Pumps and Compressors In CCS Transport Pipelines. Chima.N. Okezue Meihong Wang

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1 Pumps and Compressors In CCS Transport Pipelines Chima.N. Okezue Meihong Wang

2 PRESENTATION OUTLINE CCS: The Background Story Pipeline Transport of Dense/Supercritical CO2 Motivation Why study Pumps/Compressors? Study Objectives Concluded/Ongoing Work Future Work

CCS: BACKGROUND STORY Emission of greenhouse gases are

greenhouse gas emissions Dominant source of CO2 emission

been emitted globally (IEA Report, 2013) Carbon Capture &

3 CCS: BACKGROUND STORY Emission of greenhouse gases are responsible for climate change CO2 constitutes 67% of greenhouse gas emissions Dominant source of CO2 emission come from burning fossil fuels As of 2011, 30 Gt of CO2 had been emitted globally (IEA Report, 2013) Carbon Capture & Storage (CCS) technology proposed to reduce CO2 emissions into the atmosphere

4 CCS: THE BACKGROUND STORY CCS process chain comprises 3 aspects : CAPTURE ASPECT CO2 isolated from flue gases of power station TRANSPORT ASPECT CO2 is compressed and conveyed to place of storage STORAGE ASPECT CO2 is pumped into pre-selected underwater or underground sites

CCS BACKGROUND CO2 PIPELINE TRANSPORT CO2 transport by pipeline is the preferred to

transported either in gaseous, liquid or supercritical phases More economical to

dense/supercritical state, a larger amount of CO2 per unit time can be transported than

5 CCS BACKGROUND CO2 PIPELINE TRANSPORT CO2 transport by pipeline is the preferred to ship transport because it is more costeffective for large scale CCS CO2 can be transported either in gaseous, liquid or supercritical phases More economical to transport CO2 in supercritical or dense phase than liquid or gas phases In dense/supercritical state, a larger amount of CO2 per unit time can be transported than possible if CO2 is in gaseous or liquid state Pure CO2 at critical point: PCRIT =73.76 bar TCRIT = degc ( K)

6 PROBLEM WITH DENSE PHASE/SUPERCRITICAL CO2 TRANSPORT Effect of impurity on CO2 phase diagram moving critical points Consequences of shifting critical points on pipeline network increased energy requirement for compressors (OPEX is increased) Increases gas-liquid 2phase envelope & risk of 2phase flow in pipe Changes operational parameter of pipeline network

7 PROBLEM WITH DENSE PHASE/SUPERCRITICAL CO2 TRANSPORT Greatest challenge is effect impurities in CO2 stream imposition of variables on design & operation of pipeline network Differing compositions of impure CO2 mixtures Effect of impurities on CO2 thermodynamic properties Effect of impurities on CO2 transport pipeline system Typical impurities H2, H2S, N2, CH4, H2O, CO, O2, Ar, SOX, NOX Phase Behaviour (VLE) Critical Press /Temp Compressibility Viscosity Density Energy input for compressors/pumps Fracture propagation Corrosion rate Recompression distance Risk of 2Phase Flow Hydrate formation risk

8 PROBLEM WITH DENSE PHASE/SUPERCRITICAL CO2 TRANSPORT The performance of all components in the CCS pipeline transportation system is affected by the presence of impurities Effect of impurities on CO2 thermodynamic properties Higher Energy input for compressors and pumps Recompression distance Fracture propagation Corrosion rate Risk of 2Phase Flow Hydrate formation risk Increased CAPEX and OPEX Increased Health & Safety Risks Higher maintenance costs

9 COMPRESSORS & PUMPS IN CO2 PIPELINE TRANSPORT These machines generate and maintain the pipe pressure required to keep CO2 flowing at supercritical conditions Humberside CO2 Pipeline Project (Luo et al, 2014)

10 MOTIVATION WHY STUDY PUMPS & COMPRESSORS? Compressors/ Pumps consume most of the energy used in operating CO2 pipeline network [Power supply is a major part of OPEX]. Little or no research on performance of compressor and pumps handling CO2 at near-critical or supercritical conditions Impurities in CO2 from power plants can increase energy requirement of the machines (i.e. higher OPEX) and cause operational problems (e.g corrosion, cavitation, etc)

process equations where the machine efficiency is assumed.

