4.4 Complex Slurry Flow Measurement Technology

Slurry pipeline transportation is an efficient, energy-saving, and environmentally friendly transportation method that has been widely used for transporting minerals such as phosphorus, sulfur, kaolin, bauxite, limestone, as well as slurries such as cement and sediment. China has built slurry pipeline transportation projects for Wengfu phosphate concentrate and Dayukou phosphate concentrate. In recent years, pipeline transportation of hydrate slurry has also received much attention. Natural gas hydrates, commonly known as combustible ice, have large reserves, high energy density, and clean combustion, and are considered the most promising alternative energy source in the 21st century. The solid-state fluidized bed mining method is to transport the hydrate slurry formed by the fragmentation of natural gas hydrate reservoirs from the seabed to offshore platforms through pipelines.

Generally, materials need to be weighed and measured before pulping or transported through pipelines, and then filtered and dehydrated before weighing and measuring. Due to process limitations, some materials cannot be weighed and measured before and after pulping. Currently, online slurry flow measurement technology mainly obtains solid material quality by measuring volumetric flow rate and slurry concentration. The flow meters for measuring material volume mainly include differential pressure flow meters, rotor flow meters, volumetric flow meters, electromagnetic flow meters, ultrasonic flow meters, etc. In the field of slurry, electromagnetic flow meters and ultrasonic flow meters are the most widely used. The measurement of slurry concentration usually uses gamma ray concentration meters, radioactive isotope concentration meters, differential pressure concentration meters, differential immersion float concentration meters, vibration concentration meters, electromagnetic induction concentration meters, and ultrasonic concentration meters. In practical use, gamma ray concentration meters are considered to have the highest accuracy and the best stability.

The main difficulties faced by complex slurry flow measurement technology are as follows.

(1) Non mean flow and non full pipe flow. The pipeline system of the slurry conveying station is complex, and factors such as starting and stopping pumps and heterogeneous flow lead to poor stability of the pipeline system. Under normal circumstances, all sections of the slurry pipeline should be fully filled, but when the pipeline crosses steep slopes or is laid at an angle, the liquid will continue to flow after reaching the peak point, resulting in insufficient flow in the vertical direction of the pipeline.

(2) Erosion. Under the conditions of slurry transportation, the sensing part of the flowmeter located in the slurry environment is severely corroded and eroded, which not only affects the measurement accuracy, but also leads to a short service life and high maintenance costs.The main factors affecting erosion and wear of slurry pipelines include particle concentration, impact velocity and angle, particle shape, hardness and diameter, as well as pipe wall hardness and strength. We need to develop new erosion resistant materials and surface technologies to enhance the wear resistance and corrosion resistance of the sensing parts of flow meters.

(3) The measuring pipeline is blocked. When the slurry flow rate is lower than the critical flow rate, solid particles are prone to settling, forming a fixed or sliding bed, and even causing pipeline blockage.Due to the tendency of cage shaped hydrate particles to agglomerate into blocks in pipelines, especially when the solid fraction of hydrates is high, collisions, aggregation, and fragmentation may occur between hydrate particles during the flow of hydrate slurry in pipelines, which may cause pipeline blockage and have a significant impact on the flow, transportation, and metering of hydrate slurry in pipelines.

(4) Phase transition effects. During pipeline transportation, when the pressure inside the pipeline is lower than its three-phase equilibrium pressure, the hydrate begins to phase change and decompose into methane gas, forming a solid liquid gas three-phase flow. As the decomposition gas continues to increase, different flow patterns will evolve inside the pipeline.

Therefore, the accuracy of slurry flow measurement is closely related to the flow characteristics of the medium inside the pipeline. It is necessary to adopt flow assurance technology, reasonably control the particle size, conveying flow rate, and conveying concentration of materials, and develop advanced concentration measurement technology.

