A safety hydrogen blending system and method for an existing natural gas pipeline

Abstract

The present invention discloses a safety hydrogen blending system and method for an existing natural gas pipeline. The system includes a flow monitoring and control system, a high-efficiency blending system, and an emergency relief system. Based on the basic process and safety requirements of hydrogen blending in an existing natural gas pipeline, the present invention detects and warns in advance of changes in natural gas flow through the setting of a flow monitoring and control system, provides sufficient reaction time for hydrogen flow regulation, and ensures that the hydrogen concentration in the blended medium always remains within a safe range. By setting up a high-efficiency blending system, the introduced hydrogen is fully shunted, the mixing uniformity with natural gas is improved, and the complex static mixer is eliminated by utilizing the self-flow disturbance characteristics of the gas. By setting up an emergency relief system, the blended station yard after pipeline shutdown is safely relieved to ensure the safety of pipelines and equipment materials.

Description

Technical Field

[0001] The present invention belongs to the technical field of pipeline transportation, and particularly relates to a safety hydrogen blending system and method for an existing natural gas pipeline. Background Art

[0002] In recent years, the utilization of hydrogen energy has received increasing attention, and the development of efficient hydrogen energy utilization will be rapidly promoted. The long-distance hydrogen energy storage and transportation technology is the key issue supporting the utilization of hydrogen energy, providing unique advantages for the transportation of hydrogen-blended natural gas and playing a key supporting role in the long-distance transportation of hydrogen. By injecting hydrogen into the natural gas pipeline at the supply end, transporting the natural gas blended with hydrogen, and performing secondary extraction and separation at the end (consumption end), the long-distance migration of hydrogen is completed.

[0003] The method of transporting hydrogen-blended natural gas through natural gas pipelines has been experimentally studied on a large scale abroad. Its technical difficulties mainly focus on issues such as the physical properties of the mixed gas after hydrogen addition, the evaluation of the material-performance impact of hydrogen in the mixed gas on pipelines and equipment, and the hydrogen separation technology at the back end, and certain progress has been made. Among them, since existing natural gas pipelines often use high-grade steel materials, they are relatively sensitive to the influence of hydrogen content, which is also a key consideration factor in determining the hydrogen concentration in the transportation of hydrogen-blended natural gas.

[0004] Regarding the research on the hydrogen blending process of natural gas, some reports have been published, mainly involving aspects such as the overall hydrogen blending process and the mixing mode after hydrogen addition. As mentioned above, in the mode of hydrogen blending in natural gas pipelines, the primary concern for the hydrogen content is that the instantaneous hydrogen concentration in the mixed gas should not exceed the concentration adapted by the materials and equipment of the existing natural gas pipelines. In theory, this can be achieved by real-time detection and adjustment of the concentrations of natural gas and hydrogen; in fact, the concentration responses of natural gas and hydrogen have a sequential order. At the same time, the hydrogen blending concentration in existing natural gas pipelines has typical irreversible characteristics, that is, if the hydrogen incorporation concentration is too high within a certain period of time, the mixed gas in this section will flow downstream along the pipeline and it is very difficult to eliminate it by other means. Therefore, a detection time margin should be reserved for the amount of natural gas incorporated to adjust the amount of hydrogen incorporated in a timely manner, which has not been specifically proposed in the current public reports. At the same time, since the incorporated pipeline system is a typical linear project, before being sent to the downstream station, the hydrogen-natural gas in the pipeline can be fully mixed through flow disturbance. The existing reported blending facilities will not only increase the construction investment, improve the operation and maintenance difficulty, but also cause excessive local pressure drop, and the matching degree of the application scenarios of natural gas-hydrogen blending is actually not high.

[0005] Therefore, in view of the above problems, it is necessary to further carry out relevant research, and based on the research conclusions using advanced simulation analysis methods, propose a safety hydrogen blending system and method for long-distance natural gas pipelines to promote the development of technology in this field. Summary of the Invention

[0006] The object of the present invention is to provide a safe hydrogen blending system and method for an existing natural gas pipeline that can achieve efficient blending of natural gas and hydrogen in a long-distance pipeline, and ensure the safe and efficient operation of the system, aiming at the above existing problems.

[0007] The main technical idea of the present invention is to set up a flow priority monitoring and control system in the natural gas hydrogen blending station to control the maximum hydrogen concentration in the outbound natural gas; to set up high-efficiency hydrogen blending pipe fittings to make full use of the medium flow to achieve natural mixing, reduce the pressure loss of the blending system, and reduce the maintenance cost; to set up an emergency relief system to relieve the pressure of the pipeline in the blending station after the downstream system stops transporting, to avoid local hydrogen accumulation of unblended hydrogen and natural gas systems, which brings the risk of hydrogen damage to pipelines and pipe fittings. At the same time, a supporting instrument monitoring system is set up to detect key parameters in real time.

