A customized jet cup for measuring attrition resistance of oxygen carrier particles for chemical looping combustion has been constructed and used to evaluate 25 different material samples, all of which previously have been subject to continuous operation in chemical looping reactors at Chalmers University of Technology. The effect of continuous operation has been assessed by comparing attrition behaviour of fresh particles with that of used ones. It is concluded that the correlation between the jet cup tests and operational experience is robust, and that there is always considerable difference in attrition resistance between fresh and used particles of the same batch. Composite materials with NiO or Fe 2 O 3 as active phase and Al 2 O 3 -, NiAl 2 O 4 -or MgAl 2 O 4 -based support and materials based on the CaMnO 3-δ perovskite structure typically had high attrition resistance, which improved further following operation with fuel. Combined (Fe x Mn 1-x ) 2 O 3 oxides and all materials containing smaller or larger amounts of either CuO or ZrO 2 experienced reduced attrition resistance during operation with fuel, and usually also had low attrition resistance to begin with. Fresh particles of the commonly used oxygen carrier ilmenite had reasonably high attrition resistance, while ilmenite that had been subject to chemical looping combustion of natural gas showed higher rate of attrition. No strong correlation between the commonly used crushing strength index and attrition resistance measured with jet cup could be established, but it was clear that particles with a crushing strength above 2 N were much more likely to have high attrition resistance compared to softer particles. As compared to crushing strength, the jet cup testing were better correlated to attrition in actual operation.

In chemical-looping combustion (CLC), an oxygen carrier provides lattice oxygen for complete combustion of a fuel for heat and power production. The reduced metal oxide is then oxidized in a separate reactor. The combustion products CO2 and H2O are obtained in pure form, without any nitrogen in the gas. As no gas separation work is needed, this could be a breakthrough technology for carbon capture (CCS). Normally, the fuel-and air-reactor are designed utilizing interconnected fluidized beds. The same underlying reversible redox reactions of CLC can be used for other fuel conversion technologies. These include fluidized bed processes for gas, solid and liquid fuels for heat, power, syngas or hydrogen production. Some of these concepts were suggested as far back as the 1950's, while others have just recently been proposed. Chalmers University of Technology has been involved in CLC research for over 18 years, and this paper will provide a review of some recent developments with respect to CLC with gaseous, liquid and solid fuels. Further, the paper will provide an overview some related technologies where Chalmers is conducting research: i) Chemical-looping gasification (CLG), ii) Chemical-looping reforming (CLR) and iii) Chemical-looping tar reforming (CLTR). In these processes, a pure syngas/hydrogen can be produced effectively, which could be utilized for chemical or fuel production. CHEMICAL-LOOPING COMBUSTION (CLC) Background-As is evident from Fig. 1, the gas stream from the fuel reactor contains a concentrated stream of CO2 and H2O, while the nitrogen from the combustion air is obtained in the air reactor outlet. Possible C28E5−TR1132 (900...950°C) C28E1S2 (975°C) C28 (940°C) C14 (930...950°C) Ni−based (900°C)

An ilmenite oxygen carrier was tested in a laboratory scale chemical-looping reactor with a nominal thermal capacity of 300 W th . Ilmenite is a mineral iron-titanium oxide, which has been used extensively as an oxygen carrier in chemical-looping combustion. Two different kinds of fuels were used, a sulfur-free kerosene and one kerosene that contained 0.57 mass-% sulfur. Both fuels were continuously evaporated and directly fed into the chemical-looping reactor. Experiments were conducted for 50 h with the sulfurfree kerosene and for 30 h with the sulfurous kerosene. CO 2 yields above 99 % were achieved with both types of fuel. A significant and lasting improvement in the oxygen carrier's reactivity was observed, presumably an effect of using sulfurous kerosene. No evidence of sulfur was found on the particles' surface.

The fuel conversion properties of two oxygen carriers, based on manganese-and copper-oxide, were investigated with sulphur-free kerosene in a chemical-looping reactor with continuous particle circulation. An injection system was used, in which kerosene was evaporated, mixed with superheated steam and fed directly into the lab scale chemical-looping reactor. The manganese-based oxygen carrier M4MZ-1200 was composed of 40 wt% Mn 3 O 4 and 60 wt% MgO-ZrO 2 and was used for chemical-looping combustion (CLC) experiments for 17 h. The copper-based oxygen carrier C2Z-1050 was composed of 20 wt% CuO and 80 wt% ZrO 2 and was used for 45 h with fuel addition. With M4MZ-1200 oxygen carrier, 83 -99.3 % of the fuel carbon was converted to CO 2 at temperatures between 800°C and 950°C and fuel flows equivalent to 144 -462 W th . Higher conversions at lower temperatures than with M4MZ-1200 were achieved with C2Z-1050, which is likely due to the ability of CuO to release gas phase oxygen in the fuel reactor, i.e. CLOU properties. Here, 99.99 % CO 2 yield was achieved at 900°C and 144 W th fuel equivalent. The particles were analyzed before and after the experiments using XRD, SEM, BET surface area and particle size distribution. Whereas nearly the whole batch of M4MZ-1200 particles was disintegrated after the experiments, only about 5 % of the C2Z-1050 particles turned to fines. This is the first time that combustion of liquid fuel using CLOU is demonstrated in a continuous unit.

Chemical-looping combustion (CLC) is a promising technology for future energy production with inherent CO 2 separation. One approach is to use minerals or industrial by-products as oxygen carriers to reduce the costs of the process. This study focuses on the investigation of two iron-based oxygen carriers, which were examined under continuous operation in a 300 W laboratory reactor. Ilmenite is an iron-titanium oxide mineral, whereas iron oxide scale (IOS) is obtained as a by-product from the rolling of sheet steel. Syngas was used as a fuel -pure and with steam addition to suppress the formation of solid carbon.During the experiments the variables reactor temperature, fuel flow and air flow were changed. Furthermore the effect of steam addition to the fuel was investigated. Particle properties were compared over the span of 85 h of continuous operation for ilmenite and 37 h for IOS. The analysis is based on gas measurements from the actual CLC operation, but also on scanning electron microscopy, X-ray powder diffractometry and measurements of BET surface area and density.With ilmenite oxygen carrier it was possible to achieve full conversion of syngas up to about 190 W th fuel equivalent at 900°C. With design fuel flow of about 300 W th at 900°C the combustion efficiency was above 98 %. There was almost no visible difference in reactivity of fresh activated particles and those used for 85 h. Combustion efficiency up to 99 % was achieved with IOS oxygen carrier at 900°C and about 100 W th fuel equivalent. At 300 W th fuel equivalent and 900°C a combustion efficiency of only 90 % could be reached.Both oxygen carriers were operated for tens of hours, which allowed for a better understanding of lifetime behavior and other basic characteristics. Whereas ilmenite oxygen-carrier particles were mostly stable over the course of 85 h of experiments, a large fraction of IOS oxygen-carrier particles had disintegrated to fines after only 37 h of experiments. The gathered data indicates that both oxygen carriers could be an alternative to synthesized particles, though with more drawbacks for IOS than for ilmenite.