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Conceptual Design Method for Energy Retrofit of Waste Gas-to-Energy Units

Abstract

Many industrial waste gasses, especially from chemical and petrochemical processes, contain combustible substances enabling their utilization as a promising energy source. Thermal oxidation represents a suitable and proven technology, which is, however, very energy intensive in terms of external fuel demand dependent on exhaust heat recovery efficiency. This paper presents a systematic method developed for the Energy Retrofit of industrial units for thermal oxidation of waste gasses (waste gas-to-energy units) in order to improve the units´ waste heat recovery and thus to reduce the external energy demand. Thisresults in the reduction of operational costs and emissions and improves waste gas energy utilization.The method procedure is further applied to Energy Retrofit of a specific waste gas to energy unit, where the fuel saving of over 30% was achieved by the proposed conceptual modifications with a payback period of only 5.5 months. Finally, the developed method accuracy was successfully verified by the comparison with results of non-linear simulation.

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Conceptual Design Method for Energy Retrofit of Waste Gas-to-Energy Units

Author: Freisleben, Vít; Jegla, Zdeněk
Publisher: SDEWES Centre
Year: 2022
DOI: 10.13044/j.sdewes.d9.0396
Source: https://dspace.vut.cz/bitstreams/6c804fec-9e83-44ed-a877-7042f6627305/download
Jou nal o Sus ainable De elopmen o Ene gy, Wa e and
En i onmen Sys ems
h p://www.sdewes.o g/jsdewes
Yea 2022, Volume 10, Issue 2, 100396
1
Jou nal o Sus ainable De elopmen
W a e and En i onmen , o E ne g y
Sy s ems
9257-1848ISSN
jsdewes/o g.sdewes.www://h�ps
O iginal Resea ch A icle
Concep ual Design Me hod o Ene gy Re o i o Was e
Gas- o-Ene gy Uni s
Ví F eisleben1, Zdeněk Jegla*2
1Ins i u e o P ocess Enginee ing, Facul y o Mechanical Enginee ing,
B no Uni e si y o Technology, Technická 2896/2, B no, Czechia
e-mail: Vi .F eisleben@ u b .cz
2Ins i u e o P ocess Enginee ing, Facul y o Mechanical Enginee ing,
B no Uni e si y o Technology, Technická 2896/2, B no, Czechia
e-mail: zdenek.jegla@ u .cz
Ci e as: F eisleben, V., Jegla, Z., Concep ual Design Me hod o Ene gy Re o i o Was e Gas o Ene gy Uni s, J.
sus ain. de . ene gy wa e en i on. sys ., 10(2), 1090396, 2022, DOI: h ps://doi.o g/10.13044/j.sdewes.d9.0396
ABSTRACT
Many indus ial was e gasses, especially om chemical and pe ochemical p ocesses,
con ain combus ible subs ances enabling hei u iliza ion as a p omising ene gy sou ce.
The mal oxida ion ep esen s a sui able and p o en echnology, which is, howe e , e y
ene gy in ensi e in e ms o ex e nal uel demand dependen on exhaus hea eco e y
e iciency. This pape p esen s a sys ema ic me hod de eloped o he Ene gy Re o i o
indus ial uni s o he mal oxida ion o was e gases (was e gas- o-ene gy uni s) in o de
o imp o e he uni s´ was e hea eco e y and hus o educe he ex e nal ene gy demand.
This esul s in he educ ion o ope a ional cos s and emissions and imp o es was e gas
ene gy u iliza ion. The me hod p ocedu e is u he applied o Ene gy Re o i o a
speci ic was e gas- o-ene gy uni , whe e he uel sa ing o o e 30% was achie ed by he
p oposed concep ual modi ica ions wi h a payback pe iod o only 5.5 mon hs. Finally,
he de eloped me hod accu acy was success ully e i ied by compa ison wi h esul s o
non-linea simula ion.
KEYWORDS
The mal oxida ion, Shi ing Flue Gas Line me hod, was e gas- o-ene gy uni , Ene gy Re o i ,
uel sa ing, VOC, CO.
