The Role of Process Integration in Sub-ambient Processes · 2013-03-21 · NTNU 20.03.13 T....

NTNU

20.03.13 T. Gundersen Slide no. 1

The Role of Process Integration in Sub-ambient Processes

by

Truls Gundersen, Department of Energy and Process Engineering Norwegian University of Science and Technology (NTNU)

Trondheim, Norway

With significant Contributions from Audun Aspelund, 2005-2010

Chao Fu, 2008-2012 Danahe Marmolejo Correa, 2009-2013

Bjoern Austboe, 2011-2014

Chalmers University of Technology

NTNU


Content of the Presentation n  Special Challenges in Sub-ambient Process Design n  The Failure of ΔTmin as Economic Trade-off Parameter n  Extended Heat Recovery Problem Definition n  The ExPAnD Methodology

♦  Extended Pinch Analysis and Design Procedure ♦  From Heuristic Rules to Superstructures and MINLP

n  What is Exergy and why Use it below Ambient? n  The History of using Exergy in Pinch Analysis n  New Developments in Exergy Analysis

♦  In line with the Approach of Pinch Analysis ♦  Carnot Factor replaced by the “Exergetic Temperature” ♦  New Linear Exergy Curves suitable for Targeting

n  Sub-ambient Process Examples (ASU and LNG) n  Concluding Remarks

NTNU


Special Challenges in Sub-ambient Processes n  ΔTmin does not work as Economic Trade-off Parameter n  Refrigeration è Expensive Cold Utilities n  Power is used to produce Refrigeration è Stronger

Relationship between Thermal and Mechanical Energy n  Composite Curves cannot be drawn

♦  Process Streams often act as Utilities (vague distinction) ♦  Pressurized Streams can be expanded to produce Cooling ♦  Pressure and Phase are important Design Variables and must be

considered together with Temperature ♦  Result: The Path from Supply to Target State for Streams is

unknown è An important Part of the Optimization Problem

n  Temperature Differences are smaller to reduce the need for Refrigeration è More accurate Process Models ♦  Need Rigorous Simulators with Advanced Thermodynamics

NTNU


Using ΔTmin in Sub-ambient Processes n  Above Ambient: ΔTmin is an Economic Parameter

♦  Trade-off between Operating Cost and Investment Cost n  Several Challenges above Ambient

♦  Single global ΔTmin is unrealistic due to variations in HTFs ♦  Differences in Fluids, Phases, Exchanger Configurations,

Materials of Construction, Pressure Ratings, etc. ♦  HRAT and EMAT or ΔTi (individual Stream Contributions)

n  Below Ambient: None of the ΔT parameters will work ♦  The Exergy of Cooling (Refrigeration) increases rapidly with

decreasing Temperatures (see later Slides) ♦  Using ΔT as a Specification (in Optimization) will not give

the minimum Power or the minimum Total Annual Cost ♦  Using UA as a Specification works better, either with Pareto

Plots while minimizing Power, or when minimizing TAC n  A simple Case Study illustrates this special Feature

NTNU


Heat%exchanger

Compressor

Condenser

Throttle%valve

NATURAL%GAS

MIXED%REFRIGERANT

LNG

ΔTHX%≥%%ΔTHX,min

ΔTdew%≥%%ΔTdew,minpH

pL

ṁ1,'ṁ2,'ṁ3,'...,'ṁn

Throttle%valve

min(HẆ)

Case Study: Simple PRICO Process for LNG

Objective: Minimize Shaftwork subject to 2 Constraints by varying 2 Pressures and 5-6 Flows of Refrigerant Components

NTNU


Results from the Optimization ΔTmin as Specification UA as Specification

ΔTmin UA W UA ΔTmin W Savings

(K) (MW/K) (kJ/kg) (MW/K) (K) (kJ/kg) (%)

1 3.101 896.5 3.101 0.57 882.8 1.5

2 1.658 979.2 1.658 0.87 947.7 3.2

3 1.110 1062.3 1.110 1.13 1006.0 5.3

4 0.812 1147.1 0.812 1.33 1060.9 7.5

5 0.632 1235.3 0.632 1.52 1111.1 10.1

UA is a better Specification than ΔTmin and it is all related to Exergy

NTNU


A new Process Synthesis Methodology for Sub-ambient Processes

n  The Classical Heat Recovery Problem has been Extended w  ”Given a Set of Process Streams with a Supply and Target

