| 21. |
- Aronsson, Jesper, 1985, et al.
(författare)
-
Modeling and scale analysis of gaseous fuel reactors in chemical looping combustion systems
- 2017
-
Ingår i: Particuology. - : Elsevier BV. - 2210-4291 .- 1674-2001. ; 35, s. 31-41
-
Tidskriftsartikel (refereegranskat)abstract
- This work investigates the up-scaling to commercial scale of chemical looping combustion (CLC); a next-generation technology for carbon capture and storage. Focus lies on the bottom bed, which is considered to be the critical region in up-scaling due to its large solids inventory combined with relatively inefficient gas-solids contact. Two CLC reactors of vastly different size (bench and utility scale) are studied in order to discern the difference in effects related to up-scaling. A 1-dimensional model is used in order to simulate the units studied. The model considers kinetics dependent on the degree of oxidation of the oxygen carrier and a population distribution of the oxygen carriers, whose mixing accounts for both convective and dispersive transport. The model is validated against bench scale data and applied to evaluate the performance of a 1000 MWth CLC fuel reactor using either syngas or methane as fuel.Using the model, sensitivity analyses are carried out to depict the effect on the fuel conversion of several parameters such as solids circulation, oxygen carrier reactivity, bed height and maximum bubble size allowed. It is shown that mass transfer of gas from bubbles to the emulsion phase represents a strongly limiting factor for fuel conversion in the bottom bed of utility scale fuel reactors.
|
|
| 22. |
- Azimi, Golnar, 1985, et al.
(författare)
-
Chemical-looping with oxygen uncoupling using combined Mn-Fe oxides, testing in batch fluidized bed
- 2011
-
Ingår i: Energy Procedia. 10th International Conference on Greenhouse Gas Control Technologies; Amsterdam; 19-23 September 2010. - : Elsevier BV. - 1876-6102. ; 4, s. 370-377
-
Konferensbidrag (refereegranskat)abstract
- Chemical-looping with oxygen uncoupling (CLOU) has been studied with gaseous and solid fuel in a small fluidized bed batch reactor, using new Fe-Mn-based oxygen carriers. CLOU is a development of chemical-looping combustion, using oxygen carriers with the ability to release oxygen, which can react directly with the fuel. The carbon dioxide from the combustion is inherently obtained as separated from the rest of the flue gases. In this work manganese is combined with iron oxides, giving new bimetallic oxide compounds with different thermodynamic properties compared to pure manganese oxides. Four different combinations of iron manganese oxide have been examined by decomposition in N2 and also reaction with methane and syn-gas. F3, a material with a molar ratio of Fe:Mn of 2:1, showed the best behaviour in terms of its release of oxygen, take up of oxygen, fluidizability and methane conversion. Therefore, F3 was also tested with solid fuel using inert fludization gas, N2. The char particles effectively remove oxygen released as it is converted to CO2. Thus, CO2 will represent the oxygen release. The tests show that the particles release oxygen corresponding to approximately 0.5% of their mass. Moreover, a test where steam was added in the fluidization gas showed high gas conversion, with essentially no unconverted gas. Thus, the tests indicate that the F3 particles, if used in chemical-looping of solid fuels, could contribute both to faster fuel conversion and to higher conversion of gas, as compared to a normal oxygen carrier that does not release oxygen.
|
|
| 23. |
- Azimi, Golnar, 1985, et al.
(författare)
-
Comprehensive study of Mn–Fe–Al oxygen-carriers for chemical-looping with oxygen uncoupling (CLOU)
- 2015
-
Ingår i: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 34, s. 12-24
-
Tidskriftsartikel (refereegranskat)abstract
- The reactivity and attrition resistance of Mn–Fe oxygen carriers with addition of Al2O3 as support have been investigated. Spray-dried oxygen-carrier particles with Mn:Fe molar ratios of 80:20 and 33:67 were prepared using different amounts of Al2O3. Each material was calcined for 4 h at 950 °C, 1100 °C or 1200 °C. The oxygen carriers were studied in a batch fluidized bed reactor to investigate their reactivity with wood char, CH4, syngas and also their oxygen release in N2. In order to measure the mechanical stability of the different materials, the attrition resistance was measured in a jet-cup apparatus. Addition of Al2O3 to materials with a Mn:Fe molar ratio of 80:20 was not advantageous. Generally oxidation of these materials was problematic. The Al2O3 supported materials with a Mn:Fe molar ratio of 80:20 calcined at 950 °C and 1100 °C showed poor attrition resistance and were highly fragmented or turned to dust, whereas those calcined at 1200 °C showed high attrition resistance but poor gas conversion.Materials with a Mn:Fe molar ratio of 33:67 supported with Al2O3 generally showed better attrition resistance. Also their oxidation with 5 vol% of oxygen was possible at temperatures higher than 850 °C. Furthermore, some of these materials showed good reactivity with methane, syngas and char. Low attrition, good reactivity and CLOU properties in combination with potentially low raw materials costs, make these materials interesting for CLC.
