1-dimensional modelling and simulation of the calcium looping process

Calcium looping is an emerging technology for post-combustion carbon dioxide capture and storage in development. In this study, a 1-dimensional dynamical model for the calcium looping process was developed. The model was tested against a laboratory scale 30 kW test rig at INCAR-CSIC, Spain. The study concentrated on steady-state simulations of the carbonator reactor. Capture efficiency and reactor temperature profile were compared against experimental data. First results showed good agreement between the experimental observations and simulations

Modeling of the oxy-combustion calciner in the post-combustion calcium looping process

The calcium looping process is a fast-developing post-combustion CO2 capture technology in which combustion flue gases are treated in two interconnected fluidized beds. CO2 is absorbed from the flue gases with calcium oxide in the carbonator operating at 650 ºC. The resulting CaCO3 product is regenerated into CaO and CO2 in the calciner producing a pure stream of CO2. In order to produce a suitable gas stream for CO2 compression, oxy-combustion of a fuel, such as coal, is required to keep the temperature of the calciner within the optimal operation range of 880-920°C. Studies have shown that the calcium looping process CO2 capture efficiencies are between 70 % and 97 %. The calciner reactor is a critical component in the calcium looping process. The operation of the calciner determines the purity of gases entering the CO2 compression. The optimal design of the calciner will lower the expenses of the calcium looping process significantly. Achieving full calcination at the lowest possible temperature reduces the cost of oxygen and fuel consumption. In this work, a 1.7 MW pilot plant calciner was studied with two modeling approaches: 3-D calciner model and 1-D process model. The 3-D model solves fundamental balance equations for a fluidized bed reactor operating under steady-state condition by applying the control volume method. In addition to the balance equations, semiempirical models are used to describe chemical reactions, solid entrainment and heat transfer to reduce computation effort. The input values of the 3-D-model were adjusted based on the 1-D-model results, in order to model the behavior of the carbonator reactor realistically. Both models indicated that the calcination is very fast in oxy-fuel conditions when the appropriate temperature conditions are met. The 3-D model was used to study the sulfur capture mechanisms in the oxy-fired calciner. As expected, very high sulfur capture efficiency was achieved. After confirming that the 1-D model with simplified descriptions for the sorbent reactions produces similar results to the more detailed 3-D model, the 1-D model was used to simulate calcium looping process with different recirculation ratios to find an optimal area where the fuel consumption is low and the capture efficiency is sufficiently high. It was confirmed that a large fraction of the solids can be recirculated to both reactors to achieve savings in fuel and oxygen consumption before the capture efficiency is affected in the pilot unit. With low recirculation ratios the temperature difference between the reactors becomes too low for the cyclic carbonation and calcination. As a general observation, the small particle size creates high solid fluxes in the calcium looping process that should be taken into account in the design of the system

