Ethanol (CH5OH or EtOH) is a liquid biofuel that can be produced from several different biomass feedstocks and conversion technologies. Bioethanol is an attrac­tive alternative fuel because it is a renewable bio-based resource and is oxygenated, thereby providing the potential to reduce particulate emissions in compression — ignition engines.

Ethanol can be made synthetically from petroleum or by microbial conversion of biomass materials through fermentation. In 1995, about 93% of the ethanol in the world was produced by the fermentation method and about 7% by the synthetic method. The fermentation method generally uses three steps: (1) the formation of a solution of fermentable sugars, (2) the fermentation of these sugars to ethanol, and (3) the separation and purification of the ethanol, usually by distillation.

Ethanol has a higher octane number, broader flammability limits, higher flame speeds, and higher heats of vaporization than gasoline. These properties allow for a higher compression ratio, shorter burn time and leaner burn engine, which lead to theoretical efficiency advantages over gasoline in an internal combustion engine. The disadvantages of ethanol include its lower energy density than gasoline (but about 35% higher than that of methanol), its corrosiveness, low flame luminosity, lower vapor pressure (making cold starts difficult), miscibility with water, and toxi­city to ecosystems.

Because ethanol-based fuel contains oxygen (35% oxygen content), it can ef­fectively reduce particulate matter emission in a diesel engine. Ethanol is appro­priate for mixed fuel in gasoline engines because of its high octane number, and its low cetane number and high heat of vaporization impede self-ignition in diesel engines. The most popular blend for light-duty vehicles is known as E85, which contains 85% ethanol and 15% gasoline. In Brazil, bioethanol for fuel is derived from sugar cane and is used pure or blended with gasoline in a mixture called gasohol (24% bioethanol, 76% gasoline). In several states of the USA, a small amount of bioethanol (10% by volume) is added to gasoline; this is known as gaso­hol or E10. Blends having higher concentrations of bioethanol in gasoline are also used, e. g., in flexible-fuel vehicles (FFVs) that can operate on blends of up to 85% bioethanol — E85. Some countries have established biofuel programs on bioethanol — gasoline blends such as the USA (E10 and for flexible fuel vehicle [FFV] E85), Canada (E10 and for FFV E85), Sweden (E5 and for FFV E85), India (E5), Aus­tralia (E10), Thailand (E10), China (E10), Colombia (E10), Peru (E10), Paraguay (E7), and Brazil (E20, E25, and FFV any blend) (Kadiman 2005).

As biomass hydrolysis and sugar fermentation technologies approach commer­cial viability, advancements in product recovery technologies will be required. For cases in which fermentation products are more volatile than water, recovery by dis­tillation is often the technology of choice. Distillation technologies that will allow the economical recovery of dilute volatile products from streams containing a vari­ety of impurities have been developed and commercially demonstrated. A distilla­tion system separates the bioethanol from water in the liquid mixture.

The first step is to recover the bioethanol in a distillation or beer column, where most of the water remains with the solid parts. The product (37% bioethanol) is then concentrated in a rectifying column to a concentration just below the azeotrope (95%). The remaining bottoms product is fed to the stripping column to remove additional water, with the bioethanol distillate from stripping being recombined with the feed to the rectifier. The recovery of bioethanol in the distillation columns in the plant is fixed at 99.6% to reduce bioethanol losses.

Bioethanol can be used directly in cars designed to run on pure ethanol or blended with gasoline to make “gasohol.” Anhydrous ethanol is required for blending with gasoline. No engine modification is typically needed to use the blend. Ethanol can be used as an octane-boosting, pollution-reducing additive in unleaded gasoline.

Figure 3.3 shows the world production by country of ethanol between 1980 and 2008 (RFA 2009). Between 1991 and 2001, world ethanol production rose from around 16 billion liters a year to 18.5 billion liters. From 2001 to 2007, produc­tion is expected to have tripled, to almost 60 billion liters a year. Brazil was the world’s leading ethanol producer until 2005, when US production roughly equaled Brazil’s. The USA became the world’s leading ethanol producer in 2006. China holds a distant but important third place in world rankings, followed by India, France, Germany, and Spain. Ethanol production by country in 2007 and 2008 is given in Table 3.2.

The continued increases in the price of crude oil in 2005 and 2006 resulted in a reversal of the traditional relationship between the price of biomass energy and that of crude oil, something not seen since the 1930s. As a consequence of the high prices of traded crude oil, many countries advanced their biofuel goals, and, in the case of Brazil and the USA, large production gains occurred.

Renewable energy sources that use indigenous resources have the potential to pro­vide energy services with zero or almost zero emissions of both air pollutants and greenhouse gases. Currently, renewable energy sources supply 14% of the total world energy demand. Large-scale hydropower supplies 20% of global electricity. Renewable resources are more evenly distributed than fossil and nuclear resources. Renewable energy scenarios depend on environmental protection, which is an es­sential characteristic of sustainable developments.

For biomass resources, several potential sources may be used. Biomass resources include agricultural and forest residues, algae and grasses, animal manure, organic wastes, and biomaterials. The supply is dominated by traditional biomass used for cooking and heating, especially in rural areas of developing countries. Worldwide biomass ranks fourth as an energy resource, providing approximately 14% of the world’s energy needs (Hall et al. 1992).

Biomass now represents only 3% of primary energy consumption in industri­alized countries. However, much of the rural population in developing countries, which represents about 50% of the world’s population, is reliant on biomass, mainly in the form of wood, for fuel (Ramage and Scurlock 1996). In Europe, North Amer­ica, and the Middle East, the share of biomass averages 2 to 3% of total final energy consumption, whereas in Africa, Asia, and Latin America, which together account for three-quarters of the world’s population, biomass provides a substantial share of energy needs: a third on average, but as much as 80 to 90% in some of the poor­est countries of Africa and Asia (e. g., Angola, Ethiopia, Mozambique, Tanzania, Democratic Republic of Congo, Nepal, and Myanmar). Large-scale hydropower provides about one-quarter of the world’s total electricity supply, virtually all of Norway’s electricity, and more than 40% of the electricity used in developing coun­tries. The technically usable world potential of large-scale hydro is estimated to be over 2,200 GW.

There are two small-scale hydropower systems: micro hydropower systems (MHP), with capacities below 100 kW, and small hydropower systems (SHP), with capacity between 101 kW and 1MW. Large-scale hydropower supplies 20% of global electricity. According to the United Nations Development Programme, in de­veloping countries, considerable potential still exists, but large hydropower projects may face financial, environmental, and social constraints (UNDP 2000).

Geothermal energy for electricity generation has been produced commercially since 1913 and for four decades on the scale of hundreds of megawatts both for electricity generation and direct use. Utilization of geothermal sources of energy has increased rapidly during the last three decades. In 2000, geothermal resources were identified in over 80 countries, and there are quantified records of geothermal utilization in 58 countries in the world. Table 1.7 shows the status of geothermal energy (Fridleifsson 2001).

Geothermal energy is clean, cheap, and renewable and can be utilized in vari­ous forms such as space heating and domestic hot water supply, CO2 and dry-ice production processes, heat pumps, greenhouse heating, swimming and balneology

(therapeutic baths), industrial processes, and electricity generation. The main types of direct use are bathing, swimming and balneology (42%), space heating (35%), greenhouses (9%), fish farming (6%), and industry (6%) (Fridleifsson 2001).