INTRODUCTION
Many indus ial p ocesses gene a e was e gases. The composi ion o was e gas (WG)
is dependen on many aspec s (such as he ype o p oduc p oduced in a p ocess plan ,
used echnology, e c.). Howe e , i usually con ains ha m ul subs ances, he e o e an
app op ia e cleaning echnology mus be employed o p e en he emissions o he
en i onmen . Fo example, he WGs p oduced in chemical and pe ochemical plan s
o en con ain Vola ile O ganic Compounds (VOC) o ca bon monoxide (CO), which a e
ha m ul o human heal h and he en i onmen . The a ious p oduc ion p ocesses, such as
pain p oduc ion, oil e ine y, o ganic acid p oduc ion and o he s, gene a e ai pollu ed
wi h some amoun o VOC and/o CO. Fu he , a huge amoun o he ai con amina ed
wi h VOC is gene a ed in p in ing shops, especially in he au omo i e indus y. This
pollu ed ai (as an indus ial WG) mus be ea ed be o e i s discha ge o he en i onmen .
To con ol he VOC and CO emissions con ained in WGs a small concen a ion, he
he mal oxida ion echnology has been ound an e ec i e and eliable aba emen
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echnique which commonly eaches he pollu an emo al e iciency o o e 99%. I is
applied o p ocessing la ge quan i ies o WG wi h a low concen a ion o combus ible
subs ances (VOC/CO). The pollu an he mal oxida ion (decomposi ion) is in p inciple a
con aminan lameless igni ion which esul s in a sudden empe a u e inc ease o
p ocessed was e gas and pollu an he mal decomposi ion o ca bon dioxide (CO2) and
wa e . The mal oxida ion akes place in a combus ion chambe (CC) a high empe a u es
commonly anging be ween 730–850°C wi h necessa y esidence ime while lue gas
(FG) is p oduced [1]. Main aining he p esc ibed empe a u es in he CC o he pollu an
igni ion equi es in ensi e ene gy demand p o ided by a supplemen al uel, which is
associa ed wi h high ope a ing cos s. In o de o imp o e he economic aspec o he
uni ´s ope a ion, he was e hea con ained in a gene a ed lue gas is ypically used o
ene gy pu poses (e.g., s eam gene a ion) and echnology pu poses (WG p ehea ing
be o e i s en e ing CC o educe he supplemen al uel demand) h ough se ies o
indi idual was e hea eco e y exchange s, i.e., h ough he Hea Reco e y Sys em
(HRS). Fu he , FG cleaning echnology ( il e s, abso be s, sc ubbe s…) could be
employed o emo e acid compounds, solid pa icles, o o he gaseous pollu an s i
necessa y. A ho ough e iew o he ai pollu ion con ol echniques including he
aba emen o VOC pollu ion was published by Schnelle e al.[1]. A simpli ied
echnological layou o such was e gas o ene gy (WG E) uni is illus a ed in Figu e 1.
Figu e 1. S anda d was e gas- o-ene gy uni
Due o he con inuous uel p ice ise, he e is an e o o imp o e he exis ing WG E
uni s in e ms o he uni s´ uel demand educ ion, i.e., pe o ming he Ene gy Re o i
(ER). As sugges ed abo e, uel sa ing in a s anda d WG E uni is achie ed by p ehea ing
he WG s eam be o e i s he mal p ocessing in he CC. As he WG p ehea ing is ealized
by u iliza ion o he was e hea con ained in he lue gas (i.e., h ough some hea
exchange s om HRS), he uel sa ings could be eached by he In eg a ion and
In ensi ica ion o he exis ing HRS (Klemeš e al. [2]).
A g ea e o has been pu in he las decades in o he esea ch o inc easing he
p ocess e iciency in o de o educe he ex e nal u ili y demand ( uel, wa e esou ces)
wi h espec o minimum in es men cos s. Mos cu en echniques and me hodologies
ocused on e ec i e e o i and in ensi ica ion o hea exchange ne wo k (HEN) a e
inspi ed by o a di ec ou come o he ini ial wo ks and p inciples o P ocess In eg a ion
da ed in he la e 1970s wi h he disco e y o he Pinch Analysis concep (Linnho and
Flowe [3]). Akpomiemie and Smi h [4], o example, b ough a no el me hodology o
he cos -e ec i e hea ans e enhancemen in he exis ing HEN. Fu he , Jiang e al. [5]
discussed a possibili y o he HEN e o i by eusing he exis ing hea exchange s. To
imp o e he quali y o HEN e o i design, Lai e al. [6] also conside ed he in luence o
physical dis ance be ween hea exchange s, p essu e d op and a ailable space o
equipmen . The ad an ages o an indus ial plan ´s e o i on a p ac ical example o an
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oil e ine y we e published by Ma on e al. [7].The comp ehensi e summa y o
adi ional and mode n me hods o HEN e o i was published by Klemeš e al. [8].
