RU2843008C1 - Method of producing carbamide and apparatus for realizing said method - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to a method and apparatus for producing carbamide from by-products of oil or gas processing and can be used in chemical industry and in production of fertiliser. Invention relates to a method of producing carbamide, involving: a) a step for dehydrogenating hydrocarbons in oil or gas processing plants with production of hydrogen-containing gas and extraction of carbon dioxide from flue gases from furnaces of dehydrogenation processes; b) a step for steam-air reforming hydrogen-containing gas to produce converted gas; c) a step of converting carbon monoxide and separating carbon dioxide from the converted gas to obtain synthesis gas; d) a step of producing ammonia from the synthesis gas obtained in step c); e) a step of producing carbamide from ammonia obtained in step d), and carbon dioxide obtained in step a) and step c). Invention also relates to an apparatus for producing carbamide.

EFFECT: high energy efficiency and environmental friendliness of the technology of producing carbamide from oil and gas processing by-products while reducing metal consumption, specific energy consumption, specific consumption of fuel gas, as well as at residual content of non-converted hydrocarbons after steam-air reforming, which does not exceed 1 vol.%.

19 cl, 3 dwg, 2 tbl

Description

Field of technology

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.

Prior art

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

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 converted gas from carbon dioxide, methanation of carbon monoxide and dioxide, compression of the nitrogen-hydrogen mixture, and synthesis of ammonia at a pressure above 30 MPa (Azotchik Handbook. - M., Chemistry, 1986, v.1, pp.83, 84, 113, 213, 222, 360-364).

The disadvantage of using natural gas as a feedstock for producing ammonia is the need for efficient conversion of natural gas into carbon oxides, which necessitates the use of a primary reforming furnace – metal-intensive equipment that consumes large amounts of fuel gas. On average, 290 ^Nm3 of fuel gas per ton of ammonia is fed to the reforming furnace for combustion. Combustion of large amounts of natural gas leads to increased greenhouse gas emissions into the atmosphere, which reduces the environmental friendliness of the technology. In addition, natural gas is a primary source of raw materials: saved natural gas can be usefully used in other technological processes as fuel.

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

In addition, it is known that when using natural gas as a raw material for ammonia production, ammonia and carbon dioxide are not formed in stoichiometric quantities for subsequent urea synthesis, resulting in an excess of ammonia relative to carbon dioxide. In this case, excess ammonia is cooled, which leads to additional energy costs. Thus, another task is to find an additional source of carbon dioxide.

It is widely known that at oil and gas processing plants, hydrogen-containing gas (HCG) is a by-product of hydrocarbon dehydrogenation processes. At most plants, HCG is sent to a PSA, where hydrogen is released, which is then burned as fuel. Such technologies are characterized by low energy efficiency and environmental friendliness.

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

Thus, US patent US8932456 B2, published 13.01.2015, discloses a method for obtaining ammonia and urea from hydrogen-containing waste gas of oil refining products. In the proposed method, hydrogen-containing gas is obtained from oil fractions and then sent to steam reforming and to a hydrogen separation unit. The resulting hydrogen flow, together with a nitrogen flow obtained at an air separation unit, is sent to ammonia synthesis. Part of the resulting ammonia is then used to obtain urea.

The disadvantages of the proposed invention include obtaining ammonia from hydrogen and nitrogen flows obtained in complex hydrogen extraction and air separation units, which increases the metal intensity of the technology. In hydrogen extraction units (such as PSA), part of the hydrogen is spent on regeneration processes, which reduces the efficiency of the technology. In addition, steam reforming, used to increase the hydrogen content in hydrogen-containing gas, is carried out at low temperatures, due to which the degree of conversion of hydrocarbons into hydrogen decreases, which reduces the energy efficiency of the technology, reduces the yield of ammonia, which is then used to obtain urea. Steam reforming also involves the use of a primary reforming furnace - metal-intensive equipment that consumes a large amount of fuel gas. Burning large quantities of natural gas leads to an increase in greenhouse gas emissions into the atmosphere, which reduces the environmental friendliness of the technology. In addition, natural gas is the primary source of raw materials: saved natural gas can be usefully used in other technological processes as fuel. In addition, the proposed solution does not provide the ability to flexibly regulate the molar ratios of ammonia and carbon dioxide sent to the synthesis of urea; therefore, additional energy costs are required to utilize excess ammonia.

