THE EFFECTS OF THE BINARY AND TERNARY COMBINATIONS OF PINE NEEDLE (PINUS PINASTER ) DUST AND BAMBARA NUT (VIGNA SUBTERRANEA ) CHAFF WITH SUB-BITUMINOUS COAL DUST FOR BRIQUETTE PRODUCTION

ABSTRACT

This work studied the effect of the binary and ternary combinations of pine needle (Pinus pinaster ) dust and bambara nut (Vigna subterranea) chaff with coal dust for briquette production. Briquettes of 100% of the pure coal and the biomass were produced first. The ratios for the blending were as follows 1:1 for the binary combination of each biomass with coal and with themselves, and 1:1:1 for the ternary combination of the two biomass with coal. The feed stocks were dried to a moisture content of 5-10% and ground to a particle size of 0.8  mm.  Desulphurization,  homogeneity and binding were successfully achieved by addition of calcium hydroxide (Ca(OH)2), water and starch, respectively. The mixture was compacted into a rectangular briquetting mould of about 3.8 cm in diameter and height of about 2.5 cm using a manual briquetting machine at a pressure of 5 Mpa for 2 hour. The briquettes were brought out and sun dried for

10 days for further removal of moisture and curing. Proximate analyses, calorific value, combustion and emission analyses, thermogravimetric analyses (TGA) and differential thermogravimetric analyses (DTA) were carried out in line with ASTM D-3173 specifications. The result of the calorific values showed that coal briquette had the highest heating value (23,471 KJ/kg) while the briquette made from Bambara nut chaff had the least calorific value (16,150 KJ/kg). It was found out that the binary and ternary blends with biomass reduced the calorific value of coal briquette. The result of the TGA/DTA analyses showed that coal briquette was the most stable at higher temperatures when compared with the two biomass while pine needle briquette had the least stability during combustion. The thermal stability as well as the percentage combustible fuels increased in the binary and ternary blends with coal. The combustion and emission analyses showed that the blended briquettes had better combustion characteristics than the single coal and biomass briquettes in terms of burning rate, time required to boil water, specific fuel consumption and thermal efficiency. The concentration of CO and CO2  emitted by the coal briquette was the highest (33 ppm and 99 ppm respectively) even though they were within the permissible range stipulated by the World Health Organization Ambient Air Quality Standard (WHO-AAQS) and National Ambient Air Quality Standard (NAAQS) which is 35 ppm for CO and 600 ppm for CO2. However, it was observed that blending the various biomass with coal reduced the concentration of the CO and CO2 evolved during combustion. Therefore, the binary and ternary blends of coal with the two biomass reduced the CO and CO2  emissions. The ternary blend had the highest particulate matter (3,359 µg/m3) followed by the coal

briquette (3,051 µg/m3). However, even though the binary combinations of the biomass with coal reduced

the concentration of PM evolved, they were still higher than the permissible range in the atmosphere as stipulated by WHO-AAQS and NAAQS which is 150 µg/m3.

CHAPTER ONE

INTRODUCTION

1.1 Background of the study

There are three major forms of fossil fuels: coal, oil and natural gas. All three were formed many hundreds of millions of years ago before the time of the dinosaurs – hence the name fossil fuels. The age they were formed is called the Carboniferous Period. It was part of the Paleozoic Era. “Carboniferous” gets its name from carbon, the basic element in coal and other fossil fuels.1

Coal is a hard, black coloured rock-like substance that has been shown to have the highest potential for use as suitable fuel in industrial boiler and brick kiln for thermal application and domestic  purposes. Coal  is  the  largest  source  of  energy  for  the  generation  of  electricity worldwide, as well as one of the largest worldwide anthropogenic sources of carbon dioxide releases. Generally, coal fuel smoke contains a large number of pollutants in the air that are toxic or hazardous to humans.2  These pollutants include: Carbon monoxide (CO), Carbon dioxide (CO2), Lead (Pb), Nitrogen Dioxide (NO2), Particulate matter (PM), Sulphur dioxide (SO2), etc. Global warming has become an international concern. Global warming is caused by green house gases of which carbon dioxide is among the major contributors. Despite significant economic benefits of using coal as fuel, a number of adverse health and environmental effects of coal burning, especially in power stations, and of coal mining, exist. The London smog was caused in part by the heavy use of coal for heating and cooking.2

It has been estimated that coal-fired power plants cause nearly 24,000 premature deaths annually in the United States, including 2,800 from lung cancer. 3 Coal as an environmental air pollutant has been shown to contribute to asthma, strokes, reduced intelligence, artery blockages, heart attacks, congestive heart failure, arrhythmias, mercury poisoning, arterial occlusion, and lung cancer. 3  Due to these adverse effects of coal fuel, the need for an environmentally friendly source of energy has become paramount.