The P ocess In eg a ion is no limi ed only o he opic o hea exchange in HENs.
The mal ene gy con ained in he p ocess s eams is only a pa o he o al ene gy con en .
P essu e le els o he p ocess s eams, o example, e lec he necessi y o mechanical
wo k inpu , i.e., he pumping powe , which esul s in conside able elec ici y demand.
Indus ial p ocesses can be designed o e o i ed wi h espec o minimiza ion o bo h,
he hea du y and powe du y. Fu e al. [9] p esen ed he ad an ages o simul aneous wo k
and hea in eg a ion applying g aphical and ma hema ical app oaches. Deng e al. [10]
p oposed a me hod o u iliza ion o esidual p essu e ene gy based on Pinch Analysis. In
summa y, Yu e al. [11] published a e iew o wo k and hea exchange ne wo ks
(WHENs) e lec ing he cu en s a e-o - he-a .
The e a e a ailable many analy ical me hods enabling ene gy eco e y imp o emen
wi hin he s udied p ocess, bu he p ocess in eg a ion o la ge indus ial p ocesses
ep esen s a complex p oblem, whe e ma hema ical p og amming is applied. Wissocq e
al. [12], o example, p oposed a me hod based on a mixed-in ege -linea -p og amming
(MILP) model o an op imal design o la ge indus ial plan s enabling a sui able
echnology selec ion. Linea models´ applica ions equi e many simpli ica ions, which is
associa ed wi h a educ ion in he esul s´ accu acy. To o e come his sho coming,
Neme e al. [13] p oposed a wo-s age me hod inco po a ing he MILP model in
combina ion wi h a mixed-in ege -nonlinea -p og amming (MINLP) model.
Addi ionally, San os e al. [14] applied a MINLP model o pe o m he p ocess
op imiza ion in e ms o hea and wo k du y minimiza ion.
E en hough he p esen ed ad anced me hods can be used o educe he ene gy
demand o indus ial p ocesses, hei achie able ene gy e iciency is s ill
he modynamically limi ed. The e o e a eliable and sus ainable hea and powe sou ce is
necessa y. Nowadays a numbe o mode n echnologies a e a ailable o he e ec i e
p oduc ion o hea and powe . Fo example, he e is an e o o e o i he adi ional
ene gy p oduce s, such as coal- i ed plan s, by cos e ec i e co-gene a ion echnology
in oduc ion. The main goal is a deepe implemen a ion o enewable ene gy sou ces. The
po en ial o in oducing co-gene a ion blocks p oducing powe om biomass o he
exis ing coal- i ed plan was s udied by Kalina [15]. The mal and economic op imiza ion
o his echnological solu ion was pe o med by Tańczuk e al. [16]. Fu he mo e, he
ene gy sou ces could be used o gene a e powe and o p o ide hea ing and cooling
simul aneously. Ka sa os e al. [17], o example, p oposed such a i-gene a ion sys em
based on municipal was e gasi ica ion.
As men ioned abo e, he e is a con inuous e o o implemen mo e enewable
ene gy sou ces (e.g., sola and wind ene gy) o he cu en ene gy sys em. Howe e ,
ene gy p oduc ion om hese sou ces is uns able, which can cause s abili y issues in he
powe g id. The powe g id capaci y o accep ance o a ious enewable ene gy sou ces
was s udied by Taseska-Gjo gie ska e al. [18]. Fu he , Mo el e al. [19] p oposed a
po en ial o powe g id capaci y inc ease by implemen a ion o ba e ies and exploi ing
he kine ic ene gy o wind u bines.
Va ious ypes o indus ial and municipal was es ep esen ano he signi ican ene gy
sou ces wi h g ea po en ial o co e a pa o hea and powe consump ion. Compa ed o
discussed sola and wind ene gy, an ad an age o indus ial plan s p ocessing was e is
hei ela i ely s able ene gy gene a ion. On he o he hand, he main disad an age is he
necessi y o supplemen al uel o he mal was e p ocessing. Howe e , in case o WG E
uni s, he amoun o supplemen al uel can be signi ican ly educed by imp o ing he
was e hea eco e y (as discussed abo e). The ER o WG E uni s can he e o e educe
ope a ional cos s due o he uel demand educ ion, while he ene gy p oduc ion (e.g.,
s eam p oduc ion, he mal oil hea ing, e c.) is main ained.
