Methanol synthesis method and apparatus for carrying out same

Abstract

The proposed invention relates to a method for synthesizing methanol and an apparatus for carrying out same. A methanol synthesis method is disclosed which includes: (a) a primary stage of reforming a methane-containing gas to obtain converted gas; (b) a methanol synthesis stage carried out in a methanol synthesis loop equipped with a methanol synthesis reactor; (c) a stage of withdrawing purge gas from the methanol synthesis loop. The purge gas from stage (c) is fed to a purge gas reforming stage to obtain converted purge gas, and the converted purge gas is mixed with the gas circulating in the methanol synthesis loop and with the converted gas from stage (a) to form synthesis gas which is fed to stage (b) where it enters the methanol synthesis reactor. Also proposed is an apparatus for carrying out the above method. The technical result of the invention includes achieving a highly efficient methanol synthesis process together with low emissions of carbon dioxide into the atmosphere, increasing the environmental friendliness of the process, providing a high degree of conversion of carbon-containing feedstock and hydrogen, and reducing specific oxygen consumption and the metal requirement and complexity of secondary reforming equipment.

Description

[0001] METHOD FOR SYNTHESIS OF METHANOL AND AN APPARATUS FOR ITS IMPLEMENTATION

[0002] Field of technology

[0003] The present invention relates to a method for synthesizing methanol and an installation for its implementation.

[0004] Prior art

[0005] The publication of international application WQ2020148378A1, published on July 23, 2020, discloses a method for producing synthesis gas for producing methanol, comprising the steps of:

[0006] (a) supplying a first stream containing hydrocarbon and water vapor;

[0007] (b) feeding a second feed stream containing carbon dioxide in an amount providing a carbon dioxide / hydrocarbon ratio of from 0.1 to 0.8, preferably from 0.15 to 0.7;

[0008] (d) introducing the first and second streams into a two-stage steam reforming stage comprising a steam reforming stage and an autothermal reforming stage, wherein the first and part or all of the second stream are mixed before the steam reforming stage in step (d), preferably before the autothermal reforming stage;

[0009] (e) withdrawing a first stream of synthesis gas;

[0010] (f) providing a third stream containing hydrogen; and

[0011] (g) using the first synthesis gas stream together with the third feed stream as methanol synthesis gas.

[0012] The third hydrogen-containing stream is provided by one or more of: (a) steam reforming of a hydrocarbon-steam-containing stream, conducted in parallel with the two-stage reforming process; (b) water electrolysis; (c) an external source. Carbon dioxide is obtained from flue or off-gases, such as, for example, flue gases exiting the burners of steam reformers.

[0013] A disadvantage of the above-mentioned invention is that the entire reformed gas stream is sent to secondary reforming, which increases the metal consumption and complexity of the secondary reforming equipment. Furthermore, secondary reforming of the entire reformed gas stream requires high oxygen consumption (per ton of methanol) and, as a result, increases the metal consumption of the oxygen separation equipment (in particular, it leads to an increase in the size of the air separation unit). Furthermore, the aforementioned high oxygen consumption leads to a decrease in the hydrogen conversion rate, since an increased proportion of hydrogen is burned during reforming rather than converted to methanol. Additionally, to achieve the optimal composition of the syngas, the known method adds a hydrogen stream, the extraction of which requires energy and specialized complex equipment.

[0014] Chinese Patent CN100515925C, published July 22, 2009, discloses a method for producing CO, syngas, and methanol by converting hydrocarbons using a steam heat exchanger. Desulphurized natural gas is fed to the primary reformer in a steam reforming furnace, which also receives H2 obtained from the purge gas of the methanol synthesis unit. The converted natural gas is then fed to the secondary reformer, which also receives oxygen, as well as CO2 extracted from the flue gases and heated to regulate the H2 / C ratio in the resulting high-temperature gas. The gas thus obtained is used to produce methanol. During methanol synthesis, H2 is separated from the resulting syngas, which is sent to the primary reformer, the CO2-rich gas is fed to the secondary reformer, and the tail gases are used as fuel gas.

[0015] A disadvantage of the proposed invention is that the entire reformed gas stream is sent to secondary reforming, which increases the metal consumption and complexity of the secondary reforming equipment. Furthermore, secondary reforming of the entire reformed gas stream requires high oxygen consumption (per ton of methanol) and, as a result, increases the metal consumption of the oxygen separation equipment (in particular, it leads to an increase in the size of the air separation unit). Furthermore, the aforementioned high oxygen consumption leads to a decrease in hydrogen conversion, as an increased proportion of hydrogen is burned during reforming rather than converted to methanol. Furthermore, the purge gas is separated into hydrogen, CO2, and exhaust (tail) gases, which also leads to a complex process design and exhaust gas combustion, which is detrimental to the environment.Additionally, to achieve the optimal composition of the syngas in the known method, a stream of hydrogen is added to it, the extraction of which requires energy and specialized, complex equipment. International application WQ2019020515 A1, published on January 31, 2019, discloses a method for producing syngas for methanol synthesis, comprising the following steps:

[0016] (a) provision of hydrocarbon raw materials;

[0017] (b) preparing a separate stream containing hydrogen and a separate stream containing oxygen by electrolysis of water and / or steam;

[0018] (c) tubular steam reforming at least a portion of the hydrocarbon feedstock from step (a) to produce steam reformed gas;

[0019] (d) autothermal reforming of a mixture of steam reformed gas containing hydrogen, carbon monoxide and carbon dioxide with at least a portion of the oxygen-containing stream obtained in step (b);

[0020] (e) introducing at least a portion of the hydrogen-containing stream from step (b) into the autothermal reforming gas stream from step (d); and

[0021] (f) synthesis gas outlet.

