Method for preparing synthesis gas through hydrocarbon two-stage steam reforming

Abstract

The invention belongs to the field of chemical engineering, and particularly relates to a method for preparing synthesis gas through hydrocarbon two-stage steam reforming. The method comprises the following steps of: preparing synthesis gas by using two steam reforming furnaces which are connected in series; the method comprises the following steps: dividing raw material gas carbon dioxide-rich hydrocarbons into two parts, introducing one part into a first steam reforming furnace, introducing a certain amount of water vapor into the first steam reforming furnace to react with the hydrocarbons, mixing reaction gas from the first steam reforming furnace with the other part of carbon dioxide-rich hydrocarbons, introducing the mixture into a second steam reforming furnace, and introducing a certain amount of water vapor into the second steam reforming furnace to react with the hydrocarbons; continuously carrying out conversion reaction on the hydrocarbons in the second steam reforming furnace, carrying out heat recovery on reaction gas from the second steam reforming furnace, and finally carrying out gas-water separation to obtain synthesis gas. The synthesis gas can be produced by using hydrocarbons; the content of each gas component in the synthesis gas can be adjusted by changing the ratio of carbon dioxide, steam and hydrocarbon, the consumption is low, the operation is flexible, the application range is wide, and the synthesis gas with various ratios can be produced as required.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry and relates to a hydrocarbon gas production technology, specifically a method for producing synthesis gas by two-stage steam reforming of hydrocarbons. Background Art

[0002] Hydrocarbons refer to gases containing methane, ethane, propane and high-carbon hydrocarbons, and carbon dioxide-rich hydrocarbons refer to mixed gases of hydrocarbons and carbon dioxide. Synthesis gas refers to a mixture of hydrogen and carbon monoxide. The hydrogen-carbon ratio (H2 / CO molar ratio) in synthesis gas is one of the indicators for measuring the quality of synthesis gas. The hydrogen-carbon ratio in synthesis gas is usually required to be in the range of 2.0 to 3.0. For example, for synthesizing methanol, the hydrogen-carbon ratio needs to be as close to 2.0 as possible. Traditional methods for producing synthesis gas from hydrocarbons include hydrocarbon steam reforming and hydrocarbon steam reforming in series with pure oxygen conversion.

[0003] Hydrocarbon steam reforming process: Hydrocarbons undergo a reforming reaction with steam in a reaction tube equipped with a reforming catalyst. Since the hydrocarbon steam reforming reaction is an endothermic reaction, external heating is required to ensure the conversion rate of the hydrocarbons. Due to the influence of heat transfer and material, the hydrocarbon steam reforming reaction generally does not exceed 900°C. At the same time, in order to prevent hydrocarbons from carbonizing at high temperatures and affecting the service life of the catalyst, a certain water-carbon ratio (the ratio of water to carbon contained in hydrocarbons) must be guaranteed. For this purpose, a large amount of water vapor needs to be added. Due to the large amount of steam added, affected by the balance of the reforming reaction, the synthesis gas obtained by the hydrocarbon steam reforming process has high carbon dioxide and methane contents, and the hydrogen-carbon ratio is about 4.5 to 5. The hydrogen-carbon ratio of the synthesis gas obtained by the hydrocarbon steam reforming process is significantly different from the carbon ratio usually required, and the quality of the synthesis gas is poor. At the same time, the reforming adopts indirect heating to provide heat, which requires the combustion of a part of the hydrocarbons, increasing the consumption of raw materials, and the investment in the reforming furnace is high. The investment and cost of the unit amount of synthesis gas obtained by the hydrocarbon steam reforming process are high.

[0004] Hydrocarbon steam reforming series pure oxygen conversion process: first, a part of the hydrocarbons undergo a conversion reaction with steam in a reaction tube equipped with a conversion catalyst, and then are mixed with the remaining part of the hydrocarbons and enter a pure oxygen reformer equipped with a conversion catalyst to undergo a conversion reaction with steam under the heat provided by oxygen combustion. Since the outlet temperature of the pure oxygen reforming reactor is higher than that of the hydrocarbon steam reforming reactor, and the water-carbon ratio at the inlet of the pure oxygen reforming furnace is lower than that at the inlet of the hydrocarbon steam reforming reactor, the carbon dioxide and methane content in the synthesis gas obtained by the hydrocarbon steam series pure oxygen reforming process are lower than those of the simple hydrocarbon steam reforming process, and the hydrogen-carbon ratio is about 3.0. Therefore, the synthesis gas produced by the hydrocarbon steam reforming series pure oxygen reforming process basically meets the requirements. Since a part of the hydrocarbons in the hydrocarbon steam series pure oxygen reforming process are also steam reformed, the investment and cost per unit amount of synthesis gas obtained by the hydrocarbon steam series pure oxygen reforming process is still relatively high. Therefore, further research and development of such technologies is needed to obtain synthesis gas with reduced investment and cost. Summary of the invention

[0005] The purpose of the present invention is to provide a technology for producing synthesis gas by two-stage steam reforming of hydrocarbons in order to solve the problems existing in the current prior art. In this technology, synthesis gas can be produced by using hydrocarbons; the content of each gas component in the synthesis gas can be adjusted by changing the ratio of carbon dioxide, steam and hydrocarbons, and the consumption is low, the operation is flexible and the application range is wide.

