Method and system for operating a gas compressor in an ammonia and urea plant equipment

Abstract

Methods and systems for operating a gas compressor in an ammonia and urea plant facility. The present disclosure provides a plant facility comprising an ammonia production plant and a urea production plant. The urea production plant comprises a gas compressor, a steam turbine, and an electric motor, the steam turbine being fluidly connected to the ammonia production plant for receiving steam generated by the ammonia production plant and to the gas compressor for providing power to the gas compressor, wherein the electric motor is connected to the gas compressor and configured to provide power to the gas compressor. The present disclosure also provides a method of operating an ammonia and urea plant facility, and a method of revamping an ammonia and urea plant facility.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of urea production. In particular, the present disclosure relates to a plant facility comprising an ammonia production plant and a urea production plant comprising a gas compressor, a steam turbine and an electric motor. Furthermore, the present disclosure provides a method of operating a gas compressor in an ammonia and urea plant facility. BACKGROUND

[0002] Urea is produced by reacting ammonia (NH3) and carbon dioxide (CO2) in a two-step process: first, two ammonia molecules react with one carbon dioxide molecule to form carbamate (H2N-COONH4); second, the carbamate is decomposed into urea and water.

[0003] In the first step process, a gaseous CO2 and ammonia stream are mixed in a synthesis reactor. The reaction is carried out at high pressure (above 100 bar) to drive the reaction and increase productivity. The CO2 stream needs to be compressed at a similar pressure before being injected into the synthesis reactor: this step is performed by a gas compressor, i.e. a CO2 compressor.

[0004] A gas compressor requires a significant amount of energy to operate, and this energy can be provided by various means, such as a steam turbine and an electric motor.

[0005] A plant facility comprising a urea production plant usually also comprises an ammonia production plant, since urea synthesis requires ammonia. The ammonia production plant is a net exporter of steam, meaning that it produces more steam than it consumes, and one way of using this steam is to install a steam turbine that powers the CO2 compressor of the urea production plant, and to lead steam from the ammonia production plant to the steam turbine to save plant facility costs.

[0006] However, the ammonia production plant usually does not produce enough steam to power the CO2 compressor entirely. The remaining steam required by the compressor can be obtained in different ways, but is usually produced by boiling water using the energy released by the combustion of a combustible material, such as natural gas and coal, in so-called gas boilers. The number of boilers depends on the complexity of the site and the required flexibility.

[0007] Today, the environmental footprint of industrial production sites is under scrutiny due to the effects of using non-renewable and polluting energy sources, and there is a need to reduce the consumption of natural gas in a plant facility comprising an ammonia production plant and a urea production plant.

[0008] In the present disclosure, an ammonia and urea plant facility refers to a plant facility comprising one ammonia production plant and one urea production plant. SUMMARY

[0009] It has been found that by one or more electric motors, one or more natural gas boilers, which are used to produce steam for a steam turbine connected to a gas compressor, e.g. a carbon dioxide compressor, can be replaced or at least the natural gas consumption of the natural gas boilers can be reduced.

[0010] In a first aspect, the present disclosure provides a plant facility comprising an ammonia production plant and a urea production plant, the urea production plant comprising a gas compressor, a steam turbine and an electric motor, the steam turbine being fluidly connected to the ammonia production plant for receiving steam produced by the ammonia production plant, the steam turbine also being connected to the gas compressor and configured to power the gas compressor during operation of the urea production plant, wherein the electric motor is connected to the gas compressor and configured to power the gas compressor during operation of the urea production plant.

[0011] In another aspect, the present disclosure provides a method of operating a gas compressor in a plant facility according to the present disclosure, in particular during operation of the plant facility, the method comprising the step of powering the gas compressor from an electric motor, in particular simultaneously with powering the gas compressor from a steam turbine.