The closest analogue (prototype) of the invention is the method for producing ammonia and urea from hydrogen-containing gas formed as a by-product of the pyrolysis of the ethane-propane fraction, known from the Russian Federation patent for invention RU 2710228 C1, published on 25.12.2019. The resulting HCG, consisting of methane and hydrogen, is fed to a PSA, where hydrogen is released, part of which is fed to the synthesis of ammonia. Nitrogen for producing ammonia is obtained at an air separation unit. The proposed method does not use a metal-intensive steam reforming furnace.

The disadvantages of the proposed invention are the production of ammonia from hydrogen and nitrogen flows 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), part of the hydrogen is spent on regeneration processes, which reduces the efficiency of the technology. In addition, the proposed method does not convert the methane remaining in the VSH in principle - it is sent for combustion, which leads to a decrease in the production of a valuable product - hydrogen and, as a consequence, to a decrease in the yield of ammonia. In addition, the proposed solution does not have the ability to flexibly regulate the molar ratios of ammonia and carbon dioxide sent to the synthesis of urea - in this regard, additional energy costs are required for the disposal of excess ammonia.

Disclosure of invention

The objective and technical result of the proposed invention are to increase the energy efficiency and environmental friendliness of the technology for producing urea from by-products of oil and gas processing while reducing metal intensity, specific energy consumption, specific fuel gas consumption, and 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 a large amount of fuel gas; to increase the environmental friendliness of the technology due to the beneficial use of carbon dioxide from flue gases; the possibility of flexible regulation of the hydrogen content in ammonia synthesis gas; the possibility of producing urea from flexibly regulated amounts of ammonia and carbon dioxide; an increase in the productivity of the urea production technology by 57.2%; specific fuel gas consumption for combustion not exceeding 100 ^Nm3 per ton of ammonia, which is then used to produce urea.

To solve the problem and achieve the technical result, a method for obtaining urea is proposed, including

a) a stage of dehydrogenation of hydrocarbons at oil or gas processing plants to produce hydrogen-containing gas and release carbon dioxide from the flue gases leaving the furnaces of the dehydrogenation processes;

b) a stage of steam-air reforming of hydrogen-containing gas to obtain 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 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).

Hydrogen-containing gas (HCG) is a gas with a high hydrogen content (10% and above), which is formed in various technological processes, in particular, due to the dehydrogenation of hydrocarbons. Examples of such processes are: pyrolysis and catalytic reforming (aromatization) of hydrocarbon fractions entering oil or gas refineries.

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

Steam-air reforming is the production of gas with a high content of _H2 and CO by converting hydrocarbons with oxidizers: air and steam.

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.

The use of waste from gas and petrochemical industries as raw materials leads to an increase in the environmental friendliness of technological processes. The VSH obtained as a by-product of dehydrogenation processes is not burned with the formation of toxic emissions, but is effectively used to obtain valuable products such as ammonia. Also, the process of obtaining ammonia, which is then used to obtain urea, does not consume natural gas, which can be effectively used in other technological processes.

Steam-air reforming of VSG allows to introduce nitrogen, also contained in air, into the process flow diagram together with oxygen-oxidizer, which allows not to use metal-intensive and energy-consuming air separation unit. In addition, steam-air reforming promotes the most effective oxidation of hydrocarbons contained in VSG. In the present invention, the residual amount of hydrocarbons after steam-air reforming does not exceed 1 vol. %. In addition, the selected type of reforming consumes less fuel gas for steam generation - only 98.5 ^Nm3 per ton of ammonia, which is almost three times less than the consumption of natural gas for steam generation in primary reforming furnaces. Also, the hydrogen required to obtain ammonia is formed by converting hydrogen gas at the reforming stage, rather than by isolating it at the PSA, which eliminates the need for a metal-intensive, energy-consuming short-cycle adsorption unit, and also eliminates the loss of hydrogen consumed in the PSA for regeneration processes. In addition, isolating carbon dioxide from flue gases prevents their emissions into the atmosphere and further improves the environmental friendliness of the technology, and also allows for the production of urea exclusively from industrial waste.