[0006] In order to achieve the above invention object, the specific technical scheme of the present invention is as follows:

[0007] A method for preparing synthesis gas by two-stage steam reforming of hydrocarbons comprises the following steps: preparing synthesis gas by using two steam reformers connected in series; namely, dividing the carbon dioxide-rich hydrocarbons in the raw gas into two parts, one part entering the first steam reformer, introducing a certain amount of water vapor into the first steam reformer to react with the hydrocarbons, the reaction gas from the first steam reformer is mixed with the other part of the carbon dioxide-rich hydrocarbons and enters the second steam reformer, the hydrocarbons continue to undergo reforming reaction in the second steam reformer, the reaction gas from the second steam reformer is subjected to heat recovery, and finally the synthesis gas is obtained by gas-water separation.

[0008] Furthermore, in the method for producing synthesis gas by two-stage steam reforming of hydrocarbons, the first steam reformer and the second steam reformer are both externally heated tubular reactors with catalysts.

[0009] Furthermore, in the method for producing synthesis gas by two-stage steam reforming of hydrocarbons, the hydrocarbon distribution ratio of the two-stage steam reformers, on a dry basis, is determined by controlling the molar concentration of hydrocarbons in the mixed gas entering the second steam reformer, and the molar concentration of methane in the mixed gas at the inlet of the second steam reformer is less than 30%.

[0010] Furthermore, in the method for preparing synthesis gas by two-stage steam reforming of hydrocarbons, the mixed gas is a mixed gas of the reaction gas from the first steam reformer and carbon dioxide-rich hydrocarbons.

[0011] Furthermore, in the method for producing synthesis gas by two-stage steam reforming of hydrocarbons, a certain amount of water vapor is introduced into the first steam reformer to react with carbon dioxide-rich hydrocarbons, and the introduced water vapor should make the water-to-carbon ratio of the mixed gas at the inlet of the second steam reformer greater than 1.4.

[0012] Furthermore, in the method for preparing synthesis gas by two-stage steam reforming of hydrocarbons, the raw gas is a carbon dioxide-rich hydrocarbon, and the carbon dioxide-rich hydrocarbon material enters a preheater for heat exchange with the high-temperature flue gas in the convection section of the reformer, and the hydrocarbon material is heated; then enters a desulfurization tank to remove the sulfur contained therein, and the desulfurized gas is mixed with the carbon dioxide-rich gas and steam, and then enters the convection section of the steam reformer for heat exchange with the high-temperature flue gas, and after heating, enters a pre-reformation reactor, and a part of the reformed gas coming out of the pre-reformation reactor is mixed with steam again and enters the first steam reformer, and the natural gas reacts with the steam in the first steam reformer; the other part of the reformed gas after pre-reformation is mixed with the reaction gas coming out of the first steam reformer to form a mixed gas, and the temperature of the mixed gas is greater than 600°C, and the mixed gas enters the second steam reformer, and the natural gas reacts with steam in the second steam reformer, and the reaction gas coming out of the second steam reformer enters a steam generator for heat exchange, and then enters a heat recovery system and a cooling system for cooling, and the synthesis gas goes to subsequent processes after water vapor separation.

[0013] Furthermore, in the method of producing synthesis gas by two-stage steam reforming of hydrocarbons, the carbon dioxide-rich hydrocarbon material enters the preheater and exchanges heat with the high-temperature flue gas in the convection section of the converter. The hydrocarbon material is heated to 350°C-400°C and enters the desulfurization tank to remove the sulfur contained therein.

[0014] Furthermore, in the method for preparing synthesis gas by two-stage steam reforming of hydrocarbons, the temperature of the gas before entering the pre-reforming reactor is 500°C-650°C.

[0015] Furthermore, in the method for producing synthesis gas by two-stage steam reforming of hydrocarbons, the temperature of the reaction gas coming out of the second steam reformer is 800°C-900°C.

[0016] Furthermore, in the method for preparing synthesis gas by two-stage steam reforming of hydrocarbons, the temperature drops to 300°C-400°C after heat exchange in the steam generator.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) The use of two-stage steam reforming furnaces can utilize the excess steam in the reformed gas at the outlet of the first steam reforming furnace, which can effectively reduce the amount of process steam used.

