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STUDY of COALIFICATION. P M V Subbarao Professor Mechanical Engineering Department. An Extremely Slow Action in Nature... True Quasi-static Process to Create Permanent Entropy Vehicles…. Coal : First Kind of Entropy Vehicle. Timing of Newton’s Law???.
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STUDY of COALIFICATION P M V Subbarao Professor Mechanical Engineering Department An Extremely Slow Action in Nature... True Quasi-static Process to Create Permanent Entropy Vehicles…..
A tree converts disorder to order with a little help from the Sun • The building materials are in a highly disordered state - gases, liquids and vapors. • The tree takes in carbon dioxide from the air, water from the earth as well as a small amount from water vapor in the air. • From this disordered beginning, it produces the highly ordered and highly constrained sugar molecules, like glucose. The radiant energy from the Sun gets transferred to the bond energies of the carbons and the other atoms in the glucose molecule. In addition to making the sugars, the plants also release oxygen which is essential for animal life.
Q W m Oxygen m CO2 m vegetation m water Q First Law Analysis of Photosynthesis : SSSF The Global Reaction Equation: Conservation of Mass: First Laws for furnace in SSSF Mode:
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
Brown Coal Plant Debris Peat Lignite Diamond Sub-Bituminous Anthracite Semi Anthracite Bituminous Steps in Formation of Coal
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/m3and low furnace temperature and efficiency. • Products from Peat: Charcoal, Producer gas.
Molecular Structure of Peat Structure of smallest molecule:
m Peat m vegetation m CO2 Q m CH4 First Law Analysis of Formation of Peat :SSSF P=?? Species Conservation Equation: Conservation of Mass: First Laws for furnace in SSSF Mode:
Secondary Transformation : 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. • This is called as coalification or coal forming. • The extent to which coalification has progressed determines the rank of coal.
Modeling of Combustible 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:
Modeling of High Rank Coalification High Volatile Bituminous to Medium volatile Bituminous: Medium Volatile Bituminous to Low volatile Bituminous: Low Volatile Bituminous to semi Anthracite: Semi Anthracite to Anthracite:
Global Reaction Model for Coalification • The application of basic kinetics to the real coalification requires some algebraic manipulations
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.
Microscopic Structure of Coals • On the microscopic level, coal is made up of organic particles called macerals. • Macerals are the altered remains and byproducts of the original plant material from which the coal-forming peat originated. • Macerals are to coal as sediment grains. • Coal petrographers separate macerals into three groups, each of which includes several maceral types. • The groups are Inertinite, Liptinite, and Vitrinite. • These groups were defined according to their grayness in reflected light under a microscope.
Origin of Maceral Groups • Vitrinite is thought to be derived mainly from the original woody tissue of trees in peat swamps. • Exinite , which is derived from pollen, spores and leaf epidermis, is technologically important, because it enhances the fluidity of coal. • The inertinite group of macerals derives its name from its more or less non-reactive character shown during the carbonization process. • Whereas exinite and vitrinite melt, with an evolution of volatiles, inertinites generally remain intact. • Inertinite is derived from fungal remains, charcoal and partly charred wood.
Chemistry of Maceral Groups • The maceral content and volatile-matter yield of a coal may be considerably influenced by the post-depositional chemical environment to which the normally acid peat is subjected. • There exist a correlation between carbon content and reflectance and this is used to precisely determine rank. • Petrographers in use the mean maximum reflectance of vitrinite in oil (Romax), at 546 µ, as the level of organic maturity, or rank, of a coal sample.
Vitrinite reflectance (Ro) • Vitrinite reflectance is the proportion of incident light reflected from a polished vitrinite surface.
Coal Reactivity • The reactivity parameter was calculated using the following equation:
Closing Remarks on Coal Knowledge Reflectance Rank 0.50% - 1.12% High-volatile bituminous 1.12% - 1.51% Medium-volatile bituminous 1.51% - 1.92% Low-volatile bituminous 1.92% - 2.5% Semi-anthracite > 2.5% Anthracite
Natural Thermodynamics for Creation of Permanent of Entropy Vehicles
Mineral-Matter Composition of Coals • The ash of a coal is the uncombustible oxide residue which remains after combustion. • Mineral matter is the natural mineral assemblage of a coal that contains syngenetic, diagenetic and epigenetic species. • Mineral matter is identified more accurately by X-ray diffraction analysis of low-temperature ash (LTA). • The post-depositional chemical environment of a peat swamp, is the major factor determining the amount and kind of mineral species present in coal.
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.
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.
Biochar Production at IIT Delhi Kiln Capacity:25 L, Efficiency:20-25% Feedstock: Leaf Waste, Operating Temperature<450° C
Maximum Extra-somatic Energy Content of A Fuel • Obtained only thru Combustion. • Standard heat of combustion: • The energy liberated when a substance X undergoes complete combustion, with excess oxygen at standard conditions (25°C and 1 bar). • The heat of combustion is utilised to quantify the performance of a fuel in combustion systems such as furnaces, Combustion engines and power plants. • In industrial terminology it is identified as the Gross Heating (calorific) Value or Higher Heating (calorific) value. • In a general design calculations, only Net Heating (calorific) Value or Lower Heating (calorific) value is used.
Measurement of Calorific Value : Bomb Calorimeter : Control Mass
Thermodynamic Description of Bomb Calorimeter • It is a combination of two closed systems. • Bomb: Constant volume closed system: Interacts only with calorimeter. • Calorimeter: Outer constant volume closed system: • Interacts only with bomb. • Isolates entire system with ambience.
