| 51. |
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| 52. |
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| 53. |
- Frick, Volkmar, 1983, et al.
(författare)
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Screening of supported and unsupported Mn-Si oxygen carriers for CLOU (chemical-looping with oxygen uncoupling)
- 2015
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Ingår i: Energy. - : Elsevier BV. - 0360-5442 .- 1873-6785. ; 93, s. 544-554
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen carriers based on oxides of Mn and Si in combination with Mg, Al, Ca and Ti (Mn0.63Si0.27X0.1, X = Ca(OH)2, TiO2, MgO, AlOOH) were examined for CLOU (chemical-looping with oxygen uncoupling), in terms of oxygen uncoupling ability and ability to convert both methane and syngas. The focus was on the optimization of the production process to yield mechanically strong oxygen carrier particles with a reasonable activity. For this purpose, 15 types of oxygen carriers were produced by spray-drying and calcined for different time periods and at different temperatures. The oxygen uncoupling behavior and gas conversion of the materials were investigated in a batch fluidized-bed reactor under alternating oxidizing and reducing conditions in the temperature range 850-1050 °C. To determine attrition resistance and mechanical stability, a jet-cup attrition rig was used. Furthermore, physical and chemical properties such as specific surface area and crystal phase composition have been determined. For the oxygen carriers with additives of Mg, Al, Ca, Ti, some material combinations showed a significant increase in reactivity and improved mechanical stability compared to the unsupported Mn-Si particles. Changing the production process (milling process and calcination time) just caused slight difference in attrition resistance, gas conversion as well as oxygen release.
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| 54. |
- Frohn, Peter, et al.
(författare)
-
On the high-gasification rate of Brazilian manganese ore in chemical-looping combustion (CLC) for solid fuels
- 2013
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Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:11, s. 4346-4354
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Tidskriftsartikel (refereegranskat)abstract
- The high rate of char gasification observed when using a Brazilian manganese ore as compared to ilmenite is investigated in a batch fluidized-bed reactor. Experiments were carried out at 970°C using petroleum coke, coal and wood char as fuel with a 50% H2O in N2 as fluidizing gas. A manufactured manganese oxygen carrier was also used, however, which presented a slower char conversion rate than the manganese ore. It is concluded that decrease in H2 inhibition and oxygen release are unlikely to be the main responsible mechanisms for the ore's unexpected gasification rate. The ore was also mixed in different ratios with ilmenite and it was observed that the presence of even small amounts of ore in the bed resulted in increased gasification rate. Thus, the high-gasification rate for the manganese ore could be due to a contribution from the impurities in the ore by catalyzing the gasification reaction.
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| 55. |
- Fuss, Sabine, et al.
(författare)
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Moving toward Net-Zero Emissions Requires New Alliances for Carbon Dioxide Removal
- 2020
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Ingår i: One Earth. - : Elsevier BV. - 2590-3322 .- 2590-3330. ; 3:2, s. 145-149
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The 1.5 degrees C target will require removing at least some of the carbon dioxide (CO2) previously emitted. Knowledge on how this can be done has been increasing, though barriers remain concerning governance, policy, and acceptability. For the 26th session of the Conference of the Parties (COP26) to move beyond an academic debate on CO2 removal (CDR), a broader alliance of research and policy communities, industry, and the public is needed.
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| 56. |
- Gogolev, Ivan, 1984, et al.