One of the most abundant energy sources on the surface of the Earth is sunlight. Today, solar energy has a tiny contribution in the world total primary energy supply, less than 1.0 (Ramachandra 2007). The potential of solar energy — passive solar heat, collectors for, e. g., hot water, and photovoltaic (PV) power — is tremendous.

Following the oil crises of the 1970s, energy experts began to explore whether solar-based power generation held potential as an alternative to petroleum-based fuels. Development of solar power has progressed considerably since then, yet its record of performance has been mixed, and it has not come into widespread use in either industrialized or developing countries.

PV systems, other than solar home heating systems, are used for communica­tion, water pumping for drinking and irrigation, and electricity generation. The total installed capacity of such systems is estimated at about 1,000 kW. A solar home heating system is a solar PV system with a maximum capacity of 40 W. These sys­tems are installed and managed by a household or a small community (Garg and Datta 1998).

Like wind power markets, PV markets have seen rapid growth and costs have fallen dramatically. The total installed capacity of such systems is estimated at about 1,000 kW. Solar PV is growing fast; the PV and grid-connected, wind-installed ca­pacities are growing at a rate of 30% a year (Demirbas 2005).

Wind energy is a significant resource; it is safe, clean, and abundant. Wind en­ergy is an indigenous supply permanently available in virtually every nation in the world. Using the wind to produce electricity by turning blades on a wind turbine is known as wind energy or wind power. More recently large wind turbines have been designed that are used to generate electricity. Wind as a source of energy is non­

polluting and freely available in many areas. As wind turbines are becoming more efficient, the cost of the electricity they generate is falling.

Wind power in coastal and other windy regions is promising as well. Today there are wind farms around the world. Production of wind-generated electricity has risen from practically zero in the early 1980s to more than 7.5 TWh per year in 1995. Cumulative generating capacity worldwide topped 6,500 MW in late 1997 (Demir- bas 2005). Figure 1.1 shows the growth in world wind turbine installed capacity. Globally, wind power generation more than quadrupled between 1999 and 2005.

Wind energy is abundant, renewable, widely distributed, and clean and mitigates the greenhouse effect if it is used to replace fossil-fuel-derived electricity. Wind energy has limitations based on geography and climate, plus there may be politi­cal or environmental problems (e. g., dead birds) associated with installing turbines (Garg and Datta 1998). On the other hand, wind can contribute to air pollution by degrading and distributing pieces of pollutants such as waste paper, straw, etc.

Worldwide developments in the field of energy supply, following the oil crises of the 1970s and 2004, are showing the way to more serious decisions regarding sustainability in strategic energy planning, improvements in energy efficiency, and the rational use of energy. Renewable energy sources are increasingly becoming a key factor in this line of thought.

Figure 1.1 Growth in world wind turbine installed capacity

Starting in the 1980s important progress has been made on evaluating some low — grade oils, oil production wastes, and residues as motor fuel (Pryor et al. 1983). But direct usage of vegetable oils causes a number of problems concerning the engine because of their high viscosity and the excessive carbonaceous deposits left in the cylinders and on the injector nozzles. Therefore, chemical conversion of vegetable oils was suggested. In order to lower the viscosities and flash points of vegetable oils, the transesteriflcation method was applied, and it was reported that the alcohol­ysis products of soybean, sunflower, rapeseed, and used frying oils were proposed as diesel fuel alternatives.

The deregulation of domestic crude oil prices and the formation of OPEC have been largely responsible for high fuel prices. The farmer is highly dependent on diesel fuel for crop production. Alternative fuels such as vegetable oils could help ease the petroleum dependence of farmers. Recently, the demand for crude oil has decreased because of conservation practices but ultimately a liquid fuel resource problem exists (Pryor et al. 1983).

Vegetable oils with carbon chain lengths of between 16 and 22 carbon atoms are generally in the form of triacyl glycerides (TAG), which upon transesteriflcation with methanol produce fatty acid methyl ester (FAME) as the precursor to biodiesel and glycerol as a byproduct. Vegetable oil (m)ethyl esters, commonly referred to as “biodiesel,” are prominent candidates as alternative diesel fuels. The name biodiesel has been given to transesterified vegetable oil to describe its use as a diesel fuel. After FAME purification and testing for compliance with either EN 14214 or ASTM D6751 standards the product can be sold as biodiesel and used as blends — typically B5 (5% biodiesel) to B20, depending on the engine warranties.

Biodiesel is a mixture of methyl esters of long-chain fatty acids like lauric, palmitic, steric, oleic, etc. Typical examples are rapeseed oil, canola oil, soybean oil, sunflower oil, and palm oil and its derivatives from vegetable sources. Beef
and sheep tallow and poultry oil from animal sources and cooking oil are also the sources of raw materials. The chemistry of conversion to biodiesel is essentially the same. Oil or fat reacts with methanol or ethanol in the presence of catalyst sodium hydroxide or potassium hydroxide to form biodiesel, (m)ethylesters, and glycerin. Biodiesel is technically competitive with or offers technical advantages over con­ventional petroleum diesel fuel. Biodiesel esters are characterized for their physi­cal and fuel properties including density, viscosity, iodine value, acid value, cloud point, pure point, gross heat of combustion, and volatility. Biodiesel fuels produce slightly lower power and torque, and higher fuel consumption than No. 2 diesel fuel. Biodiesel is better than diesel fuel in terms of sulfur content, flash point, aromatic content, and biodegradability. Some technical properties of biodiesels are shown in Table 3.3.

Table 3.3 Some technical properties of biodiesels

Biodiesel is a synthetic diesel-like fuel produced from vegetable oils, animal fats, or waste cooking oil. It can be used directly as fuel, which requires some engine modifications, or blended with petroleum diesel and used in diesel engines with few or no modifications. At present, biodiesel accounts for less than 0.2% of the diesel consumed for transport (UN 2006). Biodiesel has become more attractive recently because of its environmental benefits. The cost of biodiesel, however, is the main obstacle to commercialization of the product. With cooking oils used as raw material, the viability of a continuous transesterification process and recovery of high-quality glycerol as a biodiesel byproduct are the primary methods to be considered for lowering the cost of biodiesel (Zhang et al. 2003). Table 3.4 shows the biodiesel production (2007) and production capacity (2008) of EU countries (EBB 2009). Figure 3.4 shows the world production of biodiesel between 1980 and 2008 (Demirbas 2008).

Between 1991 and 2001, world biodiesel production grew steadily to approx. 1 billion liters. Most of this production was in OECD Europe and was based on virgin vegetable oils. Small plants using waste cooking oils started to be built in

other OECD countries by the late 1990s, but the industry outside Europe remained insignificant until around 2004. Since then, governments around the world have in­stituted various policies to encourage development of the industry, and new capacity in North America, Southeast Asia, and Brazil has begun to come onstream at a brisk rate. As a result, between 2001 and 2007, biodiesel production will have grown almost tenfold, to 9 billion L (Demirbas 2008).

