-
Process modications to mintegration
Kew Hong Chewa, Jir Jaromr K
T), Facultion e CP10, H-82
Adaptation of the PluseMinus prin-ciple to select benecial
process
ntal overlap region.gions using the TSP,modied Problem
new heuristics. Theidual processes. Thecontext can furtherthe
advantages of
. All rights reserved.
1. Introduction
Efcient integration and optimisation of the energy require-ment
within a site utility system can improve the Total Site energy
efciency. Energy saving as a result of improved energy
efciencysubsequently translates into reduced CO2 emissions. Such
outcomefrom energy saving ts the European Directives 2010/75/UE
whichprioritises on the reduction of industrial emissions at the
source [1].
Total Site Heat Integration (TSHI) is a tool used to optimise
thesite-wide energy demand. It extends the application of
PinchAnalysis from a single process to multiple processes in an
industrialsite. The concept of Total Site (TS) was introduced by
Dhole and
* Corresponding author. Tel.: 60 07 5535533; fax: 60 07
5536165.
Contents lists availab
Applied Therma
sev
Applied Thermal Engineering 78 (2015) 731e739E-mail address:
[email protected] (S.R. Wan Alwi).Keywords:Total Site Heat
IntegrationPinch AnalysisProcess modicationsExtended PluseMinus
Principles
Sink and Source Proles, (b) the horizontal overlap region and
(c) below the horizoThe proposed methodology identies the options
to reduce utility targets in these reSite Utility Composite Curves
(SCC), Utility Grand Composite Curve (UGCC),Table Algorithm (PTA),
Total Site Problem Table Algorithm (TS-PTA) and someidentied
changes on the TSP are then linked to the specic changes at the
indivillustrative case study shows that the PluseMinus principle
application in the TSHIimprove heat recovery. The proposed
spreadsheet-based methodology combinesgraphical visualisation, as
well as the numerical precision.
2014 Elsevier LtdAvailable online 28 April 2014process
modication options to be selected in order to maximise energy
savings in TSHI. The Total SiteProle (TSP) is divided into three
regions: (a) the region above the horizontal overlap between the
SiteReceived 4 January 2014Accepted 18 April
2014http://dx.doi.org/10.1016/j.applthermaleng.2014.04.041359-4311/
2014 Elsevier Ltd. All rights reserved.total site heat integration
(TSHI). The PluseMinus principle has been adapted to enable the
benecialmodication options. Development of heuristic to set
pri-ority of streams.
Targeting process modications atselected process sections to
improveTSHI heat recovery.
a r t i c l e i n f o
Article history:a b s t r a c t
This paper extends the scope of the Pinch Analysis for process
modications of individual processes toZainuddin Abdul Manan a
a Process Systems Engineering Centre (PROSPECbCentre for Process
Integration and IntensicatTechnology, University of Pannonia,
Egyetem u.
h i g h l i g h t s
Extension of the Pinch Analysis forprocess modications from
singleprocesses to TSHI.aximise energy savings in total site
heat
lemes b, Sharifah Radah Wan Alwi a,*,
y of Chemical Engineering, Universiti Teknologi Malaysia, 81310
UTM Johor Bahru, Johor, MalaysiaI2, Research Institute of Chemical
and Process Engineering e M}UKKI, Faculty of Information00 Veszpr
_em, Hungary
g r a p h i c a l a b s t r a c tjournal homepage: www.el4le at
ScienceDirect
l Engineering
ier .com/locate/apthermeng
-
al ELinnhoff [2]. Klemes et al. [3] established the Total Site
Proles(TSPs) to represent the thermal prole of TS and the Site
UtilityComposite Curves (SCC), which consists of Hot and Cold
utilityComposite Curves. The Total Site Pinch is where the two
utility CCoverlap horizontally. The Utility Grand Composite Curve
(UGCC)provides a visual illustration of the external utility
requirements.These graphical tools are used to set targets for
steam usage andgeneration by the site processes, the steam required
to be producedby the boilers, and shaftwork produced by the steam
turbines. Heatrecovery depends also on the number of steam levels.
Even thoughmore steam levels may result in more heat recovery, it
has to bebalanced against the increased capital cost and higher
complexityof the utility system [4]. The TSHI has been enhanced to
LocallyIntegrated Energy System (LIES) which also integrates
residential,business, service and even agriculture areas apart from
the indus-trial site [5]. Liew et al. [6] extended their numerical
TSHI meth-odology to consider the operational changes within a
centralisedutility system planning. A brief review of the
development of TSHIover the last 40 years can be found in the
recent review paper byKlemes and Kravanja [7].
