design concepts to improve energy efficiency in a petroleum refinery

Design Concepts to Improve Energy Efficiency in a Petroleum Refinery

Group 10: Kamal Brahmbhatt, Gurpreet Chahal, Garima Dua, Fariha Siddiqui

Advisors: Ali Elkamel, Ushnik Mukherjee, Yusuf Ali (Imperial Oil)

INTRODUCTION

OPTIMIZATION ALTERNATIVES

METHODOLOGY

BASE CASE PFD

PROCESS RESULTS

ECONOMIC FEASIBILITY

ENVIRONMENTAL IMPACT

CONCLUSIONS & RECOMMENDATIONS

HEALTH & SAFETY

REFERENCES

AKNOWLEDGEMENTS

ProblemInefficient use of energy in refineries results in high OPEX and loss of valuable energy

OpportunitySteam distribution losses represent 18% of total energy losses

ObjectiveImprove energy management system in steam distribution network to:

• Minimize energy losses • Maximize cost savings• Reduce global CO2 emissions

Case #1Optimize the steam distribution network by replacing PRVs with back-pressure turbines (BPTs) to produce electricity and minimize energy losses (MILP Problem)

Case #2Redesign the steam distribution network system by determining the optimal configuration of steam turbines so that energy losses through the PRVs are minimized (MINLP Problem)

Case 1A Case 1B

Objective Function

Min Cost = [Capital Cost of BPTs + O&M costs – Electricity cost]

Min Energy Loss = ∑ Energy loss through PRVs

Constraints• Constant steam header pressure• Constant flowrate through steam headers• Constant steam output from boilers

Same as Case 1A

Case 2A Case 2B

Objective Function

Max Power Out = ∑ Power output from each steam turbine

Max Power Out = Case 2A Results + ∑ Power output from BPTs

Constraints

• Constant steam output from boilers• Energy balance between headers is constant• Each turbine & PRV can only be selected once• Capacities of turbines and PRVs are constant

Same as Case 2A

Literature Review &

PFD Selection

Base Case Energy/Power

Output

Optimization Techniques Selection(Case 1A, 1B, 2A, 2B)

Decision Variables

Specification

Constraints Definition

Economic Feasibility

Environmental Impact

Optimum Case Selection

No

YesAre the results

optimum?

Objective Function

Definition

Engineering Tools• GAMS Software for optimization • Microsoft Excel for data analysis

375 psig steam users

Deaerators

T11 T12 T13 T14 T15 T16

T32

Desuperheater Water

T31

600 psig steam

375 psig steam

150 psig steam

75 psig steam

50 psig steam

Condensate

Vent4

10

68

4

948

0

42 378 843 130

82

1 14

5

5

20

20 255

255178

52

124

330 173 98

98

173

0.3

0.3

5

330

1136

392

53

95

50

1608

145

32

T21

2

2 3 119

213

36

11

486

285

0

136

145

21

289

36

4

263

250

To Boilers

13 2 Losses

8 Losses

5 Losses

600 psig steam users

375 psig steam users

Waste Heat Boilers

Utility Boilers

CHP Boilers

150 psig Boilers

75 psig Boilers

75 psig steam users

50 psig steam users

150 psig Boilers

50 psig Boilers

Condensate users

Demin. Water make-up

Flash Steam from B/D

Flash Steam from B/D

PRV 1

PRV 2

PRV 3

PRV 5 PRV 4

PRV 6

375 psig steam users

Deaerators

T11 T12 T13 T14 T16

T32

Desuperheater Water

T31

600 psig steam

375 psig steam

150 psig steam

75 psig steam

50 psig steam

Condensate

Vent4

0

0

9

0

0

42 378 843 130

82

1 14

5

5

20

20 255

255178

52

124

330

98

98

0.3

0.3

5

330

1136

392

53

95

50

1608

145

32

T21

2

23 119

213

36

11

486

285

0

136

145

21

289

36

4

263

250

To Boilers

13 2 Losses

8 Losses

5 Losses

600 psig steam users

375 psig steam users

Waste Heat Boilers

Utility Boilers

CHP Boilers

150 psig

Boilers

75 psig Boilers

75 psig steam users

50 psig steam users

150 psig

Boilers

50 psig Boilers

Condensate users

Demin. Water make-up

Flash Steam

from B/D

Flash Steam

from B/D

T15

173

173

0 BPT 2

68

68

BPT 5

48

48

BPT 1

10

10

4

4

BPT 3

BPT 4

9

0

0

5

10

15

20

25

30

Case 1A Case 1B Case 2A Case 2B

8.4811.44

24.89 25.97

Tota

l En

erg

y Sa

vin

gs

(mill

ion

kw

h/y

r)

Potential Energy SavingsCase 1ARedirect flows from PRVs 2 & 5 to BPTs installed in parallel

Case 1BRedirect flows from PRVs 1 to 5 to BPTs installed in parallel

Case 2AReconfigure the steam network system subjected to the constraints defined (refer to PFD for optimized case #2)

Case 2BRedirect flow from PRV 3 to BPT installed in parallel. Steam flow through PRV 2 is insignificant, hence infeasible to install a BPT

