CFD studies of dual circulating fluidized bed reactors for chemical looping combustion processes

Hydrodynamics of gas–solid risers using cluster structure-dependent drag model

Chemical Looping for Energy Technology: A Special Issue

Unconverted fuel gases are normally present in the gas leaving the fuel reactor of a Chemical Looping Combustion (CLC) process. Depending on several factors, including oxygen carrier and fuel volatiles content, the unconverted gases represent 5–30% of the oxygen needed for full combustion. Further conversion of these fuel components is imperative to achieve adequate combustion and to fulfill the requirements for CO2 storage. An oxy-polishing step using highly concentrated O2 to fully oxidize the fuel components offers a straightforward one-step way to reach complete combustion. However, systematic and detailed investigation is lacking while it is essential for design, scale up and optimization. In this work, the oxy-polishing is studied in a post-oxidation chamber (POC) of a 100 kWth unit using different solid fuels and manganese ores in the CLC process. With various flows of air as oxidation agent, the POC performance was evaluated under stable operations in a wide range of operating conditions. An overall oxygen ratio was defined to analyze the effect of O2 excess in the POC. Experimental results show that the oxidation of fuel gas from the fuel reactor can be greatly enhanced by air entering the POC, with the gas conversion being improved from 87 to 90% before the POC to as high as 99–100% after the POC. Full oxidation in POC can be accomplished with excess of O2. For the cases of incomplete oxidation, CO was normally found in higher concentrations than CH4. In a few cases close to optimum, CO and O2 simultaneously have normalized concentrations below 0.5–1% with a low overall oxygen ratio of around 1.01. The POC performance was further compared to the results from a simple reactor model.

CLC, a promising concept with challenging development issues

CO2 capturing methods: Chemical looping combustion (CLC) as a promising technique

Feasibility of an integrated biomass-based CLC combustion and a renewable-energy-based methanol production systems

Cold gas efficiency enhancement in a chemical looping combustion system using staged H2 separation approach

Potential and limitations of power generation via chemical looping combustion of gaseous fuels

The flow behaviour of a lab-scale fluidised bed with a central jet has been simulated. The study has been performed with an in-house computational fluid dynamics (CFD) model named FLOTRACS-MP-3D. The CFD model is based ona multi-fluid Eulerian description of the phases, where the kinetic theory for granular flow forms the basis for turbulence modelling of the solid phases. A two-dimensional Cartesian co-ordinate system is used to describe the geometry. This paper discusses whether bubble formation and bed height are influenced by coefficient of restitution, drag model and number of solid phases. Measurements of the same fluidised bed with a digital video camera are performed. Computational results are compared with the experimental results, and the discrepancies are discussed.

Effect of H2S on the behaviour of an impregnated NiO-based oxygen-carrier for chemical-looping combustion (CLC)

Solids-based carbon dioxide (CO2)adsorption, where CO2 is adsorbed under high pressure/low temperature and desorbed at low pressure/high temperature, is a low energy consumption capture technology with high carbon uptake efficiency. Chemical looping combustion (CLC), where a solid oxygen carrier (OC) transports oxygen between two high-temperature reactors – a fuel and an air reactor –, is a low energy penalty, fuel-flexible technology with inherent CO2 capture for power/heat and syngas production. In this work, state-of-the-art equation-oriented (EO) mathematical models of a fixed-bed (FxB) contactor for CO2 adsorption and moving-bed (MB) reactors for gas-, and solid-fueled CLC processes are developed. The solid-fueled MB model is a multi-zonal model for the CLC of coal. Large-scale nonlinear optimization problems are solved for simultaneous optimization of design and operating conditions for the CLC processes. Further, a Bayesian parameter estimation and model building framework is proposed and used to quantify the parametric and model form uncertainty of CO2 adsorption isotherm and CLC OC reduction kinetic models based on experimental data. The model form discrepancy is described by a set of orthogonal functions which are naturally suitable and efficient for uncertainty propagation to the unit/process model in which the discrepancy-augmented models are implemented. By using the joint posterior distribution of the model and discrepancy function parameters and inserting discrepancy functions in the isotherm and kinetic models coupled with the EO unit/process reactor models, the effect of the uncertainty inherent to bench-scale adsorption/kinetic models on key process variables of the large-scale systems are evaluated.

A Hydrodynamic Study of Chemical Looping Combustion System for Gaseous Fuel

A study on the chemical looping combustion of sewage sludge: The emission of NOx and its precursors

Assessment of chemical looping combustion process by dynamic simulation

Modification of kinetic theory of granular flow for frictional spheres, part II: Model validation