Lecture 2: Introduction to Fossil Fuels PDF

LECTURE 2 INTRODUCTION TO FOSSIL FUELS Today, the world consumes energy in many forms, the majority of them being in the form of fossil fuels. The objectives of this lecture are to: ❑ Identify the types of fossil fuels ❑ Identify the origin of fossil fuels ❑ Identify characteristics of fossil fue...

LECTURE 2 INTRODUCTION TO FOSSIL FUELS Today, the world consumes energy in many forms, the majority of them being in the form of fossil fuels. The objectives of this lecture are to: ❑ Identify the types of fossil fuels ❑ Identify the origin of fossil fuels ❑ Identify characteristics of fossil fuels ❑ Analyze the differences in the basis for expressing the analysis and convert the basis of analysis ❑ Identify the pro and cons of fossil fuels Fossil fuels are the fuels of choice for the following energy conversion devices: The steam turbine The gas turbine The petrol engine The diesel engine THE STEAM TURBINE THE GAS TURBINE THE PETROL ENGINE THE DIESEL ENGINE Hence, fossil fuels form a very important part of our daily energy needs. Conventional fossil fuels include coal, natural gas, and the liquid forms of petroleum.  Fuels Solid Fuels o Coal o Biomass o Petroleum Coke Liquid Fuels o Gasoline o Diesel o Jet Fuel o Fuel Oils Natural Gas Today, about 80% of our daily energy consumption comes from fossil fuels. The consumption is approximated as follows: 33% Petroleum 27% Coal 20% Natural gas The remaining 20% comes from renewables and nuclear energy. Let us examine the conventional fossil fuels mentioned above. Global Carbon Cycle What is photosynthesis What is decay process? Formation of fossil fuels COAL What is coal? “Coal is a complex material composed of microscopically distinguishable, physically distinctive, and chemically different organic substances called macerals and inorganic substances called minerals.” Coal Coal has historically been one of the most important fossil fuels. Because of its abundance, ease of use, and energy density, it kick-started the Second Industrial Revolution. Today, coal is mostly used for generating electric power and making steel and cement. Even though coal has many advantages related to its cost and performance, producing and consuming coal impacts the environment. While it is mostly consumed in the same region where it is produced, a nascent global market for coal has emerged. About 90% of the coal consumed is for electric power, and the rest (10%) is for industry. For example, the steelmaking and cement-making industries use coal as a source of heat and carbon. The residential and commercial sectors use very little coal though some homes and buildings use coal for water and space heating through boilers and radiators. Botswana has tried to encourage its people to use coal through the Expanded Coal Utilization Project, but this has not taken off as anticipated. Coal Maturation Each fossil fuel shares a similar origin. Ancient organic matter stored energy from the sun through photosynthesis. Over time, ancient sedimentary layers of organic matter became coal seams, oil reservoirs, and gas pockets. Plant material in swamps or bogs subjected to several million years of high pressures, geological forces, and temperatures formed coal seams. Each specific form of coal depends on its geological age and on how it developed. Oil and gas have similar origins in ancient marine-based organic biomatter— namely algae—formed from photosynthesis. As organisms in the ocean died, they settled to the seafloor, forming sedimentary layers covered over time by water and dirt. After many millions of years enduring geological pressures and temperatures, some of these layers converted into oil and gas. Temperature increases with Depth As the coal becomes buried deeper in the earth there is an increase in temperature. Coupled with very long time scales (100’s of millions of years) transforms peat into coal. Coal Structure W. Wiser, "Research in coal technolgy," OCR/NSF-RANN Workshop Proceedings, New York, 1974. What happens when coal is burned Proximate Analysis Moisture o Loss of mass when heated to 110 °C in an inert atmosphere Volatile Matter o Loss of mass when heated from 110 to 900 °C (ISO standard) or 950 °C (ASTM) and held at that temperature for 7 minutes in an inert atmosphere Ash (related to Mineral Matter) o Mass remaining after cooling to 750 °C and changing the atmosphere to oxidizing Fixed Carbon = 100% -Moisture -VM -Ash Ultimate Analysis Carbon o Combusted and CO2 determined by I.R. spectroscopy Hydrogen o Combusted and H2O determined by I.R. spectroscopy Nitrogen o Combusted, reduced to N2, determined by thermal conductivity Sulfur o Combusted, SO2detected by I.R, or H2SO4 by titration Oxygen o Determined by difference (or by neutron excitation) Basis of Analysis  Conversion of basis Proximate Analysis (as received basis) is given as follows Moisture 23.24% Ash 3.73% VM 33.5% FC 39.53% This coal air-dry loss in accordance with Test Method 3302 = 16.36%. Report the analysis on as determined and on dry basis. Conversion of basis –Ultimate Analysis As determined coal analysis is as follows (wt.