지구온난화를?해결하기?위한?기술적?대안으로?큰?주목을?받고?있는?탄소?포집?기술은?대기?중의?이산화탄소를?제거해?온실효과를?줄이려는?기술이다.

탄소?포집?기술은?기후?위기를?극복하기?위한?가장?혁신적인?기술로?손꼽히고?있다.?IPCC?제?5차?‘지구온난화?1.5℃?특별보고서(2018)’에?따르면?2100년에?지구표면?평균?온도?상승을?1.5℃?미만으로?제한하기?위해서는?인간활동에?기인한?전?지구?이산화탄소?순배출량을?2030년까지?2010년?대비?최소?45%까지?감소하고,?2050년에는?순제로(Net?Zero)?즉,?이산화탄소의?추가?배출로?인한?이산화탄소?농도의?상승이?없어야?한다.[1]

순제로를?달성하기?위해?IPCC?보고서에서?제시하는?완화?노력은?총?세가지로,?첫번째는?화석?연료?사용?및?산업?부문의?배출량?저감,?두번째는?에너지?저수요?생활?패턴으로의?전환?그리고?세번째가?이산화탄소?제거(CDR,?carbon?dioxide?removal)?기술?활용이다.[2]?그렇다면?이산화탄소?제거?기술?중?직접?대기?포집은?어떤?방식일까?

CDR에는?크게?생태계?기반?제거?기술과?인공적인?기술?기반?이산화탄소?제거?기술로?구분된다.[3]?생태계?기반?CDR은?조림?및?재조림(AR,?afforestation?and?reforestation),?토양?탄소?격리(soil?carbon?sequestration)?가?있는데,?오랜?기간?감축?기여도가?검증되었고?사회수용성이?높다는?장점이?있지만,?식물이?활용되는?과정에서?흡수한?이산화탄소가?누출될?가능성이?있다는?단점이?존재한다.

생태-기술?CDR에는?바이오에너지?탄소?포집?및?저장(BECCS,?bioenergy?with?carbon?capture?and?storage)이?존재한다.?가장?많은?기업들이?활용하고?있는?기술?기반?CDR에는?직접?대기?탄소?포집?및?저장(DACCS,?Direct?air?carbon?capture?and?storage)과?풍화?강화(Enhanced?weathering),?해양?알칼리화(Ocean?alkalinity)가?있다.[4]

기술?기반?CDR은?안정적인?탄소?저장소를?사용하기에?포집된?이산화탄소를?누출될?위험?없이?보관할?수?있는?안정적인?보관성에도?불구하고?기술성숙도가?낮고,?그리고?생태계?기반?CDR에?비해?실제?사례가?부족하고,?기술적으로?불확실하다는?단점도?존재한다.[5][6]

◇직접?탄소?포집?기술(DAC)

이산화탄소를?직접?효율적으로?줄일?수?있는?탄소?포집?및?저장?기술(CCS)은?포집기술,?수송기술,?저장기술?그리고?전환기술로?크게?네?가지로?나눌?수?있다.

이?중?포집기술은?CCS?전체?비용의?70~80%를?차지하는?핵심?기술로,?탄소를?포집하는?배출원에?따라?연소?후?포집?기술,?연소?전?포집?기술,?순?산소?연소?기술로?구분된다.

이?중?연소?후?포집?기술에?속하는?직접?대기?탄소?포집?기술(DAC)은?화석연료를?사용하는?발전소,?철강,?시멘트?공장?등?이산화탄소?대량?발생원으로부터?연소?후?배기가스에?포함된?이산화탄소만을?추출해?분리하는?방법으로?기존?발생원에?적용하기?가장?쉬운?기술이다.[7]

직접?탄소?포집?기술(DAC)의?기술성은?크게?세?가지?분야로?구분된다.?첫?번째는?포집제,?두?번째는?공정,?세?번째는?에너지?소비이다.[8]?첫?번째?분야인?포집제는?두가지?측면에서?직접?대기?탄소?포집에?영향을?끼친다.

