EFFECTS OF DIFFERENT BINDERS ON THE PHYSICAL AND COMBUSTION PROPERTIES OF DRIED LEAVES BRIQUETTES

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ABSTRACT

Biomass Briquetting can address waste problems, reduce air pollution from direct open air burning and also reduce dependance on fossil fuels for heat generation. Dry leaves have been shown to have high calorific values; therefore the purpose of this study is to determine the effects of some binders on the physical and combustion properties of dried leaves briquettes. Dried leaves were mixed with binders such as clay, starch and Arabic gum separately at different ratios of 10%, 20%, 30% and 40%, and made into briquettes using a manual press with a hydraulic jack of 20 tons. Physical and combustion properties of these briquettes were obtained using different methods prescribed by other researchers. From the results of the properties tested, briquettes made from dried leaves and gum at 40% of binder was most resistant to water. Dried leaves and clay at 40% had the highest relative density of 0.7977g/cm3. Dried leaves and starch had a relative density at 40%, 0.4640g/cm3 while briquettes with gum binder had 30%, 0.4030g/cm3. Dried leaves and gum at 40% had the highest volatile matter of 84.110% and the highest heating value of 30.5118MJ/kg at 10%. Briquettes at this ratio failed to hold, because of its low durability. The high ash content of briquettes bonded with clay 16.353% to 34.487% made it difficult to ignite, due to the presence of non combustible matter. Dried leaves bonded with starch at 20% had high heating value of 30.2189, and was able to withstand shattering with durability of 81.752% and high relaxation ratio of 1.7427. It can then be considered as the best binder in this study.

CHAPTER ONE

  1. INTRODUCTION

1.1   Background Information

Energy generated from biomass is categorized as sustainable and renewable energy. During the plant life cycle, plant biomass materials derived from plant adsorb carbon dioxide (CO2) through photosynthesis at same rate as they release the gas in the combustion process, thus leading to no net increase in atmospheric CO2 quantity. Due to the lower contents of sulfur and nitrogen in biomass, its application also creates less environmental pollution and health risk than fossil fuel combustion. This is the reason why utilization of biomass is eco-friendly. Compared to fossil fuel, however, most of agricultural wastes have higher moisture content and lower density, thus making them technically unsuitable for direct use due to combustion and handling problems. Conversion of biomass wastes to briquettes is a solution for such problems. It improves biomass handling characteristics, increases the volumetric calorific values, and reduces transportation, collection, and storage costs (Grover and Mishra,1996).

The potential agro residues which do not pose collection and drying problems, normally associated with biomass are dried leaves, rice husk, groundnut shells, coffee husk and coir waste (obtained by drying process: Sybil 1958). If these agricultural waste products can be properly recycled, into useful products, more goods will be made available to our society, environmental pollution and other disease attack would be greatly reduced. Solid waste can be of importance when properly used or processed, among the uses of agricultural waste are products from rice mills, trees, etc utilized as solid fuel (Grover and Mishra, 1996). These are wastes from trees and plants that are usually gathered and burnt or left to decompose., e.g. stalks, leaves.

Burning a ton of leaves and agro forest residues produce 526N of carbon monoxide, 184N of particulates which are very tiny and easily absorbed in the lungs, and at least seven carcinogenic hydrocarbons which are all dangerous to health (Luke Cutis, 2002).  Briquetting of these residues are found very useful because it reduces its volumetric value, increases thermal efficiency, better transportation and handling.

Dry leaves briquettes have higher calorific values than its raw material (Madhava et al., 2011)

Fuel is defined as natural or artificial organic substance used as source of energy and raw material for industries. All kinds of fuel as regards their state of aggregation are divided into solid, liquid and gaseous and as regards their origin into natural and artificial fuels (Francis and Peters, 1965). Solid fuels for which bound or compressed rice husk (Briquettes) belong to group under the natural fuel origin. Briquetting is defined as the compaction of loose combustible material for fuel making purpose. The products obtained from the process of briquetting are known as briquettes. Briquetting is a technology, which uses either a dry or a wet process to compress solid waste (rice husk) into different shapes.

Briquetting of biomass can be considered for its economics, reliability and ease of operation. Hence briquetting of rice husk for solid fuel is used for domestic heating in cooking stove, fireplace and furnace. They also have the advantage of cleanliness, ease of handling and igniting, produce a small volume of smoke and its ash content is rich in potash and phosphate. This ash can be used as fertilizer on an unfertile soil. With briquetting of rice husk a new fuel source is found which will help in reducing wild dumping of rice husk in the rice growing regions of Nigeria.

 Renewable energy sources are being sought for domestic cooking in developing countries due to the fact that their non-renewable counterpart such as kerosene, LPG, etc., are not meeting the peoples’ demand. Also the high cost of non-renewable energy sources has made people to start deviating to the use of renewable energy sources for domestic cooking. For renewable energy resources utilization, the briquetting technology is used. Biomass-based fuels are utilized in many countries. Briquettes are produced not only from biomass, but also from different type of wastes like milled paper, plastic and other combustible wastes. Different types of briquetting equipment and its modifications are under development. Alternative fuels like biomass are making breakthrough to energy sector for production of green energy.

