Method and device for preventing carbon deposition in post-treatment process of synthesis gas with low hydrogen-carbon ratio

Abstract

The present invention discloses a method and device for preventing carbon deposition during the post-treatment process of syngas with a low hydrogen-to-carbon ratio. The method comprises the following steps: The syngas with a low hydrogen-to-carbon ratio from the outlet of the reforming device reactor is mixed with recycle gas and steam in a steam mixing device, and the recycle gas is from the synthetic product gas after temperature reduction and dehydration. This method greatly reduces the carbon deposition tendency of the syngas with a low hydrogen-to-carbon ratio in subsequent equipment and pipelines, can extend the continuous operation time of the device, improve the economic benefits of the device, and at the same time maximally blocks the metal powdering corrosion of the equipment and pipelines, reducing the safety hazards of the device.

Description

Technical Field

[0001] The present invention relates to the technical field of energy chemical engineering, and particularly relates to a method and device for preventing carbon deposition during the post-treatment process of syngas with a low hydrogen-carbon ratio. Background Art

[0002] Syngas with a low hydrogen-carbon ratio (the low hydrogen-carbon ratio means that the molar ratio of H2 to CO is 0.8 - 1.8) is an important chemical raw material. It can be used to synthesize high-value-added products such as aldehydes, esters, amides, acyl chlorides, and carboxylic acids through carbonylation reactions, and can also be converted into light olefins through the Fischer-Tropsch synthesis reaction and further polymerized into chemical materials.

[0003] Taking rich methane gas as the raw material and mixing with different oxidants such as carbon dioxide, steam, and oxygen, the process of preparing syngas through reforming reactions is an important source of syngas with a low hydrogen-carbon ratio. The main reaction of this process is the dry reforming process of carbon dioxide and methane, and the hydrogen-carbon ratio of the syngas is adjusted by adjusting the ratio of carbon dioxide, steam, and oxygen. The temperature of the syngas at the outlet of the reforming device reactor is generally higher than 850 °C. During the subsequent system cooling process, when the hydrogen-carbon ratio of the syngas is lower than 1.8, carbon deposition is extremely likely to occur in the equipment and pipelines. Such carbon deposition is mainly caused by the disproportionation reaction of carbon monoxide. After carbon deposition occurs in the equipment and pipelines, the system resistance gradually increases, and the system energy consumption continuously rises. If not treated immediately, it will cause blockage of the heat exchange equipment, resulting in forced shutdown of the device, greatly reducing the economic benefits of the device. At the same time, the carbon-deposited equipment and pipelines will also show metal powdering corrosion, bringing serious safety hazards.

[0004] Patent document CN107416769 discloses a method for preparing syngas by reforming methane and carbon dioxide. This method adds a quenching device in the preparation of syngas to quench carbon monoxide in the syngas at the outlet of the reforming furnace, and reduces carbon deposition by shortening the time for the disproportionation reaction of carbon monoxide in the subsequent reaction. The quenching method used is the conventional waste heat boiler cooling process, and this method cannot effectively prevent carbon deposition. Summary of the Invention

[0005] In view of the deficiencies of the prior art, the present invention provides a method and device for preventing carbon deposition during the post-treatment process of syngas with a low hydrogen-carbon ratio.

[0006] The technical solution adopted by the present invention is as follows:

[0007] The method for preventing carbon deposition during the post-treatment process of syngas with a low hydrogen-carbon ratio provided by the present invention includes the following steps:

[0008] The low hydrogen-carbon ratio syngas from the outlet of the reforming device reactor is mixed with recycle gas and steam in a steam mixing device, and the recycle gas comes from the synthetic product gas after cooling and dehydration.

[0009] According to an embodiment of the present invention, the temperature of the low hydrogen-carbon ratio syngas is 850 to 1030 °C, and the pressure is between 0 and 3.0 MPaG.

[0010] According to an embodiment of the present invention, the low hydrogen-carbon ratio syngas refers to syngas with a molar ratio of H2 to CO of 0.8 to 1.8, for example, 1.0 to 1.3.

[0011] According to an embodiment of the present invention, the reforming device includes, but is not limited to, a pure dry reforming device, a dual reforming device, a triple reforming device, etc.; for example, the reforming device is a pure dry reforming device using methane and carbon dioxide as raw materials, a dual reforming device using methane, carbon dioxide and steam as raw materials, or a triple reforming device using methane, carbon dioxide, steam and oxygen as raw materials.

