Process for producing ammonia and methanol from natural gas

Abstract

A process for producing ammonia and methanol from natural gas consists in purifying natural gas by catalytic hydrotreatment and the chemical adsorption of hydrogen sulphide, heating the purified natural gas, subjecting same to primary and secondary reforming and subsequently converting carbon monoxide into carbon dioxide. The obtained synthesis gas is purified of carbon dioxide then subjected to methanation, adsorption drying and low-temperature rectification, followed by the synthesis of ammonia, resulting in the formation of hydrogen-containing vent gases. Process media are heated using the flue gases from primary reforming, the hydrogen-containing vent gases are formed into low-pressure and high-pressure flows, the low-pressure vent gases being used as fuel for primary reforming and the high-pressure vent gases being divided into parts: for the catalytic hydrotreatment of the natural gas; for mixing with the synthesis gas prior to drying; and for the synthesis of methanol. A water treatment unit is supplemented with a feedwater desalination system. The technical result consists in utilitizing ammonia production resources to produce methanol, optimizing methanol production, reducing the human impact of production on the environment, and adapting production to harsh natural conditions.

Description

[0001] METHOD FOR PRODUCING AMMONIA AND METHANOL FROM NATURAL GAS

[0002] AREA OF TECHNOLOGY

[0003] The invention relates to the field of obtaining ammonia and methanol from natural gas and air and can be used in gas chemical industry enterprises.

[0004] Ammonia is the most important source of raw material for the production of nitrogen fertilizers, mainly urea and ammonium nitrate.

[0005] The raw materials for ammonia production are nitrogen and hydrogen in a 1:3 ratio. Nitrogen is primarily obtained through energy-intensive low-temperature air rectification, while hydrogen is produced by steam reforming of natural gas (66%), gasification of solid fuels, electrolysis, or thermal decomposition of water.

[0006] Given the current global economic and technological conditions, the priority is large-scale production of blue ammonia (approximately 4,000-4,500 tons / day) and urea (approximately 6,000-7,000 tons / day) on a single process line with optimal (low) natural gas consumption and electricity supply to "cover" urea consumption by 2030. In Russia, ammonia production and its main processing stages are export-oriented, which, given sanctions restrictions on natural gas exports, should offset Gazprom's losses in the European gas market. Given domestic demand and exports, the ammonia industry in Russia is rapidly developing, and to date, at least nine new major projects with urea as the end product have been announced. Their total capacity will be 6 million tons of ammonia and 10 million tons of urea per year (Analytical report Module Energy Plus, [Electronic resource] URL: http: / / solidgas.ru) faq / l_spr_ammiak.pdf).

[0007] Natural gas can also serve as feedstock for another large-scale production facility: methanol production. Over the past decade, methanol production in Russia has nearly doubled, reaching over 4 million tons per year. Some of the main consumers of methanol are phenol-formaldehyde resin producers and natural gas production and transportation systems.

[0008] 5 In this regard, the development of new technical solutions aimed at improving the technology and equipment for the processes of obtaining ammonia and methanol becomes important.

[0009] PRIOR ART

[0010] A method for producing ammonia from natural gas is known, which includes compression, heating and purification of natural gas from sulfur compounds, two-stage catalytic conversion of methane under pressure, including steam reforming in the first stage and steam-air reforming in the second stage, using the heat of the gas converted in the second stage, and also additionally

[0011] 15 portions of natural gas, purge and tank gases burned on the burner to carry out conversion in the first stage of the conversion process, catalytic conversion of carbon monoxide contained in the converted gas to obtain a nitrogen-hydrogen mixture, purification of it from carbon dioxide, purification from oxygen-containing compounds by

[0012] 20 methanation, compression of the purified nitrogen-hydrogen mixture, synthesis of ammonia in a closed cycle and separation of the obtained ammonia with its subsequent delivery to the consumer, as well as the utilization of heat from flue gases and their release into the environment, wherein the two-stage conversion of natural gas is carried out in a radial-spiral reactor divided into two sections with the steam reforming process carried out in the first section at a temperature of 800-1000°C and steam-air reforming in the second section at a temperature of 900-1400°C, the catalytic conversion of carbon monoxide is carried out at a temperature of 200-220°C in one stage in a radial-spiral reactor, and the required process temperature is maintained by water evaporative cooling with the delivery of commercial saturated water vapor to the consumer, purification of natural gas from sulfur compounds, purification of the nitrogen-hydrogen mixture from oxygen-containing compounds and the synthesis of ammonia are also carried out in reactors radial-spiral type,wherein the temperature of the flue gases after the burner before the first stage natural gas reforming reactor is maintained within the range of 900-1100°C by recirculating a portion of the cooled flue gases with their admixture with the air supplied to the burner, wherein the heat of the converted gas is used to preheat the initial natural gas before desulfurization and to generate water vapor, which is then directed to carry out steam and steam-air reforming of natural gas, and the heat of the flue gases after the first stage natural gas reforming reactor is used to preheat the mixture of air with flue gases, purge and tank gases supplied to the burner (patent RU 2445262 C1, IPC C01C 1 / 04, filed on 11.01.2011, published on 20.03.2012). The disadvantages of the invention are:

[0013] - lack of information on the method used to purify natural gas from sulfur compounds and the ways of utilizing the extracted sulfur;

[0014] - catalysts for numerous catalytic processes are not indicated, since different catalysts require different operating temperature ranges to implement the same process;

[0015] - the complexity of regulating the process to ensure an optimal ratio of nitrogen and hydrogen in the ammonia synthesis reactor by changing the flow rates simultaneously in several previous reactors;

[0016] - a complex system for regulating the flue gas temperature after the burner and before the first-stage natural gas reforming reactor by recirculating a portion of the cooled flue gases and mixing them with air. A known method for producing ammonia includes the following steps:

[0017] - distribute the supplied gas containing nitrogen and hydrogen into an ammonia converter, wherein the converter contains:

[0018] - a first shell having two or more separate layers of catalyst placed therein;

[0019] - a second shell located around the first shell;

