Energy

Energy is defined as the ability to do work and provide heat. There are different ways in which the abundance of energy around us can be stored, converted, and amplified for our use. Energy sources can be classified into three groups: fossil, renewable, and nuclear (fissile). Fossil fuels were formed in an earlier geological period and are not renewable. The fossil energy sources include petroleum, coal, bitumen, natural gas, oil shale, and tar sands. The renewable energy sources include biomass, hydro, wind, solar (both thermal and photovoltaic), geothermal, and marine. The main fissile energy sources are uranium and thorium. Despite adequate reserves, some classifications include fissile materials along with the nonrenewable sources.

For over ten thousand years, humans have used biomass for their energy needs. Wood was used for cooking, water, and space heating. The first renewable energy technologies were primarily simple mechanical applications and did not reach high energetic efficiencies. Renewable energies have been the primary energy source in the history of the human race. But in the last two hundred years, we have shifted our energy consumption toward fossil fuels. Industrialization changed the primary energy use from renewable resources to sources with a much higher energy density, such as coal or petroleum. During the last century, the promise of unlimited fossil fuels was much more attractive, and rapid technical progress made the industrial use of petroleum and coal economical.

The world is currently faced with two significant problems: fossil fuel depletion and environmental degradation. The problems are continuously being exacerbated due to increasing global population and per capita energy consumption. To overcome the problems, renewable energy has been receiving increasing attention due to a variety of environmental, economic, and societal benefits. First-generation biofuels (ethanol from sugar or corn, and biodiesel from vegetable oils) are already in the market, and second-generation biofuels from nonfood biomass are under development. The goal of this book is to introduce readers to the biofuels obtained from nonfood biomass, and for reference to provide the technologies involved in first-generation biofuels derived from food sources.

Chapter 1 discusses various nonrenewable (petroleum, natural gas, coal) and renewable forms of energy, and describes air pollution and greenhouse gas emission caused by the use of fossil fuels. Recent concern about carbon dioxide emissions, carbon sequestration, and carbon credits are discussed in Chapter 2. Chapter 3 provides an in-depth description of various renewable energy sources, including biomass; hydropower; geothermal, wind, solar, and ocean energy; and biogas. For the production of biofuels, the global availability of biomass is discussed in Chapter 4 along with the characterization and variations of biomass.

Conventional ethanol production from corn or sugarcane by fermentation technology is discussed in Chapter 5. Current techniques and various unit operations involved are presented, including saccharification, fermentation, distillation, and dehydration. The second-generation ethanol from cellulose is described in Chapter 6.

What Is Bio-Oil?

Biomass, when subjected to high temperature in the absence of oxygen (i.e., pyrolysis), converts into gas, solid char, and liquid products. The liquid product, called bio-oil or pyrolysis oil, is typically brown, dark red, or black in color with a density of about 1.2 kg/liter. Bio-oil has a water content of typically 14–33 wt%, which cannot be easily removed by conventional methods (e.g., distillation); in fact, bio-oil may phase separate above certain water content. The higher heating value of bio-oil is typically 15–22 MJ/kg, which is lower than that for conventional fuel oil (43–46 MJ/kg), mainly due to the presence of oxygenated compounds in bio-oil (Mohan, Pittman, and Steele, 2006).

Pyrolysis

Pyrolysis is the thermal decomposition of biomass, which occurs in the absence of oxygen or when significantly less oxygen is supplied than needed for complete combustion. Pyrolysis can convert biomass into more useful fuels: a hydrocarbon-rich gas mixture, an oil-like liquid, and a carbon-rich solid residue.

Pyrolysis, in the form of wood distillation, has been used since historical times. For example, ancient Egyptians practiced wood distillation by collecting tars and pyroligneous acid for use in their embalming industry and for caulking boats. In the 1800s, wood pyrolysis to produce charcoal was a major industry for supplying fuel for the industrial revolution, until it was replaced by coal.

