| 1. |
- Keller, Martin, 1985, et al.
(författare)
-
Investigation of Natural and Synthetic Bed Materials for Their Utilization in Chemical Looping Reforming for Tar Elimination in Biomass-Derived Gasification Gas
- 2014
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 28:6, s. 3833-3840
-
Tidskriftsartikel (refereegranskat)abstract
- The removal of condensable hydrocarbons or tars from raw gas derived from biomass gasification presents an obstacle in the widespread application of biomass gasification. Hot catalytic tar cleaning as a secondary tar removal strategy is discussed as a tar cleaning technology. This can be realized in a dual-fluidized-bed reactor system, in which a catalytically active bed material is continuously regenerated. Such a process is termed chemical looping reforming (CLR). In such a process, it has been suggested that oxygen carrier particles employed for chemical looping combustion may be used, with the oxygen transfer from the particles to the gas promoting tar decomposition. Experiments were conducted in a small-scale, batch-wise fluidized-bed reactor with the aim of investigating a variety of bed materials for this process. The purpose of the present work is thus to conduct a screening study of a variety of bed materials based on the transition metals Fe, Mn, Ni, and Cu. The experiments were conducted in a batch fluidized bed, where the particles are exposed to reformer and regenerator conditions alternatingly. The conversion of ethylene from a synthetic gasification gas mixture was used as an indicator for the suitability of the materials for tar conversion. It was found that the natural material bauxite and the synthetic bed materials NiO/alpha-Al2O3, CuO/MgAl2O4, and La0.8Sr0.2FeO3/gamma-Al2O3 exhibit high ethylene conversion rates and, thus, possess promising properties for their application in CLR
|
|
| 2. |
- Adanez-Rubio, Inaki, et al.
(författare)
-
Investigation of Combined Supports for Cu-based Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:7, s. 3918-3927
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping with oxygen uncoupling (CLOU) process is a novel solution for efficient combustion with inherent separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor. In the fuel reactor, the metal oxide releases gas phase oxygen which oxidizes the fuel through normal combustion. In this study, Cu-based oxygen carrier materials that combine different supports of MgAl2O4, TiO2 and SiO2 are prepared and characterized with the objective of obtaining highly reactive and attrition resistant particles. The oxygen carrier particles were produced by spray-drying and were calcined at different temperatures ranging from 950 to 1030oC for 4 h. The chemical-looping performance of the oxygen carriers was examined in a batch fluidized-bed reactor in the temperature range of 900-950oC under alternating reducing and oxidizing conditions. The mechanical stability of the oxygen carriers was tested in a jet-cup attrition rig. All of the oxygen carriers showed oxygen uncoupling behaviour with oxygen concentrations close to equilibrium. During reactivity tests with methane, oxygen carriers with lower mechanical stability showed higher reactivity, yielding almost complete fuel conversion. Oxygen carrier materials based on support mixtures of MgAl2O4/TiO2, MgAl2O4/SiO2 and TiO2/SiO2 showed a combination of high mechanical stability, low attrition rates, good reactivity with methane and oxygen uncoupling behaviour.
|
|
| 3. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
CaxLa1−xMn1−yMyO3−δ (M = Mg, Ti, Fe or Cu) as Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2013
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 27:8, s. 4097-4107
-
Tidskriftsartikel (refereegranskat)abstract
- Perovskite materials of the type CaxLa1−xMn1−yMyO3−δ (M = Mg, Ti, Fe or Cu) have been investigated as oxygen carriers for the chemical-looping with oxygen uncoupling (CLOU) process. The oxygen carrier particles were produced by mechanical homogenization of primary solids in a rotary evaporator followed by extrusion and calcination at 1300°C for 6 h. The chemical-looping characteristics of the substituted perovskites developed in this work were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900−1000°C during alternating reducing and oxidizing conditions. The oxygen carriers showed oxygen releasing behaviour (CLOU) in inert atmosphere between 900−1000°C. In addition, their reactivity with methane was high, approaching complete gas yield for all of the materials at 950°C, the exception being the Cu-doped perovskite which defluidized during reduction. The rates of oxygen release were also investigated using devolatilized wood char as solid fuel, and were found to be similar. The required solids inventory in the fuel reactor for the perovskite oxygen carriers is estimated to be 325 kg/MWth. All of the formulations exhibited high rates of oxidation and high degree of stability with no particle fragmentation or agglomeration. The high reactivity and favourable oxygen uncoupling properties make these oxygen carriers promising candidates for the CLOU process.
