| 1. |
- Sundqvist, Sebastian, 1986, et al.
(författare)
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Manganese ores as oxygen carriers for chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU)
- 2017
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437 .- 2213-2929. ; 5:3, s. 2552-2563
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Tidskriftsartikel (refereegranskat)abstract
- Manganese-based oxygen carriers can be used in chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU). This paper expands on a previous investigation into manganese ores as oxygen carriers for CLC. The paper presents reactivity data for eight ores with widely different compositions. Most importantly, the ores contained significant quantities of Fe, Si, and Ca, with Fe/Mn and Si/Mn molar ratios that varied between 0.1-4.5 and 0.07-0.48, respectively. Pre-treatment of the ores consisted of heat treatment in air at 950 °C for 24 h followed by sieving to obtain a particle size fraction of 125-180 ?m. Reactivity towards methane and synthesis gas (50 vol% CO in H2) and the oxygen uncoupling behaviour at 900, 950, and 1000 °C was investigated in a fluidized batch reactor. Material characterization of the ores included an attrition test, crushing strength, and BET surface area measurement. The oxygen carriers had a CO2 yield of 31-80% for syngas with 2 g of oxygen carriers using 450 ml/min of syngas. The performance for all ores as a function of number of cycles was stable. By using a pseudo-first-order rate constant, apparent activation energies were calculated at ? = 0.999 and 0.99 for methane and syngas, respectively, and the apparent activation energies varied in a wide range, from 110 to 328 kJ/mol for CH4 and 10 to 168 kJ/mol for CO. The attrition resistance of the particles was measured using a jet cup attrition rig. The findings indicate that a higher reactivity is associated with higher attrition, however, there is no direct correlation between the two.
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| 2. |
- Diehl, S., et al.
(författare)
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Steady-state analyses of activated sludge processes with plug-flow reactor
- 2017
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437. ; 5:1, s. 795-809
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Tidskriftsartikel (refereegranskat)abstract
- Activated sludge processes (ASPs) consisting of a plug-flow reactor (PFR) and a settler are analyzed in steady-state operation using a reduced model consisting of one soluble substrate and one particulate biomass component modelling the dominating biological process. Monod biomass growth rate is assumed. Two settler models are studied. One is the commonly used ideal settler, or point settler, which is assumed to never be overloaded and to have unlimited flux capacity. The other recently published steady-state settler model includes hindered and compressive settling, and models a realistic limiting flux capacity. Generally, the steady-state concentration profiles within the PFR and the settler are governed by nonlinear ordinary differential equations. It is shown that the steady-state behaviour of the ASP can, however, be captured by equations without derivatives. New theoretical results are given, such as conditions by means of inequalities on input variables and parameters for a steady-state solution to exist. Another novel finding is that, if the incoming substrate concentration is increased from a low or moderate stationary value and the solids residence time is kept fixed, then this results in a lower effluent concentration in the new steady state. The steady-state equations are solved numerically for different operating conditions. For common parameter values, numerical solutions reveal that an ASP having a PFR, instead of a continuously stirred tank reactor, is far more efficient in reducing the effluent substrate concentration and this can be obtained for much lower recycle ratios, which reduces the pumping energy considerably.
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| 3. |
- Kashi, Sima, et al.
(författare)
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Application of a mixture design to identify effects of susbtrates ratios and intractions on anaerobic digestion of municipal sludge, grease trapwaste, and meat processing waste
- 2017
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier BV. - 2213-3437. ; 5:6, s. 6156-6164
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic mono- and co-digestion of two municipal sludge wastes (A and C), grease trap waste (B), and meat processing waste (D) were investigated under mesophilic temperature conditions by biochemical methane potential (BMP) assays and kinetic modeling. Wastes ratios in the mixtures were systematically selected based on Simplex Lattice mixture design, and statistical analyses were performed to elucidate possible synergetic and antagonistic effects of wastes interactions on the kinetics and ultimate methane potentials of wastes co-digestion. The mixture of 1/8A + 1/8B + 1/8C + 5/8D (VS basis) showed the highest COD and VS removals of 35.0% and 33.8%, respectively. Substrates B and D with 980 and 641 mL/g-VS methane yields, respectively, had the highest BMP. However, with reaction rate constants of 0.047 and 0.070 d−1, their methane production was very slow. It was observed that diluting these organic-rich but complex substrates with readily soluble wastes (A and C) enhanced their biogas production rate markedly. Statistical analysis showed that the interactions among the substrates in co-digestion did not have a significant impact on the ultimate cumulative methane yields. Nevertheless, these interactions proved to have synergic and antagonistic effects on the reaction rates, leading to accelerated or hindered methane production rates. As a result, while the methane yield of wastes co-digestion could be predicted by proportional summation of methane yields obtained in mono-digestions of these waste fractions, such linear regressions were unable to provide a good estimation of the rate constants. Quadratic equations, however, were found to estimate the rate constants of the co-digestion process with good accuracy
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| 4. |
- Kozyatnyk, Ivan, et al.