State (Temperature, Pressure and the resulting Phase), as well as Utilities for Power, Heating and Cooling Design a System of Heat Exchangers, Expanders, Valves, Pumps and Compressors in such a way that Irreversibilities (or Cost functions) are minimized”

n  Notice that the Path from Supply to Target State is not fixed, it is an important Part of the Optimization Problem

n  10 Heuristic Rules developed in early version of ExPAnD

ExPAnD = Extended Pinch Analysis and Design

A. Aspelund, D.O. Berstad, T. Gundersen, ”An Extended Pinch Analysis and Design procedure utilizing pressure based exergy for sub-ambient cooling”, Applied Thermal Engng., vol. 27, pp. 2633-2649, 2007

NTNU


Application: A Liquefied Energy Chain (LEC)

n  Key Features of the “LEC” Concept ♦  Utilization of Stranded Natural Gas for Power Production ♦  High Exergy Efficiency of 46.4% (vs. 42.0% for traditional) ♦  Innovative and Cost Effective solution to the CCS Problem ♦  CO2 replaces Natural Gas injection for EOR ♦  Combined Transport Chain for Energy (LNG) and CO2

Aspelund A. and Gundersen T. ”A Liquefied Energy Chain for Transport and Utilization of Natural Gas for Power Production with CO2 Capture and Storage − Part 1”, Journal of Applied Energy, vol. 86, pp. 781-792, 2009.

NTNU


Developing the Liquefied Energy Chain − Manual and Automated Design Procedures

n  The ExPAnD Methodology was used ♦  Original version uses 10 Heuristic Rules ♦  Combines Pinch & Exergy Analyses

§  Composite & Grand Composite Curves in Idea Generation for Process Improvements

§  Exergy Efficiency to Quantify Improvements ♦  Optimization has also been included

§  New Superstructure allows Simultaneous Optimization of Networks with heat Exchangers, Pumps, Compressors and Expanders using Math Programming (MINLP)

E-2

C-1

E-1

C-3

E-3

C-2

TC1,in TC1,out

TC2,in TC2,out

TH1,inTC3,out

TC3,in

TH1,out

TH2,inTH2,out

TH3,inTH3,outTC4,in TC4,out

TH4,inTH4,out

E-2E-2

C-1C-1

E-1E-1

C-3C-3

E-3E-3

C-2C-2

TC1,in TC1,out

TC2,in TC2,out

TH1,inTC3,out

TC3,in

TH1,out

TH2,inTH2,out

TH3,inTH3,outTC4,in TC4,out

TH4,inTH4,out

A. Wechsung, A. Aspelund, T. Gundersen and P.I. Barton, ”Synthesis of Heat Exchanger Networks at Sub-Ambient Conditions with Compression and Expansion of Process Streams”, AIChE Jl., vol. 57, no. 8, pp. 2090-2108, 2011.

NTNU


The Onion Diagram revisited

R S H U

The “traditional” Onion

Smith and Linnhoff, 1988

R S C & E H

The “forgotten” Onion

The User Guide, 1982

The “sub-ambient” Onion

R S HEN C&E U

A. Aspelund, D.O. Berstad, T. Gundersen, ”An Extended Pinch Analysis and Design procedure utilizing pressure based exergy for sub-ambient cooling”, Applied Thermal Engng., vol. 27, pp. 2633-2649, 2007

NTNU


What is Exergy (or “Availability”)?

n  The Definition of Exergy: ♦  ”The Maximum Amount of Work that can be produced

if a “System” is brought to Equilibrium with its natural Environment through ideal i.e. Reversible Processes”

n  The Word Exergy: ♦  Suggested by Rant (1953/1956) ♦  Greek Language: Exergy means External Work

§  Ex (εξ) means “External” §  Ergon (εργον) means “Work”

n  Exergy in Thermodynamics: ♦  Linked to Entropy and the 2nd Law of Thermodynamics ♦  Entropy Production in Processes due to Irreversibilities

is Equivalent to Exergy Losses (thus Lost Work)

NTNU


Why use Exergy? n  Advantages with Exergy

♦  Unified Treatment of different Energy Forms ♦  Quality of Processes measured with Thermodynamics ♦  Exergy Losses increase Energy Consumption ♦  Obvious in Processes with Focus on Work (“pure” Exergy)