The energy targets from the TSHI analysis are dependent on
theoperating conditions of the existing site. A change in the
processoperating conditions can alter the TSP and change the energy
tar-gets. The exibility to change the process conditions can
beexploited to further improve the heat recovery. In a study to
inte-grate new CO2 capture and storage (CCS) plants into existing
coal-red power stations, Harkin et al. [8] showed that energy
penaltyassociated with CCS can be reduced when TSHI is applied.
Theirstudy also identied that the pre-drying of coal could
furtherimprove the utility targets. Process modication strategies
toimprove the Heat Integration (HI) of single processes by
exploitingthe shape of Composite Curves (CCs) and the Grand
CompositeCurve (GCC) were developed by Linnhoff and Vredeveld [9].
Therules for process modications using the CC and GCC include
thePluseMinus principle, keep hot stream hot (KHSH) and keep
coldstream cold (KCSC) as well as the appropriate placement
principle.Exploiting and optimising the process soft data, use of
the appro-priate minimum approach temperature (DTmin) and
suitableapplication of insulations above and below Pinch can be
effective inimproving heat recovery. Lee et al. [10] has shown that
knowledgeof pinch can be used to optimise the location of pipe
insulation toreduce utility targets. Applications of these rules
have beendescribed earlier by Smith [11], later by Kemp [12], and
recently inextended ways by Klemes et al. [13].
The process modication strategies such as the
PluseMinusprinciple can be used together with the TSP to identify
the scopefor process modications to improve TSHI. Hackl et al.
[14]showed that the gap between the TSP and SCC can be used
toidentify the potential utility systems changes that can reduce
theoverall site heating and cooling requirements in a
Side-WideProcess Integration study of a chemical cluster in
Sweden.Replacing the low pressure steam (LPS) heating with hot
water(generated from the Site Source) reduced the gap between
TSPand SCC, changed the shape of the SCC and shifted the TS
Pinch.This increases the overlap of the Site Source and Sink Proles
andincreases the heat recovery. Nemet et al. [15] developed
thestrategies to plan the extension of an existing site by using
thePluseMinus principle on the TS. The PluseMinus
principle,together with the Process Utility Matrix (which lists the
utilitiesconsumptions of the various processes), were used to
evaluate themerits of integrating a new process to an existing TS.
Only optionswhich are benecial, i.e. those resulting in improved
overall heatrecovery will be selected for integration. In this
study, the PluseMinus principle of process modications is used to
identify pro-
K.H. Chew et al. / Applied Therm732cess changes that can further
reduce the TS utility targets. This isessentially done by
manipulating the shape of the Site Source andSink Proles.
2. Application of pinch strategies for process modications ofa
single process to TS
Knowledge of Pinch location is crucial when exploring theprocess
modication opportunities for single processes. The TotalSite (TS)
Pinch location can provide similarly a guide during
processmodications to reduce the overall energy consumption of the
site.The TS Pinch limits the amount of heat that can be recovered
fromthe Site Source and Sink. According to Klemes et al. [3], the
TS Pinchis the point where the cold utility CC rst intersects with
the SiteSink Prole (SSiP) or when the hot utility CC rst intersects
the SiteSource Prole (SSoP). TS Pinch occurs where the horizontal
overlapbetween the Utility Composite Curves is maximised. The TS
Pinchoccurs at the utility temperatures, and spans between the
tem-peratures of two successive utility levels as shown in Fig. 1.
Anassessment of the impact of process modications of a single
pro-cess on the TS as given in Table 1 shows that Heat
Integrationstrategies applied for the single process can be
directly extended toTS. These include the exploitation of soft
data, the appropriate useof minimum temperature of approach
(considering the uids inservice and the type of heat exchanger
used) and the suitable use ofinsulation (e.g. apply insulation only
on hot streams above pinch,etc.). Adaptations of the PluseMinus
Principles to TS are describedin the subsequent sections.
3. The PluseMinus principles for TS
A TS comprising several units (e.g. chemical processing
plants,business and commercial units) typically uses steam as
theworkinguid. For an existing steam system of a TS, little can be
done tooptimise the steam utility levels to improve heat recovery.
