Hydrogen-mixed natural gas pipeline conveying and screening method based on offshore hydrogen production

Abstract

According to the hydrogen-mixed natural gas pipeline conveying and screening method based on offshore hydrogen production, conveying and screening of the hydrogen-mixed natural gas pipeline are carried out with 10% as the definition, the pipes are classified according to the hydrogen concentration, the appropriate pipes can be selected according to different hydrogen concentrations, and therefore the material cost is reduced. Under the condition that the hydrogen concentration is smaller than 10%, a pipe with the steel grade of X52 or below can be directly used, additional treatment is not needed, existing materials can be directly utilized, a hydrogen conveying pipeline with high cost does not need to be built, and cost is reduced. And meanwhile, a large amount of manpower marine cost consumed by adopting a hydrogen storage tank is avoided, the cost of high-sea hydrogen transportation is greatly reduced, the hydrogen price is reduced, and the safety of the pipeline during transportation is ensured.

Description

Technical Field

[0001] The invention relates to a method for screening pipeline transportation of mixed hydrogen natural gas based on offshore hydrogen production. Background Art

[0002] There are a lot of renewable energy sources such as wind power and photovoltaic power in the open sea, which can be used to generate a lot of electricity. However, considering the volatility of wind power / photovoltaic power and the special geographical location of the open sea, it is difficult to integrate this electricity into the power grid and it is difficult to use it directly. Hydrogen energy, as a clean, efficient and sustainable energy, will play an important role in the future world energy system. By inputting the electricity generated by renewable energy into the electrolyzer to produce hydrogen by electrolysis, the renewable energy power that is not easy to store can be converted into hydrogen that is easy to store, and then become a long-term storable and transportable energy. Therefore, with the increasing demand for renewable energy, hydrogen production by water electrolysis combined with the abundant wind and solar resources at sea will be an important source of hydrogen supply in the future.

[0003] Considering the special geographical conditions of the open sea, transporting the produced hydrogen back to the inland will face very high costs. At present, hydrogen storage tanks and hydrogen transport ships are mostly used for hydrogen transport scheme design. Chinese patent documents CN116949458A and CN116733677A designed a seawater hydrogen production and transportation method based on an offshore wind farm and its transportation equipment, and improved the replacement efficiency of hydrogen storage containers by controlling the movement of empty hydrogen storage tanks and hydrogen storage tanks full of hydrogen. However, it takes many trips to the sea to transport the hydrogen storage tanks to land, which causes a huge waste of human resources and increases the cost of hydrogen production. A few patent documents disclose the technology of hydrogen blending in natural gas pipelines. This technology can use existing natural gas pipelines to control the hydrogen doping ratio and transport hydrogen and natural gas to the mainland together, greatly reducing costs. Chinese patent document CN117993185A discloses a parameter optimization method for an integrated system for offshore wind power hydrogen production and blending transportation, which analyzes the working parameters of the alkaline electrolyzer through numerical simulation calculations and determines the diameter of the blending gas pipeline according to the delivery gas pressure. However, existing patents mainly focus on the design of hydrogen-blending pipelines, lack of pipe adaptability analysis, and lack of screening methods for whether existing pipelines are suitable for hydrogen transportation. Summary of the invention

[0004] The purpose of the present invention is to adopt a method for screening the pipeline transportation of mixed hydrogen natural gas based on offshore hydrogen production, so as to use suitable pipelines to transport mixed hydrogen natural gas to reduce costs. To this end, the present invention adopts the following technical solutions:

[0005] A method for screening pipeline transportation of mixed hydrogen natural gas based on offshore hydrogen production, characterized in that:

[0006] 1) Classification based on hydrogen concentration, divided into two intervals: hydrogen volume concentration greater than or equal to 10% and less than 10%;

[0007] 2) For the transportation of hydrogen-mixed natural gas with a hydrogen concentration greater than or equal to 10%: when the steel grade of the transportation pipeline is X60 or below, it is considered to meet the conditions for the next step of testing; when the steel grade is above X60, if the maximum allowable operating pressure does not exceed 10MPa, it is considered to meet the conditions for the next step of testing; if the maximum allowable operating pressure exceeds 10MPa, it is necessary to reduce the operating pressure to 10MPa before the next step of testing; the next step of testing includes phosphorus content testing, toughness verification and stress intensity factor comparison for the steel; if the phosphorus content testing, toughness verification and stress intensity factor comparison all meet the requirements, the pipe is suitable for hydrogen mixed transportation; otherwise, the maximum allowable operating pressure needs to be recalculated;

