A Generalized Flow Regime Diagram for Fluid-Solid Vertical Transport

An ideal generalized flow regime diagram was proposed for fluid-solids vertical transport systems with no bottom and top restrictions. Such an ideal flow regime diagram was further extended to shed light onto the understanding of the flow regimes and instabilities encountered in bottom- restricted bubbling and circulating fluidized bed systems

EFFECT OF DISTRIBUTOR DESIGN ON SOLIDS CIRCULATION AND GAS BYPASS IN AN INTERNAL CIRCULATING FLUIDIZED BED REACTOR

The effect of the distributor design on the gas bypass and solids circulation was investigated for the flat, cylindrical and conical gas distributors in a cold model internal circulating fluidized bed to provide design and operating criteria for the future application of ICFB deNOx reactor. A high gas bypass ratio from the annulus to draft tube and low from the draft tube to annulus were identified for all tested distributors. The solids circulation rates increased with the increase of both annulus and draft tube gas velocities, where the conical distributor exhibited a more flexible and stable operation. The particle size and the reactor configuration exhibited significant effects on the operating characteristics of the hot model ICFB reactor

Forestry Waste in British Columbia ‐ overcoming bad habits and perverse life cycle accounting

The western Canadian province of British Columbia (BC) is renowned for its extensive forests and forestry sector. For a number of historical reasons, practices for “harvesting” trees are BC is wasteful, with large quantities of material left to be destroyed by open-air “slash burning” to avoid providing potential fuel for wildfires. This unused waste is analogous to agricultural waste, or process waste from industrial production. It potentially represents a significant energy resource, equivalent to about 20% of the fossil fuels used in BC. This contribution will cover: - why a potential resource is currently discarded; - how combining LCA with economic analysis identifies the Pareto-optimal uses for the waste, both domestically and as an internationally traded commodity; - why the supply chain means that Canadian wood pellets sold into European markets have a different life cycle environmental profile compared to pellets from other sources; - how current international agreements on accounting for life cycle emissions of greenhouse gases give perverse signals that discourage production of wood pellets in BC. Although the case study is specific to BC, it illustrates a number of general principles in and barriers to “valorisation” of materials currently regarded as waste

Forestry Waste in British Columbia - overcoming bad habits and perverse life cycle accounting

The western Canadian province of British Columbia (BC) is renowned for its extensive forests and forestry sector. For a number of historical reasons, practices for “harvesting” trees are BC is wasteful, with large quantities of material left to be destroyed by open-air “slash burning” to avoid providing potential fuel for wildfires. This unused waste is analogous to agricultural waste, or process waste from industrial production. It potentially represents a significant energy resource, equivalent to about 20% of the fossil fuels used in BC. This contribution will cover: - why a potential resource is currently discarded; - how combining LCA with economic analysis identifies the Pareto-optimal uses for the waste, both domestically and as an internationally traded commodity; - why the supply chain means that Canadian wood pellets sold into European markets have a different life cycle environmental profile compared to pellets from other sources; - how current international agreements on accounting for life cycle emissions of greenhouse gases give perverse signals that discourage production of wood pellets in BC. Although the case study is specific to BC, it illustrates a number of general principles in and barriers to “valorisation” of materials currently regarded as waste

Experimental and Computational Studies of Gas Mixing in Conical Spouted Beds

The residence time distribution data in a conical spouted bed, obtained both from the bed bottom and the bed surface at different radial positions, were analyzed to obtain the mean residence time and the Peclet number. In parallel, local flow structures of a bed with the same dimensions and operating conditions as in the experiment were generated from the computational fluid dynamics (CFD) simulation using the FLUENT codes, and then were used for the simulation of gas dispersion. The results show that CFD simulations agree reasonably well with experiments. The radial distribution of the Peclet number is quite complex, with a maximum value at r=0.135 m under three operating conditions investigated

NUMERICAL INVESTIGATION OF GAS SAMPLING FROM FLUIDIZED BEDS

Gas mixing in a tall narrow fluidized bed operated in the slugging fluidization regime is studied with the aid of computational fluid dynamics. Three-dimensional numerical simulations are performed with an Eulerian-Eulerian model. Predicted axial and radial tracer concentration profiles for various operating conditions are generally in good agreement with experimental data from the literature. Different field variables including voidage, tracer concentration, and gas velocity at upstream and downstream levels are analysed to study gas mixing. Mean tracer concentrations in the dense phase and the bubble phase are evaluated and significant differences between them are found. The time-mean concentration is weighted heavily towards the dense phase concentration which may lead to misinterpretation of sampling data in dispersion models. Caution is needed when interpreting time-mean tracer concentration data. A flux-based mean tracer concentration is introduced to characterize the gas mixing in numerical simulations of two-phase fluidized beds

Monitoring Electrostatic Charges in Fluidized Beds

A novel analysis procedure for dynamic collision probes has been developed to monitor the charge density of particles in gas-solids fluidized beds based on the mean and normalized standard deviation of current signals. The contribution from hydrodynamic changes is decoupled from the changes in specific particle charge density based on the principles that the average current is related to charge transfer and/or triboelectrification due to the contact between the probe and particles, whereas the normalized standard deviation of current signals is mainly related to the hydrodynamic changes of the fluidized bed. The correlation between hydrodynamic changes and current signal fluctuations is confirmed from experimental data of both current fluctuations and pressure fluctuations measured from a 0.1 m diameter fluidized bed using polymer particles. Utilizing these findings, dynamic collision probes can potentially be applied in industrial fluidized bed reactors to monitor electrostatic charge build-up

Reduction of hematite (Fe2O3) to metallic iron (Fe) by CO in a micro fluidized bed reaction analyzer: A multistep kinetics study

A better understanding of the reduction kinetics of iron oxides in a fluidized bed promotes the development of relevant industrial processes, e.g. chemical looping combustion and non-blast furnace iron making. The reduction of iron oxides into iron is complex because the process is heterogeneous and several elementary reactions take place simultaneously. It is hard to figure out the reduction kinetics under fluidization in a fixed bed reactor such as in a thermogravimetry analyzer (TGA) which suffers from the limitations of heating rate, external diffusion, thermal pretreatment before reaction occurs. In this study, the reduction kinetics of hematite to metallic iron at different temperatures and carbon monoxide concentrations are experimentally investigated in a micro fluidized bed reaction analyzer (MFBRA), developed by the Institute of Process Engineering (IPE), Chinese Academy of Sciences (CAS) to develop the kinetics of fast gas-solid reactions. Results indicate that the reduction process has to be described by multistep kinetics and separated into several elementary reactions (i.e. hematite-magnetite, magnetite-wüsitite and wüsitite-iron), which proceed in parallel with different controlling mechanisms as well as with different time dependences. A multistep kinetics model based on Johnson-Mehl-Avrami (JMA) model is developed for the isothermal reduction process of hematite to metallic iron by taking into account the influences of reduction temperature and reducing gas concentration, using statistical analysis tools in the Statistical Product and Service Solutions (SPSS). The kinetics parameters, i.e. activation energy and pre-exponential factor, are determined for each elementary reaction. The contribution of each individual reaction to the whole reduction process is further discussed. The results also suggest that the reduction of hematite to wüsitite takes place fast and dominates the initial part of the entire reduction while the reduction of wüsitite to iron plays a less important role in the initial stage but controls the whole reduction in the late stage. The conclusions obtained in this study are comparable with that in the literature and indicate that the multistep kinetics model is able to capture the properties of both elementary reactions and the integrated process, providing an analysis strategy for revealing detail characteristics of the comple