[0012] According to an embodiment of the present invention, the temperature of the recycle gas is controlled at 40 to 130 °C, and / or the recycle gas volume accounts for 5% to 20% (mole fraction) of the synthetic product gas volume after water separation. For example, the temperature of the recycle gas is controlled at 70 to 100 °C, and / or the recycle gas volume accounts for 10% to 15% (mole fraction) of the synthetic product gas volume after water separation.

[0013] According to an embodiment of the present invention, the steam comes from the waste heat boiler of the post-treatment system of the low hydrogen-carbon ratio syngas, and can also come from outside the reforming device; and / or the steam can be saturated steam or superheated steam.

[0014] According to an embodiment of the present invention, the pressure of the steam is greater than the outlet pressure of the reforming device reactor.

[0015] According to an embodiment of the present invention, the steam make-up amount is used to control the disproportionation safety factor and the mixing temperature of the mixed gas, and the mixed gas refers to the gas after mixing the low hydrogen-carbon ratio syngas, the recycle gas and the steam.

[0016] Preferably, the disproportionation safety factor of the mixed gas is greater than 1.21, for example, 1.21 to 2.28, and / or the mixed gas temperature is greater than 600 °C; the calculation method of the disproportionation safety factor is as follows: disproportionation safety factor = (mole fraction of water vapor in the mixed gas + mole fraction of carbon dioxide in the mixed gas) / mole fraction of carbon monoxide in the mixed gas.

[0017] For example, when the pressure of the low hydrogen-carbon ratio syngas is less than or equal to 0.6 MPaG, the disproportionation safety factor of the mixed gas is not less than 1.21;

[0018] When the pressure of the low hydrogen-carbon ratio syngas is greater than 0.6 MPaG and less than or equal to 1.1 MPaG, the disproportionation safety factor of the mixed gas is not less than 1.38;

[0019] When the pressure of the low hydrogen-carbon ratio syngas is greater than 1.1 MPaG and less than or equal to 1.6 MPaG, the disproportionation safety factor of the said mixed gas is not less than 1.67;

[0020] When the pressure of the low hydrogen-carbon ratio syngas is greater than 1.7 MPaG and less than or equal to 2.1 MPaG, the disproportionation safety factor of the said mixed gas is not less than 2.06;

[0021] When the pressure of the low hydrogen-carbon ratio syngas is greater than 2.2 MPaG and less than or equal to 2.6 MPaG, the disproportionation safety factor of the said mixed gas is not less than 2.12;

[0022] Meanwhile, it is required that the temperature of the said mixed gas is greater than 600 °C.

[0023] According to the embodiment of the present invention, the steam mixing device has the following structure: the recycle gas pipeline is connected to the upper part of the low hydrogen-carbon ratio syngas pipeline, and whether the recycle gas pipeline is expanded in diameter is determined according to the relative sizes of the diameters of the recycle gas pipeline and the steam injection pipeline. The annular gap area between the recycle gas pipeline and the steam injection pipeline is not less than 70% of the area of the recycle gas pipeline before expansion; the steam injection pipeline is arranged on the recycle gas pipeline and extends into the recycle gas pipeline as short as possible so that the steam injection port is located inside the recycle gas pipeline, and the steam injection port is flush with the outer diameter of the low hydrogen-carbon ratio syngas pipeline.

[0024] According to the preferred embodiment of the present invention, the method includes the following steps:

[0025] The low hydrogen-carbon ratio syngas from the outlet of the reforming device reactor is mixed with recycle gas and steam in the steam mixing device to form a mixed gas;

[0026] The said recycle gas comes from the synthetic product gas after cooling and dehydration. The temperature of the recycle gas is controlled at 40 - 130 °C, and the recycle gas volume accounts for 5% - 20% (mole fraction) of the synthetic product gas volume after water separation;

[0027] The pressure of the said steam is greater than the pressure at the outlet of the reforming device reactor;

[0028] When the pressure of the low hydrogen-carbon ratio syngas is less than or equal to 0.6 MPaG, the disproportionation safety factor of the said mixed gas is not less than 1.21;

[0029] When the pressure of the low hydrogen-carbon ratio syngas is greater than 0.6 MPaG and less than or equal to 1.1 MPaG, the disproportionation safety factor of the said mixed gas is not less than 1.38;