The advantages of biodiesel as diesel fuel are its portability, ready availability, re — newability, higher combustion efficiency, lower sulfur and aromatic content (Knothe et al. 2006; Demirbas 2008), higher cetane number, and higher biodegradability (Zhang et al. 2003). The main advantages of biodiesel given in the literature include its domestic origin, reducing the dependency on imported petroleum, biodegrad­ability, high flash point, and inherent lubricity in the neat form (Knothe et al. 2005). The disadvantages of biodiesel are its higher viscosity, lower energy content, higher cloud point and pour point, higher nitrogen oxide (NOx) emissions, lower engine

speed and power, injector coking, engine compatibility, high price, and higher en­gine wear.

The cost of feedstock is a major economic factor in the viability of biodiesel production. Using an estimated process cost (Note: all costs are given in US$), ex­clusive of feedstock cost, of $0.158/L ($0.60/gal) for biodiesel production, and estimating a feedstock cost of $0.539/L ($2.04/gal) for refined soy oil, an over­all cost of $0.70/L ($2.64/gal) for the production of soy-based biodiesel was esti­mated (Haas et al. 2006). Biodiesel from animal fat is currently the cheapest option ($ 0.4 to $ 0.5/L), while traditional transesterification of vegetable oil is at present around $0.6 to $0.8/L (IEA 2007). Rough projections of the cost of biodiesel from vegetable oil and waste grease are, respectively, $0.54 to $0.62/L and $0.34 to $ 0.42/L. With pretax diesel priced at $0.18/L in the USA and $0.20 to 0.24/L in some European countries, biodiesel is thus currently not economically feasible, and more research and technological development will be needed (Bender 1999).

1.3.1 Energy Production and Future Energy Scenarios

The world energy consumption pattern is also increasing, as shown in the Figure 1.2. Energy consumption has been increasing and will triple in a period of 50 years by

Figure 1.2 World energy consumption pattern

2025 as seen from Figure 1.2. The world’s population will increase from 6 billion to 11 billion this century, life expectancy has doubled in the last two centuries, and energy requirements have increased 35 times in the same period. The main drivers of the search for alternative sources of energy are population growth, economics, technology, and agriculture.

The term bio-oil is used mainly to refer to liquid fuels from biorenewable feed­stocks. Biomass is heated in the absence of oxygen, or partially combusted in a lim­ited oxygen supply, to produce an oil-like liquid, a hydrocarbon-rich gas mixture and a carbon-rich solid residue. Pyrolysis dates back to at least ancient Egyptian times, when tar for caulking boats and certain embalming agents was made by pyrolysis. In the 1980s, researchers found that the pyrolysis liquid yield could be increased us­ing fast pyrolysis where a biomass feedstock is heated at a rapid rate and the vapors produced are also condensed rapidly (Mohan et al. 2006).

In wood-derived pyrolysis oil, specific oxygenated compounds are present in rel­atively large amounts. A current comprehensive review focuses on the recent devel­opments in wood/biomass pyrolysis and reports the characteristics of the resulting bio-oils, which are the main products of fast wood pyrolysis (Mohan et al. 2006). Sufficient hydrogen added to the synthesis gas to convert all of the biomass carbon into methanol carbon would more than double the methanol produced from the same biomass base.

The kinematic viscosity of pyrolysis oil varies from as low as 11 cSt to as high as 115mm2/s (measured at 313 K) depending on the nature of the feedstock, the temperature of the pyrolysis process, the thermal degradation degree and catalytic cracking, the water content of the pyrolysis oil, the amount of light ends that have collected, and the pyrolysis process used. Pyrolysis oils have water contents of typ­ically 15 to 30 wt% of the oil mass, which cannot be removed by conventional methods like distillation. Phase separation may partially occur above certain wa­ter content levels. The water content of pyrolysis oils contributes to their low energy density, lowers the flame temperature of the oils, leads to ignition difficulties, and, when preheating the oil, can lead to premature evaporation of the oil and resul­tant injection difficulties. The higher heating value (HHV) of pyrolysis oils is below 26 MJ/kg (compared to 42 to 45 MJ/kg for conventional petroleum fuel oils). In con­trast to petroleum oils, which are nonpolar and in which water is insoluble, biomass oils are highly polar and can readily absorb over 35% water (Demirbas 2007). Ta­ble 3.5 shows the fuel properties of diesel, biodiesel, and biomass pyrolysis oil.

The bio-oil from wood is typically a liquid, almost black through dark red brown. The density of the liquid is about 1,200 kg/m3, which is higher than that of fuel oil

and significantly higher than that of the original biomass. Bio-oils typically have water contents of 14 to 33%wt, which cannot be removed by conventional methods like distillation. Phase separation may occur above certain water content levels. The higher heating value (HHV) is below 27 MJ/kg (compared to 43 to 46 MJ/kg for conventional fuel oils).

The bio-oil formed at 725 K contains high concentrations of compounds such as acetic acid, 1-hydroxy-2-butanone, 1-hydroxy-2-propanone, methanol, 2,6-dimeth — oxyphenol, 4-methyl-2,6-dimetoxyphenol, 2-cyclopenten-1-one, etc. A significant characteristic of bio-oils is the high percentage of alkylated compounds, especially methyl derivatives. As the temperature increases, some of these compounds are transformed via hydrolysis. The formation of unsaturated compounds from biomass materials generally involves a variety of reaction pathways such as dehydration, cyclization, Diels-Alder cycloaddition reactions, and ring rearrangement. For ex­ample, 2,5-hexandione can undergo cyclization under hydrothermal conditions to produce 3-methyl-2-cyclopenten-1-one with very high selectivity of up to 81% (An et al. 1997).

Fossil fuels still represent over 80% of total energy supplies in the world today, but the trend toward new energy sources is clear thanks to recent technological devel­opments.

Oil is the fossil fuel that is most in danger of becoming scarce. The Middle East is the dominant oil province of the world, controlling 63% of the global reserves. Fig­ure 1.3 shows global oil production scenarios based on today’s production. A peak

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Figure 1.3 Global oil pro­duction scenarios based on current production

in global oil production may occur between 2015 and 2030. Countries in the Mid­dle East and the Russian Federation hold 70% of the world’s dwindling reserves of oil and gas. The geographical distribution of energy reserves and resources is important.

The peak of world gas production may not occur until 2025, but two things are certain: we will have even less warning than we had for Peak Oil, and the subsequent decline rates may be shockingly high. The NG model shows a plateau in production between 2025 and 2030. This is followed by a rapid increase in decline to 8% per year by 2050, remaining at a constant 8% per year for the following 50 years. This gives the production

Coal is the ugly stepsister of fossil fuels. Most coal today is used to generate electricity. As economies grow, so does their demand for electricity, and if electricity is used to replace some of the energy lost due to the decline of oil and natural gas, this will put yet more upward pressure on the demand for coal. Just as we saw with oil and gas, coal will exhibit an energy peak and decline. One factor in this is that we have in the past concentrated on finding and using the highest grade of coal, anthracite. Much of what remains consists of lower-grade bituminous and lignite. These grades of coal produce less energy when burned and require the mining of ever more coal to get the same amount of energy. Figure 1.5 shows global coal production, 1965 to 2100 (Kirtay 2009).

Renewable energy is a promising alternative solution because it is clean and en­vironmentally safe. Renewables also produce lower or negligible levels of green­house gases and other pollutants when compared with the fossil energy sources they replace. Table 1.8 shows the global renewable energy scenario by 2040. Approx­imately half of the global energy supply will come from renewables in 2040 ac­cording to the European Renewable Energy Council (EREC 2006). Between 2001

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and 2040 the most significant developments in renewable energy production will be observed in photovoltaics (from 0.2 to 784Mtoe) and wind energy (from 4.7 to 688 Mtoe).