[0020] - a first heat exchanger located outside the first shell and in fluid communication with it;

[0021] - a second heat exchanger located outside the second shell and in fluid communication with it; and

[0022] - a flow channel located within the first shell, wherein two or more separate layers of catalyst within the first shell are arranged around the flow channel, wherein a first portion of the feed gas is introduced into the first shell and a second portion of the feed gas is introduced into the second shell;

[0023] - provide reaction of the first part of the supplied gas in the presence of a catalyst to obtain an ammonia output stream;

[0024] - providing for the transfer of at least a portion of the heat of reaction from the ammonia outlet stream to produce steam within the first heat exchanger;

[0025] - provide transfer of at least a portion of the heat of reaction from the ammonia outlet stream of the second portion of the supplied gas within the second heat exchanger;

[0026] - introduce the heated second part of the supplied gas into the first shell;

[0027] - provide a reaction of the heated second portion of the supplied gas in the presence of a catalyst (patent RU 2469953 C2, IPC C01C 1 / 04, B01J 8 / 04, filed on 09 / 08 / 2008, published on 12 / 20 / 2012). The disadvantages of the invention are: - excessive complication of the design of the ammonia converter used, making it impossible to replace the catalyst in the converter without dismantling at least part of the converter;

[0028] - the presence in the ammonia converter of a large gap between the two shells - the first, providing the catalytic process of ammonia synthesis, and the second (the converter body itself), providing heat transfer through the wall of the first shell from the reaction mixture in the first shell to the flow of the second part of the supplied gas passing through the gap - increases the metal consumption of the body with the diameter of the first shell Di and the size of the gap Z at least by (l + Z / D times, in addition, with a low heat transfer coefficient in the gas-gas system, the relatively small surface of the first shell does not allow for sufficient heat removal of the heat of the ammonia synthesis reaction (92 kJ / mol) released inside the shell for the entire reaction mixture by only the second part of the feedstock flow;

[0029] - the temperature control system in the ammonia converter becomes more complex, as it must be maintained while balancing the heat supply and heat removal systems on two feed streams of the feed gas in four heat exchangers and a furnace (Fig. 2 of patent RU 2469953 C2).

[0030] A method for producing ammonia and ammonia derivatives from natural gas feedstock is known, which includes:

[0031] - conversion of natural gas into synthesis gas at the inlet;

[0032] - synthesis of ammonia from synthesis gas in the synthesis circuit;

[0033] - using at least part of the ammonia to obtain an ammonia derivative, wherein the method is carried out with energy consumers (2) requiring mechanical energy for operation, and heat consumers (3) requiring heat supply for operation, wherein

[0034] - part (15) of the natural gas raw material is used to supply fuel to a piston gas engine (6); - the energy (7) generated by the gas engine (6) is used to meet, at least partially, the energy needs of energy consumers (2);

[0035] - heat is recovered from the exhaust gas of the gas engine and at least part of the heat is recovered to provide it to at least one of the said heat consumers (3), wherein the heat recovered from the exhaust gas of the gas engine is at least part of the low-temperature heat (10) transferred to at least one of the heat consumers by means of a heat transfer medium that is heated by indirect heat exchange with the exhaust gas to a temperature of no higher than 200°C (patent RU 2682584 C2, IPC C01C 1 / 04, C07C 273 / 00, B01 J 19 / 00, declared on 05.08.2015, published on 19.03.2019). The disadvantages of the claimed invention are:

[0036] - the efficiency of the internal combustion engine in terms of fuel consumption - natural gas - is low (efficiency at the level of 50%) and is significantly lower than the efficiency of fire heaters (efficiency at the level of 80-85%);

[0037] - the use of heat recovered from the exhaust gas of one gas engine cannot significantly improve the heat balance of the ammonia production process as a whole, and the installation of a large number of gas engines will complicate equipment maintenance.

[0038] A method is known for the joint production of ammonia and methanol in a plant comprising a secondary reforming section, a high-temperature carbon monoxide conversion section, a low-temperature carbon monoxide conversion section arranged in a series, a methanol synthesis section and an ammonia synthesis section, characterized in that a gaseous stream containing carbon monoxide, carbon dioxide, hydrogen and water exiting said secondary reforming section is captured, said gaseous stream is fed to a cooling and water separation section, said gaseous stream is cooled and water is separated, a gaseous stream that is substantially free of water is fed to the methanol synthesis section, a gaseous stream containing carbon monoxide, carbon dioxide, hydrogen and methanol exiting the methanol synthesis section is fed to the methanol separation section, a liquid stream containing methanol is separated from a gaseous stream containing carbon monoxide that is substantially free of methanol carbon,carbon dioxide and hydrogen, in said methanol separation section, feed said substantially methanol-free gaseous stream exiting said methanol separation section to said low-temperature methanol conversion section, introduce into said substantially methanol-free gaseous stream exiting said methanol separation section a liquid stream comprising water suitably heated by indirect heat exchange with said gaseous stream exiting a secondary reforming section (patent RU 2193023 C2, IPC C07C 29 / 151, C07C 31 / 04, C01C 1 / 04, B01J 12 / 00, filed 23.08.1996, published 20.11.2002). The disadvantages of the invention are:

[0039] - the proposed process flow diagram with primary methanol production and secondary ammonia production leads to a decrease in the yield of ammonia in relation to methanol, whereas in the sphere of consumption of this product, significantly more ammonia is required than methanol;

[0040] - there is a complete lack of data regarding ammonia production;

[0041] - the methanol synthesis section (block 23) is designed with multiple reactors arranged in a row to achieve a high degree of reagent conversion, which complicates the process maintenance;

[0042] - the reduction of energy costs in the recommended scheme is declarative and has no justification.

