Analysis of FOSSILIZATION P M V Subbarao Professor Mechanical Engineering Department An Extremely Slow action in Nature... True Quasi-static Process to Create Permanent Entropy Vehicles…..

Theory of Coal Formation

Coalification Orgin of Coal : A complex mixture of plant substances altered in varying degree by physical and chemical process. Reaction time : ~~ 365 million years. Mechanism of Formation: In Situ Theory : Coal seam occupies the same site where original plants grew and accumulated. Drift Theory : Plants and trees were uprooted and drifted by rivers to lakes and estuaries to get deposited. During the course of time they got buried underground. Indian coals are formed according to drift theory.

In Situ Theory Carboniferous periods of the Paleozoic when these areas were covered with forests The humid climate of the Carboniferous Period (360 to 286 million years ago), which favoured the growth of huge tropical seed ferns and giant nonflowering trees, created the vast swamp areas

Sequence of Actions in Coalification Dead Organic Matter Living Plants & Trees Bio-Chemical Degradation of Organic Material Thermo-chemical Conversion

Bio - Chemical Degradation of Dead Plants As the plants died and fell into the boggy waters. These Boggy waters excluded sufficient oxygen. Bacteria could only partially decomposed but did not rot away the dead plants. The absence of oxygen killed the bacteria. The vegetation was changed into peat, some of which was brown and spongy, some black and compact, depending on the degree of decomposition. Peat deposition is the first step in the formation of coal.

Formation of Peat Natural Rate of reaction : 3cm layer per 100 years. Light brown fibrous at the surface and colour becomes darker with depth. Typical Composition: Moisture : 85%, Volatile Matter : 8 %, Fixed Carbon : 4%, Ash : 3%. Calorifica Value : ~2730 kJ/kg. Occurrence of Peat : Nilgiri Hills and banks of Hooghly. Sun dried Peat is very useful as a fuel with following composition: Moisture : 20%, Volatile Matter : 50 %, Fixed Carbon : 25%, Ash : 5% Bulk density : 300 kg/m3 and low furnace temperature and efficiency. Products from Peat: Charcoal, Producer gas.

First Law Analysis of Formation of Peat :SSSF m CO2 m vegetation Q m Peat m CH4 W Species Conservation Equation: Conservation of Mass: First Laws for furnace in SSSF Mode:

Thermo-chemical / Geo-Chemical Stage The decayed vegetation was subjected to extreme temperature and crushing pressures. It took several hundred million years to transform the soggy Peat into the solid mineral. 20 m of compacted vegetation was required to produce 1 m seam of coal.

Evolution of Chemical Composition during Coalification As the time passes, the tectonic plate movements carries the peat to higher depths. In the process, cellulose is substantially lost and the lignin chemical components are transformed. Oxygen content of the peat decreases, which increases the carbon content. Water content also decreases. The ratio of aromatic carbons (graphite or charcoal-like character) to aliphatic carbons (oil-like carbons) also begins to increase.  With time Oxygen continues to be lost and aromatic carbon increases even more.

Modeling of Coalification Peat to Enriched peat: (mostly due to heating) Enriched peat to lignite: (mostly due to pressure &heating) lignite to Sub-bituminous: (mostly due to pressure &heating) Sub-bituminous to High volatile Bituminous:

High Volatile Bituminous to Medium volatile Bituminous: Medium Volatile Bituminous to Low volatile Bituminous: Low Volatile Bituminous to semi Anthracite: Semi Anthracite to Anthracite:

Chemical Structure of Coal

Composition of Coals The natural constituents of coal can be divided into two groups: (i) The organic fraction, which can be further subdivided into microscopically identifiable macerals. (ii) The inorganic fraction, which is commonly identified as ash subsequent to combustion. The organic fraction can be further subdivided on the basis of its rank or maturity.

Coal Ranking

Analysis of Coal Proximate Analysis & Ultimate Analysis. Proximate analysis - to determine the moisture, ash, volatiles matter and fixed carbon Ultimate or elementary analysis - to determine the elemental composition of the coal The Energy content -- CFRI Formulae -- Low Moisture Coal (M < 2% ) -- CV (Kcal/kg) = 71.7 FC + 75.6 (VM-0.1 A) - 60 M High Moisture Coal(M > 2%) -- CV(kcal.kg) = 85.6 {100 - (1.1A+M)} - 60 M Where, M, A, FC and VM denote moister, ash , fixed carbon and Volatile mater (all in percent), respectively.

Fuel Model

Additional Characteristics of Coal Sulfur Content : Coal with sulfur > 5% is not recommended for combustion. Weatherability : Weathering or Slacking Index -- An indication of size stability -- Denotes the tendency to break on exposure to alternate wet and dry periods. Grindability Index : A measure of relative ease of grinding coals or the power required for grinding coals in a pulverizer. Burning Characteristics of Coal : Free burning coals and Caking Coals -- Caking index -- Pulverulent, sintered, weakly caked, caked and strongly caked. Ash Fusion temperature -- The temperature where the ash becomes very plastic -- Design of ash handling system. -- Stoker furnace cannot use low ash fusion temperature coals.

Theory of Oil Formation The most popular theory is known as the Organic Theory. This theory states that oil and gas have biological origins. Small sea creatures from the days when the earth was mostly covered in water died and settled to the bottom of the ocean floor. Layer upon layer of silt, sand and clay built up on top of them over time. Through the process of decay, as well as ever increasing heat and pressure, the former sea creatures were converted to oil and gas. Over millions of years, continuous pressure actually compressed those layers of silt and clay into layers of rock. This is known as "reservoir rock". The temperature under the earth's surface increases the deeper you go underground.

