Method and plant for producing urea

Abstract

The group of inventions relates to a method and plant for producing urea from by-products of oil or gas refining and can be used in the chemical industry and in the production of fertilizers. What is proposed is a method for producing urea which includes a) a stage of dehydrogenating hydrocarbons at oil or gas refining facilities to produce a hydrogen-containing gas, during which carbon dioxide is separated from the flue gases from the dehydrogenation process furnaces; b) a stage of steam-air reforming the hydrogen-containing gas to produce a converted gas; c) a stage of converting carbon monoxide and separating carbon dioxide from the converted gas to produce a synthesis gas; d) a stage of producing ammonia from the synthesis gas produced in stage c); and e) a stage of producing urea from the ammonia produced in stage d) and the carbon dioxide produced in stages a) and c). Also proposed is a plant for producing urea. The technical result of the group of inventions is an increase in the energy efficiency and environmental friendliness of technology for producing urea from by-products of oil and gas refining, together with a reduction in metal consumption, specific energy consumption and specific fuel gas consumption, in addition to which, the residual content of unconverted hydrocarbons after steam-air reforming is not more than 1 vol.%.

Description

[0001] METHOD FOR PRODUCING UREA AND AN INSTALLATION FOR ITS IMPLEMENTATION

[0002] Field of technology

[0003] The group of inventions relates to a method and installation for obtaining urea from by-products of oil or gas processing and can be used in the chemical industry and in the production of fertilizers.

[0004] Prior art

[0005] The main traditional source of raw materials for obtaining ammonia and, subsequently, urea, is natural gas (NG).

[0006] The classical method of obtaining ammonia from natural gas includes purification of natural gas from sulfur compounds, two-stage steam (stage I) and steam-air (stage II) conversion of natural gas in a tubular furnace and in a shaft reactor, respectively, two-stage conversion of carbon monoxide, purification of the converted gas from carbon dioxide, methanation of monoxide and carbon dioxide, compression of the nitrogen-hydrogen mixture, synthesis of ammonia at a pressure above 30 MPa (Azotchik Handbook. - M., Chemistry, 1986, v.1, pp.83, 84, IZ, 213, 222, 360-364).

[0007] A disadvantage of using natural gas as a feedstock for ammonia production is the need for efficient conversion of natural gas into carbon oxides, which necessitates the use of a primary reformer—a metal-intensive piece of equipment that consumes large amounts of fuel gas. On average, 290 Nm is fed to the reformer for combustion. 3Fuel gas per ton of ammonia. Burning large quantities of natural gas increases greenhouse gas emissions, reducing the environmental friendliness of the technology. Furthermore, natural gas is a primary source of raw materials: saved natural gas can be usefully used as fuel in other technological processes.

[0008] Thus, the problem of finding alternative sources of raw materials suitable for producing ammonia arises.

[0009] Furthermore, it is known that when natural gas is used as a feedstock for ammonia production, ammonia and carbon dioxide are not produced in stoichiometric quantities for subsequent urea synthesis, resulting in an excess of ammonia relative to carbon dioxide. In this case, the excess ammonia is refrigerated, leading to additional energy costs. Therefore, another challenge is finding an additional source of carbon dioxide.

[0010] It is widely known that hydrogen-containing gas (HCG) is a byproduct of hydrocarbon dehydrogenation processes at oil and gas refineries. At most refineries, HCG is sent to a PSA, where hydrogen is recovered and then burned as fuel. Such technologies are characterized by low energy efficiency and environmental friendliness.

[0011] However, technical solutions are known that disclose the use of WSG as a feedstock for the production of ammonia and urea.

[0012] Thus, US Patent No. US8932456B2, published on January 13, 2015, discloses a method for producing ammonia and urea from hydrogen-containing off-gas from petroleum refining products. In the proposed method, hydrogen-containing gas is obtained from petroleum fractions and then sent to a steam reformer and a hydrogen recovery unit. The resulting hydrogen stream, along with a nitrogen stream obtained in an air separation unit, is sent to ammonia synthesis. Part of the resulting ammonia is then used to produce urea.