Biomass is the most used renewable energy source now and will be in the fore­seeable future. The potential of sustainable large hydro is quite limited in some regions of the world. The potential for small hydro (<10MW) power is still signif­icant and will become increasingly significant in the future. Wind energy usage has grown by more than 30% annually in recent years, and this trend will likely increase in the future. Photovoltaics has already experienced impressive annual growth rates of more that 30% in recent years, and this trend promises to speed up in the future.

Geothermal and solar thermal sources will play more important roles in the future energy mix.

The use of fossil fuels as the primary energy source has led to a serious en­ergy crisis and environmental pollution on a global scale. In order to mitigate en­vironmental problems, the cost of renewable energy can be made competitive with fossil-fuel or nuclear energy by rapid technological developments in solar and wind energies. In order to mitigate environmental problems, renewable energy especially wind and solar energies at competitive costs resulting from the fast technological de­velopment. The limitations of solar power are site specific, intermittent, and, thus, not reliable for instantaneous supply. Using batteries to store any energy surplus for later consumption can resolve the time mismatch between energy supply and demand. The shortcomings of battery storage are low storage capacity, short equip­ment life, and considerable solid and chemical wastes generated. A system consist­ing of photovoltaic (PV) panels coupled with electrolyzers is a promising design for producing hydrogen (Ni et al. 2006).

A detailed analysis of the technical, economic, and regulatory issues of wind power can be found in the European Wind Energy Association (EWEA) report: “Large scale integration of wind energy in the European power supply: Analysis, issues and recommendations,” published in December 2005. In 2005, worldwide capacity of wind-powered generators was 58,982MW; although it currently pro­duces less than 1% of worldwide electricity use, it accounts for 23% of electricity use in Denmark, 4.3% in Germany, and approx. 8% in Spain. Globally, wind power generation more than quadrupled between 1999 and 2005 according to the EWEA (2005).

Figure 1.6 shows the growth scenarios for global installed wind power (IEA 2004). In 2004, the International Energy Agency (IEA) Reference Scenario pro­jections for wind energy were updated to 66 GW in 2010, 131 GW in 2020, and 170 GW in 2030. The IEA advanced strong growth scenario projected a wind en­ergy market of 82 GW in 2010,165 GW in 2020, and 250 GW in 2030.

Geothermal energy can be utilized in various forms such as electricity generation, direct use, space heating, heat pumps, greenhouse heating, and industrial heating. Electricity generation is improving faster in geothermal-energy-rich countries. As an energy source, geothermal energy has come of age. Utilization has increased rapidly during the last three decades.

Geothermal energy for electricity generation has been produced commercially since 1913, and for four decades on the scale of hundreds of megawatts both for electricity generation and direct use. In Tuscany, Italy, a geothermal plant has been operating since the early 1900s. There are also geothermal power stations in the USA, New Zealand, and Iceland. In Southampton (UK) there is a district heat­ing scheme based on geothermal energy. A hot water is pumped up from about 1,800 m below ground. Use of geothermal energy has increased rapidly during the last three decades. In 2000, geothermal resources were identified in over 80 countries, and there are quantified records of geothermal utilization in 58 countries around the world (Fridleifsson 2001). Electricity is produced with geothermal steam in 21 countries spread over all continents. Low-temperature geothermal energy is

exploited in many countries to generate heat, with an estimated capacity of approx. 10,000 MW thermal.

The world’s total installed geothermal electric capacity was 7,304 MWe in 1996. In much of the world electricity from fossil-fuel-burning electricity plants can be provided at half the cost of new geothermal electricity. A comparison of renew­able energy sources shows the current electrical energy cost to be US$0.02 to $ 0.10/kWh) for geothermal and hydro, US$ 0.05 to $ 0.13/kWh for wind, US$ 0.05 to $0.15/kWh for biomass, US$0.25 to $ 1.25/kWh for solar PV, and US$0.12 to $ 0.18/kWh for solar thermal electricity (Demirbas 2006).

Solar energy is defined as the radiant energy transmitted by the Sun and inter­cepted by the Earth. It is transmitted through space to Earth by electromagnetic radiation with wavelengths ranging between 0.20 and 15 pm. The availability of solar flux for terrestrial applications varies with season, time of day, location, and collecting surface orientation. In this chapter we shall treat these matters analytically (Kutz 2007).

One of the most abundant energy sources on the surface of the Earth is sunlight. Today, solar energy has a tiny contribution in the world total primary energy supply of less than 1%. PV systems, other than solar home heating systems, are used for communication, water pumping for drinking and irrigation, and electricity genera­tion. The total installed capacity of such systems is estimated at about 1,000 kW. A solar home heating system is a solar PV system with a maximum capacity of
40 W. These systems are installed and managed by a household or a small commu­nity.

Like wind power markets, PV markets have seen rapid growth and costs have fallen dramatically. The total installed capacity of such systems is estimated at about 1,000 kW. PV installed capacities are growing at a rate of 30% a year. Solar PV sys­tems hold great promise. One of the most significant developments in renewable energy production is observed in PVs. According to the European Wind Energy As­sociation, PV will eventually be the largest renewable electricity source with a pro­duction of 25.1% of global power generation in 2040 (EWEA 2005).

A solar thermal electricity power system is a device that uses solar radiation for the generation of electricity through solar thermal conversion. Figure 1.7 shows the plot for electricity costs from solar thermal power plants. Solar thermal electricity may be defined as the result of a process by which directly collected solar energy is converted into electricity through the use of some sort of heat-to-electricity conver­sion device. The last three decades have witnessed a trend in solar thermal electricity generation of increasing the concentration of sunlight. There are three main systems of solar thermal electricity: solar towers, dishes, and parabolic troughs. Solar ther­mal power stations based on parabolic and heliostat trough concentrating collectors may soon become a competitive option on the world’s electricity market. Table 1.9 shows the economics and emissions of conventional technologies compared with solar power generation.

PV systems convert sunlight directly into electricity. They work any time the sun is shining, but more electricity is produced when the sunlight is more intense and

strikes the PV modules directly. The basic building block of PV technology is the solar “cell.” Multiple PV cells are connected to form a PV “module,” and the small­est PV component is sold commercially. Modules range in power output from about 10 W to 300 W. A PV system connected to the utility grid has the following compo­nents: (1) one or more PV modules connected to an inverter, (2) the inverter, which converts the system’s direct-current (DC) electricity to alternating current (AC) and (3) batteries (optional) to provide energy storage or backup power in case of a power interruption or outage on the grid. Figure 1.8 shows a field of solar panels.

Figure 1.8 Solar panel field

Small, single-PV-panel systems with built-in inverters that produce about 75 W of electricity may cost around $900 installed, or $ 12 per watt. A 2-kW system that meets nearly all the needs of a very energy-efficient home could cost $ 16,000 to $ 20,000 installed, or $ 8 to $ 10 per watt. At the high end, a 5-kW system that completely meets the energy needs of many conventional homes can cost $ 30,000 to $40,000 installed, or $ 6 to $ 8 per watt. Figure 1.9 shows the schematic of a fuel cell.