§  Power Stations and CHP Systems §  Subambient Processes (Refrigeration produced by Work)

♦  Uncertainties in Cost – Thermodynamics is “safe” and will never “let us down” §  Says a Thermodynamics Lecturer … …

n  Disadvantages with Exergy ♦  Need to distinguish Internal and External Losses ♦  Difficult to distinguish Inevitable and Avoidable Losses ♦  Exergy is often in “Conflict” with Investment Cost ♦  Lack of Expertise

§  Chemical Engineers “do not know” Exergy §  Mechanical Engineers “hate” Exergy

NTNU


Air Separation Unit (ASU)

Air

N2

CW

MAC

MHE

LP

HP

CW

N2 O2

DCA

PPU

Linde’s Classical Coupled Column Design

C. Fu, T. Gundersen, ”Using Exergy Analysis to reduce Power Consumption in Air Separation Units for Oxy-Combustion Processes”, Energy, vol. 44, pp. 60-68, 2012.

NTNU


Single Column, Distributed Reboiling, Heat Pumping (RVRC)

Recuperative Vapor Recompression Cycle (RVRC)

Distillation column

Condenser1

Reboiler1

Air

A1-2

Impurities

A1-4

A1-5

A0A1-1A1-3

A12-1A13-1

A12-2

A13-2

A2-1A2-2A4A5-2 A5-3 A5-4

A5-5

A5-6

O2

N2

Blower

Compressor1

Reboiler2

Compressor3 Expander

A5-1

A14

A15-1

A15-2A15-3 A15-4

A15-5

PPU

DCA

A7-1A7-2

A7-3 A7-4 A7-5 A7-6A7-7Compressor2

Fu C., Gundersen T. and Eimer D., “Air Separation”, GB Patent, Application

number GB1112988.9, July 2011

NTNU


Natural Gas Liquefaction (NG LNG)

Linde & Statoil ”Mixed Fluid

Cascade” (MFC®) used at ”Snøhvit”

Hammerfest Norway

E. Berger, W. Förg, R.S. Heiersted, P. Paurola, ”The Snøhvit Project”, Linde Technology, no. 1, pp. 12-23, 2003.

NTNU


Exergy Representations in Pinch Analysis

Linnhoff B., Dhole V.R., “Shaftwork Targets for Low-Temperature Process Design”, Chem. Engng. Sci., vol. 47, no. 8, pp. 2081-2091, 1992.

Carnot Factor:

ηC = 1− T0

T

E = H ⋅ 1− T0

T⎛⎝⎜

⎞⎠⎟

NTNU


Dhole V.R., Linnhoff B., “Total Site Targets for Fuel, Co-generation, Emissions and Cooling”, European Symp. on Comp. Aided Process Engng., CACE, Suppl. vol. 17, pp. S101-S109, 1993.

Total Site Sink Source Profiles for Targeting Fuels, Cogeneration, Emissions, Cooling

NTNU


Classification & Decomposition of Exergy

D. Marmolejo-Correa, T. Gundersen, ”A Comparison of Exergy Efficiency Definitions with focus on Low Temperature Processes”, Energy, vol. 44, pp. 477-489, 2012.

Exer

gy

Flow Exergy

Carried by Matter

Exergy < Energy

Chemical

Reactional

Concentrational

Thermo-mechanical ETM

T-based ET

P-based Ep

Exergy = Energy

Mechanical

Kinetic

Potential

Electrical

Electrostatic

Electrodynamic

Nuclear

Carried by Energy

Exergy < Energy

Heat EQ

Radiation

Exergy = Energy Electrical

Non-flow Exergy

1st class: Open/Closed

Systems

2nd class: Carrier

3rd class: Energy Quality

4th class: Origin

Exergy Parts or Components

NTNU


0.0

0.5

1.0

1.5

2.0

0 1 2 3 4 50Dimensionless Temperature, T T

Exer

gy ra

tio o

f Hea

t, EQ

/ Q

.

.

0.5

Special Behavior of Temperature based Exergy Exergy of Heat

E = Q ⋅ 1− T0

T⎛⎝⎜

⎞⎠⎟ for T ≥ T0

E = Q ⋅ T0

T−1⎛

⎝⎜⎞⎠⎟ for T ≤ T0

ET

0

S0

p

0p

( ),T p

( )0 ,T p

( )0 0,T p

ETM

Enthalpy, H

E p

S

0T

0T T<

Exer

gy, E

.