Preferably, the dehydrogenation of hydrocarbons at oil or gas processing plants includes pyrolysis of an ethane-propane fraction, and/or pyrolysis of a gasoline fraction, and/or pyrolysis of a ligroin fraction (naphtha), and/or catalytic reforming of a gasoline fraction, and/or catalytic reforming of a ligroin fraction (naphtha).

During pyrolysis the following reaction occurs:

C _2n H _4n+2 → nC ₂ H ₄ + H ₂

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

C _2n H _2n+2 → C _n H _2n-6 + 4H ₂

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 C ₂₊ hydrocarbons.

In this application, gasoline fractions (gasoline) are understood to mean fractions of oil with a boiling point of up to 140°C. Predominantly, a mixture of hydrocarbons C ₅ -C ₁₁ .

In this application, the ligroin fraction (naphtha) is understood to mean fractions of oil with a boiling point of 140-180°C. Predominantly, a mixture of hydrocarbons C ₈ -C ₁₄ .

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 amounts of C ₂₊ hydrocarbons.

The processes of pyrolysis and catalytic reforming occur with the release of unsaturated hydrocarbons, the main product, and also 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.

Preferably, the amount of _CO2 supplied to the synthesis of urea 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 for obtaining urea.

In the process of obtaining ammonia, the carbon dioxide released in stage c) is obtained in a deficit in relation to ammonia relative to the stoichiometric ratio (1:2), which is required to obtain urea. Flue gases are an additional source of carbon dioxide - its addition allows for flexible regulation of the amount of urea obtained. That is, excess ammonia is not formed, for the utilization of which additional energy is spent: this leads to an additional increase in the energy efficiency of the process.

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

Purge gas is a portion of the circulating gas taken from the ammonia synthesis circulation loop (ammonia production unit) after the product ammonia separator. Purge gases, in addition to N ₂ , H ₂ , NH ₃ , contain inert impurities (CH ₄ , Ar, He). Their presence has a negative effect on the technological process of ammonia synthesis, which is then used to produce urea.

Removing the 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 (for lower pressure, equipment with thinner walls is needed).

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

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

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

In case of high hydrocarbon content in hydrogen-containing gas entering reforming, excess air is supplied to maximize oxidation of hydrocarbons: 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. The missing hydrogen can be obtained from the purge gas, which further increases the energy efficiency of the method.

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.

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

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

Cryogenic purification allows removing excess nitrogen from synthesis gas, i.e., ensuring the ratio of hydrogen to ammonia in synthesis gas tending to stoichiometric. In addition, cryogenic purification removes inerts from synthesis gas - as a result, the pressure in the circulation circuit and the metal consumption of the equipment are reduced (for lower pressure, equipment with thinner walls is needed).

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

Amine cleaning is carried out under process pressure, which allows for an additional reduction in energy costs of the technology. In addition, carrying out the process under pressure above atmospheric pressure allows for a reduction in absorbent consumption for cleaning.

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 at a pressure of 2-5 MPa.

The above parameters are the most preferable for the reforming processes.

Also, to solve the above-mentioned problem and achieve the stated technical result, a urea production unit is proposed, including

a hydrocarbon dehydrogenation unit at oil or gas processing plants, connected to a hydrogen-containing gas removal line and including a dehydrogenation process furnace designed with the possibility of separating and removing a flow of _CO2 from flue gases along line L1;

a steam-air reforming unit connected to a hydrogen-containing gas supply line and a converted gas discharge line;

a carbon monoxide conversion and carbon dioxide extraction 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 discharge line;

urea production unit connected to the ammonia feed line, line L1 and line L3.

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.

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

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

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.

Preferably, the ammonia feed line, lines L1, L3 are equipped with volumetric flow rate control means designed to control the amount of urea produced and to ensure maintenance of the molar ratio of the amount of ammonia to the total amount of carbon dioxide tending to the stoichiometric ratio required to produce urea.

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

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

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

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.

Preferably, the installation includes a cryogenic purification unit connected to the synthesis gas removal line L2.

Preferably, the carbon dioxide separation unit comprises an amine purification unit.

Brief description of the drawings

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 therein.

Fig. 1-2 shows block diagrams of the best embodiments of the invention.

The best embodiment of the invention

The described examples of implementation are given solely for illustrative purposes. It will be obvious to a specialist that other embodiments are possible without changing the essence of the invention.