[0043] A method for the joint production of ammonia and methanol is known, including reforming of natural gas, utilization of reforming heat, conversion of carbon monoxide, purification of the converted gas from carbon dioxide, synthesis of methanol, methanation and synthesis of ammonia, characterized in that hot converted synthesis gas from primary or secondary reforming is fed into the intertube

[0044] 5 space of the post-reforming apparatus, which is a shell-and-tube heat exchange reactor, and into the tubes filled with a catalyst - an additional raw steam-gas mixture, which is fed from a common mixing tee or from separate mixing tees, the flow from the inter-tube space for the production of ammonia is fed to the conversion of CO either directly, if the post-reforming is installed after the secondary reforming shaft furnace, or through secondary reforming, if the post-reforming is installed after the primary reforming tubular furnace (patent RU 2663167 C2, IPC C07C 31 / 04, COIC 1 / 04, C01B 3 / 38, declared on 23.08.2016, published on 01.08.2018).

[0045] 15 The disadvantages of the invention are: the solution to the problem of increasing the productivity of the plant is achieved extensively - by increasing the number of reactors through the use of additional post-reforming and an additional steam generator;

[0046] 20 - there is no justification for the principles of optimizing the composition of synthesis gases sent to the production of ammonia and methanol:

[0047] - an increase in the productivity of the synthesis gas plant cannot “increase the productivity of existing units without consuming additional fuel” - since, for example, in a distillation column for concentrating methanol, the constancy of heat supply and heat removal will lead to a decrease in the quality of the produced methanol in terms of the purity of the commercial product with an increase in the productivity of the column.

[0048] A method for producing low-carbon ammonia from natural gas, "Decarbonized Ammonia-3000", is known, which consists in the fact that natural gas and steam are heated and subjected to primary reforming on the process line, the obtained converted gas is subjected to secondary reforming using a steam-air-oxygen mixture, after which the obtained converted gas is sent to the conversion of carbon dioxide, the obtained synthesis gas is purified from carbon dioxide, then the purified synthesis gas is methanated, after which ammonia is synthesized, and the purge gas from the ammonia synthesis process is used as fuel for heating natural gas and steam, while on the fuel line natural gas and steam are heated and subjected to primary reforming, the obtained converted gas is subjected to secondary reforming using a steam-air-oxygen mixture,after which the resulting converted gas is sent to carbon dioxide conversion, the resulting synthesis gas is purified to remove carbon dioxide, then the pressure of the purified synthesis gas is reduced and part of it is used as fuel for heating natural gas and steam in the fuel line and the other part of it together with the purge gas as fuel for heating natural gas and steam in the process line (patent RU 2808874 C1, IPC C01C 1 / 04, C01B 3 / 02, SOSh 3 / 36, filed on 23.08.2023, published on 05.12.2023). The disadvantages of the claimed invention are:

[0049] - a sharp increase in the costs of ammonia production associated with the creation of an additional fuel line for syngas production, duplicating in terms of equipment almost entirely the process line with the exception of the methanation and ammonia production stages;

[0050] - the additional fuel line processes natural gas in quantities significantly lower than the capacity of the process line, requiring the use of different-capacity, single-purpose equipment on each line; - the nearly doubled number of equipment operating on both lines dramatically increases the risk of emergency situations leading to the shutdown of the entire ammonia production facility.

[0051] Also known is a method for producing ammonia from natural gas that is closest in terms of a set of technological procedures to the claimed invention, which consists in the fact that the initial natural gas is successively purified from sulfur-containing impurities in stages of a process line, heated and subjected to primary reforming, the obtained converted gas is subjected to secondary reforming with subsequent conversion of carbon monoxide into carbon dioxide, after which the obtained synthesis gas is purified from carbon dioxide, then methanation of the purified synthesis gas is carried out, after which ammonia is synthesized, while the purification of the initial natural gas from sulfur-containing impurities is ensured by catalytic hydrotreating and subsequent chemical adsorption of the formed hydrogen sulfide, while the source of hydrogen for hydrotreating the initial natural gas is part of the hydrogen-containing blowdowns formed at the stage of synthesis and condensation of ammonia;heating of process media - a mixture of initial natural gas with hydrogen, a mixture of natural gas and water vapor, process air, superheating of high-pressure steam - is carried out due to differential cooling of the flue gases of the primary reforming furnace; generation of high-pressure steam is carried out due to the heat of the synthesis gas of the secondary reforming; the process line of the produced synthesis gas between the stage of synthesis gas methanation and the stage of synthesis and condensation of ammonia is supplemented by stages of adsorption drying and low-temperature rectification of synthesis gas, and the stage of synthesis and condensation of ammonia ensures the production of liquefied ammonia; the flue gases of the primary reforming furnace are subjected to selective purification from nitrogen oxides;In this case, the process line is duplicated by a similar second process line, and both process lines are connected by direct and reverse flows to off-site facilities (Russian Federation patent application No. 2024114566 dated May 29, 2024). The disadvantages of the invention are:

[0052] - the use of part of the hydrogen-containing blowdowns from the ammonia synthesis and condensation stage as a carbon-free fuel in the primary reforming furnace will lead to the loss of hydrogen, which is valuable for gas chemistry and was obtained by an expensive catalytic method.

[0053] DISCLOSURE OF THE INVENTION

[0054] The objective of the claimed invention is to use the material resources of ammonia production to obtain a sought-after product of the third stage of natural gas processing - methanol, to optimize methanol production, to reduce the anthropogenic impact of production on the environment, and to adapt production to harsh natural conditions.

