Coal as a Source of Energy PDF

TECHNOLOGIES FOR CLEAN AND RENEWABLE ENERGY PRODUCTION COAL AS A SOURCE OF ENERGY DR. PRASENJIT MONDAL CHEMICAL ENGINEERING 1  CONTENTS  Coal and its composition  Origin of coal, its rank and energy content...

TECHNOLOGIES FOR CLEAN AND RENEWABLE ENERGY PRODUCTION COAL AS A SOURCE OF ENERGY DR. PRASENJIT MONDAL CHEMICAL ENGINEERING 1  CONTENTS  Coal and its composition  Origin of coal, its rank and energy content  Availability of coal and energy possibility from it  Types/grades of coal  Properties of coal  Pricing of coal  Coal for energy production : Some issues 2  Coal and its composition  Coal is a stored fossil fuel, occurring in the earth’s crust, which has been formed by the partial decay of plant materials accumulated millions of years ago and further altered by the action of heat and pressure.  It is a combustible black or brownish-black sedimentary rock normally occurring in rock strata in layers called coal beds or coal seams.  It is composed primarily of carbon along with variable quantities of other elements, mainly hydrogen, with smaller quantities of sulfur, oxygen and nitrogen.  The geochemical process that transforms plant material into coal is called coalification and is often expressed as: peat → lignite → bituminous → anthracite Rank of coal bituminous (subbituminous bituminous semi bituminous) 3  Coal and its composition Low Rank High Rank Lignite/ Brown Sub-bituminous Bituminous Anthracite coal C : 35-45 % C : 45-86 % C : 86-98 % C : 25-35 % O :20-10% O :10-5% O: 2-1% O: 30-20% HHV: 19000- HHV: 25000-35000 HHV: >35000 HHV: 9000-19000 30000 KJ/Kg KJ/Kg KJ/Kg KJ/Kg Ash : 11 % Ash : 40 % Ash : 6 % Ash : 10 % Source: KBR Age, Carbon, Heating value Technology Conference 2008 Moisture content and volatiles  Indian coals are mainly bituminous / lignite & ash content is very high 4  Origin of coal, its types and energy content  In situ theory Extensive accumulations of vegetable matter growing in swamps or bogs subjected to widespread submersion by sedimentary deposits  Drift theory Coal is formed largely from terrestrial plant material growing on dry land and not in swamps or bogs. The original plant debris was transported by water and deposited under water in lakes or in the sea by flood /tsunami type wave (velocity 800 km/h)  Over time, the chemical and physical properties of the plant remains were changed by geological action (high pressure and heat) to create a solid material.  15-20 m of plant material = 1 m of coal seam (In India 30 m seam of coal has been found  320 million of years may be required to form coal (earth is 4.6 billion years old) 5  Origin of coal, its types and energy content Heating Coal %C C H O value (MJ/kg) Cellulose 45 100 14 111 10 Time Wood (Dry) 50 100 12 88 10-11 Peat 60 100 10 57 10-12 Lignite 62 100 8 54 16-24 Bituminous coal 79 100 6 21 26-30 Anthracite 91 100 5 5.2 32-34 Graphite 100 100 0 0 34 6   Availability of coal and energy possibility from it Important Country names Approx. Geological ages (million years) Esaern USA 275-320 United kingdom 280-320 Germany 285-320 Poland/Czech Republic 280-320 Russia 250-320 and 175-205 China 250-320 and 70-205 Australia 205-280 India 250-280 South Africa 250-280 Western Canada 50-150 Western USA 25-85 Reference: IEA Coal Research Columbia/Venezuela 50-70 London 2000 7 Availability of coal and energy possibility from it Coal reserves in India (1.4.2014) Name of the Reserves in % of total reserves state billion tonne A total of 301.56 billion tonnes(BT) of coal JHARKHAND 80.71 26.76 reserves are estimated by GSI ODISHA 75.07 24.89 Prime coking coal: 5.313 CHATTISHGARH 52.53 17.42 Medium and semi-coking coals: 28.76 WEST BENGAL 31.31 10.38 Non-coking coals: 266.00 MADHYA 25.67 8.51 Tertiary coal: 1.49 PRADESH 1. Gondwana coals: 250-325 million years ANDHRA 22.48 7.45 carboniferous period PRADESH MAHARASTRA 10.98 3.64 2. Tertiary coals: 