Example 1

In Fig. 1, hydrogen-containing gas is fed into compression and desulphurization unit 1 via line 100 .

Hydrogen-containing gas (HCG) is a gas with a high hydrogen content (10% and above), which is formed in various technological processes, in particular, due to the dehydrogenation of hydrocarbons. Examples of such processes are: pyrolysis of the ethane-propane fraction at a gas processing plant, pyrolysis of the gasoline or ligroin fraction of oil refining processes, aromatization (catalytic reforming) of the gasoline or ligroin fraction of oil refining processes, etc.

During pyrolysis the following reaction occurs:

C _2n H _4n+2 → nC ₂ H ₄ + H ₂

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

C _2n H _2n+2 → C _n H _2n-6 + 4H ₂

In addition to hydrogen, VSH also contains methane and, in some cases, trace amounts of C ₂₊ hydrocarbons.

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

For the optimal course of the urea synthesis stages, ammonia and carbon dioxide should be fed to the urea synthesis block 10 in a molar ratio tending to stoichiometric, namely 2:1. However, it is well known that the carbon dioxide released from the converted gas is obtained in an insufficient amount relative to 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).

Lines 510 and 710 are equipped with means for measuring I2 and I3 of carbon dioxide and ammonia, respectively. Signals from the measuring means are sent to the control unit, where the missing amount of carbon dioxide is calculated. Carbon dioxide, separated from the flue gases, is sent to the urea production unit 10 via line 110 (L1), equipped with a regulator R2 , the signal to which is sent from the control unit. The urea formed in the urea production unit 10 is discharged to the consumer via line 111 .

Example 2

Fig. 2 shows another preferred embodiment of the invention.

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

The obtained converted gas is fed via line 304 to carbon monoxide conversion unit 4 , where carbon monoxide is converted into carbon dioxide. The gas obtained in unit 4 is fed via line 405 to amine purification unit 5 , carbon dioxide from unit 5 is removed via line 510 (L3) to urea production unit 10. Synthesis gas purified from carbon dioxide is fed via line 506 (L2) to methanation and compression unit 6. Then the gas from unit 6 is fed via line 607 to ammonia synthesis unit 7. A stream of ammonia is removed from ammonia synthesis unit 7 via line 710 , which is sent to urea synthesis unit 10 .

For the optimal course of the urea synthesis stages, ammonia and carbon dioxide should be fed to the urea synthesis block 10 in a molar ratio tending to stoichiometric, namely 2:1. However, it is well known that the carbon dioxide released from the converted gas is obtained in an insufficient amount relative to 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).

Lines 510 and 710 are equipped with measuring devices I2 and I3 of carbon dioxide and ammonia, 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, is sent to the urea production unit 10 via line 110 (L1), equipped with a regulator R2 , the signal to which is sent from the control unit.

The urea formed in the urea production block 10 is discharged to the consumer via line 111 .

Air is supplied to the ATR unit 3 via line 300 in such quantity that the oxygen oxidizes the hydrocarbons remaining in the HCG to carbon oxides until their residual content in the gas does not exceed 1 vol.%. Nitrogen obviously enters the system together with atmospheric oxygen. For optimal implementation of the ammonia production process, hydrogen and nitrogen should be supplied to the unit 7 via line 607 in a ratio tending to stoichiometric, namely 3:1. In case of high hydrocarbon content in the HCG entering the ATR unit, an excess amount of air is supplied via line 300 in order to maximize oxidation of the hydrocarbons: as a result, a greater amount of nitrogen is introduced into the system than is necessary to maintain the stoichiometry of the ammonia production reaction in the synthesis loop.

A purge gas flow is removed from the ammonia synthesis circuit via line 708 and enters block 8 for separating ammonia from purge gases. The liquid ammonia obtained in block 8 is returned via line 807 to block 7 for synthesizing ammonia.

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

Line 506 is equipped with a means of measuring I1 the amounts of hydrogen and nitrogen in the flow. The signal from the means of measuring I1 is fed to the control unit, where the missing amount of hydrogen is calculated (to achieve a hydrogen to nitrogen ratio of 3:1). Then the signal from the control unit is fed to the regulator R1 , and the required amount of hydrogen, taken from the purge gas, is fed to block 6 for the compression stage.