Theutility targets can be reduced by exploring the potential for
processmodications in the TS context. The TSP can be a powerful
tool toevaluate the potential for further heat recovery improvement
evenfor a TS. The Site Source Prole (SSoP) is analogous to the
HotComposite Curve and the Site Sink Prole (SSiP) is analogous to
theCold Composite Curve.
The TSP can be divided into three regions: (a) above the SSoP
andSSiP horizontal overlap, (b) at the SSoP and SSiP horizontal
overlapand, (c) below the SSoP and SSiP horizontal overlap. Note
that theoverlap between the SSoP and SSiP spans between the highest
(TPH)and lowest (TPL) process pinch temperatures on the site, as
shownin Fig. 1. Above and below the SSoP and SSiP horizontal
overlapregion, the location of TS Pinch has no implication on TS
heat re-covery. Above the horizontal overlap region, the heating
require-ment can be reduced by decreasing the duty of the cold
streams.Below the horizontal overlap region, the cooling
requirement canbe reduced by decreasing the duty of the hot
streams.
Within the SSoP and SSiP horizontal overlap region, TS
Pinchaffects heat recovery in the same way the Pinch does for a
singleprocess. For the SSoP, the TS Pinch can also be taken as the
tem-perature equal to the higher steam level of the TS Pinch. Above
thistemperature, increasing the duty of the SSoP () reduces the
hotutility. Below this temperature, decreasing the duty of SSoP
()reduces the cold utility. For the SSiP, the SP can be taken at
thetemperature equal to the lower steam level of the TS Pinch
(SP).Above this temperature, decreasing the SSiP () reduces the
hotutility. Below this temperature, increasing the duty of SSiP
reducesthe cold utility.
The UGCC provides a quick visual impression of the
externalutility requirements, and can be used to prioritise the
changes on
ngineering 78 (2015) 731e739the TSP segments in order to reduce
utilities. Fig. 1 illustrates the
-
and cold CC to set the guideline on howheat recovery can be
further improvedwith respect to pinch location [9].Above Pinch,
heating requirement canbe reduced by increasing the duty of
hotstreams or decreasing the duty of coldstream. Below Pinch,
cooling
Site Pinchhorizontal
al ELPSoverlap region
Belowhorizontal
overlap region
TPLHot utility, QHVHPS
T
HPS
MPSSSoP & SSiP
Abovehorizontal
overlap region TPH
K.H. Chew et al. / Applied Thermapplication of the PluseMinus
principle on a TS which uses fourutility levels, i.e. very high
pressure steam (VHPS), high pressuresteam (HPS), medium pressure
steam (MPS) and low pressuresteam (LPS). The results of the
application is summarised in Table 2.
4. Methodology
The suggested algorithm to target process modications forTSHI is
described below (see also Fig. 2).
(a) Data extraction: Extract the hot and cold stream data, i.e.
thesupply and target temperatures as well as the heat capacityof
the streams, from individual processes that would be
(a) Initial TSP and SCC
(b) Plus-Minus Principles
Cold utility, QcH
VHPST
H
HPS
MPS
LPS
Hot utility, QH
SSiP Pinch
SSoP Pinch
Cold utility, Qc
+
+
-
-
SSoP & SSiP horizontal
overlap region
Abovehorizontal
overlap region
Belowhorizontal
overlap region
TPH
TPL
(c) New TSP and SCC
SSoP & SSiPhorizontal
overlap region
Abovehorizontal
overlap region
Belowhorizontal
overlap region
New Site Pinch
Hot utility, QHVHP
T
H
HPS
MP
LP
Cold utility, Qc
TPH
TPL
Fig. 1. Analogy of the PluseMinus to a TS (using steam as the
working uid).Table 1Application of Pinch strategies for process
modications on TS.
Pinch strategies for singleprocess
Application on Total Site
PluseMinus principle For single process, the PluseMinusprinciple
is used together with the hot
ngineering 78 (2015) 731e739 733integrated in the TS. In
addition, obtain the existing utilitytemperatures. An example of
the data required for theanalysis is given in Table 3.
(b) TS analysis:
i. Prepare the individual process Problem Table Algorithm (PTA)e
a modied version of PTA [16] by listing the heat capacity (CP)
requirement can be reduced bydecreasing the duty of hot streams
orincreasing the duty of cold streams.This principle can be applied
on TS withsome adaptation (see Section 3). TSPand SP as dened by
Klemes et al. [3]are used.