포집제는?탄소?포집?과정에?있어서의?안정성을?도모해주고?대기?중에?아주?극소량으로?존재하는?이산화탄소를?잡아내기?쉬운?환경을?조성해준다.?현재?직접?대기?포집?과정에?관여하는?포집제는?습식?설비의?경우?강염기?수용액,?건식?설비의?경우?흡착제가?있다.?습식?설비에?사용되는?강염기는?주로?수산화물인데?수산화?나트륨(NaOH)과?수산화?포타슘(KOH)를?중심으로?사용되고?있다.[9]

건식?설비에?사용되는?흡착제는?다공성?물질을?주로?사용한다.?다공성?물질의?특성상?이산화탄소와?접촉할?수?있는?표면이?넓기에?효과적으로?이산화탄소를?포집할?수?있다.[10]?캐나다의?카본엔지니어링은?습식?흡수제를,?스위스의?클라임웍스와?미국의?글로벌써모스탯은?건식?흡착제를?포집제로?사용한다.

두?번째는?공정?기술과?관련된?분야이다.?공정?설비?또한?건식?설비와?습식?설비?분야에서?차이를?보인다.

습식?설비의?경우?포집제에?사용되는?강염기?수용액은?많은?에너지를?필요로?한다.?따라서?반응?에너지를?낮춰줄?수?있는?공정?과정이?필요하다.?캐나다의?카본엔지니어링은?세?단계에?걸친?공정?과정을?통해?반응?에너지를?줄인다.?침전(precipitation)-하소(calcination)-소화(slaking)로?이어지는?세?단계를?통해?포집에?소요되는?반응?에너지를?감소시킨다.[11]

건식?설비는?비교적?간단한?공정?과정을?가지는데?압력?변동?흡착(PSA,?pressure-swing?adsorption)과?온도?변동?흡착(TSA,?temperature-swing?adsorption)으로?구분된다.?스위스의?클라임웍스와?미국의?글로벌써모스탯은?두?방식?모두를?혼합하여?공정?과정을?거친다.[12]

세?번째는?직접?대기?포집?설비?구동?시에?필요한?에너지와?관련된다.?앞서?설명했듯이?현재?직접?대기?포집?과정을?습식과?건식으로?구분되는데?두?설비가?필요로?하는?에너지는?양에서의?차이를?보이지?않는다.

다만?건식?설비는?저온의?에너지로?충분히?구동이?가능하지만?습식?설비는?고온의?에너지를?필요로?하다는?점에서?에너지?질의?차이를?보인다.[13]

따라서?건식?설비는?경제적으로?열을?공급받기?위해?화석?연료?사용?및?산업?시설과?인접한?입지가?유리하지만?습식?설비는?천연가스로?직접?고온으로?가열을?해줘야?하기?때문에?가스?발전?설비가?함께?설치되어야?하고?설치?과정에?있어?천연가스의?가격까지?고려해야?한다.[14]

현재?직접?대기?탄소?포집?기술은?스위스의?클라임웍스,?캐나다의?카본?엔지니어링(Carbon?Engineering),?미국의?글로벌써모스탯(Global)?등?세?기업이?이끌어?나가고?있다.?세?기업?중?탄소?포집?기술?상용화에?가장?가까운?기업은?2021년?대규모?탄소?포집?발전소?오르카(Orca)를?설치하는데?성공한?클라임웍스이다.

직접?대기?포집?기술이?고려해야할?다양한?기술적?쟁점이?있음에도?불구하고?현시점에서?인류가?가장?도전해?볼만한,?현실적인?지구온난화?해결책임에는?반박할?여지가?없다.?다양한?연구가?이어져?직접?대기?포집?기술의?효율을?높일?수만?있다면?2050년에는?탄소?순배출량?0을?달성할?수?있지?않을까?기대해본다.

【안신우?지속가능바람?저널리스트,?이윤진?ESG?연구자?겸?운동가,?안치용?ESG연구소장】

[1]?기상청,?(2020?),?‘지구온난화?1.5C?특별보고서’해설서.