Baltic herring as nutrition – Risk-benefit analysis

Tämän tutkimuksen tarkoitus oli selvittää, onko silakansyönnistä enemmän terveyshyötyä kuin -haittaa Suomessa ja millainen tilanne on eri ikäryhmissä. Aiemmat hyöty-riskiarviot ovat osoittaneet, että kalansyönti on yleensä terveellisempää kuin sen syömättä jättäminen. Tämä johtuu erityisesti kalan terveellisistä omega-3-rasvahapoista. Kuitenkin iso osa hyödyistä tulee aikuisille, joilla on suurentunut sydäntautiriski, ja osa mahdollisista haitoista tulee lapsille hammasvaurioiden ja muiden kehityshäiriöiden riskinä. Eviran toimeksiantona, yhteistyössä THL:n kanssa on vuoden 2014 aikana tehty hyöty-haitta-analyysi, jossa on tarkasteltu nimenomaan eri ikäryhmiä erikseen nykyisen kalankäytön mukaan. Tulokset perustuvat Taloustutkimuksen tekemän kyselyn aineistoon vuodelta 2013, jonka pohjalta on tehty varsinainen terveysvaikutusten tarkastelu. Tulokset ilmaistiin käyttäen haittapainotettuja elinvuosia (Disability Adjusted Life Year DALY) eli yksi DALY vastaa yhtä menetettyä tervettä elinvuotta. Hyödyllisistä ravintoaineista raportissa tarkasteltiin omega-3-rasvahappoja, eikosapentaeenihappoa (EPA) ja dokosaheksaeenihappoa (DHA) sekä D-vitamiinia. Silakassa esiintyvistä terveydelle haitallisista ympäristömyrkyistä tarkasteltiin dioksiineihin luettavia yhdisteitä, joihin kuuluvat polyklooratut dibentso-p-dioksiinit ja polyklooratut furaanit sekä dioksiininkaltaiset polyklooratut bifenyylit (PCB:t). Tulosten mukaan silakansyönti aiheuttaa Suomessa noin 11 (95 % luottamusväli LV 0 – 54) DALY kehityshäiriöistä (hammasvaurio) johtuvaa haittapainotettua elinvuotta (DALY), jotka kaikki kohdistuvat lapsiin äidin välityksellä raskausajan ja imetyksen kautta. Lisäksi silakansyönti aiheuttaa noin 12 (95 % LV 1.7 – 56) DALY dioksiinien aiheuttaman syöpäriskin kautta koko väestössä. Yli 50-vuotiailla naisilla ja varsinkin miehillä silakansyönnin terveyshyödyt ovat selkeästi suuremmat kuin terveyshaitat. Suurimmat terveyshyödyt saadaan sydäntautia ja sydänkuolleisuutta vähentävästä vaikutuksesta, noin -688 (95 % LV -2126 – -41) DALY/vuosi. Tulosten mukaan silakan syönti on vähentynyt väestössä niin paljon, että nykyiset suomalaiset kalan yleiset syöntisuositukset ovat riittävät suojaamaan väestöä dioksiinien ja dioksiinien kaltaisten yhdisteiden aiheuttamilta terveyshaitoilta. Hyöty-haitta-analyysissä tulisi kuitenkin tulevaisuudessa arvioida myös muiden rasvaisten kalojen keräämien ympäristömyrkkyjen kumulatiivisia terveysvaikutuksia ja yleisten syöntisuositusten riittävyyttä.Syftet med denna undersökning var att utreda om konsumtion av strömming från Östersjön ger mer hälsofördelar än hälsoskador i Finland och hurdant läget i olika ålderskategorier är. Tidigare nytta/riskvärderingar har visat att det i allmänhet är hälsosammare att äta fisk än att låta bli att göra det. Det beror särskilt på de hälsosamma omega-3-fettsyrorna i fisken. En stor del av fördelarna tillkommer ändå vuxna personer med förhöjd risk för hjärtsjukdomar och en stor del av skadorna tillkommer barn i form av risk för skador på tänderna och andra utvecklingsstörningar. På uppdrag från Evira och i samarbete med THL har under året 2014 gjorts en nytta/riskanalys, där man uttryckligen granskat olika ålderskategorier skilt för sig i ljuset av den nuvarande konsumtionen av strömming. Resultaten bygger på ett enkätmaterial som Taloustutkimus inhämtat år 2013. Utgående från detta material har sedan den egentliga granskningen av hälsoeffekterna gjorts. Resultaten angavs i form av funktionsjusterade levnadsår (Disability Adjusted Life Year DALY). För de nyttiga näringsämnenas del granskades i rapporten omega-3-fettsyrorna eikosapentaensyra (EPA) och dokosahexaensyra (DHA) och vitamin D. Av de hälsovådliga miljögifterna som förekommer i strömming granskades dioxiner, polyklorerade dibenzo-p-dioxinerna och plyklorerade dibenzofuranerna jämte dioxinliknande polyklorerade bifenylerna (PCB). Resultaten visar att konsumtion av strömming i Finland orsakar cirka 11 (95 % förtroende intervall , FI 0-54) funktionsjusterade levnadsår (DALY) som beror på utvecklingsstörningar (tandskada) och som alla via modern drabbar barn under graviditeten och amningen. Konsumtion av strömming medför också cirka 12 (95 %, FI 1,7-56) DALY via den cancerrisk som dioxinerna orsakar i hela befolkningen. Hos över 50 åriga kvinnor och framförallt män är fördelarna av att äta strömming klart större än