[0055] The stated problem is solved due to the fact that in the method for producing ammonia and methanol from natural gas based on the method for producing ammonia from natural gas, in which the initial natural gas is successively purified in stages of the process line from sulfur-containing impurities by catalytic hydrotreating and subsequent chemical adsorption of the resulting hydrogen sulfide, heated and subjected to primary reforming, the resulting converted gas is subjected to secondary reforming followed by the conversion of carbon monoxide into carbon dioxide, after which the resulting synthesis gas is purified from carbon dioxide, then methanation of the purified synthesis gas, its adsorption drying and low-temperature rectification are carried out, after which ammonia is synthesized with the formation of high- and low-pressure hydrogen-containing blowdowns, and heating of the process media - a mixture of the initial natural gas with hydrogen, a mixture of natural gas and water vapor, process air,superheating of high-pressure steam is carried out by differential cooling of the flue gases of the primary reforming furnace, subjected to selective purification from nitrogen oxides, wherein low and high pressure flows are formed by hydrogen-containing blowdowns, the flow of low-pressure hydrogen-containing blowdowns is used as a carbon-free fuel in the primary reforming, and the flow of high-pressure hydrogen-containing blowdowns is divided into three parts, the first part of high-pressure hydrogen-containing blowdowns is sent to catalytic hydrotreating of the original natural gas, the second part of high-pressure hydrogen-containing blowdowns is fed for mixing with synthesis gas before drying, and the third part of high-pressure hydrogen-containing blowdowns is sent to an integrated methanol synthesis unit, which also uses part of the carbon dioxide waste, subjected to compression in the carbon dioxide compression section to pressure,equal to the pressure of a third of the high-pressure hydrogen-containing bleeds, a mixture of carbon dioxide and hydrogen-containing bleeds in a molar ratio of 0.10:1-0.30:1 is heated and sent to a methanol synthesis reactor in the methanol synthesis section, the reaction mixture from the reactor is cooled and separated into a liquid phase and a recirculated gas phase, wherein part of the recirculated gas phase in the form of purge gas and the liquid phase in the form of raw methanol are fed for fractionation in the fractionation section to obtain pure methanol, process water sent to the water treatment unit, and purge gas, and the water treatment unit is supplemented with a source water desalination system.

[0056] The water treatment unit is supplemented with a source water desalination system in cases where ammonia and methanol production is located in areas with harsh natural conditions that limit the use of fresh water, for example, on gravity-based offshore platforms, when only source seawater is available for technological procedures.

[0057] The common feedstock for producing ammonia and methanol is hydrogen. Ammonia also requires nitrogen, while methanol requires carbon oxides. All of these components can be obtained through the conversion of natural hydrocarbon gas, which consists primarily of methane.

[0058] Natural gas, purified from sulfur compounds, is mixed with water vapor, heated by recovering heat from flue gases, and then undergoes a process of steam (primary) reforming.

[0059] Primary reforming is carried out by breaking the H-C bonds of methane and O-H bonds of water at high temperature and proceeds according to the following equilibrium reactions (1) and (2) with the production of hydrogen:

[0060] CH4 + H2O -> CO + 3H2 (thermal effect of the reaction is 206.4 kJ / mol) (1) and

[0061] CO + H2O CO2 + H2 (heat of reaction - 41.2 kJ / mol). (2)

[0062] The reformed gas from the reforming furnace and the heated process air enter the secondary reforming reactor, the upper part of which is a combustion chamber, and the lower part of which contains a catalyst bed. Secondary reforming is a sequential combination of combustion reactions (3) and (4):

[0063] CH4 + 3 / 2O2->CO + 2H2O, (3)

[0064] 2H2+ O2— > 2H2O (4) and steam reforming reactions (1) and (2) described above.

[0065] The primary reforming process in the steam reformer and the secondary reforming process in the secondary reforming reactor produce synthesis gas containing hydrogen, nitrogen, carbon oxides, and a number of impurities (water, etc.). Subsequent synthesis gas purification procedures produce streams of sufficiently pure carbon dioxide and a hydrogen-nitrogen mixture as feedstock for the subsequent synthesis of ammonia and methanol. Ammonia is formed from a 3:1 mixture of hydrogen and nitrogen at a temperature of 400-500 °C and a pressure of 14-60 MPa in the presence of a catalyst—porous iron with aluminum and potassium oxide impurities—according to the exothermic reaction (5):

[0066] Liquefaction of gaseous ammonia produces large quantities of cold, hydrogen-containing high- and low-pressure blowdowns containing 60-72% mol. of hydrogen and 20-26% mol. of nitrogen. Since the presence of nitrogen in the feedstock during methanol synthesis does not negatively impact the process chemistry, the blowdowns can be considered a source of hydrogen for methanol production. Due to the specific nature of the technology, it is proposed to divide the hydrogen-containing high-pressure blowdown stream into three portions. The first portion is sent to catalytic hydrotreating of the feed natural gas to compensate for hydrogen loss during the conversion of sulfur compounds to hydrogen sulfide. The second portion of the hydrogen-containing high-pressure blowdowns is circulated, mixing with the syngas before drying.A third portion of the hydrogen-containing high-pressure blowdown is mixed with hydrogen-containing low-pressure blowdown for use as a carbon-free fuel and / or sent to an integrated methanol synthesis unit, which also utilizes a portion of the carbon dioxide waste. The hydrogen-containing low-pressure blowdown is used as a carbon-free fuel in the primary reformer, thereby replacing natural gas as fuel and reducing carbon dioxide emissions and environmental pollution.

[0067] Methanol is formed from a mixture of hydrogen and carbon dioxide in a ratio of 3:1 at a temperature of 200-350 °C and a pressure of 5-10 MPa in the presence of three-component copper-containing catalysts via an exothermic reaction (6):

[0068] CO2 + 3H2 <-► СН3ОН + Н2О. (6) Since the high-pressure hydrogen-containing blowdowns from the ammonia synthesis unit have a pressure sufficient for methanol synthesis, blowdown compression is not required. The carbon dioxide stream has a low pressure, therefore, in the carbon dioxide compression section of the methanol synthesis unit, carbon dioxide is compressed to a pressure equal to the pressure of the high-pressure hydrogen-containing blowdowns. Next, mixing of the streams is provided, after which a mixture of carbon dioxide and hydrogen-containing blowdowns in a molar ratio of 0.10:1-0.30:1 is heated and fed to the methanol synthesis reactor in the methanol synthesis section.The reaction mixture from the reactor is cooled and separated into a liquid phase and a recirculated gas phase, with part of the recirculated gas phase in the form of purge gas and the liquid phase in the form of raw methanol being fed for fractionation to the fractionation section to obtain pure methanol, process water sent to the water treatment unit, and purge gas.

