Search Results (4)

Bioenergy with Carbon Capture and Storage (BECCS) technologies are fundamental to reach negative CO₂ emissions by removing it from the atmosphere and storing it underground. A promising solution to implement BECCS is pressurized Chemical Looping Combustion (CLC), which involves coupling a pressurized CLC reactor system to a turboexpander. The typical configuration chosen is to have an air reactor and a fuel reactor based on coupled circulating fluidized beds. The fluidization regime in both reactors is preferred to be fast fluidization to enhance gas particle contact and solids circulation among reactors. To design the two reactors, Aspen Plus software was used, given that the new version has a module for fluidized bed modeling. At first, the oxygen carrier was designed ex novo, but given that it is a composite compound mainly made by nickel oxide freeze-granulated on alumina (Ni40Al-FG), the molecular structure has been inserted in Aspen Plus. Then, based on the power of the gas turbine, the power output per kg of evolving fluid (in this case, depleted air) is calculated using Aspen Plus. Once the nitrogen content in the depleted air is known, the total air at the inlet of the air reactor is calculated. The fuel reactor is modeled by inserting the reduction reactions for nickel-based oxygen carriers. The paper presents a useful methodology for developing pressurized Chemical Looping Combustors to be coupled to gas turbines for power generation. The provided data will be cross-validated with 0D-models and experimental results. Full article

This paper provides a simple methodology for the design of the air reactor of a chemical looping combustor to optimize its characteristics when it is employed connected to a turbo expander to produce power. The design process, given a certain objective (e.g., electric power) defines the reactor specifics, namely height and diameter, taking into account the following aspects: solids inventory of the air reactor; gas velocity; air reactor transport disengaging height (TDH); solids concentration profile along the reactor height, dense bed height; freeboard height; pressure drop depending on air reactor injectors design and configuration. The total air reactor height was about 9.5 m, while the diameter was about 1.8 m. The total inventory was about 10,880 kg; while the circulation rate in the air reactor was about 110 kg/s. The operating pressure and temperature were, respectively, 12 bar and 1200 °C. The average velocity of the gases inside the reactor was about 4 m/s. The fluidization regime resulted to be comprised between turbulent and fast fluidization. Further work must be directed into the estimate of the pressure drop of the reactor, which will affect the plant efficiency in a considerable way. Full article

To realize a carbon negative power production technology, it is interesting the option of coupling a Chemical Loping Combustor to a gas turbine. The development of this technology foreseen in the project GTCLC-NEG has some technical barriers, the most important of which is the operation of the chemical looping combustor at high temperature and high pressure conditions. To overcome these limits CFD modeling can be performed to optimize the behavior of the combustor and its design process. This work models the FUEL reactor of a chemical looping combustion plant working in batch mode and based on the reactor available at the Instituto de Carboquimica in Zaragoza, Spain. It is used an oxygen carrier mainly based on 60% mass Fe₂O₃ and 40% mass Al₂O₃. Biomethane is fed to the bottom of the fluidized bed with different velocities and mass flows and the composition of the gases at the outlet of the fuel reactor is measured. The results show that it is possible to model a 2 min duration reduction cycle by running the model for a time comprised between a minimum of 4 h and a maximum of 2 days of simulation. Another important result is the modeling of the chemical reactions happening in the reactor. Kinetics is modelled based on Activation energy (66 kJ/mol) and Pre-exponential factor (4.34 × 10¹ m³ⁿ mol⁻ⁿ s⁻¹). The simple kinetic scheme gives reasonable first approximations and can be used to determine the duration of the reaction, the composition of the exhaust gases and the biofuel conversion. Full article

The self-excited thermoacoustic instability in a two-dimensional Rijke-type burner with a center-stabilized premixed methane–air flame is numerically studied. The simulation considers the reacting flow, flame dynamics, and radiation model to investigate the important physical processes. A finite volume-based approach is used to simulate reacting flows under both laminar and turbulent flow conditions. Chemical reaction modeling is conducted via the finite-rate/eddy dissipation model with one-step reaction mechanisms, and the radiation heat flux and turbulent flow characteristics are determined by using the P-1 model and the standard k-ε model, respectively. The steady-state reacting flow is first simulated for model verification. Then, the dynamic pressure, velocity, and reaction heat evolutions are determined to show the onset and growth rate of self-excited instability in the burner. Using the fast Fourier transform (FFT) method, the frequency of the limit cycle oscillation is obtained, which agrees well with the theoretical prediction. The dynamic pressure and velocity along the tube axis provide the acoustic oscillation mode and amplitude, also agreeing well with the prediction. Finally, the unsteady flow field at different times in a limit cycle shows that flame-induced vortices occur inside the combustor, and the temperature distribution indicates that the back-and-forth velocity changes in the tube vary the distance between the flame and honeycomb in turn, forming a forward feedback loop in the tube. The results reveal the route of flame-induced thermoacoustic instability in the Rijke-type burner and indicate periodical vortex formation and breakdown in the Rijke burner, which should be considered turbulent flow under thermoacoustic instability. Full article