[0022] The amount of hydrogen added to the reforming gas after step (d) can be selected such that when hydrogen is mixed with the process gas formed in the reforming stages, the desired value of M is from 1.90 to 2.20 or preferably from 2.00 to 2.10.

[0023] A disadvantage of the proposed invention is that the entire converted gas stream is sent to secondary reforming, which increases the metal consumption and complexity of the secondary reforming equipment. Furthermore, secondary reforming of the entire converted gas stream requires high oxygen consumption (per ton of methanol) and, as a result, increases the metal consumption of the oxygen separation equipment (in particular, it leads to an increase in the size of the air separation unit). Furthermore, the aforementioned high oxygen consumption leads to a decrease in the hydrogen conversion rate, since an increased proportion of hydrogen is burned during reforming rather than converted to methanol. Additionally, to achieve the optimal composition of the syngas, the known method adds a hydrogen stream, the extraction of which requires energy and specialized, complex equipment.Furthermore, this invention does not provide for the separation of CO2 from flue gases, suggesting that this method is not environmentally friendly or requires additional CO2 production from other sources, which complicates the process and necessitates the use of additional equipment. Chinese patent CN100425586C, published on October 15, 2008, discloses a method for producing methanol syngas using a two-stage conversion process. A mixture of gaseous hydrocarbons and steam at a certain pressure is preheated and sent to a reforming unit, where a catalyst in the tubes converts the gaseous hydrocarbons and water vapor.

[0024] A portion of the gas from the reforming unit is fed into a gas mixture consisting of CO2 gas supplied by the flue gas regeneration unit and CO2-enriched gas supplied by the purge gas regeneration unit, and then enters the second stage reforming unit.

[0025] The second stage reforming unit produces high-temperature second stage reforming gas, which reaches the deep conversion index of gaseous hydrocarbons and is methanol synthesis gas.

[0026] The methanol syngas exiting the second-stage reformer recovers heat and water vapor from the byproduct via a heat exchanger. After cooling, the H2-rich gas from the purge gas recovery unit is fed to a compressor and sent to the methanol synthesis system, and the resulting crude methanol is sent for distillation to produce finished methanol.

[0027] The purge gas from the methanol synthesis system enters the purge gas recovery unit, which uses adsorption or pressure swing membrane to separate the effective gas from the purge gas, resulting in the gas being divided into three categories:

[0028] - gas with a high H2O content, which is fed to the synthesis gas compressor and returned to the methanol synthesis system;

[0029] - exhaust gas, which is mixed with gaseous hydrocarbons and sent to reformer 1 as fuel;

[0030] - gas with a high CO2 content, which is mixed with the CO2 gas recovered by the flue gas regeneration device and, after increasing the pressure, is sent to the second-stage reforming unit as a carbon-containing gas.

[0031] A disadvantage of the proposed invention is that the entire reformed gas stream is sent to secondary reforming, which increases the metal consumption and complexity of the secondary reforming equipment. Furthermore, secondary reforming of the entire reformed gas stream requires high oxygen consumption (per ton of methanol) and, as a result, increases the metal consumption of the oxygen separation equipment (in particular, it leads to an increase in the size of the air separation unit). Furthermore, the aforementioned high oxygen consumption leads to a decrease in hydrogen conversion, as an increased proportion of hydrogen is burned during reforming rather than converted to methanol. Furthermore, the purge gas is separated into hydrogen, CO2, and exhaust gases, which also leads to a complex process design and exhaust gas combustion, which is detrimental to the environment.Additionally, to obtain the optimal composition of the synthesis gas in the known method, a stream of hydrogen is added to it, the extraction of which requires energy and special complex equipment.

[0032] Disclosure of invention

[0033] The objective and technical result of the present invention is to achieve high efficiency of the methanol synthesis process, as well as additionally to achieve low carbon dioxide emissions into the atmosphere, an increase in the environmental friendliness of the process, a high degree of conversion of carbon-containing raw materials and hydrogen, a reduction in the specific oxygen consumption, metal consumption and complexity of secondary reforming equipment.

[0034] To solve the stated problem and achieve the technical result, a method for synthesizing methanol is proposed, including:

[0035] (a) a primary reforming stage of methane-containing gas, in which converted gas is obtained;

[0036] (b) a methanol synthesis stage carried out in a methanol synthesis loop equipped with a methanol synthesis reactor;

[0037] (c) a step for removing purge gas from the methanol synthesis loop; characterized in that the purge gas from step (c) is fed to a purge gas reforming step to obtain a converted purge gas, wherein the converted purge gas is mixed with the gas circulating in the methanol synthesis loop and the converted gas from step (a) to form synthesis gas, which is fed to step (b) in the methanol synthesis reactor.

[0038] Purge gas is a portion of the gas circulating in the methanol synthesis loop, withdrawn from the methanol synthesis loop after condensation of the raw methanol. It primarily contains a mixture of hydrogen, methane (which remains unconverted after reforming), nitrogen, argon, and carbon oxides. Sending only the purge gas to secondary reforming (the purge gas reforming stage), rather than all of the gas converted in the primary reforming stage, reduces the metal consumption and complexity of the secondary reforming equipment, and also results in high methanol synthesis efficiency due to the ability to flexibly adjust the functionality ("module") of the syngas fed to the methanol synthesis reactor without the need to introduce pure gas streams.