[0008] The pipes used must also be tested for hydrogen embrittlement sensitivity and marine corrosion;

[0009] The pipe can be used for hydrogen mixing and transportation only if all the above tests meet the requirements;

[0010] 3) For the transportation of hydrogen-mixed natural gas with a hydrogen concentration of less than 10%: when the steel grade is X52 or below, the pipe is suitable for hydrogenation mixed transportation; when the steel grade does not meet the requirements of X52 or below, test whether the sulfur content, phosphorus content, carbon content, grain size, weld and HAZ hardness, longitudinal and transverse impact energy meet the requirements. If all meet the requirements, the pipe is suitable for hydrogenation mixed transportation, otherwise, it is necessary to reduce the yield strength by 50%;

[0011] The pipes used must also be tested for hydrogen embrittlement sensitivity and marine corrosion;

[0012] The pipe can be used for hydrogen mixing and transportation only if all the above tests meet the requirements.

[0013] Furthermore, the next step of testing in point 2) is to check whether the phosphorus content of the steel is lower than 0.015%, whether it can pass the toughness verification, whether the critical stress intensity coefficient KIH is greater than the specified stress intensity coefficient KIA, whether the yield strength of the steel is less than the specified yield strength upper limit, and whether the theoretical service life is greater than the planned transportation life of the pipeline.

[0014] Furthermore, in point 3), for the detection of sulfur content, phosphorus content, carbon content, grain size, weld and HAZ hardness, and longitudinal and transverse impact energy, it is tested whether the sulfur content of the steel is less than 0.01%, whether the phosphorus content is less than 0.015%, whether the carbon content is less than 0.35%, whether the grain size is level 8 or finer, whether the maximum hardness of the weld and the heat affected zone of the weld is less than 95HRB, whether the longitudinal impact energy is greater than 95J, whether the transverse impact energy is greater than 118J, whether the yield strength of the steel is less than the prescribed upper limit of the yield strength, and whether the theoretical service life is greater than the planned transportation life of the pipeline.

[0015] Due to the adoption of the technical solution of the present invention, the present invention has the following technical effects:

[0016] (1) Cost saving. By classifying pipes according to hydrogen concentration, appropriate pipes can be selected for different hydrogen concentrations, thereby reducing material costs. For hydrogen concentrations less than 10%, pipes with steel grades of X52 and below can be used directly without additional processing. This allows the use of existing materials without the need to build expensive hydrogen pipelines, thus reducing costs. At the same time, it avoids the large amount of manpower required to go to sea using hydrogen storage tanks, greatly reducing the cost of offshore hydrogen transportation and lowering the price of hydrogen.

[0017] (2) Material testing and performance verification ensure the safety of pipelines during transportation.

[0018] (3) A guide for pipe material selection under different hydrogen concentrations is provided, making the method applicable to a variety of working conditions and requirements. It allows different application scenarios to be adapted by adjusting operating parameters or material usage standards when certain conditions are not met. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the screening process of the present invention. DETAILED DESCRIPTION

[0020] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] According to the hydrogen concentration in natural gas, the pipeline materials are evaluated and classified, the adaptability of the mixed gas to the steel grade material is calculated, and it is determined whether the pipeline is suitable for hydrogenation mixed transportation and whether the yield strength needs to be reduced. Figure 1 The hydrogen concentration ratios under different schemes for the transportation of hydrogen-mixed natural gas are different, and the required pipeline material evaluation is classified according to the hydrogen concentration. For hydrogen-mixed natural gas, the transport medium is mainly a mixture of methane and hydrogen. The current research is limited to the maximum hydrogen-mixed ratio of in-service pipelines of 5%. The technical solution of the present invention can be applied to the screening of hydrogen-mixed natural gas pipeline transportation with a limit of 10%.

