Summary for TEP 4215 E&P/PI

Summary forTEP 4215

E&P/PI

T. Gundersen

• Reactor System (R) Endothermic vs. Exothermic Reactions Equilibrium vs. Kinetics Temperature Dependence of Equilibrium

Constants and Reaction Rates (Arrhenius) Reactors play a key Role in the Thermal and the

Mechanical Energy System of a Plant (or Site) Correct Integration of Reactors

Sum 1

Process, Energy and System

Summary of Process Integration

R S H U

Summary forTEP 4215

E&P/PI

T. Gundersen

• Reactor / Separator Interface (R/S) Focus of the Discussion was based on the

Definition and Use of the following Terms: Degree of Conversion (Extent of Reaction) Selectivity Yield (Reactor and Process) Recycle Rate

Sum 2



R S H U

YR = X · S

YP = X · S · (1 + W)R S

FF

RR

P

PX

RXRF

BP

Summary forTEP 4215

E&P/PI

T. Gundersen

• Separation System (S) Economical Trade-offs in Distillation Columns

Operating Cost vs. Investment Cost Number of Stages, Reflux and Pressure

Combinatorial Issues & Heuristic Rules related to the Sequence of Distillation Columns

Heat Integration Opportunities between Columns (Condenser / Reboiler)

Briefly about Evaporators Multi-effect, Forward/Backward Feed, BPR

Sum 3



R S H U

T. Gundersen

Sequence of Distillation Columns

Sum 4

Separation Systems


Problem Definition by Thompson and King, AIChE Jl, 1972:

”Given a mixture of N chemical components that is to be separated into N pure component products by using a selection of M separation methods”

Seq

( 1)Alt Seq

2 ( 1) !Number of Sequences

! ( 1)!

Number of Alternatives N

NN

N N

N N M

T. Gundersen

Sequence ofColumns

Sum 5

Separation Systems


ABCD

ABCD

ABCD

ABCD

BCD

BCD

ABC

ABC

CD

BC

CD

BC

AB

AB

2 comps. 1 sequence

3 comps. 2 sequences

4 comps. 2x(1+3 comps.) + 1x(2+2 comps.) 2x2 + 1 = 5 sequences

5 comps. 2x(1+4 comps.) + 2x(2+3 comps.) 2x5 + 2x2 = 14 sequences

6 comps. 2x(1+5 comps.) + 2x(2+4 comps.) + 1x(3+3 comps.) 2x14 + 2x5 + 2x2 = 42 sequences

T. Gundersen

Sequence of Distillation ColumnsSelected Heuristic Rules

Sum 6

Separation Systems


H1: Favor Separation of the most Volatile ComponentH2: Favor near-Equimolar SeparationH3: Favor Separation of the most Plentiful ComponentH4: Favor Simple Separations<< H5: Delay Separation of Sharp Splits >>

Heuristics cause Conflicts, some can be Quantified, others just ”cast a vote”, their

main use is to Eliminate Sequences !!

T. Gundersen

Example – Distillation Sequence

Separation Systems


Comp. Name Mole Frac. α=Ki/Kj ”CES”

A Propane 0.052.00 5.26

B i-Butane 0.151.33 8.25

C n-Butane 0.252.40 114.50

D i-Pentane 0.201.25 13.46

E n-Pentane 0.35

Nadgir & Liu, AIChE Journal, 1983:

f = min (D/B, B/D) Δ = (α – 1)100 CES = f α

Sum 7

Summary forTEP 4215

E&P/PI

T. Gundersen

• Heat Recovery System (H) Targets for best Performance

Minimum Energy from the Heat Cascade Minimum Energy Cost with Multiple Utilities from

the Grand Composite Curve Fewest Number of Units from the (N – 1) Rule Minimum Area from Spaghetti Design (“Bath”) Total Annual Cost vs. ΔTmin

3-Way Trade-off (Area, Energy and Units)

Sum 8



R S H U

T. Gundersen Sum 9



Heat Cascade as Algorithm/Procedure (1)(0) Given Set of Hot Stream Temperatures: TH , i = 1,nH , Set of Cold Stream