hälsoskadorna. De största hälsofördelarna kommer av att risken för hjärtsjukdomar och dödligheten i hjärtsjukdomar minskar, cirka -688 (95 %, FI -2126 -41) DALY/år. Enligt resultaten konsumtion av strömming I Finland har sjunkit till en så låg nivå , att de nuvarande allmänna rekommenderade intagen av fisk konsumtion är tillräckliga för att skydda befolkningen mot hälsoskador av dioxiner eller dioxinlika föreningar. I risk-nytta-analys i framtiden bör ändå utvärderas totala hälsoeffekter av olika miljögifter i andra feta fiskarter ock kolla lämpligheten av rekommendationer av fisk konsumtion.The objective of this study was to determine whether the benefits of eating Baltic Sea herring exceed the risks in Finland, and what the situation is in different age groups. Previous risk-benefit analyses have shown that eating fish is in general healthier than not eating fish. This is particularly due to the healthy omega 3 fatty acids of fish. However, the benefits are largely enjoyed by adults with an elevated risk of heart disease, while children suffer the majority of the risks in the form of dental problems and other developmental disorders. In the riskbenefit analysis carried out to the order of Evira in collaboration with THL during 2014, different age groups were specifically considered separately in the light of current fish consumption. The results are based on the survey of the consumption of Baltic herring conducted by Taloustutkimus in 2013, which was used as the basis for the actual analysis of health effects. The results were expressed as Disability Adjusted Life Years (DALY). Omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) as well as vitamin D were analysed in the report as beneficial nutrients. As far as environmental toxins harmful to health are concerned, Baltic herring were analysed for compounds classified as dioxins, which include polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans, as well dioxin-like biphenyls (PCB). According to the results, in Finland eating herring causes ca. 11 (95% confidence interval, CI 0-54) Disability Adjusted Life Years (DALYs) resulting from developmental disorders (dental damage); these affect children via the mother during pregnancy and breastfeeding. In addition, eating herring causes a ca. 12 (95%, CI 1,7-56) DALY cancer risk due to dioxins in the entire population. The health benefits of eating herring clearly exceed risks to health for women and particularly men after the age of 50 years. The greatest health benefits result from the reduction in heart disease and heart-related fatality, ca. –688 (95%, CI -2126 -41) DALY/year. The results show that the consumption of Baltic herring has decreased in Finland to a low level and that the current common dietary advices on fish consumption are adequate to protect the population against the adverse health effects of dioxins and dioxin-like compounds. However, in risk benefit analysis in future it is important to estimate the total health effects of different environmental pollutants and of other fatty fish, and the sufficiency of dietary advices on fish consumption

Computational fluid dynamics derived dataset for evaluation of mixing of a secondary solid phase in a circulating fluidized bed riser

Transient Eulerian simulations of multiphase flow inside a laboratory-scale circulating fluidized bed (CFB) riser were performed with air, bed material, and a secondary solid phase to evaluate the mixing of the secondary solid phase. This simulation data can be applied in model development or for computing terms that are commonly used when modeling mixing with simplified models (pseudo-steady state, non-convective models, etc.). The data was produced with transient Eulerian modeling using Ansys Fluent 19.2. The simulations were done with one fluidization velocity and bed material, while the density, particle size, and inlet velocity of the secondary solid phase was varied and 10 simulations per each secondary solid phase case were simulated for 1 s, each simulation having different starting conditions (flow state of the air and bed material) inside the riser. These 10 cases were then averaged to provide an average mixing profile for each secondary solid phase. Both the averaged and un-average data are included. The details of the modeling, averaging, geometry, materials, and cases are described in the open-access publication by Nikku et al. (Chem. Eng. Sci. 269, 118503)