Pumps and Compressors In

CCS Transport Pipelines

Chima .N. Okezue

Meihong Wang

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

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

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: THE BACKGROUND STORY

CCS BACKGROUND—CO2 PIPELINE TRANSPORT

CO2 transport by pipeline is the preferred to ship transport because it is more cost-effective 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 = 30.97 degC (304.12 K)

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

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

• 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

Typical impurities

H2, H2S, N2, CH4,

H2O, CO, O2, Ar,

SOX, NOX

PROBLEM WITH DENSE PHASE/SUPERCRITICAL CO2 TRANSPORT

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

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

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)

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)

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

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 thermo-

fluid 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

STUDY OBJECTIVES

1 1 1V A

2 2 2V A

2 2 2 1 1 1

CV

dmV A V A

dt

2

2 (PA)2

IN

CV

dm fV mV Adt

VAW

2

2IN

CV

d mE Vmh m m q W

dt

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.

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

CONCLUDED/ONGOING WORK

THE RESULTS Results for Pure CO2 Stream

Results for 90% CO2 + 10% N2 Stream

Table 1: Statistical Evaluation of EoS Correlations (Pure CO2 Stream)

EoS CORRELATION TEMPERATURE APE AAPE

STANDARD

DEVIATION

[deg C] [%] [%] [%]

Peng-Robinson

(PR)

50 1.64 3.74 4.27

100 1.12 3.48 4.24

Soave-Redlich-

Kwong (SRK)

50 -7.55 7.55 3.00

100 -6.58 6.58 3.27

Benedict-Webb-

Rubin-Starling

(BWRS)

50 -1.79 2.51 3.43

100 -0.31 1.01 1.37

Lee-Kessler-

Plocker (LKP)

50 -0.71 1.46 1.63

100 -1.35 1.35 0.70

EoS CORRELATION TEMPERATURE APE AAPE

STANDARD

DEVIATION

[deg C] [%] [%] [%]

Peng-Robinson (PR) 50 -2.36 5.02 6.51

100 -2.54 4.10 4.50

Soave-Redlich-Kwong (SRK)

50 -10.59 10.59 4.40

100 -9.43 9.43 3.43

Benedict-Webb-Rubin-Starling

(BWRS)

50 -6.66 6.66 3.54

100 -5.33 5.33 1.91

Lee-Kessler-Plocker

(LKP)

50 -6.59 6.59 3.27

100 -5.59 5.59 0.91

THE RESULTS Results for 80% CO2 + 20% N2 Stream

Results for 90% CO2 + 10% CH4 Stream

EoS CORRELATION TEMPERATURE APE AAPE

STANDARD

DEVIATION

[deg C] [%] [%] [%]

Peng-Robinson (PR) 50 -6.24 7.41 7.28

100 -5.69 6.37 4.73

Soave-Redlich-Kwong (SRK)

50 -13.25 13.25 5.62

100 -11.78 11.78 3.55

Benedict-Webb-Rubin-Starling (BWRS)

50 -11.06 11.06 4.85

100 -9.04 9.04 2.51

Lee-Kessler-Plocker

(LKP)

50 -9.76 9.76 2.94

100 -8.59 8.59 1.64

EoS

CORRELATION

TEMPERATURE APE AAPE STANDARD

DEVIATION

[deg C] [%] [%] [%]

Peng-Robinson

(PR) 100 -10.60 10.60 5.63

Soave-Redlich-

Kwong (SRK) 100 -17.47 17.47 4.03

Benedict-Webb-

Rubin-Starling (BWRS)

100 -14.97 14.97 2.81

Lee-Kessler-Plocker (LKP)

100 -14.94 14.97 2.22

THE RESULTS Results for 80% CO2 + 20% CH4 Stream

Results for 80% CO2 + 10% N2 + 10% CH4 Stream

EoS

CORRELATION

TEMPERATURE APE AAPE STANDARD

DEVIATION

[deg C] [%] [%] [%]

Peng-Robinson (PR)

50 -24.04 24.04 8.22

100 -17.50 17.50 4.85

Soave-Redlich-Kwong (SRK)

50 -29.27 29.27 6.23

100 -22.99 22.99 3.52

Benedict-Webb-Rubin-Starling

(BWRS)

50 -28.21 28.21 6.41

100 -21.72 21.72 2.70

Lee-Kessler-

Plocker (LKP)

50 -26.65 26.65 5.66

100 -21.52 21.52 2.15

EoS

CORRELATION

TEMPERATURE APE AAPE STANDARD

DEVIATION

[deg C] [%] [%] [%]

Peng-Robinson (PR)

50 -12.78 12.78 8.33

Soave-Redlich-Kwong (SRK)

50 -19.91 19.91 6.59

Benedict-Webb-

Rubin-Starling (BWRS)

50 -18.83 18.83 6.08

Lee-Kessler-Plocker (LKP)

50 -17.43 17.43 4.25

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

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.

Continue the development of steady-state and

transient models for supercritical CO2 pump

FUTURE WORK

The End