Energy Part 2 Sources of Energy PDF

CHEM 1103: Chemistry for Engineers “Energy” Marcelino Dela Rama Tradio Jr., RCh, LPT, PhD-Chem Chemistry Analytical and Environmental Section (ChAnELS)...

CHEM 1103: Chemistry for Engineers “Energy” Marcelino Dela Rama Tradio Jr., RCh, LPT, PhD-Chem Chemistry Analytical and Environmental Section (ChAnELS) Department of Chemistry School of Arts and Sciences University of San Carlos Nasipit Talamban Cebu City 6000, Philippines “The capacity to learn is a gift. The ability to learn is a skill. The willingness to learn is a choice.” – Brian Herbert Sources of Energy According to the law of conservation of energy, energy can never be created nor destroyed (can never be consumed); it can only be change from one form to another. What is actually Consumed on a huge scale, however, are “resources or sources” that can be readily converted to a form of energy that is useful for doing work. Energy that is not used to perform work is either stored as potential energy for future use or transferred to the surroundings as heat. Sources of Energy Sources of Energy 1. Fuels 2. Nuclear reaction 3. Oxidation – Reduction Reaction (galvanic or voltaic cell) Sources of Energy FUELS Fuels are combustible substance, containing carbon as main constituents, which on proper burning gives large amount of heat, which can be used economically for domestic and industrial purposes. Sources of Energy FUELS Generally, Fuels react with other substances to release heat by way of chemical or nuclear energy Chemical Fuels – react with other proximate substances to release energy through the process of combustion Ø Divided both by their Physical Properties (as solid, liquid, or gas), and by how they occur (as a primary or natural fuel, or as a secondary or artificial fuel) Nuclear Fuels – substances that can release nuclear energy by fission or fusion Sources of Energy Combustion of FUELS During the process of combustion of fuel, the atom of carbon, hydrogen, etc. combine with oxygen with simultaneous liberation of heat at rapid rate. This energy is liberated due to the “rearrangement of valence electrons” in these atoms, resulting in the formation of compounds like CO2 and H2O. These compounds have less energy (heat content) as compared to reactants. Sources of Energy Classification of Chemical FUELS These can be classified on the basis of their occurrence and physical state on the basis of occurrence, fuels are classified as: 1. Primary Fuels: fuels which are occur in nature that can be extracted, captured, cleaned, or graded without any sort of energy conversion or transformation process. They can be renewable sources of energy (e.g. biomass, geothermal, hydroelectric, wind or solar ) or non renewable sources of energy (fossil fuels such as coal, crude oil or petroleum, and natural gas). 2. Secondary Fuels: they are derived from the primary fuels by further chemical processing such as coke, charcoal, kerosene, coal gas, producer gas, etc. They Sources of Energy Classification of Chemical FUELS On the basis of physical state, fuels are classified as: 1. Solid Fuels: woods, peat, lignite 2. Liquid Fuels: crude oil, Tar, Diesel, Petrol, kerosene 3. Gaseous Fuels: natural gas, coal gas Sources of Energy Characteristics of Good Chemical FUELS 1. Suitability 2. High Calorific Value 3. Ignition Temperature 4. Moisture Content 5. Non Combustible Matter Content 6. Velocity of combustion 7. Nature of the Products 8. Cost of fuel 9. Less smoke 10. Control of the process Chemical Fuels Chemical Fuels 1. Solid Fuels – materials that can be used as fuel to burn and release energy through combustion, which provide heat and light Wood : firewood, charcoal, woodchips, pellets, sawdust Charcoal: produced by heating wood in the absence of oxygen Biomass: natural plant materials such as wheat, straw, and other fibrous materials Peat: organic matter and decayed vegetation that can be burned when dry Coal: it comes from dead plants burned several million years Coke: high carbon material derived from coal Waste: include all types of waste as long as it does not contain toxic materials. Chemical Fuels Chemical Fuels 2. Liquid Fuels – mostly used to create mechanical energy from the gas generated when the liquid fuels burned. Fossil fuels account for the majority of liquid fuels Petroleum: most common type of liquid formed from dead plants, and animals Ø gasoline/petrol – produced by removing crude oil from petroleum and distilling it in refineries Ø Diesel – a mixture of aliphatic hydrocarbons that are extracted from petroleum and processed to reduce the sulfur level Ø Kerosene – extracted from petroleum Ø Liquefied petroleum gas (LPG) – mixture of propane and butane that are compressed at constant pressure Ø Biodiesel – diesel fuel based on vegetable oils or animal fat Ø Alcohols – include methanol, ethanol, and butanol Ø Liquefied hydrogen – commonly used as liquid rocket fuel Chemical Fuels Chemical Fuels Fractional distillation of crude oil Chemical Fuels Chemical Fuels Fractional distillation of crude oil Chemical Fuels Chemical Fuels 3. Gaseous Fuels – distributed through pipes from the point