4.5 Traceability of Pipeline Flow Values

With the increasing demand for domestic energy, oil and gas pipelines are developing towards high pressure and large diameter. The variety, source, and composition of imported oil and gas are relatively complex. Whether the calibration capability and measurement technology of metrology institutions can meet the measurement requirements of foreign trade handover, and how to maintain the legitimate rights and interests of oil and gas docking metrology and avoid oil and gas handover disputes have become urgent problems to be solved. Measurement is a measurement that can be traced back to standard quantities to ensure the accuracy of measurement data. From the perspective of metrological data, the calibration or verification of measuring equipment or instruments is essentially an activity of transferring and assigning values to metrological standard data.

For pipeline liquid flow calibration, most domestic and foreign methods use the loop detection method, with representative devices mainly including Euroloop, Cameron in the United States, and Faure H-Ermanrma in France.Chengdu, Nanjing, and Wuhan have built three sets of primary standard devices for natural gas flow using the mass time method and high-pressure piston volume tube method with pressures ranging from 0.4 to 10.0 MPa and measurement uncertainties ranging from 0.05% to 0.07%. There are also 11 national natural gas professional metering stations, including the Guangzhou substation, Urumqi substation, and Tarim substation, with measurement uncertainties ranging from 0.16% to 0.29% for secondary and working standards.However, in the current international trend of using 70MPa and higher pressure hydrogen refueling machines, China's measurement traceability capability is not yet perfect. Therefore, it is urgent to solve the livelihood measurement and hydrogen refueling machine traceability problems in trade settlement after the commercial operation of 70MPa hydrogen refueling stations.In terms of calorific value determination, although China has issued a series of national standards for direct and indirect determination methods of natural gas calorific value, there is still a gap compared to advanced foreign levels in terms of the standardization of terminology and definitions involved in the implementation of these standards, the architecture of traceability chain structure, the confirmation of standard methods, the development of standard gas mixtures, and the evaluation of uncertainty in determination results.

The existing calibration is based on the traditional physical based calibration system. From the highest level physical benchmark to specific application scenarios, the measurement values need to be transmitted multiple times for accuracy, which poses the challenge of a large and complex measurement value transmission verification system.The quantum metrology system was officially implemented globally on International Metrology Day (May 20, 2019), using Planck's constant h, fundamental charge e, Avogadro's constant NA, and Boltzmann's constant k to redefine the SI basic units kg, A, mol, and K, respectively.

Developed countries and regions around the world have been competing to establish advanced measurement systems centered around quantum metrology. In December 2018, the United States signed the National Quantum Initiative Act, which will invest 0 million in researching quantum metrology technology and measurement standards.The National Institute of Standards and Technology (NIST) in the United States proposed the concept of embedded chip level metrology standards. The chip integrates several American metrological standards, which is expected to achieve the integration of metrological standards and measuring instruments (sensors), as well as the development of parameter measurement and calibration fusion.The European Union launched the Quantum Technology Flagship Program in 2016, making quantum metrology and sensing one of the four priority development areas. The UK has established a specialized Institute for Advanced Quantum Metrology to strengthen research on quantum metrology standards.

The new measurement system based on natural constants has changed the previous measurement mode that relied on physical benchmarks for step-by-step transmission. The traceability of measurement values does not change with time, space, and environmental conditions, making the traceability chain shorter, faster, and the measurement results more accurate, stable, and secure.China has released the "Metrology Development Plan (2021-2035)", which clearly states the implementation of the "Quantum Metrology" plan, focusing on researching quantum metrology technology based on quantum effects and physical constants, as well as miniaturization technology for metrology benchmarks and standard devices, breaking through quantum sensing and chip level metrology standard technology, and forming core device development capabilities.In the field of pipeline quantity traceability, it is also necessary to lay out and establish national level high-precision pipeline flow measurement facilities in advance, build an advanced measurement system based on quantum measurement, accelerate the development of embedded chip level measurement standards, and achieve online automatic calibration of flow sensors.