[0008] The technical solution adopted by the present invention is: a safe hydrogen blending system for an existing natural gas pipeline, characterized in that it includes a flow monitoring and control system, a high-efficiency blending system, and an emergency relief system;

[0009] The flow monitoring and control system includes a main pipeline natural gas flow detection unit arranged outside the existing natural gas transmission station yard and a hydrogen transmission unit connected to the natural gas main pipeline in the existing natural gas transmission station yard. The main pipeline natural gas flow detection unit is used for real-time monitoring and early warning of the main pipeline natural gas flow in the blending station yard, and the hydrogen transmission unit is used for blending upstream hydrogen into the natural gas main pipeline;

[0010] The high-efficiency blending system is arranged on the natural gas main pipeline in the existing natural gas transmission station yard. The hydrogen transmission unit is connected to the high-efficiency blending system, and hydrogen is injected into the natural gas main pipeline by means of multi-point injection;

[0011] The emergency relief system is respectively connected to the upstream pipeline outside the existing natural gas transmission station yard and the pipeline in the existing natural gas transmission station yard, and is used for relieving the mixed gas of unblended hydrogen and natural gas when the blending station yard stops transporting.

[0012] In the safe hydrogen blending system for an existing natural gas pipeline of the present invention, the main pipeline natural gas flow detection unit includes a flow transmitter and a bypass pipeline of a metering valve group. The flow transmitter is arranged on the natural gas main pipeline outside the existing natural gas transmission station yard. A first cut-off valve of the metering valve group and a second cut-off valve of the metering valve group are respectively arranged at the upstream and downstream ends of the flow transmitter. A bypass cut-off valve of the metering valve group is arranged on the bypass pipeline of the metering valve group to form a bypass pipeline system for connecting the upstream and downstream pipelines during the maintenance of the flow transmitter.

[0013] For the existing natural gas pipeline safety hydrogen blending system of the present invention, the installation point of the flow transmitter is not less than 100 m away from the existing natural gas transmission station yard.

[0014] For the existing natural gas pipeline safety hydrogen blending system of the present invention, the hydrogen delivery unit includes a hydrogen pipeline, and a hydrogen pipeline block valve, a hydrogen regulating valve and a hydrogen pipeline flow transmitter arranged in sequence on the hydrogen pipeline. One end of the hydrogen pipeline is connected to the upstream hydrogen supply point, and the other end is connected to the high-efficiency blending system. The hydrogen regulating valve adjusts the hydrogen flow rate according to the set maximum volume ratio of natural gas to hydrogen under the input of the natural gas flow rate detected by the flow transmitter.

[0015] For the existing natural gas pipeline safety hydrogen blending system of the present invention, the high-efficiency blending system includes a hydrogen multi-point injection branch pipe, a blending pipeline and a mixed medium sampling pipeline. The blending pipeline is connected to the natural gas main pipeline in the existing natural gas transmission station yard. The hydrogen pipeline is connected to the blending pipeline near the upstream end through the hydrogen multi-point injection branch pipe, and the mixed medium sampling pipeline is connected to the blending pipeline near the downstream end.

[0016] For the existing natural gas pipeline safety hydrogen blending system of the present invention, the hydrogen multi-point injection branch pipe is composed of at least three branch pipes, which are respectively connected to the bottom of the blending pipeline and inject gas in a vertically upward direction in the blending pipeline.

[0017] For the existing natural gas pipeline safety hydrogen blending system of the present invention, the gas injection position of the hydrogen multi-point injection branch pipe is in the middle and lower part of the blending pipeline, and the distance between the injection points of adjacent branch pipes is not less than 0.5 m. The mixed medium sampling pipeline forms multi-point test comparisons on the blending pipeline, and the sampling points are evenly distributed on the same circumference of the blending pipeline.

[0018] For the existing natural gas pipeline safety hydrogen blending system of the present invention, the emergency relief system includes a natural gas intake and vent valve, a station yard relief valve, a choke orifice and a vent pipeline. The natural gas intake and vent valve is arranged on the branch pipe connected to the natural gas main pipeline outside the existing natural gas transmission station yard. The station yard relief valve is arranged on the branch pipe connected to the natural gas main pipeline in the existing natural gas transmission station yard. The choke orifice is installed on the vent pipeline.