KHSH, KCSC This describes how the change instream duty can be
effected by thechange in stream mass heat capacity soas to reduce
utility targets. This isencompassed within the
PluseMinusprinciple.
Appropriate placementprinciple
For single process this is used withprocess GCC to explore the
integrationof key equipment for e.g. distillationcolumns,
evaporators, heat pumps, etc.in order to reduce the
utilityrequirements. Detail descriptions ofthis principle and other
examples canbe found in Smith [11], Kemp [12] andKlemes et al.
[4]
Exploiting and optimising ofprocess soft data
Such operation exibility has beensuccessfully exploited to
reduce utilitytargets for single process [12].Walmsley et al. [18]
demonstrated thesuccessful optimisation of soft data inimproving
the heat recovery of aindustrial milk powder plant.In the context
of TS, application of thisprinciple will be at the
individualprocess level. For e.g. once thelocation of the
favourable processmodication is targeted using the PluseMinus
principle and TSP, the specicprocess modication can be broughtabout
by the use of this principle.
Appropriate use of DTmin Reducing DTmin increases the
overlapbetween the hot and cold CC hencereduces the cooling and
heatingutilities. Innovation in heatenhancement and type of
heatexchanger that allow smaller DTmin canfurther improve heat
recovery.Application of this can simply beextended to TS. Note that
the TSHImethodology has been extended toallow specication of
individual DTminfor each process and between processand utilities
by Varbarnov et al. [19]
Suitable use of insulation This is used when heat loss to
theenvironment is signicant compared tothe process heating
duties.Application of this can simply beextended to TS.
-
contribution of individual streams and total CP contributions
ofeach process at various temperature levels. In generating the
pro-cess PTA, the temperatures are shifted by half of the DTmin
(be-tween process and process) to ensure that the
minimumtemperature difference between hot and cold streams are
main-tained. The shifted temperature, T*:
For hot stream; T* T DTminprocesseprocess.2 (1)
For cold stream; T* T DTminprocesseprocess.2 (2)
ii. Prepare the TS PTA e an expanded version of TS PTA
[17]listing the heat capacity contribution of individual processes
forthe site source and the site sink. The utility usage and
generationare directly interpolated on the TS-PTA at the utility
temperatures.
shifted back to their original values, and then shifted again
byDTmin(between process and utility) to ensure that the minimum
tem-perature difference between process and utility is maintained.
Thedouble shifted temperature, T**:
For TS Sink; T** T DTminprocesseprocess.2
DTminprocesseutility(3)
For TS Source; T** T DTminprocesseprocess.2
DTminprocesseutility(4)
Table 3Stream data and utilities level for analysis.
Process Stream Temperature, C Mass CP Utilities Temperature,
CSupply Target kW/C Supply Target
A Hot H1 230 55 200.0 Hot VHPS 300 eH2 155 80 733.3 HPS 260
e
Cold C1 120 270 296.8 MPS 200 eC2 70 150 750.0 LPS 150 e
B Hot H1 240 200 800.0 Cold CW 32 40H2 230 70 187.5H3 150 60
444.4 DTmin between process and
process used is 20 CCold C1 50 210 500.0C2 90 250 312.5
C Hot H1 250 90 275.0 DTmin between process andutilities used is
15 CH2 220 80 428.6
Cold C1 150 260 390.9
Table 2Application of the PluseMinus principles to a Total Site
(Using steam as the workinguid).
SSoP SSiP
Above SSoP and SSiP overlap areaY duty () QH Y
SSoP and SSiP overlap areaAbove SSoP Pinch, QH Y, limited
by Site PinchAbove SSiP Pinch, QH Y, limited
by Site Pinch[ duty () Y duty ()Below SSoP Pinch, QC Y,
limited
by Site PinchBelow SSiP Pinch, QC Y, limited
by Site PinchY duty () [ duty ()
Below SSoP and SSiP overlap areaY duty () QC Y
K.H. Chew et al. / Applied Thermal Engineering 78 (2015)
731e739734In generating the TS-PTA, the shifted temperatures, T*
are rstFig. 2. Algorithm to target prociii. Prepare the TSP, SCC
(for hot and cold utilities) and the UGCC.ess modications for
TSHI.
