Supercritical water oxidation for energy production by hydrothermal flame as internal heat source. Experimental results and energetic study

Supe c i ical wa e oxida ion o ene gy p oduc ion by hyd o he mal lame as in e nal hea sou ce. Expe imen al esul s and ene ge ic s udy Pablo Cabeza, Joao Paulo Sil a Quei oz1,, Manuel C iado, C is ina Jimenez, Ma ia Dolo es Be mejo∗ , Fidel Ma o, Ma ia Jose Coce o High P essu e P ocess G oup, Dep . o Chemical Enginee ing and En i onmen al Technology - Uni e sidad de Valladolid - Doc o Me gelina, s/n, 47011, Valladolid - Spain Abs ac This wo k p esen s expe imen al and model esul s om a new configu a ion o a cooled wall eac o wo king wi h wo ou le s: an uppe ou le h ough which a sal - ee ho effluen (500 - 600 ◦C) is ob ained and a lowe ou le h ough which an effluen a subc i ical empe a u e dissol ing he p ecipi a ed sal s is ob ained. Diffe en flow dis ibu ions we e es ed in o de o find he bes elimina ion condi ions. To al o ganic ca bon emo al o e 99.99% was ob ained a injec ion empe a u es as low as oom empe a u e, when he ac ion o p oduc s lea ing he eac o in he uppe effluen is lowe han 70% o he eed flow. The pe o mance o he eac o was es ed wi h he oxida ion o a ecalci an compound such as ammonia, using isop opyl alcohol as co- uel. Remo als highe han 99% o N-NH+ 4we e achie ed in bo h effluen s, wo king wi h empe a u es nea 700 ◦C. Sligh ly be e elimina ions we e ob ained in he bo om effluen because i s esidence ime in he eac o is longe . The beha io o he eac o wo king wi h eeds wi h a high concen a ion o sal s was also es ed. Feeds con aining up o 2.5% w Na2SO4could be injec ed ∗Co esponding au ho . Phone: +34 983423166 Email add esses: [email p o ec ed] (Pablo Cabeza), [email p o ec ed] (Joao Paulo Sil a Quei oz), [email p o ec ed] (Manuel C iado), [email p o ec ed] (C is ina Jimenez), [email p o ec ed] (Ma ia Dolo es Be mejo), [email p o ec ed] (Fidel Ma o), [email p o ec ed] (Ma ia Jose Coce o) 1P esen add ess: Dep . o Chemical Enginee ing - Uni e sidade Fede al de Pe nambuco - P o . A u de S´a, s/n, - Cidade Uni e si ´a ia - 50740-521, Reci e, PE - B azil P ep in submi ed o Ene gy Ma ch 2, 2015 in he eac o wi hou plugging p oblems and a o al o ganic ca bon emo al o 99.7% was achie ed in hese condi ions. Uppe effluen always p esen ed a concen a ion o sal lowe han 30 ppm. Finally, a heo e ical analysis o he ene gy eco e y o he eac o wo king wi h wo ou le s was made. Keywo ds: Supe c i ical wa e oxida ion, Hyd o he mal flames, Renewable Ene gy, Reac o design 1. In oduc ion1 Since F anck and cowo ke s disco e ed hyd o he mal flames [1] and i could2 be applied o he Supe c i ical Wa e Oxida ion (SCWO), new challenges came3 up o he s udy o SCWO. Fo flammable compounds such as me hane o 4 me hanol, hyd o he mal flame can occu a empe a u es as low as 400 ◦C [2].5 SCWO is he oxida ion o o ganics in wa e unde condi ions abo e i s c i ical6 poin . In p esence o hyd o he mal flames he eac ion imes can be educed o7 he o de o milliseconds [3] wi hou he p oduc ion o sub-p oduc s ypical o 8 con en ional combus ion such as NOx [4] o dioxins [5].9 SCWO wi h a hyd o he mal flame has a numbe o ad an ages o e he10 flameless p ocess. Some o hese ad an ages pe mi o e coming he adi ional11 challenges ha make he success ul and p ofi able comme cializa ion o SCWO12 echnology difficul . The ad an ages include he ollowing [3]:13 •The educed esidence imes (in he o de o milliseconds) allows he con-14 s uc ion o smalle eac o s.15 •I is possible o ca y ou he eac ion wi h eed injec ion empe a u es16 nea o oom empe a u e when using essel eac o s [6, 7]. This a oids17 p oblems such as plugging and co osion in a p ehea ing sys em, ha ing18 an ad an age om he ope a ional and ene gy in eg a ion pe spec i e.19 •Highe ope a ion empe a u es imp o e he ene gy eco e y.20 The fi s eac o p obably wo king wi h a hyd o he mal flame inside was21 he MODAR eac o , wo king in condi ions o concen a ion, empe a u e and22 2 p essu e abo e he igni ion condi ions o me hanol and