Following the approval of my application for the UKCCSRC International Research Collaboration Fund, I visited North China Electric Power University (NCEPU) over the period from 1 September 2016 to 30 April 2017. The following is a report on the activities that were undertaken during my visit.
The main activity of my visit was to undertake an experimental programme on the CO2 two-phase flow test rig at NCEPU. The first part of the experimental programme was to observe the transient behaviors of CO2 under variable process conditions. A range of sensors and flow instruments were installed on the horizontal test section of the rig. These include a Coriolis mass flowmeter manufactured by KROHNE Ltd, a high-speed camera and a differential-pressure transducer. Due to the scale of the test work and manpower required for rapid changes in the flow conditions and associated data logging, several researchers from NCEPU supported my work throughout the experimental programme. Figure 1 shows the experimental set-up. The characteristics of CO2 flow in the test section were observed under variable load, startup and shutdown conditions. When the load changed, a step change in the mass flow rate of liquid-phase or gaseous CO2 was observed. A piston pump in the liquid-phase loop was used to create the startup and shutdown conditions. As expected, transient CO2 two-phase flow regimes were observed. Images of the flow regimes and corresponding mass flow rate, density, pressure and temperature data of CO2 under a range of test conditions were recorded for further analysis.
Effect of Impurity Gases
The presence of impurity gasses in the CO2 stream could affect the flow characteristics and hence the performance of the flow metering system. As preliminary experimental observations, Nitrogen was diluted as a contaminant into the pure CO2 gas flow for various mass fractions to create an adulterated mixture of the CO2 gas. The results indicate that no significant changes in flow characteristics were observed and the Coriolis flowmeters still performed well in the presence of the impurity gas under single-phase and two-phase flow conditions. Unfortunately, we were unable to conduct the planned tests with other impurity gases as significant changes were to be made to the test rig in order to control the quantity and flow rate of impurity gases. This area of work will be undertaken in the near future.
The phase behaviors of CO2 under CCS conditions are different from those of other chemicals in transportation pipelines. Difficult flow conditions impose significant challenges in the metering and characterisation of CO2 flows. We have combined Coriolis mass flowmeters, high-speed imaging equipment and an ECT system to measure and observe the CO2 flow under steady and transient conditions. In addition to the experimental programme, several discussion meetings were held between the researchers from the University of Kent, NCEPU, Beihang and Tianjin Universities on topics concerning the improvement of the CO2 two-phase flow rig, measurement of two-phase CO2 flow and identification of CO2 flow regimes. At the time of writing, the joint research team is still processing the data from the experimental programme. It is planned that such data will be published in the near future.