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Howe e , om he abo e desc ip ion o WG E uni s, i is ob ious ha he ER o he
WG E p ocess canno employ hese sophis ica ed HEN e o i s a egies since HRS o
WG E p ocess has subs an ially di e en speci ici y han he s anda d p ocess HEN,
especially ha HRS does no con ain any U ili y Pa h. E en hough some me hods a e
a ailable o an e icien e o i o HENs no con aining U ili y Pa h (such as Jegla and
F eisleben [20]), none o hese me hods can be applied o he case o WG E uni s, as hei
HRS does no allow c ea ing a new U ili y Pa h due o he absence o ho and cold u ili y.
So, o ER o WG E uni s, i is necessa y o apply some speci ic e o i app oaches
ocusing on he lue gas s eam as a was e hea sou ce and aking in o accoun he
speci ici y o he WG E p ocess. As no sui able app oaches a e cu en ly a ailable o he
ER o he WG E uni s, his esea ch wo k p esen s a decision making and e alua ing
me hod, which is called he Shi ing Flue Gas Line (SFGL) me hod, ha ep esen s a
concep ual design me hod o ER o WG E uni s. The SFGL me hod will be p esen ed in
de ail in his a icle. I is a me hod de eloped o he e o i o WG E uni s in o de o
educe hei ene gy demand, while high pollu an emo al e iciency is main ained.
An accu a e e alua ion o uel sa ings is ano he impo an aspec o he p ope ER o
WG E uni s. I could be pe o med by he p ocess non-linea simula ion using
comme cial so wa e. This ad anced sys em modelling migh howe e be a d awback in
e ms o acquisi ion cos s and also in e ms o applicabili y o WG E p ocess e o i
a ge ing, whe e concep ual modi ica ions enabling he desi ed ene gy sa ings should be
p oposed. The e o e, he non-linea simula ion does no ha e o be necessa ily
con enien du ing he a ge ing and concep ual design s age.
F eisleben and Jegla [21] p esen ed a simple and ai ly accu a e me hod o calcula e
he uel sa ings o uni s o was e he mal p ocessing which does no equi e an ad anced
non-linea sys em modelling. This analy ical me hod is based only on he ini ial
empe a u e o he supplemen al uel/oxidize (Tini ), he Theo e ical Flame Tempe a u e
(TTFT), he uel Lowe Hea ing Value (LHV), and he lue gas empe a u e (TCC)
p esc ibed o su icien pollu an emo al (see Figu e 1). This calcula ion p ocedu e
was applied in he de eloped SFGL me hod p esen ed in his pape .
I should be emphasized ha he pu pose o he de eloped me hod is o enable ai ly
accu a e WG E uni s modelling and a speci ic ER e alua ion and no ha o inding an
op imal solu ion o ER. I is an analy ical app oach, which does no equi e in oduc ion
o ad anced ma hema ical models and op imiza ion app oach p esen ed abo e.
The de eloped SFGL me hod is desc ibed in he pape and u he p ac ically
in oduced by i s applica ion o a case s udy o a speci ic WG E uni ´s Ene gy Re o i .
The ob ained esul s a e hen compa ed o he non-linea simula ion o e i y he
accu acy o he de eloped me hod. The non-linea simula ion was ca ied ou in so wa e
CHEMCAD (in he la es e sion CHEMCAD 7) om Chems a ions Inc. [22] in
combina ion wi h so wa e Xchange Sui e® om Hea T ans e Resea ch Inc. (HTRI)
[23].
METHODS
As men ioned in he In oduc ion sec ion, he Shi ing Flue Gas Line (SFGL) me hod
is designed o ER o s anda d WG E uni s, i.e., he uni s o he mal p ocessing o was e
gases, speci ically was e gases con aining combus ible subs ances such as VOC o CO. I
bene i s om a ela i ely simple WG E uni echnological a angemen , whe e only a
small numbe o WG p ocessing and hea eco e y equipmen is employed. The me hod
enables es ima ing se e al key ea u es, such as he ollowing:
• Flue gas hea eco e y e iciency and Ene gy Re o i a ge ing. The amoun o he
lue gas was e hea which is cu en ly los is calcula ed and could be u ilized o
educe he supplemen al uel demand.