It will be obvious to the skilled person that an alternative method of achieving a hydrogen to nitrogen ratio of 3:1 is cryogenic purification of the gas in line 506 in the cryogenic purification unit, followed by feeding the resulting synthesis gas to the ammonia synthesis unit 7 .

Prototype

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

The VSH is fed via line 100 to compression and desulphurisation unit 1. Then the gas is fed via line 112 to unit 12 of the KSA, where hydrogen is released and discharged via line 213 to compression unit 13. The waste gas, containing a large amount of methane, is discharged via line 120 for combustion. Nitrogen obtained in unit 15 (air separation unit) is also fed to compression unit 13. The obtained gas is fed via line 134 to the ammonia synthesis unit. The obtained ammonia is discharged via line 710 to unit 10 for obtaining urea, where carbon dioxide is also supplied via line 110. The urea formed in unit 10 for obtaining urea is discharged to the consumer via line 111 .

Tables 1 and 2 below show the results of the experiment.

Table 1. Compositions of VSH and sources of its production

Example 1 Example 2 Prototype Dehydrogenation process to produce a stream of H2S Pyrolysis of ethane-propane fraction of gas processing plant Catalytic reforming of gasoline fraction of refineries Pyrolysis of ethane-propane fraction of gas processing plant Composition of the WASH flow _H2 : 90%
CH ₄ : 10% _H2 : 85%
CH ₄ : 15% _H2 : 85%
CH ₄ : 15%

Table 2. Parameters for the implementation of ammonia and urea production processes

Indicator Meaning (example 1) Meaning (example 2) Meaning (prototype) Gas in line 100 - temperature 370°С 370°С 47°C - pressure 44.6 kgf/ ^cm2 44.6 kgf/ ^cm2 27.5 kgf/ ^cm2 - volumetric flow rate 177020 ^Nm3 /h 146887 ^Nm3 /h 146887 ^Nm3 /h Gas in line 102 - - - temperature 520°С - pressure 43.2 kgf/ ^cm2 - volumetric flow rate 283233 Nm3/h Gas in line 203 - - temperature 650°С 650°С - pressure 41.7 kgf/ ^cm2 38.5 kgf/ ^cm2 - volumetric flow rate 283233 ^Nm3 /h 235159 ^Nm3 /h Air in line 300 - - temperature 25°C 25°C - pressure 0.0 kgf/ ^cm2 0.0 kgf/ ^cm2 - volumetric flow rate 82944 ^Nm3 /h 82433 ^Nm3 /h Gas in line 304 - - temperature 360°С 360°С - pressure 36.5 kgf/ ^cm2 36.5 kgf/ ^cm2 - volumetric flow rate 222644 ^Nm3 /h 346081 ^Nm3 /h Gas in line 405 - - temperature 40°С 40°С - pressure 36.2 kgf/ ^cm2 36.2 kgf/ ^cm2 - volumetric flow rate 273994 ^Nm3 /h 257935 ^Nm3 /h - Gas in line 506 - temperature 310°С 300°С - pressure 35.2 kgf/ ^cm2 33.5 kgf/ ^cm2 - volumetric flow rate 256946 ^Nm3 /h 237306 ^Nm3 /h - molar ratio of hydrogen to nitrogen 3:1 2.72:1 Carbon dioxide in line 510 - - temperature 40°С 40°С - pressure 35.7 kgf/ ^cm2 34.5 kgf/ ^cm2 - volumetric flow rate 16399 ^Nm3 /h 19976 ^Nm3 /h - molar flow rate 730.27 kmol/hour 888.06 kmol/hour Gas in line 607 - - temperature 35.0°C 36.8°C - pressure 76.8 kgf/ ^cm2 32.5 kgf/ ^cm2 - volumetric flow rate 256354 ^Nm3 /h 236492 ^Nm3 /h - molar ratio of hydrogen to nitrogen 3:1 3:1 Purge gas in line 708 - - temperature 50°C 50°C - pressure 120 kgf/ ^cm2 120 kgf/ ^cm2 - volumetric flow rate 15450 ^Nm3 /h 38612 ^Nm3 /h Hydrogen in line 906 - - - temperature 38°C - pressure 36.5 kgf/ ^cm2 - volumetric flow rate 23028 ^Nm3 /h Gas in line 112 - - - temperature 35°C - pressure 27.5 kgf/ ^cm2 - volumetric flow rate 146887 ^Nm3 /h Hydrogen in line 213 - - - temperature 35°C - pressure 27.2 kgf/ ^cm2 -volume flow rate 106129 ^Nm3 /h Nitrogen in line 130 - - - temperature 21°C - pressure 0.1 kgf/ ^cm2 -volume flow rate 35411 ^Nm3 /h Gas in line 134 - - - temperature 33.7°C - pressure 65.1 kgf/ ^cm2 - volumetric flow rate 141539 ^Nm3 /h Ammonia in line 710 - temperature 11.3°C 11.3°C 11.3°C - pressure 16.4 kgf/ ^cm2 16.4 kgf/ ^cm2 16.4 kgf/ ^cm2 - volumetric flow rate 120269 ^Nm3 /h 110609 ^Nm3 /h 70383 ^Nm3 /h - molar flow rate 5361.68 kmol/hour 4917.21 kmol/hour 3145.94 kmol/hour Carbon dioxide in line 110 - temperature 40°С 40°С 40°С - pressure 35.7 kgf/ ^cm2 35.7 kgf/ ^cm2 35.7 kgf/ ^cm2 - volumetric flow rate 43829 ^Nm3 /h 35424 ^Nm3 /h 35382 ^Nm3 /h - molar flow rate 1951.77 kmol/hour 1577.45 kmol/hour 1575.61 kmol/hour Urea in line 111 - mass flow 161171 kg/hour 148249 kg/hour 94323 kg/hour Residual content of unconverted hydrocarbons 0.41% 0.76% 15%