5. Development Trends and Suggestions

5.1 Development Trends

1) Implementing energy metering for pipeline fuel transportation

The implementation of energy metering is an inevitable trend in the development of fuel pipeline transportation medium handover metering, and it is also a necessary condition for maintaining fair and just natural gas trade transactions. In the field of natural gas energy measurement in China, the standard system for energy measurement has been basically established, but the construction of energy measurement systems for hydrogen blended natural gas and even liquid fuels urgently needs to be put on the agenda.Energy metering requires rapid and accurate measurement of medium flow rate, pressure, temperature, and composition, with component measurement being the most critical. The current component measurement and determination cycle is relatively long, making it difficult to adapt to the rapid detection requirements of high-speed pipeline transportation.With the deepening of the "carbon peak and carbon neutrality" (referred to as "dual carbon") goals, the proportion of natural gas mixed with hydrogen will continue to increase. At present, the highest proportion of hydrogen added to natural gas pipelines internationally has reached 30%, which undoubtedly brings significant changes to the composition and physical properties of natural gas, posing new challenges to natural gas flow measurement, component analysis, heat generation calculation, energy measurement, and other aspects.We should accelerate the research on online chromatography equipment and heat value assignment methods. The heat generation testing based on laser absorption, light refraction ultrasound principle has great potential for application and should be accelerated for development.

2)Artificial intelligence and big data empower pipeline flow measurement

Data is an important factor of production in the new era and a fundamental strategic resource for the country. Oil and gas pipeline engineering uses Supervisory Control and Data Acquisition (SCADA) system to monitor and collect real-time flow data from flow sensors at various nodes of the pipeline on a daily basis. The collected parameters include volumetric flow rate, as well as temperature, pressure, and even medium composition related to flow rate.The long-term operation of pipelines has accumulated massive amounts of data, but most of the data information lacks effective utilization, resembling "data garbage". The strategic significance of big data technology lies not in mastering vast amounts of data information, but in deeply mining and processing these meaningful data.

In January 2022, the State Council issued the "14th Five Year Plan" for the development of the digital economy, promoting the industrialization of digital technology and the digitization of industries. Data has become an important production factor, and how to scientifically and efficiently utilize these historical measurement data to achieve scientific allocation and scheduling of pipeline flow and predict future trends is an urgent problem that needs to be solved.In recent years, with the rapid advancement of artificial intelligence technology, structures such as deep belief networks, convolutional neural networks, recurrent neural networks, and physical information neural networks have been developed. The combination of pipeline big data and artificial intelligence has begun to be applied in load forecasting, safety warning, scheduling evaluation and optimization, performance monitoring, and other aspects of pipeline networks to ensure safe and efficient operation, highlighting the powerful data deduction capability.

3) Practice "carbon measurement" service for green and low-carbon pipeline transportation

Pipelines are not only carriers of energy such as oil and gas, but also major energy consumers, consuming a large amount of electrical and thermal energy during pipeline transportation.To achieve the "dual carbon" goal, it is necessary to conduct precise carbon emission measurement and evaluation, and then formulate a reasonable and feasible implementation path for the "dual carbon". Carbon emission measurement, also known as carbon inventory, refers to the calculation of greenhouse gas emissions directly or indirectly into the atmosphere from the production or various social activities of enterprises and governments.There are three main methods for measuring carbon emissions: emission coefficient method, material balance algorithm, and actual measurement method. Among them, the actual measurement method has the advantages of continuous detection and is a key development direction in the future. There is currently no unified calculation method and evaluation standard for real-time measurement of carbon emissions in the field of pipeline transportation.The next step is to improve the carbon emission measurement system, enhance the ability and level of carbon emission monitoring, and develop real-time monitoring methods for comprehensive carbon emission parameters such as flow rate and carbon concentration. Strengthen the application of carbon measurement in carbon footprint accounting and carbon tracking.