Introduction

Ethanol

Ethanol – also known as ethyl alcohol, pure alcohol, grain alcohol, alcohol, spirit, and hydroxyethane – is a flammable and colorless liquid with a boiling point of 78.4°C, melting point of −114.3°C, and density of 0.79 g/cm3. Ethanol is used in alcoholic beverages, solvents, scents, flavorings, coloring, medicines, chemical synthesis, and thermometers. With its molecular formula of C2H5OH, ethanol contains 52 wt% carbon, 13 wt% hydrogen, and 35 wt% oxygen. Due to its heating value, ethanol has a long history of use as a fuel for heating and lighting; recently, it has been used as a fuel for internal combustion engines. The fermentation of sugar into ethanol is one of the earliest organic reactions employed by humanity. In modern times, ethanol intended for industrial use is also produced by hydration of ethylene byproduct in the petroleum industry.

Ethanol Fuel

When compared with gasoline, ethanol has a higher octane number, broader flammability limits, higher flame speeds, and higher heats of vaporization. These properties allow for a higher compression ratio, shorter burn time, and leaner burn engine, resulting in a higher efficiency. Ethanol is an oxygenated fuel that contains 35% oxygen, which reduces particulate and nitrogen oxides emissions from combustion. Disadvantages of ethanol include a lower energy density than gasoline, corrosiveness, difficult cold start due to low vapor pressure, low flame luminosity, miscibility with water, and some toxicity to the ecosystems.

Process Energy Needs for Biofuel Production

Biofuel production has a variety of process heating needs depending on the conversion route adopted (Figure 11.1). In overall, the biomass thermochemical conversion processes are endothermic, and the heat required can be supplied by concentrated solar energy in such a way that the energy evolved from the fuel produced ideally represents the sum of energy stored during the photosynthesis and the direct thermal collection (Lede, 1998). Some of the reaction steps are exothermic in nature, which can provide part of the energy needed for the other steps in the plant. Nonetheless, if extra energy is supplied from solar and wind resources, then more of the biomass carbon can be converted into the liquid fuels.

Drying of biomass can put a heavy heat load on the process. For example, the external heating needs are about 3000–4000 kJ/kg of water removed (Lede, 1998). Hence, for a 1-kg water + 1-kg dry biomass feedstock, it will cost about 3000–4000 kJ in drying to get dry biomass with a heating value of 15,000 kJ; therefore, the drying needs are about 20–27% of the energy content of biomass.

The electrical (or mechanical) energy needs of the process are for conveying, grinding, and pumping. Energy needed for biomass grinding depends on the initial biomass size, final particle size, moisture content, material properties, scale of operation, and machine variables (Mani et al., 2004). Some of these values for four biomasses are shown in Table 11.1.

Biomass and the Natural Carbon Cycle

In the natural carbon cycle, carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the earth. During photosynthesis, atmospheric carbon dioxide (CO2) is converted into plant biomass. When carbon in the biomass is combusted or used for energy and materials for industry and agriculture, the biomass carbon is released back in different ways, but mostly as CO2 to the atmosphere. When biomass species are reproduced again by photosynthesis, the cycle repeats (Figure 12.1). For a steady operation, the concentration of CO2 in the atmosphere remains constant. However, the heavy use of fossil fuels, which is not part of the regular carbon cycle, has caused increase in the atmospheric CO2 concentration.

The conversion of biomass into energy is receiving increasing interest due to the need for maintaining the carbon cycle, and the depletion of petroleum fuels. Biomass is likely to play an important role in limiting CO2 emissions while supplying energy needs related to electric power, transportation fuels, and heating. Compared with the redesign of fossil fuel processes for lower CO2 emissions, biomass has a higher effectiveness in reducing CO2 emissions due to potential net zero carbon emission considering the production/use cycle (Hall, Mynick, and Williams, 1991; Overend, 1996; Williams and Larson, 1996). Given the growing shortage of petroleum fuels and environmental pollution (especially the greenhouse gas effect), the need for developing a carbon-neutral renewable source of energy is greater now than ever before (Lal, 2005).