[0019] A method for safely blending hydrogen into an existing natural gas pipeline, characterized in that: the specific hydrogen blending method is as follows:

[0020] Carry out renovation operations inside and outside the station yard of an existing natural gas transmission pipeline, including adding a flow monitoring and control system, an efficient blending system, an emergency relief system, and an instrument monitoring system. Determine the normal blending ratio according to the hydrogen concentration adaptation value and the planned blending value of the downstream existing main pipeline and equipment. According to the blending ratio and the main pipeline diameter of the existing pipeline system, use computational fluid dynamics to simulate and analyze the farthest blending uniformity length value at the designed blending ratio, and consider a 10%-15% margin as the actual length of the blending pipeline, and simulate the highest hydrogen concentration on the inner wall of the pipeline within the range from the injection point to the blending uniformity point;

[0021] During normal operation, natural gas is introduced from the natural gas main pipeline, and hydrogen is introduced from the hydrogen pipeline. Natural gas and hydrogen are mixed in the blending pipeline. During the blending process, hydrogen is introduced into the blending pipeline through multiple branches. In the blending pipeline, natural gas and hydrogen undergo sufficient flow disturbance and are mixed evenly. The mixed medium is transported downstream;

[0022] During normal operation, intermittently open the sampling pipeline for the mixed medium to take samples of the mixed gas and measure the gas content at each sampling position;

[0023] When it is necessary to urgently relieve the gas inside the blending system, first introduce the natural gas in the natural gas main pipeline outside the existing natural gas transmission station yard into the vent pipeline to displace the air in the vent pipeline, and then introduce the mixed gas inside the existing natural gas transmission station yard into the vent pipeline for relief.

[0024] For the method of safely blending hydrogen into an existing natural gas pipeline described in the present invention, during normal operation, the volumetric flow rate of natural gas is detected in real time by a flow transmitter, and the detection result is transmitted to the station yard control system; when the volumetric flow rate of natural gas decreases, the control system calculates the opening degree of the hydrogen regulating valve and sends a signal to control the hydrogen regulating valve to reduce the opening degree, and adjusts the volumetric flow rate of hydrogen according to the set blending ratio; when the volumetric flow rate of natural gas rises, the control system additionally considers the opening degree action delay time of the hydrogen regulating valve and sends an opening degree control signal to the hydrogen regulating valve to complete the control of the hydrogen regulating valve; when the hydrogen regulating valve fails, the control system sends an emergency closing instruction to the hydrogen pipeline shut-off valve to stop hydrogen from entering the station yard;

[0025] During normal operation, if the deviation degree between the hydrogen concentration of the mixed gas sampled through the sampling pipeline for the mixed medium and the calculated concentration of the natural gas and hydrogen flow monitored by the flowmeter is greater than the set value, or the hydrogen concentration of the sampled mixed gas exceeds the hydrogen partial pressure safety design value of the downstream pipeline material, it indicates that the internal flow field of the blending system is abnormal. Immediately stop the blending operation and perform fault repair on the hydrogen blending system;

[0026] When it is necessary to urgently release the gas inside the blending system, first shut off the inlet block valve of the existing station yard, the outlet block valve of the existing station yard, and the block valve of the hydrogen pipeline; then open the natural gas extraction and vent valve to use the natural gas in the upstream main pipeline to displace the air remaining in the vent pipeline for at least 10 s; immediately close the natural gas extraction and vent valve and open the station yard relief valve to release the mixed gas inside the blending station yard.

[0027] Compared with the prior art, the positive effects of the present invention are as follows: Based on the basic process and safety requirements of blending hydrogen into the existing natural gas pipeline, by setting up a flow monitoring and control system, the change of natural gas flow is detected and warned in advance, providing sufficient reaction time for the adjustment of hydrogen flow, and ensuring that the hydrogen concentration in the blended medium always remains within a safe range; by setting up an efficient blending system, the hydrogen introduced is fully shunted to improve the mixing uniformity with natural gas, and by utilizing the characteristics of self-flow disturbance of gas, the complex static mixer is cancelled; by setting up an emergency relief system, the blending station yard after pipeline shutdown is safely relieved to ensure the safety of pipelines, equipment and materials.

[0028] Specifically manifested as:

[0029] (1) Scientifically designed

[0030] Based on the potential market demand for blending hydrogen into the existing natural gas pipeline, aiming at the technical difficulties of blending hydrogen in the existing natural gas station yard, from the perspective of flow detection and response, the present invention proposes to conduct remote flow detection on the natural gas pipeline to provide sufficient control time for the input flow of the hydrogen pipeline, ensure that the hydrogen concentration of the blended gas always remains within a safe ratio, and overcome the problems such as untimely control of the hydrogen pipeline flow and irreversible control of the medium exceeding the safe ratio caused by the internal flow detection and feedback of the existing disclosed station yard; with the help of the advanced fluid flow field analysis conclusion, by utilizing the self-flow disturbance of the blended gas in the short pipe and combining with multi-branch hydrogen injection, self-flow mixing is realized to replace the static mixer with large pressure loss and high cost; considering the accumulation problem of the locally unmixed medium after pipeline shutdown and the spontaneous combustion problem of hydrogen release, a sequential relief system is set up to ensure the safety of the station yard materials and relief safety, and finally the purpose of safely blending hydrogen into the existing natural gas is achieved collaboratively.

[0031] (2) Good economy

[0032] By deeply analyzing the key problems of blending hydrogen into the existing natural gas pipeline, the present invention cancels the post-detection system for the blended medium online, large-diameter static mixers and other systems and facilities by setting reasonable monitoring, blending and safety control measures, resulting in a direct economic optimization effect; by controlling the maximum blending ratio, the material safety of downstream pipelines and equipment is ensured, resulting in an indirect economic optimization effect.