5.2 Development Suggestions

1) Intensify research and development efforts on multiphase flow meters for new business models and scenarios, establish standards for multiphase pipeline flow measurement, and put forward new requirements for multiphase pipeline flow measurement technology in new business models and scenarios. At present, the working range and accuracy of multiphase flow instruments are affected by various factors such as gas content, oil content, water content, viscosity, salinity, and pipeline flow pattern.It is urgent to develop and research a new generation of multiphase flow meters that can adapt to 0-100% gas content and 0-100% water content, covering stratified flow, wave flow, slug flow, and annular flow. At present, there is a lack of corresponding standards and specifications in the field of multiphase pipeline flow measurement. A pipeline multiphase flow committee should be established to provide guidance for the standardization and development of multiphase flow meters.

2) Accelerate the research and development of models driven by data and mechanisms, and promote the large-scale application of virtual metrology. Virtual measurement can save a lot of physical measurement equipment and significantly reduce measurement costs.However, its computational complexity is higher, requiring a large amount of on-site data with flow markers and accurate mining of parameters for extracting flow features.Suggest increasing support for the development of reliable multiphase flow models and robust and efficient modeling and solving algorithms, combining multiphase flow models with data-driven approaches, using multiphase flow models to clean and reduce data dimensions, and improving the prediction accuracy and generalization ability of virtual measurement systems from both data and mechanism dimensions.

3) Construct a pipeline flow quantum traceability system to achieve rapid calibration of flow meters. China generally adopts a traceability model based on physical objects, but the basic technology and facilities for traceability are still weak, and there are shortcomings in the traceability of natural gas calorific value.China already has quantum benchmarks in terms of length, time, and electricity, but there has not been a comprehensive breakthrough in miniaturization, distributability, and calibration free quantum metrology standards and instruments. It is suggested to accelerate the establishment of a national level single-phase and multi-phase pipeline flow traceability system, providing support for the rapid and accurate traceability of tens of thousands of pipeline flow measuring instruments in China.

4) Establish a unified and open pipeline data sharing center to promote the deep utilization of measurement data resources. The long-term accumulation of measurement data in pipelines has become a valuable resource for enterprises. The strategic position of measurement data should be enhanced, and the accumulation and application of data should be strengthened.However, there are issues with human pollution, inconsistent formats, and non-standard data; Data is reported layer by layer from bottom to top, lacking a unified and direct data upload and management application platform; In the Internet era, the defects of centralized data, such as tampering, forgery, fabrication, poor traceability and easy to be stolen by illegal organizations, have become increasingly prominent.It is necessary to formulate and promulgate application standards for pipeline flow data, utilize technologies such as big data, blockchain, and artificial intelligence, promote the digital industrialization and large-scale application of the metrology industry, and enhance process supervision capabilities and service levels.

6. Conclusion

Pipeline flow measurement is a fundamental project to ensure the safe and efficient operation of pipelines and achieve fair trade. After decades of development, China's pipeline flow measurement technology has made significant progress and established a relatively complete measurement system. However, it should also be noted that there is still a gap compared to advanced levels abroad, especially in the field of multiphase pipeline flow measurement. Underwater multiphase flow meters used for deepwater oil and gas development are mostly monopolized by foreign oil giants.The "Development Plan for Metrology (2021-2035)" points out the need to strengthen research on metrology foundations, cutting-edge technologies, new value transmission and traceability technologies, and other related technologies, and to build a national modern advanced measurement system that meets the needs of the times and the trend of international development.Currently, the new wave of technology represented by big data, artificial intelligence, and cloud computing has empowered thousands of industries and is bound to bring significant changes to measurement technology and application scenarios. In the field of pipeline flow measurement, it is urgent to establish a modern advanced flow measurement system and technology ecosystem that is intelligent, networked, and easy to trace, to achieve original breakthroughs in multiphase, multi field, complex and harsh flow conditions, and to provide independent and controllable technical and equipment support for accurate and efficient measurement of pipelines in China.