Introduction

Today's world is facing two environmental problems: global warming and air pollution. Both of these are linked to the large-scale use of fossil fuels. Energy use is being reevaluated because of the quadrupling of oil prices in the 1970s and rapid increase in 2008, the growing awareness of energy-related pollution, and the possibility of climate change. As a result, there has been a significant improvement in energy efficiency in all sectors, including industry, power generation, lighting, household appliances, transportation, and climate control of buildings. In fact, efficient use of energy has historically helped increase the energy intensity in all Organization for Economic Cooperation and Development (OECD) countries and more recently in transition economies. Unfortunately, a rapid increase in the per capita use of fossil energy has accelerated the rate of atmospheric pollution.

Air Pollution

Air pollution (Figure 2.1) is due to the harmful substances (natural or man-made) that we breathe, including fine particles (produced from burning of fossil fuels), ground-level ozone (a reactive form of oxygen that is a component of urban smog), and gases such as carbon monoxide, chemical vapors, nitrogen oxides, and sulfur dioxide. The ill effects of air pollutants on human health have been known for the last 30 years; these include asthma, cardiovascular diseases, decreased lung function, and allergies. Of urgent concern is the long-term ill effect on lung development in children. In addition, air pollution causes damage to plant and animal lives.

Introduction

Energy policy deals with issues related to the production, distribution, and consumption of energy. It is the manner by which a government/entity has decided to address these issues, including international treaties, legislation on commercial energy activities (trading, transport, storage, etc.), incentives to investment, guidelines for energy production, conversion and use (efficiency and emission standards), taxation and other public policy techniques, energy-related research and development, energy diversity, and avoidance of possible energy crises. Current energy policies also address environmental issues, including cleaner technologies, more efficient energy use, air pollution, greenhouse effect (mainly reducing carbon dioxide emissions), global warming, and climate change (Demirbas, 2007a, 2008a, 2008c).

For commercial biofuel operations, there is considerable uncertainty in the economic analysis, mostly associated with the costs of feedstock, rapid technological changes, and petroleum prices against which the biofuels have to compete. Because the biofuel industry is in its infancy, supportive policies are needed that can foster the initial growth for both first-generation (ethanol and diesel) and second-generation biofuels. Policy options include incentive payments or tax breaks. Due to rising prices of petroleum fuels, the competitiveness of biomass use has improved considerably over time. Biomass and bioenergy are now a key option in energy policies for several countries, mainly driven by the security of supply, reducing both petroleum import and carbon dioxide (CO2) emissions. Biofuel can provide new economic opportunities for people in rural areas of countries with biofuel potential.

What Is Biocrude?

In search of renewable fuels, as early as the mid-twentieth century, researchers started to convert biomass into petroleum-like liquids. For example, Berl (1944) treated biomass using alkaline water at 230°C to produce a viscous liquid that contained 60% carbon and 75% heating value of the starting material. The liquid, termed biocrude, contains 10–20 wt% oxygen and 30–36 MJ/kg heating value as opposed to <1 wt% and 42–46 MJ/kg for petroleum (Aitani, 2004). The high oxygen content imparts lower energy content, poor thermal stability, lower volatility, higher corrosivity, and tendency to polymerize over time (Peterson et al., 2008). Hence, biocrude needs to be deoxygenated to make it compatible with conventional petroleum. Because biocrude contains less oxygen and more heating value than biomass, the hydrothermal liquefaction process is also referred to as hydrothermal upgrading. Compared with bio-oil from fast pyrolysis, biocrude produced from hydrothermal liquefaction has higher energy value and lower moisture content but requires longer residence time and higher capital costs. Typical hydrothermal liquefaction conditions range from 280 to 380°C, 70 to 20 Mpa, with liquid water present and reaction occurring for 10–60 minutes.

