AC
UNIT-4Fuel and Energy Q1) Define Fuels?A1) fuel is a material which can react with other substance to release energy in the form of heat energy, the energy is otherwise used to do work. Initially this concept was applied only to those materials that are able to produce chemical energy, but has now applied to other sources of heat energy like nuclear energy.A fuel is a substance that contains carbon and hydrogen undergoes combustion in presence of oxygen to gives large amount of energy. 
Fuel + O2 CO2 + H2O + Energy Q2) Explain Calorific Value and its Types? A2) Calorific value: Efficiency of combustible fuels can be measured in terms of their calorific value. It is the heat evolved on combustion of a unit quantity of fuel.Types of calorific value (Higher and lower)Higher Calorific ValueGross calorific value of a fuel can be defined as the total amount of heat obtained on complete combustion of unit mass of a solid or liquid fuel or unit volume of a gaseous fuel (S T P) and on cooling the products of combustion to 15-degree c. The gross calorific value is also called as higher calorific value. The G.V.C is of only theoretical importance because in actual practice we do not have any provision of cooling the products of combustion during combustion of fuel in an engine, furnace or any other fuel burning device. Lower Calorific Value:Net calorific value is defined as the amount of heat obtained practically on complete combustion of unit mass of solid or liquid fuel or unit mass of solid or liquid fuel or unit volume of a gaseous fuel at step and the products of combustion are allowed to escape with some heat N.C.V is also called as lower calorific value. Q3) Explain the Estimation of Calorific value through Bomb Calorimeter A3) Bomb CalorimeterThe gross calorific value of solid fuels and liquid fuels can be determined by bomb calorimeter. (If the liquid is volatile, then it is filled in a polythene capsule of negligible mass then used in experiment. Construction: A bomb colorimeter consists ofBomb pot Calorie meter Water and air jackets Accessories Pellet press Oxygen cylinder Bomb pot: -It is a cylindrical strong stainless-steel pot having a lid. the lid can be fitted air. Tight to bomb pot by screwing.There are two type of electrodes fitted through lid and there is an oxygen inlet valve as its center. One of these electrodes is provided with a ring to hold the crucible containing fuel. there is thin resistance wire tied to the electrodes in loop form and the loop touches the fuel. The weighed fuel is burnt in the bomb pot in the presence of high-pressure oxygen. Calorimeter: -There is a stainless steel or copper calorimeter in which the bomb pot is kept .it contains a known volume of water and the water is kept circulating around the bomb pot with the help of a stirrer. A Beckman thermometer or digital thermometer is kept in the water of calorimeter, which can record the rise in temperature of welter due to absorb in a heat generated. There are insulator stands between calorimeter and water jacket. Accessories: - There is a pellet press to convert the powder of solid fuel to pellet form. for a liquid fuel a capsule of negligible weight can be used. There is an oxygen cylinder with pressure gauge to fill oxygen in the bomb pot at the pressure of nearly 25 kg / cm². There is also a D.C battery of a about 6 volts to start combustion of fuel.
