EVALUATION OF THE FUEL PROPERTIES AND THERMAL EFFICIENCY OF SUB-BITUMINOUS COAL-BIOMASS BLENDS

ABSTRACT

The  improvement  of  the  combustion  properties  of  coal  and  biomass  by  blending  and carbonization was investigated. Proximate and ultimate analysis of coal, sawdust,  corn cob and their blends were carried out using ASTM methods. The proximate and ultimate analyses were repeated on the five blends after carbonization at 500oC for one hour. Ten mixtures of coal-sawdust  and coal-corn cob blends were made into briquettes using starch binder. The

calorific values of the samples were determined using a bomb calorimeter, while the thermal efficiency  of the  briquettes  was obtained  using  the  water boiling  test  analysis. Pollution potential of the fuel samples were derived using a hypothetical power plant simulation. The quantity of CO2, NO2  and SO2  that would be emitted per hour in a 20MW power plant were calculated. The result of the proximate analysis of the raw samples (coal, sawdust and corn cob) showed that coal had the highest fixed carbon (42.38%) and the lowest moisture content (4.28%). Sawdust had the lowest fixed carbon (12.35%) while corn cob had a fixed carbon content  of  15.65%.  The  results  obtained  showed  considerable  correlation  between  the uncarbonized coal-sawdust and coal-corn cob blends. The carbonized blends of both the coal- sawdust  and coal-corn cob blends  showed  an improved  fixed carbon content  and volatile matter, relative to the uncarbonized. The calorific values and other fuel properties were of similar  trends.  The results  of the  ultimate  analysis  for coal were 70.04%  carbon,  5.32% hydrogen,  2.03% nitrogen and 1.02% sulphur. Corn cob had 48% carbon, 5.79% hydrogen and 0.89% nitrogen while sawdust had 48.78% carbon, 5.79% hydrogen and 0.89% nitrogen. Corn cob and sawdust had no sulphur content, while the uncarbonized coal-sawdust and coal- corn  cob  blends  showed  decreasing  carbon  content.  This  study  revealed  that  the  fuel properties  of  coal  and  biomass  can  be  improved  by  blending  and  carbonization.  The simulated power plant analysis of the fuel showed that blending of coal with biomass reduced the SO2 and NO2 emissions to an extent. For NO2, the value of coal-sawdust blends ranged from 82.8-190.8 kg/hr, reduced from 198 kg/hr in coal,  while the SO2  content was reduced from 60.5 kg/hr in coal to 5.6 – 50.4 kg/hr in different blends.  Therefore, blending of coal with either sawdust or corn cob should be  encouraged in coal fired power plants to reduce environmental pollution.

CHAPTER ONE

1.1General Introduction

INTRODUCTION

History has revealed that many centuries ago,man made use of energy in its natural form to aid daily living. From burning wood for cooking, to utilizing the force of flowing water for irrigation and using sun light to dry and preserve foods. The use  of energy has remained  unabated  till date, only that  energy use has changed  from  the  brute  and basic methods, into more sophisticated and industrial ways.

The period from the late 1700s into early 1800s in England and Western Europe have

been called the Industrial Revolution. The dawn of the Industrial Revolution paved way for an age of energy. This period witnessed drastic changes in virtually every aspect of human life. It was an advent of machines and use of mechanized methods. Ever since, man’s desire to live a better and civilized  life, with the help of modern technology has  caused a great demand for energy in its many forms. This also came with the adoption of lifestyles that has an increased  demand  for energy use.The technological  advances  that occurred  during the industrial revolution of the 1700s have numerously been credited to coal. Before this period, wood was the major source of energy.

Consequently, the increasing adoption of a lifestyle that was energy intensive  came with the quest for a better energy resource. Today, these energy needs are majorly supplied by fossil fuels such as coal, natural gas and petroleum. These fuels are known as primary energy  sources,  and  they  provide  most  of  the  energy  that  powers  man’s  modern  life. Petroleum was discovered by Edwin Drake in 1859 in the United States. It was first used for lightening  lamps and other  basic uses.  With the  breakthrough  of  petroleum  refining  into various fractions, and increased use of internal combustion  engines in automobiles,  motor cycles and aero planes, the demand  for petroleum  never  dwindled.  In 1992, the National Energy  Strategy  in  the  United  States  concluded  that,  “for  the  foreseeable  future,  oil [Petroleum]  will remain  a  critical  fuel  for  the  United  States  and  all other  industrialized nations.”  The quest  for oil has  continued  up to the point that  it has become  a potential economic  and security  concern  for developed  countries,  especially  after the 1970s crisis. Despite these, coal has not been totally abandoned.  It is used for electricity generation  in countries with large coal reserves, with no cheaper alternative. For example, 73% of South

Africa’s primary energy is derived from coal1. In China’s energy strategy, coal plays the most

important role especially for its electricity sector2.