being able o wo k wi h23 injec ion empe a u es o 25 ◦C and injec ing he ai a 220 ◦C [7]. In he24 ETH o Zu ich, he di ec injec ion o he was e in o a diffusion hyd o he mal25 flame gene a ed inside he eac o was de eloped as a solu ion o a oid he26 ex e nal p ehea ing o he was e up o supe c i ical condi ions [8, 9]. P ´ıkopsk´y27 and cowo ke s in es iga ed he easibili y o injec ing eeds wi h a 3%w o 28 sodium sul a e (Na2SO4) in he anspi ing wall eac o (TWR) wi h a diffusion29 hyd o he mal flame as in e nal hea sou ce [10]. No plugging was obse ed30 du ing he expe imen s, bu sal deposi s we e de ec ed in he uppe ho zone31 o he eac o . In a p e ious in es iga ion o ou esea ch g oup [6], i was32 ound ha using a anspi ing wall eac o , a p emixed hyd o he mal flame33 inside he eac ion chambe could be main ained when injec ing he eed a a34 empe a u e as low as 110 ◦C. Using a simila eac o , eeds wi h up o 4.74% w 35 Na2SO4could be injec ed [11]. The eac o wo ked wi hou plugging, bu he36 eco e y o sal s was only be ween 5% and 50%. Bo h esea ch g oups epo ed37 an inc ease in he empe a u e when sal was injec ed in he eac o [10, 11].38 Zhang e al. [12] s udied he ope a ional pa ame e s o a TWR de eloped o39 gene a e he mal fluids o oil eco e y. They used wa e -me hanol as a ificial40 uel p io o ea ing oil explo a ion was ewa e , and hey ound he limi s o 41 empe a u e o anspi ing flow in o de o a oid he quenching and ex inc ion42 o hyd o he mal flame.43 I has been p o ed ha injec ion o cold eeds o e a hyd o he mal flame is44 only possible when wo king wi h essel eac o s [9, 10, 11] and i is no possible45 when wo king wi h ubula eac o s [13]. This beha io was due o he low46 flame on eloci ies in hyd o he mal flames ha is lowe han 0.1 m/s, in47 compa ison o he highe flame on eloci ies a a mosphe ic condi ions (0.4-348 m/s). This is he eason why flow eloci ies lowe han 0.1 m/s a e necessa y49 o keep a s able hyd o he mal flame whe e cold eagen s can be injec ed [14].50 Ou esea ch g oup has succeeded in keep wo king con inuously a essel eac o 51 injec ing eeds a empe a u es as low as 25 ◦C [15].52 E en hough he mos immedia e applica ion o hyd o he mal flames is in53 3 he SCWO p ocess o was e des uc ion, which is he mos indus ially de el-54 oped hyd o he mal p ocess, i is possible o mo e om he idea o hyd o he mal55 flame as a echnology o he des uc ion o was es o conside i as a echnol-56 ogy o he gene a ion o clean ene gy, which could e en ually subs i u e he57 ac ual echnologies based on a mosphe ic combus ion [16]. Supe c i ical wa e 58 is al eady applied in ene gy fields h ough gasifica ion p ocesses o was e al-59 o iza ion Facchine i e al. [17], R¨onnlund e al. [18]. The efficiency in ene gy60 p oduc ion by SCWO o coal and di ec expansion o he effluen was compa ed61 o he efficiency o o he con en ional powe plan s by Be mejo e al. [19]. I 62 he s eam was p oduced a 650 ◦C and 30 MPa, efficiencies as high as 38% we e63 ob ained by SCWO. Efficiency was as high as 41% i he effluen was ehea ed64 and expanded a second ime. The efficiencies a he same s eam condi ions o 65 pul e ized coal powe plan and p essu ized fluidized bed powe plan we e 3266 and 34% espec i ely. Compa ison is mo e a o able using oxygen en iched ai 67 o e en using pu e oxygen as he oxidan . In his las op ion he cos o he oxi-68 dan mus be assumed. Ne e heless, i is known ha in adi ional combus ion69 powe plan s, oxygen is used o imp o e efficiency. Dona ini e al. [20] simula ed70 a powe plan based on di ec combus ion o pul e ized coal in a SCWO eac o 71 wi h a sys em o CO2cap u e. They epo ed ne efficiencies a ound 27% and72 ound ha he consump ion o he ai sepa a ion uni o oxygen p oduc ion73 s ongly affec s he iabili y o he plan . A simila analysis has been made by74 Ko owicz and Michalski [21], whom ha e p oposed se e al ope a ions in o de 75 o inc ease efficiency o each s ep in a powe plan model: ai sepa a ion uni ,76 boile (SCWO eac o bu ning coal) and s eam u bine.77 A ai e al. [22] p oposed he supe c i ical oxida