[2]?V.?Masson-Delmotte,?P.?Zhai?&?Others,?(2018),’?IPCC,?2018:?Global?warming?of?1.5°C.?An?IPCC?Special?Report?on?the?impacts?of?global?warming?of?1.5°C?above?pre-industrial?levels?and?related?global?greenhouse?gas?emission?pathways,?in?the?context?of?strengthening?the?global?response?to?the?threat?of?climate?change,?sustainable?development,?and?efforts?to?eradicate?poverty?‘,?p.?14,?In?Press

[3]?UNEP?[United?Nations?Environment?Programme].?2017.?The?Emissions?Gap?Report?2017.?Nairobi.?(n.d.).?Retrieved?November?3,?2022,?from?https://www.unep.org/resources/emis?sions-gap-report-2017

[4]?IPCC,?2018:?Global?warming?of?1.5°C.?An?IPCC?Special?Report?on?the?impacts?of?global?warming?of?1.5°C?above?pre-industrial?levels?and?related?global?greenhouse?gas?emission?pathways,?in?the?context?of?strengthening?the?global?response?to?the?threat?of?climate?change,?sustainable?development,?and?efforts?to?eradicate?poverty?(Sec.?4.3.7)?[V.?Masson-Delmotte,?P.?Zhai,?H.?O.?P?rtner,?D.?Roberts,?J.?Skea,?P.R.?Shukla,?A.?Pirani,?W.?Moufouma-Okia,?C.?P?an,?R.?Pidcock,?S.?Connors,?J.?B.?R.?Matthews,?Y.?Chen,?X.?Zhou,?M.?I.?Gomis,?E.?Lonnoy,?T.?Maycock,?M.?Tignor,?T.?Waterfield?(eds.)].?In?Press

[5]?UNEP?[United?Nations?Environment?Programme].?2017.?The?Emissions?Gap?Report?2017.?Nairobi.?(n.d.).?Retrieved?November?3,?2022,?from?https://www.unep.org/resources/emis?sions-gap-report-2017

[6]?국립기상과학원,?(2021),?‘기상기술정책’.?Vol.14.?No.2.?기상청

[7]?대한민국?교육부,?(2012.9.89)?CO2?잡는?기술??이산화탄소?포집?및?저장?기술!,?교육부?공식블로그?https://if-blog.tistory.com/2084

[8]?송예원,?&?오채운.?(2022).?직접대기탄소포집???저장(DACCS)?기술에?대한?우리나라?R&D?정책?방향성?연구?:?DAC?기술?중심으로.?Journal?of?Climate?Change?Research?2022,?13(1),?075?096.?doi:https://doi.org/10.15531/KSCCR.2022.13.1.075

[9]?Gambhir?A,?Tavoni?M.?2019.?Direct?Air?Carbon?Capture?and?Sequestration:?How?It?Works?and?How?It?Could?Contribute?to?Climate-Change?Mitigation.?One?Earth.?1(4):405?409.?doi:10.1016/j.oneear.2019.11.006?1

[10]?de?Jonge?MMJ?&?others,?(2019),?Life?cycle?carbon?efficiency?of?Direct?Air?Capture?systems?with?strong?hydroxide?sorbents.?Int?J?Greenh?Gas?Control.?80(October?2018):25?31.?doi:10.1016/j.ijggc.2018.11.011

[11]?Sanz-P?rez?ES?&?others.?(2016).?Direct?Capture?of?CO2?from?Ambient?Air.?Chem?Rev.?116(19):11840?11876.?doi:10.1021/acs.chemrev.6b00173

[12]?Gambhir?A,?Tavoni?M.?2019.?Direct?Air?Carbon?Capture?and?Sequestration:?How?It?Works?and?How?It?Could?Contribute?to?Climate-Change?Mitigation.?One?Earth.?1(4):405?409.?doi:10.1016/j.oneear.2019.11.006?1

[13]?McQueen?N,?Gomes?KV,?McCormick?C,?Blumanthal?K,?Pisciotta?M,?Wilcox?J.?2021.?A?review?of?direct?air?capture?(DAC):?scaling?up?commercial?technologies?and?innovating?for?the?future.?Prog?Energy.?3(3):032001.?doi:10.1088/2516-1083/abf1ce

[14]?Keith?DW,?Holmes?G,?St.?Angelo?D,?Heidel?K.?2018.?A?Process?for?Capturing?CO2?from?the?Atmosphere.?Joule.?2(8):1573?1594.?doi:10.1016/j.joule.2018.05.006

안신우(바람 저널리스트)[email protected]

<저작권자 ? 지속가능저널, 무단 전재 및 재배포 금지>