Temperatures: TC , j = 1,nC , and Set of mCps, i = 1,nH , j = 1,nC

(1) Calculate Shadow Temperatures from Hot Streams: THS , TH,S=TH−ΔTmin

(2) Calculate Shadow Temperatures from Cold Streams: TCS , TC,S=TC+ΔTmin

(3) Obtain Total Set of Hot Stream Temperatures, THT, by merging and sorting TH and TCS Notice that dim (THT) = nH + nC

(4) Obtain Total Set of Cold Stream Temperatures, TCT, by merging and sorting TC and THS Notice that dim (TCT) = nC + nH

(5) Remove possible Duplicates in THT and TCT. The number of Temperature Intervals is then K = dim (THT) − 1

(6) Temperature Intervals are now obtained by using one Temperature from THT and one from TCT starting at the highest Temperatures

(7) Identify Heat Flows from all the Hot Streams to the respective Temperature Intervals based on mCp values and Interval Temperatures

T. Gundersen Sum 10



Heat Cascade as Algorithm/Procedure (2)(8) Identify Heat Flows from the respective Temperature Intervals to all the

Cold Streams based on mCp values and Interval Temperatures

(9) Calculate the Enthalpy (Heat) Balance (Surplus or Deficit) for each Temperature Interval

(10) Cascade Heat from the first Interval to the second, and from the second to the third Interval. Continue to the end of the Cascade

(11) If all Residuals (i.e. Heat from one Interval to the next) are non-negative (Rk ≥ 0), then no External Heating is required, QH,min = 0, and Minimum External Cooling is obtained as the Residual from the last Interval, i.e. QC,min = RK

(12) If at least one Residual is negative, then Minimum External Heating and Cooling are: QH,min = − min ( Rk) , k = 1,K-1 , QC,min = RK + QH,min

(13) The Process Pinch is the Interval Temperature with the most negative Residual which has zero heat flow after adding Minimum External Heating to the Cascade

T. Gundersen Sum 11



Example: Stream Data from Assignment 3

Stream Ts(°C) Tt (°C) mCp (kW/°C) ΔH (kW)

H1 170 60 3.0 330 H2 150 30 1.5 180 C1 20 135 2.0 230 C2 80 140 4.0 240

ΔTmin = 10°C

THT = 170, 150, 145, 90, 60, 30TCT = 160, 140, 135, 80, 50, 20 K = 6 – 1 = 5

T. Gundersen Sum 12



Example: Stream Data from Assignment 3

90°C 80°C

+ 2.5

- 82.5

+ 75

- 15

C1

C2

H2

H160 kW

15 kW

170°C 160°C

150°C 140°C

145°C 135°C

60°C 50°C

30°C 20°C

7.5 kW

165 kW

82.5 kW

45 kW

90 kW

45 kW

20 kW

220 kW

110 kW

60 kW

60 kW

+ 60

R1=60

R4=55

R5=40

R2=62.5

R3=−20

T. Gundersen


Investment Cost

WS-8 cont.Vertical Design:

2 − 3 and 1 − 4

Criss-Cross Design:2 − 4 and 1 − 3

200

250

300

350

0 500 1000

1

2

3

4

T(°C)

Q(kW)

2

2

500 500 1616.4 m0.00909 68.05 0.00909 68.05

500 500 1000 250 1250 m0.005 100 0.05 40

vertical

criss cross

A

A

Explanation: Optimal Distribution of (UΔT) - not only ΔT

Sum 13

Summary forTEP 4215

E&P/PI

T. Gundersen

• Heat Recovery System (H) Design of Network using PDM

Decomposition at Pinch (Process and Utility Pinch) Start the Design at the Pinch Pinch Exchangers and Requirements

mCp Rules: mCpout ≥ mCpin

Population: nout ≥ nin

Focus on ΔT, not ΔH Tick-off Rule Check Design against Targets !!