|
|
| 4. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
CaZrO3 and SrZrO3-based CuO Oxygen Carriers for Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
-
Ingår i: Energy Procedia. - : Elsevier BV. - 1876-6102. ; 51, s. 75-84
-
Konferensbidrag (refereegranskat)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are novel solutions for efficient combustion with inherent separation of carbon dioxide. In this work, oxygen carriers based on CuO supported by zirconates of SrZrO3 and CaZrO3 are investigated. The oxygen carriers were produced by mechanical homogenization of primary solids in a rotary evaporator followed by extrusion, drying and calcination at 950 and 1030 degrees C for 6 h. Their chemical-looping performance was evaluated in a laboratory-scale fluidized-bed reactor at 900 and 925 degrees C under cyclic oxidizing, inert (N-2) and reducing (CH4) conditions. All oxygen carriers exhibited rapid release of oxygen in the inert environment (CLOU) with high conversion of methane. The carrier calcined at 1030 degrees C with SrZrO3 as support showed no agglomeration or deactivation and exhibited the highest reactivity. Thus, the use of this oxygen carrier could be of interest for the CLOU process.
|
|
| 5. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
Evaluation of CuAl2O4 as an Oxygen Carrier in Chemical-Looping Combustion
- 2012
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 51:43, s. 13924-13934
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with intrinsic separation of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor where the fuel, or gasification products of the fuel, reacts with the solid oxygen carrier. In this work, copper(II) aluminate (CuAl2O4) was assessed as a potential oxygen carrier using methane as fuel. The carrier particles were produced by freeze–granulation and calcined at 1050 °C for a duration of 6 h. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900–950 °C during 45 alternating redox cycles. The oxygen carrier exhibited reproducible and stable reactivity behavior in this temperature range. Neither agglomeration nor defluidization was noticed in any of the cycles carried out at 900–925 °C. However, after reactivity tests at 950 °C, soft agglomeration and particle fragmentation were observed. Systematic phase analysis of the Cu–Al–O system during the redox cycle was carried out as a function of duration of reduction and oxygen concentration during the oxidation period. It was found that the CuAl2O4 is reduced to copper(I) aluminate (CuAlO2; delafossite), Cu2O, and elemental Cu. The CuAlO2 phase is characterized by slow kinetics for oxidation into CuO and CuAl2O4. Despite this kinetic limitation, complete conversion of methane with reproducible reactivity of the oxygen carrier is achieved. Thus, CuAl2O4 could be a potential oxygen carrier for chemical-looping combustion.
|
|
| 6. |
|
|
| 7. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
Investigation of Different Manganese Ores as Oxygen Carriers in Chemical-Looping Combustion (CLC) for Solid Fuels
- 2014
-
Ingår i: Applied Energy. - : Elsevier BV. - 1872-9118 .- 0306-2619. ; 113, s. 1883-1894
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) process is a novel solution for efficient combustion with direct capture of carbon dioxide. The process uses a metal oxide as an oxygen carrier to transfer oxygen from an air to a fuel reactor, where the fuel reacts with the solid oxygen carrier. In this work, six different manganese ores are investigated as oxygen carriers for CLC application. The chemical-looping characteristics of the oxygen carriers were evaluated in a laboratory-scale fluidized-bed reactor in the temperature range of 900-970oC during alternating reducing and oxidizing conditions. Three of the manganese ores showed a small oxygen release in inert environment between 850 and 950oC. During reactivity tests, the gas yield with methane increased with the temperature and complete conversion of 50% CO in H2 was obtained for all of the ores. The rates of char gasification of two fuels, namely Mexican petroleum coke and Swedish wood char, were compared for the different manganese ores at 970oC and with 50% H2O in N2 as fluidizing gas. Ilmenite and a manufactured Mn-oxide oxygen carrier consisting of Mn3O4 and MgO-stabilized ZrO2 as support were also included for comparison. The char gasification rate and the gas conversion were higher with the manganese ores and the Mn-oxide oxygen carrier compared to ilmenite. However, the higher reactivity of the manganese ores with H2 and the ensuing decrease in H2 inhibition for manganese ores is not sufficient to explain their higher rate of char gasification. Surface analysis of partially gasified petcoke particles in the presence of manganese ores showed formation of cavities and channels as well as a uniform distribution of potassium and sodium elements. The rate of char gasification also increased with the concentration of potassium and sodium impurities in the manganese ores. Thus the results suggest that the increased rate of char conversion for manganese ores is due to alkali-catalyzed steam gasification. The increase in rate of char gasification, in combination with potentially low costs of these materials suggests that manganese ores could be interesting materials for CLC with solid fuels.
