Investigation of a Coupled Fuel Reactor for Coal-Fueled Chemical Looping Combustion

This work presents an experimental investigation and modeling study of a fuel reactor designed for in situ gasification chemical looping combustion (iG-CLC). The fuel reactor is designed to couple a bubbling fluidized-bed reactor and a downer reactor. The downer reactor can enhance gas–solid contact in the freeboard region and eliminate the unburned gases from the fuel reactor. The fuel reactor consists of an annular bubbling fluidized bed and a center-located riser. Cold-model experiments were conducted. The solids circulation rate and gas bypassing between the annular fluidized bed and the riser were studied. Experiments in a hot downer reactor were performed, and a two-dimensional model was developed and validated with experimental data. The verified model shows that a downer reactor with proper solids dispersion can eliminate more than 78% of the fuel gas exiting the fuel reactor with an overall solids dropping rate of 8 kg/m²·s

Annular Carbon Stripper for Chemical-Looping Combustion of Coal

The carbon stripper (CS), which is a fluidization bed aimed at separating char particles from oxygen carriers during coal-fired chemical looping combustion (CLC), is vital for achieving high carbon capture efficiency of a CLC system. An effectively designed CS could transport most char particles back to the fuel reactor and simultaneously allow most oxygen carriers to reach the air reactor. An annular carbon stripper was designed, and a cold model apparatus was built for operation and optimization. The CS consists of an annular fluidized bed and a center riser. The riser was inserted into the annular fluidized bed, and the fluidized bed was divided into the annular zone and the cylindrical zone. Plastic beads were used to simulate char particles, and ilmenite was used as the oxygen carrier. The effect of operational parameters (solid feeding rate and gas velocities) and particle properties (average size of plastic beads and mass concentration of plastic beads) on the separation efficiencies of plastic beads and ilmenites was investigated in detail. The main parameters of the CS structure (the length of the annular zone and the diameters of the riser and annular fluidized bed) were studied and optimized. The axial distribution of the solid volume fraction and the mass concentration of light particles along the annular fluidized bed were measured, and the fluidization behavior in the CS was analyzed. The separation process in the annular CS and the important factors influencing the separation of binary particles were discussed. Under the optimized structure and operational conditions, the annular CS could be an effective apparatus to completely separate char particles from oxygen carriers, which could greatly improve carbon capture efficiency during the operation of a coal-fired CLC

Electrochemical Reduction of Carbon Dioxide in an MFC–MEC System with a Layer-by-Layer Self-Assembly Carbon Nanotube/Cobalt Phthalocyanine Modified Electrode

Electrochemical reduction of carbon dioxide (CO₂) to useful chemical materials is of great significance to the virtuous cycle of CO₂. However, some problems such as high overpotential, high applied voltage, and high energy consumption exist in the course of the conventional electrochemical reduction process. This study presents a new CO₂ reduction technique for targeted production of formic acid in a microbial electrolysis cell (MEC) driven by a microbial fuel cell (MFC). The multiwalled carbon nanotubes (MWCNT) and cobalt tetra-amino phthalocyanine (CoTAPc) composite modified electrode was fabricated by the layer-by-layer (LBL) self-assembly technique. The new electrodes significantly decreased the overpotential of CO₂ reduction, and as cathode successfully reduced CO₂ to formic acid (production rate of up to 21.0 ± 0.2 mg·L^–1·h^–1) in an MEC driven by a single MFC. Compared with the electrode modified by CoTAPc alone, the MWCNT/CoTAPc composite modified electrode could increase the current and formic acid production rate by approximately 20% and 100%, respectively. The Faraday efficiency for formic acid production depended on the cathode potential. The MWCNT/CoTAPc composite electrode reached the maximum Faraday efficiency at the cathode potential of ca<i>.</i> −0.5 V vs Ag/AgCl. Increasing the number of electrode modification layers favored the current and formic acid production rate. The production of formic acid was stable in the MFC–MEC system after multiple batches of CO₂ electrolysis, and no significant change was observed on the performances of the modified electrode. The coupling of the catalytic electrode and the bioelectrochemical system realized the targeted reduction of CO₂ in the absence of external energy input, providing a new way for CO₂ capture and conversion

Molecular Insights into the Transformation of Dissolved Organic Matter in Landfill Leachate Concentrate during Biodegradation and Coagulation Processes Using ESI FT-ICR MS

Landfill leachate concentrate is a type of refractory organic wastewater with high environmental risk. Identification of refractory components and insights into the molecular transformations of the organics are essential for the development of efficient treatment process. In this report, molecular compositions of dissolved organic matter (DOM) in leachate concentrate, as well as changes after anaerobic/aerobic biodegradation and coagulation with salts, were characterized using electrospray ionization (ESI) coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). DOM in leachate concentrate were more saturated and less oxidized with more nitrogen and sulfur-containing substances (accounting for 50.0%), comparing with natural organic matter in Suwannee River. Selectivity for different classes of organics during biodegradation and coagulation processes was observed. Substances with low oxidation degree (O/C < 0.3) were more reactive during biodegradation process, leading to the formation of highly oxidized molecules (O/C > 0.5). Unsaturated (H/C < 1.0) and oxidized (O/C > 0.4) substances containing carboxyl groups were preferentially removed after coagulation with Al or Fe sulfate. The complementary functions of biodegradation and coagulation in the treatment of DOM in leachate concentrate were verified at the molecular level. Lignin-derived compounds and sulfur-containing substances in leachate concentrate were resistant to biodegradation and coagulation treatments. To treat leachate concentrate more effectively, processes aimed at removal of such DOM should be developed