[0030] When the pressure of the low hydrogen-carbon ratio syngas is greater than 1.1 MPaG and less than or equal to 1.6 MPaG, the disproportionation safety factor of the said mixed gas is not less than 1.67;

[0031] When the pressure of the low hydrogen-carbon ratio syngas is greater than 1.7 MPaG and less than or equal to 2.1 MPaG, the disproportionation safety factor of the mixed gas is not less than 2.06;

[0032] When the pressure of the low hydrogen-carbon ratio syngas is greater than 2.2 MPaG and less than or equal to 2.6 MPaG, the disproportionation safety factor of the mixed gas is not less than 2.12;

[0033] Meanwhile, it is required that the temperature of the mixed gas is greater than 600 °C;

[0034] The calculation method of the disproportionation safety factor is as follows: Disproportionation safety factor = (mole fraction of water vapor in the mixed gas + mole fraction of carbon dioxide in the mixed gas) / mole fraction of carbon monoxide in the mixed gas.

[0035] The present invention also provides a steam mixing device having the above structure.

[0036] The present invention also provides the application of the above steam mixing device in preventing carbon deposition from occurring during the post-treatment of low hydrogen-carbon ratio syngas.

[0037] Advantages of the present invention:

[0038] The present invention provides a brand-new method for preventing carbon deposition during the post-treatment of low hydrogen-carbon ratio syngas. By supplementing recycle gas and steam, the carbon deposition tendency of the low hydrogen-carbon ratio syngas in subsequent equipment and pipelines is greatly reduced, the continuous operation time of the device can be prolonged, the economic benefits of the device can be improved, and at the same time, the metal powdering corrosion of the equipment and pipelines is blocked to the greatest extent, reducing the safety hazards of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic process flow diagram for preventing carbon deposition during the post-treatment of low hydrogen-carbon ratio syngas of the present invention.

[0040] Figure 2 is a schematic diagram of the steam mixing device of the present invention.

[0041] Figure 3 is a schematic process flow diagram of the traditional syngas post-treatment process. DETAILED DESCRIPTION OF THE INVENTION

[0042] The steam mixing device used in the present invention is as Figure 2 shown. The recycle gas pipeline is connected to the upper part of the syngas pipeline. Whether the recycle gas pipeline is expanded in diameter is determined according to the relative sizes of the diameters of the recycle gas pipeline and the steam injection pipeline. The annular gap area between the recycle gas pipeline and the steam injection pipeline is not less than 70% of the area of the recycle gas pipeline before expansion. The steam injection pipeline inside the pipeline is as short as possible and needs to be entirely arranged inside the recycle pipeline. The steam injection port is flush with the outer diameter of the syngas pipeline.

[0043] AsFigure 1 As shown, the adjusted formed mixed gas enters the waste heat boiler to by-produce steam, and part of the obtained steam can be used as the steam for adjusting the disproportionation safety factor and is supplemented into the syngas with a low hydrogen-carbon ratio. The mixed gas at the outlet of the waste heat boiler continues to enter the gas cooling system for heat recovery, and the temperature of the mixed gas is adjusted to between 40 and 130 °C according to process requirements and then enters the gas-liquid separation tank for water separation. 5% to 20% of the product gas after water separation is used as recycle gas and mixed with the high-temperature syngas with a low hydrogen-carbon ratio, and the remaining gas is sent out of the battery limit as a product. The post-treatment method of the mixed gas and the equipment used are all methods and equipment commonly used in this technical field and well-known to those skilled in this technical field.

[0044] The technical solution of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only for illustrative explanation of the present invention and should not be construed as limiting the protection scope of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0045] Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by known methods. The steam mixing device in the following examples has the structure as Figure 2 shown.

