| 1. |
|
|
| 2. |
- Arjmand, Mehdi, 1986, et al.
(author)
-
Screening of Combined Mn-Fe-Si Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU)
- 2015
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 29:3, s. 1868-1880
-
Journal article (peer-reviewed)abstract
- Combined oxygen carriers of Mn, Fe, and Si were screened for the chemical looping with oxygen uncoupling process with the objective of identifying materials with high reactivity and sufficient attrition resistance. Eleven oxygen carrier materials were produced by spray-drying and then calcined for 4 h at 1100 and 1200 degrees C. The ability of the oxygen carriers to release oxygen and to convert gaseous fuels was investigated in a batch fluidized-bed reactor under alternating reducing and oxidizing conditions for temperatures ranging from 850 degrees C to 1050 degrees C. The attrition behavior of the different materials was evaluated in a jet-cup attrition rig. All investigated oxygen carriers proved to release oxygen and showed high reactivity toward synthesis gas (50% CO in H-2). Oxygen carrier materials with comparably lower mechanical stability were found to have a higher reactivity toward methane. One of the investigated formulations showed to have both high mechanical stability and resistance toward attrition, as well as good methane conversion and oxygen release.
|
|
| 3. |
- Arjmand, Mehdi, 1986, et al.
(author)
-
Sulfur Tolerance and Rate of Oxygen Release of Combined Mn-Si Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 53:50, s. 19488-19497
-
Journal article (peer-reviewed)abstract
- Sulfur tolerance and rate of oxygen release of combined Mn-Si oxygen carriers for chemical-looping with oxygen uncoupling (CLOU) is investigated. The oxygen carriers were produced by spray-drying and calcined at 1150 degrees C. The resistance toward sulfur and the rates of oxygen release were evaluated in a laboratory-scale fluidized-bed reactor. It was found that the combined Mn-Si oxygen carrier is tolerant to SO2, at least up to a partial pressure of 5000 vppm. The rates of oxygen release were determined in the temperature range of 975 to 1100 degrees C using devolatilized wood char as fuel while fluidizing with N-2, to maintain a low oxygen partial pressure surrounding the particles. The Arrhenius parameters k(o) and E-app for the release of oxygen were estimated for the investigated materials assuming a zero-order reaction with respect to oxygen. The rates of oxygen release were relatively high, particularly at above 1050 degrees C. From the obtained reaction rates, the solids inventory required for combustion of coal was determined to be as low as 40 kg/MWth in the fuel reactor at 1100 degrees C. The results indicated that combined Mn-Si oxygen carriers could be interesting materials for the CLOU process by virtue of their resistance to sulfur deactivation and high rate of oxygen release.
|
|
| 4. |
- Arjmand, Mehdi, 1986, et al.
(author)
-
Sulfur Tolerance of CaxMn1–yMyO3−δ (M = Mg, Ti) Perovskite-Type Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:2, s. 1312-1324
-
Journal article (peer-reviewed)abstract
- Perovskite-structured oxygen carriers of the type CaxMn1–yMyO3−δ (M = Mg, Ti) have been investigated for the CLOU process. The oxygen carrier particles were produced by spray-drying and were calcined at 1300 °C for 4 h. A batch fluidized-bed reactor was used to investigate the chemical-looping characteristics of the materials. The effect of calcium content, dopants (Mg and Ti), and operating temperature (900, 950, 1000, and 1050 °C) on the oxygen uncoupling property and the reactivity with CH4 in the presence and absence of SO2 was evaluated. In addition, the attrition resistance and mechanical integrity of the oxygen carriers were examined in a jet-cup attrition rig. All of the investigated perovskite-type materials were able to release gas phase oxygen in inert atmosphere. Their reactivity with methane was high and increased with temperature and calcium content, approaching complete gas yield at 1000 °C. The reactivity decreased in the presence of SO2 for all of the investigated oxygen carriers. Decreasing the calcium content resulted in a less severe decrease in reactivity in the presence of SO2, with the exception of materials doped with both Mg and Ti, for which a higher resistance to sulfur deactivation could be maintained even at higher calcium contents. The drop in reactivity in the presence of SO2 also decreased at higher temperatures, and at 1050 °C, the decrease in the reactivity of the Mg- and Ti-doped material was minimal. Sulfur balance over the reactor system indicated that the fraction of the introduced SO2 that passed through the reactor increased with temperature. It was shown that it is possible to regenerate the oxygen carriers during reduction in the absence of SO2. Most of the materials also showed relatively low attrition rates. The results indicate that it is possible to modify the operating conditions and properties of perovskite-type oxygen carriers to decrease or avoid their deactivation by sulfur.
|
|
| 5. |
- Aronsson, Jesper, 1985, et al.