[0033] (3) Promote technological development

[0034] At present, the technology of hydrogen blending in natural gas needs to be further developed. In response to key problems, the present invention has taken effective measures, put forward relatively advanced concepts for specific problems, and provided reference for the technological development in the field of hydrogen blending in natural gas transmission. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be described by way of specific embodiments with reference to the accompanying drawings, in which

[0036] Figure 1 is a schematic structural diagram of the present invention.

[0037] Reference numerals in the figures: 1 is the main natural gas pipeline, 2 is the inlet block valve of the existing station yard, 3 is the outlet block valve of the existing station yard, 11 is the first block valve of the metering valve group, 12 is the flow transmitter, 13 is the second block valve of the metering valve group, 14 is the bypass block valve of the metering valve group, 15 is the bypass pipeline of the metering valve group, 16 is the hydrogen pipeline, 17 is the hydrogen pipeline block valve, 18 is the hydrogen regulating valve, 19 is the hydrogen pipeline flow transmitter, 21 is the hydrogen multi-point injection branch pipe, 22 is the mixing pipeline, 23 is the sampling pipeline for the mixed medium, 31 is the natural gas extraction and vent valve, 32 is the station yard relief valve, 33 is the orifice plate, and 34 is the vent pipeline. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0038] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Generally, the components of the embodiments of the present invention described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0039] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0040] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other.

[0041] It should be noted that like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0042] In the description of the embodiments of the present invention, it should be noted that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the invention product is customarily placed during use, or the orientation or positional relationship commonly understood by those skilled in the art, or the orientation or positional relationship in which the invention product is customarily placed during use. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present invention. In addition, the terms "first" and "second" are only used for distinguishing descriptions and should not be construed as indicating or implying relative importance.

[0043] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, the terms "set" and "connect" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection or an indirect connection through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0044] As Figure 1 shown, a safety hydrogen blending system for an existing natural gas pipeline includes a flow monitoring and control system, an efficient blending system, an emergency relief system, and an instrument monitoring system added on the basis of the existing gas transmission station field system.

[0045] The existing gas transmission station field system includes facilities such as existing station field pipelines, valves, and pig launchers and receivers. Specifically, it is the existing natural gas main pipeline 1, the existing station field inlet block valve 2, and the existing station field outlet block valve 3, which are part of the existing natural gas pipeline system and form specific station field functions. It should be noted that the existing gas transmission station field system is the basis and reliance of the present invention and is not the innovation point of the present invention.

[0046] The flow monitoring and control system includes a main pipeline natural gas flow detection unit arranged outside the existing natural gas transmission station field and a hydrogen transmission unit connected to the natural gas main pipeline 1 in the existing natural gas transmission station field. The main pipeline natural gas flow detection unit is used to monitor and give early warnings of the main pipeline natural gas flow in the blending station field in real time. The hydrogen transmission unit is used to blend the upstream hydrogen into the natural gas main pipeline 1 and feedback-adjust the hydrogen input amount to strictly control the upper limit of the natural gas and hydrogen mixing ratio, ensuring that the hydrogen concentration in the blended gas meets the service requirements of downstream pipelines and equipment.

[0047] The efficient blending system is installed on the natural gas main pipeline 1 in the existing natural gas transmission station yard. The hydrogen transmission unit is connected to the efficient blending system, which is mainly used to provide a blending space for natural gas and hydrogen, and injects hydrogen into the natural gas main pipeline 1 in a multi-point injection manner to disperse the concentration distribution of hydrogen in the blending space, promote the mixing effect, and utilize the self-flow disturbance of the pipeline medium to replace the expensive and cumbersome static mixer to achieve the purpose of uniform mixing of the medium in a short distance.

[0048] The emergency relief system is respectively connected to the upstream pipeline outside the existing natural gas transmission station yard and the pipeline inside the existing natural gas transmission station yard, and is used to relieve the mixed gas of hydrogen and natural gas that has not been evenly blended when the blending station yard stops transporting, so as to avoid local hydrogen accumulation in the pipeline system, which may pose a hidden danger to the safety of pipeline materials and operation in the later stage; further, the emergency relief system preferably first introduces natural gas to replace the air in the relief system to avoid deflagration of the relief system after hydrogen is introduced.

[0049] The instrument monitoring system includes pressure transmitters, temperature transmitters, flow transmitters, etc. arranged in the aforementioned systems, which are used to monitor parameters at key points.

[0050] By setting up this system, it supports issues such as the hydrogen blending process and safety control in the existing natural gas pipeline station yard, avoids the irreversible problem of too high hydrogen blending concentration caused by insufficient response time of natural gas flow detection in the hydrogen blending system, optimizes the hydrogen blending system, replaces the complex blending device with high investment and difficult maintenance, and further considers the problem of local hydrogen accumulation after the system stops transporting. A safety relief system of "first replace with natural gas and then relieve the hydrogen-containing medium" is set up, which provides an important impetus and support for the development of hydrogen blending technology in the existing natural gas pipeline station yard.