The availability of energy resources and its effective utilization has a bearing on national development  and  living  standards.  Energy  is  required  for  national  development,  and  its presence directly betters the standard of living. The availability of vast amounts of energy resources in a nation is supposed to bring significant  progress to the economy, and living standards of her citizenry. The effect of energy can be seen in its ability to multiply the work of a few labourers by many folds e.g  an automobile would move many folds faster than man. The  value  of  energy  is  noticed  when  its  utilization  results  in  a  final  product.  Good management  practices should  aim at reducing  the rate of exhaustion of the resource base,

rather than increase or even sustain the rate of consumption3.Consumers  and manufacturers,

who enjoy the efficient use of energy, should become more knowledgeable about it.

1.2 ENERGY AND ITS USES

The use of energy has increased tremendously with sophistication of technology, and the ease it brings to living. Energy usage can be divided into four main sectors; Electricity generation, Transportation, Industrial and Domestic.

1.2.1  Electricity  Generation:  Electric  power  is  the  largest  energy  demand  sector  in developed nations. Most electrical power is generated by converting mechanical energy to electrical  energy  with  a  turbine.  Water  is  heated  to  steam,  and  steam  at  a  very  high temperature and pressure is used to turn the turbine. The heat used to produce the steam is gotten by burning fuel like coal, natural gas or fuel oil. Most of the electricity produced in the United States is produced by Steam turbines. Electricity is a secondary source of energy,

it is referred to as an energy carrier4.

1.2.2 Transportation: Economic development of nations has caused the need for man and goods to move, more than before. Transportation  system is very essential for  trade  in an increasingly globalized world. With increasing use of trains, cars, trucks, speed boats and air planes, transportation has become a high demand energy sector.  The  transportation sector accounts for 63% of the total growth in world consumption of petroleum and other liquid

fuels.   Transportation activities accounted for 28% of all US energy use in 19875.

1.2.3 Industrial Sector:The industrial sector encompasses a large number of industries. This includes; manufacturing  (food, paper, chemicals,  refining,  iron and steel, and  others) and non-manufacturing  (agriculture,  mining,  telecommunication  and  construction).  Energy  is consumed in the industrial sector for a wide range of purposes, such as processing, assembly, heating,  cooling/  air conditioning,  packaging  and  lighting  in  buildings.  The type of fuel consumed  by  the  industrial  sector  varies,  and  depends  on  the  level  of  technological

development,  among other factors. Although the   industrial sector energy consumption is largely based on secondary energy sources like electrical power, it also make use of primary energy like natural gas and petroleum products (naphtha and natural gas liquids)   which is used  as  feedstock  to  produce       fertilizers  for  agriculture  and  petrochemicals  for  the manufacture of plastics.

1.2.4 Domestic Use: Energy is also used to a considerable extent in homes. Activities like

cooking,  heating,  (during  winter)  and  lightening,  take  a  bulk  of  domestic  energy  use. Increase in population and household, causes a correlating increase in domestic energy use. The fuel used varies widely based on factors like climate, technological development, and cheap energy source. In the U.K, the fuel mix for domestic  consumption has significantly changed  since  1990  when  8%  of  consumption  was  coal,  63%,  natural  gas  and  20%,

electricity, to 1%, coal, 68%, natural gas and 23%, electricity in 2012.6

1.3 RENEWABLE AND NON-RENEWABLE ENERGY SOURCES

Renewable energy sources refer to those sources that cannot be exhausted by  their continual  usage.  These  energy  sources  are  naturally  replaced  at  a  rate  faster  than  its consumption.  Non renewable  energy sources are the direct  opposite  of the  former.  They diminish and can be exhausted after a period of usage. Presently, the world uses more of non- renewable   energy  than  renewable  energy.  With  increasing  world   population  and  the corresponding increasing need of energy for every day life,the world’s non-renewable energy resources are depleting at a very fast rate. Scientists are already estimating the period when individual non-renewable resource would be exhausted. Hence, there is a need to balance the world’s use of energy so that a future energy crisis is avoided. In the United States, most of its  energy  sources  come  from  non-renewable  energy  sources,  though  there  have  been government push for increased renewable energy use. While it may be difficult to totally stop the use of  non-renewable  energy sources,  it is important to carry out research in order to make them environmentally friendly.