10-60 million years, high S OTHERS 2.81 0.95 content 2-8% Cokes are the solid carbonaceous material Years to consume this coal with present derived from destructive distillation of low- rate: 600 ash, low-sulfur bituminous coal. 8  Types/grades of coal Unconventional coal Based on coking Based on age A. Cannels: property of maturity  Found rarely  High hydrogen content  Coking  Gondwana  Burn with smoke and  Semi coking  Tertiary bright flame  Non-coking  Does not fall in any category B. Torbanites:  Known as Boghead coal  Named after Torbane Hill of Scotland  Rich in paraffin oil 9  GRADING OF COKING COAL GRADE ASH CONTENT Steel Grade-I Not exceeding 15% Steel Grade-II Exceeding 15% but not exceeding 18% Washery Grade-I Exceeding 18% but not exceeding 21% Washery Grade-II Exceeding 21% but not exceeding 24% Washery Grade-III Exceeding 24% but not exceeding 28% Washery Grade-IV Exceeding 28% but not exceeding 35% Steel Grade Coal is used in Steel Industries. Washery Grade Coal is used as fuel in thermal power plants. 10  GRADING OF NON-COKING COAL Ash% + Moisture % (at Useful Heat Value (UHV) (in kcal/kg) Grade 60% RH & 40o C) UHV= 8900-138(Ash% + Moisture % ) A Not exceeding 19.5 Exceeding 6200 B 19.6 to 23.8 Exceeding 5600 but not exceeding 6200 C 23.9 to 28.6 Exceeding 4940 but not exceeding 5600 D 28.7 to 34.0 Exceeding 4200 but not exceeding 4940 E 34.1 to 40.0 Exceeding 3360 but not exceeding 4200 F 40.1 to 47.0 Exceeding 2400 but not exceeding 3360 G 47.1 to 55.0 Exceeding 1300 but not exceeding 2400 11 GRADING OF SEMI-COKING AND WEAKLY-COKING COAL GRADE ASH+MOISTURE CONTENT Semi coking grade-I Not exceeding 19% Semi coking grade-II Exceeding 19% but not exceeding 24% 12  Heat treatment of coking coal/ bituminous coal Coke Coal tar Coal gas Coal tar is a brown or black Contains a variety of Cokes from coal are grey, liquid of extremely high calorific gases hard, and porous. viscosity, which smells of including hydrogen, Coke is used as a fuel naphthalene and aromatic carbon monoxide, and as a reducing agent hydrocarbons. methane and volatile in smelting iron ore in a Complex and variable hydrocarbons blast furnace mixtures of phenols, together with small It is there to reduce the polycyclic aromatic quantities of non- iron oxide (haematite) in hydrocarbons (PAHs), and calorific gases such as order to collect iron heterocyclic compounds, carbon dioxide and about 200 substances in all nitrogen 13  Important properties of coal  Caking and coking properties  Caking vs. coking  Heating value On the application of heat, in absence of air,  Moisture content some coal swells and leaves coherent residue.  Volatile matter content This property is called caking and the coal is  Fixed carbon called caking coal.  MM/Ash content Some caking coal residue possesses metallic  Chemical composition grayish luster and all physical and chemical (C,H,O,N,S,P, Fe etc.) properties of coke manufactured commercially  Particle size and porosity is called as coking coal.  Caking index A non caking coal leaves a powdery residue  Swelling index (not coherent) under above treatment.  Petrographic analysis and reflectance  All coking coals are caking but the reverse is not always true 14   Heating value Gross/High heating value (water vapor getting condensed after combustion) Useful/low heating value (determined by subtracting the heat of vaporization of the water from the higher heating value) Latent heat of vaporization of water: 2.26 MJ/kg  Moisture content http://www.uky. edu/KGS/coal/co al-analyses- moisture.php 15 Surface Moisture (water) adheres to the outside of a coal sample or particle. Inherent moisture (IM) : It is an integral part of the coal seam in its natural state, including water in pores but excluding that in macroscopically visible fractures Equilibrium moisture: It means the moisture as determined after equilibrating at 60% relative humidity (RH) and 40 ºC as