[0039] Furthermore, sending only purge gas to secondary reforming reduces the specific oxygen consumption (per ton of methanol) and, consequently, reduces the metal requirements of the oxygen production equipment (specifically, the air separation unit's size). Reduced oxygen consumption, in turn, increases hydrogen conversion, as less hydrogen is burned during the reforming stage, and, as a result, more hydrogen is converted to methanol.

[0040] The absence of a stage for separating purge gas into hydrogen, CO2 and tail gases allows for a simplification of the process flow chart.

[0041] The above mentioned features allow to achieve high efficiency of methanol synthesis process.

[0042] Preferably, steam reforming of methane-containing gas is carried out at the primary reforming stage.

[0043] Any known type of reforming of methane-containing gas (natural gas), or a combination thereof, can be used as the primary reforming, but the use of steam reforming allows for an increase in the yield of hydrogen and the most effective use of all the advantages of the present invention to further improve the efficiency of the methanol synthesis process.

[0044] Preferably, the converted purge gas is first mixed with the gas circulating in the methanol synthesis loop to form a mixed stream, and then this mixed stream is mixed with the converted gas from step (a) to form synthesis gas, which is fed to step (b) in the methanol synthesis reactor.

[0045] The above gases can be mixed in any order, but it has been found that the above sequence allows for a significant simplification of the process of regulating the parameters of the synthesis gas.

[0046] Preferably, oxygen-containing gas, water vapor, and carbon dioxide separated from the flue gases coming from stage (a) of primary reforming are fed to the purge gas reforming stage. Directing the carbon dioxide separated from the flue gases to the purge gas reforming stage allows for their maximum utilization, resulting in low carbon dioxide emissions and a more environmentally friendly process.

[0047] Preferably, the amount of purge gas removed in step (c), as well as the amount of water vapor, the amount of oxygen-containing gas and the amount of carbon dioxide are adjusted in such a way that in the synthesis gas that is fed to step (b) in the methanol synthesis reactor, the ratio (H2-CO2Y CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 is the number of moles of H2, CO and CO2, respectively.

[0048] Methanol synthesis proceeds optimally with a syngas functional close to 2. The functional (otherwise known as the "modulus") is the ratio:

[0049] F = (H2-CO2) / (CO+CO2), where H2, CO, COg are the number of moles of H2, CO and CO2 in the synthesis gas, respectively.

[0050] The functional value of syngas after the primary reforming stage is approximately 3, so sending this gas directly to methanol synthesis is inefficient. Previous solutions utilize secondary reforming of the entire syngas, but this increases the metal consumption and complexity of the secondary reforming equipment. In the present invention, only the purge gas withdrawn during the methanol synthesis stage undergoes secondary reforming, converting methane into CO2 and CO by feeding it oxygen, steam, and carbon dioxide.

[0051] By regulating the amount of removed purge gas, water vapor, oxygen-containing gas and carbon dioxide, it is possible to influence the parameters of the synthesis gas obtained from the purge gas and returned to the methanol synthesis stage, and thus influence the functionality of the synthesis gas, which is fed to stage (b) in the methanol synthesis reactor, in order to obtain an optimal ratio, which allows for further increasing the efficiency of the methanol synthesis process.

[0052] Preferably, the amount of purge gas removed in step (c) is adjusted so that the degree of conversion of the carbon-containing feedstock supplied to the stage of primary reforming of methane-containing gas and the stage of reforming of purge gas is not less than 90%, preferably not less than 93%.

[0053] This further increases the efficiency of the methanol synthesis process by achieving high conversion of hydrocarbons (methane and its homologues). The conversion rate of carbon-containing feedstock is the ratio of the amount of carbon-containing feedstock converted to methanol to the amount of carbon-containing feedstock fed to the reforming process (at the reforming stage). Carbon-containing feedstock primarily includes hydrocarbons and carbon dioxide contained in natural gas and carbon dioxide extracted from flue gases and sent to the purge gas reforming stage.

[0054] Preferably, the amount of carbon dioxide is adjusted depending on the amount of purge gas removed in step (c) so that in the synthesis gas that is fed to step (b) in the methanol synthesis reactor, the ratio (H2-CO2) / (CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 are the number of moles of H2, CO and CO2, respectively.

[0055] This makes it possible to further increase the efficiency of the methanol synthesis process by achieving a high degree of conversion of carbon-containing raw materials.

[0056] Preferably, the amount of water vapor and the amount of oxygen-containing gas are adjusted so as to maintain the temperature of the converted purge gas at the outlet from the purge gas reforming stage in the range of 900-1350°C.

[0057] This allows for an additional increase in the efficiency of the methanol synthesis process due to the fact that high temperatures lead to an increase in the degree of conversion of carbon-containing raw materials.

[0058] Preferably, the amount of purge gas removed in step (c) is adjusted depending on the amount of carbon dioxide so that in step (b) the ratio (H2-CO2Y CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 is the number of moles of H2, CO and CO2, respectively.

[0059] This allows the maximum possible amount of carbon dioxide to be removed from flue gases and makes the process more environmentally friendly.