[0012] In another aspect, the present disclosure provides a method of reducing steam consumption of a urea production plant, the urea production plant comprising a gas compressor connected to a steam turbine and configured to receive power from the steam turbine, the method comprising the steps of: installing an electric motor; connecting the electric motor to the gas compressor; powering the gas compressor from the electric motor during operation of the urea production plant; and simultaneously powering the gas compressor from the steam turbine. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A system comprising a steam turbine and a CO2 gas compressor according to the prior art is represented.

[0014] Figure 2 A system comprising a steam turbine, a CO2 gas compressor and an electric motor according to the present disclosure is represented. DETAILED DESCRIPTION

[0015] Unless otherwise defined, all terms used in disclosing the application, including technical and scientific terms, have the meaning commonly understood by one of ordinary skill in the art to which this application belongs. By means of further guidance, term definitions are included to better define the teaching of the present application.

[0016] All references cited in this description are hereby incorporated by reference in their entirety.

[0017] As used herein, the following terms have the following meanings:

[0018] As used herein, "a," "an," and "the" mean one or more, unless the context clearly dictates otherwise. For example, "a device" means one or more devices.

[0019] As used herein, "about" for a measurable value or a range of values, such as an amount, a duration, a time, or the like, means that the value or range of values is not limited to the recited value or range of values, but rather means that the value or range of values is approximated, and that the approximated value or range of values is suitable for the intended purpose, unless the context clearly dictates otherwise. For example, "about" means + / - 20% or less, particularly + / - 10% or less, more particularly + / - 5% or less, even more particularly + / - 1% or less, and again more particularly + / - 0.1% or less of the recited value or range of values, within these ranges the approximated values are suitable for use in the disclosed application. However, it is understood that the value or range of values to which the modifier "about" refers is also expressly disclosed.

[0020] As used herein, "comprises," "comprising," "includes," "including," "has," "having," "contains," "containing," "characterized by," "including the features of," "comprised of," "comprising the features of," "having the features of," "including the features of the" and "comprising the features of the" are synonymous with "containing," "comprising" or "including," and are inclusive or open-ended terms that indicate the presence of whatever follows the term, e.g., features, elements, components, steps, and the like, and that are not limited to any specific combinations of the items, but rather "include," "comprise" or "contain" the stated features, elements, components, steps, and the like, but not excluding others.

[0021] Numerical ranges expressed in ranges from about a number to about a number, or from about a number to about a number, should be interpreted as being inclusive of the numbers disclaimer endpoints and all the fractions within the range.

[0022] Unless otherwise defined, the expressions "weight percent," "%wt," or "wt.%" mean herein and throughout the description the relative weight of the respective component based on the total weight of the formulation.

[0023] A plant facility is disclosed, the plant facility comprising an ammonia production plant and a urea production plant, the urea production plant comprising a gas compressor, a steam turbine and an electric motor, the steam turbine being fluidly connected to the ammonia production plant for receiving steam produced by the ammonia production plant and to the gas compressor for powering the gas compressor, wherein the electric motor is connected to the gas compressor and configured to power the gas compressor.

[0024] In a first aspect, the present disclosure provides a plant facility, the plant facility comprising an ammonia production plant and a urea production plant, the urea production plant comprising a gas compressor, a steam turbine and an electric motor, the steam turbine being fluidly connected to the ammonia production plant for receiving steam produced by the ammonia production plant, the steam turbine also being connected to the gas compressor and configured to power the gas compressor during operation of the urea production plant, wherein the electric motor is connected to the gas compressor and configured to power the gas compressor during operation of the urea production plant.

[0025] As used herein, the term "during operation" of a plant or plant facility, in particular a urea production plant, refers to the continuous mode of operation of the plant or plant facility to produce a product, in particular urea. The production cycle of a plant or plant facility comprises a start-up phase in which different processes are started up; a continuous and substantially constant phase or mode of operation in which the processes are run at a given work load which is typically kept constant during the production cycle; and a shut-down phase in which the processes are slowly and safely stopped.

[0026] The present invention describes a plant facility and a method in which the steam consumption of the plant facility is reduced during the continuous mode of operation, i.e. the second phase as described above.