ion o biomass was es and78 o he sus ainable uels wi h a hyd o he mal flame as a clean ene gy sou ce o 79 eaching a sus ainable socie y wi h a decen alized p oduc ion based on enew-80 able esou ces. Augus ine and Tes e [3] also p opose i s u iliza ion wi h low81 g ade uels. In gene al, his echnology can be applied o he alo iza ion o 82 was e such as was e wa e ea men plan sludge, biomass o plas ic was es o 83 any kind o was e wi h high ene ge ic con en . Basic heo e ical calcula ions84 4 indica e ha eeds wi h an ene gy con en o 930 kJ/kg ( oughly equi alen 85 o an aqueous solu ion wi h 2% ww o hexane) can supply enough ene gy o86 p ehea he eed om oom empe a u e up o 400 ◦C, and o gene a e elec-87 ic powe equi alen o ha consumed by he high p essu e pump and he ai 88 comp esso [23]. A ema kable aspec abou wo king wi h hyd o he mal flames89 is imp o ing ene gy eco e y in SCWO sys em [19]. Hyd o he mal flames allow90 new eac o designs ha no only a e able o injec eeds wi hou p ehea ing91 because o he possibili y o injec ing eac an s a oom empe a u e bu also92 use he hea eleased by he flame o o he pu poses as he ene ge ic in eg a ion93 o he p ocess o o p oduc ion o elec ici y by u bines [24]. Smi h J . e al.94 [25] used exe gy analysis o s udy he pa ial and o al oxida ion o me hane in95 supe c i ical wa e o a hea -in eg a ed supe c i ical wa e eac o and elec i-96 cal ene gy p oduc ion sys em. They assume a di ec expansion o p oduc s (a 97 400 ◦C) in a u bine, ollowed by hea eco e y o he expanded s eam. I was98 ound ha he p ocess could be ene gy sel -sufficien and op imum flow a es99 we e calcula ed in o de o minimize eac o hea equi emen s o maximize ne 100 elec ical wo k. The high empe a u e effluen can also be used as hea sou ce101 in o he hyd o he mal p ocesses, such as lique ac ion o gasifica ion, whe e he102 hea eco e y is a c i ical issue [26, 27]. In he case o was e wi h high con-103 cen a ion o ino ganic subs ances, new eac o designs able o sepa a e hese104 sal s om he effluen mus be de eloped in o de o make i possible o di ec ly105 expand he effluen in an elec ici y p oduc ion u bine.106 The main goal o his wo k is he s udy o he beha io o new cooled wall107 eac o wi h he main pa icula i y o ha ing wo ou le s in o de o y o keep108 he maximum hea eleased by he flame in a clean and high empe a u e flow109 lea ing he eac o om he uppe zone and o he flow a subc i ical condi ions110 wi h he sal s dissol ed going ou o he bo om o he eac o . In his way he111 uppe /lowe effluen ela ion was op imized aking in o accoun he empe a u e112 p ofiles inside he eac o and he o ganic ma e elimina ion in bo h s eams.113 The pe o mance o he eac o wi h ecalci an pollu an s such as ammonia114 was es ed as well as he pe o mance o he eac o wi h eeds con aining sal s.115 5 Figu e 1: Diag am o SCWO acili y wi h wo ou le s. A CFD model is also used o desc ibe he beha iou o he eac o . Finally, a116 pu ely heo e ical ene gy eco e y s udy o he p ocess wi h he new eac o was117 pe o med, including he possibili y o di ec expansion in hypo he ical de ices.118 2. Expe imen al119 2.1. Expe imen al se up120 All he expe imen s analyzed in his esea ch ha e been ca ied ou in he121 SCWO acili y ins alled in he Uni e si y o Valladolid. I consis s o a con in-122 uous acili y wo king wi h a eed flow o 22.5 L/h, and ai supplied by a ou 123 s age comp esso , wi h a maximum eed a e o 36 kg/h is used as he oxidan .124 The eac o consis o a p essu e essel made o AISI 316 s ainless s eel able o125 s and a maximum p essu e o 30 MPa and a maximum wall empe a u e o 400126 ◦C, con aining a eac ion chambe made o Ni-alloy 625 whe e he empe a u e127 be as high as 700 ◦C. Was e wa e eed and ai a e p e iously p essu ized and128 p ehea ed wi h elec ical esis ances o he desi ed empe a u e be o e being129 injec ed by he bo om o he eac o . The eagen s a e conduc ed o he op o 130 he eac o chambe by means o a ubula injec o . A he ou le o he injec-131 6 o he hyd o he mal flame is o med. Cooling wa e , p e iously p essu ized is132 ci cula