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• The concep ual design o he echnological modi ica ions ha a e equi ed o
achie e he desi ed ene gy sa ings.
• P ocess pa ame e s e-e alua ion, such as empe a u e p o iles and low a es o
p ocess s eams and basic pa ame e s o newly added o modi ied equipmen (as
e.g., hea exchange s´ hea loads).
The main ad an age o he de eloped me hod is i s p ac icabili y and simplici y. I is
based on a linea model o s udied p ocesses ha employs a limi ed numbe o WG
p ocessing and FG hea eco e y equipmen , so he me hod can be pe o med by simple
desk calcula ion.
The main d awback o he de eloped me hod is i s limi ed applicabili y. I canno be
e ec i ely applied o he wide ange o indus ial p ocesses as i was ailo -made o
WG E uni s using hei speci ic cha ac e is ics, which a e discussed u he in he
pape .The SFGL me hod is in p inciple a simple calcula ion p ocedu e suppo ed by
g aphical ep esen a ion o pe o med modi ica ions o p omo e he designe ’s
in e ac i i y when pe o ming he ER.
The key equipmen is an indus ial u nace whe e he pollu an he mal oxida ion akes
place. The SFGL me hod is he e o e inspi ed by analy ical app oaches o Fu nace Hea
In eg a ion, especially by lue gas line ep esen a ion (o lue gas empe a u e-en halpy
p o ile). The FG line was i s p oposed by Linnho and de Leu [24] and la e jus i ied
by S ehlík e al. [25]. Following hese wo ks, Jegla e al. [26] hen in oduced he speci ic
manipula ion wi h he FG p o ile o e icien u nace e o i . Inspi ed by his FG line
ope a ion, he SGFL me hod p esen ed he e is di ided in o se e al sys ema ic s ages,
which a e desc ibed below.
The s udied uni da a ex ac ion
The Ene gy Re o i p ocedu e s a s wi h a p epa a ion s age, whe e all key pa ame e s
o he exis ing uni a e ob ained. I consis s o se e al poin s:
• P ocess s eams and equipmen cha ac e is ics including he empe a u es,
p essu es, composi ion, a e age speci ic hea capaci ies and low a es o all
s eams p esen in he cu en WG E uni (FG, WG, s eam, ho wa e o ano he
ene gy medium…). Fu he , he cha ac e is ics o applied hea exchange s a e
ob ained, like ype, geome y, and hea loads.
• Supplemen al uel/oxidize cha ac e is ics, which includes a uel Lowe Hea ing
Value (LHV), Theo e ical Flame Tempe a u e (TTFT), ini ial empe a u e (Tini ),
and mixing a io (K) o oxidize / uel mix u e being combus ed in WG E uni ´s
u nace.
• D awing o he empe a u e-en halpy diag am con aining empe a u e-en halpy
p o iles (–he ea e e e ed o as jus p o iles) o all (ho and cold) p esen
s eams. An example o such a diag am, co esponding o he uni echnological
layou p esen ed in Figu e 1, is shown in Figu e 2.
WG E uni s con ain ypically only one ho s eam, which is he FG coming ou o CC.
In p ac ice, he spli ing o he FG s eam is no applied in WG E uni s due o he
addi ional in es men cos s o he FG duc and dec eased ope a ional eliabili y. The FG
p o ile (o FG line) is plo ed in an in e al be ween a CC ou le empe a u e (TCC) and a
s ack empe a u e (Ts ack). This in e al ep esen s he amoun o hea , which is u ilized in
he exis ing uni .The FG line is hen linea ly ex apola ed o he dew poin empe a u e
(TDP), whe e he condensa ion is expec ed o occu .
The in e al be ween Ts ack and TDP ep esen s an app oxima e alue o he amoun o
hea wi h a po en ial o be u ilized bu is cu en ly los (Qloss). TDP is chosen as a limi
empe a u e o a oid he gene a ion o he condensed subs ances (especially acidic) in FG
o p e en he equipmen om co osion and damage.

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The cold s eam p o iles a e no combined in o a Cold Composi e Cu e (unlike he
s anda d p ac ice in he adi ional P ocess In eg a ion app oach based on Pinch Analysis
[2]), bu hey a e plo ed sepa a ely. As he FG s eam is no usually spli , his g aphical
ep esen a ion (shown in Figu e 2) e lec s he ac ual hea exchange a angemen in he
exis ing HRS, whe e he FG hea is used a i s o a s eam gene a ion (Qs eam) and hen
o WG p ehea ing (QWG).
