into high-pressure steam with a pressure of 1.5 MPa to 11 MPa by means of a steam compressor;

[0017] - Directing the high pressure steam generated by the steam compressor to the first steam network. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The following description of the drawings of specific embodiments of the system according to the present disclosure is given by way of example only and is not intended to limit the present description, its application, or uses. In the drawings, the same reference numerals refer to the same or similar parts and features.

[0019] Figure 1 An embodiment of a urea plant according to the present disclosure is represented.

[0020] Figure 2 shows another embodiment of a urea plant according to the present disclosure. DETAILED DESCRIPTION

[0021] Unless otherwise defined, all terms, including technical and scientific terms, used to disclose the present invention have the meanings commonly understood by ordinary technicians in the field to which the present invention belongs. By way of further guidance, term definitions are included to better understand the teachings of the present invention.

[0022] All references cited in this specification are hereby deemed to be incorporated by reference in their entirety.

[0023] As used herein, the following terms have the following meanings:

[0024] As used herein, "a", "an", and "the" refer to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a device" means one or more than one device.

[0025] As used herein, "comprising" and its variations and "consisting of" are synonymous with "including" and its variations or "containing" and its variations, and are inclusive or open-ended terms that specify the presence of what follows, for example, a component, and do not exclude or preclude the presence of additional, unrecited components, features, elements, members, steps known in the art or disclosed herein.

[0026] "Urea plant" means a plant suitable for producing urea. The final product of the plant may be solid or liquid.

[0027] In a first aspect, the present disclosure provides a urea production device, comprising: a first steam network, which is configured to receive high-pressure steam; and a second steam network, which is configured to receive low-pressure steam, wherein the device includes a steam compressor, which is configured to receive steam from the second steam network, convert the low-pressure steam into high-pressure steam, and transport the high-pressure steam to the first steam network.

[0028] The results show that CO2 emissions can be reduced by using a steam compressor to convert the unused low-pressure steam generated by one or more units of a urea plant into valuable high-pressure steam that can be reused in the plant.

[0029] As mentioned above, several steps in urea production are endothermic and therefore require energy input. This energy is usually provided in the form of superheated steam or saturated steam, the pressure of which can vary.

[0030] The urea production plant comprises at least two steam networks containing steam at different pressures: a high pressure (HP) steam network, which is also referred to herein and used interchangeably with the term "first steam network", configured to receive steam at a (high) pressure of at least 1.5 MPa; and a low pressure (LP) steam network, which is also referred to herein and used interchangeably with the term "second steam network", configured to receive steam at a (low) pressure of 0.1 MPa to 0.7 MPa.

[0031] High pressure steam is usually produced by a boiler which burns a fossil fuel such as natural gas or oil and thus produces carbon dioxide. Alternatively, if the plant comprises a steam turbine, for example for driving a CO2 compressor, high pressure steam can also be obtained from the steam turbine as steam extraction. However, this requires the production of steam at an even higher pressure, thus increasing the carbon dioxide release from the boiler. Therefore, one way to reduce carbon dioxide emissions from a urea plant is to reduce the amount of steam that needs to be produced for the operation of the plant.

[0032] Urea plants include many devices that require steam to operate, such as evaporators, strippers, carbamate decomposers, desorbers, steam ejectors and hydrolyzers. For example, some high-pressure devices (such as HP strippers and urea hydrolyzers) require HP steam as input and are connected to the HP steam network. In addition, some high-pressure devices produce low-pressure steam, i.e. steam with a pressure of 0.1 MPa to 0.7 MPa, such as carbamate condensers that operate at a pressure (process) above 3.0 MPa.

[0033] In some embodiments, the urea production facility includes a high pressure carbamate condenser configured to provide low pressure steam to the second steam network.

[0034] In some embodiments, the steam compressor is fluidly connected to the high pressure carbamate condenser. In some embodiments, the steam compressor is configured to receive steam from the high pressure carbamate condenser via the second steam network.