ing be ween he p essu e essel and he eac ion chambe in oduced by133 he op o he eac o in o de o cool down he essel a a empe a u e lowe 134 han 400 ◦C. This cooling wa e is en e ing in he eac ion chambe h ough i s135 lowe pa and lea ing he eac o by he bo om oge he wi h a ac ion o he136 p oduc s. The es o he p oduc s lea e he eac o by ano he ou le si ua ed137 in he op o he eac o chambe . A e lea ing he eac o , bo h effluen s a e138 cooled down in he in e coole s and dep essu ized. The flow diag am o he a-139 cili y wi h wo ou le s is shown in Figu e 1. Mo e in o ma ion abou he acili y140 can be ound elsewhe e [6, 13]. Figu e 2 shows a scheme o he eac o wi h he141 diffe en posi ion o he mocouples inside he eac ion chambe . The diffe en 142 empe a u e p ofiles a e e e ed a he posi ion o hese ou he mocouples.143 Each effluen ( op and bo om flow) is measu ed wi h a o ame e in o de o144 know he dis ibu ion o he eed flow espec he wo ou le s. 13 mm Feed Ai Bo om P oduc s Cooling wa e 945 mm 520 mm 250 mm 120 mm Top P oduc s T1 T2 T3 T4 Figu e 2: Scheme o he eac o wi h he flow dis ibu ion and he posi ions (mm) o he empe a u e measu emen inside he eac ion chambe . 145 7 2.2. Ma e ials and expe imen al p ocedu e146 The expe imen s analyzed in his esea ch we e pe o med using eeds p e-147 pa ed wi h isop opyl alcohol (IPA, 99% pu i y) and ap wa e wi hou u he 148 pu ifica ion. Fo expe imen s made wi h ammonia i was used ammonia (25%149 in mass). Syn he ic was e con aining sal s we e p epa ed using Na2SO4(pu i y150 >98%).151 P e ious o he beginning o he expe imen he eac o mus be p ehea ed152 elec ically o 400 ◦C. The eac ion is ini ia ed by injec ed ai and was e wa e 153 s eams p ehea ed elec ically up o a empe a u e highe han 400 ◦C. A ew154 minu es a e con inuous injec ing o IPA solu ion and ai s eam he hyd o he -155 mal flame is igni ed. A ha momen a sha p inc ease he empe a u es a he156 op o he eac o (T1 and T2) is egis e ed. Then, he elec ical hea ing o he157 wall o he eac o is u ned off and he cooling wa e flow is connec ed. Fo 158 keeping he maximum empe a u e cons an in alues a ound 600-700 ◦C ill159 he desi ed injec ion empe a u e is eached, IPA concen a ion was inc eased as160 he injec ion empe a u e was dec eased down o he selec ed injec ion empe -161 a u e. A e he a ge injec ion empe a u e is eached ( om 300 ◦C ill oom162 empe a u e, a ound 20-30 ◦C), he uppe flow and bo om flow a e egula ed163 opening o closing he decomp ession al es keeping he ai and he p essu e164 cons an . P essu e mus be s abilized a ound 23 MPa. Se e al s a iona y s a es165 wi h diffe en p epa ed eeds and diffe en flow up/bo om a io a e eached and166 samples o he liquid effluen a e aken.167 To al O ganic Ca bon (TOC) and To al Ni ogen (TN) analysis o he sam-168 ples we e pe o med wi h a TOC 5050 SHIMADZU To al O ganic Ca bon Ana-169 lyze which uses combus ion and IR analysis. The de ec ion limi is 1 ppm. Sal 170 concen a ion is measu ed using a conduc ime e Basic 30 p o ided by C ison.171 Fo doing his, conduc i i ies o solu ions o known Na2SO4concen a ion a e172 measu ed ob aining a linea calib a ion line be ween conduc i i y and Na2SO4 173 concen a ion. Ni a es and ni i es we e cha ac e ized in he liquid effluen by174 ionic ch oma og aphy wi h an IC PAK A column o Wa e s. The de ec ion limi 175 is 1 ppm. NH3and NOxa he gas effluen we e analyzed wi h D ¨age ubes176 8 de ec o s Lab Sa e y Supply CH29401 and CH31001. The NOxde ec ion limi s177 o hese ubes anged om 0.5 o 100 ppm and he NH3de ec ion limi s anged178 om 5 o 70 ppm (s anda d de ia ion o bo h ubes a e be ween 10 and 15%).179 3. Modeling180 A CFD model was pe o med in o de o s udy he in e nal beha io o he181 new eac o . The main elemen s o he eac o ha e been included in he model182 geome y, like he injec o , he eac ion chambe , and he space be ween he183 p essu e shell and he chambe . The eac o is modeled as an axisymme ic 2D184 sys em. The u bulen flow dynamics is modeled by Reynolds-A e aged-Na ie -185 S okes equa ions, using he Realizable