(författare)
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Alkali emissions characterization in chemical looping combustion of wood, wood char, and straw fuels
- 2022
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 237
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion of wood pellets (WP), wood char (WC), and straw pellets (SP) was conducted in a 60 kW CLC pilot with ilmenite and braunite oxygen carriers (OCs). Alkali emissions were investigated with impactor-based and surface ionization detector (SID) measurements. Particle size distributions for WP and WC fuels were dominated by coarse particles formed by refractory species. For SP fuel, the distribution was bimodal with a distinct fine particle mode formed by nucleation of volatile ash species. Thermodynamic modelling of stable alkali species at 800 °C predicted that high KOH(g) and lower concentrations of KCl(g) are stable for WP and WC fuels. For SP fuel, equilibrium K species were dominated by condensed-phase K species, followed by KCl(g), and KOH(g). Modelling of fuel-OC interactions showed that ilmenite decreases equilibrium levels of KOH(g) and KCl(g). Braunite impacted only KOH(g) levels. Impactor sample leachate analysis showed that for WP-braunite operation, the leachate contained KCl, NaCl, KOH, and NaOH, in decreasing order. For WC-ilmenite operation, the samples contained KOH and KCl. For SP fuel, most detected alkalis were KCl. For most cases, speciation of impactor samples qualitatively agreed with modelling predictions. Impactor and SID alkali measurements showed reasonable agreement for WC-braunite and SP-braunite tests.
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| 57. |
- Gogolev, Ivan, 1984, et al.
(författare)
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Chemical-looping combustion in a 100 kW unit using a mixture of synthetic and natural oxygen carriers - Operational results and fate of biomass fuel alkali
- 2019
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Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 88, s. 371-382
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Tidskriftsartikel (refereegranskat)abstract
- Biomass fuel use in chemical looping combustion enables negative CO2 emissions through BECCS (Bio-Energy Carbon Capture and Storage). Effective biomass utilization in CLC requires an economical and effective oxygen carrier to achieve high fuel conversion, effective CO2 capture, and management of the harmful effects of biomass alkali release (bed agglomeration, oxygen carrier deactivation, fouling and corrosion). These issues were addressed in 100 kW CLC pilot experiments. Building on previous work, a mixture of a synthetic calcium manganite perovskite and natural ilmenite was used as the oxygen carrier. Four biomass fuels of varied alkali content were tested: black pellets of steam-exploded stem wood (BP), BP impregnated with K2CO3, a mixture of 50% BP with 50% straw pellets, and wood char. Experiments showed high fuel conversion and very high CO2 capture, with overall performance exceeding that of ilmenite and manganese ore. More than 95% gas conversion was achieved with black pellets at around 950 degrees C. The fate of biomass alkali, previously virtually unknown in CLC research, was explored by implementing online surface-ionization-based measurement of alkali released in the flue gases of the fuel reactor (FR) and air reactor (AR). Release levels were found to correlate with the fuel alkali content. The flue gas measurements and bed material elemental analyses suggest that most of the fuel alkali are accumulated in the oxygen carrier. Unexpectedly, it was found that flue gas alkali release occurs in both the FR and AR, with AR exhibiting an equal or higher rate of release vs. the FR.
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| 58. |
- Gogolev, Ivan, 1984, et al.
(författare)
-
Commissioning, performance benchmarking, and investigation of alkali emissions in a 10 kWth solid fuel chemical looping combustion pilot
- 2021
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Ingår i: Fuel. - : Elsevier BV. - 0016-2361 .- 1873-7153. ; 287
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Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion of biomass-sourced fuels (bio-CLC) is a novel bio-energy with carbon capture and storage (BECCS) technology for power and heat generation with net negative CO2 emissions. In this study, a new 10 kWth CLC pilot designed for high-volatiles biomass fuels was commissioned with ilmenite oxygen carrier and five different biomass fuels of varying volatile and alkali content fractions. The system was tested for its ability to convert high and low volatile content biomass, while achieving high carbon capture efficiency. The new pilot achieved carbon capture close to 100% for high-volatiles biomass, and >94% for low-volatiles biomass char fuels. Furthermore, due to the implementation of a volatiles distributor, the new pilot demonstrated an improvement of up to 10 percentage points of gas conversion efficiency for high-volatiles biomass vs. the previous generation reactor. Gaseous alkali emissions were measured with a surface ionization detection system. Flue gas alkali release levels were found to rise with higher fuel alkali content. Alkali emissions were found to be approximately similar in the AR and the FR for all but the straw pellet mixture fuel (highest alkali content fuel). For the straw pellet mixture, gaseous alkali release levels in the AR were up to seven times higher than those of the FR. In all cases, over 96% of the fuel's alkalis were absorbed by the ilmenite bed material. Ilmenite's strong alkali absorption characteristics were concluded to be the key determinant of gas-phase release of biomass alkali in the conducted experiments.