[0035] This low pressure steam can be used by one or more of the devices in the urea plant. The LP steam can also be injected into a steam turbine present in the plant to generate power, for example for a compressor. If the LP steam produced by the plant is in excess and is not consumed by any of the devices, the LP steam may be released to the atmosphere as atmospheric steam or condensed in a cooler as process condensate. In both cases, this represents a waste of energy for the plant.

[0036] However, it has been found that the LP steam can be reused in the urea plant by converting it into high pressure steam which is used by one or more HP units in the plant, such as the HP stripper and the urea hydrolyzer. The conversion is accomplished by a steam compressor connected to both the LP steam network and the HP steam network, wherein the steam compressor is configured to receive low pressure steam from the second steam network (i.e., the low pressure steam network) to convert the low pressure steam into high pressure steam and deliver the high pressure steam to the first steam network (i.e., the high pressure steam network).

[0037] In some embodiments, the steam compressor is a two-stage compressor. It may be desirable to use a two-stage compressor because the pressure difference between the LP steam received by the compressor and the HP steam used by the device may be so significant that a single-stage compressor cannot perform this conversion, particularly requiring a two-stage compressor to convert 0.5 MPa LP steam into 2.3 MPa HP steam.

[0038] As used herein, the term "high pressure steam", particularly as it relates to the first steam network, generally refers to steam having a pressure of at least 1.5 MPa. In some embodiments, the first or high pressure steam network is configured to receive steam at a pressure of 1.5 MPa to 11 MPa, 2.0 MPa to 11 MPa, 2.0 MPa to 10 MPa, 2.0 MPa to 9.0 MPa, 2.0 MPa to 8.0 MPa, 2.0 MPa to 7.0 MPa, 2.0 MPa to 6.0 MPa, 2.0 MPa to 5.0 MPa, 2.0 MPa to 4.0 MPa, 2.0 MPa to 3.0 MPa, 2.0 MPa to 2.9 MPa, 2.0 MPa to 2.7 MPa, 2.0 MPa to 2.6 MPa, 2.0 MPa to 2.5 MPa, 2.0 MPa to 2.4 MPa, 1.5 MPa to 2.9 MPa, 2.0 MPa to 2.7 MPa, 2.0 MPa to 2.8 MPa, 2.0 MPa to 2.9 MPa, 1.5 MPa to 2.9 MPa, 2.0 MPa to 2.9 MPa, 2.0 MPa to 2.7 MPa, 2.0 MPa to 2.6 MPa, 2.0 MPa to 2.5 MPa, 2.0 MPa to 2.4 MPa, 1.5 MPa to 2.9 MPa, 2.0 ... The HP steam network can be configured to receive steam at a pressure specific to the plant. Urea plants use different technologies depending on the company that built the plant. For example, in the Stamicarbon plant, i.e., the plant built by the technology provider Stamicarbon, the HP steam network is configured to receive steam at a pressure of 1.8 MPa to 2.5 MPa.

[0039] As used herein, the term "low pressure steam", particularly the term relating to the second steam network, generally relates to steam having a pressure between 0.1 MPa and 1.0 MPa. In some embodiments, the second or low pressure steam network is configured to receive steam at a pressure of 0.1 MPa to 0.7 MPa, 0.2 MPa to 0.7 MPa, 0.1 MPa to 0.6 MPa, 0.2 MPa to 0.6 MPa, 0.3 MPa to 0.6 MPa, or 0.3 MPa to 0.7 MPa. The LP steam network can be configured to receive steam at a pressure specific to the device.

[0040] In some embodiments, the high pressure device connected to the first or high pressure steam network is a high pressure stripper. The HP stripper is a device configured to remove ammonium carbamate, ammonia and carbon dioxide from the aqueous solution produced by the synthesis reactor. The HP stripper uses HP steam to heat the aqueous solution containing urea, ammonium carbamate and free ammonia. After heating, the ammonium carbamate decomposes into ammonia and carbon dioxide and escapes from the aqueous solution in gaseous form. The HP stripper can be connected to a condenser, which is configured to condense the gas stream containing water, ammonia and carbon dioxide produced by the HP stripper.