(author)
-
Improved Gas-Solids Mass Transfer in Fluidized Beds: Confined Fluidization in Chemical-Looping Combustion
- 2019
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 33:5, s. 4442-4453
-
Journal article (peer-reviewed)abstract
- © 2019 American Chemical Society. Fluidized bed processes with reactive bed material have become increasingly popular as research topics, with applications such as chemical-looping technologies, oxygen carrier aided combustion, and fluidized bed gasification being extensively investigated. When used at commercial scale the performance of such processes may be limited not by gas-solid reactivity, but by mass transfer of reactants from bubbles to the emulsion phase. In an effort to break down the two-phase flow structure, and thereby increase the bubble-emulsion mass transfer coefficient, spherical packing material was added to a fluidized bed using ilmenite as bed material. Two types of packing were tested: expanded clay aggregate (ECA) and aluminum silicate balls (ASB). Both packings had a diameter of about 12 mm but drastically different bulk densities of 240 kg/m 3 and 1400 kg/m 3 , respectively. These were tested in chemical-looping-combustion batch experiments using a stainless-steel reactor with a diameter of 78 mm, with syngas or carbon monoxide as fuel at 915 °C. The lighter packing formed a floating plug while the heavier remained stationary at the reactor bottom. To compare the confined fluidized bed to a reference conventional one, a simple reaction model was implemented based on the experiments. It showed that in the confined fluidized bed the associated effective reaction rate constant increased by up to a factor of 2 for a given bed mass. Further, up to 4 times less oxygen carrier bed mass was needed to achieve the same gas conversion, at a lower total pressure drop. Experiments with only carbon monoxide showed similar gains when using aluminum silicate balls, indicating that catalysis of the water gas shift reaction was not the main factor for improved gas conversion. It can be concluded that the concept of confined fluidization has great potential to increase mass transfer in fluidized beds with active bed material.
|
|
| 6. |
- Aronsson, Jesper, et al.
(author)
-
Increasing gas-solids mass transfer in fluidized beds by application of confined fluidization-A feasibility study
- 2019
-
In: Applied Sciences (Switzerland). - : MDPI AG. - 2076-3417. ; 9:4
-
Journal article (peer-reviewed)abstract
- Fluidized bed applications where the bed material plays an active role in chemical reactions, e.g. chemical looping combustion, have seen an increase in interest over the past decade. When these processes are to be scaled up to industrial or utility scale mass transfer between the gas and solids phases can become a limitation for conversion. Confined fluidized beds were conceptualized for other purposes in the 1960's but are yet to be applied to these recent technologies. Here it is investigated if they can prove useful to increase mass transfer but also if they are feasible from other perspectives such as pressure drop increase and solids throughflow. Four spherical packing solids, 6.35-25.4 mm in diameter at two different densities, were tested. For mass transfer experiments the fluidizing air was humidified and the water adsorption rate onto silica gel particles acting as fluidizing solids was measured. Olivine sand was used in further experiments measuring segregation of solids and packing, and maximum vertical crossflow of solids. It was found that mass transfer increased by a factor of 1.9-3.8 with packing solids as compared to a non-packed reference. With high-density packing, fluidizing solids voidage inside the packing was found to be up to 58% higher than in a conventional fluidized bed. Low density packing material favoured its flotsam segregation and with it higher fluidization velocities yield better mixing between packing and fluidizing solids. Maximum vertical cross-flow was found to be significantly higher with low density packing that fluidized, than with stationary high-density packing. Conclusively, the prospect of using confined fluidized beds for improving mass transfer looks promising from both performance and practical standpoints.
|
|
| 7. |
- Azimi, Golnar, 1985, et al.
(author)
-
Comprehensive study of Mn–Fe–Al oxygen-carriers for chemical-looping with oxygen uncoupling (CLOU)
- 2015
-
In: International Journal of Greenhouse Gas Control. - : Elsevier BV. - 1750-5836. ; 34, s. 12-24
-
Journal article (peer-reviewed)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.
|
|
| 8. |
- Azimi, Golnar, 1985, et al.
(author)
-
Investigation of Different Mn–Fe Oxides as Oxygen Carrier for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
-
In: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:1, s. 367-377
-
Journal article (peer-reviewed)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.
|
|
| 9. |
|
|
| 10. |
- Azimi, Golnar, 1985, et al.
(author)
-
Mn–Fe Oxides with Support of MgAl2O4, CeO2, ZrO2 and Y2O3–ZrO2 for Chemical-Looping Combustion and Chemical-Looping with Oxygen Uncoupling
- 2014
-
In: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 53:25, s. 10358-10365
-
Journal article (peer-reviewed)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.
|
|