per the provisions (relating to determination of equilibrated moisture at 60% RH and 40 ºC) of BIS 1350. Total moisture (TM) is the total moisture content (including SM) expressed as percentage of coal and determined on as-delivered basis. TM = IM + SM Residual moisture: It remains in coal after air-drying a sample and minor heating in a moisture oven to 10 to 15°C (depending on coal rank) above room temperature 16  Basis for reporting coal properties data and their conversion As received (AR) [compositions are measured after delivery of coal sample to a lab] Air dried (AD) [compositions are measured after air drying the coal sample] Dry basis (DB) [compositions are measured after drying (moisture free) the coal sample] Dry ash free (DAF) [ Compositions are expressed in % excluding the ash and moisture] Dry mineral matter free (DMMF) [Compositions are expressed in % excluding the mineral matter and moisture] Mineral matter generates ash after oxidation The value in other basis is more than that of AR 17  Conversion of as received basis to dry ash free basis  Proximate analysis as received basis Moisture : 1.11 %; Ash : 5.63 %; Volatile matter : 37.26 % Fixed carbon : 56.00 %  Proximate analysis on dry, ash free basis Moisture + Ash : 1.11 + 5.63 = 6.74% Fixed carbon : 56.0 x 100/(100-6.74) = 60.04 % or : 56.0/(37.26+56.00)*100=60.04% Volatile matter : 37.26 x 100/(100-6.74) = 39.95 % or : 37.26/(37.26+56.00)*100=39.95% 18  Caking index It gives idea about caking property of a coal sample. Normally caking index for coking coal should vary from 20-24 ; for bee-hive oven the minimum index should be 13 and maximum 24.  Swelling index It helps to test the coking property of coal. Swelling index varying between 2-5 is ideal for coke manufacturing. The high swelling coal is not charged for coke making as it would create unnecessary pressure on the side wall of the oven will also produce a coke porous structure.  Petrographic analysis and reflectance The coking coal should have a minimum of 60% virtrain (active constituents) and maximum of 40% Inertinite (nonreactive constituent). The ideal value of reflectance will be within 1.3 – 1.5. Generally the coking property develops in coal if its reflectance is between 0.9 – 1.3. Reflectance is the fraction of incident electromagnetic power that is reflected at an interface. 19   Pricing of coal The coal payments for indigenous collieries are being made on the basis of Equilibrated moisture (IM at 60 % RH and 40 ºC). Generally Indian coals are low in TM (6-10 %) and the high moisture in Indian coals is due to physical addition of SM during the process or mining, transfer or handling. On the other hand imported coals contain high TM as high as 25-40 % but most of it is in the form of IM and there is virtually no SM. Therefore the coals are absolutely dry to handle even though they contain high TM just like lignite. Imported coals do not present any difficulty in pre-combustion processing like crushing, transfer, etc. and the loadability of the generating units are not affected due to transfer and flow related issues outside the boilers. The drop in GCV (kcal/kg) of coal for 1 % increase in TM is given by, GCV(kcal/kg) = 6.1 + (0.01*GCV) 20  Coal for energy production : Some issues Indian coals are mainly bituminous / lignite:  Ash content (ranging from 35–50%)  High moisture content (4–20%)  Low sulfur content (0.2–0.7%), and  Low calorific values (between 10 - 20 MJ/kg, (much less than the normal range of 20 - 35 MJ/kg of imported coals) CO2 emissions and ash disposal (Ash generation from combustion of Indian coal is very high and needs to be disposed off in an environment friendly way) Hg (0.1 ppm in coal), Arsenic (1.4-71 ppm in coal) and Selenium emissions ( 3 ppm in coal) Ground water and surface water contamination because of mine drainage Social issues with inadequate compensation of affected communities 21 Thanks 22