11 MOTIVATION WHY STUDY PUMPS & COMPRESSORS? In literature, CO2 pipeline models calculate compressor energy input with isentropic process equations where the machine efficiency is assumed. Such models cannot be used to carry out a detailed assessment of compressors and pumps because the internal thermo-fluid flow processes within these machines are neglected

STUDY OBJECTIVES Development of steady-state & transient models to evaluate the performance of compressors/pumps handling CO2 at near critical and supercritical conditions The model will account for

12 STUDY OBJECTIVES Development of steady-state & transient models to evaluate the performance of compressors/pumps handling CO2 at near critical and supercritical conditions The model will account for thermofluid dynamic behaviour of pure or impure supercritical CO2 flowing in the internal channels within the compressors and pumps Comparative study of various EoS Correlations in order to select one most appropriate for calculating the thermo-physical properties of pure CO2 and CO2 mixture 1VA 1 1 dm dt CV 2VA 2 2 V A V A V 2 dm f V2 mv (PA) A dt CV 2 d me dt CV 2 V 2 AW mh m m q W IN IN

13 CONCLUDED/ONGOING WORK Equations of State (EoS) play a key role in the accurate modelling and simulation of CO2 flow in compressors, pumps and transport pipelines. A comparative study of four EoS correlations was carried out to determine which one produced predictions that were closest to experimental data for a given range of pressures and temperatures. This study was carried out for pure CO2 and CO2/impurity mixtures of various concentrations.

14 CONCLUDED/ONGOING WORK EoS Correlations that were compared : 1. Peng-Robinson (PR) 2. Lee-Kessler-Plocker (LKP) 3. Benedict-Weber- Rubin-Starling (BWRS) 4. Soave-Redlich-Kwong (SRK) Each correlation was used to predict density in a pipeline for the following composition of working fluid: 1. Pure CO2 stream 2. CO2+N2 stream. 3. CO2+CH4 stream 4. Ternary CO2+N2+CH4 stream

15 THE RESULTS Results for Pure CO2 Stream Table 1: Statistical Evaluation of EoS Correlations (Pure CO 2 Stream) EoS CORRELATION Peng-Robinson (PR) Soave-Redlich- Kwong (SRK) Benedict-Webb- Rubin-Starling (BWRS) Lee-Kessler- Plocker (LKP) TEMPERATURE APE AAPE STANDARD DEVIATION [deg C] [%] [%] [%] Results for 90% CO2 + 10% N2 Stream EoS CORRELATION Peng-Robinson (PR) Soave-Redlich-Kwong (SRK) Benedict-Webb- Rubin-Starling (BWRS) Lee-Kessler-Plocker (LKP) TEMPERATURE APE AAPE STANDARD DEVIATION [deg C] [%] [%] [%]

16 THE RESULTS Results for 80% CO2 + 20% N2 Stream EoS CORRELATION Peng-Robinson (PR) Soave-Redlich-Kwong (SRK) Benedict-Webb-Rubin- Starling (BWRS) Lee-Kessler-Plocker (LKP) TEMPERATURE APE AAPE STANDARD DEVIATION [deg C] [%] [%] [%] Results for 90% CO2 + 10% CH4 Stream EoS CORRELATION Peng-Robinson (PR) Soave-Redlich- Kwong (SRK) Benedict-Webb- Rubin-Starling (BWRS) Lee-Kessler- Plocker (LKP) TEMPERATURE APE AAPE STANDARD DEVIATION [deg C] [%] [%] [%]

17 THE RESULTS Results for 80% CO2 + 20% CH4 Stream EoS CORRELATION Peng-Robinson (PR) Soave-Redlich- Kwong (SRK) Benedict-Webb- Rubin-Starling (BWRS) Lee-Kessler- Plocker (LKP) TEMPERATURE APE AAPE STANDARD DEVIATION [deg C] [%] [%] [%] Results for 80% CO2 + 10% N2 + 10% CH4 Stream EoS CORRELATION Peng-Robinson (PR) Soave-Redlich- Kwong (SRK) Benedict-Webb- Rubin-Starling (BWRS) Lee-Kessler- Plocker (LKP) TEMPERATURE APE AAPE STANDARD DEVIATION [deg C] [%] [%] [%]

18 CONCLUDED/ONGOING WORK Analysis of the results indicated that under supercritical conditions: For pure CO2, LKP and BWRS gave the most accurate predictions. PR also generated predictions of reasonable accuracy. For different binary & ternary CO2-impurity combinations, PR EoS consistently generated the most accurate predictions followed by LKP EoS and BWR EoS. SRK EoS consistently generated the least accurate predictions for all CO2 streams

19 CONCLUDED/ONGOING WORK From this study, the author of this report concludes that for various compositions of CO2 stream in a pipeline under supercritical conditions, Peng-Robinson EoS generally performed the best correlation to use.

20 FUTURE WORK Continue the development of steady-state and transient models for supercritical CO2 pump

21 The End

Modelling of liquid-vapor-solid equilibria in the NH 3 -CO 2 -H 2 O system. Maria G. Lioliou, Statoil ASA

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