Thermo-mechanical Exergy of a Stream

ETM = ET + E p

NTNU


Consider Heat and Exergy Transfer above/below Ambient Temperature

-150

-100

-50

0

50

100

150

200

0 20 40 60 80 100 120

Tem

pera

ture

(°C

)

E (kW)

Hot Stream (exergy) Cold Stream (exergy)

1

2 3

4

2

1

4

3

Source

Sink

Source

Sink

Heat Transfer Exergy Transfer

-150

-100

-50

0

50

100

150

200

0 50 100 150 200

Tem

pera

ture

(°C

)

H (kW)

Hot Stream (energy) Cold Stream (energy)

1

2

3

4

1

2

3

4

Source

Sink

Source

Sink

NTNU


Process orUnit Operation

ExergyConsumed

ExergyProduced

(Internal)

Exergy Efficiency Definitions

D. Marmolejo-Correa, T. Gundersen, ”Exergy Transfer Effectiveness for Low Temperature Processes”, to be submitted to Intl. Jl. of Thermodynamics, 2013.

Brodyansky et al. (1994)

”Exergy Efficiency”

ηe =

Eout − EtransitEin − Etransit

Bejan et al. (1996)

”Exergetic Efficiency”

ε =Eproducts

Efuels

Kotas (1995)

”Rational Efficiency”

ψ =

Eout , desired

Ein, necessary

Marmolejo-Correa and Gundersen (2013)

”Exergy Transfer Effectiveness (ETE)”

ε tr =

EsinksEsources

NTNU


Applied to the simple PRICO Process

Brodyansky et al. (1994)

ηe =E8T

E6T + Δ E6−8

p + Wtot

= 0.508

Bejan et al. (1996)

ε = Δ E6−8TM

Wtot

= 0.323

Kotas (1995)

ψ = Δ E6−8T

Δ E6−8p + Wtot

= 0.500

Marmolejo-Correa and Gundersen (2013)

ε tr =E8T

E6T + Δ E6−8

p + Wtot

= 0.508

NTNU


How and When is Exergy used?

n  Exergy Analysis is used as a Post-Design Tool ♦  Existing Plants or Complete Grassroot Designs

n  Exergy Analysis requires substantial Information ♦  Calculated from Enthalpy and Entropy Data

n  Exergy Analysis is done on the Equipment Level ♦  Exergy Losses or Exergy Efficiency for each Unit ♦  Not suited to study Connection between Units ♦  Very few (if any) Guidelines for Design/Retrofit

n  Our Objective: ♦  Move Exergy from Post-Design to Conceptual Design ♦  Develop Graphical Tools similar to Pinch Analysis

§  Exergy Composite Curves and Exergy Cascades §  Targeting, Conceptual Design and Optimization

NTNU


Limitations of Existing Exergy Diagrams

n  The Curves are Non-Linear (of course) n  Simulations required to generate Curves n  Targets not explicitly available from the Graphs

Similar Diagrams: Exergy Grand Composite Curve (EGCC) Exergy Column Grand Composite Curve (ECGCC)

Heat Pinch

Heat Recovery 0, 0C Tη =

Car

not F

acto

r, η C

QDeficit ,min

EDestruction,min

QSurplus,min Enthalpy, H

Carnot Factor:

ηC = 1− T0

T

E = H ⋅ 1− T0

T⎛⎝⎜

⎞⎠⎟

Exergy Composite

Curves (ECCs)

NTNU


Developing “Exergetic Temperatures” (1)

eTM = h T , p( )− h T0, p0( )⎡⎣ ⎤⎦ −T0 ⋅ s T , p( )− s T0, p0( )⎡⎣ ⎤⎦ = eT + ep

Thermo-mechanical Exergy can be decomposed:

Differential Form of Thermo-mechanical Exergy:

deTM = ∂eTM

∂T⎛⎝⎜

⎞⎠⎟ p

⋅dT + ∂eTM

∂p⎛⎝⎜

⎞⎠⎟ T

⋅dp and deTM = deT + dep

− Wmax = Δ E = Δ H −T0 ⋅ ΔSGouy-Stodola Theorem:

Exergy Components: (NB: Not Unique)

eT = h T , p( )− h T0, p( )⎡⎣ ⎤⎦ −T0 ⋅ s T , p( )− s T0, p( )⎡⎣ ⎤⎦

ep = h T0, p( )− h T0, p0( )⎡⎣ ⎤⎦ −T0 ⋅ s T0, p( )− s T0, p0( )⎡⎣ ⎤⎦

NTNU


Developing “Exergetic Temperatures” (2)

Required Partial Derivatives

∂h∂T

⎛⎝⎜

⎞⎠⎟ p

= cp ∂s∂T

⎛⎝⎜

⎞⎠⎟ p

=cpT

∂h∂p

⎛⎝⎜

⎞⎠⎟ T

= v −T ⋅ ∂v∂T

⎛⎝⎜

⎞⎠⎟ p

∂s∂p

⎛⎝⎜

⎞⎠⎟ T

= − ∂v∂T

⎛⎝⎜

⎞⎠⎟ p

More Differential Forms

deT = ∂eTM

∂T⎛⎝⎜

⎞⎠⎟ p

⋅dT = ∂h∂T

⎛⎝⎜

⎞⎠⎟ p

−T0 ⋅∂s∂T

⎛⎝⎜

⎞⎠⎟ p

⎡

⎣⎢

⎤

⎦⎥ ⋅dT

dep = ∂eTM

∂p⎛⎝⎜

⎞⎠⎟ T

⋅dp = ∂h∂p

⎛⎝⎜

⎞⎠⎟ T

−T0 ⋅∂s∂p

⎛⎝⎜

⎞⎠⎟ T

⎡

⎣⎢

⎤

⎦⎥ ⋅dp

T-based and p-based Exergy Components

eT = cp ⋅ 1−T0T

⎛⎝⎜

⎞⎠⎟ ⋅dT

T0

T

∫

ep = v − T −T0( ) ⋅ ∂v∂T

⎛⎝⎜

⎞⎠⎟ p

⎡

⎣⎢

⎤

⎦⎥

p0

p

∫ ⋅dp

NTNU


Developing “Exergetic Temperatures” (3) Assuming constant cp

eT = cp ⋅ 1− ToT

⎛⎝⎜

⎞⎠⎟ ⋅dT

T0

T

∫ = cp ⋅ T −T0( )−T0 ⋅ ln TT0

⎛⎝⎜

⎞⎠⎟

⎡

⎣⎢

⎤

⎦⎥

eT = cp ⋅T0 ⋅TT0

- 1 - ln TT0

⎡

⎣⎢

⎤

⎦⎥ = cp ⋅T

ET

Assuming Ideal Gas and constant cp

ep = v − T −T0( ) ⋅ ∂v∂T

⎛⎝⎜

⎞⎠⎟ p

⎡

⎣⎢

⎤

⎦⎥ ⋅dp

p0

p

∫ = RTp

− T −T0( ) ⋅ Rp

⎡⎣⎢

⎤⎦⎥p0

p

∫ ⋅dp

ep = R ⋅T0 ⋅ lnpp0

= cp ⋅T0 ⋅k -1k

⋅ ln pp0

= cp ⋅T0 ⋅ lnpp0

⎛⎝⎜

⎞⎠⎟

k-1k= cp ⋅T

E p

Linear Relationships

NTNU


A small illustrating Example

Energy Targets:

ΔTmin = 0°C

QH ,min = 3.5 MW

QC ,min = 6.0 MW

Exergy Targets:T0 = 15°C , p0 = 1 bar

ESurplus,miin = ?? MW , EDeficit ,miin = ?? MWEDestructed ,min = ?? MW

ERequired ,min = ?? MW , ERejected ,min = ?? MW

D. Marmolejo-Correa, T. Gundersen, ”A new Graphical Representation of Exergy applied to Low Temperature Process Design”, submitted to I&EC, 2012.