k-ϵ u bulence model wi h enhanced wall186 ea men [28]. The densi y o he supe c i ical mix u e is calcula ed by Peng-187 Robinson equa ion o s a e wi h Van de Waals mixing ules, and olume ans-188 la ion (VTPR-EoS) [29]. The olume ansla ion used in densi y calcula ions189 was fi ed o each componen ha cons i u es he sys em (H2O, O2, N2, CO2 190 and IPA), a he ope a ion p essu e o 23 MPa. The olume ansla ion has191 no influence on en halpy calcula ions, hus, specific en halpy (and also cp) is192 gi en by o iginal Peng-Robinson equa ion o s a e (PR-EoS) [30]. The he -193 mal conduc i i y and he molecula iscosi y o he mix u e a e calcula ed as194 a mass- ac ion a e age o he p ope ies o he pu e componen s as unc ion195 o empe a u e. The u bulen diffusion usually o e whelms lamina diffusion,196 and he specifica ion o de ailed lamina diffusion p ope ies in u bulen flows197 is no necessa y. E en so, lamina diffusion coefficien a e es ima ed using he198 me hod o Ma hu and Thodos [31].199 4. Resul s and discussion200 As gene al esul , he new eac o wi h wo ou le s success ully elimina es201 o ganic ma e ial and p o ides a clean s eam wi h high ene gy con en . The202 injec ion a low empe a u es (20 ◦C), a om he c i ical egion, keeps he203 sal s dissol ed inside he injec o , a oiding plugging and co osion. Finally,204 9 !! "!! #!! $!! %!! &!! ! !! #!! %!! '!! (!!! !"#$% &"''% $) *+,-. %)'*+,-. /)(*+,-. 01234567*685935 (a) ! " # $ % & % ' ( !! !"#!$%&'%#())*+ ",,&-./#01%'2#3&,0#(4/56+ )*+,-.//.0123304 )*+,/.3123304 (b) Figu e 9: (a) Tempe a u e p ofiles o diffe en cooling wa e flows. (b) TOC alues in op and bo om effluen s o diffe en cooling wa e flows. we e compa ed wi h esul s ob ained wi h mix u es o ammonia and IPA es ed285 in he same eac o wo king wi h only he bo om ou le [4]. Figu e 10 shows286 Ammonia and TOC emo al ep esen ed e sus maximum empe a u e egis-287 e ed inside he eac o . The uppe effluen ac ion was kep cons an a alues288 a ound 50% which means ha he 50% o he eed injec ed (liquid) has been289 aken ou by he uppe ou le . I can be app ecia ed ha empe a u es highe ! " # $ % &!! $!! $#! $%! '"! '$! %!! ! "#$%&'()*+,%-./ 0%1+2%-34/ ()(*#+,-./01/,/-2 ()(*#+,-./01/,3-//-4 ()(*#+,-51,-./01/ (a) !" !# !$ !% !& '""!" %"" %$" %&" (#" (%" &"" !"#$%&'()*#+,- #.)/#+0"- )*+,-./01/,/-2 )*+,-./01/,3-//-4 )*+,-51,-./01/ (b) Figu e 10: Ammonia emo al (a) and TOC emo al (b) s max empe a u e inside he eac o o eeds wi h concen a ions be ween 0.5-3% o ammonia and 9-11.5% o IPA wo king wi h 100% bo om flow and wi h 50% op flow. 290 han 700 ◦C a e equi ed o achie e N-NH+ 4 emo als o e 99%. These em-291 pe a u es a e highe han hose needed o ob ain he same emo al wi h he292 eac o wo king wi h only one ou le . Table 1 summa izes he a e age esul s293 o emo al o he diffe en expe imen s made wi h mix u es o ammonia and294 IPA. Wo king wi h wo ou le s, i is obse ed ha ammonia emo al is sligh ly295 16 Table 1: Remo al esul s om he expe imen s made wi h diffe en concen a ions o ammonia. NH+ 4o IPAo Tmax TOC TOC N-NH+ 4N-NH+ 4N-NO− 3N-NO− 3 (%) (%) (◦C) Rem.(%) Rem.(%) Rem.(%) Rem.(%) op bo om op bo om op bo om (ppm) (ppm) 0.5 11.5 744 99.99 99.99 99.13 99.41 49 38 0.5 10.5 706 99.97 99.96 99.07 99.41 47 21 0.5 10.0 634 99.93 94.71 97.94 91.77 50 14 1.0 10.0 708 99.99 99.99 98.99 99.88 36 74 3.0 9.0 686 99.99 99.97 99.83 99.79 186 78 3.0 9.5 729 99.97 99.98 99.29 99.82 26 27 highe in he bo om effluen han in he op effluen , p obably because he296 esidence ime o he p oduc s comp ising he lowe effluen is longe han he297 one o he op effluen , ha i seems o be oo sho o ha e comple e oxida ion298 o ammonia [4]. Ni a e concen a ion is in gene al highe in he op effluen 299 due o he highe empe a u es. The concen a ions o NOx and NH+ 4in he300 gas effluen we e unde he de ec ion limi o 0.5 and 5 ppm espec i ely o all301 he expe imen al condi ions es ed.302 4.7. Beha io o he eac o wo king wi h high sal con en eeds303 The main goal o his new design o he eac o is o ob ain a op effluen 304 a high empe a u e and ee o