Based on the specific situation of city gas in Beijing, the technical scheme of city gas energy measurement for different users was proposed in this paper. Combined with the experimental data, the sources of the uncertainty of city gas energy measurement were analyzed from the aspects of volume flow, calorific value per unit volume, integration method and other relevant factors under the measurement reference conditions.Meanwhile, the uncertainty of city gas energy measurement was evaluated. This study puts forward the technical scheme and uncertainty evaluation of natural gas energy measurement for different users, which has certain reference significance for promoting the implementation of city gas energy measurement in China.

Flow parameters measurement is beneficial for understanding oil-water two-phase flow. Due to the changeable flow structures of oil-water two-phase flow, the prediction of superficial velocity of oil-water two-phase flow in large diameter pipes is still a challenging problem. In this paper, a novel soft measurement technique based on Capsule Network (CapsNet) is developed to predict the superficial velocity. Firstly, a vertical upward oil-water two-phase flow experiment in a 125 mm ID pipe was conducted, and response signals at different flow conditions were obtained by a vertical multi-electrode array (VMEA) conductance sensor. Then, in order to increase the number of samples without losing information, a new data pre-processing (1D-to-2D) technique is used. Finally, a novel multi-task learning network based on CapsNet is designed to predict the flow pattern and superficial velocity of each phase. To verify the advancedness of the method, we compared the proposed network with its variations and other competitive networks. The results suggest the proposed network achieves the best performance for prediction of flow pattern and superficial velocity. The proposed method presents great potential for handling high-dimensional, time-varying and nonlinear problems in multiphase flow.

Although turbine flow meters (TFM) have made good progress in measuring flow with accurate response characteristics in single-phase flow, TFM combined with other sensors to measure two-phase flow is still a difficult and hot issue. Due to the leakage after the collection, the flow state change and slippage between the gas and liquid phases in the pipeline after the diversion are complicated, and all these factors have a significant impact on the TFM modelling. Therefore, the meter factor models of the TFM with diverter in two-phase flows have not been thoroughly solved. Thus, this study mainly investigates the performance of TFM in gas-liquid two-phase flows combined with the rotating electric field conductance sensor (REFCS). Among them, the gas holdup is implemented through the REFCS. We examine three two-phase flows TFM models including mass model, momentum model and torque model, and analyse slip ratio, an essential parameter in the meter factor models. Subsequently, based on model tests, the evaluation finds that the Chisholm slip ratio model combined with the torque model achieved the best accuracy. Consequently, the average absolute deviation (AAD) and average absolute percentage deviation (AAPD) of total flow rate are 1.23 m³/d and 7.69 %.

Ultrasonic flow meter has become the mainstream measuring instrument in the natural gas trade because of its advantages of large measuring range, small pressure loss and high measurement accuracy. In the measurement of natural gas with high pressure and large flow, the advantage of ultrasonic flow meter is particularly obvious. Ultrasonic flow meter based on transit-time method can measure the speed of sound and the flow velocity of fluid at the same time. With the continuous improvement of on-site monitoring and diagnosis technology of ultrasonic flow meter, the on-line audit of flow meter based on speed of sound checking has attracted extensive attention. According to AGA No.10 report, the on-line audit based on speed of sound checking was carried out with a 4-path ultrasonic flow meter used in a natural gas station was studied. The studies showed that within 2 years, the signal quality indicators of the ultrasonic flowmeter were basically the same, the variation of flow velocity deviation was within ± 0.5 %, and the variation of the speed of sound deviation of acoustic path was within ± 0.03 %. With the comparison of the real flow calibration, it could be concluded that the metering performance of the flowmeter was stable and reliable, but the installation conditions should be checked to see if they meet the requirements. The results showed that the method of on-line audit can effectively monitor the performance of ultrasonic flowmeter and could be a powerful supplement to the real flow calibration.

The main source of errors while applying modern ultrasonic flow measurement principle is the deviation of the actual velocity profile of the measured flow from the calculated one. If the velocity profile is known, the corresponding correction can be evaluated and considered during calibration. However, in practice, the distribution of velocities in the cross section of the pipeline differs from the theoretical one, which leads to errors of hydrodynamic origin.To determine the flow rate of the measuring medium, it is necessary to transform the flow velocity averaged along the acoustic path to the velocity averaged for the cross section of the flow meter. To do this, use the hydrodynamic correction factor, which is a function of the Reynolds number. The inaccuracy of this factor is the largest component of the total error of ultrasonic flowmeters. This is due to the fact that velocity distribution (and hence the hydrodynamic factor) use dependences obtained on the assumption that measuring flow is axisymmetric and the trajectory of the ultrasonic beam lies in the plane passing through the pipeline axis. Nevertheless, most industrial flow media have a distorted profile due to installation effects, which are an integral part of any hydraulic system. As a result, the determined average flow velocity does not correspond to the real one. Therefore, the problem of studying the influence of flow non-symmetry on the value of the hydrodynamic correction factor is relevant. The effect of distortion of the velocity profile on the measurement results of ultrasonic flowmeters was evaluated using theoretical dependences describing non-symmetric velocity profiles. For this purpose, functions based on the power law of velocity distribution in smooth pipes with the imposition of some influence function, which depends on the radial and angular distances from the observation point to the pipeline axis, were used. However, some dependencies can only be applied to approximate real flow profiles.For velocity profiles that do not have axial symmetry, the only correct way to accurately estimate the flow rate is to reconstruct 2D velocity field using algebraic techniques. The implementation of one of these methods was performed based on the inverse Abel’s transform.For velocity profiles that do not have rotational symmetry around the axis of the pipeline, the value of the measured velocity will depend on the angle of orientation of the measuring plane relative to the diametrical plane of the flow meter. The calculation of the actual average flow velocity in the cross section of the meter was obtained from a specific mathematical dependencies describing velocity distribution by integration technique.This research allows us to conclude that it is possible to calculate the performance of ultrasonic flowmeters under conditions of distorted non-symmetric flows at Re > 104 with sufficient accuracy using computational hydrodynamics, integration based on Abel’s transform, methods of theoretical research and mathematical processing.