NTNU


Heat and Exergy Cascades

6.00

3.50

3.00

-4.50

2.00

-4.00

12.00

-2.0

-4.00

6.50

2.00

4.00

0.00

12.00

10.00

250°C

230°C

200°C

180°C

140°C

80°C

40°C

20°C

250°C

230°C

200°C

180°C

140°C

80°C

40°C

20°C

H131.50 kW

3.00

4.50

3.00

5.00

6.00

10.00

12.00

8.00

6.00

12.00

8.00

4.00

15.00

9.00

H230.00 kW

C132.00 kW

C227.00 kW

9.00

6.00

PinchPinch

Heat Deficit

Heat Surplus

2.49

1.11

1.32

-1.85

0.76

-1.34

2.96

-0.27

-0.20

2.43

0.58

1.34

0.00

2.96

2.69

63.15K

54.38K

42.10K

34.54K

21.17K

6.39K

1.03K

0.04K

63.15K

54.38K

42.10K

34.54K

21.17K

6.39K

1.03K

0.04K

H19.32 kW

1.32

1.84

1.13

1.89

2.01

3.34

4.01

2.67

2.26

2.96

1.07

0.20

3.70

3.69

H28.93 kW

C16.90 kW

C29.96 kW

2.22

0.80

PinchPinch

Exergy Deficit

Exergy Surplus

Corresponding Intervals & Pinch

T (°C) and T ET (K)

NTNU


New Linear Exergy Composite Curves

ERequired = EDeficit + EDestructed and ERejected = ESurplus − EDestructed

4 8 12 16 20 0

10

20

30

40

50

60

70 T ET

ET

EDeficit ,min = 1.11 MW

ESurplus,min = 2.49 MW

EDestructed ,min = (1.47 −1.11)+ (2.49 − 0.80) = 2.05 MW

ERequired ,min = 1.47 MW

ERejected ,min = 0.80 MW

NTNU Stream Type TsET

TtET

TsEp

TtEp

Δ ET Δ E p

(ID) Exergy (K) (K) (K) (K) (MW) (MW)

NG Sink 0.00 117.73 555.33 0.00 8.13 -27.21

N2a Sink 0.00 117.73 462.94 177.98 14.32 -34.65

N2b Source 117.73 0.00 177.98 462.94 -14.32 34.65

!


Small Industrial Case Study – LNG Process

ΔTmin = 0°C , T0 = 25°C , p0 = 1 bar

Stream Type Ts Tt ps pt mcp κ =cpcv

Δ H

(ID) Energy (°C) (°C) (bar) (bar) (kW/ºC) (–) (MW)

NG Hot 25 -168 65.0 1.0 varying varying -13.84

N2a Hot 25 -168 120.0 6.3 121.6 1.48 -23.46

N2b Cold -168 25 6.3 120.0 121.6 1.48 23.46

!

NTNU


Energy Composite Curves

Energy Targets:

ΔTmin = 0°C

QH ,min = 0.0 MW

QC ,min = 13.8 MW

n  Natural Gas is divided into Segments to account for cp = f(T) n  Nitrogen treated as Ideal Gas with constant cp

-200

-150

-100

-50

0

50

0 5 10 15 20 25 30 35 40

Cold Hot ( )Enthalpy MW

H1 = 37.3 MWTH ,1 = TC ,2 = 25°C

H2 = 13.8 MWTH ,2 = −92.5°CTC ,1 = −168°C

2

1

1

2

3

Tem

pera

ture

(°C)

H3 = 0 MWTH ,3 = −168°C

NTNU


Exergy Composite Curves before Pressure Changes

ESurplus,min = 0.0 MW , EDeficit ,min = 22.4 −14.3= 8.1 MW

EDestructed ,min = 14.3− 6.8 = 7.5 MW

ERequired ,min = 8.1+ 7.5 = 15.6 MW , ERejected ,min = 0.0 MW

0

25

50

75

100

125

150

0 5 10 15 20 25

Source Sink

EH ,2 = 6.8 MW

TH ,2ET

= 31.9 K

EC ,1T = 14.3 MW

TC ,1ET

= 117.7 K

ETH ,3 = 22.4 MW

TH ,3ET

= 117.7 K

3

2

1

2

1

Exe

rget

ic T

empe

ratu

re (K

)

( )− T based Exergy MW

NTNU


Process Modifications to save Energy

Energy Targets:

ΔTmin = 0°C

TPinch = 25°C

QH ,min = 0.0 MW

QC ,min = 13.8 MW

n  The “Plus/Minus” Principle applied below Pinch u  (A) Increase Heat Sink (Exergy Source) u  (B) Decrease Heat Source (Exergy Sink)

n  (A) means added refrigeration, (B) means utilizing the Pressure of N2a to create cooling through Expansion