Hydrothermal Medium

Generally, hydrothermal medium refers to water that has been heated and compressed simultaneously. A phase diagram of pure fluid is shown in Figure 10.1; in the case of water, the critical point is 374°C and 221 bar (Note: a mixture may have a different critical point depending on the components and concentrations).

Challenges with Corn-Based Ethanol

Today, the world's ethanol supply is mainly derived from U.S. corn or Brazilian sugarcane. Corn and other grain (as farmers planted corn instead of other grains) prices have soared internationally, and the corn-to-ethanol industry has been blamed for driving up food prices worldwide (Figure 6.1). The Food and Agriculture Organization of the United Nations and the World Bank have said that soaring world food prices are due in part to increased demand for biofuels. However, additional factors that contribute to increased food prices include higher energy prices and increased consumption of meat and dairy products in developing economies of China and India. Note that it requires about 13 kg of corn to raise 1 kg of meat; hence, a shift toward nonvegetarian diet will put even more pressure on the food supply. The U.S. energy bill of 2007 allows for the doubling of corn-based ethanol with a ceiling of 15 billion gallons per year. The bill also calls for an additional 21 billion gallons per year of advanced biofuels, including 16 billion gallons per year of ethanol from nonfood sources, by 2022. The energy policy means that corn is likely to rule the U.S. ethanol industry for many years. However, soaring food prices and questions about whether corn-for-fuel can reduce global warming have sparked a debate about whether the United States is going down the wrong road in the search for alternatives to fossil fuels.

Biofuel Economy

High petroleum prices, increasing trade deficits due to fuel import, depleting petroleum supplies, and increased concern over the greenhouse gas emissions from fossil fuels have driven interest in transportation biofuels (Hill et al., 2006). For many developing countries, petroleum import accounts for the major share of their outflow of foreign exchange, putting a high strain on the growth. For such countries, a locally produced fuel can help with the economy. The first-generation biofuels (ethanol and biodiesel) are already in the market, and the second-generation biofuels from biomass are emerging. The U.S. Energy Independence and Security Act of 2007 provides major support for the biofuel industry by setting a renewable fuel requirement for use of 36 billion gallons per year of biofuel by 2022, with corn ethanol limited to 15 billion gallons. Any other ethanol or biodiesel may be used to fulfill the balance of the mandate, but the balance must include 16 billion gallons per year of cellulosic ethanol by 2022 and 5 billion gallons per year of biodiesel by 2012.

With increasing global interest in biofuels, there is a considerable discussion on the biomass supply and conversion costs. Production and use of life cycle analysis are being carried out to determine whether biofuels provide any benefit over fossil fuels, accounting for various aspects such as farm yields, commodity and fuel prices, farm energy and agrichemical inputs, production plant efficiencies, coproducts, greenhouse gas emissions, and so on.

Introduction

Although fossil fuels (petroleum, coal, and natural gas) are still being created at a geological rate, they are being consumed at a much faster rate. Hence, fossil fuels are not renewed fast enough to be replenished. That is why fossil fuels are considered nonrenewable. Presently on Earth, renewable sources of energy are due to the sun's energy and its direct and indirect effects on the earth (solar radiation, wind, falling water, and various plants, i.e. biomass), gravitational forces (tides), and the heat of the earth's core (geothermal). Renewable energy sources (RES) will replenish themselves within our lifetime and may be used with suitable technology to produce predictable quantities of energy when required. Additionally, renewable resources are more evenly distributed than fossil and nuclear resources on the earth. The most important benefit of renewable energy systems is the decrease of environmental pollution.

The main RES and their usage forms are shown in Table 3.1. Some of these energy sources have been used by humans for over five thousand years. During the preindustrial era, RES were primarily used for heating and simple mechanical applications that did not reach high energy efficiency. In the industrial era, the energy use shifted from low energy value RES to much higher energy value coal and petroleum. In fact it is said that RES such as water and wind power probably would not have provided the same fast increase in industrial productivity as fossil fuels (Edinger and Kaul, 2000).

What Is Biodiesel?