-
(f) Similarly, the contributing streams corresponding to the
TSP
(h) Asspinoth
(i) Selreson
5.3%. VHPS consumption reduces by 1.5 MW while MPS con-
al E(j) Reconstruct TSP, SCC and UGCC using the new stream
data.(k) Check if the resulting heat recovery from the TSP changes
is
limited by Site Pinch as in Table 2. If yes, go back to step
(h). Ifno, the option is acceptable.
5. Illustrative example
The TS consists of processes A, B and C. Table 3 gives the
streamdata and utilities available on-site. Table 4 shows the
extended PTAfor each process listing the CPs of the contributing
streams. Themodied TS-PTA for Site Sink and Source is given in
Tables 5 and 6.From the TS-PTA (Tables 5 and 6) and TSP (Fig. 3),
the corre-sponding Site Source and Site Sink enthalpies (hH1, hH2,
hH3, hC1,hC2, hC3 and hC4) at each utilities level (VHPS, HPS, MPS
and LPS) canbe directly interpolated and the utility consumptions
and genera-tions can be determined as follows:Utilityreduce QH (hot
utility), reduce the duty of the coldstreams that lie above the
Process Pinch. For cold streamsthat straddle across the Process
Pinch, those streams thathave larger proportion of their
temperatures above theProcess Pinch should be given the
priority.Heuristic #3: Within the horizontal overlap region,
toreduce Qc (cold utility), increase the duty of hot streamsthat
lie above the Process Pinch. For hot streams thatstraddle across
the Process Pinch temperatures, thosestreams that have larger
proportion of their temperaturesbelow the Process Pinch should be
given the priority.Heuristic #4: Below the horizontal overlap
region, hotstreams with temperatures lower than TPL should
beprioritised for process modications. For hot streams thatstraddle
across TPH, those streams that have larger pro-portion of their
temperatures below TPL should be giventhe priority.Heuristic #5:
Stream with larger CP should be prioritisedfor process
modications.ess the scope of feasible process modications, using
thech techniques for single process. Repeat steps (e)e(h) forer
utilities.ect only the process modication options that wouldult in
a net reduction in hot and cold utilities consumptionthe TS.segment
and the specic process can be traced back from theprocess PTA.
(g) The priority of the streams to be investigated for
processmodications can be set based on the heuristics:
Heuristic #1: Above the horizontal overlap region, coldstreams
which lie above TPH should be prioritised forprocess modications.
For cold streams that straddleacross TPH, those streams that have
larger proportion oftheir temperatures above TPH should be given
the priority.Heuristic #2: Within the horizontal overlap region,
to(c) From the UGCC, prioritise the utilities to be targeted.(d)
Starting with the rst utility, identify the corresponding
segment on the TSP using the PluseMinus principle.(e) From the
TSP segment identied, trace back the contributing
process or processes from the TS-PTA at the
correspondingtemperature intervals. This can be done easily as the
TS-PTAlists the contribution from each process by the
temperatureintervals of TSP. If more than one process is involved,
there is achoice of whether to eliminate some or to include all
forfurther evaluation. The priority of processes to be targeted
canbe set by examining the process heat capacity on the TS PTA.
K.H. Chew et al. / Applied Thermconsumption by the Sink:that
stream C2 of Process B has a target temperature reduction of5 C.
The targeted utility, HPS consumption reduces by 1.6 MW orVHPS hC1
hC2 (5)
HPS hC2 hC3 (6)
MPS hC3 hC4 (7)
LPS hC4 (8)Utility generation by the Source:
MPS hH1 (9)
LPS hH1 hH2 (10)
CW hH2 hH3 (11)TSP represents the overall proles of the heat
sources and sinks
on the TS. The SP location is obtained by plotting the SCC (Fig.
4).The net utility requirements are summarised in the UGCC (Fig.
5)and Table 8. The overlap of the Site Sink and Site Source
spansbetween 105 C (TPL) and 205 C (TPH). The SSoP only
extendsslightly above the MPS temperature of 200 C with very little
MPSgeneration. The 0.33 MWof excess LPS that cannot be used is to
berejected to CW.
