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Conceptual Engineering for Energy Efficiency
Texas Industry Energy Management Forum -
Houston, November 06, 2008Presenter: Rian
Reyneke, Aspentech
Advanced Process Design Group
2©2007 Aspen Technology, Inc. All rights reserved
Topics Covered
•
Introduction to APD•
Project Approach
•
Process and Site Pinch Analysis•
Distillation Optimization
•
Project Examples
3©2007 Aspen Technology, Inc. All rights reserved
Aspentech’s Advanced Process Design Group
•
We provide consulting services that:–
Reduce Energy and Emissions –
Increase Capacity–
Produce Better Process Designs
•
Our Focus Areas:–
Process and Utilities Modeling–
Conceptual Process Design–
Operational Improvement
•
Our Tools:–
Aspen process simulation and equipment design software –
Process synthesis and conceptual design tools
4©2007 Aspen Technology, Inc. All rights reserved
Energy Management Focus Areas
Design Utilities to maximize efficiency
Design the process to use less energy & be
more efficient
OperateOperate
Operate Utilities to deliver at the lowest
cost
Sustain the process at lowest energy cost
DesignDesign
UtilitiesUtilities SupplySupply
ProcessProcess DemandDemand
Process/Demand –
Use less energyUse less energy
Utilities/Supply –
Provide at lowest costProvide at lowest cost
Project Approach
6©2007 Aspen Technology, Inc. All rights reserved
Energy Reduction Issues
•
Significant opportunity for improvement:−
Average US chemical facilities relatively old, inefficient, e.g.
average EEI for US ethylene plant is 175, with State-of-the-art =100 (DOE report, 2000)
−
Older unit designs based on low energy cost−
Design methods 20-30 years ago may not have considered all options, e.g. distillation sequencing
•
Challenges:−
Tight capital, short payback requirements−
Limited resources−
How to identify the best energy projects and turn into real savings•
Ad-hoc addition of energy projects are often uneconomical or may not yield the expected benefits when overall impact is not considered
•
The best approach should be systematic, holistic and based on current operation to ensure that the right opportunities are identified and that no opportunities are overlooked
7©2007 Aspen Technology, Inc. All rights reserved
Model Centric Approach to Process Improvement
Pinch and Column AnalysisIdentify design improvements
TEMPERATURE COMPOSITES (Real T, No Utils)
Case: PX1Simplified
HOT COLD
ENTHALPY X10 3 kW
TE
MP
ER
AT
UR
E C
0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 0.0
50.0
100.0
150.0
200.0
250.0
300.0
350.0
400.0DTMIN =10.00 Heat Balance
Design Definition and Equipment specification
Model Idea, develop Scope/Benefits/Cost
•High Load Test Run•Operating data review•P&ID review
Process and utilities modelling
Identify operating improvement opportunities
Equipment RatingUnderstand performance
8©2007 Aspen Technology, Inc. All rights reserved
Evaluation of current operation and equipment performance
Process and utilities modelling
Identifying operating improvement opportunities:
•Are columns over-refluxed?•If multiple column feed nozzles, is current feed location optimum?•Are column operating pressures optimal?•Exchangers underperforming/bypassed?•Compressor recycles open?
Process and Site Pinch Analysis
10©2007 Aspen Technology, Inc. All rights reserved
Pinch Analysis
Evaluation of existing or new heat exchanger network
Base Case
Target Case
Pinch Analysis purpose:Establish minimum utility targets
Identify location of inefficiencies in network
Develop viable energy saving projects that improve process-process heat recovery
Utility energy targets======================
Name Used TARGET DifferenceMMBTU/hr MMBTU/hr MMBTU/hr
MPS 75.5 74.4 -1.1LPS 139.5 9.8 -129.7
C3R45 22.4 15.7 -6.7CW 656.5 523 -133.5
(Example)
11©2007 Aspen Technology, Inc. All rights reserved
Pinch Analysis
Cross Pinch Heat Transfer PenaltiesPenalty units : MMBTU/hr
Pinch# Hxer ID Ti = 153.41 F-------- --------------E101 9.40659-------- --------------Sum --> 9.40659
299.5 158.4 100.0
DTMIN: 10.0 (Duty based) Case: Final BaseHot1
CONDFEED
QW
LPS
CW
252.0 69.3
158.4 100.0
299.5 299.5
90.0 75.0
299.5 158.4 100.0
DTMIN: 10.0 (Duty based) Case: Final BaseHot1
CONDFEED
QW
LPS
CW
252.0 69.3
158.4 100.0
299.5 299.5
90.0 75.0
142.7
148.4
HEN Analysis:Identify cross-pinch exchangers in network
Use pinch design techniques to identify best modification to eliminate cross-pinch
Also consider process modifications in conjunction with pinch analysis
12©2007 Aspen Technology, Inc. All rights reserved
A Systematic Approach to Site-Wide Energy / Emissions Reduction
BLACK BOX UNITS
INITIAL PINCH STUDY
Unit by Unit Pinch Analysis
Process Streams(Heat Sinks)
Process Streams(Heat Sources)
Site WidePinch Analysis
T
Q
Hot utilities
Cold utilities
13©2007 Aspen Technology, Inc. All rights reserved
LP
MP
HPHP
MP
LP
Fue l
+
+
Are your steam levels/loads optimum?
