Search

Cyclones are commonly used in the process industry to separate entrained particles from gas streams. Particles entering a cyclone are subjected to a centrifugal force field, driving them to the cyclone walls, where they experience collisional and rapid shearing stresses. Consequently, particle attrition and erosion of the cyclone walls occur, depending on the mechanical properties of the particles and cyclone walls. In this work, the attrition of manganese oxide particles, intended for use in the Chemical Looping Combustion (CLC) process, flowing through a standard design cyclone (Stairmand design) is analysed as an example by considering surface damage processes of chipping and wear. A new methodology is developed, whereby Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) simulations are used to analyse the particle motion and interactions with the cyclone walls. The approach is then coupled with breakage models of chipping and wear to predict the extent of attrition. The impact breakage due to chipping is evaluated experimentally first as a function of particle size and impact angle and velocity. The data are fitted to the chipping model of Ghadiri and Zhang. The model is then coupled with the frequency of collisions and impact velocity, obtained from the CFD-DEM simulation, to work out the particle attrition by chipping. For surface wear the model of Archard is used to account for particle wear by shearing against the walls. The outcome of the work provides a methodology for describing the extent of attrition in different regions of the cyclone.

International audience; One of the best low-cost approaches for capturing carbon dioxide from the combustion of solid fuels is chemical looping combustion (CLC) technology, where the processes of fuel oxidation and extraction of oxygen from the air are split in two separate reactors. In order to model the petroleum coke (petcoke) conversion in a CLC method, detailed knowledge about the reactions of pet-coke with O2, CO2, and H2O at temperatures between 750 and 1100 °C is required. Due to the lack of sufficient literature data, in this paper, the reactivity of these reactions is investigated in a custom-built test rig that enabled measurements of the mass loss of the fuel sample and the composition of the released gases. The Avrami, Random Pore, Shrinking Core, and Hybrid models were applied to the experimental results to determine the kinetic parameters of petcoke gasification. At temperatures up to 1000 °C, the reaction with CO2 was found to be negligibly slow. An activation energy of 103.91 kJ/mol was obtained for petcoke gasification in 10–40 vol% of H2O, while a value of 15.87 kJ/mol was found for oxidation in 2–4 vol% O2, as described by best-fitting models, i.e. Hybrid and Random Pore models, respectively.

Chemical Looping Combustion (CLC) is a promising technique to achieve fuel combustion in a nitrogen free atmosphere, therefore giving the possibility to separate and store or use CO2. Several potential applications are considered in the field of power generation with gas, liquid and mostly solid fuels. In the Carbon Capture, Storage and Utilization (CCSU) context, energy penalty is reduced with CLC compared to other routes. In addition, other applications of Chemical Looping Technology are considered in the field of H2 production or gasification for instance. In the past years, a huge effort has been conducted worldwide to investigate CLC materials and process issues. In 2008, IFPEN and Total have started an ambitious collaboration to develop CLC applications. Nowadays, the CLC concept is well demonstrated on the pilot scale. The next step is to demonstrate the technology over time on a larger scale. For further developments, some challenges should be addressed, both on market and technical aspects: • Short term market is limited. Uncertainties around CO2 emission market (i.e. carbon credits) and storage issues are hindering policy and public acceptance and still must evolve in the right direction, • Financing of industrial Carbon Capture and Storage units in this context is challenging and other applications of CLC may require to be investigated such as utilization of captured CO2 for EOR purpose, • The industrial use of synthetic metal oxides or natural ores at large scale generates a lot of issues related to availability, price, waste disposal, health and safety, additionally to chemical and mechanical aging, reactivity, and oxygen transfer capacity, • Chemical looping reactor and process technology concepts have to be explored, developed, modeled and scaled-up in order to ensure adequate power production together with good gas solid contact and reaction requirement, controlled circulation of mixtures of particle (oxygen carrier, ash, solid fuel for instance). All these points should be considered on very large scales for carbon capture and storage (CCS) applications in order to minimize energy penalty and cost in severe operating conditions (temperatures above 800 °C and intense solid circulation). Technical challenges remain to be solved and proven with large demonstration over long periods of time. In this context, research in the field of fluidization technology is essential and we will address some key points investigated at IFPEN as related to control of solid circulation, oxygen carrier attrition, conceptual design of CLC reactors and process performance.