Figu e 2.Tempe a u e-en halpy diag am o exis ing Was e Gas- o-Ene gy uni
Was e gas hea e in ensi ica ion
As men ioned in he In oduc ion, he hea con ained in FG is commonly used o p ehea
he WG s eam in o de o educe he uni ´s ene gy demand. Fo ha eason, he WG hea e
is commonly employed as shown in Figu e 1. The WG p ehea ing enhancemen is
ecommended as he i s hing o conside while he ER o he exis ing WG E uni is
desi ed. This could be pe o med, o example, by inc easing hea ans e a ea (usually
ela i ely cos ly), o implemen a ion o hea ans e in ensi ica ion echnology o he
exis ing WG hea e , which p o ides a cheap solu ion o each he exchange enhancemen .
The selec ion o app op ia e in ensi ica ion echnology depends on se e al aspec s, such as
a ype and geome y o he exis ing WG hea e and media p ocess pa ame e s, such as
empe a u es, ouling sensi i i y, o allowed p essu e d op. The analysis and compa ison o
he mos sui able and e icien hea ans e enhancemen echnologies o ube WG hea e
was pe o med, o example, in [27].
A e a sui able me hod o WG p ehea ing in ensi ica ion is selec ed, he uel sa ing
could be e alua ed acco ding o he ollowing s eps:
• Hea ans e inc ease e alua ion. Based on he selec ed enhancemen echnology
o me hod, he in ensi ied hea ans e (Qin ) o he WG s eam is e alua ed.
• Fuel sa ing calcula ion. I is pe o med using he equa ions (1) and (2) below [21].
𝐹𝐹𝐹𝐹𝑉𝑉𝐶𝐶𝐶𝐶 =𝑛𝑛𝑐𝑐×𝐿𝐿𝐹𝐹𝑉𝑉 ×
𝑇𝑇
𝑇𝑇𝑇𝑇𝑇𝑇
− 𝑇𝑇
𝐶𝐶𝐶𝐶
𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 − 𝑇𝑇𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖
(1)
𝛥𝛥𝑓𝑓
𝑠𝑠=
𝑄𝑄
𝑖𝑖𝑖𝑖𝑖𝑖
𝐹𝐹𝐹𝐹𝑉𝑉𝐶𝐶𝐶𝐶
(2)
FHVCC de ines he uel ene gy con en u ilizable o keep he high empe a u e inside
CC, Δ s is an achie ed uel sa ing and nc is a co ec ion ac o anging be ween 1.07-1.09.
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• Flue gas low a e eassessmen . Because he supplemen al uel combus ed in CC is
a pa o he FG s eam and uel sa ings a e achie ed by WG p ehea ing
in ensi ica ion, he amoun o FG is educed by he alue o Δ s oge he wi h he
co esponding amoun o combus ion ai (as an oxidize ) calcula ed acco ding o
he oxidize / uel a io K (see equa ion (5) below).
• Modi ied diag am plo . While he FG low a e is co ec ed, he diag am o he
exis ing uni (Figu e 2) is modi ied as illus a ed in Figu e 3. By designed hea
ans e in ensi ica ion, he WG p o ile is ex ended by he alue Qin , which causes
a shi o he FG p o ile by he same alue o he igh . The FG g adien is also
sligh ly inc eased due o he educed low a e.
F om he abo e p ocedu e desc ibed and Figu e 3, he FG high sensi i i y o he ER
modi ica ions is ob ious. This is an impo an aspec o be conside ed ca e ully du ing he
concep ual design s age because i conside ably in luences he accu acy o he ob ained
esul s.
The FG p o ile shi causes a change o hea exchange d i ing o ces in pa icula hea
exchange s, hus i is ecommended o e-e alua e he hea loads and o epea he
calcula ion p ocedu e se e al imes un il he FG p o ile shi be ween i e a ions is educed
o a minimum.