sal s, becoming his way a ailable o be used305 in sys ems o p oduce ene gy. To achie e ha , sal s con ained in he eed306 mus p ecipi a e and all, lea ing he eac o dissol ed in he bo om effluen 307 while he op effluen is ee o sal s. Fo his pu pose, eeds wi h Na2SO4 308 concen a ions un il 2.5% (25,000 ppm) we e injec ed in he eac o , using IPA309 as uel o ob ain eac ion empe a u es o 700 ◦C, and a eed flow a es o 13-14310 kg/h. In able 2 he main esul s o he expe imen s made wi h eed con aining311 sal s a e summa ized. Equa ion (6) explains how he sal eco e y is calcula ed.312 As can be obse ed in able 2, i is possible o eco e a op effluen almos 313 ee o sal s (wi h conduc i i ies below alues o he ap wa e , equi alen o314 concen a ions o Na2SO4lowe han 30 ppm) and a empe a u es o e 500315 ◦C, a ailable o be expanded in a u bine o o he p oduc ion o s eam a high316 17 Table 2: Main esul s o he expe ience made wi h eed con aining 2.5% w o Na2SO4. F op Fbo om TOC TOC Tmax Tbo om Na2SO4Na2SO4 (kg/h) (kg/h) op bo om (◦C) (◦C) op Reco e y (ppm) (ppm) (ppm) bo om (%) 7.2 10.2 1.0 209 749 239 24 2.4 7.2 10.2 0.3 352 712 244 23 32.1 7.2 10.2 0.5 599 740 250 24 21.1 7.2 10.2 0.8 23 742 254 23 1.8 7.2 10.2 0.7 69 683 258 23 45.5 7.2 10.2 0.7 16 691 258 26 0.7 A e age 0.7 211 719 251 23.8 17.3 empe a u e ha could be also expanded in a u bine. Paying a en ion o he317 sal eco e y a he bo om flow, i was possible o ob ain an a e age o 17% o 318 sal eco e y. This eco e y is highe han he ob ained wi h he eac o wo king319 wi h only one ou le [32] (a e age o 10%) bu i was no possible o imp o e320 and s abilize he eco e y du ing long imes. This ac could be in e p e ed as321 he possible o ma ion o solid clus e s o sal s swep away by he ou le s eam322 and dissol ed in he cooling sys ems.323 4.8. Ene gy eco e y324 In o de o analyze he possibili y o using he high empe a u e o he325 effluen o SCWO eac o s o p oduce ene gy, an analysis o he op ions o 326 gene a ing ene gy was pe o med.327 4.8.1. Pa ame e calcula ions328 The ollowing equa ions explain how he diffe en pa ame e s o he s udy we e calcula ed. Fi s ly, he amoun o ene gy eleased by he was e and uel con ained in he eed is calcula ed as shown in eq. (7). kW injec ed a he eed = F eedC uel∆Hc, uel 3,600 (7) whe e ∆Hc, uel is he en halpy o combus ion o IPA (3,750 kJ/kg). The ene gy consumed is due mainly o he pumping equipmen (pumps and 18 comp esso s). The ac ion o ene gy consumed wi h espec o he ene gy con- ained in he eed is calcula ed as shown in eq. (8). Consump ion = kW Consumed kW injec ed a he eed ·100 (8) The ene gy p oduc ion is calcula ed using Peng-Robinson Equa ion o S a e wi h Bos on-Ma hias alpha unc ion conside ing a u bine wi h an isen opic efficiency o 72 %. The ac ion o ene gy p oduced wi h espec o he ene gy in oduced in he eed is calcula ed as shown in eq. (9). Rela i e p oduc ion = kW p oduced kW injec ed a he eed ·100 (9) kW p oduced is he ene gy p oduced by di ec expansion o s eam expansion p oduc ion. F om he p oduc ion and consump ion is ob ained he pe cen age o he effi- ciency in ene gy p oduc ion o he sys em o each eac o and kind o oxidan as shown in eq. (10). Efficiency = kW p oduced −kW Consumed kW injec ed a he eed ·100 (10) Mass and ene gy balances we e sol ed in Aspen Plus so wa e conside ing he -329 mal and olume ic p ope ies calcula ed using Peng-Robinson Equa ion o 330 S a e.331 4.8.2. Ene gy p oduced by s eam expansion332 The mos con en ional me hod o elec ic gene a ion is using he p oduc s333 s eam as hea sou ce o a Rankine cycle. As a guidance o easibili y o he334 p ocess, i has been calcula ed he amoun o s eam which could be gene a ed a 335 diffe en condi ions o h ee small u bines comme cialized by Siemens ( able336 3).337 Inc easing he p essu e o he powe cycle, inc eases he specific wo k p o-338 duced by expanding he s eam. Howe e , he o al amoun o s eam is educed,339 since he hea sou ce is limi ed. Tha can be seen in figu e 11, ha shows he340 composi e cu es o he ho s eam ( eac o p oduc s) and h ee possibili ies o 341 19 Table 3: Cha ac e is ics o comme cial s eam u bines. Inle P Inle T Powe (ba ) (◦C) (kWh/(kg-s eam)) SST-040 40 400 0.232 SST-050 101 500 0.272 SST-060 131 530 0.278 cold s eam (wa e -s eam), wi h a diffe ence o 10 ◦C a pinch poin . The hea 342 sou ce is a s eam a 700 ◦C and 23 MPa, wi h he ypical composi ion o SCWO343 effluen using ai as oxidan . Finally, figu e 12 p esen s he amoun o s eam344 ha could be p oduced pe kilog am o ho p oduc s and he ne efficiency o 345 each p essu e le el. ! " # $ % & ' ( % ! !