%) (H and oxygen include H and O in moisture). C 60.08 H 5.44 N 0.88 S 0.73 Ash 7.86 O (by difference) 25.01 Moisture as determined 9.00 Report analysis on dry basis  Calorific Value (Heating Value) The heating value of a fuel is of fundamental importance Varies from one fuel to another Heating or Calorific Value is the amount of heat released when a unit mass of fuel is burned (Btu/lb. or kcal/kg (international trade)) , MJ/kg Calorific value has implications for pollution measurements such as SO2 whose emissions are calculated on a lb/MBtu or kg/MJ basis Higher and Lower heating Value LHV =HHV-hfg(H*9+M) =HHV-10.3(H*9+M) (Btu/lb) =HHV-5.72(H*9+M) (kcal/kg) =HHV-2.395(H*9+M) MJ/kg Where, LHV=lower (or net) heating value HHV= higher (or gross) heating value H=% Hydrogen (a.r. basis) M= % Moisture (total, a.r.basis)  Estimation of Gross Caloric Value Dulong – Petit Formula  O HHV = 33.83C + 144.45  H −  + 9.83S MJ/kg  8 C= % Carbon, H= % Hydrogen, O= % Oxygen, S= % Sulfur (ie mass fractions of C,H,O,S) The calorific value of coal varies considerably depending on the mineral matter and moisture content and the type of coal while calorific values of fuel oils are much more consistent  Dulong equation for calculating the calorific value  O Btu/lb HHV = 146C + 620  H −  + 40.5S  8 1   O  HHV = 8080C + 34500  H −  + 2240 S  kcal/kg 100   8  C,H,O,S are the mass fractions of carbon, hydrogen, oxygen and sulfur in the coal kcal Btu lb = kg 1.8 MJ Btu lb = kg 429.92  Coal Rank Degree of coalification o Determined using dmmf Volatile matter o Moist, mineral matter free basis o Heating value o Vitrinite reflectance (is the proportion of incident light reflected from a polished vitrinite surface.Vitrinite is a maceral (an organic component) of coal). ASTM Classification of Coals Parr Formula Variation in Properties Industry broadly categorizes coal into two types: Thermal coal, for producing heat, for example at power plants, and Metallurgical coal, for making metals, for example at steel plants. There are four main ranks of coal, which are used primarily for electric power and industry. The Four Ranks of Coal Coal for electric power generation is generally classified into 4 ranks namely: ▪ Lignite ▪ Sub-bituminous ▪ Bituminous ▪ Anthracite Each rank describes the type of coal and depends on the coal’s carbon content. Lower rank generally indicates lower carbon: Lignite contains less carbon than sub-bituminous, which contains less carbon than bituminous, which in turn has less carbon than anthracite. Lignite Lignite is the lowest grade coal. Sometimes known as brown coal, it is the youngest coal in geological terms. Contains less carbon. It also has a high moisture content, which lowers its energy density, as evaporating the embedded water consumes much of the energy from its combustion. Many power plants still burn lignite to generate electricity due to its affordable price especially where lignite reserves are abundant. Sub-bituminous Sub-bituminous coal generally contains more carbon than lignite. Its geological age exceeds 100 million years. Due to higher carbon content, sub-bituminous coal has a higher heating value. Its use is mostly for electricity generation. In the USA for example, sub-bituminous and bituminous coal are the most prevalent. Bituminous Bituminous coal shows greater variability depending on where it is produced because each coal field differs. Its age ranges between 100 and 300 million years. On average, bituminous coal exhibits about two to three times the heat content of lignite. Bituminous coal is used for electricity and as a raw material in steel production. It is the most prevalent coal in Botswana. Anthracite Anthracite, the highest rank of coal, contains between 85% and 97% carbon. A shiny black luster characterizes anthracite. Because of its use since the mid-1800s, anthracite mines are almost completely depleted. Anthracite is not used today in power plants due to its scarcity and expense, but minor quantities are used for specialty purposes such as metal making and carbon filters. Reserves Coal is one of those abundant resources found in many continents of the world. More than 80% of the world total coal reserves are located in just ten countries United States of America, (237 Bt), Russia (157Bt), China(114Bt), Australia(76Bt), India (60.6Bt), Germany (40.7Bt), Ukraine, Kazakhstan, Colombia, Canada…South Africa(36Bt) World reserves (860Bt) of which 405 billion (47%) is classified as bituminous coal (including anthracite), 260 billion (30%) as sub-bituminous and 195 billion (23%) lignite. BIDPA 2012 A simple calculation of how long we could use coal at the current rate, fall in the range of 100-250 years. Even more pessimistic are recent studies suggesting that we might only be sure of having enough coal until 2030, or that coal production will peak around 2030-2050 and decline thereafter. 