-200

-150

-100

-50

0

50

0 5 10 15 20 25 30 35 40

Cold Hot ( )Enthalpy MW

H1 = 37.3 MWTH ,1 = TC ,2 = 25°C

H2 = 13.8 MWTH ,2 = −92.5°CTC ,1 = −168°C

2

1

1

2

3

Tem

pera

ture

(°C)

H3 = 0 MWTH ,3 = −168°C

NTNU


Energy Composite Curves with Pressure Changes

N2a 25°C

120 bar

-52.64°C

120 bar

-168°C

6.3 bar

Energy Targets:

ΔTmin = 0°C

QH ,min = 0.0 MW

QC ,min = 46.9 MW

External Cooling increased, but moved to above Ambient

-175

-125

-75

-25

25

75

125

0 20 40 60 80

Cold Hot

H3 = 0 MWTH ,3 = −165°CTC ,1 = −168°C

H1 = 70.0 MWTH ,1 = 85.7°C

H2 = 23.1 MWTH ,2 = 25°CTC ,2 = 22°C

2

1

1

2

3

( )Enthalpy MW

Tem

pera

ture

(°C)

NTNU


Exergy Composite Curves with Pressure Changes

Above Below

ESurplus,min = 4.4 MW

ERejected ,min = 4.4 MW

All others are 0.0 MW

Above

ESurplus,min = EDeficit ,min = 0.0 MWEDestructed ,min = 9.4 − 4.4 = 5.0 MW (was 7.5 MW)

ERequired ,min = ERejected ,min = 0.0 MW

Below

0

25

50

75

100

125

150

0 5 10 15 20

Source (above T0) Source (below T0) Sink

ETC ,1 = 18.8 MW

TC ,1ET

= 117.7 K

TH ,3ET

= 112.3 K

ETH ,2 = 9.4 MW

TH ,2ET

= 0.0 K

TH ,1ET

= 6.1 K

ETC ,2 = 4.4 MW

TC ,2ET

= 0.0 K2

1

3

2 1

Exe

rget

ic T

empe

ratu

re (K

)


NTNU


No Surprise:

We have actually “discovered” the Reverse Brayton LNG Process

6 (Natural gas)

7

3 AC-1002

COM-100-51 (Nitrogen)

4TUR-100

5

HX-100

LIQ-EXP-100

8

c

b

a

d

e

b

c

-175

-125

-75

-25

25

75

125

0 10 20 30 40 50 60 70 80

Cold Hot

Hc,d = 0 MWTc = −165°CTd = −168°C

Ha = 70.0 MWTa = 85.7°C

Hb,e = 23.1 MWTb = 25°CTe = 22°C

a

b

c

( )Enthalpy MW

Tem

pera

ture

(°C)

d

e

-25

0

25

50

75

100

125

150

0 5 10 15 20

Source Sink

ETc,d = 18.8 MW

TdET

= 117.7 K

TcET

= 112.3 K

ETb' = 9.4 MW

TH ,b'ET

= 0.0 K

ETb,e = 4.4 MW

Tb,eET

= 0.0 K

TaET

= 6.1 K

Exe

rget

ic T

empe

ratu

re (K

)


d

c

e

b a b'

NTNU


Concluding Remarks: Our modest Contributions to using Exergy Analysis in Sub-ambient Process Design

n  Discussed special Challenges in Sub-ambient Design n  Discussed the Classification of Exergy Forms n  Illustrated the importance of Decomposition

♦  Explains behavior of Compressors/Expanders above/below T0 ♦  Results in Exergy Efficiencies that measure Design Quality

n  Discussed various Exergy Efficiencies ♦  Compared existing ones applied to LNG Processes ♦  Proposed a new Exergy Efficiency based on Sources & Sinks

n  New Exergetic Temperature as an Energy Quality Parameter that can replace the Carnot Factor

n  New Linear Graphical Diagrams for Exergy n  New Targeting Procedure for Exergy n  Developments + ExPAnD è New Design Procedure

The Role of Process Integration in Sub-ambient Processes · 2013-03-21 · NTNU 20.03.13 T....

Documents

Transcript of The Role of Process Integration in Sub-ambient Processes · 2013-03-21 · NTNU 20.03.13 T....