[0060] Preferably, a portion of the purge gas removed in step (c) is diverted for combustion, and the amount of purge gas that is diverted for combustion is adjusted such that the amount of argon and nitrogen in the methanol synthesis loop does not exceed 5 mol.%, preferably does not exceed 3 mol.%.

[0061] Reducing the amount of argon and nitrogen in the methanol synthesis loop allows for an additional increase in the efficiency of the methanol synthesis process, since non-convertible inert gases (argon and nitrogen) do not react and accumulate in the methanol synthesis loop, ultimately reducing the partial pressure of the reagents in the methanol synthesis loop, which leads to an increase in energy costs for circulating the gas flow in the methanol synthesis loop.

[0062] Preferably, the amount of purge gas removed in step (c) is controlled so that the specific consumption of oxygen contained in the oxygen-containing gas and supplied to the purge gas reforming step does not exceed 3000 m 3 per ton of methanol, preferably not exceeding 245 Nm 3 per ton of methanol.

[0063] This allows for further improvement of the efficiency of the methanol synthesis process.

[0064] Reducing the specific oxygen consumption leads to a reduction in the metal consumption of the equipment used for oxygen generation (in particular, to a reduction in the size of the air separation unit). Furthermore, reducing oxygen consumption leads to an increase in the degree of hydrogen conversion, since less hydrogen is burned during the reforming stage, and, as a result, more hydrogen is converted into methanol. Furthermore, the addition of both oxygen and carbon dioxide leads to a reduction in the functionality of the converted purge gas. That is, the less oxygen that needs to be added to the purge gas reforming stage, the more carbon dioxide can be recovered from the flue gases and introduced into the purge gas reforming process, maintaining optimal process functionality.

[0065] Preferably, the amount of purge gas removed in step (c) is adjusted such that the degree of hydrogen conversion is at least 65%, preferably at least 70%.

[0066] This makes it possible to further increase the efficiency of the methanol synthesis process by achieving high hydrogen conversion.

[0067] The degree of hydrogen conversion is the ratio of the amount of hydrogen converted into methanol to the amount of hydrogen obtained at the stage of primary reforming of methane-containing gas and the stage of reforming of purge gas.

[0068] Preferably, the converted purge gas has a ratio of (H2-CO2) / (CO+CO2) equal to 1.3-1.8, preferably 1.4-1.6, the gas circulating in the methanol synthesis loop has a ratio of (H2-CO2) / (CO+CO2) equal to 1.7-2.3, preferably 1.8-2.2, and the converted gas from step (a) has a ratio of (H2-CO2Y CO+CO2) equal to 2.5-3.5, preferably 2.7-3.1. The above parameters make it possible to further increase the efficiency of the methanol synthesis process, since they ensure maximum use of hydrogen and carbon oxides in the methanol synthesis process.

[0069] Preferably, the converted purge gas at the outlet from the purge gas reforming stage has a temperature of 900-1350°C, preferably 950-1050°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2, wherein the converted purge gas is cooled to a temperature of 35-55°C, preferably 40-50°C, before mixing with the gas circulating in the methanol synthesis loop, the water vapor has a temperature of 400-600°C, preferably 450-550°C, and a pressure of 100-130 kg / cm 2 , the oxygen-containing gas has a temperature of 200-300°C, preferably 220-270°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 , carbon dioxide has a temperature of 550-750°C, preferably 600-700°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 , the gas circulating in the methanol synthesis circuit has a temperature of 35-55°C, preferably 40-50°C, and a pressure of 40-100 kg / cm 2 , preferably 50-60 kg / cm 2 , and the converted gas from step (a) has a temperature of 35-55°C, preferably 40-50°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 .

[0070] The above parameters further enhance the efficiency of the methanol synthesis process. Increasing the temperature of all streams entering the purge gas reforming unit reduces oxygen consumption to heat the gas mixture. However, adding both oxygen and carbon dioxide reduces the efficiency of the converted purge gas. Therefore, the less oxygen required to heat the gas mixture, the more carbon dioxide can be recovered from the flue gases and fed into the purge gas reforming process, maintaining optimal process efficiency.

[0071] Also, in order to solve the stated problem and achieve the technical result, a methanol synthesis plant is proposed, comprising: a primary reforming unit for methane-containing gas connected to a converted gas withdrawal line; a methanol synthesis loop, including a methanol synthesis reactor, a synthesis gas supply line to the methanol synthesis reactor, a methanol withdrawal line, and a purge gas withdrawal line; characterized in that the purge gas withdrawal line is configured to supply purge gas to the purge gas reforming unit, which is equipped with a converted purge gas withdrawal line, wherein the converted purge gas withdrawal line, the converted gas withdrawal line, and the methanol synthesis loop are connected in such a way as to ensure the possibility of mixing the converted purge gas, the gas circulating in the methanol synthesis loop, and the converted gas for producing synthesis gas supplied to the synthesis gas supply line to the synthesis reactor.

[0072] Preferably, the methane-containing gas primary reforming unit includes a methane-containing gas steam reforming unit.

[0073] Preferably, the converted purge gas withdrawal line is designed in such a way that the converted purge gas is mixed with the gas circulating in the methanol synthesis loop to obtain a mixed stream, and the methanol synthesis loop is designed in such a way that this mixed stream is mixed with the converted gas from the primary reforming unit of methane-containing gas to form synthesis gas fed into the synthesis gas supply line to the synthesis reactor.