[0069] The combustion heat of hydrogen-containing low-pressure blowdowns and natural gas in the steam reformer of the ammonia synthesis unit provides both heating of the process fluids and the subsequent endothermic steam reforming reaction. Heating of all process fluids—the mixture of feedstock natural gas and hydrogen entering the desulfurization process, the mixture of natural gas and steam entering the primary reformer, the process air entering the secondary reformer, and the superheated high-pressure steam—is achieved through differential cooling of the primary reformer's flue gases, enabling maximum flue gas heat recovery through the formation of an optimal sequence of recuperative heat exchangers. Excess heat from the secondary reformer is used to generate high-pressure steam.Thus, the efficient redistribution of internal energy-rich flows in the ammonia synthesis unit, as well as the use of low-pressure hydrogen-containing blowdowns for fuel needs, makes it possible to reduce the consumption of natural gas as a fuel and, accordingly, carbon dioxide emissions into the atmosphere.

[0070] Suitable as a feedstock for methanol synthesis unit

[0071] 5 use high-pressure hydrogen-containing blowdowns while maintaining their energy potential, which allows for a further reduction in the costs of their compression before the methanol synthesis reactor.

[0072] It is useful to divide the high-pressure hydrogen-containing bleeds into three parts in the following mass ratios: the first part to the third in the range of -0.6:1 -0.8:1 and the second part to the third in the range of -4.1:1 -4.7:1. This distribution of high-pressure hydrogen-containing bleeds ensures the required purification of raw natural gas from sulfur compounds, the required production of ammonia, as well as the required removal of inert components from the ammonia synthesis circuit.5 It is useful to feed a third of the high-pressure hydrogen-containing bleeds to the integrated methanol synthesis unit in the range of 80-100% by weight of the total amount of a third of the high-pressure hydrogen-containing bleeds, while feeding the remaining volume for mixing with low-pressure hydrogen-containing bleeds for use as a carbon-free fuel, which ensures an optimal balance between energy savings and costs and profit from methanol production: with a decrease in this range, fuel savings in the ammonia synthesis unit increase and energy costs in the methanol synthesis unit decrease, but at the same time the methanol yield and profit from its sale decrease, and with an increase, fuel savings in the ammonia synthesis unit decrease, and environmental pollution and energy costs in the methanol synthesis unit increase, but at the same time the methanol yield and profit from the sale of methanol increase.

[0073] It is also useful to use low-pressure hydrogen-containing blow-offs generated in the ammonia synthesis unit as an additional source of raw material for the synthesis of methanol, which must be compressed to the pressure of high-pressure hydrogen-containing blow-offs and then fed to the methanol synthesis section of the integrated methanol synthesis unit.

[0074] It is useful to compress hydrogen-containing process streams, in particular expansion gas from amine purification of syngas and regeneration gas from syngas drying, and feed them to the integrated methanol synthesis unit as additional sources of hydrogen.

[0075] For regions with limited water resources, it is useful to consider purifying the process condensate formed during methanol synthesis for further use of the condensate as softened water at the water treatment unit, which will reduce operating costs during desalination of river or sea water.

[0076] It is advisable to use the excess amount of medium-pressure water vapor from the ammonia synthesis unit for steam drives of compressor equipment and as a coolant in the methanol synthesis unit, which, on the one hand, will reduce the costs associated with steam condensation in the ammonia synthesis unit and will reduce the costs of electricity and heat in the methanol synthesis unit.

[0077] It is advisable for the integrated methanol synthesis unit to be a methanol production line connected by common flows and a pipeline system with at least two ammonia production lines, which significantly reduces the risk of stopping the production of ammonia and methanol in the event of an emergency in one of the sections or during routine or major repairs.

[0078] LIST OF DRAWINGS

[0079] Figure 1 shows a schematic diagram of one of the possible options for implementing the method for producing ammonia and methanol using the following designations: 100 - ammonia production line;

[0080] 101 - process air compression section;

[0081] 102 - desulfurization department;

[0082] 103 - primary and secondary reforming department;

[0083] 104 - carbon monoxide conversion section;

[0084] 105 - amine gas purification department;

[0085] 106 - methanation department;

[0086] 107 - gas drying section;

[0087] 108 - cryogenic gas purification department;

[0088] 109 - gas compression section;

[0089] 110 - ammonia synthesis department;

[0090] 111 - refrigeration cycle compartment;

[0091] 112 - exhaust gas washing section;

[0092] 113 - separation of process condensate stripping;

[0093] 114 - separation of the steam and boiler water system;

[0094] 200 - technological line for methanol production;

[0095] 201 - carbon dioxide compression section;

[0096] 202 - methanol synthesis department;

[0097] 203 - fractionation department;

[0098] 204 - steam system compartment;

[0099] 1-44 - pipelines.

[0100] BRIEF DESCRIPTION OF DRAWINGS

[0101] The method for producing ammonia and methanol according to the claimed invention is illustrated by a variant of the basic flow chart for producing ammonia and methanol, consisting of two identical ammonia production lines 100 and one methanol production line 200, using thirds of the hydrogen-containing high-pressure purges and portions of the carbon dioxide streams from both ammonia production lines 100 in equal quantities. In Figure 1, to simplify the description of the ammonia and methanol production operation, one ammonia production line 100 and a connection with one methanol production line 200 are shown, since the connection of the methanol production line 200 with the second ammonia production line 100 is identical.

[0102] One of the possible options for implementing the method for producing ammonia and methanol is carried out as follows.

[0103] The feedstock natural gas stream from the plant boundaries is sent via pipeline 1 to desulfurization section 102 of the first ammonia production line 100. Since sulfur is a catalytic poison for the catalysts used in the ammonia production process chain, the feedstock natural gas stream is purified from sulfur by means of hydrotreating and chemical adsorption processes in desulfurization section 102. The feedstock natural gas stream is also sent via pipeline 2 to the primary and secondary reforming section 103 for fuel purposes. For the hydrotreating process, a stream of purified purge gas from purge gas washing section 112 is sent via pipeline 25 to desulfurization section 102 as a hydrogen source. The hydrotreating process in desulfurization section 102 is carried out in one reactor. The process of chemical binding of sulfur from hydrogen sulfide formed during hydrotreating is carried out in two reactors installed in series.The reactor piping allows for the discharge of spent catalyst without stopping the process.