90% of global coal reserves are expected to be exhausted by 2070. Abundance does not imply affordability because coal becomes more expensive to extract the deeper the mines extend. Trade-offs Coal has trade-offs like every other fuel choice. Coal extraction incurs significant land disturbance, especially for surface mining in the mountains. Coal combustion is very carbon-intensive, which exacerbates concerns about global climate change. Over millennia, coal has served as nature’s water filter, cleaning the water by removing heavy metals and other elements and trapping them. Unfortunately, un- scrubbed coal combustion releases those heavy metals and other pollutants into the environment, including sulfur, mercury, and other toxins. In general, coal is dirtier than the other fossil fuels? Coal is just a rock until you start to burn it…. Sulfur dioxide (SO2) released during coal combustion is a major contributor to acid rain. On the other hand, coal is abundant, domestic, and historically cheap. The ease of storing coal—usually done by creating massive piles of the unburned rock—provides another advantage when compared to other fuels. Storage benefits power plant operators because it ensures fuel availability, even in the event of a supply disruption. It is not unusual for a 30-to-60-day supply of coal to sit outside a power plant. The main benefits of coal include its significant price advantages. Natural gas prices vary, like those of petroleum, although natural gas is typically cheaper than crude oil which is the most expensive. Coal consistently ranks as the least expensive and least volatile. Low price volatility is a major advantage for energy companies investing several billion dollars to build a power plant that will last 40 years. If the company can predict the fuel price for decades into the future, it can make better decisions about the economic viability of that power plant. By contrast, natural gas power plants are easier to build, but natural gas price volatility makes estimating true life-cycle operating costs comparatively difficult. Thus, coal’s price stability is very valuable, especially in comparison with other options. End-Uses As noted earlier, the world uses coal mainly to fuel the electric power sector. Historically, transportation used some coal for steam-driven trains. Coal for steelmaking has been in decline in the developed world because an upswing in recycled steel has displaced virgin steel manufacturing.While making steel uses coal, recycling steel generally uses electricity instead. At the same time, overall production and consumption of coal in places like the United States and Europe started declining in the 2010s because of market share lost to natural gas and renewables, and because of tightening environmental standards, which require coal users to install expensive scrubbers Extraction There are two approaches to coal mining: underground mining and surface mining. Mining companies either remove the coal from the mountain (underground mining) or remove the mountain from the coal (surface mining). Underground mining is the more familiar and classic approach to mining and consists of room and pillar system where miners create tunnels below the surface. Room and pillar the coal seam is mined in a checker board style leaving pillars of coal to support the roof. It allow for instant coal access at a lower investment, however it only utilizes 50-75% of the coal Equipment cuts through the rock and removes the coal and other cuttings from the mountain, with some variation. One variation is the slope mine, which angles down below the ground rather than cutting in a perpendicular fashion. (MCM) Another version is a shaft mine, in which elevators might extend kms below the surface. One elevator transports the miners, and another elevator transports coal up to the surface. This system is even more energy intensive, because moving people, equipment, and coal up and down requires energy. Additional depth requires an investment of more energy and more money to extract the coal, so each meter deeper becomes more expensive. Underground methods produce relatively little disturbance on the surface. The mine’s footprint might be as small as a mineshaft, an elevator shaft, or a truck-sized opening. While underground mining impacts the land less significantly than surface mining, dangers arise from being underground. Pressure from rock above constantly induces the risk of cave-ins or collapse. Also, leaking gases from coal bed methane introduce a risk of explosion. Underground mining is a trade-off between decreased environmental impacts and increased danger to miners. UNDERGROUND MINING IS THE MORE FAMILIAR AND CLASSIC APPROACH TO MINING COAL AND CONSISTS OF A ROOM AND PILLAR SYSTEM WHERE MINERS CREATE TUNNELS BELOW THE SURFACE. By contrast, surface mining methods, rather than tunneling or boring through a mountain to reach a coal seam, completely remove the rock and dirt overburden to extract the coal. In mountainous area, surface mining removes dirt and rocks which are often dumped in nearby valleys. One variation, the contour bench, requires cutting away the side of the mountain to reach the coal beds. Miners can also remove an entire mountaintop to reach the coal beneath. The environmental impacts of both are quite severe. However, surface mining exposes miners and workers to less risk and often costs substantially less than underground mining. THE ENVIRONMENTAL IMPACTS OF SURFACE MINING CAN BE QUITE SEVERE. HOWEVER, IT EXPOSES MINERS AND WORKERS TO LESS RISK AND COSTS SUBSTANTIALLY LESS THAN UNDERGROUND MINING.  