Figure 1.10 shows the configuration of PV system with AC appliances (e. g., household lighting, heating, refrigeration, television, or video).

The term biofuel refers to liquid or gaseous fuels for the transport sector that are predominantly produced from biomass. Biofuels are mainly bioethanol, bio­methanol, biodiesel, biohydrogen, and biogas. There are several reasons for biofu­els to be considered as relevant technologies by both developing and industrialized countries. They include energy security reasons, environmental concerns, foreign exchange savings, and socioeconomic issues related to the rural sector.

Biofuels are important because they replace petroleum fuels. Biofuels are gen­erally considered as addressing many of today’s energy-related concerns, including sustainability, reduction of greenhouse gas emissions, regional development, social structure and agriculture, and security of supply (Reijnders 2006).

Biomass provides a number of local environmental gains. Energy forestry crops have a much greater diversity of wildlife and flora than the alternative land use, which is arable or pasture land. In industrialized countries, the main biomass pro­
cesses utilized in the future will be expected to be direct combustion of residues and wastes for electricity generation, bioethanol and biodiesel as liquid fuels, and combined heat and power production from energy crops. The future of biomass electricity generation lies in biomass integrated gasiflcation/gas turbine technology, which offers high energy-conversion efficiencies. Biomass will compete favorably with fossil mass for niches in the chemical feedstock industry. Biomass is a renew­able, flexible, and adaptable resource. Crops can be grown to satisfy changing end use needs.

In the future, biomass will have the potential to provide a cost-effective and sus­tainable supply of energy, while at the same time aiding countries in meeting their greenhouse-gas-reduction targets. By the year 2050, it is estimated that 90% of the world’s population will live in developing countries.

According to the IEA, scenarios developed for the USA and the EU indicate that near-term targets of up to 6% displacement of petroleum fuels with biofuels appear feasible using conventional biofuels, given available cropland. A 5% displacement of gasoline in the EU requires about 5% of available cropland to produce ethanol, while in the USA 8% is required. A 5% displacement of diesel requires 13% of US cropland, 15% in the EU (IEA 2006).

The recent commitment by the US government to increase bioenergy threefold in 10 years has added impetus to the search for viable biofuels. The advantages of biofuels are that they (a) are easily available from common biomass sources, (b) indicate a carbon dioxide cycle in combustion, (c) have a very environmentally friendly potential, (d) benefit the environment, economy, and consumers, and (e) are biodegradable and contribute to sustainability (IEA 2004).

Dwindling fossil fuel sources and the increasing dependency of the USA on im­ported crude oil have led to a major interest in expanding the use of bioenergy. In addition to increased interest by the US government, the EU has also adopted a pro­posal for a directive on the promotion of the use of biofuels with measures ensuring that biofuels account for at least 2% of the market for gasoline and diesel sold as transport fuel by the end of 2005, increasing in stages to a minimum of 5.75% by the end of 2010 (Puppan 2002). Bioethanol is a fuel derived from renewable sources of feedstock, typically from plants such as wheat, sugar beet, corn, straw, and wood. Bioethanol is a petrol additive/substitute. Biodiesel is superior to diesel fuel in terms of sulfur content, flash point, aromatic content, and biodegradability (Hansen et al. 2005).

If biodiesel is used for engine fuel, this would in turn benefit the environment and local populations. The benefits of biofuels over traditional fuels include greater energy security, reduced environmental impact, foreign exchange savings, and so­cioeconomic issues related to the rural sector.

Figure 1.11 shows the rate of consumption of alternative fuels compared to to­tal automotive fuel consumption worldwide as a futuristic view (Demirbas 2006). Hydrogen is currently more expensive than conventional energy sources. There are different technologies presently being applied to produce hydrogen economically from biomass. Biohydrogen technology will play a major role in the future because it will allow for the use of renewable sources of energy (Nath and Das 2003).

Figure 1.11 Rate of con­sumption of alternative fuels compared to total automotive fuel consumption worldwide

Biofuels include bioethanol, biobutanol, biodiesel, vegetable oils, biomethanol, pyrolysis oils, biogas, and biohydrogen. There are two global biomass-based liquid transportation fuels that might replace gasoline and diesel fuel. These are bioethanol and biodiesel. World production of biofuel was about 68 billion L in 2007 (59 bil­lion L bioethanol and 9 million L biodiesel). The primary feedstocks of bioethanol are sugar cane and corn.

Bioethanol is a gasoline additive/substitute. Bioethanol is by far the most widely used biofuel for transportation worldwide. Global bioethanol production more than doubled between 2000 and 2005. About 60% of global bioethanol production comes from sugar cane and 40% from other crops. Biodiesel refers to a diesel-equivalent mono-alkyl-ester-based oxygenated fuel. Biodiesel production using inedible veg­etable oil, waste oil, and grease has become more attractive recently. The economic performance of a biodiesel plant can be determined once certain factors are iden — tifled, such as plant capacity, process technology, raw material cost, and chemical costs. Even with today’s high oil prices, biofuels cost more than conventional fuels. The central policy of biofuels grows out of concerns related to job creation, greater efflciency in the general business environment, and protection of the environment.

The biggest difference between biofuels and petroleum feedstocks is oxygen content. Biofuels have oxygen levels from 10 to 45%, while petroleum has essen­tially none, making the chemical properties of biofuels very different from those of petroleum. All have very low sulfur levels and many have low nitrogen levels. Bio­fuels are nonpolluting, locally available, accessible, sustainable, and reliable fuels obtained from renewable sources.

Sustainable biofuel production mainly depends on the productivity and the plant­ing options. A sustainable use of biomass for bioenergy production is expected to reduce environmental contamination. Achieving a solution to environmental prob­lems requires long-term policies for sustainable development. In this view, renew­able energy sources appear to be one of the most efflcient and effective solutions. Sustainability of renewable energy systems must support both human and ecosys­
tem health over the long term; goals on tolerable emissions should look well into the future. The sustainability of biofuels for energy use requires a high efficiency recyc­ling of energy and low emissions of carbon compounds, NOx, persistent organics and acidifying compounds, and heavy metals due to biomass combustion. Electric­ity generation from biofuels holds great promise in the near future. Electricity costs are in the 6 to 8 c/kWh range.

Liquid biofuels for transportation have recently attracted consierable attention in various countries because of their renewability, sustainability, biodegradability, and common availability, as well as for their potential role in regional development, creation of rural manufacturing jobs, and reduction of greenhouse gas emissions. Table 1.10 shows the availability of modern transportation fuels. The advantage of biofuels in this regard is that they are derived from natural products. Policy drivers for renewable liquid biofuels have attracted particularly high levels of assistance in some countries given their promise of benefits in several areas of interest to govern­ments, including agricultural production, greenhouse gas emissions, energy secu­rity, trade balances, rural development, and economic opportunities for developing countries. The EU ranks third in biofuel production worldwide, behind Brazil and the USA. In Europe, Germany is the largest produce of biofuels, while France is the second largest. Most biofuels in commercial production in Europe today are based on sugar beet, wheat, and rapeseed, which are converted into bioethanol/ETBE and biodiesel.