[0074] Preferably, the purge gas reforming unit is connected to an oxygen-containing gas supply line, a water vapor supply line, and a supply line for carbon dioxide separated from the flue gases coming from the methane-containing gas primary reforming unit.

[0075] Preferably, the purge gas outlet line, the oxygen-containing gas supply line, the water vapor supply line, and the carbon dioxide supply line are equipped with volumetric flow measurement and control means designed in such a way that the amount of purge gas removed, as well as the amount of water vapor, the amount of oxygen-containing gas, and the amount of carbon dioxide can be controlled in such a way that in the synthesis gas supplied to the methanol synthesis reactor, the ratio (H2-CO2Y CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 are the number of moles of H2, CO, and CO2, respectively.

[0076] Brief description of the drawings

[0077] The drawings are provided to provide a better understanding of the invention, but it will be obvious to those skilled in the art that the disclosed invention is not limited to the embodiment shown therein. Fig. 1 shows a block diagram of the best embodiment of the invention.

[0078] The best embodiment of the invention

[0079] The described embodiments are provided for illustrative purposes only. Those skilled in the art will readily recognize that other embodiments are possible without changing the essence of the invention.

[0080] Methane-containing gas (natural gas) mixed with steam is fed into block 1 of the primary reforming (steam reforming) of methane-containing gas via line 101.

[0081] Next, the converted gas from the primary reforming unit 1 is cooled in heat exchanger H4 and enters methanol synthesis loop 2 via line 102, which includes lines 201-208. Methanol synthesis loop 2 is a circulation loop in which the gas used to produce methanol circulates.

[0082] The converted gas entering through line 102 is mixed with the recycle gas exiting through line 208, resulting in the formation of syngas. This syngas enters heat exchanger H1 through line 201, where it is heated and then enters methanol synthesis reactor 22 through line 202.

[0083] The hot stream leaving the methanol synthesis reactor 22 passes through the heat exchanger H1 via line 203, giving up its heat to the synthesis gas in line 201, and then via line 204 enters the heat exchanger H2, where it is cooled until it is separated from the condensate stream and via line 205 enters the separator 23, in which the stream is separated into condensate and a gas stream.

[0084] The condensate, which is raw methanol, is removed via line 200 for further processing, and the gas flow is returned as circulating gas to line 206 of methanol synthesis circuit 2.

[0085] In this case, purge gas is removed from the circulation gas in the methanol synthesis circuit 2 via line 401, which is fed to the purge gas reforming stage, carried out in the purge gas reforming block 4, to obtain converted purge gas.

[0086] Steam is also fed to the purge gas reforming unit 4 via line 504, oxygen via line 604, and carbon dioxide via line 304. Oxygen is separated in an oxygen separation unit (specifically, in an air separation unit, not shown). Carbon dioxide, fed via line 304, is preliminarily separated in a carbon dioxide separation unit 3 from the flue gases entering via line 103 from the primary reforming unit 1. The converted purge gas leaving the purge gas reforming unit 4 is cooled in the heat exchanger H3 and is fed through line 402 into the methanol synthesis circuit 2 for mixing with the gas circulating in the methanol synthesis circuit 2, as well as with the converted gas entering through line 102 from the primary reforming unit 1, with the aim of forming synthesis gas, which is fed through line 201 and line 202 into the methanol synthesis reactor 22.

[0087] Line 304 contains means R3 for measuring and regulating the volumetric flow rate of carbon dioxide, which is capable of sending signals to the control unit (not shown). Line 401 contains means R4 for measuring and regulating the volumetric flow rate of purge gas. Line 504 contains means R5 for measuring and regulating the volumetric flow rate of water vapor. Line 604 contains means R6 for measuring and regulating the volumetric flow rate of oxygen.

[0088] The said means R3, R4, R5, R6 are configured to send signals to the control unit and receive a signal from the control unit to change their operating parameters - the volumetric flow rate of the stream passing through them.

[0089] The control unit is configured to receive data on the composition of the synthesis gas in the methanol synthesis unit in line 202, to calculate the ratio (H2-CO2) / (CO+CO2), where H2, CO, CO2 are the number of moles of H2, CO and CO2, respectively, in the synthesis gas, in the synthesis gas in the methanol synthesis unit, and to transmit signals to means R3, R4, R5, R6 in order to adjust the volumetric flow rate of carbon dioxide, purge gas, water vapor and / or oxygen, respectively, to achieve the value of the above ratio in the range of 1.90-2.20, preferably 2.00-2.10.

[0090] The above regulation can also be carried out manually by the operator.

[0091] In the first variant, the amount (in moles) of purge gas removed through line 401, as well as the amount of water vapor in line 504, the amount of oxygen-containing gas in line 604 and the amount of carbon dioxide in line 304 were regulated in such a way that the ratio of (H2-CO2) / (CO+CO2) for the synthesis gas in line 201-202 fed to the synthesis of methanol was approximately 2.

[0092] In the second variant, the amount (in moles) of purge gas removed through line 401 was adjusted in such a way that the degree of conversion of the carbon-containing feedstock supplied to the stage of primary reforming of methane-containing gas and the stage of reforming of purge gas was not less than 93%. The degree of conversion of carbon-containing feedstock (X) is the ratio of the amount of carbon-containing feedstock that was converted into methanol to the amount of carbon-containing feedstock supplied to the reforming process (at the reforming stage).