% !"#!$%&'$!()*+, -.&/%0#1()234/, )*+,-./0 1123 $ 1123 % 1123 & Figu e 11: P oduc ion o s eam a h ee diffe en p essu e le els. !"#$# !"#%# !"#&# "'#( ")%( ")#( # #*) #*' #*+ #*$ #*% #*& # % )# )% !!"#"$%#& '()*+$,-.'()/0123#+ 40$**30$5674,8 ,-./0 .11232.435 Figu e 12: S eam p oduc ion and efficiency o comme cial u bines. 346 Gi en hese esul s, he ollowing sec ions assume ha he cha ac e is ics347 20 o he s eam ha can be p oduced om he hea con ained in he effluen o 348 he eac o a e hose shown in able 4. The low p essu e s eam p esen ed in Table 4: Cha ac e is ics o he s eam. P essu e Tempe a u e (ba ) (◦C) High P essu e S eam 46 400 Low P essu e S eam 10 180 349 able 4 could be p oduced wi h eac o effluen s a empe a u es up o 400 ◦C350 ( ypical effluen empe a u es o essel eac o s like he anspi ing wall eac o 351 and cooled wall eac o ) and he high p essu e s eam by he effluen s up o 700352 ◦C (effluen s o ubula eac o s o he effluen o he new cooled wall eac o 353 desc ibed in his wo k).354 Wi h hese assump ions, he possibili ies o ene gy eco e y o some eac o 355 designs a e compa ed.356 Compa ison o he eco e y ene gy o diffe en eac o s by s eam p oduc ion:357 •Tubula eac o [4, 13]358 This eac o consis ed on a s aigh and emp y ube made o Ni alloy359 C-276 wi h a o al leng h o 5400 mm and a diame e o 1/4” (i.d. 3.86360 mm) gi ing an in e nal olume o 63.2 ml and i was he mally isola ed.361 In his case (figu e 13), he effluen is used fi s ly o p ehea he eed un il362 he injec ion empe a u e (a ound 400 ◦C) and he emaining hea flow is363 used o p oduce s eam. !"!#$%&%'$()*% +'', -%*,!(). /*0&-&.)'$1 2%*,!()3*4 Figu e 13: Sys em eco e y design o a ubula eac o . 364 21 •O iginal cooled wall eac o designed in he Uni e si y o Valladolid (Val-365 ladolid, Spain) [33]366 This eac o is composed by wo concen ic ubes; he inne one is made367 o Inconel 625, and he ou e shell is made o SS 316. Oxida ion eac ion368 akes place inside he inne ube ( eac ion chambe ). In he gap be ween369 bo h ubes, he p essu ized eed s eam is going down and cooling he370 eac ion media a he same ime. In such way, he inne ube does no 371 wi hs and any p essu e a all; ha ing he same p essu e in one side han372 on he o he , and he hickness o he inne ube (Inconel 625) can be373 educed. The effluen o he o iginal CWR (a 400 ◦C) can be used in a374 Rankine cycle as i is shown in figu e 14. !" #$$% &'(%)*+, Figu e 14: Sys em eco e y design o he o iginal CWR. 375 •New cooled wall eac o design [32]376 The new eac o consis s o a e ical Ni-alloy eac ion chambe ha is377 inside o a p essu e essel made o AISI 316 able o s and a maximum378 p essu e o 30 MPa and 400 ◦C. Be ween he walls o he wo essels a379 s eam o cold wa e e ige a es he eac ion essel. The eagen s ( eed380 and oxidan ) a e in oduced in he eac o h ough a ubula injec o up o381 he op o he eac ion chambe . The flame is p oduced ou side o he in-382 jec o , no mally a he op o he eac ion chambe , whe e he maximum383 empe a u e is egis e ed. Reac ion chambe is e ige a ed wi h oom384 empe a u e p essu ized wa e ha flowed be ween he eac ion chambe 385 wall and he inne wall which suppo ed he p essu e, keeping he p essu -386 ized wall a empe a u es lowe han 400 ◦C, and en e ing in he eac ion387 chambe by i s lowe pa mixing wi h he eac ion p oduc s. The p od-388 22 uc s flowed down he eac o lea ing i by i s lowe pa oge he wi h he389 cooling wa e . Following he idea o he o iginal CWR, he p oduc s come !"#$%& '#()*+!* ,!!- ./(-)0*1 $((+234 "5*!/ 6("#.