Magnus Rydén

Hydrogen and power production with integrated carbon dioxide capture by chemical-looping reforming

Chemical-looping combustion is a novel combustion technology that can be used for CO2 capture in power generating processes. Two separate reactors, one for air and one for fuel, are used. Oxygen is transferred between the two by means of an oxygen carrier. Since fuel and combustion air never mix, the combustion products, mostly CO2 and H2O, are not diluted with N2. Consequently, a condenser is sufficient to obtain almost pure CO2. In this paper, the opportunity to utilize chemical-looping for H2 production, with CO2 capture, is examined. The focus is on the thermodynamics and layout of a chemical-looping reformer for natural gas, but system integration for cogeneration of electricity has also been considered. It is found that the proposed reformer systems are very interesting and that their expected performances in several cases are considerably better than for the reference system - a steam reformer with CO2 capture by amine scrubbing. It has been known for more than 100 years that CO2 is a greenhouse gas that affects the climate of the earth. In the last few years, concerns about increasing emissions of greenhouse gases and looming global warming have been growing steadily. It is also well known that fossil fuels can be used as raw material for H2 production. This is already in commercial practice, since H2 is used for a wide range of purposes, such as petrochemical processing and production of ammonia and methanol. These processes, however, emit CO2 to the atmosphere just like ordinary combustion processes. If the CO2 is captured and prevented from reaching the atmosphere, H2 could be used as a CO2-free fuel for engines, power plants, fuel cells and other applications. In this paper, H2 production with inherent CO2 capture based on chemical-looping is examined. 1.1 Chemical-looping combustion

Sulfur Tolerance of CaxMn1–yMyO3−δ (M = Mg, Ti) Perovskite-Type Oxygen Carriers in Chemical-Looping with Oxygen Uncoupling (CLOU)

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.

Experimental investigation of CaMnO3-δ based oxygen carriers used in continuous Chemical-Looping Combustion

Three materials of perovskite structure, (M = Mg or Mg and Ti), have been examined as oxygen carriers in continuous operation of chemical-looping combustion (CLC) in a circulating fluidized bed system with the designed fuel power 300 W. Natural gas was used as fuel. All three materials were capable of completely converting the fuel to carbon dioxide and water at 900°C. All materials also showed the ability to release gas phase oxygen when fluidized by inert gas at elevated temperature (700–950°C); that is, they were suitable for chemical looping with oxygen uncoupling (CLOU). Both fuel conversion and oxygen release improved with temperature. All three materials also showed good mechanical integrity, as the fraction of fines collected during experiments was small. These results indicate that the materials are promising oxygen carriers for chemical-looping combustion.

Examination of Perovskite Structure CaMnO 3-δ with MgO Addition as Oxygen Carrier for Chemical Looping with Oxygen Uncoupling Using Methane and Syngas

Perovskite structure oxygen carriers with the general formula CaMnxMg1-xO3-δ were spray-dried and examined in a batch fluidized bed reactor. The CLOU behavior, reactivity towards methane, and syngas were investigated at temperature 900°C to 1050°C. All particles showed CLOU behavior at these temperatures. For experiments with methane, a bed mass corresponding to 57 kg/MW was used in the reactor, and the average CH4 to CO2 conversion was above 97% for most materials. Full syngas conversion was achieved for all materials utilizing a bed mass corresponding to 178 kg/MW. SEM/EDX and XRD confirmed the presence of MgO in the fresh and used samples, indicating that the Mg cation is not incorporated into the perovskite structure and the active compound is likely pure CaMnO3-δ. The very high reactivity with fuel gases, comparable to that of baseline oxygen carriers of NiO, makes these perovskite particles highly interesting for commercial CLC application. Contrary to NiO, oxygen carriers based on CaMnO3-δ have no thermodynamic limitations for methane oxidation to CO2 and H2O, not to mention that the materials are environmentally friendly and can utilize much cheaper raw materials for production. The physical properties, crystalline phases, and morphology information were also determined in this work.

Oxygen Carriers for Chemcial-Looping Combustion

© 2015 Elsevier Ltd. All rights reserved. Experiences from actual operation with oxygen carriers have been reported from more than 20 pilot plants in the size range 0.3kW-3MW using gaseous, solid and liquid fuels. Total operational experience is 6700h and includes both manufactured materials and low-cost materials. The manufactured materials include oxides of nickel, copper, manganese, iron and cobalt, as well as combined oxides. The low-cost materials include iron ores, ilmenite ores, manganese ores, waste materials and calcium sulphate. Several materials studied show good performance with respect to both conversion and expected lifetime. Several materials can be expected to give low costs, and an oxygen carrier cost as low as 1/tonne CO2 captured may not be unrealistic.