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The hydrodynamic characteristics of RFJLB was studied with superficial liquid velocity (Ul), nozzle diameter (Dn) and nozzle height (Hn) in the range of 0.0293-0.094m/s, 17.4-22.0mm and 50-400mm, respectively. For Dn=17.4mm, Hn=50 and 200mm, with ejector mode and regular operating procedure i.e. simultaneous entry of gas with increasing liquid velocity, had limitation of not establishing the circulation loop. To overcome this limitation a modified operating procedure i.e. entry of gas after established liquid circulation loop is proposed. Also the comparison of gas holdups with ejector and injector mode proves the effectiveness of ejector mode and can eliminate the supply of compressed gas. Thus proper choice of Dn, Hn and also the operating procedure becomes necessary., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

A hazardous waste stream, generated during the manufacture of carbaryl (1-naphthyl-n-methylcarbamate), an insecticide, was explored for assessing its suitability for incineration. The physico-chemical characteristics such as proximate analysis (moisture, volatile matter, fixed carbon and ash), ultimate analysis (carbon, hydrogen, nitrogen, sulphur and oxygen), calorific value and the heavy metal content of the waste indicated that carbaryl waste was suitable for incineration. The incineration experiments were conducted in a bench-scale (25 mm ID, 450 mm long) quartz reactor at various operating temperatures (800 to 1200 degrees C) at a fixed gas-phase residence time of two seconds. Results of the experiments showed that carbaryl waste could be effectively incinerated at a temperature of 1200 degrees C with a gas-phase residence time of two seconds. The destruction and removal efficiency (DE) at these operating conditions was > 99.99% for carbaryl, which was monitored as a principal organic hazardous compound (POHC). The ash generated at these operating conditions was subjected to the Toxicity Characteristic Leaching Procedure (TCLP) and was found to be non-toxic in nature.

This paper presents a detailed computational fluid dynamics (CFD) based approach for modeling thermal destruction of hazardous wastes in a circulating fluidized bed (CFB) incinerator. The model is based on Eular - Lagrangian approach in which gas phase (continuous phase) is treated in a Eularian reference frame, whereas the waste particulate (dispersed phase) is treated in a Lagrangian reference frame. The reaction chemistry hasbeen modeled through a mixture fraction/ PDF approach. The conservation equations for mass, momentum, energy, mixture fraction and other closure equations have been solved using a general purpose CFD code FLUENT4.5. Afinite volume method on a structured grid has been used for solution of governing equations. The model provides detailed information on the hydrodynamics (gas velocity, particulate trajectories), gas composition (CO, CO2, O2) and temperature inside the riser. The model also allows different operating scenarios to be examined in an efficient manner.