1.3.1 Renewable Energy Sources

1.3.1.1 Biomass Energy: Biomass is the term used to describe all organic matter produced by photosynthesis. Bioenergy from biomass comes either from dedicated energy crops, or from residues generated in the processing of food crops or other products such as wood shaving and saw dust from the wood furniture  industry.  As long as plants  photosynthesize,  there would always be an inexhaustible biomass energy resource. The interest in biomass as a raw material for producing energy has emerged rapidly in many countries7.

1.3.1.2 Solar Energy: The sun is the source of solar energy.  It is an extremely hot gaseous sphere. The sun is the source of most of the energy used on earth. It is renewable, naturally replenished and does not run out. It does not produce pollutants and has minimal impacts on

the environment8. Though solar energy is abundant, it is distributed over a wide area. Hence

it needs collectors with large surface area to gather and utilize it. Also, it is very costly and requires a lot of technical knowledge for effective utilization.

1.3.1.3 Wind Energy: Wind has a potential to provide a substantial amount of clean global energy needs. It is available everywhere,  does not cause pollution nor any  environmental hazard during utilization for power generation. Extracting power from wind turbines is an established  technology.  With turbines,  wind can be used for  on-grid and off-grid electric power generation. It can also be used for water pumping and milling.

1.3.2 Non Renewable Energy Sources

1.3.2.1 Coal:This is a fossil fuel formed from the remains of plants that have under  gone biochemical and geochemical changes over a long period of time. It is non-renewable, and is the fuel for most of the world’s power plants.

1.3.2.2 Petroleum:It is sometimes called oil or crude oil and is a dark, viscous fluid, found in subsurface rock formations. It is formed from the fossilized remains of algae, zoo and animal plankton over millions of years. The long period of time it takes to be formed, and the present rate of consumption, makes it non-renewable. Petroleum and its refined products, is the major source  of energy  for  many technological  equipment.  A  large  percentage  of fuel used  in transportation  is from petroleum,it  is also the major  feedstock  used by the petrochemical industry.

1.4  ENERGY RESOURCES IN NIGERIA

Nigeria  has often been referred  to as giant of Africa.  This is because  of the  vast amounts of energy resources she possesses.  Nigeria  has been faced with the  challenge of effectively utilizing the vast energy resources bestowed on her. These resources range from abundant sunlight, wind, hydropower, petroleum, natural gas, coal and many others. Despite these resources, the country is in short supply of electricity. The presence of energy resources should expectedly catalyze economic growth, technological advancement and creates better living standards for the people. Access to energy,  specifically electricity, is an impetus for economic and social development. But in Nigeria, lack of policy implementation, corruption and  rigid  government  control  of  electricity  generation  has  caused  a  dismal  failure  of achieving  reliable  electric  power  supply.  The  electricity  needed  to  power  and  grow  the

economy, drive local development and tackle urban and rural poverty is simply inadequate or not  available  at  all.  A well-managed  electric  power  sector  has  profound  benefits  to the economy.

In Nigeria, non-renewable energy resources includepetroleum  and natural  gaswhich accounts  for  over  90  percent  of Nigeria’s  GDP.  Although  Nigeria  has  been  among  the world’s top ten petroleum producing nation, she still imports most of her fuel needs because of lack of adequate infrastructure for refining.Renewable energy resources like hydro power and solar are being used, but their impact is very minimal on a national scale. Dams have been constructed at Kainji in Niger State for electricity generation. The use of solar energy from sunlight has been restricted to off grid use like street lightening, solar borehole pumps and for backup  systems.  In recent  times,  energy  resources  like coal and wind have been virtually neglected.

1.4.1  Coal and Biomass in Nigeria

Nigeria is blessed with an abundance of good quality coals, as well as a vast amount of biomass resource. For a long period of time, coal and biomass have been the fuel used as primary energy resource. These fuels were burnt to provide heat and power for domestic and industrial  uses.  Nigeria  has  extensive  coal resource,  with  proven  reserve  of 639  million

tonnes9. The demonstrated coal reserves in the world are enough for consumption for over

215 years at the 1998 level10.

Coal was first discovered in Nigeria in 1909 at Udi by the mineral survey of Southern Nigeria11.  Exploitation  of Nigerian  coal  began  in  1916.  As  exploration  and  exploitation continued, mines were opened at Okpara, Ribadu, Onyeama and later Okaba in present day Benue State. Elsewhere mines were also opened at Ezimo, Orukpa, Ogboyoga and Inyi. The mining methods were both surface/open cast and underground mining. By 1967, production ceased  as  a result  of the  civil war,  and  started  again  in  1971  with  about  25000 tonnes produced that year9.