[0104] The natural gas stream, purified from sulfur compounds, supplied through pipeline 3, is mixed with steam supplied through pipeline 10 from the process condensate stripping section 113, heated and then subjected to the primary reforming process in the steam reforming furnace in the primary and secondary reforming section 103. Synthesis gas is generated in furnace tubes filled with a nickel-based catalyst. The streams of purified purge gas, exhaust regeneration gas, expansion gas, and raw natural gas supplied to the furnace burners through pipelines 24, 17, 12 are used as sources of heat required for the steam reforming process.

[0105] 5 and 2 respectively.

[0106] Provision is made for the recovery of heat from flue gases to heat the flows of a mixture of raw natural gas purified from sulfur compounds and water vapor supplied through pipelines 3 and 10, process air supplied through pipeline 5, high-pressure water vapor (not shown in the figure), a mixture of raw natural gas and purified blowdown gas supplied through pipelines 1 and 25 for purification from sulfur compounds in the desulfurization section 102.

[0107] The converted gas from the steam reformer and the heated process air enter the secondary reformer reactor where

[0108] 15 undergo secondary reforming.

[0109] The source of nitrogen for the synthesis of ammonia is a flow of atmospheric air supplied through pipeline 4, which, after filtration and compression on a compressor in the process air compression section 101, is supplied through pipeline 5 to the primary and

[0110] 20 secondary reforming units 103 as process air. They provide interstage cooling of the compressed process air flow and separation of the resulting condensate.

[0111] To generate additional hydrogen and to purify the converted gas from the bulk of carbon monoxide after separation of primary and secondary reforming 103, the converted gas stream is fed through pipeline 6 to the carbon monoxide conversion section 104. Conversion is carried out in two reactors installed in series with intermediate heat removal for heating the boiler water. The first reactor uses an iron-based catalyst, and the second uses a copper-based catalyst. The use of two reactors is due to the reduced load on the copper catalyst, which is more expensive, but which provides a deeper conversion of CO to CO2.

[0112] The converted gas stream from the carbon monoxide conversion section 104 is fed via pipeline 7 to the amine gas scrubbing section 105, which removes carbon dioxide from the converted gas stream through absorption with an aqueous amine solution. Carbon dioxide absorption is performed at elevated pressure and reduced temperature. The saturated amine solution is regenerated at reduced pressure and elevated temperature and then reused for absorption (not shown in the figure). Intermediate removal of light gases dissolved in the amine is provided, forming the expansion gas stream, which is sent via pipeline 12 to the primary and secondary reforming section 103 and used as fuel in the steam reforming furnace.The flow of extracted carbon dioxide is removed from the amine gas purification section 105 via pipeline 8, partially sent to the methanol production line 200 via pipeline 43, and the remaining carbon dioxide is sent to the boundaries of the installation via pipeline 37.

[0113] Oxygen-containing components are contaminants for the ammonia synthesis catalyst, so the final step in syngas purification is methanation—a process in which residual carbon monoxide is converted to methane, which serves as an inert gas during ammonia synthesis. The converted gas stream obtained in amine gas treatment section 105 is sent via pipeline 13 to methanation section 106.

[0114] The process condensate stream generated during the methanation of synthesis gas in methanation section 106 is sent via pipeline 14 to amine gas purification section 105 for mixing with the condensate stream generated during the cooling and separation of the converted gas. The total process condensate stream is sent via pipeline 9 to process condensate stripping section 113, where the condensate is purified by stripping with a medium-pressure steam stream supplied via pipeline 29 to the bottom of the stripping column as a stripping agent.

[0115] The stripping gas stream is fed through pipeline 10 to the primary and secondary reforming section 103 for mixing with the stream of raw natural gas purified from sulfur compounds, fed through pipeline 3. The process condensate stream, purified from impurities of ammonia, methanol and carbon dioxide in the process condensate stripping section 113, is removed from the plant through pipeline 11.

[0116] The converted gas stream from methanation section 106 enters gas drying section 107 via pipeline 15, where the synthesis gas is purified from water by moisture adsorption on zeolites. The dried gas descends through drying adsorbers and is then filtered to remove entrained zeolite dust. Desiccant regeneration is accomplished at reduced pressure by an ascending flow of regeneration gas supplied via pipeline 18. The heat required for desiccant regeneration is supplied by medium-pressure steam in a regeneration gas heater (not shown).

[0117] The flow of dried converted gas is fed through pipeline 16 to cryogenic gas purification section 108 to remove excess nitrogen, the main amount of methane and part of the argon from the synthesis gas, which are then used as a flow of regeneration gas sent through pipeline 18 to gas drying section 107. In cryogenic gas purification section 108, a flow of purified converted gas is generated, fed through pipeline 19 to gas compression section 109, with the nitrogen:hydrogen ratio required for ammonia synthesis, equal to 1:3.The flows of purified converted gas and recycled gas are fed through pipelines 19 and 22, respectively, to gas compression section 109, where the flows are compressed to the pressure required for ammonia synthesis, after which the flow of compressed converted gas is sent through pipeline 20 to ammonia synthesis section 110, where it is heated and sent to a reactor in which ammonia is formed from hydrogen and nitrogen (an exothermic reaction limited by chemical equilibrium).

[0118] The flow of gas product mixture entering the refrigeration cycle section 111 via pipeline 21 from the ammonia synthesis reactor of the ammonia synthesis section PO is cooled in sequentially installed heat exchangers and then sent to a separator in which the liquid phase, consisting of condensed ammonia, is separated from the gas phase, consisting primarily of unreacted nitrogen and hydrogen, returned in the form of a flow of recirculated gas via pipeline 22 after cold recovery to the gas compression section 109.