[0027] For a long time, ammonia and urea plant facilities have used gas-consuming boilers to provide the steam required for different processes in the plant facility. The production of ammonia requires hydrogen gas, which is typically produced by steam reforming, a process in which natural gas is converted into hydrogen and carbon dioxide. Therefore, ammonia and urea plant facilities require a lot of equipment to receive and store natural gas, and the addition of extra boilers in the plant facility is seen as a cost-effective way to produce extra steam. Ammonia and urea plant facilities are typically located at natural gas production sites to have a competitive price for a large supply of natural gas and to be able to use some of it to produce steam.

[0028] A urea production plant typically comprises three steam networks operating at different pressures: a high-pressure steam network comprising steam between 100 bar and 120 bar, in particular 110 bar, a medium-pressure steam network comprising steam between 30 bar and 50 bar, in particular 40 bar, and a low-pressure steam network comprising steam between 1 bar and 5 bar.

[0029] In one embodiment, the steam turbine connected to the gas compressor is operated using 40 bar steam. The pressure and amount of steam received by the steam turbine determines the maximum power that the steam turbine can generate.

[0030] However, burning natural gas to generate steam also produces a lot of CO2, which is a natural by-product of this reaction. Carbon dioxide, of course, has a strong greenhouse gas effect, and there is a broad consensus among the political, industrial, and scientific communities to reduce CO2 emissions.

[0031] Another important source of CO2 emissions is thermal power plants. Many of these power plants use non-renewable heat sources, such as natural gas and / or coal. This industry is also working to reduce the greenhouse effect, and the installation of power plants based on renewable energy sources, such as wind, sunlight, and waterfalls, is also accelerating worldwide. Therefore, there is an opportunity to improve the energy consumption of ammonia and urea plant facilities to reduce their CO2 emissions.

[0032] It has been found that by installing an electric motor that will power a gas compressor, one or more natural gas boilers that are used to provide steam to steam turbines connected to the gas compressors of a urea production plant can be replaced, or at least the natural gas consumption of the natural gas boilers can be reduced. The less steam the steam turbines receive, the less power is delivered to the compressors, but this power difference is compensated by the electric motor. The presence of an electric motor and a steam turbine connected to a single machine (the CO2 gas compressor) increases the complexity of the plant equipment, as these two power sources need to be constantly balanced in order to provide a stable power supply to the gas compressor. Therefore, this configuration is generally not preferred compared to a simple configuration in which the CO2 gas compressor is powered by a single (steam) turbine or a single (electric) motor. Moreover, this configuration can also require more maintenance and space in the plant equipment, which increases the costs of installing and operating the plant equipment.

[0033] During the operation of the urea production plant, the electric motor and the steam turbine simultaneously provide power to the gas compressor. Depending on parameters such as the steam available in the plant equipment, the electricity available in the plant equipment, or the cost of electricity, the amount of power provided by the electric motor and the steam turbine can differ during the production process of the urea production plant.

[0034] As mentioned above, it is of interest to have a steam turbine in a urea production plant to consume steam produced by other production plants, such as an ammonia production plant. In addition, the urea plant equipment also produces steam at a lower pressure (e.g. 4 bar). This low pressure steam is used in the urea production plant or other processes that require steam to operate, such as heat exchangers. Excess steam can be introduced into the steam turbine to provide additional power.

[0035] Electric motors are a well-known type of equipment that can be used to power a gas compressor, such as a CO2 compressor in a urea production plant. The electric motor can be powered from the grid to which the plant equipment is connected, but can also be powered by a power plant located within the plant equipment. For example, it is conceivable to install solar panels and / or wind turbines within the plant equipment to power the electric motor. As is well known, renewable energy sources are intermittent, so the electric motor is usually connected to the local grid to compensate for irregular power generation due to renewable energy sources.