[0013] The disadvantages of the proposed invention include the production of ammonia from hydrogen and nitrogen streams obtained in complex hydrogen extraction and air separation units, which increases the metal consumption of the technology. In hydrogen extraction units (such as PSA), some of the hydrogen is consumed in regeneration processes, reducing the efficiency of the technology. Furthermore, steam reforming, used to increase the hydrogen content in hydrogen-containing gas, is carried out at low temperatures, which reduces the degree of conversion of hydrocarbons to hydrogen, reducing the energy efficiency of the technology and reducing the yield of ammonia, which is then used to produce urea. Steam reforming also requires the use of a primary reforming furnace—a metal-intensive piece of equipment that consumes large quantities of fuel gas. Combustion of large quantities of natural gas leads to increased greenhouse gas emissions, reducing the environmental friendliness of the technology.Furthermore, natural gas is a primary source of feedstock: saved natural gas can be usefully used as fuel in other processes. Furthermore, the proposed solution lacks the ability to flexibly adjust the molar ratios of ammonia and carbon dioxide used for urea synthesis, requiring additional energy expenditures to utilize excess ammonia.

[0014] The closest analogue (prototype) of the invention is the method known from Russian patent RU2710228C1, published on December 25, 2019, for producing ammonia and urea from hydrogen-containing gas formed as a byproduct of the pyrolysis of an ethane-propane fraction. The resulting hydrogen-containing gas, consisting of methane and hydrogen, is fed to a PSA, where hydrogen is recovered, some of which is used for ammonia synthesis. Nitrogen for ammonia production is obtained in an air separation unit. The proposed method does not use a metal-intensive steam reforming furnace.

[0015] The disadvantages of the proposed invention include the production of ammonia from hydrogen and nitrogen streams obtained in complex hydrogen extraction and air separation units, which increases the metal consumption of the technology and reduces energy efficiency. In hydrogen extraction units (such as PSA), some of the hydrogen is consumed in regeneration processes, reducing the efficiency of the technology. Furthermore, the proposed method does not convert the methane remaining in the hydrogen sulfide gas (HSG) at all; it is sent for combustion, which reduces the production of the valuable product hydrogen and, consequently, reduces ammonia yield. Furthermore, the proposed solution lacks the ability to flexibly adjust the molar ratios of ammonia and carbon dioxide used for urea synthesis, requiring additional energy expenditures for the disposal of excess ammonia.

[0016] Disclosure of invention

[0017] The objective and technical result of the proposed invention is to increase the energy efficiency and environmental friendliness of the technology for obtaining urea from by-products of oil and gas processing while reducing metal consumption, specific energy consumption, specific fuel gas consumption, and also with a residual content of unconverted hydrocarbons after steam-air reforming not exceeding 1 vol.%.Additionally, there is no need to use a metal-intensive air separation unit and a metal-intensive primary reforming furnace that consumes large quantities of fuel gas; the technology is more environmentally friendly due to the beneficial use of carbon dioxide from flue gases; the ability to flexibly regulate the hydrogen content in the ammonia synthesis gas; the ability to produce urea from flexibly regulated quantities of ammonia and carbon dioxide; an increase in the productivity of the urea production technology by 57.2%; the specific fuel gas consumption for combustion does not exceed 100 Nm. 3 per ton of ammonia, which is then used to produce urea.

[0018] In order to solve the stated problem and achieve the technical result, a method for producing urea is proposed, which includes a) a stage of dehydrogenation of hydrocarbons at oil or gas processing plants with the production of hydrogen-containing gas and the separation of carbon dioxide from flue gases leaving the furnaces of the dehydrogenation processes; b) a stage of steam-air reforming of the hydrogen-containing gas with the production of converted gas; c) a stage of conversion of carbon monoxide and the separation of carbon dioxide from the converted gas with the production of synthesis gas; d) a stage of obtaining ammonia from the synthesis gas obtained in stage c), e) a stage of obtaining urea from ammonia obtained in stage d) and carbon dioxide obtained in stage a) and stage c).