Liquid Fuels Gasoline Diesel Kerosene Fuel oil Shale oil Petroleum fractions Fractional Distillation  Liquid Fuel Properties Specific Gravity - Ratio between the weight of any volume of oil at 15 °C to the weight of equal volume of water at 15 °C (is the ratio of the density p of the substance to the density p ref of a reference substance at a specific condition) Viscosity- a measure of resistance to motion of a fluid Dynamic (Absolute) Dynamic viscosity is the force needed by a fluid to overcome its own internal molecular friction so that the fluid will flow. or Kinematic is the resistive flow of a liquid under weight of gravity (inherent resistance to flow when no external force except gravity is acting on it) (ratio of dynamic viscosity to density) Saybolt Universal Viscosity: time in seconds that it takes to run 60 ml of a petroleum product through a standard (calibrated) size orifice Saybolt Furol Viscosity (Furol is acronym for fuel road oil) - specific standardized tests producing measures of kinematic viscosity Flash point The temperature at which the vapors generated “flash” when ignited by external ignition source (important for safety especially storage & transportation of fuels) Pour point :The temperature at which the oil ceases to flow when cooled under prescribed conditions PETROLEUM PRODUCTS Starting in the twentieth century, petroleum has been the most important popular fuel worldwide. Since the popularization of the internal combustion engine in the early 1900s, petroleum consumption has grown primarily for use in the transportation sector, as consumers worldwide have acquired cars and driven trillions of kilometres. There are also many stationary engines for different services that derive their energy from petroleum products. Crude oil production, consumption, and trade are measured in million barrels per day (MMBD). (One Barrel of oil = 42 US gallons = 159 litres) Petroleum is mainly consumed as follows: About 72%) used for transportation About 23% used in petrochemical industries (to make products such as plastics, polyurethane, solvents, and hundreds of other intermediate and end-user goods) and/or heat for manufacturing processes About 4% used for domestic and commercial sector mainly for space heating Less than 1% used for electricity generation Characteristics of Petroleum Sweet crude has low sulfur content, and sour crude has high sulfur content. Lightness refers to the viscosity of the petroleum. Low viscosity renders light crudes easy to handle. Heavy crudes flow less easily and are harder to manage. Therefore, most industrial customers prefer light, sweet crude. Light crudes are easier to refine, and sweet crudes are cleaner. Fuel Flexibility Petroleum-based fuels are better because they have excellent performance characteristics and are flexible in ways other fuels are not. Petroleum-based fuels have both high gravimetric energy density, (energy density per unit mass), and high volumetric energy density, (energy density per unit volume). Hence, a small amount of mass or volume stores large quantities of energy. A single tank of petrol can move a car hundreds of kilometres, a feat difficult for other fuels to match. Also, petroleum and petroleum products can be piped thousands of kilometers without losing their molecular attributes. Therefore, crude oil pumped through pipelines or transported in a ship’s hold over thousands of kilometers remains crude oil. The same applies for gasoline and other refined fuels. This product stability is an advantage for storing and distributing the fuels for a global customer base. In addition to molecular stability, these fuels have convenient boiling and freezing points for liquid fuels. Constituents of Petroleum-based fuels Petroleum-based fuels lack purity. Several constituents make up petroleum. Even the distilled fuels, such as gasoline, kerosene, and diesel, are not pure chemicals. The full range of chemicals in a barrel of petroleum includes paraffins, olefins, isomers, naphthas, iso-octanes, and iso-pentanes. Small concentrations of aromatics such as benzene and toluene, and heteroatoms like sulfur round out each barrel. Petroleum Constituents Fraction Class Example Species 75–85% Paraffins & Isomers Methane, ethane, propane, isooctane, n-pentane, cyclic paraffins (naphthenes) 13–22% Aromatics Benzene, toluene, xylene, etc.