A Chemical Looping Combustion (CLC) unit for solid fuels has been designed, erected and\ud operated. The design was based on a thermal power of 20 kWth for in-situ Gasification\ud Chemical Looping Combustion (iG-CLC) or 50 kWth for Chemical Looping with Oxygen\ud Uncoupling (CLOU). Fuel and air reactors are two interconnected circulating fluidized beds\ud reactors, with the coal being fed at the bottom of the fuel reactor to maximize the contact\ud between the volatile matter and the oxygen carrier particles. A carbon stripper has been\ud included between fuel and air reactors to increase the CO2 capture rates. In this unit, the char\ud particles are separated from the oxygen carrier particles and recirculated to the fuel reactor.\ud The solids flow exiting from the fuel reactor is split into two different streams by using a\ud double loop seal down the fuel reactor cyclone. One goes to the carbon stripper and the other is recirculated to the fuel reactor. In this way it is possible to have an independent control of\ud solids inventory in the fuel reactor and the global solid circulation flow rate between fuel and\ud air reactors. First operational results at steady state have been obtained with stable operation\ud in iG-CLC mode during combustion of a bituminous coal with ilmenite being the oxygen carrier. A CO2 capture value of 88% at 991 ºC and a total oxygen demand value of 8.5% were\ud obtained with a solids inventory in the fuel reactor of 470 kg/MWth.This work was supported by the Spanish Ministry for Science and Innovation (Project\ud ENE2013-45454-R). R. Pérez-Vega thanks for the FPI Fellowship.Peer reviewe

In-situ Gasification Chemical-Looping Combustion (iG-CLC) with coal has been proposed as a low-cost process for the capture of CO2 during the energy generation. Previous experimental works have highlighted that high CO2 capture efficiency, close to 100%, can be achieved. However, a certain amount of unburnt gases (mainly CH4, CO and H2) are present in the CO2 stream. These gases can be treated in an oxygen polishing step placed downstream from the CLC unit where they are burnt with pure oxygen, which defines the so-called oxygen demand for the process. The aim of this work was to optimize the performance of the iG-CLC process with coal in order to minimize oxygen demand while maintaining CO2 capture at high levels. Ilmenite was used as the oxygen carrier to burn a bituminous coal in a 50 kWth CLC unit, which consisted of a fuel reactor, an air reactor and a carbon stripper unit between them. The fuel reactor temperature, solids inventory in the fuel reactor, solids circulation rate, coal feeding rate and carbon stripper efficiency were varied, and the CO2 capture efficiency and oxygen demand were calculated for each set of operating conditions. The effect of the fuel reactor temperature was higher on the CO2 capture than on the oxygen demand, with a temperature close to 1000 °C advisable in order to reach CO2 capture rates higher than 90%. In order to further increase CO2 capture, the efficiency of char separation in the carbon stripper was increased. The solids circulation flow rate and the coal feeding rate -which define the oxygen carrier-to-fuel ratio-, in addition to the solids inventory in the fuel reactor, showed a strong influence on the combustion efficiency. Thus, the total oxygen demand was able to be decreased from 10% to 7% by increasing the oxygen carrier-to-fuel ratio from 1.1 to 1.5 and the solids inventory from 450 to 720 kg/MWth. However, an increase in the circulation rate showed a detrimental effect on CO2 capture, which could be offset by increasing the carbon stripper efficiency.This work was supported by the Spanish Ministry for Economy and Competitiveness via the ENE2013-45454-R project and the European Regional Development Fund (ERDF). Raúl Pérez-Vega thanks MICINN for the FPI Fellowship.Peer reviewe

Chemical looping with oxygen uncoupling (CLOU) is a chemical looping combustion (CLC) process for the combustion of solid fuels with the use of a solid oxygen carrier that releases gaseous oxygen inside the fuel reactor. The aim of this work was to study the fate of pollutant elements present in fuel, i.e. S, N and Hg, during CLOU combustion. Experiments using lignite as fuel were carried out in a 1.5 kWth unit operating continuously for more than 35 h of coal combustion. Novel particles containing 50 wt.% CuO, 10 wt.% Fe2O3 and 40 wt.% MgAl2O4 prepared by spray drying were used as the oxygen carriers in the CLOU process. Most of the sulphur introduced with the fuel exited as SO2 at the fuel reactor outlet, although a small amount of SO2 was measured at the air reactor outlet. Most of the nitrogen present in coal was found as N2 at the outlet of the fuel reactor, although 20 wt.% of N in the coal was converted to NO. Mercury speciation was also analyzed. The major mercury species in the fuel reactor was Hg0 (g), and the Hg0 (g)/Hgtotal (g) ratio in the air reactor was 0.5.This work was partially supported by the European Commission, under the RFCS program (ACCLAIM Project, Contract RFCP-CT-2012-00006), ALSTOM Power Boilers (France), the Spanish Ministry of Economy and Competitiveness (ENE2013-45454-R), and the European Regional Development Fund (ERDF). Raul Pérez-Vega thanks to Spanish Ministry of Economy and Competitiveness for the FPI fellowship.Peer reviewe