Chemical Looping Combustion (CLC) is a promising combustion technology with inherent CO2 capture. This process consists in use of metal oxides, called oxygen carriers, to transfer oxygen from Air Reactor into the Fuel Reactor for combustion of Fuels. Accordingly, Air and Fuel are not mixed and the produced flue gas is concentrated in CO2 and not diluted with nitrogen. This inherent CO2 capture results in higher energy and carbon capture efficiencies compared to conventional capture technologies. This paper presents recent achievements of TOTAL in collaboration with IFPEN on CLC development for the refining and chemical industry with petcoke feedstock. A novel concept has been developed with a two-stage combustion reactor, an integrated solid-solid separator (Carbon Stripper), and non-mechanical solid flow control devices. These technologies have been demonstrated at different scales up to a 1 MWth equivalent cold flow prototype and in a 10 kWth continuous pilot plant. These experimental works permitted to carry out a full-scale process simulation with steam and electricity cogeneration. Different sections of CLC are represented in this simulation including reactor system, flue gas treatment, CO2 compression, and steam cycle. In addition, the cost of avoided CO2 has been evaluated for power generation with Chemical Looping technology. Finally, CHEERS project is introduced in which CLC process will be demonstrate in 3 MWth scale via an international collaboration including nine partners from Europe and China.

International audience; This work aims to study the evolution of NiO/NiAl2O4 redox performance with CO as fuel for Chemical Looping Combustion (CLC) applications. The oxygen carrier (OC) was investigated under alternating oxidizing and reducing conditions in a fixed bed reactor simulating the cyclic conditions of CLC. The study of the operating temperature influence reveals that total reduction capacity increases with temperature, due to the reaction of the binder NiAl2O4. Regeneration step performed under low oxygen concentration (5 vol.%) shows that the decrease in total reduction capacity during multiple cycles is minimized and the purity of produced CO2 is higher. Therefore, carrying out the regeneration step at lower oxygen concentrations can increase oxygen carrier lifetime. Characterization studies revealed the formation of a nickel rich layer at the surface (up to 20 μm thick at 900 °C) and a partial sintering of particles regenerated under 20 vol.% of oxygen. However, these phenomena are not observed on the particles regenerated under low oxygen concentration. The formation of this layer can be explained by the fact that nickel oxidation is carried out by migration of Ni2+ cations through the layer of NiO initially oxidized at the surface of the particle, the layer becomes thicker during cycles, because NiO does not return to its initial position. At higher temperature, the diffusion velocity increases and therefore the layer formed is thicker.Specific surface area of the oxygen carrier decreases as cycles number increases from 9.4 m2/g for the fresh material to 4.4 and 2.3 m2/g after thirty cycles at 750 °C and 900 °C respectively. The same trend is observed for porous volume. However, the decrease is lower when particles are regenerated under low oxygen concentration (6 m2/g).

Particles attrition is an important phenomenon to account for when developing and scaling up new fluidized bed processes. Most of the time, little amount of particles is available at the early development stage and only lab scale experiments can be carried out. Most of the available tools and methodologies to investigate attrition at small scale were developed for the FCC process on group A particles. However, attrition also needs to be evaluated for new applications such as Chemical Looping Combustion (CLC) with different particle properties. In this work, we propose a method using a jet cup apparatus that aims to compare attrition rate of solids having different properties. Materials studied in this paper are a Group A FCC catalyst (Dp50 of 70 μm, grain density of 1450 kg/m3) and a Group B CLC oxygen carrier (Dp50 of 180 μm, grain density of 3600 kg/m3). Based on experimental data and CFD modeling, comparative testing conditions could be defined in order to apply the same mechanical stress for all solids tested. Classical attrition indexes usually quantify the generation of fine particles below 40 μm which does not describe fully attrition of Group B powders. Therefore, a new attrition index was defined to calculate the total amount of particles generated by attrition over the entire size range of all solids tested. Finally, the attrition rates of both materials were compared applying the methodology developed. It was found that attrition rate is less important for the oxygen carrier. It is important to notice that attrition due to thermal or chemical stresses is not investigated in this study and needs separate evaluation.