Sum 14



R S H U

Summary forTEP 4215

E&P/PI

T. Gundersen

• Heat Recovery System (H) Optimization of Heat Exchanger Networks

Stream Splitting (start with: α/β = mCp1/mCp2) Heat Load Loops and Paths

The HEN Design Process as a “Flow Diagram” Retrofit Design of Heat Exchanger Networks

Targeting for good value of HRAT XP Analysis (QP = QPP + QPH + QPC) Shifting to reduce XP Heat Transfer UA Analysis (existing and new) followed by Loops

and Paths for maximum Reuse of existing Units

Sum 15



R S H U

T. Gundersen Sum 16



H1

C3

I CaQI = 3500 kW QCa = 4300 kW

180ºC

130ºC

60ºC

50ºC

H2

C2 C1

CbIIIII

H 105ºC

190ºC

70ºC

40ºC100ºC

200ºC

QH = 3600 kW

QCb = 300 kW

QIII = 1300 kW

QII = 3600 kW

Exam 2 June 2008 – Retrofit (60%)

mCp = 60 kW/°C

mCp = 50 kW/°C

mCp = 40 kW/°C

mCp = 20 kW/°C

mCp = 80 kW/°C

ΔTmin = 10°C

T. Gundersen Sum 17



Exam 2008

50°C 40°C

200

+ 1200

CW

ST

C2

C3

H1

H2800 kW

2800 kW

200°C 190°C

180°C 170°C

110°C 100°C4200 kW

5600 kW

2000 kW

1600 kW 800

QH

R1

QC

R2

1600 kW

1500 kW

2400 kW

+ 800

70°C 60°CR3

1200 kWC1

100 kW

800 kW

400 kW

50°C 40°C

200

+ 1200

CWCW

ST

C2C2

C3C3

H1H1

H2H2800 kW

2800 kW

200°C 190°C

180°C 170°C

110°C 100°C4200 kW

5600 kW

2000 kW

1600 kW 800

QH

R1

QC

R2

1600 kW

1500 kW

2400 kW

+ 800

70°C 60°CR3

1200 kWC1C1

100 kW

800 kW

400 kWH,exist

C,exist

H,min

C,min

H C

3600 kW

4600 kW

1000 kW

2000 kW

2600 kW

Q

Q

Q

Q

Q Q

Simplified Cascade withSupply Temperatures only

T. Gundersen Sum 18



Exam 2008 Cross-Pinch Analysis

H1

H2 Cb

C1

180°

77.5°200°

105°

130°

121.67°

60°

40°

70°

50°

mCp(kW/°C)

[60]

[40]

[20]

[50]I C3

II

I

III

110°

100°

190°100° [80]II C2

Ca

H

III

145°

110°

3500

36003600

1300

4300

300

XP 50 (100 60) 60 (121.67 110) 20 (105 100) 2000 700 100 2600 kWQ

T. Gundersen Sum 19



Exam 2008

y can be found by ΔTmin requirements y = 1500 kW

Next: What about Investments ??

H1180°

200°

130°

121.67°

60°

50°

mCp(kW/°C)

[60]

[50]I C3

I

190°145°

[80]IV C2

Ca

H

3500

0 + y3600-y

4300-y

IV

“Shifting”

TH1

T. Gundersen Sum 20



Exam 2008

Next: UA Analysis for maximumReuse of existing Exchangers

H1

H2 Cb

C1

180°

77.5°200°

105°

130°

96.67°

60°

40°

70°

50°

mCp(kW/°C)

[60]

[40]

[20]

[50]I C3

II

I

III

190° 100°[80]II C2

Ca

H

III

145°

110°

3500

36002100

1300

2800

300

IV

IV

1500

155°

163.75°

Summary forTEP 4215

PI

T. Gundersen

• Separation/Heat Recovery Interface (S/H) Columns integrated above/below Pinch

Condenser above, Reboiler below Which Pinch – Columns often create Pinch

Extended Grand Composite Curve (Andrecovich) Distinguish Columns from “Background” Process

Evaporators and Heat Integration The Tool is again the Grand Composite Curve Play with Pressure and the Number of Effects

Sum 21



R S H U

Summary forTEP 4215

PI

T. Gundersen

• Heat Recovery / Utility Interface (H/U) Correct Integration of Heat Pumps (open/closed) Correct Integration of Turbines (back pressure

or extraction vs. condensing turbines) Co-production of Heat & Power (cogeneration) The quantitative Tool with Information about

Load (heat duty) and Level (temperature) is: The Grand Composite Curve Modified Temperatures are important !!