[0019] Hydrogen-containing gas (HCG) is a gas with a high hydrogen content (10% or more) that is formed in various industrial processes, particularly through the dehydrogenation of hydrocarbons. Examples of such processes include pyrolysis and catalytic reforming (aromatization) of hydrocarbon fractions entering oil or gas refineries.

[0020] Dehydrogenation is the reaction of hydrogen removal from a molecule of an organic compound.

[0021] Steam-air reforming is the production of gas with a high content of H2O and CO by converting hydrocarbons with oxidizing agents: air and steam.

[0022] It will be obvious to a specialist that steam-air reforming is a special case of autothermal reforming (ATR) - in the case when air is used as an oxidizer in ATR.

[0023] Using waste from gas and petrochemical production as feedstock leads to more environmentally friendly processes. The hydrogen sulfide gas (H2S), a byproduct of dehydrogenation processes, is not burned, creating toxic emissions, but is effectively used to produce valuable products such as ammonia. Furthermore, the ammonia production process, which is then used to produce urea, does not consume natural gas, which can be effectively used in other processes.

[0024] Steam-air reforming of HSG allows for the introduction of nitrogen, also present in the air, into the process flow along with the oxygen oxidizer, eliminating the need for a metal- and energy-intensive air separation unit. Furthermore, steam-air reforming facilitates the most efficient oxidation of hydrocarbons contained in HSG. In the present invention, the residual amount of hydrocarbons after steam-air reforming does not exceed 1 vol.%. Furthermore, the selected reforming type consumes less fuel gas for steam generation—only 98.5 Nm. 3per ton of ammonia, which is almost three times less than the natural gas consumption for steam generation in primary reformers. Furthermore, the hydrogen needed for ammonia production is generated by the conversion of hydrogen-carbon dioxide during the reforming stage, rather than by separation in a PSA. This eliminates the need for a metal-intensive, energy-consuming pressure swing adsorption unit and eliminates the loss of hydrogen used in the PSA regeneration processes. Furthermore, the separation of carbon dioxide from flue gases prevents their atmospheric emissions, further enhancing the environmental friendliness of the process, and allows urea to be produced exclusively from industrial waste.

[0025] Preferably, the dehydrogenation of hydrocarbons in oil or gas refining plants includes pyrolysis of the ethane-propane fraction and / or pyrolysis of the gasoline fraction and / or pyrolysis of the ligroin fraction (naphtha) and / or catalytic reforming of the gasoline fraction and / or catalytic reforming of the ligroin fraction (naphtha).

[0026] During pyrolysis the following reaction occurs:

[0027] С211Н4П+2 — ШС2Н4 + Нг

[0028] During the aromatization process (catalytic reforming), the following reaction occurs:

[0029] SgpNgp+g SpNgp-b + 4Ng

[0030] Pyrolysis of the ethane-propane fraction occurs with the release of the main products - ethylene and propylene, as well as a by-product - hydrogen-containing gas, which, in addition to hydrogen, also contains methane and, in some cases, impurity amounts of C2+ hydrocarbons.

[0031] In this application, gasoline fractions (gasoline) are defined as petroleum fractions with a boiling point of up to 140°C, primarily a mixture of C5-C11 hydrocarbons. Naphtha fractions (ligroin, naphtha) in this application are defined as petroleum fractions with a boiling point of 140-180°C, primarily a mixture of C4-C6 hydrocarbons.

[0032] Catalytic reforming and pyrolysis of gasoline and ligroin fractions occurs with the release of the main products - unsaturated hydrocarbons, in particular aromatic ones, as well as with the formation of a by-product - hydrogen-containing gas, which, in addition to hydrogen, also contains methane and, in some cases, impurity quantities of Cr+ hydrocarbons.

[0033] The processes of pyrolysis and catalytic reforming proceed with the release of unsaturated hydrocarbons - the main product, as well as with the release of a large amount of hydrogen sulfide as a by-product, which can be effectively used to produce ammonia, which is then used to produce urea.