0

20

40

60

80

Case 1A Case 1B Case 2A Case 2BCO

2sa

vin

gs (

mill

ion

lbs/

year

)

Potential CO2 Savings

Natural Gas Coal

Case 1A Case 1B Case 2A Case 2B

NG Coal NG Coal NG Coal NG Coal

No. of Cars730 2,148 985 2,897 2,143 6,304 2,237 6,580

No. of Households

477 1,403 643 1,893 1,400 4,119 1,461 4,299

• CO2 emissions savings can be translated into everyday terms such as annual emissions from cars and number of households

375 psig steam users

Deaerators

T11

T12

T13 T14 T15 T16

T32

Desuperheater Water

T31

600 psig steam

375 psig steam

150 psig steam

75 psig steam

50 psig steam

Condensate

Vent4

0

0

0

42 378 843 130

82

114

7.5

7.5

4

4

379.533.5

124

495 179.7 27

0.45

0.45

5

495

1136

392

53

95

50

1608

145

32

T21

3

3 3 119

213

36

11

486

285

0

136

145

21

289

36

4

263

250

To Boilers

13 2 Losses

8 Losses

5 Losses

600 psig steam users

375 psig steam users

Waste Heat Boilers

Utility Boilers

CHP Boilers

150 psig

Boilers

75 psig Boilers

75 psig steam users

50 psig steam users

150 psig

Boilers

50 psig Boilers

Condensate users

Demin. Water make-up

Flash Steam

from B/D

Flash Steam

from B/D

BPT

69

69

379.5 179.7 27

2.5

CASE 1 CASE 2

Case 1A

Case 1B

Case 2A

Case 2B

• Potential CO2 savings from selling additional electricity to a natural gas (NG) or coal fired power plant

$0

$200,000

$400,000

$600,000

$800,000

Case 1A Case 1B Case 2A Case 2B

$117,569$77,244

$631,464 $617,096

Tota

l Co

st S

avin

gs (

$/y

r)

Potential Yearly Cost Savings

0

2

4

6

8

10

Case 1A Case 1B Case 2A Case 2B

Pay

bac

k P

eri

od

(Ye

ars)

Payback Period & Capital Investment

Payback Period (yrs) 4.2 9.2 0 1.5

665,385 1,223,833 0 192,500Capital Investment ($)

Optimal Solution

Case 2AReconfigure the steam network system subjected to the constraints defined

• 22M lbs in CO2

savings (NG basis)• 66M lbs in CO2

savings (Coal basis)

25M kWh/yr in energy savings

~ $630,000 in net profit/yr

$0 in capital investment

• We would like to express our gratitude and appreciation to Ushnik Mukherjee for providing assistance with GAMS programming

• We would also like to thank Prof. Ali Elkamel and Yusuf Ali for providing valuable advice regarding the project

• Venkatesan, V., & Lordanova, N. (2003). Proceedings from the Twenty-Fifth Industrial Energy Technology A case study of Steam System Evaluation in a Petroleum Refinery. Houston: Armstrong Service.

• OSHA. (2015). Section IV: Chapter 2 - Petroleum Refining Process. From U.S. Department of Labor | Occupational Safety & Health Administration: https://www.osha.gov/dts/osta/otm/otm_iv/otm_iv_2.html#3

• Constantine, S., & Phillips, K. (2003). Steam System Efficiency Improvements in Refineries in Fushun, China. Beijing: Beijing Tuofeng Armstrong Steam System Energy Conservation Technologies.

• Magalhães, E., Wada, K., & Secchi, A. (2005). Steam production optimization in a petrochemical industry. Mercosur Congress on Process Systems Engineering.

HAZARDS CONSEQUENCES MITIGATION STEPS

High pressure steam build-up

• Pipe rupture• Explosions which can

lead to fatalities

• Installation of pressure relief valves (PRVs)

Steam Leaks (distribution)

• Health risks associated with severe steam burns

• Steam can displace O2

in an enclosed area resulting in an asphyxiation hazard

• Ensure proper insulation of pipes• Perform walk down surveys on

routine basis to detect steam leaks or "out-of-tolerance" conditions

• Use of piping material suitable for HP steam

Inadequate amount of

feedwater to the boilers

• Risk of running boilers dry leading to extreme temperatures

• Explosions which can lead to fatalities

• Usage of suitable process control measures to supply fuel in accordance with boiler feedwaterflow

Metal corrosion

• Can lead to wall thinning and catastrophic failures of equipment

• Usage of high-grade material• Application of coatings• Change in procedures to minimize

corrosion possibilities• Regular corrosion monitoring and

maintenance

Noise resultingfrom high steam

velocities• Can lead to hearing loss • Use of double hearing protection

S

E

V

E

R

I

T

Y

L

E

V

E

L

Table 2: Health & Safety Analysis

Table 1: Translation of CO2 emissions into everyday terms

Note: All numbers in 1000 lbs/hr

Note: All numbers in 1000 lbs/hr Note: All numbers in 1000 lbs/hr