The UGCC sets the priority for utilities to be targeted
forreduction. The larger enthalpy and more costly utility should be
setas the priority to be reduced rst. For this example, let x be
the baseunit cost per MWof utility. Let the cost of VHPS, HPS, MPS,
LPS andCW equals to 2.5x, 2x, 1.5x, x and 0.2x. From Tables 5 and
6, the netutilities requirements are VHPS 14.8 MW, HPS 30.0 MW,MPS
32.5 MW, LPS 0, CW 95.9 MW. The corresponding utilityrequirements
in terms of x, i.e. utility requirement (MW)multiplieswith utility
unit cost per MW, are VHPS 37.1x, HPS 59.9x,MPS 51.1x, and CW
19.2x. The priorities are (1) HPS, (2) MPS, (3)VHPS and (4) CW.
The application of PluseMinus Principles is shown in Fig. 6
andsummarised in Table 7. Segment A2 above the overlap region
(i.e.between 205 C and 260 C) has the rst priority, process
modi-cations that reduce the heating requirements would directly
reducethe TS HPS usage. Segment B within the overlap region
(between150 C and 205 C) has the second priority. Process
modicationsreducing the duty of Segment B would reduce MPS usage.
SegmentA1 (above 260 C) has the third priority. Process
modicationsreducing the duty of this segment would directly reduce
the VHPSrequirement. Segment C can be ignored since there is
alreadyexcess LPS. Segments D1 and D2 have the lowest priority.
Reducingthe duty of these segments could reduce the CW
requirement.
For Segment A2: from the Site Sink TS-PTA (Table 5), Process
Bhas slightly larger CP and should be targeted rst compared
toProcess A [Heuristic #5]. From Process B PTA (Table 4), the
onlycontributing stream is C2. The heat duty can be modied
bychanging the stream heat capacity (CP) and/or stream
temperature.Changing of CP is possible only when the stream mass ow
can bechanged since specic capacity is the physical attribute of a
stream.When a stream mass ow is not dictated by the
productionthroughput, such as that of a recycle stream or a reux,
the streamow can be optimised with the aim to maximise Heat
Integration.The stream temperature can be changed by exploiting the
exibilitythat exists in the operating conditions of the process.
For illustra-tion purposes, supposed process modications are
feasible such
ngineering 78 (2015) 731e739 735sumption reduces slightly by 0.5
MW. There is no change to the
-
Table 4Process PTA (listing streams CP).
Streams CP Cascade DH MW 1st pass
T* DT H1 H2 H3 C1 C2PCP DH DH DH
C C kW/C kW/C kW/C kW/C kW/C kWC MW MW MW
PROCESS A280 0 38.58220 60 296.8 296.8 17.81 17.81 20.78160 60
200.0 296.8 96.8 5.81 23.61 14.97145 15 200.0 296.8 750.0 846.8
12.70 36.31 2.27125 20 200.0 733.3 296.8 750.0 113.4 2.27 38.58
0.0080 45 200.0 733.3 750.0 183.3 8.25 30.33 8.2570 10 200.0 733.3
933.3 9.33 21.00 17.5845 25 200.0 200.0 5.00 16.00 22.58
PROCESS B260 0 37.72230 30 312.5 312.5 9.38 9.38 28.35220 10
800.0 312.5 487.5 4.88 4.50 33.22190 30 800.0 187.5 500.0 312.5
175.0 5.25 0.75 38.47140 50 187.5 500.0 312.5 625.0 31.25 30.50
7.22100 40 187.5 444.4 500.0 312.5 180.6 7.22 37.72 0.0060 40 187.5
444.4 500.0 131.9 5.28 32.44 5.2850 10 444.4 444.4 4.44 28.00
9.72
K.H. Chew et al. / Applied Thermal Engineering 78 (2015)
731e739736excess LPS generation and CW requirement. The same
procedure
PROCESS C270240 30 390.9210 30 275.0 390.9160 50 275.0 428.6
390.980 80 275.0 428.670 10 428.6may be applied to Process A to
further reduce the utilityconsumptions.
At the overlap region, changes can be made on the SSiP or SSoPor
both as shown in Fig. 6. The effects of changes are not as
explicitas with the regions above or below the overlap due to the
in-teractions between the sink and the source in heat integration.