Ethanol has attracted considerable interest in both industry and research as a plausible renewable energy source in the future. Bioethanol is a gasoline ad — ditive/substitute. Biomass wastes that with a high hydrocarbon content, such as sugar cane, sugar beets, corn, and molasses, can be good sources of bioethanol. Bioethanol is an alternative fuel that is produced almost entirely from food crops. Bioethanol represents an important, renewable liquid fuel for motor vehicles. It is derived from alcoholic fermentation of sucrose or simple sugars, which are pro­duced from biomass by hydrolysis. In order to produce bioethanol from cellulosic biomass, a pretreatment process is used to reduce the sample size, break down the hemicelluloses into sugars, and open up the structure of the cellulose component. The cellulose portion is hydrolyzed by acids or enzymes into glucose sugar that is fermented into bioethanol.

The sugars from hemicelluloses are also fermented bioethanol. Producing and using bioethanol as a transportation fuel can help reduce carbon dioxide buildup in two important ways: by displacing the use of fossil fuels and by recycling the carbon dioxide that is released when combusted as fuel. The use of ethanol-blended fuel for automobiles can significantly reduce petroleum use and greenhouse gas exhaust emissions. An important advantage of crop-based ethanol is its greenhouse benefits. Corn stover consists of the stalks, leaves, cobs, and husk. It is possible to convert corn stover economically into bioethanol.

Ethanol can be produced in a culture medium. For this purpose, an alginate-loofa matrix was developed as a cell carrier for ethanol fermentation owing to its porous structure and strong fibrous nature. The matrix was effective for cell immobilization and had good mechanical strength and stability for long-term use (Phisalaphong etal. 2007).

Partly due to the oil crises, biomass-derived syngas (biosyngas) has become an important part of alternative energy since the 1980s. Once clean biosyngas is avail­able, the known process technology can be used to produce biomethanol, Fischer- Tropsch diesel oil, and hydrogen. Methanol can be produced from hydrogen-carbon oxide mixtures by means of the catalytic reaction of carbon monoxide and some carbon dioxide with hydrogen. Biosynthesis gas (biosyngas) is a gas rich in CO and H2 obtained by gasification of biomass. The mixture of gases from organic waste materials is converted into methanol in a conventional steam-reforming/water-gas shift reaction followed by high-pressure catalytic methanol synthesis.

Biodiesel is known as a monoalkyl; examples include methyl and ethyl, which are esters of fatty acids. Biodiesel is produced from triglycerides by transesterification (Demirbas 2003). Environmental and political concerns are generating a growing interest in alternative engine fuels such as biodiesel. Biodiesel is the best candidate for diesel fuels in diesel engines. Biodiesel refers to a diesel-equivalent processed fuel derived from biological sources. Biodiesel is the name given to a variety of ester-based oxygenated fuel from renewable biological sources. It can be made from processed organic oils and fats. Biodiesel production using inedible vegetable oils, waste oil, and grease has also become more attractive recently. Biodiesels will play an important role in meeting future fuel requirements in view of their lower toxicity and have an edge over conventional diesel as they are obtained from renewable sources (Sastry et al. 2006).

In one study, cottonseed methyl ester was used in a four-stroke, single-cylinder, air-cooled diesel engine as an alternative fuel. Engine tests were carried out at full load and at different speeds. The engine torque and power of cottonseed oil methyl ester were found to be lower than that of diesel fuel in the range of 3 to 9% and specific fuel consumption was higher than that of diesel fuel by approx. 8 to 10%. CO2, CO, and NOx emissions of cottonseed methyl ester were lower than that of diesel fuel (Yucesu and Ilkilic 2006).

In general, the physical and chemical properties and the performance of the cot­tonseed oil methyl ester were comparable to those of diesel fuel (Ilkilic and Yucesu 2008). The effects of cottonseed oil methyl ester and diesel fuel on a direct-injected, four-stroke, single-cylinder, air-cooled diesel engine performance and exhaust emis­

sions were investigated. Test quantities of cottonseed oil methyl ester of renewable fuels were processed and characterized, and performance and exhaust gas emis­sions were tested in various injection pressures. In order to determine emission and performance characteristics, the engine was tested with a full load and at various injection pressures and constant speed. The results showed that engine performance using cottonseed oil methyl ester fuel differed little from engine performance and torque with diesel fuel. As for the emissions, there was an approx. 30% reduction in CO and approx. 25% reduction in NOx (Yucesu and Ilkilic 2006).

An engine performance test using sunflower methyl esters exhibited characteris­tics very similar to regular diesel. The test values obtained from a 2.5-L, 4-cylinder Peugeot XD3p157 engine showed that torque values obtained by the two types of fuels are 5 to 10% in favor of regular diesel. Specific fuel consumption, however, is better with biodiesel. This means that a better combustion characteristic is achieved with biodiesel, which compensates for its lower calorific value. Soot emissions are slightly less with biodiesel, as expected, due to the improvement in specific fuel con­sumption (Kaplan et al. 2006). The physical and chemical properties of methyl ester of waste cooking oil were determined in the laboratory. The methyl ester was tested in a diesel engine with turbocharged, four cylinders, and direct injection. Obtained results were compared with No. 2 diesel fuel (Utlu 2007).

A new lipase immobilization method, textile cloth immobilization, was devel­oped for the conversion of soybean oil into biodiesel. Immobilized Candida lipase sp. 99-125 was applied as the enzyme catalyst. The effect of flow rate of the re­action liquid, solvents, reaction time, and water content on the biodiesel yield was investigated. The test results indicated that the maximum yield of biodiesel of 92% was obtained with hexane as the solvent, water content of 20 wt%, and reaction time of 24 h (Lv et al. 2008).

The dynamic transesterification reaction of peanut oil in supercritical methanol medium was investigated. The reaction temperature and pressure were in the range of 523 to 583 K and 10.0 to 16.0 MPa, respectively. The molar ratio of peanut oil to methanol was 1:30. It was found that the yield of methyl esters was higher than 90% in the supercritical methanol. The apparent reaction order and activation energy of transesterification was 1.5 and 7.472 kJ/mol, respectively. In this method, the reaction time was shorter and the processing was simpler than that of the common acid catalysis transesterification (Cheng et al. 2008).

The existing biodiesel production process is neither completely “green” nor re­newable because it utilizes fossil fuels, mainly natural gas as an input for methanol production. Also the catalysts currently in use are highly caustic and toxic. To over­come the limitation of the existing process, a new method was proposed that used waste vegetable oil and nonedible plant oils as biodiesel feedstock and nontoxic, in­expensive, and natural catalysts. The economic benefit of the proposed method was also discussed. The new method will render the biodiesel production process truly green (Chhetri and Islam 2008).

A four-stroke, three-cylinder, 30-kW TUMOSAN (Turkish Motor Industry and Trade) diesel engine was used for experimentation with biodiesel. The kinematic viscosity, density, flash point, cloud point, pour point, freezing point, and copper strip corrosion values of all biodiesel fuels stayed within the limit values described by DIN-TSE EN 14214. They can readily be used without any need for modification to the engine. Even though specific fuel consumption for biodiesel fuels tended to be higher than that for normal diesel fuel, the exhaust smokiness values of biodiesel fuels were considerably lower than that for petroleum diesel fuel. On the other hand, there were no significant differences observed for torque, power, and exhaust smoki­ness (Oguz et al. 2007).

Problems to be studied include fuel storage stability, fuel solubility, and oxidative stability of recycled soybean-derived biodiesel. Unlike newly manufactured soy oils, it was found that this recycled soy oil was not stable in fuels. The question was what in the recycled oil led to the observed fuel degradation (Mushrush et al. 2007).