Biodiesel refers to a renewable fuel for diesel engines that is derived from animal fats or vegetable oils (e.g., rapeseed oil, canola oil, soybean oil, sunflower oil, palm oil, used cooking oil, beef tallow, sheep tallow, and poultry oil). Biodiesel is a clear amber–yellow liquid with a viscosity similar to petroleum diesel (petrodiesel, diesel). With the flash point of 150°C, biodiesel is nonflammable and nonexplosive, in contrast to petrodiesel, which has a flash point of 64°C. This property makes biodiesel-fueled vehicles much safer in accidents than those powered by diesel or gasoline. Unlike petrodiesel, biodiesel is biodegradable and nontoxic and significantly reduces toxic and other emissions when burned as a fuel. Technically, biodiesel is a diesel engine fuel comprised of monoalkyl esters of long-chain fatty acids derived from animal fats or vegetable oils, designated B100, and meeting the requirements of the ASTM D-6751 standard. Some of its technical properties are listed in Table 7.1. Chemically, biodiesel is referred to as a monoalkyl ester, especially (m)ethylester, of long-chain fatty acids derived from natural lipids via the transesterification process. Biodiesel is typically produced by reacting a vegetable oil or animal fat with methanol or ethanol in the presence of a catalyst to yield methyl or ethyl esters (biodiesel) and glycerin (Demirbas, 2002a). Generally, methanol is preferred for transesterification, because it is less expensive than ethanol.

Biodiesel produces slightly lower power and torque, which results in a higher consumption than No. 2 diesel fuel for driving.

Overview

An aircraft design, construction, and operation is an expensive endeavor, and not all nations can afford it. Countries that can must be cost-conscious, whether in a totalitarian or a free-market-economy society – the ground rules for accounting may differ but all strive for the least expensive endeavor for the task envisaged. The success or failure of an aircraft project depends on its cost-effectiveness. Cost-consciousness starts in the conceptual design phase to ensure competitive success. In fact, cost estimation should start before the conceptual design phase in a topdown analysis. If funds cannot be managed through the end of the project, then starting it is not viable.

Visibility on costing forces long-range planning and provides a better understanding of the design's system architecture for trade-off studies to explore alternate designs and the scope for sustainability and eco-friendliness of the product line. The product passes through well-defined stages during its lifetime: conception, design, manufacture, certification, operation, maintenance and modification, and finally disposal at the end of the life cycle. Cost information for previous products should be sufficiently comprehensive and available during the conceptual stages of a new project. The differential evaluation of product cost and technology – offering reliability and maintainability – as well as risk analysis are important considerations in cost management. Cost details also assist preliminary planning for procurement and partnership sourcing through an efficient bidding process. The final outcome ensures acquisition of an aircraft and its components with the objective of balancing the trade-off between cost and performance, which eventually leads to ensuring affordability and sustainability for operators over a product's life cycle.

Overview

Although the main tasks of the aircraft configuration are now completed, there are other topics of interest that require understanding of design. This chapter is an overview of the impact made by technological advances that must be considered at the conceptual stages to arrive at a “satisfying” design. It offers an understanding of specialized topics, some of which may appear out of context during the conceptual phase, but they do contribute to aircraft design. The aircraft external geometry is not affected by these considerations (unless a radical approach is taken); however, there could be weight and cost changes. The semi-empirical weight equations in Chapter 8 are sufficient and can be modified with improved data. In the industry, a more accurate weight estimation is required to reflect the changes affected by the topics discussed in this chapter.

A detailed study is beyond the scope of this book. Most academic institutions offer separate courses on some of the topics, such as aircraft structure, associated materials, and aircraft systems. Some of these topics sometimes escape attention because the undergraduate curriculum is already full with the main aeronautical subjects. Conceptual aircraft design is not only producing a geometry capable of meeting performance specifications; it also involves early thinking about environmental issues, safety issues, materials and structures, human interface with the flight deck, systems considerations, and military survivability issues that affect aircraft weight and cost.