Conceptual Engineering for Energy Efficiency - TexasIOF...

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


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


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


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


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


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


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)


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


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


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


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


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


T

H

Reboiler

Condenser

Scope forRefluxreduction

Reflux ModificationReflux ModificationReflux Modification

Column targeting


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


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


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


Examples of Revamp Applications


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


Tem

pera

ture

F


-35

-30

-25

-20

-15

-10

-50

5

0 4 8 12 16 20 24 28 32


Base Case Option 1

Side Reboil?

Side Cooling?

Use Split feedinstead



Tem

pera

ture

F


-35

-30

-25

-20

-15

-10

-50

5

0 4 8 12 16 20 24 28 32



Tem

pera

ture

F


-35

-30

-25

-20

-15

-10

-50

5

0 4 8 12 16 20 24 28 32


C2 Splitter 1DeC2

Overhead (vapor)

C2 Splitter 2

C3R

EthyleneEthylene

EthaneProcess cooling

C2 Splitter Options –

Include 1st

column

Option 2 Option 3


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


Column Grand Composite Curve (T-H)

Tem

pera

ture

F


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


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


Column Grand Composite Curve (T-H)

Tem

pera

ture

F


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


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


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


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


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


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


Questions?

Emial: [email protected]: 281-5043475

mailto:[email protected]

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