Oxidative and thermal degradation occurs on the double bonds of unsaturated aliphatic carbon chains in biolipids. Oxidation of biodiesel results in the formation of hydroperoxides. Oxidative and thermal instability is determined by the amount and configuration of the olefinic unsaturation on the fatty acid chains. The viscos­ity of biodiesel increases with an increase in the thermal degradation degree due to transisomer formation on double bonds. The decomposition of biodiesel and its cor­responding fatty acids linearly increases from 293 to 625 K. The density of biodiesel fuels decreases linearly with temperature from 293 to 575 K. The combustion heat of biodiesel partially decreases with an increase in thermal degradation degree (Arisoy 2008).

The emission-forming gases, such as carbon dioxide and carbon monoxide from the combustion of biodiesel, generally are less than those of diesel fuel. Sulfur emis­sions are essentially eliminated with pure biodiesel. The exhaust emissions of sulfur oxides and sulfates from biodiesel are essentially eliminated compared to diesel. The smog-forming potential of biodiesel hydrocarbons is less than that of diesel fuel. The ozone-forming potential of speciated hydrocarbon emissions is 50% less than that measured for diesel fuel (Dincer 2008).

Biogas can be obtained from several sources. There are a number of processes for converting biomass into gaseous fuels such as methane or hydrogen. One uses plant and animal wastes in a fermentation process leading to biogas from which the de­sired fuels can be isolated. This technology is established and in widespread use for waste treatment. Anaerobic digestion of biowastes occurs in the absence of air, the resulting gas, called biogas, is a mixture consisting mainly of methane and carbon dioxide. Biogas is a valuable fuel that is produced in digesters filled with feedstock like dung or sewage. The digestion is allowed to continue for a period of 10 d to a few weeks. A second process uses algae and bacteria that have been genetically modified to produce hydrogen directly instead of the conventional biological energy carriers. Finally, high-temperature gasification supplies a crude gas, which may be transformed into hydrogen by a second reaction step. This process may offer the highest overall efficiency.

Anaerobic digestion (AD) is a bacterial fermentation process that is sometimes employed in wastewater treatment for sludge degradation and stabilization. This is also the principal process occurring in the decomposition of food wastes and other biomass in landfills. The AD operates without free oxygen and results in biogas containing mostly CH4 and CO2 but frequently carrying other substances such as moisture, hydrogen sulfide (H2S), and particulate matter that are generally removed prior to use of the biogas. The AD is a biochemical process for converting biogenic solid waste into a stable, humuslike product. Aerobic conversion uses air or oxygen to support the metabolism of the aerobic microorganisms degrading the substrate. Aerobic conversion includes composting and activated sludge wastewater treatment processes. Composting produces useful materials, such as mulch, soil additives and amendments, and fertilizers.

AD is known to occur over a wide temperature range from 283 to 344 K. It re­quires attention to the nutritional needs of the facultative and methanogenic bacteria degrading the waste substrates as well as maintenance of reasonable temperatures for those bacteria. The carbon/nitrogen (C/N) ratio of the feedstock is especially important. Biogas can be used after appropriate gas cleanup as a fuel for engines, gas turbines, fuel cells, boilers, industrial heaters, other processes, and the manu­facture of chemicals. AD is also being explored as a route for direct conversion into hydrogen.

Cellulose and hemicelluloses can be hydrolyzed into simple sugars and amino acids that are consumed and transformed by fermentive bacteria. Lignin is refrac­tory to hydrolysis and generally exits the process undigested. In fact, lignin may be the most recalcitrant naturally produced organic chemical. Lignin polymers are cross-linked carbohydrate structures with molecular weights on the order of 10,000 atomic mass units. As such, lignin can bind with or encapsulate cellulose, mak­ing that cellulose unavailable to hydrolysis and digestion. Lignin degradation (or deligniflcation of lignocellulosics) in nature is due principally to aerobic fllamen — tous fungi that decompose the lignin in order to gain access to the cellulose and hemicelluloses.

For anaerobic systems, methane gas is an important product. Depending on the type and nature of the biological components, different yields can be obtained for different biodegradable wastes. For pure cellulose, for example, the biogas product is 50% methane and 50% carbon dioxide. Mixed waste feedstocks yield biogas with methane concentrations of 40 to 60% (by volume). Fats and oils can yield biogas with 70% methane content.

Anaerobic digestion functions over a wide temperature range from the so-called psychrophilic temperature near 283 K to extreme thermophilic temperatures above 344 K. The temperature of the reaction has a very strong influence on the anaero­bic activity, but there are two optimal temperature ranges in which microbial ac­tivity and biogas production rate are highest, the so-called mesophilic and ther­mophilic ranges. The mesophilic regime is associated with temperatures of about 308 K, a thermophilic regime of about 328 K. Operation at thermophilic tempera­ture allows for shorter retention time and a higher biogas production rate; however, maintaining the high temperature generally requires an outside heat source because anaerobic bacteria do not generate sufficient heat. Aerobic composting can achieve relatively high temperatures (up to 344 K) without heat addition because reaction rates for aerobic systems are much higher than those for anaerobic systems. If heat is not conducted away from the hot center of a compost pile, then this could cause thermochemical reactions that might lead to spontaneous combustion if sufficient oxygen reaches the hot areas. Managed compost operations use aeration to pro­vide oxygen to the bacteria but also to transport heat out of the pile. The molec­ular structure of the biodegradable portion of the waste that contains proteins and carbohydrates is first broken down through hydrolysis. The lipids are converted to volatile fatty acids and amino acids. Carbohydrates and proteins are hydrolyzed to sugars and amino acids. In acetogenesis, acid forming bacteria use these byproducts to generate intermediary products such as propionate and butyrate. Further micro­

bial action results in the degradation of these intermediary products into hydrogen and acetate. Methanogenic bacteria consume the hydrogen and acetate to produce methane and carbon dioxide.

After the first 6 d of digestion, methane production from manure increases expo­nentially, after 16 d it reaches a plateau value, and at the end of day 20, the digestion reaches the stationary phase. For wheat straw and mixtures of manure and straw the rates of digestion are lower than that of manure.

The maximum daily biogas productions are between 4 and 6 d. During a 30-d digestion period, approx. 80 to 85% of the biogas is produced in the first 15 to 18 d. This implies that the digester retention time can be designed to 15 to 18 d instead of 30 d. For the first 3 d, methane yield is almost 0% and carbon dioxide generation is almost 100%. In this period, digestion occurs as fermentation to carbon dioxide. The yields of methane and carbon dioxide gases are 50/50 at day 11. At the end of day 20, digestion reaches the stationary phase. The methane content of the biogas is in the range of 73 to 79% for the runs, the remainder being principally carbon dioxide. During digestion, the volatile fatty acid concentration is lower and the pH higher. The pH of the slurry with manure increases from 6.4 initially to 6.9 to 7.0 at the maximum methane production rate. The pH of the slurry with wheat straw is around 7.0 to 7.1 at the maximum methane production rate.