(författare)
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Multivariate assessment of barriers materials for treatment of complex groundwater rich in dissolved organic matter and organic and inorganic contaminants
- 2017
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier. - 2213-3437. ; 5:4, s. 3075-3082
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Tidskriftsartikel (refereegranskat)abstract
- This study focused on the challenges of treating groundwater rich in dissolved organic matter and contains both heavy metals and organic pollutants. Activated carbon, fly ash, lignite, peat, torrefied organic material and zero-valent iron were tested as prospective materials for permeable barriers. Removal of different pollutants was analyzed using coefficients of the Freundlich equation for adsorption isotherms. Principal components analysis was used to visualize similarities and differences in pollutant removal efficiency and sorbent capacity between barrier materials. Fly ash, iron (aerobic conditions) and activated carbon were found to be promising materials for dissolved organic matter removal. Fly ash was the most effective material for metal removal, and fly ash, activated carbon and peat were the most effective materials for removal of organic contaminants. Thus, fly ash shows the most potential for simultaneous removal of metals and organic pollutants. However, it has limited capacity for removing neutral halogenated aromatic compounds. For these, zero-valent iron (aerobic conditions) has greater capacity, probably because of the formation of a porous layer of iron oxyhydroxide. In summary, batch adsorption experiments followed by principal components analysis evaluation of the results are useful tools for selecting suitable materials for treatment of groundwater contaminated with multiple organic and inorganic pollutants.
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| 5. |
- Soleimanisalim, Amir H, et al.
(författare)
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Effects of second metal oxides on zirconia-stabilized Ca-based sorbent for sorption/catalyst integrated gasification
- 2017
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Ingår i: Journal of Environmental Chemical Engineering. - : Elsevier Ltd. - 2213-3437. ; 5:1, s. 1281-1288
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Tidskriftsartikel (refereegranskat)abstract
- Zirconia-stabilized Ca-based sorbent has been previously investigated for cyclic CO2 capture processes; however, the cost of pure zirconia may be a matter of concern. The cost of sorbent can be decreased by addition of a low cost second metal oxide with zirconia-stabilized Ca-based sorbent. This study examined a number of mixed metal oxides supports, such as alumina, silica, titania, magnesia and molybdena, with zirconia (ZrO2) for stabilization of calcium (Ca) based sorbents directly produced from a co-precipitation method. Selected metal oxide supports (i.e. alumina and silica) are commonly used in catalytic steam gasification. The proposed novel strategy aimed at enhancing sorbent stability, increasing surface area, decreasing cost of zirconia-stabilized sorbents and investigating the effects of the common used supports in catalytic steam gasification on the performance of Ca-based sorbents. The optimal composition for the activity of ceramic-stabilized calcium oxide (CaO) samples under mild operating conditions was determined to be 10 wt.% ceramic incorporated in the sorbent. The results indicated considerable sorbent stability and capacity improvement for mixed metal oxide zirconia-stabilized CaO over those of pure CaO, which showed significant cyclic capacity decay under similar conditions. Among the studied materials, aluminum zirconate, calcium zirconate, and zirconium molybdate stabilized sorbents showed the best initial uptake and performances in severe operating conditions over 60 cycles. However, titania, silica and magnesia supports showed negative effect on the sorbent performance.
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