[0093] Calculation of the degree of conversion of carbon-containing raw materials (X):

[0094] X = (FR+FR2-FB)) / (FR+FR2)

[0095] FR is the molar consumption of carbon in the methane-containing gas fed to the primary reforming,

[0096] FR = FR(CH4) + 2*FR(C2H6) + 3 *FR(C3H8) + 4*FR(C4H10) + 5*FR(C5H12) + 6*FR(C6H14) + FR(CO2), where FR(CH4), FR(C2H6), FR(C3H8), FR(C4HIO), FR(C5HI2), FR(C6HI4), FR(CO2) are the molar consumption of methane (CH2), ethane (CrHb), propane (C3Pk), butane (C4H10), pentane (C5H12), hexane (C6Hm), carbon dioxide (CO2), respectively, in the methane-containing gas fed to the primary reforming.

[0097] FR2 is the molar flow rate of carbon in the CO2 stream fed to the purge gas reforming,

[0098] FB is the molar flow rate of carbon in the purge gas flow supplied for combustion.

[0099] FB = FB(CH4) + FB(CO) + FB(CO2) + FB(CH3OH), where FB(CH4), FB(CO), FB(CO2), PB(CH3OH) are the molar flow rates of methane (CH4), carbon monoxide (CO), carbon dioxide (CO2), and methanol (CH3OH), respectively, in the purge gas flow supplied for combustion.

[0100] F (FR, FR2, FB) – molar flow rate of carbon in the flow, calculated using the formula:

[0101] F(i) = yi*Fo6nj, where yi is the molar fraction (ppm) of substance i in the flow, Ptotal is the total molar flow rate.

[0102] Calculation of the degree of conversion of carbon-containing raw materials (X) based on the experimental results:

[0103] FR(NG) = FR(CH4) + 2*FR(C2H6) + 3 *FR(C3H8) + 4*FR(C4H10) + 5*FR(C5H12) + 6*FR(C6H14) + FR(CO2) = 96600 + 2*2390 + 3*180 + 4*70 + 5*10 + 6*20 + 280 = 102650 Nm 3 / h

[0104] FR2 ( CO2) = 1 * 12220 = 12220 Nm 3 / h

[0105] FB = FB(CH4) + FB(CO) + FB(C02) + bb(снzon) = 3766 + 2008 +2232 +182 = 8188 Nm 3 / h

[0106] X = (FC(NG)+FC(RCO2)-FC(BG)) / (FC(NG)+ FC(RCO2)) = (102650+12220-8188) / (102650+12220) = 93%

[0107] In the third variant, the amount of purge gas removed through line 401 was adjusted in such a way that the specific consumption of oxygen-containing gas supplied to the purge gas reforming stage did not exceed 245 Nm 3 per ton of methanol.

[0108] In a fourth embodiment, the amount of purge gas removed through line 401 was adjusted so that the degree of hydrogen conversion was at least 70%.

[0109] Calculation of the total conversion of hydrocarbons into H2 and CH3OH

[0110] Molar flow rate of methane-containing gas FNG = 100,000 Nm 3 / h

[0111] Hydrocarbon conversion reactions occurring in a methane-containing gas stream:

[0112] CH4 + H2O CO + Zn2

[0113] C2H6 + 2H2O 2CO + 5H2

[0114] СзН8+ ЗН2О ЗСО + 7Н2

[0115] C4Hio + 4H2O 4CO + 9H2

[0116] C5HI2 + 5H2O 5CO + 11H2

[0117] SbNm + 6H2O 6CO + 13H2

[0118] CO2 + H2— CO + H2O

[0119] O2+ 2H22H2O

[0120] Molar consumption of hydrogen obtained from methane-containing gas (theoretical hydrogen consumption for complete conversion of hydrocarbons):

[0121] FH2= 3 *FR(CH4) + 5*FR(C2H6) + 7*FR(C3H8) + 9*FR(C4HIO) + 11 *FR(C5H12) + 13 *FR(C6HI4) - F R( CO2) = 3*96600 + 5*2390 + 7*180 + 9*70 + 11*10 + 13*20 - 280 = 303730 Nm 3 / h where FR(CH4), FR(C2H6), FR(C3H8), FR(C4H10), FR(C5H12), FR(C6H14), FR(CO2) are the molar consumption of methane (CH4), ethane (CrHb), propane (C3H8), butane (C4Hu), pentane (CsHu), hexane (CbHm), carbon dioxide (CO2), respectively, in the methane-containing gas fed to the primary reforming.

[0122] Hydrogen losses with purge gas supplied for combustion:

[0123] FBH2 = 3 *FB(CH4) + 5*FB(C2H6) + FB(H2) - FB(C02) = 3*3766 + 5*0 + 11334 - 2232 = 20400 Nm 3 / h where FB(CH4), FB(C2H6), FB(H2), FB(CO2) are the molar flow rates of methane (CH4), ethane (C2H6), hydrogen (H2), and carbon dioxide (CO2), respectively, in the purge gas flow supplied for combustion.

[0124] The molar flow rate of the purge gas supplied for combustion at the reforming stage = 20,000 Nm 3 / h

[0125] Hydrogen losses with oxygen-containing gas supplied for combustion during purge gas reforming (secondary reforming): FH2(BURN) = 2*FO2 = 2*34485.5 = 68971 Nm 3 / h, where F02 is the molar flow rate of oxygen (O2) supplied for combustion at the purge gas reforming stage.