[0036] In countries where a majority of the electricity is produced using non-CO2 emitting sources, electric motors powering the gas compressors are especially beneficial. Renewable energy sources such as wind, sunlight, and waterfalls are non-CO2 emitting sources. Nuclear power plants are not based on renewable energy (uranium); however, they do not emit CO2. Even when the local power grid is powered by power plants that use non-renewable energy sources, using electric motors can save some CO2 because large power plants are generally more efficient than small boilers installed in chemical fertilizer plants (such as ammonia and urea plant equipment).

[0037] As used herein, an electric motor is a device capable of converting electrical power into mechanical power. In the context of the present disclosure, the electric motor is connected to a shaft that transmits the power generated by the electric motor to the gas compressor. The electric motors described herein generally do not convert mechanical power back into electrical power.

[0038] The size of the electric motor can be determined according to the power required by the compressor and the loss of power generated by the steam turbine, thereby removing the natural gas boiler or reducing the productivity of the boiler.

[0039] In one embodiment, the electric motor is configured to provide 20%-80% of the power required by the gas compressor. In one embodiment, the electric motor is configured to provide 20%-50% of the power required by the gas compressor. In one embodiment, the electric motor is configured to provide 50%-80% of the power required by the gas compressor. In one embodiment, the electric motor is configured to provide 30%-70% of the power required by the gas compressor. The power to be provided by the electric motor depends on the amount of steam that should be saved. The more steam that needs to be removed from the plant equipment consumption, the more power the electric motor needs to supply.

[0040] In one embodiment, the steam turbine receives steam only from an ammonia production unit. The ammonia production unit can generate enough steam to be provided to the steam turbine and the required power generation is achieved by the steam turbine. In this case, a natural gas boiler is not required to generate additional steam. The plant equipment can also include multiple (i.e., more than one) ammonia production units and all of the multiple ammonia production units provide steam to the steam turbine of the urea production unit. When the plant equipment includes more than one ammonia production unit, it is more likely that a natural gas boiler is not required to provide steam to the steam turbine of the urea production unit.

[0041] In one embodiment, the plant equipment including an ammonia production unit and a urea production unit further includes another steam production unit. The chemical fertilizer plant can include other production units related or unrelated to chemical fertilizer production. These units can generate steam that is not consumed within the unit and can be directed to the steam turbine in the urea production unit.

[0042] In an embodiment, the plant facility comprising an ammonia production plant and a urea production plant further comprises a nitric acid production plant. Nitric acid is another important chemical for the production of fertilizers. It reacts with a base, such as ammonia or phosphate rock, to produce a solid fertilizer compound. The production of nitric acid requires ammonia, so a plant facility comprising an ammonia production plant can also comprise a nitric acid production plant to make use of the ammonia produced in the plant facility. The nitric acid production plant comprises a number of pieces of equipment, such as reactors, heat exchangers, etc. The nitric acid production plant is also a net exporter of steam, which can be provided to the steam turbine of the gas compressor of the urea production plant.

[0043] In an embodiment, the nitric acid production plant provides steam to the steam turbine connected to the gas compressor of the ammonia and urea plant facility according to the present disclosure.

[0044] In an embodiment, the steam turbine receives steam only from the ammonia production plant and the nitric acid production plant.

[0045] In an embodiment, the gas compressor connected to the electric motor is a carbon dioxide compressor.

[0046] The present disclosure also discloses a method of operating a gas compressor in a plant facility according to the present disclosure, the method comprising the step of providing power to the gas compressor from an electric motor. The present disclosure also discloses a method of operating a gas compressor in a plant facility according to the present disclosure, in particular during continuous operation of the plant facility according to the present disclosure or the urea production plant, the method comprising the step of providing power to the gas compressor from an electric motor and simultaneously providing power to the gas compressor from a steam turbine.

[0047] It has been found that connecting the gas compressor of the urea production plant to a steam turbine and an electric motor is an advantage. The ammonia production plant and optionally the nitric acid production plant comprised in the plant facility provide steam to the steam turbine. A natural gas boiler can also produce steam.

[0048] The electric motor can be provided with electricity from a local power plant, in particular a power plant based on renewable energy, as well as from the national grid. This electric motor reduces the natural gas consumption of the plant facility by providing power to the gas compressor. This method is particularly advantageous in countries where a large part of the electricity is produced using non-CO2 emitting methods.

