Online Measurement Of CO₂ Flow Rate

As one of major options of CO2 emission reduction,Carbon Capture and Storage(CCS)technology which can effectively reduce the CO2 content in the atmosphere,is the focus of attention over the international society.The CCS chain involves three defined stages:capture,transportation and storage.Their technical development level is not balanced,and there are some challenges,which are the hot issues for the research.This paper mainly investigates the flow measurement in CO2 pipeline transportation.CO2 flow measurement plays an important role in flow measurement and monitoring of pipeline operation during pipeline transportation.In addition,it is also an important basis for carbon transactions.However,due to the influence of the physical characteristics of CO2,pipeline transportation conditions and the limitation of the existing flow meters,the measurement of CO2 flow in pipeline transportation is facing many challenges.In order to realize the accurate measurement of C02 flow in pipeline transportation under CCS conditions,a gas-liquid two-phase CO2 flow experimental rig was designed and built jointly by the Center for Multiphase Flow Measurement and Combustion Process Monitoring Technology of North China Electric Power University and the flow lab of Tianjin University.This rig simulates the operation conditions of CO2 pipeline transportation,which has the functions of flow measurement and flow meter calibration.It can accomplish the experimental analysis in the single gas phase CO2,the single liquid phase CO2 and the gas-liquid two-phase CO2.On the basis of experimental setup,this paper mainly conducted the following work for the measurement of gas-liquid two-phase CO2 flow in a horizontal pipeline:(1)The weighing problem of CO2 under the condition of high pressure and airtight is studied.Through the improvement of the weighing device and the establishment of detailed weighing operation steps,the problem of phase change,abrupt change of pressure and flow rate and stress effect caused by hard connection were solved.(2)A multi-modal sensing system incorporating clustering and least square support vector machine algorithms is presented to measure the mass flow rate.The outputs from the sensing system,including apparent mass flow rate,observed density,temperature,differential-pressure and absolute pressure are fed into a data processing system.The two-phase flow regime is firstly identified through the application of an unsupervised clustering method,and four types of flow regimes are obtained,which are stratified,wavy,bubbly and mist flow.For each flow regime,SVM model is developed to measure the CO2 mass flow rate.The results obtained indicate that the proposed method is capable of measuring the CO2 mass flow rate with a maximum error of 1.5%under two-phase flow conditions.(3)In this paper,some transient behaviors of C02 pipeline transportation are also studied,including load change,start-up and shutdown.The results show that there is a significant error in the measurement of mass flow during the load change operation,especially when there is a step increase or decrease in the mass flow rate of gaseous C02.The flow regimes of liquid slug flow,stratified flow and gas bubbly flow are generated after the start of the liquid phase pump.Meanwhile,two-step changes in the mass flow rate and corresponding variations in the density of C02 flow were observed.After the stop of the liquid phase pump,the depressurization and evaporation of liquid C02 in the pipeline were observed.In addition,it also shows that the Coriolis mass flowmeter can measure the C02 flow in the transient process.