Fore.g., to modify Segment D1 (i.e. the SSoP): from site source
TS-PTA,the only contributing process is Process C. From Process C
PTA, twostreams lie at Segment D1, i.e. H1 and H2. H2 is selected
as it lies
Table 5TS-PTA for Sink (listing contributing processes CP).below
the Process Pinch [Heuristic #3] and its CP is larger than that
0 15.20390.9 11.73 11.73 3.48115.9 3.48 15.20 0.00312.7 15.63
0.43 15.63703.6 56.29 56.71 71.92428.6 4.29 61.00 76.20of H1
[Heuristic #5]. Supposed process modications allow thestream H2 CP
to be reduced by 10%. The change only marginallyreduces the VHPS,
HPS and MPS consumptions, between 0.7 and2.7%. This is expected
since Segment D1 has the lowest priority (seeTable 7). The excess
LPS reduces by about 20% (1.3 MW) as expectedof a targeted utility.
Applying the same procedure on Segment B(i.e. the SSiP): supposed
the CP of the selected stream C1 (Process B)can be reduced by 5%
and its target temperature can be lowered by5 C. The targeted
utility consumption, MPS, reduces by 14%
-
Table 6TS-PTA for Source (listing contributing processes
CP).
K.H. Chew et al. / Applied Thermal Engineering 78 (2015) 731e739
737200
250
300
350
SSiP
SSoP
VHPS
T** C(4.5 MW) while the VHPS and HPS consumptions remain
un-changed. However there is an 18% increase in excess LPS (1.2
MW)and subsequently, 19% (18.5 MW) increase in CW requirement.
Below the overlap region, at Segment D2: from site source
TS-PTA, Process C is the larger CP contributor compared to Process
Aand B therefore selected for further investigation. From Process
CPTA, streams H1 and H2 are good candidates for exploring
potentialchange in stream duty as both streams lie below the
Process Pinch
1.6 MW (10.8%) VHPS, 3.9 MW (12.0%) MPS and 7.1 MW (7.4%)
CWconsumptions. The HPS consumption increased marginally by
0
50
100
150
-120 -100 -80 -60 -40 -20 0 20 40 60 80 100
HPS
MPS
LPS
CWhC1hC2hC3hC4hH1hH2hH3
Fig. 3. Total Site Prole (TSP).
Fig. 4. Site utilities composite curves: CUCC, HUCC.0.4MW
(1.3%). The TSP shows that the lowgrade heat is not neededby the
processes on site. The cooling duty can be reduced either
bymodifying the existing process design to exploit this low
gradeheat, or by exporting it to other users in the neighbouring
sites.
6. Conclusion
A systematic TSHI methodology to identify and target the
po-tential process modications and further increase energy
conser-vation at Total Sites has been developed. The case
studydemonstrates that the PluseMinus Principles developed for
asingle process can be successfully adopted and applied to a TS.
TheTSP, SCC and UGCC can provide useful insights for the
plant[Heuristic #4]. H1 is selected since H2 has already been
modiedwith changes at Segment D1. Supposed process modication
isfeasible and the CP of H1 can be reduced by 5% and its
targettemperature can be increased by 5 C. The reduction in CWusage
isminor at 1.5 MW or 3.2%. The HPS usage increases marginally by0.1
MW (0.5%). Excess LPS reduces slightly by 4.1 MW (4.3%).
A summary of the results is given in Table 8. The
combinedchanges of Segments A2, D1, B and D2 resulted in reduction
ofdesigner to identify where, in terms of which temperature
in-terval, and which streams within the entire TS to focus the
process
Fig. 5. Utility Grand Composite Curve (UGCC).
-
modication efforts to improve the site HI. The implementation
ofthe PluseMinus Principles on TSP identies the potential
changesthat would increase the energy conservation. The
proposedchanges to the selected streams should be assessed from
feasibility,practicality and economic perspectives. This requires
the expertiseof the plant designer/manager to explore potential
feasible andpractical process modications to achieve the targeted
changesidentied. The selected and potentially acceptable process
modi-cation options can be conveniently merged with potential
retrotproject (e.g. to increase plant capacity) considered for the
TotalSite.
The proposed methodology can benet from the
visualisationadvantages of the graphical method [4], and from the
precision ofthe numerical method [17]. The TSP, SCC and UGCC can be
easilygenerated using the chart function e.g. in the Excel
spreadsheet setup for the process PTA and TS-PTA analysis. The
methodologyprovides an uncomplicated and relatively fast way of
assessing theimpacts of proposed process modications on the TS hot
and/orcold utilities without the need for a time consuming detailed
pro-cess simulation efforts.