[0046] Example 1

[0047] The treatment capacity of the syngas with a low hydrogen-carbon ratio from the dual reforming reactor is 539 Nm 3 / h, the temperature is 900 °C, and the pressure is 2.5 MPaG. The composition of the syngas with a low hydrogen-carbon ratio is as follows: the molar composition of H2O is 24.98%, the molar composition of H2 is 34.47%, the molar composition of CO2 is 14.12%, the molar composition of CO is 24.56%, the molar composition of CH4 is 1.87%, and the hydrogen-carbon ratio is 1.4. The high-temperature syngas with a low hydrogen-carbon ratio is mixed with recycle gas and steam through the steam mixing device to form a mixed gas. The flow rate of the recycle gas is 47 Nm 3 / h (with a molar composition of 4.09% H2O, 44.09% H2, 18.03% CO2, 31.4% CO, and 2.39% CH4), accounting for 10% (mole fraction) of the product gas volume after water separation, at a temperature of 100°C. The steam is saturated steam at 3.82 MPaG generated by a waste heat boiler, with a flow rate of 73 kg / h. At this time, the temperature of the mixed gas is 757°C, and the disproportionation safety factor is 2.12. Subsequently, the mixed gas enters the waste heat boiler and is cooled to 350°C, generating saturated steam at 3.82 MPaG. A portion of the generated steam is supplemented into the high-temperature low-hydrogen-carbon ratio synthesis gas to adjust the composition of the mixed gas. The mixed gas at the outlet of the waste heat boiler enters the gas cooling system for further heat recovery, and the gas temperature is adjusted to 100°C. The cooled mixed gas enters the gas-liquid separation tank for water separation. The gas phase of the gas-liquid separation tank is the product gas. 10% of the product gas is supplemented as recycle gas into the high-temperature low-hydrogen-carbon ratio synthesis gas, and the remaining part is sent out of the battery limit as the product. The carbon deposition amount of this system is 0.79 g per thousand Nm 3 The CO treatment capacity is far less than 8.41 g per thousand Nm in Comparative Example 1 3 CO treatment capacity. After the device has been continuously operating for 4000 h, the carbon deposition amount in the system is very small, and the system pressure drop hardly changes afterwards. There is no metal powdering corrosion phenomenon on the metal wall surfaces of the equipment and pipelines

[0048] Example 2

[0049] The treatment capacity of the high-temperature low-hydrogen-carbon ratio synthesis gas from the pure dry reforming reactor is 461 Nm 3 / h, at a temperature of 850°C and atmospheric pressure. The composition of the high-temperature low-hydrogen-carbon ratio synthesis gas is as follows: molar composition of H2O is 11.64%, H2 is 33.98%, CO2 is 11.56%, CO is 42.47%, and CH4 is 0.35%, and the hydrogen-carbon ratio is 0.8. The high-temperature low-hydrogen-carbon ratio synthesis gas is mixed with the recycle gas and steam through a steam mixing device to form a mixed gas. The flow rate of the recycle gas is 31 Nm 3 / h (with a molar composition of 31.07% H2O, 26.51% H2, 9.02% CO2, 33.13% CO, and 0.27% CH4), accounting for 5% (mole fraction) of the product gas volume after water separation, at a temperature of 130°C. The steam is saturated steam at 1.5 MPaG generated by a waste heat boiler, with a flow rate of 104 kg / h. At this time, the temperature of the mixed gas is 673°C, and the disproportionation safety factor is 1.21. Subsequently, the mixed gas enters the waste heat boiler and is cooled to 350°C, producing saturated steam at 1.5 MPaG. A portion of the produced steam is supplemented into the high-temperature syngas to adjust the composition of the mixed gas. The mixed gas at the outlet of the waste heat boiler enters the gas cooling system for further heat recovery, and the gas temperature is adjusted to 100°C. The cooled mixed gas enters the gas-liquid separation tank for water separation. The gas phase in the gas-liquid separation tank is the product gas. 5% of the product gas is supplemented into the high-temperature low-hydrogen-carbon-ratio syngas as recycle gas, and the remaining part is sent out of the battery limit as a product. The carbon deposition amount of this system is 0.79 g per thousand Nm 3 CO treatment capacity. After the device has been continuously operating for 4000 h, the carbon deposition amount in the system is very small, and the system pressure drop hardly changes afterwards. No metal powdering corrosion phenomenon appears on the metal wall surfaces of the equipment and pipelines.

