Depressurization of CO2-N2 and CO2-He in a pipe: Experiments and modelling of pressure and temperature dynamics

Svend Tollak Munkejord,Han Deng,Anders Austegard,Morten Hammer,Ailo Aasen,Hans L Skarsvåg

doi:10.1016/j.ijggc.2021.103361

Abstract

To design and operate safe and efficient CO2-transportation systems for CO2 capture and storage (CCS), engineers need simulation tools properly accounting for the fluid and thermodynamics of CO2. As the transportation systems evolve into networks, it becomes important that these tools also account for impurities in the CO2, which may significantly affect the thermophysical properties, directly impacting system design and safety. Tube-depressurization experiments provide crucial data to develop and validate models describing transient multiphase multicomponent flow in pipes. In this work, we perform experiments in a new facility with dense and fast instrumentation for both pressure and temperature. One experiment is for CO2 with 1.8 mol % N2, and one has 1.92 mol % He, both starting from 12 MPa and 25 ∘C. In order to quantify the effect of impurities, the experiments are compared to results for pure CO2 and analysed on the background of simulations. We employ a homogeneous equilibrium model (HEM) augmented in this work to account for the appearance of solid CO2 in CO2 mixtures. We observe that the moderate amounts of impurities significantly influence both pressure and temperature dynamics. In particular, the ‘pressure plateau’, a key quantity for the assessment of running-ductile fracture, increases as much as 4 MPa for CO2-He compared to pure CO2. A further insight is that models must account for solid CO2 in order to capture the correct temperature development as the pressure decreases towards atmospheric conditions.

Highlights

In order to mitigate climate change, CO2 emissions must be reduced, and to attain the required scale, a portfolio of technologies are needed
In order to study the effect of impurities on the decompression behaviour of a CO2 stream, we retain the conditions of Test 8 for pure CO2, reported in Munkejord et al (2020a)
The new ECCSEL Depressurization Facility has been commissioned for non-flammable impurities

Summary

Introduction

In order to mitigate climate change, CO2 emissions must be reduced, and to attain the required scale, a portfolio of technologies are needed. Several gigatonnes of CO2 will need to be transported from the emitters to storage sites each year (IEA, 2017). Much of this transportation will be through pipeline networks. To design and operate safe and efficient transportation systems, engineers need simulation tools properly ac counting for the fluid and thermodynamics of CO2 (Aursand et al, 2013). One needs to consider that the critical point (7.38 MPa, 31.0 ∘C), above which there is no difference between vapour and liquid, and the triple point (517 kPa, − 56.6 ∘C), where solid CO2 forms, are within a range that could be attained during normal operation

Methods

Results

Conclusion