Acknowledgements
The authors gratefully acknowledge the nancial supports fromthe
Universiti Teknologi Malaysia (UTM) Research University Grantunder
Vote No. Q.J130000.2509.07H35 and the EC FP7
projectENER/FP7/296003/EFENIS Efcient Energy Integrated Solutions
forManufacturing Industries e EFENIS. The support from the
Hun-garian project Trsadalmi Megjuls Operatv Program TMOP
-4.2.2.A-11/1/KONV-2012-0072 - Design and optimisation
ofmodernisation and efcient operation of energy supply and
uti-lisation systems using renewable energy sources and ICTs
signi-cantly contributed to the completion of this analysis.
Nomenclature
CP heat capacity owrate, MW/ChC corresponding Site Sink
enthalpies at utilities level, MWhH corresponding Site Source
enthalpies at utilities level,
MWQ cooling utilities heat owrate, MW
Table 7TSP analysis for application of PluseMinus principles
(Case Study) (Refer to Fig. 6).
Segment Temperature Location Utility Usage/G
SSiPA1 T > 260 C Above overlap region VHPS
A2 260 > T > 205 C Above overlap region HPS
B 205 > T > 150 C At overlap region MPS
C 150 > T > 105 C At overlap region LPS
SSoPD1 205 > T > 105 C At overlap region LPS
D2 T < 105 C Below overlap region CW
Cs
1321M
he db values represent an increase in utility consumption
compared to base case.c Excess LPS has be accounted for in the
increase in CW consumption.
K.H. Chew et al. / Applied Thermal E738Table 8Summary of results
(case study).
Utility level Utility consumption, MW
Base study Changesegment A2
Changesegment D1
VHPS 14.8 13.3 14.7HPS 30.0 28.4 29.2MPS 32.5 32.0 31.9LPS 6.5a
6.5 5.2CWc 95.9 95.9 90.2Targeted reduction as per Table 7 HPS
LPS
a values represent excess LPS generation. The CW consumption has
included tFig. 6. TSP with PluseMinus principles.eneration G
Principle Priority Potential process modications
Y duty () QH Y 3 Y CP and/orY target temperature
Y duty () QH Y 1 Y CP and/orY target temperature
Y duty () QH Y 2 Y CP and/orY target temperature
[ duty () QC Y e None, since there isalready excess LPS
Y duty () QC Y 4 Y CP and/or[ target temperature
Y duty () QC Y 4 Y CP and/or[ target temperature
Overall saving
hangeegment B
Changesegment D2
Combined changeof A2, B, D1 & D2
MW %
4.8 14.8 13.3 1.6 10.80.0 30.4 30.4 0.4b 1.48.0 32.6 28.6 4.0
12.17.7 5.8 4.5 ec e14.1 91.8 88.8 7.0 7.4PS CW
issipated of this excess heat.
ngineering 78 (2015) 731e739cQh heating utilities heat owrate,
MW
-
DH process heat owrate, MWDTmin minimum approach temperature,
CDTmin (processeprocess) minimum approach temperature between
process and process, CDTmin (processeutility) minimum approach
temperature between
process and utility, CT* shifted temperature for process PTAT**
double shifted temperature for TSP plot and TS-PTA, CTPH the
highest Process Pinch temperature on site, CTPL the lowest Process
Pinch temperature on site, C
AbbreviationsCC Composite CurveCCS Carbon capture and Carbon
storageCUCC Cold Utility Composite CurveGCC Grand Composite CurveEU
European UnionHC hydrocarbonsHI Heat IntegrationHPS high pressure
steam, bargHUCC Hot Utility Composite CurveKHSH Keep Hot Stream
HotKCSC Keep Cold Stream ColdLPS low pressure steam, barg
Control), (accessed 14.05.13).
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K.H. Chew et al. / Applied Thermal Engineering 78 (2015) 731e739
739MPS medium pressure steam, bargPTA Problem Table AnalysisSCC
Site Utility Composite CurvesSSiP Site Sink ProleSSoP Site Source
ProleTS Total SiteTS-PTA Total Site Problem Table AnalysisTSHI
Total Site Heat IntegrationTSP Total Site ProleUGCC Utility Grand
Composite CurveVHPS very high pressure steam, barg
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Process modifications to maximise energy savings in total site
heat integration1. Introduction2. Application of pinch strategies
for process modifications of a single process to TS3. The PlusMinus
principles for TS4. Methodology5. Illustrative example6.
ConclusionAcknowledgementsNomenclatureReferences