|
|
| 24. |
- Azimi, Golnar, 1985, et al.
(författare)
-
Investigation of Different Mn–Fe Oxides as Oxygen Carrier for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:1, s. 367-377
-
Tidskriftsartikel (refereegranskat)abstract
- The appropriate oxygen carrier for chemical-looping with oxygen uncoupling (CLOU) should be thermodynamically capable of being oxidized in the air reactor and also release gaseous O2 in the fuel reactor at appropriate temperatures and oxygen partial pressures. It should also be mechanically durable, cheap, and environmentally friendly. Iron–manganese oxides appear to be especially promising due to favorable thermodynamics. In this work, combined metal oxides of iron and manganese were investigated for the CLOU process. Particles with different ratios of Mn/Fe were produced using spray drying. The particles were calcined at 950 and 1100 °C for 4 h and then tested with respect to parameters important for CLOU. The crushing strength for these materials was between 0.1 to 1.7 N, depending on their composition and sintering temperature. The ability of the iron–manganese oxide particles to release oxygen in the gas phase was examined by decomposition of the material in a stream of N2. Moreover, the reaction with both methane and synthesis gas (50/50% CO/H2) was examined in a batch fluidized bed reactor. Here, the particles were alternately oxidized with 5% O2 and reduced in N2 or with fuel at 850 °C, 900 and 950 °C. From the results, it can be concluded that during the nitrogen period, the oxygen carriers with Mn3O4 content in the range from 20 wt % to 40 wt % release oxygen at 900 °C, whereas the materials with higher manganese content show no oxygen release. This is because they could not be oxidized to bixbyite. By decreasing the temperature from 900 to 850 °C, it was possible to oxidize oxygen carriers with manganese oxide content of 50 wt % and higher, and consequently, oxygen release during the nitrogen period was seen for these materials. This is in agreement with the phase diagram for this system. The reaction rate with methane follows the oxygen release trend very well. At the higher reaction temperature, 950 °C, oxygen carriers with manganese content in the range from 25% to 33% show the best gas conversion of methane. At 850 °C, on the other hand, high methane conversion is seen for particles with high manganese content. In fact, several particles had almost full conversion of methane to CO2 and H2O at 850 °C using a bed mass in the batch reactor corresponding to 70 kg oxygen carrier/MW.
|
|
| 25. |
|
|
| 26. |
- Azimi, Golnar, 1985, et al.
(författare)
-
Mn–Fe Oxides with Support of MgAl2O4, CeO2, ZrO2 and Y2O3–ZrO2 for Chemical-Looping Combustion and Chemical-Looping with Oxygen Uncoupling
- 2014
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 53:25, s. 10358-10365
-
Tidskriftsartikel (refereegranskat)abstract
- The feasibility of utilizing a combined oxide (Mn0.75Fe0.25)(2)O-3 as an oxygen carrier for chemical-looping with oxygen uncoupling (CLOU) has been investigated. To increase the strength and attrition resistance of such particles, the oxygen carrier was prepared together with MgAl2O4, CeO2, ZrO2 and Y2O3-ZrO2 as supports. The oxygen-carrier particles were prepared using spray-drying. Each material was calcined for 4 h at 950, 1100 or 1200 degrees C. The materials were studied in a batch fluidized bed reactor to investigate their oxygen release and uptake potential and also their reactivity with CH4 and syngas. To gauge the mechanical stability of the different materials, the attrition resistance was measured in a jet-cup apparatus. With the exception of the material with MgAl2O4, the oxygen uncoupling property of the active combined oxides was largely kept intact using the added support materials. On the basis of the results from the reactivity tests and the measured attrition rates for all the particles, the material utilizing ZrO2 support seems to be the most promising candidate as an oxygen carrier for gaseous and solid fuels. However, due to phase transformations of the ZrO2 at higher temperatures, the calcination and operational temperature should likely not exceed 950 degrees C.
|
|
| 27. |
- Azimi, Golnar, 1985, et al.