[0034] Preferably, the amount of CO2 supplied to the urea synthesis from flue gases is adjusted depending on the amount of ammonia obtained in step d) and CO2 obtained in step c), so that the molar ratio of the amount of ammonia to the total amount of carbon dioxide tends to the stoichiometric ratio required to obtain urea.

[0035] During the ammonia production process, the carbon dioxide released in step c) is produced in a deficit relative to ammonia, relative to the stoichiometric ratio (1:2) required for urea production. Flue gases provide an additional source of carbon dioxide; its addition allows for flexible regulation of the amount of urea produced. This prevents the formation of excess ammonia, which requires additional energy to utilize, further increasing the energy efficiency of the process.

[0036] Preferably, step d) comprises removing purge gas from the ammonia synthesis loop.

[0037] Purge gas is a portion of the recycle gas withdrawn from the ammonia synthesis circuit (ammonia production unit) after the product ammonia separator. Purge gases, in addition to N2, H2, and NH3, contain inert impurities (CH4, Ar, He). Their presence negatively impacts the ammonia synthesis process, which is then used to produce urea.

[0038] Removing purge gas from the synthesis circuit reduces the amount of inerts in the circulation circuit and, as a consequence, reduces the pressure in the circulation circuit and reduces the metal consumption of the equipment (lower pressure requires equipment with thinner walls).

[0039] Preferably, the purge gas is directed to a hydrogen recovery unit.

[0040] The purge gas contains hydrogen, which can be used in the technology, further increasing its energy efficiency.

[0041] Preferably, the hydrogen separated from the purge gas is added to the synthesis gas obtained in step c).

[0042] If the hydrogen-containing gas entering the reformer has a high hydrocarbon content, excess air is added to maximize hydrocarbon oxidation. Consequently, more nitrogen is introduced into the system than is necessary to maintain the stoichiometry of the ammonia production reaction in the synthesis loop. The missing hydrogen can be obtained from the purge gas, further increasing the energy efficiency of the process.

[0043] Preferably, the amount of hydrogen added to the synthesis gas obtained in step c) is adjusted so that the ratio of hydrogen to nitrogen in the synthesis gas sent to step d) tends to the stoichiometric ratio required to produce ammonia.

[0044] The ability to flexibly regulate the hydrogen content in synthesis gas allows for further improvement of the energy efficiency of the technology.

[0045] Preferably, at step c), cryogenic purification of the obtained synthesis gas is carried out.

[0046] Cryogenic purification removes excess nitrogen from syngas, thereby ensuring a hydrogen-to-ammonia ratio in the syngas that approaches stoichiometric values. Furthermore, cryogenic purification removes inerts from the syngas, which reduces the pressure in the circulation loop and the metal requirements of the equipment (lower pressures require equipment with thinner walls).

[0047] Preferably, step c) of separating carbon dioxide comprises amine scrubbing.

[0048] Amine purification is carried out at process pressure, which further reduces energy consumption. Furthermore, conducting the process at pressures above atmospheric pressure reduces the consumption of absorbent for purification.

[0049] Preferably, hydrogen-containing gas is fed to stage b) of steam-air reforming at a temperature of at least 650°C and a pressure of 2-5 MPa; air is fed at a temperature of 450-650°C and a pressure of 2-5 MPa; and converted gas is obtained at a temperature of 900-1050°C and a pressure of 2-5 MPa.

[0050] The above parameters are the most preferable for the reforming processes.

[0051] Also, in order to solve the above-mentioned problem and achieve the claimed technical result, a urea production unit is proposed, comprising a hydrocarbon dehydrogenation unit at oil or gas processing plants, connected to a hydrogen-containing gas removal line, and comprising a dehydrogenation process furnace configured to separate and remove a CO2 stream from flue gases along line L1; a steam-air reforming unit connected to a hydrogen-containing gas supply line and a converted gas removal line; a carbon monoxide conversion and carbon dioxide separation unit connected to a converted gas supply line, a synthesis gas removal line L2, and a carbon dioxide removal line L3; an ammonia production unit connected to a synthesis gas supply line and an ammonia removal line; a urea production unit connected to an ammonia supply line, line L1, and line L3.