[0041] In some embodiments, the plant includes a urea hydrolyzer connected to the first or high pressure steam network. A urea hydrolyzer is a device configured to remove urea from a process condensate produced in a urea plant. Process condensate refers to an aqueous solution obtained by condensing a gas stream containing water vapor. The gas stream containing water vapor may contain other components, such as urea, and the condensate of the gas stream also contains urea. However, it is preferred that the process condensate does not contain urea, and a urea hydrolyzer can be used to achieve this goal. The urea hydrolyzer also uses HP steam to decompose urea back into ammonia and carbon dioxide.

[0042] The urea plant comprises at least one low pressure device connected to the LP steam network. As used herein, a low pressure device refers to a device that requires input of low pressure steam to operate.

[0043] In some embodiments, the low-pressure device connected to the second or low-pressure steam network is an evaporator. Evaporators are widely used in urea plants to remove water from an aqueous solution to increase the concentration of components contained therein, such as concentrating an aqueous solution containing urea. The evaporator can use steam to heat the aqueous solution and evaporate water from the aqueous solution. Evaporating water is an exothermic operation, so the evaporator receives steam at the first pressure and produces a steam condensate.

[0044] In some embodiments, the low pressure device connected to the second or low pressure steam network is a carbamate decomposer. The carbamate decomposer is a device configured to receive an aqueous composition comprising urea and ammonium carbamate. The carbamate decomposer is configured to heat the aqueous composition so that the ammonium carbamate present therein decomposes into ammonia and carbon dioxide, which can be separated from the aqueous composition. The carbamate decomposer can use LP steam as a heat source to heat the aqueous composition.

[0045] In some embodiments, the low pressure device connected to the second or low pressure steam network is a desorber. A desorber is a device configured to remove gases (particularly ammonia and / or carbon dioxide) from an aqueous solution. The desorber receives partially condensed LP steam.

[0046] In some embodiments, the device connected to the second or low pressure steam network is a steam ejector.

[0047] The synthesis section of the urea plant requires a supply of high pressure (particularly 13 MPa to 16 MPa) carbon dioxide. In order to obtain this high pressure carbon dioxide, the urea plant comprises a carbon dioxide compressor. The carbon dioxide compressor requires a large amount of mechanical power, which can be provided by a variety of devices, such as a gas turbine or a steam turbine or an electric motor.

[0048] In some embodiments, the first electric motor is connected to the CO2 compressor and is configured to provide power to the CO2 compressor. The advantage of the electric motor is that it does not produce any greenhouse gas emissions, in particular no CO2 emissions, and can be powered by electricity generated from a source that does not emit any greenhouse gases. Gas turbines use natural gas, which produces greenhouse gas emissions. Steam turbines may have advantages in urea plants because they are able to convert low-pressure steam into mechanical power for the compressor. However, the supply of LP steam may not be sufficient to produce enough power, and the turbine requires an additional supply of HP steam, which is usually produced by burning fossil fuels and therefore produces CO2 emissions.

[0049] In some embodiments, the apparatus includes a second motor configured to provide power to the steam compressor. The steam compressor requires an input of mechanical power to operate. In order not to further increase greenhouse gas emissions, it may be advantageous to find a method of powering the steam compressor that does not emit carbon dioxide or any other greenhouse gas. If the electricity provided to the motor is generated without generating carbon dioxide emissions, such as wind power, solar power, hydroelectric power, or nuclear power, the motor may be considered to be carbon dioxide-free.

[0050] In some embodiments, the device includes a steam turbine configured to provide power to the steam compressor. In many cases, the industrial site including the urea plant also includes an ammonia plant that produces ammonia used in the urea plant. The ammonia plant produces 4.0 MPa HP steam, particularly in the third steam network. Since the urea plant may only require HP steam at a pressure of 2.0 MPa to 3.0 MPa, the device may include a system for producing HP steam at a pressure of 2.0 MPa to 3.0 MPa (particularly in the first steam network) from 4.0 MPa steam (particularly in the third steam network). In contrast, the back-pressure steam turbine may be configured to receive high-pressure steam, such as 4.0 MPa steam, generate mechanical power to supply power to the steam compressor, and release HP steam at a pressure of 2.0 MPa to 3.0 MPa, which is directed to the first HP steam network of the urea plant. Although the presence of the steam turbine increases the steam consumption of the urea plant compared to the urea plant in which the steam compressor is powered by an electric motor, and thus increases greenhouse gas emissions, this configuration still represents an improvement over conventional urea plants that do not include steam compressors. A person skilled in the art understands that since the steam turbine provides HP steam to the urea plant (to the first steam network) and simultaneously powers the steam compressor, this enables the plant to increase the LP steam pressure and reuse its LP steam, resulting in a net gain, i.e. reduced steam consumption.