[0051] Specifically, the main-line natural gas flow detection unit includes a flow transmitter 12 and a metering valve group bypass pipeline 15. The flow transmitter 12 is arranged on the natural gas main pipeline 1 outside the built natural gas transmission station yard. Among them, the flow transmitter is a natural gas flow transmitter, preferably an ultrasonic flowmeter, and the installation point is not less than 100 m away from the built natural gas transmission station yard. The main purpose is to reserve sufficient time for adjusting the hydrogen pipeline flow transmitter 19 after the detection signal is transmitted to the central control system, so as to avoid the actual hydrogen mixing amount increasing due to untimely control of the hydrogen pipeline flow transmitter, which affects the material safety of the downstream pipeline and equipment; a metering valve group first shut-off valve 11 and a metering valve group second shut-off valve 13 are respectively arranged at the upstream and downstream ends of the flow transmitter 12. Among them, both the metering valve group first shut-off valve and the metering valve group second shut-off valve are preferably electric ball valves, full-bore ball valves, which are used to control the commissioning and decommissioning of the flow transmitter, and are opened during normal operation of the flow transmitter and closed during the maintenance and repair of the flow transmitter; a metering valve group bypass shut-off valve 14 is arranged on the metering valve group bypass pipeline 15 to form a bypass pipeline system, which is used to connect the upstream and downstream pipelines to maintain production during the maintenance of the flow transmitter 12. The metering valve group bypass shut-off valve is preferably an electric ball valve, a full-bore ball valve, and the metering valve group bypass pipeline and the main pipeline adopt the same pipe diameter.

[0052] Specifically, the hydrogen transportation unit includes a hydrogen pipeline 16 and a hydrogen pipeline shut-off valve 17, a hydrogen regulating valve 18, and a hydrogen pipeline flow transmitter 19 arranged in sequence on the hydrogen pipeline 16. One end of the hydrogen pipeline 16 is connected to the upstream hydrogen supply point, and the other end is connected to the high-efficiency mixing system, and it is made of carbon steel; the hydrogen pipeline shut-off valve 17 is arranged after the hydrogen pipeline 16 enters the built natural gas station yard, and it is an electric ball valve, which is used to control the access and disconnection of the hydrogen pipeline, and performs a closing operation after the hydrogen regulating valve fails or the regulation fails, and is urgently closed in case of a fire or other situations in the built natural gas station yard; the hydrogen regulating valve 18 is a hydrogen flow regulating valve, which is electrically controlled, and adjusts the hydrogen flow according to the set maximum natural gas to hydrogen volume ratio under the input of the natural gas flow detected by the flow transmitter 12; further, in order to maintain the stable operation of the system and avoid the hydrogen regulating valve from operating too frequently, preferably after the natural gas flow rebounds, the hydrogen flow regulating valve is set with an upward (flow increasing regulation) delay response time of 2 - 5 s; the hydrogen pipeline flow transmitter 19 is preferably an ultrasonic flowmeter, and preferably a maintenance and calibration bypass is provided.

[0053] Specifically, the high-efficiency blending system includes a hydrogen multi-point injection branch pipe 21, a blending pipeline 22, and a mixed medium sampling pipeline 23. The blending pipeline 22 is connected to the natural gas main pipeline 1 in the existing natural gas transmission station yard. The hydrogen pipeline 16 is connected to the blending pipeline 22 near the upstream end through the hydrogen multi-point injection branch pipe 21. The mixed medium sampling pipeline 23 is connected to the blending pipeline 22 near the downstream end.

[0054] In this embodiment, the hydrogen multi-point injection branch pipe 21 is composed of at least three branch pipes that are respectively connected to the bottom of the blending pipeline 22 and inject gas in a vertically upward direction within the blending pipeline 22. The gas injection position of the hydrogen multi-point injection branch pipe 21 is in the middle and lower part of the blending pipeline 22, preferably at a height of 0.25 times the inner diameter of the blending pipeline. The injection point spacing between adjacent branch pipes is not less than 0.5 m. The purpose of this setting is to disperse the injection volume of a single support point, promote the mixing effect of the injected hydrogen and natural gas, and utilize the characteristic that the density of hydrogen is less than that of natural gas. The injected hydrogen has a tendency to move towards the top of the blending pipeline, further promoting the mixing contact volume of hydrogen and natural gas, and effectively avoiding the contact between the injected high-concentration hydrogen cluster and the inner wall of the pipeline. Among them, the blending pipeline is a carbon steel pipeline, preferably 12 m in length, and is verified by numerical simulation to ensure that the hydrogen concentration distribution at the end cross-section of the blending pipeline reaches a uniform effect. The pipeline material is selected as a steel grade below L415. The mixed medium sampling pipeline 23 is a gas detection and extraction pipeline arranged at the end point of the blending pipeline 22, including a ball valve and a short pipe, which is used to periodically extract the gas near the inner wall of the pipeline for mixed concentration detection. Further, the mixed medium sampling pipeline 23 is arranged at four places, distributed at the 0 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock positions of the same cross-section position for multi-point test comparison.