[0022] Example 1, hydrogen volume concentration is greater than or equal to 10%

[0023] 1. Check the steel grade. When the steel grade of the pipeline is X60 or below, it is considered to meet the conditions for the next step of testing. When the steel grade is above X60, if the maximum allowable operating pressure (MAOP) does not exceed 10MPa, it is considered to meet the conditions for the next step of testing. If the maximum allowable operating pressure exceeds 10MPa, the operating pressure needs to be reduced to 10MPa before the next step of testing;

[0024] 2. Test the properties of steel. Test whether the phosphorus content of steel is less than 0.015%, whether it can pass the toughness test, and the critical stress intensity coefficient K IH Is it greater than the specified stress intensity factor K? IA If all three conditions are met, the steel can be used for hydrogenation mixed transportation. If not all conditions are met, the allowable operating stress needs to be recalculated before it can be used for hydrogenation mixed transportation.

[0025] 3. Detect hydrogen embrittlement sensitivity. Hydrogen embrittlement is a phenomenon in which hydrogen dissolved in steel polymerizes into hydrogen molecules, causing stress concentration, exceeding the strength limit of the steel, and forming tiny cracks inside the steel. The hydrogen embrittlement phenomenon is very sensitive to the strength of the material. The higher the strength, the more serious the hydrogen embrittlement. Therefore, when testing whether steel can be used for hydrogenation mixed transportation, the upper limit of the yield strength of the steel must also be required. Generally, the upper limit is set to 1.3-1.5 times the specified minimum yield strength. When the measured yield strength of the steel is less than the specified upper limit of the yield strength, the steel can be used for hydrogenation mixed transportation.

[0026] 4. Pipeline corrosion detection. The marine environment will corrode pipelines, which is manifested in several aspects. In the marine environment, due to the generally high humidity, a thicker corrosive water film tends to form on the surface of the pipe, which reduces the speed at which external oxygen contacts the steel surface. Generally, when the humidity of the ocean exceeds 70%, the corrosion rate increases significantly. Temperature and its fluctuations have an impact on the condensation of water vapor on the surface of the pipe, the solubility of corrosive gases and salts in the water film, and the resistivity of the water film. Studies have shown that as the temperature rises, the problem of metal corrosion becomes more serious. In addition, due to the differences in ambient temperature in different sea areas and different time periods, the corrosion rates in these areas and periods will also be different. Chloride ions are common anions in seawater. They have a high adsorption capacity in the marine environment and are easy to form electrolyte solutions on the metal surface. In the liquid film formed on the surface of steel, chloride ions can promote the acceleration of the corrosion process. As the salt content increases, the conductivity of the liquid film will also increase, thereby accelerating the corrosion rate. When there is a lot of chloride salt deposition, the conductivity of the steel surface will gradually increase, which can easily destroy the microstructure of the material. By considering these influencing factors, the theoretical corrosion rate of the pipeline is calculated according to formula (1):

[0027]

[0028] In the formula, v is the theoretical corrosion rate, a, b, c are parameters related to temperature, humidity, and chloride ion concentration, x, y, z are function expressions related to temperature, humidity, and chloride ion concentration, T is temperature, φ is humidity, C is chloride ion concentration, and d is other influencing factors. The corrosion margin of the pipeline can be measured and the theoretical service life can be calculated according to formula (2).

[0029] t=s÷v (2) Where s is the corrosion allowance of the pipeline and t is the theoretical service life. If the theoretical service life is greater than the planned transportation life of the pipeline, the steel can be used for hydrogenation mixed transportation.

[0030] 5. The pipe can be used for hydrogen mixing and transportation only if all the above tests meet the requirements.

[0031] Example 2, hydrogen volume concentration is less than 10%

[0032] 1. Test the steel. Steels with a steel grade below X52 can be used for hydrogenation mixed transportation, and the rest of the steel will proceed to the next step of testing.

[0033] 2. Steel performance testing. Test whether the sulfur content of the steel is less than 0.01%, the phosphorus content is less than 0.015%, the carbon content is less than 0.35%, the grain size is 8 or finer, the maximum hardness of the weld and the heat affected zone (HAZ) is less than 95HRB, the longitudinal impact energy is greater than 95J, and the transverse impact energy is greater than 118J. If all of them are met, the steel can be used for hydrogenation mixed transportation. If not all of them are met, the yield strength needs to be reduced by 50% before it can be used for hydrogenation mixed transportation.