Biomass,  particularly agricultural residues  seems  to  be  one  of the  most  promising  energy resources for developing countries. Rural households and minority urban dwellers depend solely on wood fuel (charcoal, firewood, and saw dust) as their primary source of energy for the past decades.

Agro waste is the most alternative renewable energy resource for developing countries. The decreasing availability of fossil fuel and its hazardous effects has necessitated that efforts be made  towards  efficient   utilization  of  agricultural  wastes.  These  wastes  have  acquired considerable  importance  as  fuels  for  many  purposes,  for  instance,  domestic  cooking  and industrial heating. Some of these agricultural wastes such as coconut shell, wood pulp and wood

wastes can be utilized directly as fuel. 4

Fortunately, researches have shown that a cleaner, affordable fuel source which is substitute to fuel wood can be produced by blending biomass (agricultural residues and wastes) with coal.

Nigeria has large coal deposits which has remained untapped since the 1950’s, following the discovery of petroleum in the country. Again, millions of tonnes of agricultural wastes are generated in Nigeria annually. However, it is unfortunate that farmers still practice “slash-and- burn” agriculture. These agricultural wastes they encounter during clearing of land for farming or during processing of agricultural produce are usually burnt off. By this practice, not only the useful raw materials are wasted, but they further pollute the environment and reduce soil fertility.

On the other hand, the majority of the huge materials are not suitable to be used directly as fuel without undergoing some processes. This is probably as a result of inappropriate density and high moisture contents and these factors may cause problems in transportation, handling and storage. Most of these wastes are left to decompose or when they are burnt, there would be environmental pollution and degradation. Researchers have shown that lots of potential energies abound in these residues. However, these health hazards faced by people from the use of fossil fuel and reduction of pressure mounted on the forest can be mitigated if people switch over to production and utilization of bio-coal briquette; a cleaner and environmentally friendly fuel wood substitute made from agricultural wastes and coal.  Moreover, this will offer a  good potential for utilization of the large coal reserves in Nigeria for economic diversification and

employment generation through bio-coal briquette. The major residues that can be used for this purpose are rice husk, corn cob, coconut shell, jute stick, groundnut shell, cotton stalk, etc. These wastes provide energy by converting them into high-density fuel briquettes. These briquettes are very cheap, even cheaper than coal briquettes. Adoption of briquette technology will not only create a safe and hygienic way of disposing the waste, but turn them into cash rich ventures by converting the wastes to energy and also contribute towards a better environment.

Coal can be blended with a small quantity of these agricultural wastes (agro residues) to produce briquettes (bio-coal briquettes) which ignites fast, burn efficiently, producing little or no smoke and are cheaper than coal briquettes.

1.2 Statement of problem

Burning  fossil  fuels  (especially  coal)  are  considered the  most  economic  ways  to  generate electricity. The release of hazardous emissions from fossil fuel especially coal combustion cause unknown number of people to be diagnosed with ailment such as heart disease, cancer and respiratory  disease  and  developmental  impairments-  especially  vulnerable  groups  such  as children and the elderly.  Global systems and processes are overly-dependent on fossil fuels and need more non-fossil fuel-derived power to ensure security of supply over the coming decades and to reduce if not terminate the quantity of harmful emissions which are given off every second as a result of utilization of fossil fuels.

1.3 Aim of Research

The aim of the research work is to compare the fuel properties of the coal briquettes, biomass briquette and bio-coal briquettes and to investigate the effect of the biomass on the properties of coal briquettes for energy generation.

1.4 Objectives of the study

Considering the  rate  of global  warming,  health  problems  and  other  aquatic  and  terrestrial problems being experienced, which is attributed to the rate of pollutants in the atmosphere as a result of the utilization of fossil fuel especially coal, it is therefore important to :

i.      Analyze the concentration of harmful emissions in a sub-bituminous coal sample as a source of fuel.

ii.       Produce an alternative source of energy which is environmentally friendly using the waste from the environment and from agriculture like Bambara nut chaff and Pine needle.

iii.       Analyze their calorific values when they are used separately and in combination with coal sample.

iv.       Analyze  the  combustion  characteristics  and  emission  profile  of  coal  when  used separately and in combination with the biomass. v.      Analyze the degradation temperature and peak temperature of coal briquette and when blended with the biomass.

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