[0019] (ii) Since the amount of steam required for steam reforming is reduced, the amount of heating fuel required for steam conversion can be reduced, thereby reducing carbon dioxide emissions.

[0020] (III) The present invention can produce synthesis gas by using hydrocarbons; the content of each gas component in the synthesis gas can be adjusted by changing the ratio of carbon dioxide, steam and hydrocarbons. It has low consumption, flexible operation and wide applicability, and can produce synthesis gas with various ratios according to demand.

[0021] (iv) The hydrogen-to-carbon ratio of the synthesis gas obtained is more appropriate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a schematic diagram of the process flow of Example 1 of the present invention.

[0023] Figure 1 In the figure, V1 is a desulfurization tank, R1 is a pre-conversion reactor, R2 is the first steam reformer, R3 is the second steam reformer, E1 is a preheater, E2 is a mixing heater, E3 is a medium-pressure steam generator, E4 is a boiler feed water heater, E5 is a decarbonization reboiler, E6 is a desalted water preheater, E7 is a lithium bromide preheater, E8 is a water cooler, 1 and 2 are hydrocarbon feedstocks, 3 and 6 are carbon dioxide-rich hydrocarbons, 4 is steam, 5 is supplementary carbon dioxide, 9 is a mixed gas, 10, 11, 12, 13, 14, 15 are conversion gases, 16 is a condensate, and 17 is synthesis gas. DETAILED DESCRIPTION

[0024] A method for preparing synthesis gas by two-stage steam reforming of hydrocarbons comprises the following steps:

[0025] 1) Fine desulfurization: The raw gas is subjected to hydrodesulfurization treatment to remove sulfides in the raw gas;

[0026] 2) Pre-conversion: convert high hydrocarbons in the raw gas to reduce the high hydrocarbon content in the raw material entering the steam reformer;

[0027] 3) Two-stage steam reforming: hydrocarbons and steam undergo steam reforming reaction to obtain reformed gas containing H2, CO, and CO2;

[0028] 4) Heat recovery: The heat in the high-temperature conversion gas is recovered through multi-stage heat exchange.

[0029] Preferably, the fine desulfurization step described in step 1) is: the feed gas is preheated and enters the hydrogenation reactor to hydrogenate and saturate the olefins in the feed gas and convert the organic sulfur into inorganic sulfur, and then enters the zinc oxide tank to remove the sulfur in the feed gas.

[0030] Preferably, the total sulfur in the coke oven gas after desulfurization in step 1) is reduced to ≤0.1 ppmv.

[0031] Preferably, the specific steps of step 2) are: after adding appropriate water vapor to the desulfurized raw gas, it enters the pre-conversion reactor after heating, and the gas after the reaction is directly sent to the steam reformer.

[0032] Preferably, step 2) can be adjusted according to the composition of the raw gas. For example, if the high hydrocarbon content in the raw gas is extremely low, this step can even be omitted.

[0033] Preferably, the specific steps of step 3) are as follows: the raw gas is divided into two, one part of which is mixed with a certain proportion of water vapor and then enters the first steam reformer, and the reformed gas after the reaction is mixed with the other raw gas and then enters the second steam reformer for reaction.

[0034] Preferably, both steps 2) and 3) require supplementary steam.

[0035] Preferably, the specific steps of step 4) are as follows: the conversion gas is respectively passed through a medium-pressure steam generator, a boiler feed water heater, a decarbonization reboiler, a desalted water preheater, and a lithium bromide preheater for heat recovery, and finally cooled by a water cooler.

[0036] Preferably, the heat recovery equipment in step 4) can be increased or decreased according to process requirements.

[0037] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0038] Any feature disclosed in this specification (including claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0039] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0040] In the present application, unmarked % indicates mass percentage, i.e. v / v%.

[0041] Embodiment 1:

[0042] The technical process of producing synthesis gas by two-stage steam reforming of hydrocarbons in this embodiment is as follows:

[0043] Process such as Figure 1 The raw material of this embodiment is natural gas, and the raw gas from the upstream process has a flow rate of ~47700Nm 3 / h, the temperature is room temperature, the pressure is ~3.0MPa(G), and it enters the preheater E1, where the raw gas is heated to ~390℃, and then enters the desulfurization tank V1 to remove the sulfur contained in the raw gas. The desulfurized raw gas is mixed with steam (water-carbon ratio 2.5) and carbon dioxide-rich gas from the decarbonization process to form carbon dioxide-rich natural gas. The carbon dioxide-rich natural gas enters the mixing heater E2, where it is heated to 550℃ and then enters the pre-conversion reactor R1.