[0052] In this application, a line is understood to mean a means for delivering a flow from one place to another, which, in particular, includes the pipes and connecting elements necessary for this, as well as, if necessary, control means and devices.

[0053] In this application, a block is understood to mean a device or a set of devices that ensure the implementation of the function specified for a given block.

[0054] All advantages of the present invention stated in relation to the method for producing ammonia are equally applicable to the claimed installation and are not repeated here in order to avoid unnecessary duplication.

[0055] Preferably, the hydrocarbon dehydrogenation unit at oil or gas refining plants includes an ethane-propane fraction pyrolysis unit and / or a gasoline fraction pyrolysis unit and / or a ligroin fraction (naphtha) pyrolysis unit and / or a gasoline fraction catalytic reforming unit and / or a ligroin fraction (naphtha) catalytic reforming unit.

[0056] Preferably, the ammonia feed line, lines LI, L3 are equipped with volumetric flow rate control means designed to control the amount of urea produced and to ensure that the molar ratio of the amount of ammonia to the total amount of carbon dioxide is maintained, tending to the stoichiometric ratio required to produce urea.

[0057] Preferably, the ammonia production unit is configured to divert a purge gas flow from the ammonia synthesis circuit.

[0058] Preferably, a purge gas hydrogen extraction unit connected to the purge gas supply line and the hydrogen removal line L4.

[0059] Preferably, the synthesis gas outlet line L2 is connected to the hydrogen supply line L4.

[0060] Preferably, lines L2, L4 are equipped with volumetric flow rate control means designed in such a way as to ensure that the molar ratio of hydrogen to nitrogen in the synthesis gas sent to the ammonia production unit is maintained, tending to the stoichiometric ratio required for producing ammonia.

[0061] Preferably, the installation includes a cryogenic purification unit connected to the synthesis gas discharge line L2.

[0062] Preferably, the carbon dioxide separation unit includes an amine purification unit.

[0063] Brief description of the drawings

[0064] The drawings are presented for a better understanding of the invention, however, it will be obvious to a person skilled in the art that the disclosed invention is not limited to the embodiment shown in them.

[0065] Fig. 1-2 show block diagrams of the best embodiments of the invention.

[0066] The best embodiment of the invention

[0067] The described embodiments are provided for illustrative purposes only. Those skilled in the art will readily recognize that other embodiments are possible without changing the essence of the invention.

[0068] Example 1 In Fig. 1, hydrogen-containing gas is fed into compression and desulfurization unit 1 through line 100.

[0069] Hydrogen-containing gas (HCG) is a gas with a high hydrogen content (10% or more) that is formed in various industrial processes, particularly through the dehydrogenation of hydrocarbons. Examples of such processes include: pyrolysis of the ethanepropane fraction at a gas processing plant, pyrolysis of the gasoline or naphtha fraction in oil refining processes, aromatization (catalytic reforming) of the gasoline or naphtha fraction in oil refining processes, etc.

[0070] During pyrolysis the following reaction occurs:

[0071] С211Н4П+2 — ШС2Н4 + Нг

[0072] During the aromatization process (catalytic reforming), the following reaction occurs:

[0073] SgpNgp+g SpNgp-b + 4Ng

[0074] In addition to hydrogen, VSH also contains methane and, in some cases, trace amounts of C2+ hydrocarbons.

[0075] Next, the hydrogen-containing gas is fed to the pre-reforming unit 2 via line 102, where steam from the fired heater (not shown) is also fed via line 200. The resulting stream of partially converted gas is fed via line 203 to the autothermal reforming (ATR) unit 3, where air is also fed via line 300. The resulting converted gas is fed via line 304 to the carbon monoxide conversion unit 4, where the carbon monoxide is converted into carbon dioxide. The gas obtained in unit 4 is fed via line 405 to the amine purification unit 5, and carbon dioxide from unit 5 is removed via line 510 (L3) to the urea production unit 10. The synthesis gas purified from carbon dioxide is fed via line 506 (L2) to the methanation and compression unit 6. Next, gas from block 6 enters ammonia synthesis block 7 via line 607. A purge gas stream is withdrawn from the ammonia synthesis circuit via line 708, which is diverted for combustion in the fired heater via line 708.From the ammonia synthesis block 7, a flow of ammonia is removed via line 710 and sent to the urea synthesis block 10.

