Numerička simulacija sustava za selektivnu katalitičku redukciju

master's thesis

• Title (english): Numerical simulation of Selective Catalytic Reduction (SCR) system
• Author: Matija Martinjak
• Mentor: Milan Vujanović (mentor)
• Granter: University of Zagreb; Faculty of Mechanical Engineering and Naval Architecture; Zagreb
• Defense date and country: 2016-07-15, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Mechanical Engineering; Process Energy Engineering

Abstract

Zbog sve strože ekološke legislative, primarne mjere kontrole ispušnih plinova, poglavito NOx-a, u velikom broju slučajeva više nisu dovoljne. Rješenje za daljnje smanjenje koncentracija NOx-a je u naknadnoj obradi ispušnih plinova. Najperspektivnija tehnologija u tom području je selektivna katalitička redukcija. Kod selektivne katalitičke redukcije (eng. Selective Catalytic Reduction) vodena otopina uree u obliku spreja ubrizga se u struju vrućih dimnih plinova prije katalizatora, pri čemu dolazi do isparavanja vode iz otopine i stvaranja amonijaka termalnom dekompozicijom uree i hidrolizom izocijanske kiseline. Pri tome rezultirajuća prostorna raspodjela amonijaka prije katalizatora predstavlja ključan faktor učinkovite konverzije NOx-a. Zbog kompleksnosti reakcija i prostorne raspodjele plinova unutar katalizatora, veliki resursi ulažu se u razvoj matematičkih modela pomoću kojih bi se dovoljno dobro opisao proces selektivne katalitičke redukcije.

U ovome radu izvršena je validacija najvažnijih matematičkih modela za opis SCR procesa integriranih u komercijalni kod za računalnu dinamiku fluida FIRE na bazi rezultata dobivenih simulacijama s postojećim eksperimentalnim podacima, preuzetim iz akademskog članka. Validacijom je dokazano relativno dobro slaganje eksperimentalnih rezultata i rezultata dobivenih simulacijom po kriteriju efikasnosti pretvorbe NH3. Također je dokazano da simulacije prate trend eksperimentalnih rezultata, te da odstupanja koja su prisutna nisu značajna. Nadalje, izvršena je simulacija realne geometrije industrijskog katalizatora pri različitim radnim uvjetima. Razmatrani su radni uvjeti pri čemu se varirala veličina kapljica ubrizganog spreja, kao i smjer ubrizgavanja spreja. Pokazano je da smjer ubrizgavanja spreja vodene otopine uree u odnosu na strujanje ispušnih plinova (istosmjerno/protusmjerno) nije pokazao neki učinak na konverziju NH3, dok je kod bočnog ubrizgavanja konverzija uvjerljivo najlošija. Na kraju je dokazano da je pobjeg amonijaka kod protusmjernog ubrizgavanja znatno manji nego kod istosmjernog, pri čemu ova vrsta ubrizgavanja postaje zanimljiva za daljnja istraživanja.

Abstract (english)

Due to ever stringent ecological legislation, primary measures for exhaust gases control, especially NOx, in large number of cases are not sufficient any more. The solution for further NOx concentration decrease lays in exhaust gas aftertreatment. Selective Catalytic Reduction (SCR) represents the most promising technology in that area. In the SCR Urea Water Solution (UWS) spray is injected into the hot exhaust gas stream before SCR catalyst, with simultaneous water evaporation taking place. Afterwards, ammonia is generated through thermal decomposition of urea and hydrolysis of isocyanic acid. The resulting spatial distribution of the ammonia before the catalyst is a crucial factor for the efficient conversion of NOx. Due to the complexity of the reactions and the spatial distribution of gases within the catalyst, great amount of resources is invested in the development of mathematical models which will prove sufficiently accurate to describe the process of selective catalytic reduction.

In this work validation of the most important mathematical models for SCR process description integrated in the commercial Computational Fluid Dynamics (CFD) code FIRE has been conducted on the basis of existing experimental results taken from the academic paper. Validation proved relatively good agreement of simulation results with experimental data in terms of NH3 conversion efficiency. Also, it was proved that simulation results follow experimental trend without significant discrepancies. Furthermore, the simulation of real industrial catalyst geometry was conducted for different working conditions, where spray droplet size was varied together with the injection direction. It was shown that UWS spray direction relative to the exhaust gases flow (in the direction of flow and against it) doesn’t have significant impact on the NH3 conversion, whilst during the perpendicular injection, NH3 conversion is by far the worse. Finally, ammonia slip was significantly lower during counterflow injection direction, making this kind of injection interesting for future investigations.

• Keywords: obrada dimnih plinova; selektivna katalitička redukcija; vodena otopina uree; redukcija dušikovih oksida; računalna dinamika fluida
• Keywords (english): flue gas aftertreatment; selective catalytic reduction; urea water solution; nitrogen oxides reduction; computational fluid dynamics
• Language: croatian
• URN:NBN: urn:nbn:hr:235:450885
• Study programme: Title: Mechanical Engineering; Study programme type: university; Study level: graduate; Academic / professional title: magistar/magistra inženjer/inženjerka strojarstva (magistar/magistra inženjer/inženjerka strojarstva)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Open access
• Created on: 2019-05-22 16:57:33