Figu e 3. The exis ing WG hea e in ensi ica ion
Inse ion o a new p ehea e
Acco ding o he ene gy balance o a combus ion chambe , whe e he pollu an he mal
decomposi ion akes place, he uel sa ings could be eached by p ehea ing any s eam
en e ing he CC. Besides he WG p ehea ing, which is commonly employed (see Figu e 1),
ano he iable choice is, o example, p ehea ing he combus ion ai (CA). I he WG E uni
p ocesses se e al WG s eams, while some o hem a e no p ehea ed (mos ly mino
s eams), he addi ional hea exchange s (p ehea e s) could be inse ed in o de o imp o e
he FG hea u iliza ion by p ehea ing hose s eams.
The usual ER equi emen is i s minimal impac on he gene a ion o ene gy media (e.g.
s eam gene a ion illus a ed in Figu e 1). Fo his eason, new p ehea e s a e ecommended
o be placed downs eam o he ene gy media gene a o s. A sui able posi ion is commonly a
he end o he FG low pa h, whe e he was e hea (Qloss) could be di ec ly u ilized o educe
he cu en uel demand wi hou signi ican in luence on o he hea exchange s in HRS.
F eisleben, V., Jegla, Z.
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The inse ion o a new p ehea e , howe e , in luences he FG low a e acco ding o he
same p inciple as in he case o he exis ing WG hea e in ensi ica ion discussed p e iously.
The p ocedu e o new p ehea e inse ion consis s o he ollowing s eps:
• Exchange minimum app oach empe a u e (EMAT) alue de e mina ion. EMAT
e alua ion is dependen on he exis ing HRS pa ame e s and is discussed, o
example, by Zhu and Asan e [28].
• New p ehea e hea load calcula ion. Acco ding o he se EMAT alue and known
s eam p ope ies, he hea load (Qp h) and co esponding media (FG and, o
example, CA) inle /ou le empe a u es a e calcula ed.
• Fuel sa ing calcula ion and lue gas low a e eassessmen . Ob aining he uel
sa ing alue Δ s and FG low a e co ec ion ollows he same ules as in he case
o he exis ing WG hea e in ensi ica ion.
• Modi ied diag am plo . A g aphical ep esen a ion o he SFGL me hod is
pe o med acco ding o sligh ly di e en ules han in he case o exis ing WG hea e
in ensi ica ion. I is p esen ed in he case o CA p ehea e inse ion. When he FG
low a e is co ec ed, he modi ied diag am can be plo ed as shown in Figu e 4.
The di e ence be ween he in ensi ica ion o he exis ing p ehea e (Figu e 3)
and he inse ion o he new one (Figu e 4) is ha he new p ehea e is placed o
he le o he T-axis. This app oach causes only he FG line o a ion ins ead o
shi ing o he igh as in he case o he exis ing p ehea e in ensi ica ion.
Figu e 4. The new p ehea e inse ion
The o a ion o he FG p o ile (as shown in Figu e 4) causes b eaking he CA p ehea e
EMAT alue in an ini ial i e a ion. The CA low a e is also changed due o he eached uel
sa ings. Fo hese easons, i is necessa y o pe o m se e al i e a ions o he p ocedu e
desc ibed abo e un il he CA p o ile and FG p o ile (SFGL) a e s able and he EMAT alue
equi emen is ul illed.
The ER pe o med by he inse ion o a new p ehea e in luences he hea exchange
d i ing o ces in exis ing hea exchange s in he same way as in he case o exis ing WG
hea e in ensi ica ion desc ibed ea lie . Thus he e-e alua ion o hea loads in exis ing hea
exchange s is ecommended. Howe e , i he FG low a e change is small, he dec ease in
he hea ans e in exis ing hea exchange s could be neglec ed.
The de eloped SFGL me hod is u he applied o a case s udy o a speci ic WG E uni
p ocessing he WGs gene a ed in an ac ylic acid p oduc ion plan .
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CASE STUDY
The de eloped SFGL me hod he e is p ac ically in oduced by i s applica ion o he
ER design o a speci ic indus ial WG E uni , which se es he mal ea men o was e
gas p oduced mainly om an ac ylic acid p oducing p ocess. The p oduc ion p ocess is a
sou ce o se e al was e gases con aining VOC and CO in low concen a ions (0.85 and 0.5
% ol). The cu en supplemen al uel consump ion is equi ed o be educed by a leas 30
% wi h as li le modi ica ion o he cu en uni as possible. The pa ag aphs below
in oduce he s udied WG E uni wi h all key equipmen .