[0119] Refrigeration cycle section 111 consists of an ammonia cooling system, which is an open refrigeration cycle consisting of a refrigerant compressor, a refrigerant condenser, a refrigerant buffer tank, and one or more refrigerant evaporators (not shown in Figure 1). Ammonia is condensed from the gas product mixture stream supplied through pipeline 21 from the ammonia synthesis section 110 in one or more refrigerant evaporators in refrigeration cycle section 111. Refrigerant vapor from the evaporators is directed to the appropriate stages of the refrigerant compressor, which ensures its circulation. The refrigerant from the compressor enters the condenser and then, in the liquid phase, enters the refrigerant collector (not shown in Figure 1). The flow of liquefied ammonia through pipeline 27 from the refrigeration cycle section 111 is removed from the plant as a commercial product.

[0120] In order to prevent the accumulation of inert gases in the ammonia synthesis circuit, provision is made for blowing off a portion of the recirculated synthesis gas flow, which is sent as a purge gas, which is a high-pressure hydrogen-containing purge, through pipeline 23 to the purge gas washing section 112. In order to capture ammonia, which is part of the purge gas transported through pipeline 23, and uncondensed gases, which are low-pressure hydrogen-containing purges, of the refrigeration cycle section 111 transported through pipeline 33, provision is made for water washing of high- and low-pressure gases in the purge gas washing section 112.The purified purge gas stream obtained in the purge gas scrubbing section 112 and representing a high-pressure hydrogen-containing purge is partially directed via pipeline 25 to the desulfurization section 102 and is used as a source of hydrogen for hydrotreating the raw natural gas, partially fed via pipeline 32 to the methanation section for recycle, and partially directed to the process needs of methanol production on the methanol production process line 200 via pipeline 34. The purified purge gas stream obtained in the purge gas scrubbing section 112 and representing a low-pressure hydrogen-containing purge is fed via pipeline 24 to the primary and secondary reforming section 103 and is used as fuel. The ammonia stream extracted from the purge gases is returned via pipeline 26 to the refrigeration cycle section 111.

[0121] The steam and boiler water system section 114 provides deaeration of the demineralized water flow coming from the boundaries of the plant through pipeline 28. Also, the steam and boiler water system section 114 provides the supply of prepared boiler water to the process sections for heat recovery and generation of high-pressure (in the primary and secondary reforming section 103) and low-pressure (in the amine gas cleaning section 105) steam and

[0122] 5 distribution of steam between high, medium and low pressure headers, as well as supply of steam from the headers to consumers. The flow of excess medium pressure steam is removed from the steam and boiler water system section 114 via pipeline 31 and is partially directed to the steam system section via pipeline 41

[0123] 10 204 technological line for producing methanol 200, and the remainder is sent outside the boundaries of the installation via pipeline 42.

[0124] The second ammonia production line operates similarly to the first, with the same numbering of sections and pipelines. Having two ammonia production lines significantly reduces the risk of ammonia and methanol production shutdowns in the event of an emergency in one section or during routine or major repairs.

[0125] The methanol production line 200 receives from each of the two ammonia production lines 100

[0126] 20 corresponding high-pressure hydrogen-containing purge streams and corresponding carbon dioxide streams.

[0127] The low-pressure carbon dioxide stream is fed through pipeline 43 to carbon dioxide compression section 201, where its pressure is increased to a pressure equal in magnitude to the pressure of a third of the high-pressure hydrogen-containing purges, and is fed through pipeline 44 to methanol synthesis section 202. The carbon dioxide fed to methanol synthesis section 202 under the same pressure through pipeline 44 and the high-pressure hydrogen-containing purge through pipeline 34 are mixed, heated, and converted into the target product in the methanol synthesis reactor. The reaction mixture leaving the methanol synthesis reactor is cooled, partially condensed, and separated into a liquid phase and a recycled gas phase, wherein a portion of the recycled gas phase in the form of purge gas and the liquid phase in the form of raw methanol, transported through pipelines 35 and 36, are fed to fractionation section 203.After processing the input streams in the mass transfer columns, high-quality methanol is removed through pipeline 38, blowdown gas, consisting mainly of ballast nitrogen, through pipeline 39, and process condensate from the methanol synthesis through pipeline 40.

[0128] Example. Using the technology discussed above, a calculation was performed for the combined production of ammonia and methanol in accordance with the claimed invention with a natural gas throughput of 300 t / h. One ammonia production line 100 receives 150 t / h of natural gas. Carbon dioxide and a high-pressure hydrogen-containing purge from both ammonia production lines 100 are fed to methanol production line 200. The calculation results for determining the compositions of the main process streams and their flow rates for one ammonia production line 100 are presented in Table 1. The calculation results for determining the compositions of the main process streams and their flow rates for the common methanol production line 200 are presented in Table 2.

[0129] In addition to hydrogen sulfide, the original natural gas contains mercaptans (the concentration of mercaptan sulfur is 0.0063 g / m3 3), therefore, as a result of hydrotreating, about 1.4 kg / h of mercaptans are converted into hydrogen sulfide, which is then chemisorbed by zinc oxide. The highly purified natural gas stream, containing 96.6% methane and about 2.7% Cr-C6 hydrocarbons, is almost completely converted during primary and secondary reforming into synthesis gas, in which the residual methane concentration is 1.32%. The resulting synthesis gas with a carbon monoxide concentration of 8.1% during carbon monoxide conversion provides for the production of additional hydrogen, and the resulting synthesis gas contains about 42% hydrogen, 21% nitrogen, and 36% ballast carbon dioxide and water vapor. Next, in the amine purification section, water vapor is removed from the synthesis gas stream by condensation with the utilization of condensation heat in recuperative heat exchangers, and carbon dioxide is extracted from the synthesis gas stream cooled from 231 to 45°C with an aqueous solution of diethanolamine, which is released as a by-product of the process during the regeneration of the absorbent.Part of the carbon dioxide (5 t / h) is sent to the methanol production line 200, the remaining carbon dioxide can then be used at gas or oil production plants to maintain reservoir pressure, at gas chemical plants for the production of urea, methanol and other products, at food and other industrial plants.