What is the optimum cogeneration system?
LP
MPHPHP
MP
LP
Fuel
+
LLP LLP
IP
+
+
Power generationincreased
Reduction in fuelconsumption
Opportunity for new LLP steam level – increases heat recovery
Opportunity for additional turbine to
exploit IP steam sink
Site-wide Utility Infrastructure Analysis
Smaller boilers!
Smaller CW towers!
Distillation Optimization
15©2007 Aspen Technology, Inc. All rights reserved
Column Targeting
•
A tool for thermal and hydraulic analysis of distillation columns •
Column Grand Composite Curves: A graphical representation of the ideal minimum stage-wise heating and cooling demands in a distillation column
Minimum Thermodynamic Condition
H
Reboiler
Condenser
Column Grand Composite Curve
Min Duty in Temp Interval
Condenser
Reboiler
16©2007 Aspen Technology, Inc. All rights reserved
Move the feed!
Stage Number
H
Reboiler
Condenser
Distortion due to feed
Bad Feed Location => Distorted Profile
Feed RelocationFeed RelocationFeed Relocation
Column targeting
Shaded area implies inefficiency
17©2007 Aspen Technology, Inc. All rights reserved
T
H
Reboiler
Condenser
Scope forRefluxreduction
Reflux ModificationReflux ModificationReflux Modification
Column targeting
18©2007 Aspen Technology, Inc. All rights reserved
Temp
H
CGCC (Temp-H)
Stage
H
Reboiler
Condenser
Scope for
No.
CGCC (Stage-H)
Feed Preheat
Reboiler
Condenser
Feed Preheat
Feed ConditioningFeed ConditioningFeed Conditioning
Column targeting
19©2007 Aspen Technology, Inc. All rights reserved
Temp
H
Reboiler
Condenser
ReboilerSide
Targeting For Side Reboiling
H
Reboiler
Condenser
Temp
SideCond.
Targeting For Side Condensing
Side Condensing/ReboilingSide Condensing/ReboilingSide Condensing/Reboiling
Column targeting
20©2007 Aspen Technology, Inc. All rights reserved
Distillation Synthesis/Analysis
•
Residue curve maps (generated using Aspen Split) provide a graphical tool for synthesis and analysis of non-ideal distillation schemes
•
Helps to understand and visualize complex component interactions•
Can be applied to −
Conceptual design for new processes−
Re-configuration of process for low cost retrofits−
Providing insight for operational improvement
Residue curves track the composition of residue liquid in simple
distillation -
Useful to represent complex distillation processes as well
21©2007 Aspen Technology, Inc. All rights reserved
Examples of Revamp Applications
22©2007 Aspen Technology, Inc. All rights reserved
Column Analysis Example 1: C2 Splitter debottlenecking
Block D8-401-2: Column Grand Composite Curve (T-H)
Tem
pera
ture
F
Enthalpy Deficit MMBtu/hr
-35
-30
-25
-20
-15
-10
-50
5
0 4 8 12 16 20 24 28 32
Ideal ProfileActual Profile
Block D8-401-2: Column Grand Composite Curve (T-H)
Tem
pera
ture
F
Enthalpy Deficit MMBtu/hr
-35
-30
-25
-20
-15
-10
-50
5
0 4 8 12 16 20 24 28 32
Ideal ProfileActual Profile
Base Case Option 1
Side Reboil?
Side Cooling?