Desc ip ion o he s udied uni
The uni consis s o a u nace, e e ed o as a combus ion chambe (CC), whe e wo
WG s eams a e he mally ea ed – main was e gas (MWG) and seconda y was e gas
(SWG). The na u al gas bu ne is employed in he u nace o p omo e he mal oxida ion o
he pollu an s and hus o gene a e a lue gas (FG) a a high empe a u e (800 °C). FG was e
hea is a i s used o gene a e high-p essu e (HP) sa u a ed s eam, as a supplemen al
hea ing medium in he plan , and o supe hea a medium-p essu e (MP) s eam as a medium
o powe cycle (elec ici y gene a ion).The MWG is hen p ehea ed in he main was e gas
hea e be o e en e ing he u nace (CC) o educe he supplemen al ene gy demand. The uni
is illus a ed in Figu e 5.
Figu e 5. S udied WG E uni
The cu en uni is ene gy e y in ensi e, he e o e he Ene gy Re o i is eques ed in
o de o educe he uni ´s uel consump ion. The SFGL me hod was applied o design he
echnological modi ica ions in he cu en HRS enabling i o each he desi ed uel sa ing
by imp o ing he FG hea eco e y.
RESULTS AND DISCUSSION
The uni ´s HRS consis s o h ee hea exchange s – HP s eam gene a o , MP s eam
supe hea e , and MWG hea e as shown in Figu e 5. In he uni da a ex ac ion s age,
hei basic p ocess and geome y cha ac e is ics we e p o ided (see Table 1). Acco ding
o he desc ibed SFGL p ocedu e, he p ocess s eam cha ac e is ics a e gi en in Table 2
and uel/oxidize cha ac e is ics in Table 3.
Wi h he ob ained da a, he empe a u e-en halpy diag am o he cu en uni was
gene a ed (see Figu e 6). The FG line was ex apola ed o he dew poin empe a u e
(TDP = 68.5 °C), which is acco ding o he FG composi ion calcula ed as he empe a u e
o wa e apou condensa ion.
F eisleben, V., Jegla, Z.
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Jou nal o Sus ainable De elopmen o Ene gy, Wa e and En i onmen Sys ems 16
TDP
lue gas dew poin empe a u e
[°C]
Tin
inle empe a u e
[°C]
Tini
ini ial empe a u e o oxidize / uel mix u e
[°C]
Tou
ou le empe a u e
[°C]
Ts ack
lue gas s ack empe a u e
[°C]
TTFT
Theo e ical Flame Tempe a u e
[°C]
Δ s
uel sa ing
[kg/h]
ΔmCA
combus ion ai low a e educ ion
[kg/h]
ηDP
lue gas u iliza ion he mal e iciency ela ed o dew poin ,
[%]
Abb e ia ions
CA
combus ion ai
CC
combus ion chambe
EMAT
exchange minimum app oach empe a u e
ER
Ene gy Re o i
FG
lue gas
HEN
Hea Exchange Ne wo k
HP
high-p essu e (s eam)
HRS
Hea Reco e y Sys em
LHV
Lowe Hea ing Value
MP
medium-p essu e (s eam)
MWG
main was e gas
SFGL
Shi ing Flue Gas Line
SWG
seconda y was e gas
VOC
Vola ile O ganic Compound
WG
was e gas
WG E
Was e Gas- o-Ene gy (uni )
ACKNOWLEDGMENT
This esea ch has been suppo ed by he p ojec LTACH19033 “T ansmission
Enhancemen and Ene gy Op imised In eg a ion o Hea Exchange s in Pe ochemical
Indus y Was e Hea U ilisa ion”, unde he bila e al collabo a ion o he Czech Republic
and he People´s Republic o China (pa ne s Xi´an Jiao ong Uni e si y and Sinopec
Resea ch Ins i u e Shanghai; SPIL VUT, B no Uni e si y o Technology and EVECO
B no s. .o.), p og am INTER-EXCELLENCE, INTER-ACTION o he Czech Minis y
o Educa ion, You h and Spo s; and by Na ional Key Resea ch and De elopmen
P og am o China (2018YFE0108900).
Fu he , his esea ch has been also suppo ed by he EU p ojec S a egic Pa ne ship
o En i onmen al Technologies and Ene gy P oduc ion, unded as p ojec No.
CZ.02.1.01/0.0/0.0/16_026/0008413 by Czech Republic Ope a ional P og amme
Resea ch, De elopmen and Educa ion, P io i y Axis 1: S eng hening capaci y o
high-quali y esea ch.
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