Fig: Bomb Caloriemeter Working: -Weigh the pellet of solid fuel or liquid capsule and keep it in the crucible. keep the crucible in the ring of the electrode. keep the resistance wire touching to the fuel. Add about 10 ml of distilled water at the bottom of bomb pot and fix the lid tightly to bomb by screwing. Fill the bomb with oxygen at the pressure about 25 kg / cm². Place the bomb in calorimeter add known volume of water in the calorimeter so that the bomb gets immersed in the water. Place the calorimeter in the water jacket over the plastic studs. keep the thermometer and stirrer in the water of calorimeter. Put the plastic cover on the and make electrical connections from battery to electrodes. Operate the stirrer for s minutes and note the initial temperature of water (t1° c). Pass the current for about 5 – 10 seconds to heat the wire so that the fuel catches fire. If the fuel contains S and N elements, they get converted to SO3 and N2O5. these gases get dissolved in the distilled water in bomb to form H2SO4 and HNO3 (along with liberation little heat). Note the maximum temperature reached. after that note the rate of fall of temperature per minute and the time taken for reaching to initial temp. are noted. Open the bomb pot and wash the contents at its bottom into a beaker to find out the amount of H2SO4 and HNO3 formed. Q4) Differentiate between proximate and Ultimate analysis? A4) The key difference between proximate and ultimate analysis of coal is that proximate analysis is the technique used to analyse the moisture content, ash content and fixed carbon of coal whereas ultimate analysis is the technique used to analyse the chemical composition of coal.The technique of proximate analysis involves the determination of the different compounds present in a mixture. Ultimate analysis, on the other hand, involves the determination of the number and types of different chemical elements present in a particular compound. Therefore, these two techniques are related to each other.Proximate analysis of coal is the process of determining the presence of different compounds and their amounts in coal. The technique of proximate analysis was developed by Henneberg and Stohmann (German scientists) in 1860. This analysis technique involves the partitioning of compounds into different categories depending on the chemical properties of these compounds. Mainly, there are six categories of compounds as moisture, ash, crude protein, crude lipid, crude fibre, and nitrogen-free extracts. In the process of proximate analysis of coal, the moisture content of coal, ash content of coal and the fixed carbon content of coal are determined.The ultimate analysis of coal is the process of determining different chemical elements present in coal. This technique allows us to get more comprehensive results compared to the proximate analysis process.In this analysis technique, we test moisture, ash, carbon, hydrogen, nitrogen, sulphur and oxygen content of the sample to determine the elemental composition of the coal sample. Therefore, each and every chemical element in the sample is analysed through chemical routes and then we can express the contents as percentages with respect to the total mass of the sample. Mostly, this analysis technique is useful in the coal and coke industry.Q5) What are Octane and Cetane numbers? A5) Octane and Cetane numbers Octane Number and Cetane Number are the standards to measure the tendency of fuel to ignite spontaneously. The performance of gasoline is measured by the Octane number on the other hand the cetane number measures the performance of diesel. The reason why petrol can’t be used in diesel engine and diesel can’t be used in a petrol engine is that when the fuel that has high octane number will have low cetane number and high cetane number fuel has low octane number. As per the Standard operating conditions the Octane number of a fuel defines the percentage of Iso-butene present in a mixture of Iso-octane and heptane. When used in a gasoline engine the Octane rating signifies the ability to resist auto ignition. As air and fuel are compressed together, gasoline tends to ignite a spark at the end of compression by a spark plug. If gasoline with low octane number is used it creates problems during ignition and tends to adapt to auto combustion easily due to excess of heat and pressure effects on the other hand, fuels that have high octane value takes more time to burn but provides maximum efficiency to the gasoline engine.Cetane is a type of chemical compound known as a Hexadecane. Cetane number is opposite to octane number, and measures how quickly the engine burns inside a compressed engine. Cetane compounds tend to ignite spontaneously under compression, therefore they are assigned as cetane number of hundred. Cetane number of a fuel can be defined as the percentage volume of n-hexadecane in the mixture of n-hexadecane and 1-methylnaphthalene which is responsible to provide ignition delay period. Q6) Define Doping Agents? A6) A dopant, also called a doping agent, is a trace of impurity element that is introduced into a chemical material to alter its original electrical or optical