The coal fuel was used by the Nigerian Railway Corporation to fuel their locomotives. Other  users were the Electricity  Company  of Nigeria  and Nigerian  Cement  Company  at Nkalagu. Thus, coal was the fuel that supplied most of Nigeria’s industrial energy needs at that  time.  This  was  before  the  discovery  and  wide  spread  use  of  petroleum  products. However,  in recent times, it is obvious that there is the  need to reintroduce coal into our

national energy matrix, hence the renewed interest in coal technology12.

Biomass is an energy source that has interested many researchers since the awareness for the need to reduce Greenhouse  gas (GHG)  emissions and  environmental  degradation.

Biomass consists mainly of the remains of dead plants and animals. Biomass is considered the renewable energy source with the highest potential to the energy needs of modern society for both developed and developing economies worldwide.13,14 The early man made use of fire wood, a biomass resource, as fuel for cooking. In temperate regions of the world, wood logs

and shavings were burnt to keep the house warm during the winter cold. Wide availability, carbon  neutrality,  environmental  friendliness  and  cheap  nature  of  biomass  fuel  are  its advantages. The drawbacks to biomass fuel are its low heating  value and the difficulty in striking a food-fuel balance, since most foods consumed by man are biomass based.

Biomass,  in the form of firewood is the major fuel source for people in the  rural communities. About 70% of Nigeria’s population lives in rural areas. Many rural dwellers cannot  afford  alternative  fuels  to  biomass  fuel.  This  is  because  of their  low  income  in addition  to  low  purchasing  power,  and their  low  standard  of living.  Biomass  fuel used consist  of dried  wood,  corn  cobs,  saw  dust,  wood  shavings,  bagasse  e.t.c.  This  energy resource is used for cooking, heating and drying.

1.5  ENERGY CRISIS AND ENVIRONMENTAL PROBLEMS

The world energy crisis of the 1970s was a big problem for many world leaders. In an attempt  to avoid a repeat  of such, proactive  leaders started creating  what  was  called an energy mix. This would help in reducing their over dependence on fossil fuels such as crude oil and natural gas. The energy mix of a nation is a combination of two  or more energy sources which is readily available and can be easily used. The negative economic effect of overdependence  on only one energy source, especially when it is  imported is grave. This spurred  up researches,  seeking  to open up other  energy  sources.Beyond  the past energy crisis, there is a bigger challenge ahead. The world’s depleting crude oil reserves are already a source of concern.  Scientists  are already  setting  probable  dates when specific  reserves would be exhausted. At present levels of production and consumption, Nigeria’s oil reserves

are expected to run out in about forty years.15

Meanwhile, the negative environmental impacts of many energy resources have raised concerns. Energy exploration and delivery has its attendant cost to the environment. These range from Greenhouse gas (GHG) emissions, noise pollution,  oilspillage, gas flaring and land  disturbances  from  coal  mining.  Over  time  these  activities  has  been  significantly detrimental to man’s wellbeing and environmental stability. Greenhouse gas and its effects; global warming and climate change are the result of using fuels that harm the environment. The  use  of  these  fuels  releases  potentially  dangerous  gases  to  the  atmosphere.  This

causesacid rain and fog that destroys vegetation and create health problems like lung cancer, asthma, and pneumonia. They also deplete the ozone layer. One of the  agreements of the Kyoto agreement  is to reduce greenhouse  gas emissions and  problems related to climate change.

In Nigeria, irrespectiveof  her vast petroleum and natural gas deposits and  despite being a leading petroleum exporter in the world, shestill faces serious energy crisis. About

60-70 percent of Nigerians are excluded from the national grid, which is also plagued  by frequent power outages that lasts about 20 hours daily in places connected to the grid16.There is also the problem of poor waste management. Municipal and industrial wastesare disposed into  rivers,  streams  e.t.c.Exploration  and  exploitation  of  crude  petroleum  have  caused devastating  environmental  problems  within  the  vicinity  where  crude  oil is  mined.    The

problem of oil spillage has been a reoccurring one which has led to the genocide of fishes in rivers of the Niger delta. Local communities no longer have access to clean drinking water. Waste waters from mining  operations,  boilers and cooling systems  may  be contaminated with  heavy  metals,  acids,  organic  materials  and  suspended  solids  which  affect  water

quality.17  Added to these are social and political problems like oil bunkering, militancy, and

inter-ethnic conflict. The problems caused by some energy sources have raised the need for a better,  efficient  and environmentally  friendly  energy  source.  With advances  in  research, there have been developments of energy sources that make little or no negative impact on the environment.