[0126] The molar flow rate of oxygen-containing gas supplied for combustion at the purge gas reforming stage = 35,000 Nm 3 / h

[0127] Hydrogen conversion degree (Hc) is the ratio of the amount of hydrogen converted into methanol to the amount of hydrogen obtained at the stage of primary reforming of methane-containing gas and the stage of reforming of purge gas.

[0128] Хн2 = (FH2 - FBH2 - FH2(BURN)) / F H 2 = (303730 - 20400 - 68971) / 303730 = 70.6%

[0129] In this case, the amount of carbon dioxide in line 304 was adjusted depending on the amount of purge gas removed through line 401 in such a way that the ratio (H2-CO2Y CO+CO2) of the synthesis gas in line 201-202 fed to the synthesis of methanol was approximately 2, and the amount of water vapor in line 504 and the amount of oxygen-containing gas in line 604 were adjusted in such a way as to maintain the temperature of the converted purge gas at the outlet from the purge gas reforming stage in the range of 900-1100°C. In line 402, the temperature of the converted purge gas at the outlet from the purge gas reforming stage is measured by a temperature sensor (not shown).

[0130] The calculation of the ratio (H2-CO2) / (CO+CO2) in the synthesis gas in line 201-202 in the methanol synthesis unit, as well as the calculation of the necessary adjustment of the volumetric flow rate of carbon dioxide, water vapor and oxygen depending on the parameters of the specified gases, was performed by the control unit (not shown).

[0131] Oxygen consumption was determined based on the converted purge gas flow reaching a temperature of 1015°C at the outlet of the purge gas converter (purge gas reforming unit 4) (based on the calculation of the adiabatic heating of the conversion reaction). Water vapor consumption was determined based on the maximum gas temperature in the combustion zone of the purge gas converter (purge gas reforming unit 4) not exceeding 1500°C.

[0132] The purge gas is further converted in purge gas reforming unit 4, which reduces its functional value. In unit 4, methane is converted into CO2 and CO by feeding it oxygen, water vapor (water vapor is also used to lower the temperature in unit 4), and carbon dioxide. By returning the converted purge gas, which has a low functional value, to methanol synthesis loop 2, the functional value of the syngas entering methanol synthesis reactor 22 is reduced.

[0133] A portion of the purge gas is diverted through line 210 for combustion, and the amount of purge gas that is diverted for combustion is adjusted so that the amount of argon and nitrogen in the methanol synthesis circuit does not exceed 3 mol.%.

[0134] Non-convertible inert gases (argon and nitrogen) do not react and accumulate in methanol synthesis loop 2, ultimately reducing the partial pressure of the reagents in methanol synthesis loop 2, which leads to an increase in energy costs for conversion and a decrease in the degree of conversion.

[0135] Temperature sensors, pressure sensors, and volumetric flow measuring devices (not shown) are installed on lines 101, 102, 103, 200, 201, 202, 203, 204, 205, 206, 207, 208, 210, 304, 401, 402, 504, 604.

[0136] The table below shows the results of the experiment.

[0137] The amount of non-convertible inert gases in the methanol synthesis circuit did not exceed 3 mol.%, the degree of conversion of carbon-containing feedstock fed to the primary reforming stage of methane-containing gas and the purge gas reforming stage was at least 93%, and carbon dioxide emissions into the atmosphere were less than 3%.

[0138] Thus, the claimed inventions provided:

[0139] - high efficiency of the methanol synthesis process,

[0140] - low carbon dioxide emissions into the atmosphere and increased environmental friendliness of the process,

[0141] - high degree of conversion of carbon-containing raw materials and hydrogen,

[0142] - reduction of metal consumption and complexity of secondary reforming equipment.

Claims

Invention formula 1. A method for synthesizing methanol, comprising: (a) a primary reforming stage of methane-containing gas, in which converted gas is obtained; (b) a methanol synthesis stage carried out in a methanol synthesis loop equipped with a methanol synthesis reactor; (c) a step for removing purge gas from the methanol synthesis loop; characterized in that the purge gas from step (c) is fed to a purge gas reforming step to obtain a converted purge gas, wherein the converted purge gas is mixed with the gas circulating in the methanol synthesis loop and the converted gas from step (a) to form synthesis gas, which is fed to step (b) in the methanol synthesis reactor.

2. The method according to paragraph 1, characterized in that at the primary reforming stage, steam reforming of methane-containing gas is carried out.

3. The method according to claim 1, characterized in that the converted purge gas is first mixed with the gas circulating in the methanol synthesis loop to obtain a mixed stream, and then this mixed stream is mixed with the converted gas from stage (a) to form synthesis gas, which is fed to stage (b) in the methanol synthesis reactor.

4. The method according to claim 1, characterized in that oxygen-containing gas, water vapor, and carbon dioxide released from the flue gases coming from stage (a) of primary reforming are fed to the purge gas reforming stage.

5. The method according to claim 4, characterized in that the amount of purge gas removed in stage (c), as well as the amount of water vapor, the amount of oxygen-containing gas and the amount of carbon dioxide are adjusted in such a way that in the synthesis gas, which is fed to stage (b) in the methanol synthesis reactor, the ratio (H2-CO2) / (CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 are the number of moles of H2, CO and CO2, respectively.

6. The method according to item 4, characterized in that the amount of purge gas removed at stage (c) is regulated in such a way that the degree of conversion of the carbon-containing feedstock fed to the primary reforming stage 19 SUBSTITUTE SHEET (RULE 26) methane-containing gas and the purge gas reforming stage, was at least 90%, preferably at least 93%.