#1*!57 8/(-)0*2(3 Figu e 15: Sys em eco e y designed o he new CWR wi h he configu a ion wi h one ou le . 390 ou he eac o a empe a u es a ound 325 ◦C and can p oduce s eam o391 be expanded in a Rankine cycle (figu e 15).392 O he configu a ion o his eac o is wo king wi h an ou le a he op o 393 he eac o , hus ha ing wo ou le s: one a high empe a u e and o he 394 a subc i ical empe a u es wi h he sal dissol ed wi h he cooling wa e 395 (figu e 16). Fo pe o ming he compa a i e ene ge ic analysis among he !"#$%& '#()*+!*, -!!. /(**(0#12(.)3* $((+456 "7*!2 8("#9#,*!70 12(.)3*4(5 :(1#12(.)3* ;46<#9#,*!70 12(.)3*4(5 Figu e 16: Sys em eco e y designed o he new CWR wi h he configu a ion wi h wo ou le s. 396 diffe en eac o s ypes, ypical ope a ional pa ame e s o each eac o 397 such as uel concen a ion, oxidan excess o e he s oichiome ic amoun 398 (based on he a e age excess used in he majo i y o he expe imen s and399 he accep able oxidan excess o oxidize ni ogen compounds), he pe -400 cen age o cooling wa e and he effluen empe a u e we e fixed. These401 pa ame e s a e shown in able 5. In fi s place, he analysis was pe o med402 conside ing ha he effluen s a e used o gene a e s eam o a Rankine403 cycle. The esul s a e also shown in able 5, a he las wo columns.404 23 As can be obse ed, p oducing elec ici y h ough Rankine cycles p esen Table 5: Condi ions fixed o he s udy o each eac o , eco e ing ene gy h ough a Rankine cycle. 5% excess o oxidan is assumed in all cases. Type o eac o Hea Cooling Injec ion Effluen Efficiency flow eed wa e T (◦C) T (◦C) (kW) (% o eed) Ai O2 O iginal CWR 1,202 0 Room T 400 -16.9% 8.6% New CWR 1 ou le 1,202 35 Room T 325 -16.8% 4.8% Tubula eac o 372 0 350-400 700 -21.1% 5.7% New CWR 2 ou le s 1,208 35 Room T Top 700 -8.0% 19.0% 100% Bo . 300 New CWR 2 ou le s 1,208 35 Room T Top 700 -11.0% 14.0% 70% Bo . 300 405 only posi i e efficiencies ( o be able o co e he ene gy consump ion e-406 qui ed by he pumping equipmen ) when he sys em is using oxygen as407 he oxidan . This is due o he much highe consump ion o ai comp es-408 so s compa ed o liquid oxygen c yogenic pumps. Ac ually, he ene gy409 equi ed (defined in equa ion (8)) when using ai and oxygen ascends o410 28% and 0.2%, espec i ely.411 4.8.3. Ene gy eco e y wi h he new cooled wall eac o 412 Focusing on he new CWR eac o design, a de ailed analysis o he ene ge ic413 eco e y possibili ies is shown abo e. In figu e 17 i is shown ano he possibili y414 o ene gy eco e y o each effluen o he new CWR design, besides scheme415 shown in figu e 16. I was assumed, as obse ed expe imen ally, ha all he416 gases in ol ed in he combus ion lea es he eac o wi h he op effluen : CO2 417 p oduced in he eac ion, N2(when ai is used as oxidan ) and O2 om he418 oxidan mixed wi h he wa e flow, being he bo om effluen conside ed as419 pu e wa e .420 Influence o he dis ibu ion flow h ough diffe en pa ame e s421 To analyze he elec ici y p oduc ion wi h he new CWR eac o , he condi ions422 assumed a e: 5% oxidan excess; 1,208 kW o hea flow eed; flow o cooling423 24 !"#$%& '#()*+!*, -!!. /(**(0#12(.)3* $((+456 "7*!2 8("#9#,*!70 12(.)3*4(5 :(1#12(.)3* ;42!3*# !<175,4(5 Figu e 17: Scheme o he di ec expansion o op effluen o he eco e y ene gy wi h he CWR wi h 2 ou le s. wa e equi alen o 35% o eed flow; and effluen empe a u es o 700 ◦C and424 300 ◦C, a op and bo om ou le s, espec i ely. The selec ed pe cen age o 425 cooling wa e is based on he op imal ope a ional pa ame e s ob ained wi h he426 new eac o .427 (a) (b) Figu e 18: Efficiency o he eco e y ene gy o he new eac o wi h (a) di ec expansion and (b) s eam p oduc ion. Influence o he kind o ene gy p oduc ion sys em428 Figu e 18 shows he efficiency o he new eac o ob ained by di ec expansion o 429 he flow and s eam p oduc ion wo king wi h ai and wi h oxygen. Diffe en flow430 dis ibu ions a e assumed. As can be obse ed, he ene gy p oduced by di ec 431 expansion o he flow om he eac o is bigge han he ene gy ob ained by he432 p oduc ion o s eam in a Rankine cycle ha could be expanded a e wa ds.433 25