[0055] Specifically, the emergency relief system includes a natural gas intake and vent valve 31, a station yard relief valve 32, a choke orifice 33, and a vent pipeline 34. The natural gas intake and vent valve 31 is arranged on the branch pipe connected to the natural gas main pipeline 1 outside the existing natural gas transmission station yard, normally closed, and is first opened after emergency relief, which is used to introduce natural gas into the vent system to displace the air in the vent system, avoiding the contact between the not yet fully mixed natural gas / hydrogen and the air after being introduced into the vent pipeline, thus causing deflagration. The station yard relief valve 32 is arranged on the branch pipe connected to the natural gas main pipeline 1 in the existing natural gas transmission station yard, normally closed, and is opened 10 s after the natural gas intake and vent valve is opened under emergency relief conditions, which is used to introduce the mixed gas in the blending system into the vent pipeline for relief. The choke orifice 33 is installed on the vent pipeline 34 to limit the flow rate of the relief medium. The vent pipeline 34 connects the choke orifice to the vent flare or the vent riser, which is used to introduce the relief medium into the safety treatment system.

[0056] The working principle of the present invention is:

[0057] During the blending process of the natural gas pipeline, the blending standard is to strictly control the upper limit of the hydrogen flow rate being incorporated to avoid the risk of material damage to downstream pipelines and equipment systems due to excessive hydrogen concentration. Since the blending process is dynamic and continuous, it is very difficult to measure the blending concentration in real time and promptly. Moreover, once the hydrogen concentration in the detected mixed gas exceeds the standard, it is also difficult to reverse and control this part of the mixed gas. Therefore, sufficient time must be reserved according to the actual situation for the detection of the natural gas incorporation flow rate and the control of the hydrogen incorporation flow rate. This is one of the basic principles of the present invention. At the same time, to avoid frequent operation of hydrogen flow control, a certain amount of time is reserved for the process of the natural gas flow rate decreasing and then increasing again, such as a 10s hydrogen concentration adjustment time, which effectively controls the frequency of blending adjustment while ensuring that the incorporated hydrogen concentration meets the design requirements.

[0058] Secondly, for the gas mixing process, the present invention adopts a multi-point hydrogen injection mode, which disperses the injection amount at a single point and improves the mixing efficiency of natural gas and hydrogen. Moreover, a low-grade carbon steel straight pipe is used as the mixing place, and the self-flow disturbance of the gas is utilized for mixing. It is only necessary to ensure effective gas mixing within a limited length, replacing the static mixer and avoiding problems such as increased pressure loss and mixer maintenance.

[0059] Since there may be accidental emergency incidents at the station yard, emergency gas release is considered. For the gas release in the blending station yard, considering that the mixed gas at some positions has not been safely mixed and there are dispersed high-concentration hydrogen gases, to avoid the risk of internal spontaneous combustion and deflagration of the hydrogen-based vent pipeline when this part of the high-concentration hydrogen directly contacts the air after entering the venting system, during emergency release, first a part of natural gas is introduced. Utilizing the characteristics that natural gas has a higher ignition energy and is not easily accidentally ignited, the air in the vent pipeline is displaced, and then the mixed gas is introduced for release.

[0060] The present invention also provides a method for safely blending hydrogen into an existing natural gas pipeline, specifically as follows:

[0061] Step 1: Carry out renovation operations inside and outside the station yard of the existing natural gas transmission pipeline, including adding a flow monitoring and control system, an efficient blending system, an emergency release system, and an instrument monitoring system. According to the hydrogen concentration adaptation value and the planned blending value of the downstream existing main pipeline and equipment, determine the normal blending ratio. According to the blending ratio and the main pipeline diameter of the existing pipeline system, use computational fluid dynamics to simulate and analyze the farthest blending uniform length value at the designed blending ratio, and consider a 10%-15% margin as the actual length of the blending pipeline, preferably not exceeding 12m. Also, simulate the highest hydrogen concentration on the inner wall of the pipeline within the range from the incorporation point to the blending uniform point, and evaluate the material safety of the steel grade proposed to be selected for the blending pipeline.