[0050] Example 3

[0051] The treatment capacity of the low-hydrogen-carbon-ratio syngas from the dual reforming reactor is 496 Nm 3 / h, at a temperature of 950°C and a pressure of 1.0 MPaG. The composition of the low-hydrogen-carbon-ratio syngas is as follows: molar composition of H2O is 16.64%, H2 is 34.72%, CO2 is 13.21%, CO is 34.71%, and CH4 is 0.72%, and the hydrogen-carbon ratio is 1.0. The high-temperature low-hydrogen-carbon-ratio syngas is mixed with recycle gas and steam through a steam mixing device to form a mixed gas. The flow rate of the recycle gas is 75 Nm 3 / h (mole composition of H2O is 2.83%, H2 is 40.48%, CO2 is 15.39%, CO is 40.46%, CH4 is 0.84%), accounting for 15% (mole fraction) of the product gas volume after water separation, at a temperature of 70°C. The steam is saturated steam at 2.5 MPaG generated by a waste heat boiler, with a flow rate of 47 kg / h. At this time, the temperature of the mixed gas is 732°C, and the disproportionation safety factor is 1.38. Subsequently, the mixed gas enters the waste heat boiler and is cooled to 350°C, generating saturated steam at 2.5 MPaG. A part of the generated steam is supplemented into the high-temperature syngas to adjust the composition of the mixed gas. The mixed gas at the outlet of the waste heat boiler enters the gas cooling system for further heat recovery, and the gas temperature is adjusted to 700°C. The cooled mixed gas enters the gas-liquid separation tank for water separation. The gas phase of the gas-liquid separation tank is the product gas. 15% of the product gas is supplemented into the high-temperature low-hydrogen-carbon-ratio syngas as recycle gas, and the remaining part is sent out of the battery limit as product. The carbon deposition amount of this system is 0.74 g per thousand Nm 3 CO treatment capacity. After the device has been continuously operating for 4000 h, the carbon deposition amount in the system is very small, and the system pressure drop hardly changes afterwards. There is no metal powdering corrosion phenomenon on the metal wall surfaces of the equipment and pipelines.

[0052] Example 4

[0053] The treatment capacity of the low-hydrogen-carbon-ratio syngas from the tri-reformer is 554 Nm 3 / h, at a temperature of 1030°C and a pressure of 2.0 MPaG. The composition of the low-hydrogen-carbon-ratio syngas is as follows: mole composition of H2O is 27.23%, H2 is 38.31%, CO2 is 11.95%, CO is 21.18%, CH4 is 1.33%, and the hydrogen-carbon ratio is 1.8. The high-temperature low-hydrogen-carbon-ratio syngas is mixed with recycle gas and steam through a steam mixing device to form. The flow rate of the recycle gas is 101 Nm 3 / h (mole fraction of H2O is 0.32%, H2 is 52.48%, CO2 is 16.36%, CO is 29.02%, CH4 is 1.81%), accounting for 20% (mole fraction) of the product gas volume after water separation, at a temperature of 40°C. The steam is saturated steam at 4.4 MPaG generated by a waste heat boiler, with a flow rate of 55 kg / h. At this time, the temperature of the mixed gas is 835°C, and the disproportionation safety factor is 2.06. Subsequently, the mixed gas enters the waste heat boiler and is cooled to 350°C, producing saturated steam at 4.4 MPaG. A part of the produced steam is supplemented into the high-temperature syngas to adjust the composition of the mixed gas. The mixed gas at the outlet of the waste heat boiler enters the gas cooling system to continue heat recovery, and the gas temperature is adjusted to 40°C. The cooled mixed gas enters the gas-liquid separation tank for water separation. The gas phase of the gas-liquid separation tank is the product gas. 20% of the product gas is supplemented into the high-temperature low-hydrogen-carbon ratio syngas as recycle gas, and the remaining part is sent out of the battery limit as a product. The carbon deposition amount of this system is 0.53 g / thousand Nm 3 CO treatment capacity. After the device runs continuously for 4000 h, the carbon deposition amount in the system is very small, and the system pressure drop hardly changes later. There is no metal powdering corrosion on the metal wall surfaces of the equipment and pipelines.