[0051] In some embodiments, the device includes an electric motor and a steam turbine connected to a steam compressor and configured to provide power to the steam compressor. A steam turbine can be an interesting device if there is some excess steam in the device that is not used by any device. However, the amount of excess steam available may not be sufficient to provide all the power required by the steam compressor. Increasing steam production may increase the CO2 emissions of the device, but installing an electric motor to provide the missing power to the steam compressor may be an advantage.

[0052] In some embodiments, a steam turbine is connected to the first or high pressure steam network and is configured to provide power to the steam compressor.

[0053] In another aspect, the present disclosure provides a method for reducing carbon dioxide emissions from a urea production facility, comprising the steps of:

[0054] - providing low pressure steam to the steam compressor from a second or low pressure steam network;

[0055] -Convert low-pressure steam into high-pressure steam in a steam compressor;

[0056] - directing the high pressure steam to a first or high pressure steam network.

[0057] In some embodiments, the method comprises the following steps:

[0058] - providing low pressure steam from a second or low pressure steam network to one or more low pressure devices;

[0059] - providing low pressure steam to the steam compressor from a second or low pressure steam network;

[0060] -Convert low-pressure steam into high-pressure steam;

[0061] - directing the high pressure steam generated by the steam compressor to a first or high pressure steam network;

[0062] - Providing high pressure steam from the first or high pressure steam network to one or more high pressure devices.

[0063] In another aspect, the present disclosure provides a method for reducing carbon dioxide emissions from a urea production facility, comprising the following steps:

[0064] - providing low-pressure steam at a pressure of 0.1 MPa to 0.7 MPa from the second steam network to the steam compressor;

[0065] - Converting low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa into high-pressure steam with a pressure of 1.5 MPa to 11 MPa by means of a steam compressor;

[0066] - Directing the high pressure steam generated by the steam compressor to the first steam network.

[0067] In some embodiments, the low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa provided to the steam compressor is generated by a high-pressure device, in particular a high-pressure carbamate condenser.

[0068] In another aspect, the present disclosure provides use of a steam compressor in a urea production plant for reducing carbon dioxide emissions from the urea production plant.

[0069] Figure 1An embodiment of a urea plant according to the present disclosure is shown. The plant includes a synthesis reactor 1 configured to mix ammonia and carbon dioxide and produce an aqueous solution 20, the aqueous solution comprising urea, ammonium carbamate and free ammonia. The synthesis section 1 is connected to an HP stripper 2. The HP stripper 2 is also connected to an HP steam network 10, which is configured to receive and distribute steam at a pressure of 2.0 MPa to 3.0 MPa. The HP stripper 2 is configured to remove some ammonium carbamate, free ammonia and water from the aqueous solution 20 and produce an aqueous solution 21 with fewer impurities and a higher urea concentration than the solution 20. The HP stripper 2 is also configured to produce a gas stream 22 comprising ammonia, carbon dioxide and water. The HP stripper 2 is connected to an HP carbamate condenser 5, which is configured to receive the gas stream 22. The HP carbamate condenser 5 is configured to condense the gas stream 22 into an aqueous solution and produce LP steam. The HP carbamate condenser 5 is connected to the LP steam network 11 so that the LP steam produced by the HP carbamate condenser 5 can be directly directed to the LP steam network 11. The HP stripper 2 is also connected to the LP section 3. The LP section 3 includes one or more devices configured to consume LP steam, such as a carbamate decomposer, an evaporator, a desorber and / or a steam ejector. The LP section 3 is connected to the LP steam network 11 so that the devices of the LP section can receive LP steam. The device includes a steam compressor 4, which is driven by an electric motor (not shown), connected to the HP steam network 10 and the LP steam network 11, and is configured to convert the LP steam into HP steam.

