CO₂ Flow Measurement Under CCS Condition Using Ultrasonic Flowmeter

In order to address the serious global warming problem,China proposes the development vision of achieving carbon peak in 2030 and carbon neutrality in 2060.In this context,promoting the large-scale application of carbon capture and storage(CCS)technologies has become an important path to achieving this goal,which can significantly reduce CO2 emissions to effectively mitigate the greenhouse effect.CO2 transportation is a key step in connecting the carbon capture and storage in the CCS process,while the pipeline transportation can considerate both safety and cost.Traditional flowmeters are not suitable for the accurate measurement of liquid CO2 flow in pipes with a large diameter,so it is of urgent significance to study accurate measurement methods suitable for liquid CO2 flow in pipelines under CCS conditions.Due to the fact that ultrasonic flowmeters do not generate significant pressure losses,and their costs are essentially independent of the pipe diameter,ultrasonic flowmeters have great potential for the accurate measurement of CO2 flow under CCS conditions.In this paper,a time difference ultrasonic flowmeter for measuring the flow of liquid CO2 under CCS conditions has been designed.Simulation studies have been conducted on the flow of liquid CO2 and the propagation of acoustic waves in the flow field,while experimental verifications have been performed using a CO2 flow measurement rig.The main research work is given as follows:(1)For the ultrasonic flow measurement of liquid CO2 under CCS conditions,different time difference ultrasonic flowmeter models are constructed in the finite element simulation software.which are used for the simulations of CO2 flow measurement under CCS conditions.The simulated data are used to calculate the time of flight(TOF)with three different methods.After comparing the simulation results and considering factors such as installation cost,signal-to-noise ratio of received signals,and real-time measurement performance,a single channel Z-shaped configuration with a channel angle of 45° is selected as the configuration of the time difference ultrasonic flowmeter,and the threshold method is selected as the method for the TOF calculation using the collected signals.(2)Using the existing CO2 flow measurement rig,a complete experimental system,including ultrasonic flowmeters,ultrasonic signal generation and acquisition units,has been built.Based on the control system of the experimental rig,important parameters such as temperature and pressure,do not fluctuate extensively during the experimental process.(3)To find a more suitable frequency for ultrasonic propagation in liquid CO2,ultrasonic measurement experiments are conducted on empty and full tubes using 1 MHz and 500 kHz ultrasonic probes before the flow measurement experiment,confirming that 500 kHz ultrasonic probe is more suitable for the flow measurement of liquid CO2.Within the specified fluctuation range of experimental temperature and pressure,a series of flow measurement experiments are conducted between 200 kg/h and 2000 kg/h.After obtaining experimental flow measurement data,threshold method and dynamic threshold method combined with the step method are used to find out effective feature points in the excitation and received signals respectively.The TOF between each group of ultrasonic excitation and received signals is calculated.Comparing the TOF calculated from experimental data with the theoretical TOF value corresponding to the actual flow rate,it is found that the relative error of the experimental results is lower than 6%and the average relative error at high flow rate is around 5%,which proves the feasibility of using a time difference ultrasonic flowmeter for measuring liquid CO2 flow rate under CCS conditions.