[0044] The reformed gas from the pre-reforming reactor R1 is divided into two parts. One part is mixed with a certain proportion of steam (water-carbon ratio 2.5) and then enters the first steam reformer R2, where methane reacts with steam; the other part is mixed with the reformed gas from the first steam reformer and enters the second steam reformer R3 at a temperature of 600°C, where methane reacts with steam. The reformed gas from the second steam reformer, at a temperature of 900°C, enters the medium-pressure steam generator E3 for heat exchange, where the temperature drops to 300°C, and then enters the boiler feed water heater E4, the decarbonization reboiler E5, the desalted water preheater E6, and the lithium bromide preheater E7 in turn for heat recovery, and finally enters the water cooler for cooling. After water vapor separation, the syngas goes to the subsequent process.

[0045] Compared with the traditional one-stage steam reforming process, the annual reduction of fuel natural gas is 10.4 million Nm 3 , reducing carbon dioxide emissions by 20,430 tons annually.

[0046] The above-mentioned embodiments only express the specific implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the protection scope of the present application. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the technical solution concept of the present application, and these all belong to the protection scope of the present application.

[0047] This background section is provided to generally present the context of the invention, and the work of the presently named inventors, the work to the extent described in this background section, and aspects of this section that did not constitute prior art at the time of application are neither explicitly nor implicitly admitted to be prior art to the present invention.

Claims

1. A method for preparing synthesis gas by two-stage steam reforming of hydrocarbons, characterized in that: Synthesis gas is produced by using two steam reformers connected in series; that is, the raw gas rich in carbon dioxide and hydrocarbons is divided into two parts, one part enters the first steam reformer, a certain amount of water vapor is introduced into the first steam reformer to react with the hydrocarbons, the reaction gas from the first steam reformer is mixed with the other part of the carbon dioxide rich hydrocarbons as a mixed gas and enters the second steam reformer, the hydrocarbons continue to undergo a conversion reaction in the second steam reformer, the reaction gas from the second steam reformer is subjected to heat recovery, and finally the synthesis gas is obtained by gas-water separation.

2. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 1, characterized in that: The first steam reformer and the second steam reformer are both externally heated tubular reactors with catalysts.

3. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 1, characterized in that: On a dry basis, the hydrocarbon distribution ratio of the two-stage steam reformer is determined by controlling the molar concentration of hydrocarbons in the mixed gas entering the second steam reformer. The molar concentration of methane in the mixed gas at the inlet of the second steam reformer is less than 30%.

4. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 1, characterized in that: The mixed gas is a mixed gas of the reaction gas from the first steam reformer and carbon dioxide-rich hydrocarbons.

5. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 1, characterized in that: A certain amount of water vapor is introduced into the first steam reformer to react with the carbon dioxide-rich hydrocarbons, and the introduced water vapor should make the water-to-carbon ratio of the mixed gas at the inlet of the second steam reformer greater than 1.

4.

6. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to any one of claims 1 to 5, characterized in that: The raw gas is a carbon dioxide-rich hydrocarbon. The carbon dioxide-rich hydrocarbon enters a preheater for heat exchange with the high-temperature flue gas in the convection section of the reformer, and the hydrocarbon is heated; then it enters a desulfurization tank to remove the sulfur contained therein, and the desulfurized gas is mixed with carbon dioxide-rich gas and steam, and then enters the convection section of the steam reformer for heat exchange with the high-temperature flue gas, and after heating, it enters a pre-conversion reactor, and a part of the conversion gas coming out of the pre-conversion reactor is mixed with steam again and enters the first steam reformer, and the natural gas reacts with steam in the first steam reformer; the other part of the conversion gas after pre-conversion is mixed with the reaction gas coming out of the first steam reformer, and the temperature after mixing is greater than 600°C, and the mixed gas enters the second steam reformer, and the natural gas reacts with steam in the second steam reformer, and the reaction gas coming out of the second steam reformer enters a steam generator for heat exchange, and then enters a heat recovery system and a cooling system for cooling, and the synthesis gas after water vapor separation goes to subsequent processes.

7. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 6, characterized in that: The carbon dioxide-rich hydrocarbons enter the preheater and exchange heat with the high-temperature flue gas in the convection section of the converter. The hydrocarbons are heated to 350°C-400°C and enter the desulfurization tank to remove the sulfur they contain.

8. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 6, characterized in that: The gas temperature before entering the pre-conversion reactor is 500°C-650°C.

9. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to claim 6, characterized in that: The temperature of the reaction gas coming out of the second steam reformer is 800℃-900℃.

10. The method for preparing synthesis gas by two-stage steam reforming of hydrocarbons according to any one of claims 7 to 9, characterized in that: After heat exchange in the steam generator, the temperature drops to 300℃-400℃.

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