[0049] This aspect of the present disclosure can exhibit the same or similar features and technical effects as the first aspect, i.e. the plant facility according to the present disclosure, and vice versa.

[0050] During continuous production of urea by the urea production plant, both the electric motor and the steam turbine continuously and simultaneously provide power to the gas compressor. The power provided by each device can differ during the production run.

[0051] In another aspect, the present disclosure provides a method of reducing steam consumption of a urea production plant, the urea production plant comprising a gas compressor connected to a steam turbine and configured to receive power from the steam turbine, the method comprising the steps of: installing an electric motor; connecting the electric motor to the gas compressor; providing power to the gas compressor from the electric motor during operation of the urea production plant; and simultaneously providing power to the gas compressor from the steam turbine.

[0052] The electric motor is installed and connected to the gas compressor. During operation of the urea production plant, the electric motor is supplied with electricity, which can be generated from renewable sources such as hydroelectric, wind, solar and tidal, and provides mechanical power to the gas compressor. Thus, the existing steam turbine does not need to provide the same power to the gas compressor as in prior art systems (i.e. without the electric motor), and therefore the amount of steam provided to the steam turbine can be reduced. In such a urea production plant, steam is typically produced by burning natural gas and heating water with the resulting heat. Thus, reducing the amount of steam required by the plant equipment or plant can reduce the amount of natural gas that is burned to produce steam, and reduce carbon dioxide emissions resulting from the production of steam.

[0053] The gas compressor can be a syngas compressor, a carbon dioxide compressor or an ammonia compressor.

[0054] In one embodiment, the ammonia production plant supplies steam to the steam turbine of the urea production plant.

[0055] In one embodiment, the plant equipment comprises a nitric acid production plant, and the nitric acid production plant supplies steam to the steam turbine of the urea production plant.

[0056] In another aspect, the present disclosure provides a method of retrofitting a plant equipment, the plant equipment comprising an ammonia production plant and a urea production plant, the urea production plant comprising a gas compressor and a steam turbine and a natural gas boiler connected to the steam turbine, the steam turbine being fluidly connected to the ammonia production plant to receive steam produced by the ammonia production plant, the steam turbine being connected to the gas compressor to provide power to the gas compressor. The method comprises the steps of: installing an electric motor connected to the gas compressor and configured to provide power to the gas compressor; and optionally disconnecting the natural gas boiler from the steam turbine.

[0057] This aspect of the present disclosure can exhibit the same or similar features and technical effects as the first aspect (i.e. the plant equipment according to the present disclosure), and vice versa.

[0058] This can be applied to existing ammonia and urea plant equipment in which the steam turbine for the gas compressor of the urea plant is supplied with steam from one or more natural gas boilers. It is certainly possible, and relatively easy, to install an electric motor to power the gas compressor. Electric motors can come in a variety of designs, sizes and performance, so it is possible to find a suitable electric motor for most existing ammonia and urea plant equipment. Once the electric motor is installed, the steam turbine's demand for steam is reduced. This reduction can bring the one or more natural gas boilers to a state in which they are not needed to run at all, and can therefore be disconnected from the steam turbine. They can be reallocated to another task within the plant, or simply removed. Alternatively, if the natural gas boilers are used, the reduction in steam required can simply reduce the usage rate. Instead of running the boilers at 90% of their capacity, they can be run at less than 80%, and in particular at less than 70% of their capacity, to extend their useful life and / or facilitate maintenance.

[0059] In one embodiment, an electric motor is installed and connected to the CO2 compressor of the urea plant.

[0060] Example 1

[0061] In a plant comprising an ammonia plant, a urea plant and a nitric acid plant, the urea plant comprises a steam turbine (1) powering a CO2 compressor (2).