1.5.1  Biomass and Climate Change

The  use  of  biomass  materials  as  a  source  of renewable  energy  is  a  big  step  at combating the increasing effects of climate change. The release of greenhouse gases into the atmosphere  overtime  causes  a  gradual  increase  in  the  earth’s  atmospheric  temperature because the gases trap heat from the sun. The slow but steadily increasing earth’s temperature causes some climatic changes. These include the melting of ice caps, increased sea levels and drought.

One of the greenhouse gases that cause global warming is carbon (IV) oxide. This is released from the combustion of fuels. The atmospheric concentration of carbon (IV) oxide is increasing, based largely on the consumption of fossil fuels. The combustion of fossil fuels (coal, petroleum and natural gas) releases large amounts carbon (IV) oxide stored and is a major source of greenhouse gases. Considering the  impact of fossil fuels, it is important to seek ways of controlling carbon (IV) oxidein sustainable methods that would not negatively

impact technological advancement. Unlike fossil fuels, biomass is not stored up for long. The combustion of biomass also releases carbon (IV) oxide, which is estimated as the net carbon (IV)  oxide  taken  up  during  the  biomass  photosynthesis.  In  essence,  the  combustion  of biomass is CO2  neutral, as no extra CO2  is given off. Biomass represents anabundant carbon- neutral renewable resource for the production of bioenergy andbiomaterials, and its enhanced

use  would  address  several  societal  needs18.  The  CO2   emitted  from  biomass  based  fuels

combustion does not increase atmospheric CO2 concentrations, assuming the biogenic carbon emitted is offset by the uptake of CO2    resulting from the growth of new  biomass19. Field trials have been done on the use of Miscanthus, a rhizomatous grass.IfMiscanthus was grown

on 10 percent of suitable land area in the European Union, the total carbon mitigation could be 76 Mt Carbon yr−1, which is about 9 percent of the EU total Carbon emissions.20Hence, biomass contribution to global warming is low. It contains negligible amount of sulphur, so nosulphur oxide pollution from its use. The use of biomass for fuel would ultimately reduce

the net release of greenhouse gases, and would steadily lower climate change.

1.6JUSTIFICATION OF THE STUDY

Literature has revealed that very few studies have been done on Nigerian coal and biomass  blends  (especially  sawdust   and  corn  cob),  in  an  attempt  to   evaluate   their environmental suitability and as an alternative energy source for the nation.

The combustion of coal in its natural form releases potentially dangerous gases like CO2, SOx, and NOx, which cause air pollution, acid rain, global warming and ultimately, climate change. This study seeks to alleviate this problem by combining coal with biomass and carbonizing  it. Biomass combustion is carbon neutral and  environmental friendly and would  make  coal a  better  fuel  in  combination  with  coal  in  moderate  amounts.  This  is expected to reducegreenhouse gas emissions.

Sawdust and corn cobs, the biomass to be used for this study, are usually burnt up at dump sites.  This creates a great  waste of an energy resource  that  could  be  used when processed into a better form. Studies have revealed that the lignocellulosic part of biomass is a heavy energy carrier. Also, biomass energy resource like poultry droppings and cow dung give out an odour that pollutes the air. This pollution can be minimized by converting it to a form in which it can be used as fuel.

This research is also justified by the need to have a national energy mix. In Nigeria, there is no major alternative  energy resource to petroleum.  This has made  Nigerians the direct  recipient  of  the  unfriendly  petroleum  price  hike  and  inadequate  availability  of

petroleum products.  Nigeria’s energy use needs to be diversified from only petroleum into other energy sources. This diversification can only be achieved when alternative fuels like coal and biomass are brought into the nations’ energy mix and  overdependence  on oil is stopped. The energy mix provides alternative energy sources that can cushion the negative impact of depending on just one energy source; oil, in the case of Nigeria.

1.7      OBJECTIVES OF THE STUDY

This study is aimed at achieving the following objectives:

1.   To  characterize  sub-bituminous  coal  and  its  blends  with  corn  cobs  and  sawdust

(biomass)

2.   To  determine   the  most  suitable   sub-bituminous   coal-biomass   blend   ratio   for combustion

3.   To improve the thermal efficiency of coal and its biomass blends.

4.   To reduce the environmental pollution effects of coal.

5.   To produce suitable fuels from waste materials e.gsawdust and corn cob.

6.   To propose  briquetting  as a suitable way of using coal and its biomass  blends  as domestic fuel.

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