of origin of use, although some are liquefied for storage. Odorisers are often added to gaseous fuels so that they can be detected since, and an undetected build up of gas can lead to an explosion Natural gas – composed mainly of methane Coal gas – derived from coal Water gas – a mixture of carbon monoxide and hydrogen Syngas – synthetic gas consisting of hydrogen, carbon monoxide and carbon dioxide Biogas – a mixture of gases derived from organic matter breaking down in the absence of oxygen Blast Furnace Gas – derived from the manufacture of metallic iron in blast furnaces Chemical Fuels Analysis of Fuels In order to assess the quality of fuels (e.g. Coal), the following three types of analysis are made: 1. Proximate Analysis 2. Ultimate Analysis 3. Heating Value (HHV and LHV) Analysis Chemical Fuels Proximate Analysis Determines the moisture, ash, volatile matter and fixed carbon of the fuel (e.g. coal) It gives information about the practical utility of the fuels Chemical Fuels Proximate Analysis 1. Moisture Content Analysis: about 1 g of finely powdered air dried fuel sample is weighted in crucible. The crucible is placed in electric hot air oven, maintained at 105 – 110 ∘C. The crucible is allowed to remain in electric hot air oven for about one hour and then taken out, cooled in a dessicator and weighed. Loss in weight is reported as percent moisture. !"## %& '(%)*+ percentage of moisture = '(%)*+ ", ,-(. +/0(& x 100 Chemical Fuels Proximate Analysis 2. Volatile Matter Analysis: It is determined by heating a known weight of moisture- free fuel sample in a covered platinum crucible with lid at 950 + 20 ∘C for 7 minutes in an electrical furnace. The crucible is cooled in a dessicator and weighed. Loss in weight is reported as volatile matter !"## %& '(%)*+ percentage of volatile matter = '(%)*+ ", ,-(. +/0(& x 100 Chemical Fuels Proximate Analysis 3. Ash Analysis: fuel contains inorganic mineral substances (e.g. coal) which are converted into ash by chemical reactions during the combustion of fuel. Ash usually consists of silica, alumina, iron oxide, and small quantities of lime, magnesia, etc. Ash content is determined by heating the residue left after the removal of volatile matter at 700 + 50 ∘C for ½ an hour without covering. The crucible is taken out, cooled first in air, then inside a dessicator and weighed. The residue is reported as ash on percentage basis '(%)*+ ", /#*.(,+ percentage of ash = x 100 '(%)*+ ", ,-(. +/0(& Chemical Fuels Proximate Analysis 4. Fixed Carbon: the percentage fixed carbon is given by: percentage of fixed carbon = 100 – [% of moisture + volatile matter + ash] Chemical Fuels Ultimate Analysis It is carried out to ascertain the composition of fuels It includes the estimation of carbon, hydrogen, sulfur, nitrogen, and oxygen Chemical Fuels Ultimate Analysis 1. Carbon and Hydrogen: a known amount of fuel is taken in a combustion tube and is burnt in excess of pure oxygen. Carbon and hydrogen of fuel are converted in CO2 and H2O respectively. These gaseous products are absorbed respectively in KOH and CaCl2 tubes of known weight. Chemical Fuels Ultimate Analysis 1. Carbon and Hydrogen Chemical Fuels Ultimate Analysis 2. Nitrogen: Nitrogen present in fuel sample can be estimated by Kjeldahl’s method Chemical Fuels Ultimate Analysis 2. Nitrogen: Nitrogen present in fuel sample can be estimated by Kjeldahl’s method Chemical Fuels Ultimate Analysis 3. Sulfur: Sulfur is determined conveniently from the bomb washing from combustion of a known mass of fuel in bomb calorimeter experiment. The washing containing sulfur in the form of sulfate which is precipitate as BaSO4. Chemical Fuels Ultimate Analysis 4. Oxygen = 100 – % of (C + H + N + Ash) Chemical Fuels Heating Value Analysis Heating of calorific values of fuels is defined as the total heat produced when a unit mass of fuel (e.g. volume or mass of fuel) is completely burnt with pure oxygen. Measured using bomb calorimetry when water is present in the flue gases, the heating value is said “higher heating value (HHV)” If the water is present in the liquid form it is said “lower heating value (LHV)” if water is present in the vapor form; i.e. a quantity of heat equal to the latent heat of vaporization of water Chemical Fuels Heating Value Analysis Higher Heating Value (HHV) of Fuel Also known as Gross Calorific Value (GCV) Defined as the amount of heat released during the combustion of a specified quantity (initially at 25 ∘C It is determined by bringing all the products of combustion back to original pre-combustion temperature (25 ∘C), and in particular condensing any vapor produced Chemical Fuels Heating Value Analysis Lower Heating Value (LHV) of Fuel Also known as net calorific value (NCV) Determined by subtracting the heat of vaporization of the water vapor from higher heating value This treat any water formed as vapor The energy required to vaporize the water therefore is not released as a heat A common method of relating HHV to LHV is: HV = LHV + Hv (nwater out/nfuel) Where Hv = heat of vaporization nwater out = number of moles of water vaporized nfuel = number of moles of fuel combusted END