[0130] Then, after methanation, the synthesis gas with a hydrogen:nitrogen ratio of 2:1 (the hydrogen concentration is 64.6%, and the nitrogen concentration is 32.3%) is subjected to deep drying and low-temperature rectification, during which excess nitrogen is removed from the synthesis gas and the hydrogen:nitrogen ratio is brought to three to one. This made it possible to obtain 276 t / h of commercial liquid ammonia with a purity of 99.975% in the ammonia synthesis process on one process line, as well as 4 t / h of blowdowns through pipelines 24 and 25, consisting largely of hydrogen (65.83% and 71.08% mol., respectively), which forms a carbon-free fuel for the production operation and ensures the operation of the hydrotreating of the feedstock, as well as 4 t / h of hydrogen-containing blowdowns sent through pipeline 34 to the methanol production line 200.At the methanol production line 200, carbon dioxide coming from the ammonia production line 100 is compressed from a pressure of 0.14 MPa to 8.52 MPa, mixed with high-pressure hydrogen-containing blowdown, heated, and then synthesized into methanol in a reactor at a temperature of 250-300°C and a pressure of 8.0-8.5 MPa. The resulting reaction mixture is then separated into high-quality commercial methanol, blowdown gas consisting primarily of ballast nitrogen, and methanol synthesis process condensate.

[0131] In total, 552 t / h of high-quality liquid ammonia meeting the requirements of the Interstate Standard for Exported Ammonia (according to GOST 6221-90, the purity of liquid ammonia is at least 99.9%), as well as 8 t / h of hydrogen-containing gas - feedstock for methanol production, can be produced from 300 t / h of hydrocarbon feedstock supplied to the ammonia and methanol production plant through two ammonia 100 production lines. 5 t / h of methanol with a purity of 94.4% mol were obtained on methanol 200 production line from 10 t / h of carbon dioxide and 8 t / h of hydrogen-containing blowdowns with a composition of 71.08% mol. hydrogen, 23.78% mol. nitrogen and 5.14% mol. impurities.

[0132] A total of 557 tons of marketable product was obtained from the three-stage processing of 300 tons of natural gas per hour. The developed method for producing ammonia and methanol is highly economically efficient. With the cost of feedstock natural gas at $100 per ton, liquid ammonia at $350 per ton, and methanol at $265 per ton, and the company's feedstock costs at $274.4 million per year, revenue from the final product will amount to $1,556 million.

[0133] Thus, the technical result of the claimed method for obtaining ammonia and methanol from natural gas is the use of material resources from ammonia production to obtain additional, in-demand products of the third stage of natural gas processing - methanol, the optimization of methanol production due to the effective separation of high-pressure hydrogen-containing bleeds for fuel use and for the production of methanol, the reduction of the anthropogenic impact of production on the environment, the adaptation of production to harsh natural conditions, and the reduction of the risks of ceasing the production of ammonia and methanol by the enterprise in the event of an emergency in one of the departments or during its routine or major repairs.

Claims

CLAUSES OF THE INVENTION 1. A method for producing ammonia and methanol from natural gas based on a method for producing ammonia from natural gas, in which the initial natural gas is sequentially purified in stages of a process line to remove sulfur-containing impurities by catalytic hydrotreating and subsequent chemical adsorption of the resulting hydrogen sulfide, heated and subjected to primary reforming, the resulting converted gas is subjected to secondary reforming followed by the conversion of carbon monoxide into carbon dioxide, after which the resulting synthesis gas is purified to remove carbon dioxide, then the purified synthesis gas is methanated, adsorption dried and subjected to low-temperature rectification, after which ammonia is synthesized to form high- and low-pressure hydrogen-containing blowdowns, and the heating of the process media - a mixture of the initial natural gas with hydrogen, a mixture of natural gas and water vapor, process air,superheating of high-pressure steam - carried out by differential cooling of the flue gases of the primary reforming furnace, subjected to selective purification from nitrogen oxides, characterized in that low and high pressure flows are formed by hydrogen-containing blowdowns, the flow of low-pressure hydrogen-containing blowdowns is used as a carbon-free fuel in the primary reforming, and the flow of high-pressure hydrogen-containing blowdowns is divided into three parts, the first part of high-pressure hydrogen-containing blowdowns is sent to catalytic hydrotreating of the original natural gas, the second part of high-pressure hydrogen-containing blowdowns is fed for mixing with synthesis gas before drying, and the third part of high-pressure hydrogen-containing blowdowns is sent to an integrated methanol synthesis unit, which also uses part of the carbon dioxide waste subjected to compression in the compression section, carbon dioxide to a pressure equal to the pressure of a third of the high-pressure hydrogen-containing blowdowns, a mixture of carbon dioxide and hydrogen-containing blowdowns in a molar ratio of 0.10:1-0.30:1 is heated and sent to a methanol synthesis reactor in a methanol synthesis section, the reaction mixture from the reactor is cooled and separated into a liquid phase and a recirculated gas phase, wherein part of the recirculated gas phase in the form of purge gas and the liquid phase in the form of raw methanol are fed for fractionation in the fractionation section to obtain pure methanol, process water sent to a water treatment unit, and blowdown gas, and the water treatment unit is supplemented with a source water desalination system.

2. The method according to paragraph 1, characterized in that the first and second parts of the high-pressure hydrogen-containing blowdowns are divided in the following mass ratios in relation to the third part: 0.6: 1-0.8: 1 and 4.1: 1-4.7:

1.

3. The method according to paragraph 2, characterized in that a third portion of the hydrogen-containing high-pressure blowdowns is fed to the integrated methanol synthesis unit in the range of 80-100% by weight of the total amount of the third portion of the hydrogen-containing high-pressure blowdowns, the remaining volume being fed for mixing with the hydrogen-containing low-pressure blowdowns for use as a carbon-free fuel.

4. The method according to claim 1, characterized in that the low-pressure hydrogen-containing blowdowns are compressed to a pressure equal to the pressure of the high-pressure hydrogen-containing blowdowns and fed to the methanol synthesis section of the integrated methanol synthesis unit.

5. The method according to paragraph 1, characterized in that the integrated methanol synthesis unit is formed from a process line for producing methanol, connected by common flows and a pipeline system with at least two process lines for producing ammonia.

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