Currently in Estonia as milled plastic packaging wastes are used in rotary cement kiln by blowing the milled compounded plastic particles (25 mm) into the combustion chamber. In the future these wastes could be grinded and briquetted for gasification in power stations (Jaan, 2010).  Before the waste briquetting, preconditioning of the material is necessary. First step is processing of municipal waste by disintegrator mills for the size reduction. Smaller particle size helps to obtain better properties of the product by drying, mixing and briquetting.

Mixing of milled plastic waste with biological materials (wood sawdust, paper, etc.) leads to better briquette pressing as well as to greater calorific value. Before briquetting, the moisture content of the material should be reduced by drying process. Lower moisture content improves the briquetting process. The technology uses mechanical and chemical properties of materials to compress them into compact shape (briquettes) without use of additives or binders in the high pressure compacting process. Briquetting is mostly used for compacting of biomass (rice husk, sawdust, wood shavings, bark, straw, cotton, paper, etc.). The biomass undergoes the process of briquetting, while high pressure and temperature simultaneously act upon the mass, the cellular structures within the material release lignin, which binds individual particles into a compact unit – briquette. Briquetting, however, can also be used for compacting of compounded plastic waste or municipal waste etc. Briquetting is executed by briquetting presses. The material is pressed into the pressing chamber with high compacting pressure and high pressing temperature. For briquette quality control, the physical parameters, such as density, moisture content and compressive strength, were found to be the best indicators of the quality. (Jaan, 2010).

Studies have been carried out on different biomass briquettes like wood, charcoal, rice husk, determining the effect of a particular binder on the briquette. Also studies have been carried out on the development of rice husk briquettes as fuel for water boiling test, (Yahaya and Ibrahim, 2012). Also on Rice husk production using molasses, cowdung and clay as binder, after carbonizing the rice husk and bagasse in a muffle furnace (Jaan, 2010).

It has therefore become necessary to consider dried leaves for briquetting because of its high calorific value. The binders to be used are readily available and cheap. They are starch gel, clay and Arabic gum. They are grouped into organic and inorganic binders. The organic binder is the Starch gel, while the inorganic are the Clay and Arabic gum. The reason for this choice is that they are more readily available in the South Eastern part of Nigeria, than the other binders and also less expensive. Also they have been tested and do not contain toxic materials when burnt.

1.2    Problem Statement

Dried leaves can be seen lying waste in most houses, industries, schools, markets, walk ways, gardens, fields, etc. Most times these leaves are left to litter the entire surroundings, other times they could be gathered and burnt openly. Open burning of leaves has been proven to cause health hazards (Luke Cutis, 2002).  Most of these agricultural wastes have been highly promoted to be used in various heating systems, during the past decades. Compared to fossil fuel, however, most of agricultural wastes have higher moisture content and lower density, thus making them technically unsuitable for direct use due to combustion and handling problems (Grover and Mishra, 1996). Conversion of wastes to briquettes is a solution for such problems. It improves biomass handling characteristics, increases the volumetric calorific values, and reduces transportation, collection, and storage costs (Grover and Mishra, 1996).

Briquetting of dried leaves is relatively new. The effect of a binder on the heating properties of dried leaves briquettes amongst other briquettes like rice husk, saw dust and groundnut shell was studied (Madhava et el., 2011) but no detailed study has been carried out on the effect of the organic and inorganic binders which will be used in this study on the physical and combustion properties of briquettes. These binders to be used are readily accessible and available.

This search will enable briquette producers to produce the best quality dried leaves briquettes bearing in mind which binders that are locally accessible to use for best results.

1.3    Objectives Of The Study

The general objective of the study is to produce dried leaves briquettes using some specific organic and inorganic binders, then to determine the effect of these binders on the physical and combustion properties of the briquette. The specific objectives are:

  1. To produce dried leaves briquettes using three different binders
  2. To determine the effect of the binders on the physical and combustion properties of the dried leaves briquette.

1.4    Justification Of The Work

Briquetting technology is being encouraged in developing countries as it serves as a cheaper alternative to cooking gas and kerosene used in most homes which are on the high side in terms of cost. It also serves as a cleaner, more presentable, less stressful and safer alternative to the use of firewood and charcoal for cooking. Therefore, there is a necessity to invest in briquetting and achieve the best results.

The result of this study will thereby help in understanding how binders affect the combustion properties of briquettes and also help researchers and producers choose type of binder to be used in dried leaves briquette production.

1.5    Limitation Of This Study

This study is limited to dried leaves briquettes production. Other biomass could have different effects when mixed with the binders. The interest in this study is dried leaves because it burns well and most times are lying waste and causing pollution in our environment.

Also only three binders are used, one organic binders which are starch gel, and two inorganic binders which are Arabic gum and clay. There exists a number of other binders whose effects could also be determined.

EFFECTS OF DIFFERENT BINDERS ON THE PHYSICAL AND COMBUSTION PROPERTIES OF DRIED LEAVES BRIQUETTES