[0034] 3. Detect hydrogen embrittlement sensitivity. Hydrogen embrittlement is a phenomenon in which hydrogen dissolved in steel polymerizes into hydrogen molecules, causing stress concentration, exceeding the strength limit of the steel, and forming tiny cracks inside the steel. The hydrogen embrittlement phenomenon is very sensitive to the strength of the material. The higher the strength, the more serious the hydrogen embrittlement. Therefore, when testing whether steel can be used for hydrogenation mixed transportation, the upper limit of the yield strength of the steel must also be required. Generally, the upper limit is set to 1.3-1.5 times the specified minimum yield strength. When the measured yield strength of the steel is less than the specified upper limit of the yield strength, the steel can be used for hydrogenation mixed transportation.

[0035] 4. Pipeline corrosion detection. The marine environment will corrode pipelines, which is manifested in several aspects. By considering the influencing factors such as temperature, humidity, and chloride ion concentration, the theoretical corrosion rate of the pipeline is calculated according to formula (1). Then, the corrosion margin of the pipeline can be measured and the theoretical service life can be calculated according to formula (2). If the theoretical service life is greater than the planned transportation life of the pipeline, the steel can be used for hydrogenation mixed transportation.

[0036] 5. The pipe can be used for hydrogen mixing and transportation only if all the above tests meet the requirements.

[0037] The above description is only a specific implementation case of the invention, and the technical features of the invention are not limited thereto. Any changes or modifications made by any technician in the relevant field within the field of the invention are all covered by the protection scope of the invention.

Claims

1. A method for screening hydrogen-mixed natural gas pipeline transportation based on offshore hydrogen production, characterized in that: 1) Classification based on hydrogen concentration, divided into two intervals: hydrogen volume concentration greater than or equal to 10% and less than 10%; 2) For the transportation of hydrogen-mixed natural gas with a hydrogen concentration greater than or equal to 10%: when the steel grade of the transportation pipeline is X60 or below, it is considered to meet the conditions for the next step of testing; when the steel grade is above X60, if the maximum allowable operating pressure does not exceed 10MPa, it is considered to meet the conditions for the next step of testing; if the maximum allowable operating pressure exceeds 10MPa, it is necessary to reduce the operating pressure to 10MPa before the next step of testing; the next step of testing includes phosphorus content testing, toughness verification and stress intensity factor comparison for the steel; if the phosphorus content testing, toughness verification and stress intensity factor comparison all meet the requirements, the pipe is suitable for hydrogen mixed transportation; Otherwise, the maximum allowable operating pressure needs to be recalculated; The pipes used must also be tested for hydrogen embrittlement sensitivity and marine corrosion; The pipe can be used for hydrogen mixing transportation only if all the above tests meet the requirements; 3) For the transportation of hydrogen-mixed natural gas with a hydrogen concentration of less than 10%: when the steel grade is X52 or below, the pipe is suitable for hydrogenation mixed transportation; when the steel grade does not meet the requirements of X52 or below, test whether the sulfur content, phosphorus content, carbon content, grain size, weld and HAZ hardness, longitudinal and transverse impact energy meet the requirements. If all meet the requirements, the pipe is suitable for hydrogenation mixed transportation, otherwise, it is necessary to reduce the yield strength by 50%; The pipes used must also be tested for hydrogen embrittlement sensitivity and marine corrosion; The pipe can be used for hydrogen mixing and transportation only if all the above tests meet the requirements.

2. A method for screening pipeline transportation of mixed hydrogen natural gas based on offshore hydrogen production according to claim 1, characterized in that: The next step in point 2) is to check whether the phosphorus content of the steel is less than 0.015%, whether it can pass the toughness test, and the critical stress intensity factor K IH Is it greater than the specified stress intensity factor K? IA , whether the yield strength of the steel is less than the specified upper limit of the yield strength, and whether the theoretical service life is greater than the planned transportation life of the pipeline.

3. A method for screening pipeline transportation of mixed hydrogen natural gas based on offshore hydrogen production according to claim 1, characterized in that: In point 3), for the detection of sulfur content, phosphorus content, carbon content, grain size, weld and HAZ hardness, longitudinal and transverse impact energy, check whether the sulfur content of the steel is less than 0.01%, the phosphorus content is less than 0.015%, the carbon content is less than 0.35%, the grain size is grade 8 or finer, the maximum hardness of the weld and welding heat affected zone is less than 95HRB, the longitudinal impact energy is greater than 95J, the transverse impact energy is greater than 118J, the yield strength of the steel is less than the specified upper limit of the yield strength, and the theoretical service life is greater than the planned transportation life of the pipeline.

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