(författare)
-
(MnzFe1—z)yOx combined oxides as oxygen carrier for chemical-looping with oxygen uncoupling
- 2013
-
Ingår i: AICHE Journal. - : Wiley. - 1547-5905 .- 0001-1541. ; 59:2, s. 582-588
-
Tidskriftsartikel (refereegranskat)abstract
- Oxygen carrier particles with the composition (Mn0.8,Fe0.2)2O3 were found to readily release gas phase oxygen at 850°C, and were capable to oxidize CH4 completely and convert wood char rapidly to CO2 during experiments in a batch fluidized bed reactor. The particles were able to release oxygen corresponding to more than 3% of their mass in less than 40 s. Because of the low price and favourable environmental properties of manganese and iron oxides, this finding could be of great importance for the development of chemical-looping combustion with oxygen uncoupling
|
|
| 28. |
|
|
| 29. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
-
On evaluation of synthetic and natural ilmenite using syngas as fuel in chemical-looping combustion (CLC)
- 2010
-
Ingår i: Chemical Engineering Research and Design. - : Elsevier BV. - 0263-8762 .- 1744-3563. ; 88:11A, s. 1505-1514
-
Tidskriftsartikel (refereegranskat)abstract
- Chemical-looping combustion (CLC) is a combustion technique where the CO2 produced is inherently separated fromthe rest of the flue gases with a considerably low energy penalty. For this reason, CLC has emerged as one of the moreattractive options to capture CO2 from fossil fuel combustion. When applying CLC with solid fuels, the use of a lowcost oxygen carrier is highly important, and one such low cost oxygen carrier is the mineral ilmenite. The currentwork investigates the reactivity of several ilmenites, some which are synthetically produced by freeze granulationand two natural minerals, one Norwegian ilmenite and one South African ilmenite.A laboratory fluidized bed reactor made of quartz was used to simulate a two reactor CLC system by alternatingthe reduction and oxidation phase. The fuel was syngas containing 50% CO and 50% H2. A mixture of 6 g of ilmenitewith 9 g inert quartz of diameter 125–180μm was exposed to a flow of 900mLn/min syngas in the reduction phase.During the oxidation phase, a 900mLn/min flow of 10% O2 diluted in N2 was used.The experimental results showed that all ilmenites give higher conversion of H2 than of CO. Generally, syntheticilmenites have better CO and H2 conversion than natural ilmenites and synthetic ilmenites prepared with an excessof Fe generally showed higher total conversion of CO than synthetic ilmenites with an excess of Ti. Most syntheticilmenites and the Norwegian ilmenite showed good fluidization properties during the experiments. However, for twoof the synthetically produced materials, and for the South African ilmenite, particle agglomerations were visible atthe end of the experiment.
|
|
| 30. |
- Azis, Muhammad Mufti, 1983, et al.
(författare)
-
The Effect of Bituminous and Lignite Ash on the Performance of Ilmenite as Oxygen Carrier in Chemical‐Looping Combustion
- 2013
-
Ingår i: Chemical Engineering and Technology. - : Wiley. - 0930-7516 .- 1521-4125. ; 36:9, s. 1460-1468
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of ash in chemical-looping combustion (CLC) has been studied in a lab-scale fluidized bed reactor. The oxygen carrier, ilmenite, was investigated with German lignite coal, Chinese bituminous coal, Mexican pet coke, wood char, and methane. Lignite ash and ash from gasified Chinese bituminous coal were compared in this study. Up to 50 wt % and 33.3 wt % loadings of ash from the combustion of lignite and ash from the gasification of coal were added. The gas conversion was clearly affected by the addition of ash, and very similar results were seen both for methane conversion and for CO conversion in the solid fuel tests. Thus, both ashes showed initial decrease in gas conversion with the addition of some ash due to the presence of inert/deactivating material in the ashes. At higher ash loading, a beneficial effect of ash could be seen. Furthermore, no negative effect of ash addition on the fluidizability of the bed material could be seen.
|
|