Sum 22



R S H U

Summary forTEP 4215

PI

T. Gundersen

• Utility System (U) Not treated in much Detail in this Course Topics could (or should?) have been:

Design of Steam Systems (turbines, boilers, deaerators, etc.)

Design of fired Heaters (Furnaces) with optimal preheat of Combustion Air

Design of Refrigeration Cycles including Integration with the Process (“economizers”)

Etc., etc.

Sum 23



R S H U

Summary forTEP 4215

PI

T. Gundersen

• Other Topics Optimization: Only Demo with Examples from

Heat Recovery using Math Programming Forbidden Matches & Extended Cascade is relevant

Operational Aspects (especially related to Flexibility and Controllability)

The Importance of Topology (Structure) Extensions of the Pinch Principle

Heat Pinch, Mass Pinch, Water Pinch and Hydrogen Pinch (whenever an “amount” has a “quality”)

Sum 24



R S H U

More on the Grand Composite Curve

Reactor

Feed

Product

DistillationColumn

Compressor

50°

210°

160°

210°

130°

220°

160°

270°

60°Reboiler

Condenser

T. Gundersen

Heat Integration − Introduction


Extra 01

H1

H2

C1

C2

Grand CompositeCurve is based

on the HeatCascade

T. Gundersen Extra 02


Heat Integration − Targeting

270ºC - - - - - - - 250ºC

230ºC - - - - - - - 210ºC

220ºC - - - - - - - 200ºC

180ºC - - - - - - - 160ºC

160ºC - - - - - - - 140ºC

70ºC - - - - - - - - 50ºC

H1

H2

CW

C1

C2

ST

720 kW

180 kW

720 kW

880 kW

440 kW

1980 kW

500 kW

200 kW

800 kW

1800 kW

+ 720

- 520

- 1200

2000 kW

400 kW

+ 180

+ 220

+ 400

60ºC - - - - - - - - 40ºC

360 kW

220 kW

ΔTmin = 20°C

The necessarydata are modified

Temperatures and thecorresponding Heat Flows

T6’ = 50 QC,min = 800

CW

ST

+ 720

- 520

- 1200

+ 180

+ 220

+ 400

T0’ = 260 QH,min = 1000

T1’ = 220 R1 = 1720

T2’ = 210 R2 = 1200

T3’ = 170 R3 = 0

T4’ = 150 R4 = 400

T5’ = 60 R5 = 580

Grand Composite Curve(or Heat Surplus

Diagram)




250

200

150

100

50

Q (kW)

500 15000

MP

HP

0

LP

CW

T' (°C)

Question: Is thisanother Pinch?

T6’ = 50 QC,min = 800

CW

ST

+ 720

- 520

- 1200

+ 180

+ 220

+ 400

T0’ = 260 QH,min = 1000

T1’ = 220 R1 = 1720

T2’ = 210 R2 = 1200

T3’ = 170 R3 = 0

T4’ = 150 R4 = 400

T5’ = 60 R5 = 580

Grand Composite Curve




250

200

150

100

50

Q (kW)

500 15000

MP

HP

0

LP

CW

T' (°C)

Answer: No

“New” CCs based on Heat Surplus and Deficit Part of Gr.CC and balanced by Hot and Cold Utilities (not representative for Area demand)




300

250

200

150

100

50

00 1000 1500 2000500 2500

PPUP

UP

CW

MP

HP

LP

T(°C)

Q(kW)

Another way of showing it is not another Process

Pinch

True Balanced Composite Curves with Utilities

(Notice difference in shape and scale)




T(°C)

Q(kW)

7000

300

250

150

100

50

0

200

6000500040003000200010000

UP

PP

UP

Summary for TEP 4215 E&P/PI

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