[0076] For optimal urea synthesis, ammonia and carbon dioxide should be fed to urea synthesis unit 10 in a molar ratio approaching stoichiometric, namely -2:1. However, it is well known that the carbon dioxide released from the reformed gas is insufficient relative to the ammonia. The missing amount of carbon dioxide is obtained from the flue gases of hydrocarbon fraction dehydrogenation furnaces (not shown) – in particular, pyrolysis furnaces and aromatization furnaces (catalytic reforming).

[0077] Lines 510 and 710 are equipped with carbon dioxide and ammonia measuring devices 12 and 13, respectively. Signals from the measuring devices are sent to the control unit, where the missing amount of carbon dioxide is calculated. Carbon dioxide separated from the flue gases enters the urea production unit 10 via line 110 (L1), equipped with regulator R2, the signal to which comes from the control unit. The urea formed in the urea production unit 10 is discharged to the consumer via line 111.

[0078] Example 2

[0079] Fig. 2 shows another preferred embodiment of the invention.

[0080] Hydrogen-containing gas is fed to compression and desulfurization unit 1 via line 100. The gas is then fed via line 203 to ATR unit 3, which also receives steam from the fired heater (not shown) via line 200 and air via line 300.

[0081] The resulting converted gas enters carbon monoxide conversion unit 4 via line 304, where carbon monoxide is converted to carbon dioxide. The gas obtained in unit 4 enters amine purification unit 5 via line 405, and carbon dioxide from unit 5 is removed via line 510 (L3) to urea production unit 10. The synthesis gas, purified from carbon dioxide, enters methanation and compression unit 6 via line 506 (L2). Next, the gas from unit 6 enters ammonia synthesis unit 7 via line 607. An ammonia stream is removed from ammonia synthesis unit 7 via line 710, which is sent to urea synthesis unit 10.

[0082] For optimal urea synthesis, ammonia and carbon dioxide should be fed to urea synthesis unit 10 in a molar ratio approaching stoichiometric, namely -2:1. However, it is well known that the carbon dioxide released from the reformed gas is insufficient relative to the ammonia. The missing amount of carbon dioxide is obtained from the flue gases of hydrocarbon fraction dehydrogenation furnaces (not shown) – in particular, pyrolysis furnaces and aromatization furnaces (catalytic reforming).

[0083] Lines 510 and 710 are equipped with carbon dioxide and ammonia measuring devices 12 and 13, respectively. Signals from the measuring devices are sent to the control unit, where the missing amount of carbon dioxide is calculated. Carbon dioxide, released from the flue gases, enters the urea production unit 10 via line 110 (L1), equipped with regulator R2, which receives a signal from the control unit.

[0084] The urea formed in the urea production unit 10 is supplied to the consumer via line 111

[0085] Air is supplied to the ATR unit 3 via line 300 in such a quantity that oxygen oxidizes the hydrocarbons remaining in the hydrogen sulfide gas to carbon oxides, with a residual content in the gas not exceeding 1 vol.%. Nitrogen is obviously supplied to the system along with atmospheric oxygen. For optimal ammonia production, hydrogen and nitrogen should be supplied to unit 7 via line 607 in a ratio approaching stoichiometric, namely 3:1. In the case of a high hydrocarbon content in the hydrogen sulfide gas entering the ATR unit, an excess amount of air is supplied via line 300 to maximize hydrocarbon oxidation. As a result, more nitrogen is introduced into the system than is necessary to maintain the stoichiometry of the ammonia production reaction in the synthesis loop.