Use Split feedinstead
23©2007 Aspen Technology, Inc. All rights reserved
Block D8-401-2: Column Grand Composite Curve (T-H)
Tem
pera
ture
F
Enthalpy Deficit MMBtu/hr
-35
-30
-25
-20
-15
-10
-50
5
0 4 8 12 16 20 24 28 32
Ideal ProfileActual Profile
Block D8-401-2: Column Grand Composite Curve (T-H)
Tem
pera
ture
F
Enthalpy Deficit MMBtu/hr
-35
-30
-25
-20
-15
-10
-50
5
0 4 8 12 16 20 24 28 32
Ideal ProfileActual Profile
C2 Splitter 1DeC2
Overhead (vapor)
C2 Splitter 2
C3R
EthyleneEthylene
EthaneProcess cooling
C2 Splitter Options –
Include 1st
column
Option 2 Option 3
24©2007 Aspen Technology, Inc. All rights reserved
Impact of Feed conditioning option
•
Potential to increase column 2 capacity by >30% (unload trays, condenser, reboiler)
•
Energy saving covers capital cost, capacity “free”•
Significantly unloads refrigeration system
25©2007 Aspen Technology, Inc. All rights reserved
Column Grand Composite Curve (T-H)
Tem
pera
ture
F
Enthalpy Deficit MMBtu/hr
150.
017
5.0
200.
022
5.0
250.
027
5.0
300.
032
5.0
0.0 5.0 10.0 15.0 20.0 25.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0
Ideal ProfileActual Profile
Feed
Solvent
LP Stripping
HP Extraction
Solvent
QW
> 250oF
Existing process:
Issues:•Compressor suction at atm. pres•System sensitive to ΔP across condenser –
poor heat transfer•Column analysis shows large Condenser duty available at useful T
(>150F)
Options Previously Considered:•Direct integration: long lines, adds ΔP on overhead, impractical.•Indirect integration with e.g. TW system: driving force loss, cost.
Column Analysis Example 2: US Client
Opportunity
C
26©2007 Aspen Technology, Inc. All rights reserved
Column Grand Composite Curve (T-H)
Tem
pera
ture
F
Enthalpy Deficit MMBtu/hr
125.
015
0.0
175.
020
0.0
225.
025
0.0
275.
030
0.0
325.
0
0.0 2.5 5.0 7.5 10.0 12.5 15.0 17.5 20.0 22.5 25.0 27.5 30.0 32.5 35.0 37.5 40.0 42.5 45.0 47.5 50.0 52.5 55.0 57.5 60.0 62.5 65.0
Ideal ProfileActual Profile
Proposed Modification
Benefits:•~80% of condenser Q recovered•Reduce condenser DP•Reduce condenser outlet temperature•Reduce compressor load•Option to re-pipe an existing reboiler
Feed
Solvent
LP Stripping
HP Extraction
Solvent
QW
250oF 150oF
Re-pipe existing reboiler
Direct-contactcooling
Top Feed
Bottom Feed
C
27©2007 Aspen Technology, Inc. All rights reserved
Split Example: Revamp for US Client
Existing process: •
Process:−
Desired product is component b−
Conventional fractionation of b from c−
Extractive distillation for a from b•
Key Issues:−
Incomplete removal of c, despite high number of trays and reflux on columns C1/2
−
Low product b purity
28©2007 Aspen Technology, Inc. All rights reserved
Split Analysis
Ternary Map (Mass Basis)
13T-PTD(70.45 C)
ISOPRENE(61.95 C)
PENTANE (64.16 C)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
61.56 C
64.06 C
29©2007 Aspen Technology, Inc. All rights reserved
Alternative Sequence Proposed
Proposed Solution:Use only one column (C1) for sloppy split of b/c to get near distillation boundaryUse second column (C2) for final separation of c from b in absence of aResult:Significant improvement in product purity with >$10mill potential value upgrade
30©2007 Aspen Technology, Inc. All rights reserved
Summary
•
Rigorous simulation model of process and utility systems−
Helps to identify operational opportunities often overlooked−
Helps to understanding and exploit unit-wide interactions/trade-offs that may simultaneously
save energy/ reduce capital / increase capacity
−
Provides a consistent basis for process analysis, equipment rating and project benefit assessment
•
Process analysis insights lead to more/better project ideas, more savings
•
Utility system evaluation ensures savings are real •
Helps to identify most attractive projects with best payback