[0054] Comparative Example 1

[0055] The treatment capacity of the low-hydrogen-carbon ratio syngas from the dual reforming reactor is 539 Nm 3 / h, at a temperature of 900°C and a pressure of 2.5 MPaG. The composition of the low-hydrogen-carbon ratio syngas is as follows: mole fraction of H2O is 24.98%, H2 is 34.47%, CO2 is 14.12%, CO is 24.56%, CH4 is 1.87%, and the hydrogen-carbon ratio is 1.4. The gas is subsequently processed using a traditional process, and the process is as Figure 3 shown. The low-hydrogen-carbon ratio syngas first enters the waste heat boiler and is cooled to 350°C, producing saturated steam at 4.4 MPaG. Subsequently, it enters the gas cooling system to continue heat recovery. The cooled gas enters the gas-liquid separation tank for water separation, and the gas after water separation is sent out of the battery limit as a product. The carbon deposition amount of this system is 8.41 g / thousand Nm 3 CO treatment capacity. After the device runs continuously for 1500 h, the system has serious carbon deposition, the device is forced to stop, and the metal wall surface of the carbon deposition is severely corroded by metal powdering.

[0056] Comparative Example 2

[0057] The treatment capacity of the low-hydrogen-carbon ratio syngas from the dual reforming reactor is 539 Nm 3 / h, temperature 900 °C, pressure 2.5 MPaG. The composition of the syngas with a low H2 / CO ratio is as follows: molar composition of H2O is 24.98%, molar composition of H2 is 34.47%, molar composition of CO2 is 14.12%, molar composition of CO is 24.56%, molar composition of CH4 is 1.87%, and the H2 / CO ratio is 1.4. The syngas with a high temperature and a low H2 / CO ratio is mixed with recycle gas and steam through a steam mixing device to form a mixed gas. The flow rate of the recycle gas is 47 Nm 3 / h (molar composition of H2O is 4.09%, molar composition of H2 is 44.09%, molar composition of CO2 is 18.03%, molar composition of CO is 31.4%, molar composition of CH4 is 2.39%), accounting for 10% (mole fraction) of the product gas volume after water separation, temperature 100 °C. The steam is saturated steam at 3.82 MPaG generated by a waste heat boiler, with a flow rate of 15 kg / h. At this time, the temperature of the mixed gas is 823 °C, and the disproportionation safety factor is 1.63. Subsequently, the mixed gas enters the waste heat boiler to be cooled to 350 °C, generating saturated steam at 3.82 MPaG. A part of the generated steam is supplemented into the syngas with a high temperature and a low H2 / CO ratio to adjust the composition of the mixed gas. The mixed gas at the outlet of the waste heat boiler enters the gas cooling system to continue heat recovery and adjusts the gas temperature to 100 °C. The cooled mixed gas enters a gas-liquid separation tank to separate water. The gas phase of the gas-liquid separation tank is the product gas. 10% of the product gas is used as recycle gas and supplemented into the syngas with a high temperature and a low H2 / CO ratio, and the remaining part is sent out of the battery limit as a product. The carbon deposition amount of this system is 4.35 g per thousand Nm 3 CO processing capacity. After the device operates continuously for 2900 h, the system has serious carbon deposition, and the device is forced to stop. The metal wall surface of the carbon deposition is severely corroded by metal powdering.

[0058] Comparative Example 3

[0059] The processing capacity of the syngas with a low H2 / CO ratio from the dual reforming reactor is 510 Nm 3 / h, temperature 920 °C, pressure 1.5 MPaG. The composition of the syngas with a low H2 / CO ratio is as follows: molar composition of H2O is 20.01%, molar composition of H2 is 35.82%, molar composition of CO2 is 13.2%, molar composition of CO is 29.76%, molar composition of CH4 is 1.2%, and the H2 / CO ratio is 1.2. The syngas with a high temperature and a low H2 / CO ratio is mixed with recycle gas and steam through a steam mixing device to form a mixed gas. The flow rate of the recycle gas is 74 Nm 3 / h (mole fraction of H2O is 2.97%, H2 is 43.46%, CO2 is 16.02%, CO is 36.1%, and CH4 is 1.45%), accounting for 15% (mole fraction) of the product gas volume after water separation, at a temperature of 80°C. The steam is saturated steam at 3.82 MPaG generated by a waste heat boiler, with a flow rate of 25 kg / h. At this time, the temperature of the mixed gas is 800°C, and the disproportionation safety factor is 1.2. Subsequently, the mixed gas enters the waste heat boiler and is cooled to 350°C, producing saturated steam at 3.82 MPaG. A part of the produced steam is supplemented into the high-temperature and low-hydrogen-carbon-ratio syngas to adjust the composition of the mixed gas. The mixed gas at the outlet of the waste heat boiler enters the gas cooling system for further heat recovery, and the gas temperature is adjusted to 80°C. The cooled mixed gas enters the gas-liquid separation tank for water separation. The gas phase of the gas-liquid separation tank is the product gas. 15% of the product gas is supplemented as recycle gas into the high-temperature and low-hydrogen-carbon-ratio syngas, and the remaining part is sent out of the battery limit as the product. The carbon deposition amount of this system is 4.03 g per thousand Nm 3 CO treatment capacity. After the device has been continuously operating for 3130 h, the system has serious carbon deposition, and the device is forced to stop. The metal wall surface of the carbon deposition is severely corroded with metal powdering.