The first methane digester plant was built at a leper colony in Bombay, India, in 1859 (Meynell 1976). Most of the biogas plants utilize animal dung or sewage. A schematic of biogas plant utilizing cow dung is illustrated in Figure 3.5 (Balat 2008). AD is a commercially proven technology and is widely used for treating high-moisture-content organic wastes including +80 to 90% moisture. Biogas can be used directly in spark-ignition gas engines (SIGEs) and gas turbines. Used as a fuel in SIGEs to produce electricity only, the overall conversion efficiency from biomass to electricity is about 10 to 16% (Demirbas 2006).

2.1 Introduction

Modern bioenergy involves commercial energy production from biomass for indus­try, power generation, or transport fuels. Bioenergy is an all-inclusive term for all forms of biomass and biofuels. Green energy is an alternate term for renewable energy used to indicate that the energy is generated from sources considered envi­ronmentally friendly. Various biomasses such as wood, straw, and even household wastes may be economically converted into bioethanol. Bioethanol is derived from the alcoholic fermentation of sucrose or simple sugars, which are produced from biomass by a hydrolysis process. Biodiesel is an environmentally friendly alterna­tive liquid fuel that can be used in any diesel engine without modification.

The importance of biomass in different world regions is given in Table 2.1. For large portions of the rural populations of developing countries, and for the poorest sections of urban populations, biomass is often the only available and affordable

source of energy for basic needs such as cooking and heating. As shown in Ta­ble 2.1, the importance of biomass varies significantly across regions. In Europe, North America, and the Middle East, the share of biomass averages 2 to 3% of total final energy consumption, whereas in Africa, Asia, and Latin America, which to­gether account for three-quarters of the world’s population, biomass provides a sub­stantial share of the energy needs: a third on average, but as much as 80 to 90% in some of the poorest countries of Africa and Asia (e. g., Angola, Ethiopia, Mozam­bique, Tanzania, Democratic Republic of Congo, Nepal, and Myanmar).

Traditional biomass markets have been inefficient, but technological develop­ments have reduced energy, emissions, and material flows through the system thus improving the efficiency of biomass energy systems. The energy market demands cost effectiveness, high efficiency, and reduced risk to future emission limits. Mod­ern biomass conversion technologies offer (a) the potential for high yields, (b) eco­nomic fuel availability, (c) low adverse environmental impacts, and (d) suitability to modern energy systems. A number of systems that meet the aforementioned criteria for modernized biomass conversion can be identified (Larson 1993).

The term biomass (Greek bio, life + maza or mass) refers to nonfossilized and biodegradable organic material originating from plants, animals, and microorgan­isms derived from biological sources. Biomass includes products, byproducts, residues and waste from agriculture, forestry, and related industries as well as the nonfossilized and biodegradable organic fractions of industrial and municipal solid wastes. The term biomass refers to wood, short-rotation woody crops, agricultural wastes, short-rotation herbaceous species, wood wastes, bagasse, industrial residues, waste paper, municipal solid waste, sawdust, biosolids, grass, waste from food pro­cessing, aquatic plants and algae animal wastes, and a host of other materials.

Biomass is organic material that has stored sunlight in the form of chemical energy. It is commonly recognized as an important renewable energy; during the growth of plants and trees, solar energy is stored as chemical energy via photosyn­thesis, which can be released via direct or indirect combustion.

Biomass is very important for implementing the Kyoto agreement to reduce car­bon dioxide emissions by replacing fossil fuels. Surging energy requirements in parallel with technological developments have forced research and development ac­tivities to focus on new and biorenewable energy.

There are three ways to use biomass. It can be burned to produce heat and elec­tricity, changed to gaslike fuels such as methane, hydrogen, and carbon monoxide, or changed to a liquid fuel. Liquid fuels, also called biofuels, include mainly two forms of alcohol: ethanol and methanol. Because biomass can be converted directly into a liquid fuel, it could some day supply much of our transportation fuel needs for cars, trucks, buses, airplanes, and trains. This is very important because nearly one-third of our nation’s energy is now used for transportation.

Biomass feedstocks are marked by their tremendous diversity, which makes them rather difficult to characterize as a whole. Feedstocks that can be utilized with con­version processes are primarily the organic materials now being landfilled. These include forest product wastes, agricultural residues, organic fractions of municipal solid wastes, paper, cardboard, plastic, food waste, green waste, and other waste. Nonbiodegradable organic feedstocks, such as most plastics, are not convertible by biochemical processes. Biobased materials require pretreatment by chemical, phys­ical, or biological means to open up the structure of the biomass. The general cate­gories of biomass feedstock are shown in Table 2.2.

Table 2.2 Major categories of biomass feedstocks

Wood; logging residues; trees, shrubs, and wood residues; sawdust, bark, etc. Agricultural wastes, crop residues, mill wood wastes, urban wood wastes, urban organic wastes

Short-rotation woody crops, herbaceous woody crops, grasses, starch crops, sugar crops, forage crops, oilseed crops, switchgrass, miscanthus Algae, Water weed, water hyacinth, reed and rushes Grains, oil crops

Sugar cane, sugar beets, molasses, sorghum

Hazardous waste, nonhazardous waste, inert waste, liquid waste

Manucipal solid waste, industrial organic wastes, municipal sewage and

sludges

Prokaryotic algae, eukaryotic algae, kelps Bryophyta, polytrichales

Crustose lichens, foliose lichens, fruticose lichen

Green energy is an alternate term for renewable energy used to indicate that the energy is generated from sources considered environmentally friendly (e. g., hydro, solar, biomass, or wind). Green power is sometimes used in reference to electricity generated from “green” sources. Green energy production is the principal contribu­tor to the economic development of developing countries, whose economic develop­ment is based on agricultural production and where most people live in rural areas. Implementation of integrated community development programs is therefore very necessary.

Green power refers to electricity supplied from energy sources that are more readily renewable than traditional electrical power sources. Green power products, which can be derived from renewable energy sources, have become widespread in many electricity markets worldwide. The environmental advantages of green elec­tricity seem clear. Market research indicates that there is a large potential market for green energy in Europe generally. Green power marketing has emerged in more than a dozen countries around the world.

Many green electricity products are based on renewable energy sources like wind, biomass, hydro, biogas, solar, and geothermal (Murphya and Niitsuma 1999). There has been interest in electricity from renewable sources known as green electricity or green pools as a special market (Elliott 1999). The term green energy is also used to describe green energy produced from cogeneration, energy from municipal waste, natural gas, and even conventional energy sources. The use of green energy sources like hydro, biomass, geothermal, and wind energy in electricity production reduces CO2 emissions (Fridleifsson 2003). Emissions such as SO2, CO2, and NOx are reduced considerably and the production and use of green electricity contributes to diminishing the greenhouse effect (Arkesteijn and Oerlemans 2005).

In general, a sustainable energy system includes energy efficiency, energy reli­ability, energy flexibility, energy development and continuity, combined heat and power (CHP) or cogeneration, fuel poverty, and environmental impacts. The en­vironmental impacts of energy use are not new. For centuries, wood burning has contributed to the deforestation of many areas. On the other hand, the typical char­acteristics of a sustainable energy system can be derived from political definitions. A sustainable energy system can be defined also by comparing the performance of different energy systems in terms of sustainability indicators (Alanne and Sari 2006). Because, by definition, sustainable energy systems must support both human and ecosystem health over the long term, goals on tolerable emissions should look well into the future. They should also take into account the public’s tendency to demand more (UNDP 2000).