[0086] A purge gas stream is withdrawn from the ammonia synthesis circuit via line 708 and fed to unit 8 for separating ammonia from purge gases. The liquid ammonia obtained in unit 8 is returned to ammonia synthesis unit 7 via line 807.

[0087] The purge gas flow enters the hydrogen recovery unit 9, the hydrogen flow is removed via line 906 (L4), and the waste gas is removed via line 900 for combustion in the combustion heater (not shown).

[0088] Line 506 is equipped with a measuring device II for measuring the amount of hydrogen and nitrogen in the flow. The signal from measuring device II is fed to the control unit, where the required amount of hydrogen is calculated (to achieve a hydrogen to nitrogen ratio of 3:1). The signal from the control unit is then sent to regulator R1, and the required amount of hydrogen, extracted from the purge gas, is sent to unit 6 for the compression stage.

[0089] It will be obvious to the skilled person that an alternative way to achieve a hydrogen to nitrogen ratio of 3:1 is to cryogenically clean the gas in line 506 in the cryogenic cleaning unit and then feed the resulting synthesis gas to the ammonia synthesis unit 7.

[0090] Prototype

[0091] Fig. 3 shows a method for producing ammonia according to the prototype.

[0092] The hydrogen gas enters compression and desulfurization unit 1 via line 100. Next, the gas enters the PSA unit 12 via line 112, where hydrogen is recovered and sent via line 213 to compression unit 13. Waste gas, containing a large amount of methane, is sent via line 120 for combustion. Nitrogen obtained in unit 15 (the air separation unit) is also fed to compression unit 13. The resulting gas enters the ammonia synthesis unit via line 134. The resulting ammonia is sent via line 710 to urea production unit 10, where carbon dioxide is also supplied via line 01. The urea formed in urea production unit 10 is sent to the consumer via line 111.

[0093] Tables 1-2 below show the experimental results.

[0094] Table 1. Compositions of VSH and sources of its production. Table 2. Parameters for the implementation of ammonia and urea production processes.

[0095] As can be seen from Table 2, the urea yield in Example 2 was 148,249 kg / hour, while in the prototype, the urea yield was 94,323 kg / hour. This means that the efficiency of the proposed urea production method is 57.2% higher than that of the prototype urea production method. Furthermore, the residual content of unconverted hydrocarbons in Example 2 was 0.76%, while in the prototype, all 15% of the residual methane was sent for combustion.

[0096] Thus, the proposed group of inventions made it possible to ensure

[0097] - increasing the energy efficiency and environmental friendliness of the technology for producing urea from by-products of oil and gas processing while reducing metal consumption, specific energy consumption, specific fuel gas consumption, and with a residual content of unconverted hydrocarbons after steam-air reforming not exceeding 1 vol.%

[0098] - no need to use a metal-intensive air separation unit and a metal-intensive primary reforming furnace that consumes a large amount of fuel gas;

[0099] - improving the environmental friendliness of the technology by using carbon dioxide from flue gases for the synthesis of urea;

[0100] - the possibility of flexible regulation of the hydrogen content in ammonia synthesis gas;

[0101] - the possibility of obtaining urea from flexibly controlled quantities of ammonia and carbon dioxide,

[0102] - increase in the productivity of urea production technology by 57.2%,

[0103] - specific fuel gas consumption for combustion not exceeding 100 Nm 3 per ton of ammonia.

Claims

Invention formula 1. A method for producing urea, comprising a) a stage of dehydrogenation of hydrocarbons in oil or gas processing plants to produce hydrogen-containing gas and to separate carbon dioxide from flue gases leaving dehydrogenation process furnaces; b) a stage of steam-air reforming of hydrogen-containing gas to produce converted gas; c) a stage of converting carbon monoxide and separating carbon dioxide from the converted gas to produce synthesis gas; d) a stage of producing ammonia from the synthesis gas obtained in stage c); e) a stage of producing urea from the ammonia obtained in stage d) and the carbon dioxide obtained in stage a) and stage c).

