Thesis Abstract

This research work investigates the effect of gasification operating parameters, namely equivalence ratio (ER), gasification agent, reaction zone temperature, and residence time on quality of syngas produced using sawdust.The research experiments were conducted using a pilot scale downdraft gasifier with constricted throat and a rotating grate. Temperatures at reaction zone of the gasifier were monitored directly using a digital thermometer whereas an online gas analyzer capable of detecting percentage composition and calorific value was employed to monitor quality of the syngas.Two sets of experiments were carried out separately; one using air and the other using oxygen-enriched air as gasifying agents. With air, flow rates at 6.4, 1.9 and 0.7 litre per minute (LPM) were used for the study. The results obtained shows that the higher air flow level favours better quality of syngas. Air flow rate at 0.64LPM generated the best quality of syngas containing 13.55 and 2.59% of CO and H2, respectively. Syngas maximum caloric value of nearly 3MJ/Nm3 at a temperature of 550°C was observed. Using oxygen enriched-air on the other hand, flow rate was maintained at 10LPM while varying the percentage oxygen at 21, 30, 40, 50, 60 and 80%.It was found that 40% oxygen enrichment generated the best quality of syngas containing29.57 and 14.29% of CO and H2 respectively.Syngas calorific value was observed to rise consistently from 2.08 to a maximum of 6.69MJ/Nm3 as percentage oxygen in the gasifying agent was increased from 21 to 40%. Gasification performance shows that both cold gas efficiency (CGE) and carbon conversion efficiency(CCE) reaches peak value of 46.81 and 82.04% respectively at ER value of 0.2953 which also corresponds to the 40% oxygen level in gasifying agent.

Thesis Overview

INTRODUCTION

1.1              Background

The alarming rate of global warmingas a result of harmful gases released into the atmosphere combined with continual depletion of fossil fuel resources at unprecedented rate led researchers to devote effort in developing alternative energy technologies from agricultural wastes like sawdust, rice husk andsugar cane bagasse to meet up future energy demand (Christus et al., 2014).

Although it is not known how much fossil fuel is still available, it is generally accepted that it is being depleted and is non-renewable. With these challenging circumstances, search for other alternative renewable forms of energy sources becomes imperative. Other consequences associated with fossil fuel use include the release of the trapped carbon in the fossil fuels to the atmosphere in the form of carbon dioxide which has led to increased concerns about global warming. Also, fossil fuel resources are not distributed evenly around the globe which makes many countries heavily dependent on imports (Ajay et al.,

2009).Evidence suggests that conventional oil production has a limited capacity to meet growing demand, and most additional demand will have to be met by unconventional sources. Since the globe is turning towards the sustainable development, renewable energy technologies are getting more attention all over the world (Bergerson and Keith, 2006).

The combustion of biomass of different varieties has gaindramatic applications ranging from woodstove for domestic usage to industrial power generation.