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. That is, the efficiency of the proposed method for producing urea is 57.2% higher than the efficiency of the method for producing urea according to the prototype. In addition, 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.

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

- increasing 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 with a residual content of unconverted hydrocarbons after steam-air reforming not exceeding 1 vol.%;

- 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;

- improving the environmental friendliness of the technology by using carbon dioxide from flue gases to synthesize urea;

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

- the possibility of obtaining urea from flexibly regulated quantities of ammonia and carbon dioxide;

- increase in the productivity of urea production technology by 57.2%;

- specific fuel gas consumption for combustion not exceeding 100 ^Nm3 per ton of ammonia.

Claims (29)

1. A method for producing urea, comprising a) a stage of dehydrogenation of hydrocarbons at oil or gas processing plants to produce hydrogen-containing gas and release carbon dioxide from the flue gases leaving the furnaces of the dehydrogenation processes; b) a stage of steam-air reforming of hydrogen-containing gas to obtain 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 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). 2. The method according to paragraph 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) in such a way 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 stage d) includes removing purge gas from the ammonia synthesis circuit. 5. The method according to paragraph 4, characterized in that the purge gas is directed to a hydrogen extraction unit. 6. The method according to claim 5, characterized in that the hydrogen separated from the purge gas is added to the synthesis gas obtained in stage 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 claim 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 claim 1, characterized in that at stage b) of steam-air reforming, hydrogen-containing gas is fed 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 with a temperature of 900-1050°C at a pressure of 2-5 MPa. 11. Urea production plant, including a hydrocarbon dehydrogenation unit at oil or gas processing plants, connected to a hydrogen-containing gas removal line and including a dehydrogenation process furnace designed with the possibility of separating and removing a flow of _CO2 from flue gases along line L1; a steam-air reforming unit connected to a hydrogen-containing gas supply line and a converted gas discharge line; a carbon monoxide conversion and carbon dioxide extraction 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 discharge line; urea production unit connected to the ammonia feed line, line L1 and line L3. 12. The installation according to item 11, characterized in that the hydrocarbon dehydrogenation unit at oil or gas processing 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 installation according to item 11, characterized in that the ammonia supply line, lines L1, L3 are equipped with means for regulating the volumetric flow rate, designed in such a way as to regulate the amount of urea obtained and ensure the maintenance of the molar ratio of the amount of ammonia to the total amount of carbon dioxide, tending to the stoichiometric ratio required to obtain urea. 14. The installation according to item 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 item 15, characterized in that the synthesis gas discharge line L2 is connected to the hydrogen supply line L4. 17. The installation according to item 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 producing 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 extraction unit includes an amine purification unit.