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| 59. |
- Gogolev, Ivan, 1984, et al.
(författare)
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Effects of Temperature, Operation Mode, and Steam Concentration on Alkali Release in Chemical Looping Conversion of Biomass-Experimental Investigation in a 10 kWthPilot
- 2022
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Ingår i: Energy & Fuels. - : American Chemical Society. - 0887-0624 .- 1520-5029. ; 36:17, s. 9551-9570
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Tidskriftsartikel (refereegranskat)abstract
- Alkali release was studied in a 10 kWthchemical looping pilot operated with a Linz-Donawitz (LD) slag oxygen carrier (OC) and three biomass fuels. Experiments were performed at three temperatures and in three operation modes: chemical looping combustion (CLC), chemical looping gasification (CLG), and oxygen-carrier-aided combustion (OCAC). Gas-phase alkali release was measured with a surface ionization detector (SID). Fuel reactor (FR) gas-phase alkali emissions increased with the temperature. This occurred as a result of increased evaporation of KCl and enhanced decomposition of alkali salts during char conversion. Air reactor (AR) alkali emissions were lower than in the FR and independent of the operating temperature. In comparison of operating modes, CLC and CLG modes resulted in similar gas-phase alkali emissions due to the similar extent of char conversion. In contrast, operation of the reactor system in OCAC mode resulted in significantly lower levels of gas-phase alkalis. The difference in alkali emission was attributed to the steam-rich atmosphere of CLC. The effect of steam was further investigated in CLC and OCAC tests. Lowering steam concentrations in CLC operation resulted in lower gas-phase alkali emissions, while introducing steam to the FR during OCAC operation resulted in higher alkali emissions. It was concluded that steam likely enhances gas-phase K release through a reaction of K2CO3within the fuel char with steam to produce KOH(g). Solid sampling and analysis for K content was used along with SID measurements to develop a K mass balance for the reactor system. Mass balance results for the straw pellet fuel tests showed that LD slag OC absorbs approximately 15-51% of fuel K, 2.2% of fuel K is released to the gas phase, and up to 3.4% of fuel K is captured in the AR fly ash. The residual 40-80% of fuel K was determined to leave the FR as K-rich fly ash.
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| 60. |
- Gogolev, Ivan, 1984, et al.
(författare)
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Investigation of biomass alkali release in a dual circulating fluidized bed chemical looping combustion system
- 2021
-
Ingår i: Fuel. - : Elsevier BV. - 0016-2361. ; 297
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical looping combustion (CLC) of biomass is a promising technology for power generation with integrated carbon capture. In CLC, alkali content of biomass poses potential issues of bed agglomeration, as well as heat exchanger fouling and corrosion. The fate of biomass alkalis was investigated in a dual-interconnected circulating fluidized bed CLC system. Experiments were conducted in oxygen carrier aided combustion (OCAC) and CLC modes. Ilmenite and braunite oxygen carriers and three biomass fuels (wood pellets, wood char, straw pellets) were tested. Flue gas alkali emissions in the air reactor (AR) and fuel reactor (FR) were measured with a surface ionization detector (SID). Results showed that CLC operation yields gas-phase alkali emissions that are up to 15 times higher than in comparable OCAC operation. Results analysis concluded that increased alkali emissions in CLC arise from the steam atmosphere in the FR, whereby steam accelerates the decomposition of alkali compounds in the biomass. Retention of alkalis in the condensed phase was found to be >97% for ilmenite and >92% for braunite CLC operation. Up to 60?80% of the retention was attributed to fuel ash formation. The residual retention was attributed to absorption of alkalis by the oxygen carriers. Absorption likely occurred mainly through formation of alkali manganates and silicates in braunite, and formation of alkali silicates, aluminosilicates, manganates, and titanates in ilmenite. Gas-phase alkali emissions in the AR, although less than in the FR, were found to occur due to combustion of unconverted fuel carried over from the FR to the AR.
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