[0060] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preventing carbon deposition in the post-treatment process of syngas with a low hydrogen-carbon ratio, characterized in that The method includes the following steps: The syngas with a low hydrogen-carbon ratio from the reactor outlet of the reforming unit is mixed with recycle gas and steam in a steam mixing device, and the disproportionation safety factor of the formed mixed gas is greater than 1.21 and the temperature is greater than 600 °C; The recycle gas comes from the synthetic product gas after cooling and dehydration; The syngas with a low hydrogen-carbon ratio refers to syngas with a molar ratio of H2 to CO of 0.8 to 1.8, the temperature of the gas is 850 to 1030 °C, and the pressure is 0 to 3.0 MPaG; The calculation method of the disproportionation safety factor is as follows: Disproportionation safety factor = (mole fraction of water vapor in the mixed gas + mole fraction of carbon dioxide in the mixed gas) / mole fraction of carbon monoxide in the mixed gas.

2. The method according to claim 1, wherein The molar ratio of H2 to CO in the syngas with a low hydrogen-carbon ratio is 1.0 to 1.

3.

3. The method according to claim 1, characterized in that The reforming unit includes, but is not limited to, a pure dry reforming unit, a dual reforming unit, and a triple reforming unit.

4. The method according to claim 1, wherein The temperature of the recycle gas is controlled at 40 to 130 °C; And / or, the recycle gas volume accounts for 5% to 20% of the synthetic product gas volume after water separation, in mole percentage.

5. The method according to claim 1, characterized in that, The steam comes from the waste heat boiler of the post-treatment system of the syngas with a low hydrogen-carbon ratio or from outside the reforming unit; and / or, the steam is saturated steam or superheated steam.

6. The method according to claim 1, wherein The pressure of the steam is greater than the pressure at the reactor outlet of the reforming unit.

7. The method according to any one of claims 1-6, characterized in that, When the pressure of the syngas with a low hydrogen-carbon ratio is less than or equal to 0.6 MPaG, the disproportionation safety factor of the mixed gas is not less than 1.21; When the pressure of the syngas with a low hydrogen-carbon ratio is greater than 0.6 MPaG and less than or equal to 1.1 MPaG, the disproportionation safety factor of the mixed gas is not less than 1.38; When the pressure of the syngas with a low hydrogen-carbon ratio is greater than 1.1 MPaG and less than or equal to 1.6 MPaG, the disproportionation safety factor of the mixed gas is not less than 1.67; When the pressure of the syngas with a low hydrogen-carbon ratio is greater than 1.7 MPaG and less than or equal to 2.1 MPaG, the disproportionation safety factor of the mixed gas is not less than 2.06; When the pressure of the syngas with a low hydrogen-carbon ratio is greater than 2.2 MPaG and less than or equal to 2.6 MPaG, the disproportionation safety factor of the mixed gas is not less than 2.

12.

8. A steam mixing device for the method according to any one of claims 1 to 7, characterized in that, The steam mixing device has the following structure: The recycle gas pipeline is connected to the upper part of the syngas pipeline with a low hydrogen-carbon ratio, and whether the recycle gas pipeline is expanded in diameter is determined according to the relative sizes of the diameters of the recycle gas pipeline and the steam injection pipeline. The annular area between the recycle gas pipeline and the steam injection pipeline is not less than 70% of the area of the recycle gas pipeline before expansion; The steam injection pipeline is arranged on the recycle gas pipeline and extends into the recycle gas pipeline as short as possible so that the steam injection port is located inside the recycle gas pipeline, and the steam injection port is flush with the outer diameter of the syngas pipeline with a low hydrogen-carbon ratio.

9. Application of the steam mixing device according to claim 8 in preventing carbon deposition from occurring during the post-treatment of syngas with a low hydrogen-carbon ratio.

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