http://digital.csic.es/bitstream/10261/78793/1/Progress%20in%20chemical-looping%20combustion%20and%20ref....2012.pdf

Progress in chemical-looping combustion and reforming technologies

Chemical looping processes offer a compelling way for effective and viable carbonaceous fuel conversion into clean energy carriers. The uniqueness of chemical looping processes includes their capability of low cost in situ carbon capture, high efficiency energy conversion scheme, and advanced compatibility with state-of-the-art technologies. Based on the different functions of looping particles, two types of chemical looping technologies and associated processes have been developed. Type I chemical looping systems utilize oxygen carrier particles to perform the reduction–oxidation cycles, while Type II chemical looping systems utilize CO2 carrier particles to conduct carbonation–calcination cycles. The exergy analysis indicates that the chemical looping strategy has the potential to improve fossil fuel conversion schemes. Chemical looping particle performance and looping reactor engineering are the key drivers to the success of chemical looping process development. In this work, the desired particle characterization and recent progress in mechanism studies are generalized, which is followed by a discussion on the looping reactor design. This perspective also illustrates various chemical looping processes for combustion and gasification applications. It shows that both Type I and Type II looping processes have great potentials for flexible and efficient production of electricity, hydrogen and liquid fuels.

Chemical looping processes for CO2 capture and carbonaceous fuel conversion – prospect and opportunity

Chemical looping offers a versatile platform to convert fuels and oxidizers in a clean and efficient manner. Central to this technology are metal oxide materials that can oxidize fuels, affording a reduced material that can be reoxidized to close the loop. Recent years have seen substantial advances in the design, formulation and manufacture of these oxygen carrier materials and their incorporation into chemical looping reactors for the production of various chemicals. This Review describes the mechanisms by which oxygen carriers undergo redox reactions and how these carriers can be incorporated into robust chemical looping reactors. One promising technology for modern energy and chemical conversions is chemical looping, central to which are redox cycles of metal oxides. This Review describes chemical looping schemes and the mechanisms by which metal oxide particles enable these technologies.

Metal oxide redox chemistry for chemical looping processes

Hydrogen is an attractive energy carrier due to its potentially high energy efficiency and low generation of pollutants, which can be used for transportation and stationary power generation. However, hydrogen is not readily available in sufficient quantities and the production cost is still high. Steam methane reforming (SMR) process is now the most widely used technology for H 2 production, but this process is complex and cannot get thorough carbon capture. Hydrogen production using chemical looping technology has received a great deal of attention in recent years because it can produce hydrogen with higher process efficiency and can capture carbon dioxide. Many researchers have carried out intensive research work on the hydrogen production processes using chemical looping technology. Based on the previous studies stated in the literature, the authors try to give an overview on the recent advances of two categories, chemical looping reforming (CLR) and chemical looping hydrogen production (CLH) processes. Besides, the characteristics of the processes are pointed out based on the comparison with the conventional SMR process. The existing technical problems and the aspects of future research of each approach are also summarized.

Review of hydrogen production using chemical-looping technology

Although the processing of coal is an ancient problem and has been practiced for centuries, the constraints posed on today's coal conversion processes are unprecedented, and utmost innovations are required for finding the solution to the problem.With a strong demand for an affordable energy supply which is compounded by the urgent need for a CO2 emission control, the clean and efficient utilization of coal presents both a challenge and an opportunity to the current global R&D efforts in this area. This paper provides a historical perspective on the utilization of coal as an energy source as well as describing the progress and challenges and the future prospect of clean coal conversion processes. It provides background on the historical utilization of coal as an energy source, along with particular emphasis on the constraints in current coal conversion technologies. It addresses the energy conversion efficiencies for current coal combustion and gasification processes and for the membrane and looping based novel processes which are currently under development at various stages of testing. The control technologies for pollutants including CO2 in flue gas or syngas are also discussed. The coal conversion process efficiencies under a CO2 constrained environment are illustrated based on data and ASPEN Plus® simulations. The challenges for future R&D efforts in novel coal conversion process development are also presented.