2. The method according to item 1, characterized in that the dehydrogenation of hydrocarbons at oil or gas processing plants includes the pyrolysis of the ethane-propane fraction and / or the pyrolysis of the gasoline fraction and / or the pyrolysis of the ligroin fraction (naphtha) and / or the catalytic reforming of the gasoline fraction and / or the catalytic reforming of the ligroin fraction (naphtha).

3. The method according to claim 1, characterized in that the amount of CO2 supplied for the synthesis of urea from flue gases is regulated depending on the amount of ammonia obtained in step d) and CO2 obtained in step c), so that the molar ratio of the amount of ammonia to the total amount of carbon dioxide tends to the stoichiometric ratio required for obtaining urea.

4. The method according to claim 1, characterized in that step d) includes removing purge gas from the ammonia synthesis circuit.

5. The method according to item 4, characterized in that the purge gas is directed to a hydrogen extraction unit.

6. The method according to item 5, characterized in that the hydrogen separated from the purge gas is added to the synthesis gas obtained in step c).

7. The method according to claim 6, characterized in that the amount of hydrogen added to the synthesis gas obtained in step c) is adjusted so that the ratio of hydrogen to nitrogen in the synthesis gas sent to step d) tends to the stoichiometric ratio required to obtain ammonia.

8. The method according to paragraph 1, characterized in that at stage c) cryogenic purification of the obtained synthesis gas is carried out.

9. The method according to claim 1, characterized in that stage c) of isolating carbon dioxide includes amine purification.

10. The method according to item 1, characterized in that hydrogen-containing gas is fed to stage b) of steam-air reforming at a temperature of at least 650°C and a pressure of 2-5 MPa; air is fed at a temperature of 450-650°C and a pressure of 2-5 MPa; and converted gas is obtained at a temperature of 900-1050°C at a pressure of 2-5 MPa.

11. A unit for producing urea, comprising a hydrocarbon dehydrogenation unit at oil or gas processing plants, connected to a hydrogen-containing gas removal line, and comprising a dehydrogenation process furnace configured to separate and remove a CO2 stream from flue gases along line L1; a steam-air reforming unit connected to a hydrogen-containing gas supply line and a converted gas removal line; a carbon monoxide conversion and carbon dioxide separation unit connected to the converted gas supply line, a synthesis gas removal line L2, and a carbon dioxide removal line L3; an ammonia production unit connected to the synthesis gas supply line and the ammonia removal line; a urea production unit connected to the ammonia supply line, line L1, and line L3.

12. The installation according to item 11, characterized in that the hydrocarbon dehydrogenation unit at oil or gas refining plants includes an ethane-propane fraction pyrolysis unit and / or a gasoline fraction pyrolysis unit and / or a ligroin fraction (naphtha) pyrolysis unit and / or a gasoline fraction catalytic reforming unit and / or a ligroin fraction (naphtha) catalytic reforming unit.

13. The plant according to item 11, characterized in that the ammonia supply line, lines LI, L3 are equipped with volumetric flow rate control means designed in such a way as to control the amount of urea obtained and ensure maintenance of the molar ratio of the amount of ammonia to the total amount of carbon dioxide, tending to the stoichiometric ratio required for obtaining urea.

14. The installation according to paragraph 11, characterized in that the ammonia production unit is designed with the possibility of removing the flow of purge gas from the ammonia synthesis circuit.

15. The installation according to item 14, characterized in that it includes a unit for separating hydrogen from the purge gas, connected to the purge gas supply line, and the hydrogen removal line L4.

16. The installation according to paragraph 15, characterized in that the synthesis gas discharge line L2 is connected to the hydrogen supply line L4.

17. The installation according to paragraph 16, characterized in that lines L2, L4 are equipped with means for regulating the volumetric flow rate, designed in such a way as to ensure the maintenance of the molar ratio of hydrogen to nitrogen in the synthesis gas sent to the ammonia production unit, tending to the stoichiometric ratio required for the production of ammonia.

18. The installation according to item 11, characterized in that it includes a cryogenic purification unit connected to the L2 synthesis gas discharge line.

19. The installation according to item 11, characterized in that the carbon dioxide separation unit includes an amine purification unit.

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