G. Venkat Reddy

Effect of secondary air injection on the combustion efficiency of sawdust in a fluidized bed combustor

Agricultural wastes like bagasse, paddy husks, sawdust and groundnut shells can be effectively used as fuels for fluidized bed combustion; otherwise these biomass fuels are difficult to handle due to high moisture and fines content. In the present work the possibility of using sawdust in the fluidized bed combustor, related combustion efficiencies and problems encountered in the combustion process are discussed. The temperature profiles for sawdust with an increase in fluidizing velocity along the vertical height above the distributor plate indicate that considerable burning of fuel particles is taking place in the freeboard zone rather than complete burning within the bed. Therefore, an enlarged disengagement section is provided to improve the combustion of fines. The temperature profiles along the bed height are observed at different feed rates. The feed rate of sawdust corresponding to the maximum possible temperature was observed to be 10.2 kg/h. It is observed that 50-60% excess air is optimal for reducing carbon loss during the burning of sawdust. The maximum possible combustion efficiency with sawdust is 99.2% and is observed with 65% excess air.

EFFECT OF DISTRIBUTOR DESIGN ON TEMPERATURE PROFILES IN FLUIDIZED BED DURING THE COMBUSTION OF RICE HUSK

Abstract The conventional method of paddy husk combustion in grate type furnaces is slow and inefficient yielding low combustion efficiency. Fluidized bed combustion of paddy husks was proved to be a feasible solution for efficient combustion along with high combustion intensity. In the present work combustion studies of rice husk were conducted in an atmospheric fluidized bed in high excess air environment with variation in distributor design. Significant changes in temperature profiles in the fluidization vessel have been observed with variation of opening area of distributor. It is found that a straight, multi-orifice type with opening area of 2.6% is appropriate distributor to maintain uniform temperatures along the bed.

The Fluidized Bed Combustion of Groundnut Shells for Energy Recovery

Abstract Fluidized bed combustion is suitable for burning of a wide range of waste materials and gives reasonable combustion efficiency along with high combustion intensity. In the present work, combustion studies of groundnut shells were conducted in an atmospheric fluidized bed under high excess air environment. The temperature profiles in the fluidized bed during the combustion process indicate a considerable burning of fuel particles in the free board zone rather than complete burning within the bed. Therefore, an enlarged disengagement section is provided to improve combustion of fines. The change in temperature profiles along the bed height at different feed rates is observed. The feed rate of groundnut shells corresponding to the maximum possible temperature has been observed at 9.3 kg/h, respectively. It is observed that 35–45% excess air is optimal to reduce carbon loss during burning of groundnut shells. The maximum possible combustion efficiency with groundnut shell is 99.3% and is observed at 72% excess air.

Comparison of the Combustion Characteristics of Rice Husk, Sawdust, and Groundnut Shells in a Bubbling Fluidized Bed

Abstract Agricultural residues, such as rice husk, sawdust, wood waste, groundnut shells, etc., could play an important role as energy sources. These biomass fuels are difficult to handle due to high moisture and fines content and also due to fuel ash softening at relatively low temperatures. Fluidized bed energy technology offers several unique characteristics for using biomass in small-scale energy conversion operations. In the present work, combustion studies of rice husk, sawdust, and groundnut shells were conducted in an atmospheric bubbling fluidized bed in high excess air environment and observed considerable reduction in CO levels in flue gases and unburned carbon in residual ash. The combustion efficiency, temperature distribution in the reactor, ash characteristics, etc. are also studied in a fluidized bed at various operating conditions. Secondary air is introduced in the enlarged free board to provide high turbulence for flue gases and unburned particles in the reactor vessel.

Stability and Dynamic Behaviour of a Fluidised Bed Bioreactor Treating Phenolic Effluent

Abstract Stability aspects and dynamic behaviour of a draft-tube fluidised bed bioreactor treating phenolic effluent from a coal carbonisation plant have been investigated in the present study. Experiments were carried out to study the biodegradation of phenolic wastewater using the microorganism Pseudomonas sp., immobilised on solid support particles. The dynamics of the reactor system were monitored at various experimental conditions viz., feed (substrate) flow rates and phenol concentrations in the feed. The draft tube fluidised bed bioreactor was assumed to operate in a completely backmix mode and a model to predict the outlet phenol concentration for given inlet and equipment parameters was developed. The model equations were solved using 4 th order Runge-Kutta technique. The predictions made by the dynamic model were compared with experimental findings and the agreement between the two was good. Stability of the reactor to input disturbances was examined and it was found to be stable.

Simulation of continuous packed bed reactive distillation column for the esterification process using activity based kinetic model

A mathematical model for the continuous packed bed reactive distillation process of esterification of acetic acid with methanol is developed. The kinetic rate equation, which plays a major role for the performance of reactive distillation and it is the part of model, is required for the liquid phase reversible esterification reaction. The mineral sulphuric acid is used as the catalyst. The kinetic experiments are carried out under different temperatures in the range of 305.15 to 333.15 K and catalyst concentrations in the range of 0.1267 mole H+/lit to 0.6537 mole H+/lit. From that experimental data the kinetic model is developed and the same is used for the simulation of reactive distillation process. Equilibrium stage model, in which the vapour and the liquid leaving a stage are assumed to be in equilibrium with each other, has been used for the simulation of reactive distillation process by incorporating our kinetic model. Conversion of acetic acid as function of reflux ratio and reboiler ratio has been predicted. The liquid composition and temperature profiles versus stage number have been also predicted. Finally, the optimum operating conditions obtained from the simulation results for high pure methyl acetate by reactive distillation process.

Studies on Gas Holdup in a Draft Tube Fluidised-bed Bioreactor

Abstract Studies on gas holdup have been carried out in a draft tube gas-liquid-solid fluidised-bed bioreactor treating phenolic wastewater at different feed concentrations of phenol, feed flowrates and air flowrates. From the data obtained through a set of experimental runs, an empirical correlation was developed for the overall gas holdup using dimensional analysis. It was found that the gas holdup increases with the flow rate of air and decreases with increase in the flow rate of water. In the concentration range considered in the study the variation of feed concentration of phenol did not affect the gas holdup.