Clean coal conversion processes – progress and challenges

The syngas redox (SGR) process to produce hydrogen from coal derived syngas is described. The process involves reduction of a metal oxide to metallic form with syngas and subsequent regeneration wi...

Syngas Redox (SGR) Process to Produce Hydrogen from Coal Derived Syngas

The syngas chemical looping process co-produces hydrogen and electricity from syngas through the cyclic reduction and regeneration of an iron oxide based oxygen carrier. In this article, the reducer, which reduces the oxygen carrier with syngas, is investigated through thermodynamic analysis, experiments, and ASPEN Plus® simulation. The thermodynamic analysis indicates that the countercurrent moving-bed reducer offers better gas and solids conversions when compared to the fluidized-bed reducer. The reducer is continuously operated for 15 h in a bench scale moving-bed reactor. A syngas conversion in excess of 99.5% and an oxygen carrier conversion of nearly 50% are obtained. An ASPEN Plus® model is developed which simulates the reducer performance. The results of simulation are consistent with those obtained from both the thermodynamic analysis and experiments. Both the experiments and simulation indicate that the proposed SCL reducer concept is feasible. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Syngas chemical looping gasification process: Bench‐scale studies and reactor simulations

A method for producing hydrogen gas is provided and comprises reducing a metal oxide in a reduction reaction between a carbon-based fuel and a metal oxide to provide a reduced metal or metal oxide having a lower oxidation state, and oxidizing the reduced metal or metal oxide to produce hydrogen and a metal oxide having a higher oxidation state. The metal or metal oxide is provided in the form of a porous composite of a ceramic material containing the metal or metal oxide. The porous composite may comprise either a monolith, pellets, or particles.

Combustion looping using composite oxygen carriers

Volumetric gas−liquid mass-transfer coefficients are investigated in bubble columns under high-pressure and moderate-temperature conditions by utilizing an oxygen desorption method. The oxygen concentration in the liquid phase, water or Paratherm NF heat-transfer fluid, is monitored with a high-pressure optical fiber oxygen probe. The study covers operating conditions up to pressures of 4.24 MPa and up to temperatures of 92 °C. The superficial gas and liquid velocities vary up to 40 and 0.89 cm/s, respectively. Experimental results show that system pressure, temperature, gas and liquid velocities, liquid properties, and column dimensions are major factors affecting mass transfer. The mass-transfer coefficient increases with both pressure and temperature. Both gas and liquid velocities improve mass transfer due to higher turbulence at high-velocity conditions. Liquid properties and column dimensions also have significant effects on mass transfer. The effect of liquid velocity on kla is mainly due to the ch...

Gas−Liquid Mass Transfer in High-Pressure Bubble Columns

A moving bed scale reactor setup for studying complex gas-solid reactions has been designed in order to obtain kinetic data for scale-up purpose. In this bench scale reactor setup, gas and solid reactants can be contacted in a cocurrent and countercurrent manner at high temperatures. Gas and solid sampling can be performed through the reactor bed with their composition profiles determined at steady state. The reactor setup can be used to evaluate and corroborate model parameters accounting for intrinsic reaction rates in both simple and complex gas-solid reaction systems. The moving bed design allows experimentation over a variety of gas and solid compositions in a single experiment unlike differential bed reactors where the gas composition is usually fixed. The data obtained from the reactor can also be used for direct scale-up of designs for moving bed reactors.

Luis G. Velazquez-Vargas

Papers

Syngas Redox (SGR) Process to Produce Hydrogen from Coal Derived Syngas

Syngas chemical looping gasification process: Bench‐scale studies and reactor simulations

Combustion looping using composite oxygen carriers

Gas−Liquid Mass Transfer in High-Pressure Bubble Columns

Moving bed reactor setup to study complex gas-solid reactions.