[0070] Figure 2 Another embodiment of a urea plant according to the present disclosure is shown. Figure 1 The device shown is similar, and the device includes a synthesis reactor 1, an HP stripping tower 2, an HP carbamate condenser 5 and an LP section 3, and the synthesis reactor is configured to produce an aqueous solution 20, and the aqueous solution contains urea, ammonium carbamate and free ammonia. The device includes a steam compressor 4, which is connected to an HP steam network 10 and an LP steam network 11, and is configured to convert LP steam into HP steam. The device also includes a back-pressure steam turbine 6, which is connected to a 4.0 MPa (or higher pressure, if available) steam network (i.e., the third steam network) through a connector 7. The steam turbine 6 is connected to the compressor 4 and is configured to provide power to the compressor. The steam turbine 6 is also connected to the HP steam network 10 and is configured to release HP steam at the same pressure as the steam contained in the HP steam network 10.

Claims

1. A urea production equipment, comprising: a first steam network configured to receive high pressure steam at a pressure of 1.5 MPa to 11 MPa; and a second steam network, wherein the second steam network is configured to receive low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa, characterized in that the equipment includes a steam compressor, which is configured to: receive steam from the second steam network, convert the low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa into high-pressure steam with a pressure of 1.5 MPa to 11 MPa, and transport the high-pressure steam to the first steam network.

2. The urea production facility according to claim 1, wherein the urea production facility comprises a high-pressure carbamate condenser configured to provide low-pressure steam to the second steam network.

3. The urea production plant according to claim 1 or 2, wherein the plant comprises one or more high-pressure devices connected to the first steam network, these one or more high-pressure devices being high-pressure strippers or urea hydrolyzers.

4. Urea production plant according to any one of claims 1 to 3, wherein the plant comprises one or more low-pressure devices connected to the second steam network, in particular wherein these one or more low-pressure devices are selected from the group consisting of: evaporators, carbamate decomposers, desorbers, steam ejectors, steam turbines and carbamate condensers.

5. The urea production plant according to any one of claims 1 to 4, wherein the steam compressor is connected to a steam turbine connected to the first steam network and configured to provide power to the steam compressor.

6. The urea production plant according to any one of claims 1 to 5, wherein the steam compressor is a two-stage compressor.

7. A urea production plant according to any one of claims 1 to 6, wherein the plant comprises a carbon dioxide compressor and a first electric motor connected to the carbon dioxide compressor and configured to provide power to the carbon dioxide compressor.

8. Urea production plant according to any one of claims 1 to 7, wherein the plant comprises a second electric motor connected to the steam compressor and configured to provide power to the steam compressor.

9. A method for reducing carbon dioxide emissions from a urea production plant according to any one of claims 1 to 8, the method comprising the following steps: - providing low-pressure steam at a pressure of 0.1 MPa to 0.7 MPa from a second steam network to the steam compressor; - converting the low-pressure steam with a pressure of 0.1 MPa to 0.7 MPa into high-pressure steam with a pressure of 1.5 MPa to 11 MPa by the steam compressor; - directing said high pressure steam generated by said steam compressor to a first steam network.

10. The method according to claim 9, wherein the low-pressure steam having a pressure of 0.1 MPa to 0.7 MPa provided to the steam compressor is generated by a high-pressure carbamate condenser.

11. The method according to claim 9 or 10, further comprising the following steps - Providing low-pressure steam at a pressure of 0.1 MPa to 0.7 MPa from the second steam network to one or more low-pressure devices; -Providing high pressure steam at a pressure of 1.5 MPa to 11 MPa from the high pressure steam network to one or more high pressure devices.

12. Use of a steam compressor in a urea production plant according to any one of claims 1 to 8 for reducing carbon dioxide emissions from the urea production plant.

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