|
|
| 8. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
Oxygen Release and Oxidation Rates of MgAl2O4-Supported CuO Oxygen Carrier for Chemical-Looping Combustion with Oxygen Uncoupling (CLOU)
- 2012
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 26:11, s. 6528-6539
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are novel solutions for efficient combustion with inherent separation of carbon dioxide. These processes use a metal oxide as an oxygen carrier to transfer oxygen from an air reactor to a fuel reactor, where the fuel reacts with the solid oxygen carrier. When solid fuel is used in CLC, the char must be gasified by, e.g., steam to form H2 and CO, that can be subsequently oxidized to H2O and CO2 by the oxygen carrier. In the case of CLOU, the oxygen carrier releases oxygen gas in the fuel reactor. This enables a high rate of conversion of char from solid fuels, because it eliminates the need for the gasification step needed in normal CLC with solid fuels. In this work, the rate of oxygen release and oxidation of an oxygen carrier consisting of CuO supported by MgAl2O4 (40/60 wt %) for the CLOU process is investigated. The oxygen carrier was produced by freeze-granulation, calcined at 950 °C, and sieved to a size range of 125–180 μm. The reaction rates were obtained in a laboratory-scale fluidized-bed reactor in the temperature range of 850–900 °C, under alternating reducing and oxidizing conditions. The rate of oxygen release was obtained using devolatilized wood char as the fuel in N2 fluidization. Care was taken to obtain reliable measurements not affected by the availability of the fuel and temperature increase in the bed during combustion of the fuel with the released oxygen from the carrier. The Avrami–Erofeev mechanism was used to model the rates of oxygen release and the values of ko and Eapp were estimated to be 2.5 × 105 s–1 and 139.3 kJ mol–1, respectively. The rates of Cu2O oxidation were investigated in a flow of 5% O2 at the inlet of the reactor. However, it was observed that the oxidation rate is limited by the oxygen supply, indicating rapid conversion of the oxygen carrier. From the obtained reaction rates, the minimum total amount of the investigated oxygen carrier needed in the air and the fuel reactor is estimated to be between 69–139 kg MWth–1.
|
|
| 9. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
Prospects of Al2O3 and MgAl2O4-Supported CuO Oxygen Carriers in Chemical-Looping Combustion (CLC) and Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2011
-
Ingår i: Energy & Fuels. - : American Chemical Society (ACS). - 1520-5029 .- 0887-0624. ; 25:11, s. 5493-5502
-
Tidskriftsartikel (refereegranskat)abstract
- The chemical-looping combustion (CLC) and chemical-looping with oxygen uncoupling (CLOU) processes are attractive solutions for efficient combustion with direct separation of carbon dioxide. In this work, the feasibility of CuO supported on Al2O3 and MgAl2O4 for CLC and CLOU processes is investigated. The oxygen carriers were produced by freeze-granulation and calcined at 950 and 1050 degrees C. The chemical-looping characteristics were evaluated in a laboratory-scale fluidized bed at 900 and 925 degrees C under alternating reducing and oxidizing conditions. Tendencies toward agglomeration, defluidization, and loss of active phase were analyzed by changing the experimental process variables, such as reaction time, temperature, and reducing and inert environments. Complete conversion of methane was obtained for all oxygen carriers investigated in this work Three out of four oxygen carriers also featured the rapid release of oxygen in an inert environment (CLOU). In the case of Al2O3) as support, a CLC and a CLOU oxygen carrier were obtained depending on the calcination temperature. In addition, analyses of the CuO-Al2O3 phase equilibria system under oxidizing and reducing conditions have been carried out. At the investigated temperatures, it is inferred for the case of Al2O3 as support that part of the active phase (either CuO or CuAl2O4 is bound as CuAlO2 during incomplete reduction with slow kinetics for reoxidation. However, when complete reduction is attained, the original active phase composition is rejuvenated upon oxidation. As a result, the use of CuAl2O4 is suggested for CLC processes from the point of agglomeration and attrition-free functioning of the oxygen carrier. In the case of MgAl2O4 as support, the oxygen carrier exhibited a stable oxygen-releasing behavior due to the existence of relatively intact CuO. Together with the absence of agglomeration and major morphological changes, the use of MgAl2O4-supported CuO is suggested as a suitable oxygen carrier for CLOU processes.
|
|
| 10. |
- Arjmand, Mehdi, 1986, et al.
(författare)
-
Sulfur Tolerance and Rate of Oxygen Release of Combined Mn-Si Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)
- 2014
-
Ingår i: Industrial & Engineering Chemistry Research. - : American Chemical Society (ACS). - 1520-5045 .- 0888-5885. ; 53:50, s. 19488-19497
-
Tidskriftsartikel (refereegranskat)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.
|
|