Structure of Oil & Gas Reservoirs

Formation of Oil & Gas At about 600C, oil begins to form. Oil formation ceases at about 1500 C. Oil formed at lower temperatures (i.e. closer to the surface) is called immature and is heavy. Oil formed deeper under the surface is called mature and is light. At temperatures above 1500C, oil is thermally cracked to produce light gases (i.e. natural gas). Since temperature increases with depth, natural gas wells are typically drilled much deeper than oil wells.

Structure of Oil & Gas Reservoirs

History of Petroleum Refining The modern history of petroleum began in the 19th century with the refining of paraffin from crude oil. The Scottish chemist James Young in 1847 noticed a natural petroleum seepage in the Riddings colliery at Alfreton, Derbyshire. He distilled a light thin oil suitable for use as lamp oil, at the same time obtaining a thicker oil suitable for lubricating machinery. In 1846, Baku (settlement Bibi-Heybat) the first ever well drilled with percussion tools to a depth of 21 meters for oil exploration. In 1848, Young set up a small business refining the crude oil. The new oils were successful, but the supply of oil from the coal mine soon began to fail (eventually being exhausted in 1851).

Hydro carbon Chemistry & Classification of Crude Oils Paraffin based crudes (a waxy residue) Asphalt based crudes (an asphalt type residue) Mixed type-based crudes ( a combination residue) Components of Crude Oils. Paraffins (CnH(2n+2)) Olefins Aromatics Ultimate Analysis C : 84 -- 87% ; H : 11 -- 16% ; O : 0.3 -- 1.8% ; N : 0.1 -- 1.5% ; S : 0.1 -- 3%

Petroleum refining : Basic refinery processes Functions of Refinery Units: (1) separating the many types of Hydrocarbon present in crude oils into fractions of more closely related properties, (2) chemically converting the separated hydrocarbons into more desirable reaction products, and (3) purifying the products of unwanted elements and compounds. Types of Distillation: Fractional Distillation Vacuum Distillation Super fractionation Thermal Cracking Catalytic Cracking

Boiling range, and molecule size for typical refinery BOILING RATE # CARBON ATOMS Refinery Gas <25oC 3 Gasoline 40-150oC 4-10 Naptha 150-200oC 10-12 Kerosene 200-300oC 12-16 Diesel Fuel 300-400oC 16-25 Residual Oil >400oC >25

Major Components of Gasoline (Petrol)

Major Components of Gasoline (Petrol)

Properties of Petroleum Derivatives Specific Gravity Calorific Value Viscosity Flash Point Fire Point Pour Point Volatility Ash content Carbon Residue Octane Number / Cetane Number / Performance Number

Engineering Significance of Fuel Properties Specific Gravity = (Weight of fuel/unit volume)/(weight of water/unit volume at 15oC) API Gravity = 141.5/(SG15.6/15.6oC) - 131.5 Significance of SG: Origin of the fuel Combustion characteristics A high API G : Paraffin fuel with good ignition quality; low c/H ratio. A high API G : aromatic asphaltic fuel with poor combustion characteristics APT G < 10 : Difficult or impossible to separate-out water and solid. Good quality paraffin straight run fuels : 35 -- 40 (API G) Aromatic fules : 27 -- 30

Engineering Significance of Fuel Properties Calorific Value: HCV (MJ/kg) = {51.916 - 8.792 * (SG)2} * {1 - (M+A+S)} + 9.42 * S LCV = {46.392 - 8.792 * (SG)2 + 3.187 *(SG)} * {1 - (M+A+S)} + 9.42 *S - 2.449 * M Flash Point: The temperature at which the oil must be heated under prescribed conditions for sufficient vapour to be given off to form an flammable mixture with air. Determines the type of blend indicates safe sotrage temperatures. Gasoline : 40oC; Kerosene: 40oC; Diesel Oile: 90 -- 95 oC Fire Point: The temperature at which continuous flame is seen . Indication of fire risk.

Engineering Significance of Fuel Properties Ash content: Amount of totally non combustible products. Contaminants such as dirt, sand, rust and scales. Solid ash forming compounds can cause Severe abrasive wear in IC enginescylinder liners. High temperature slagging in fire tubes and super heater tubes. Blade deposition on gas turbine blades.

Engineering Significance of Fuel Properties Viscosity: Kinematic viscosity (Centi Stokes) and Dynamic viscosity (Centi Dynes). Design of burners/ IC engine injectors. Decreases with increasing temperature but becomes constant at 120oC Heating of fuel helps in atomization. Maximum viscosity for easy atomization in commercial burners : 25 cStokes. For easy pumping 1200 cStokes. Diesel fuel : Low viscosity causes excessive leakage. High viscosity produces coarse drops. -- results in formation of engine deposits -- incomplete combustion. VISCOSITY IS NOT AN PROPORTIONATE PROPERTY.

Engineering Significance of Gaseous Fuel Properties Can be easily piped into furnace -- no physical handling is required. Natural Gas -- True Fossil fuel Odorless and colorless Mainly CH4 + heavier HCs HHV = 55,000 kJ/kg. Manufactured Gases LPG -- light distillates of petroleum. -- Heavier than air!!! Stored and transported under pressure (0.4 -- 2 Mpa). SNG : Produced from coal by Hydrogenation -- cheap and clean.. Pressurized Hydrogen at 9000C is combined with coal to produce a number of light HCs. Producer gas, Bio-gas, Water gas, Coke-oven gas etc….