7. The method according to claim 6, characterized in that the amount of carbon dioxide is adjusted depending on the amount of purge gas removed in stage (c) in such a way that in the synthesis gas, which is fed to stage (b) in the methanol synthesis reactor, the ratio (H2-CO2Y CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 are the number of moles of H2, CO and CO2, respectively.

8. The method according to item 7, characterized in that the amount of water vapor and the amount of oxygen-containing gas are regulated in such a way as to maintain the temperature of the converted purge gas at the outlet from the purge gas reforming stage in the range of 900-1350°C.

9. The method according to item 4, characterized in that the amount of purge gas removed in step (c) is adjusted depending on the amount of carbon dioxide so that in step (b) the ratio (H2-CO2Y CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 are the number of moles of H2, CO, and CO2, respectively.

10. The method according to claim 1, characterized in that part of the purge gas removed in step (c) is diverted for combustion, and the amount of purge gas that is diverted for combustion is adjusted in such a way that the amount of argon and nitrogen in the methanol synthesis circuit does not exceed 5 mol.%, preferably does not exceed 3 mol.%.

11. The method according to item 4, according to which the amount of purge gas removed at stage (c) is adjusted in such a way that the specific consumption of oxygen contained in the oxygen-containing gas and supplied to the purge gas reforming stage does not exceed 3000m 3per ton of methanol, preferably not exceeding 245 Nm 3 per ton of methanol.

12. The method according to point 4, wherein the amount of purge gas removed in step (c) is adjusted so that the degree of hydrogen conversion is at least 65%, preferably at least 70%.

13. The method according to item 1, characterized in that the converted purge gas has a ratio (H2-CO2Y CO2+CO2) equal to 1.3-1.8, preferably 1.4-1.6, 20 SUBSTITUTE SHEET (RULE 26) the gas circulating in the methanol synthesis loop has a ratio of (H2-CO2) / (CO+CO2) equal to 1.7-2.3, preferably 1.8-2.2, and the converted gas from step (a) has a ratio of (H2-CCY CO+CO2) equal to 2.5-3.5, preferably 2.7-3.

1.

14. The method according to claim 1, characterized in that the converted purge gas at the outlet from the purge gas reforming stage has a temperature of 900-1350°C, preferably 950-1050°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 , wherein the converted purge gas is cooled to a temperature of 35-55°C, preferably 40-50°C, before mixing with the gas circulating in the methanol synthesis loop, the water vapor has a temperature of 400-600°C, preferably 450-550°C, and a pressure of 100-130 kg / cm 2 , the oxygen-containing gas has a temperature of 200-300°C, preferably 220-270°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 , carbon dioxide has a temperature of 550-750°C, preferably 600-700°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 , the gas circulating in the methanol synthesis circuit has a temperature of 35-55°C, preferably 40-50°C, and a pressure of 40-100 kg / cm 2, preferably 50-60 kg / cm 2 , and the converted gas from step (a) has a temperature of 35-55°C, preferably 40-50°C, and a pressure of 30-100 kg / cm 2 , preferably 50-60 kg / cm 2 .

15. A methanol synthesis plant comprising: a primary reforming unit for methane-containing gas connected to a converted gas withdrawal line; a methanol synthesis loop including a methanol synthesis reactor, a synthesis gas feed line to the methanol synthesis reactor, a methanol withdrawal line, and a purge gas withdrawal line; characterized in that the purge gas withdrawal line is configured to supply purge gas to the purge gas reforming unit, which is equipped with a converted purge gas withdrawal line, wherein the converted purge gas withdrawal line, the converted gas withdrawal line, and the methanol synthesis loop are connected in such a way as to allow mixing of the converted purge gas, gas, 21 SUBSTITUTE SHEET (RULE 26) circulating in the methanol synthesis circuit, and converted gas for obtaining synthesis gas fed into the synthesis gas supply line to the synthesis reactor.

16. The installation according to paragraph 15, characterized in that the primary reforming unit for methane-containing gas includes a steam reforming unit for methane-containing gas.

17. The plant according to paragraph 15, characterized in that the line for removing the converted purge gas is designed in such a way that the converted purge gas is mixed with the gas circulating in the methanol synthesis loop to obtain a mixed stream, and the methanol synthesis loop is designed in such a way that this mixed stream is mixed with the converted gas from the primary reforming unit of methane-containing gas to form synthesis gas fed into the synthesis gas feed line to the synthesis reactor.

18. The installation according to paragraph 15, characterized in that the purge gas reforming unit is connected to a supply line of oxygen-containing gas, a supply line of water vapor, and also a supply line of carbon dioxide released from the flue gases coming from the primary reforming unit of methane-containing gas.

19. The plant according to claim 18, characterized in that the purge gas outlet line, the oxygen-containing gas supply line, the water vapor supply line, and also the carbon dioxide supply line are equipped with means for measuring and regulating the volumetric flow rate, designed in such a way that the amount of purge gas removed, as well as the amount of water vapor, the amount of oxygen-containing gas and the amount of carbon dioxide can be regulated in such a way that in the synthesis gas supplied to the methanol synthesis reactor, the ratio (H2-CCY CO+CO2) is 1.90-2.20, more preferably 2.00-2.10, where H2, CO, CO2 are the number of moles of H2, CO and CO2, respectively. 22 SUBSTITUTE SHEET (RULE 26)