[0062] Step 2: During normal operation, natural gas is introduced from the natural gas main pipeline, and hydrogen is introduced from the hydrogen pipeline. The natural gas and hydrogen are mixed in the mixing pipeline. During the mixing process, hydrogen is introduced into the mixing pipeline through multiple branches. In the mixing pipeline, the natural gas and hydrogen undergo sufficient flow disturbance and are mixed evenly. The mixed medium is transported downstream. The volumetric flow rate of the natural gas is detected in real time by a flow transmitter, and the detection result is transmitted to the station control system. When the volumetric flow rate of the natural gas decreases, the control system calculates the opening degree of the hydrogen regulating valve and sends a signal to control the hydrogen regulating valve to reduce the opening degree, adjusting the volumetric flow rate of hydrogen according to the set mixing ratio. When the volumetric flow rate of the natural gas rebounds, the control system additionally considers the action delay time for adjusting the opening degree of the hydrogen regulating valve and sends an opening degree control signal to the hydrogen regulating valve to complete the control of the hydrogen regulating valve. When the hydrogen regulating valve fails, the control system sends an emergency closing instruction to the hydrogen pipeline shut-off valve to stop hydrogen from entering the station.

[0063] Step 3: During normal operation, the sampling pipeline for the mixed medium is intermittently opened to take samples of the mixed gas, and the gas content at each sampling position is measured. If the deviation degree between the hydrogen concentration of the mixed gas sampled through the sampling pipeline for the mixed medium and the concentration calculated based on the flow rates of the natural gas and hydrogen monitored by the flowmeter is greater than the set value, or the hydrogen concentration of the sampled mixed gas exceeds the hydrogen partial pressure safety design value of the downstream pipeline material, it indicates that the internal flow field of the mixing system is abnormal. Immediately stop the mixing operation and perform fault maintenance on the hydrogen-doping system.

[0064] Step 4: When a fire occurs in the mixing system or it is necessary to urgently release the gas inside the mixing system, first introduce the natural gas in the natural gas main pipeline outside the existing natural gas transmission station into the vent pipeline to displace the air in the vent pipeline, and then introduce the mixed gas inside the existing natural gas transmission station into the vent pipeline for release. Specifically: First, shut off the inlet shut-off ball valve of the existing station, the outlet shut-off valve of the existing station, and the hydrogen pipeline shut-off valve. Then open the natural gas extraction vent valve to use the natural gas in the upstream main pipeline to displace the air remaining in the vent pipeline for at least 10 s. Immediately close the natural gas extraction vent valve and open the station release valve to release the mixed gas inside the mixing station.

[0065] The present invention is not limited to the foregoing specific embodiments. The present invention extends to any new feature disclosed in this specification or any new combination, as well as any new method or process step disclosed or any new combination.

Claims

1. A method for safely blending hydrogen into an existing natural gas pipeline, characterized in that: The specific hydrogen doping method is as follows: Reconstruction operations are carried out inside and outside the stations of the existing natural gas transmission pipelines, including adding a flow monitoring and control system, an efficient mixing system, an emergency relief system, and an instrument monitoring system. According to the hydrogen concentration adaptation values and the planned mixing values of the downstream existing main pipelines and equipment, the normal mixing ratio is determined. According to the mixing ratio and the main pipeline diameter of the existing pipeline system, the computational fluid dynamics method is used to simulate and analyze the farthest mixing uniform length value under the designed mixing ratio, and a 10%-15% margin is considered as the actual length of the mixing pipeline, and the highest hydrogen concentration on the inner wall of the pipeline within the range from the injection point to the mixing uniform point is simulated; The flow monitoring and control system includes a main pipeline natural gas flow detection unit arranged outside the existing natural gas transmission station and a hydrogen transmission unit connected to the natural gas main pipeline (1) inside the existing natural gas transmission station. The main pipeline natural gas flow detection unit is used to monitor and give early warnings of the main pipeline natural gas flow in the mixing station, and the hydrogen transmission unit is used to mix the upstream hydrogen into the natural gas main pipeline (1); The efficient mixing system is arranged on the natural gas main pipeline (1) inside the existing natural gas transmission station. The hydrogen transmission unit is connected to the efficient mixing system, and hydrogen is injected into the natural gas main pipeline (1) by means of multi-point injection; The efficient mixing system includes a hydrogen multi-point injection branch pipe (21), a mixing pipeline (22), and a mixed medium sampling pipeline (23). The mixing pipeline (22) is connected to the natural gas main pipeline (1) inside the existing natural gas transmission station. The hydrogen pipeline (16) is connected to the mixing pipeline (22) near the upstream end through the hydrogen multi-point injection branch pipe (21), and the mixed medium sampling pipeline (23) is connected to the mixing pipeline (22) near the downstream end; The emergency relief system is respectively connected to the upstream pipeline outside the existing natural gas transmission station and the pipeline inside the existing natural gas transmission station, and is used to relieve the mixed gas of hydrogen and natural gas that has not been evenly mixed when the mixing station stops transporting; During normal operation, natural gas is introduced from the natural gas main pipeline (1), and hydrogen is introduced from the hydrogen pipeline (16) of the hydrogen transmission unit. Natural gas and hydrogen are mixed in the mixing pipeline (22) of the efficient mixing system. During the mixing process, hydrogen is introduced into the mixing pipeline (22) through multiple branches. In the mixing pipeline (22), natural gas and hydrogen are fully flow-disturbed and mixed evenly, and the mixed medium is transported downstream; During normal operation, the mixed medium sampling pipeline (23) of the efficient mixing system is intermittently opened to take samples of the mixed gas, and the gas content at each sampling position is measured; When it is necessary to urgently relieve the gas inside the mixing system, first introduce the natural gas in the natural gas main pipeline (1) outside the existing natural gas transmission station into the vent pipeline (34) of the emergency relief system to displace the air in the vent pipeline (34), and then introduce the mixed gas inside the existing natural gas transmission station into the vent pipeline (34) for relief.

2. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 1, wherein: The main-line natural gas flow detection unit includes a flow transmitter (12) and a metering valve group bypass pipeline (15). The flow transmitter (12) is arranged on the natural gas main-line pipeline (1) outside the existing natural gas transmission station. A first cut-off valve (11) of the metering valve group and a second cut-off valve (13) of the metering valve group are respectively arranged at the upstream and downstream ends of the flow transmitter (12). A bypass cut-off valve (14) of the metering valve group is arranged on the metering valve group bypass pipeline (15) to form a bypass pipeline system for connecting the upstream and downstream pipelines during the maintenance of the flow transmitter (12).

3. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 2, characterized in that: The installation point of the flow transmitter (12) is not less than 100 m away from the existing natural gas transmission station.

4. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 2, characterized in that: The hydrogen transmission unit includes a hydrogen pipeline (16), a hydrogen pipeline cut-off valve (17), a hydrogen regulating valve (18), and a hydrogen pipeline flow transmitter (19) arranged in sequence on the hydrogen pipeline (16). One end of the hydrogen pipeline (16) is connected to the upstream hydrogen supply point, and the other end is connected to the high-efficiency mixing system. The hydrogen regulating valve (18) adjusts the hydrogen flow rate according to the set maximum volume ratio of natural gas to hydrogen under the input of the natural gas flow rate detected by the flow transmitter (12).

5. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 4, characterized in that: The hydrogen multi-point injection branch pipes (21) are respectively connected to the bottom of the mixing pipeline (22) by at least three branch pipes and inject gas in a vertically upward direction in the mixing pipeline (22).

6. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 4, characterized in that: The gas injection position of the hydrogen multi-point injection branch pipes (21) is in the middle and lower part of the mixing pipeline (22). The distance between the injection points of adjacent branch pipes is not less than 0.5 m. The mixed medium sampling pipeline (23) forms multi-point test comparisons on the mixing pipeline (22), and its sampling points are evenly distributed on the same circumference of the mixing pipeline (22).

7. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 4, wherein: The emergency relief system includes a natural gas intake vent valve (31), a station relief valve (32), a choke orifice plate (33), and a vent pipeline (34). The natural gas intake vent valve (31) is arranged on the branch pipe connected to the natural gas main-line pipeline (1) outside the existing natural gas transmission station. The station relief valve (32) is arranged on the branch pipe connected to the natural gas main-line pipeline (1) inside the existing natural gas transmission station. The choke orifice plate (33) is installed on the vent pipeline (34).

8. The method for safely blending hydrogen into an existing natural gas pipeline according to claim 7, characterized in that: During normal operation, the natural gas volume flow rate is detected in real time by the flow transmitter (12), and the detection result is transmitted to the station control system. When the natural gas volume flow rate decreases, the control system calculates the opening degree of the hydrogen regulating valve and sends a signal to control the hydrogen regulating valve (18) to reduce the opening degree and adjust the hydrogen volume flow rate according to the set blending ratio. When the natural gas volume flow rate rises, the control system additionally considers the opening degree action delay time of the hydrogen regulating valve (18) and sends an opening degree control signal to the hydrogen regulating valve (18) to complete the control of the hydrogen regulating valve (18). When the hydrogen regulating valve (18) fails, the control system sends an emergency closing instruction to the hydrogen pipeline cut-off valve (17) to stop the hydrogen from entering the station. During normal operation, if the deviation between the hydrogen concentration of the mixed gas sampled through the mixed medium sampling pipeline (23) and the calculated concentration of natural gas and hydrogen flow monitored by the flowmeter is greater than the set value, or the hydrogen concentration of the sampled mixed gas exceeds the hydrogen partial pressure safety design value of the downstream pipeline material, it indicates that the internal flow field of the blending system is abnormal. Immediately stop the blending operation and conduct fault repair on the hydrogen blending system; When it is necessary to urgently vent the gas inside the blending system, first close the inlet block valve (2) of the existing station yard, the outlet block valve (3) of the existing station yard, and the hydrogen pipeline block valve (17); then open the natural gas extraction and vent valve (31) to displace the air remaining in the vent pipeline (34) with natural gas in the upstream main line for at least 10 seconds; immediately close the natural gas extraction and vent valve (31) and open the station yard vent valve (32) to vent the mixed gas inside the blending station yard.

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