[0062] Figure 1 The initial system, i.e. the prior art, is represented: the steam turbine receives 40 bar steam (steam (10)) at 215 tons / hour (t / h) and produces 19.7 MW of power for the CO2 compressor. Steam is produced at 215 t / h, 145 t / h in the ammonia plant and the nitric acid plant, and the natural gas boilers produce steam at 70 t / h. In addition, 4 bar steam (steam (11)) produced at 18 t / h in the urea plant is injected into the steam turbine, 20 bar steam (steam (12)) is extracted from the steam turbine at 138 t / h and used in the urea plant.

[0063] Figure 2A system according to the present disclosure is shown. An electric motor (3) is installed and connected to the CO2 compressor (2). The electric motor is configured to produce 10.2 MW of power and to provide this power to the CO2 compressor (2). The steam turbine (1) only needs to produce 9.5 MW, so the steam supply is reduced to 175 t / h (steam (13), which is still produced by the ammonia production plant and the nitric acid production plant at 145 t / h. Now, the natural gas boiler produces 40 bar steam at only 30 t / h instead of 70 t / h, which corresponds to a saving of 5.4 tons of CO2 equivalent per hour. The steam turbine still receives 4 bar steam (steam (14)) at 18 t / h and extracts 20 bar steam (steam 15) from the steam turbine at 138 t / h.

Claims

1. A plant comprising: - an ammonia production unit; and - a urea production unit comprising: a gas compressor; a steam turbine fluidly connected to the ammonia production unit for receiving steam produced by the ammonia production unit, the steam turbine being connected to the gas compressor and configured to power the gas compressor during a continuous operation of the urea production unit, the continuous operation being a continuous phase in a production cycle in which the unit produces urea and operates at a given work load; and an electric motor; characterized in that the electric motor is connected to the gas compressor and configured to power the gas compressor during the continuous operation of the urea production unit; and in that the electric motor is configured to provide 20-80% of the power required by the gas compressor during the continuous operation of the urea production unit.

2. The plant according to claim 1, wherein, The plant comprises a nitric acid production unit.

3. The plant according to claim 1 or 2, wherein, The gas compressor is a carbon dioxide compressor.

4. A method of operating a gas compressor in a plant according to any one of claims 1 to 3, the method comprising the steps of powering the gas compressor from an electric motor during a continuous operation of a urea production unit, the continuous operation being a continuous phase in a production cycle in which the unit produces urea and operates at a given work load, and simultaneously powering the gas compressor from a steam turbine.

5. A method of reducing steam consumption of a urea production plant, the urea production plant comprising a gas compressor connected to a steam turbine and configured to receive power from the steam turbine, the method comprising the steps of: installing an electric motor; connecting the electric motor to the gas compressor; powering the gas compressor from the electric motor during a continuous operation of the urea production unit, the continuous operation being a continuous phase in a production cycle in which the unit produces urea and operates at a given work load; and simultaneously powering the gas compressor from the steam turbine; in that the electric motor is configured to provide 20-80% of the power required by the gas compressor during the continuous operation of the urea production unit.

6. The method of claim 4 or 5, wherein, The ammonia production unit provides steam to the steam turbine of the urea production unit.

7. The method of claim 4 or 5, wherein, The plant comprises a nitric acid production unit and the nitric acid production unit provides steam to the steam turbine of the urea production unit.

8. A method of retrofitting a plant comprising an ammonia production unit and a urea production unit, the urea production unit comprising a gas compressor and a steam turbine and a natural gas boiler connected to the steam turbine, the steam turbine being fluidly connected to the ammonia production unit for receiving steam produced by the ammonia production unit, the steam turbine being connected to the gas compressor for powering the gas compressor, the method comprising the steps of: installing an electric motor connected to the gas compressor and configured to power the gas compressor during a continuous operation of the urea production unit, the continuous operation being a continuous phase in a production cycle in which the unit produces urea and operates at a given work load; and wherein the electric motor is configured to provide 20-80% of the power required by the gas compressor during continuous operation of the urea production plant.

9. The method of claim 8, further comprising the step of: disconnecting the natural gas boiler from the steam turbine.

Images