properties. The amount of dopant necessary to cause changes is typically very low. An antiknock agent is a gasoline additive that is used to reduce knocking that occurs in engines, the fuels octane number is increased by increasing the temperature and pressure at which auto-ignition occurs. As the gasoline engine developed, gasoline and the engine were harmonized to attain the best possible matching of characteristics. One of the important characteristics of gasoline is it is volatile in nature and antiknock quality, Volatility is a measure of the ease of vaporization of gasoline, Gasoline also helps to start engines in cold weather and to avoid vapour lock in hot weather conditions. AntioxidantsAn antioxidant are molecules that are able to inhibit the oxidation of other molecules. Oxidation involves a chemical reaction where electron or hydrogen from a substance moves to an oxidizing agent, the reaction produces free radicles that can initiate chain reactions.Anti-icingFuels posses’ properties that make it difficult to store them and transport fuels for longer periods, fuel additives are compounds that are soluble and affect the properties of fuel, one on the most important additive in Anti-icing. They are mainly fluid base known as monoethylene glycol and additives. The air temperature at very high altitudes drops to minus 60 and 70 degree. The additives that are used in anti-icing form useful tools that help prevent clogging of fuel transmission lines and freezing of storage tanks in cars and aircrafts.When aircrafts are at a high altitude, there is decrease in temperature during which the dissolved water turns into ice or superheated liquid. Extreme cold water becomes ice when they come in contact with pipes or filters eventually causing clogged paths.These additives have low solubility to fuel and high solubility towards water, this property becomes effective when the dissolved water is separated from the fuel additive quickly reach the water and dissolve into them thus preventing the freezing by reducing the freezing point of water.Q7) Explain the Fisher tropsch process? A7) Fischer-Tropsch ProcessIt is a process for the preparation of gasoline from a non-petroleum origin, the process involvesThe H2 and water gas are passes through the Fe2O2 tower where the H2S that is present as an impurity is removed. They are then passed through Fe2O2 and N2CO2 tower, here the organic sulfur is removed. The resulting gases are compressed to 5-25 atmps and passed through catalyst bed, these catalyst beds have a ratio200:0C, the catalyst bed is made up of cobalt: thoria: magnesia: kieselguhr earth present in the ratio 100:5:8:200. The gaseous mixture that is thus formed are sent through coolers, and a liquid resembling crude oil is obtained. The crude oil thus formed are passed through fractional distillation in a fractionating column, where gasoline and heavy oil is formed. Heavy oil is again used for cracking purposes The quality of the product formed depends on the Fischer tropic catalysts pressure and temperature.
Fig: Process over view Q8) Define Biodiesel? A8) The common plants used for biodiesel production is Soybean and oil palm. Microorganisms such as algae and bacteria also form sources of biodiesel, they seem promising but are economically difficult to develop Few species of algae have up to 40% lipids by weight that can be converted to synthetic petroleum or biodiesel.it is estimated that few algae and cyanobacteria yield between 10 and 100 times more fuel per unit area than plant-based biofuels.Is a fuel where the chemical energy stored in the fuel is converted into mechanical energy, any internal combustion engine, where air is compressed to very high temperatures to ignite the diesel fuel injected into the cylinder. The piston is actuated by combustion and expansion, the mechanical energy can to use to drive freight expansion, The tractors and marine vessels. A limited number of automobiles also are diesel-powered, as are some electric-power generator sets. Q9) Define CNG and its advantages and disadvantages? A9) CNG is mainly composed of ethane and is obtained by compressing natural gas, to less than 1% of the volume it occupies at Standard atmospheric pressure. It is stored and distributed in hard containers at a pressure of 20–25 MPa (2,900–3,600 psi), usually in spherical or cylindrical shapes. Advantages of CNG The octane number is 110, therefore it forms an excellent spark ignition engine fuels, due to the high-octane number flame speed is high and can operate with high compression rates. They have low engine emissions and aldehyde emission is lower than alcohols There are present naturally in abundance and can be produced from Coal It is environmentally friendly It is Safer and easier to store, and also reliable It’s less expensive than other fossil fuel energy sources It Minimizes dependency on foreign oil Disadvantages of CNGLow energy density shows poor engine performance. It has Low engine volumetric efficiency because of gaseous fuel It Needs Large storage tanks, which is a safety concern It has Inconsistent fuel properties Its Refuelling is a slow process It’s highly combustible It is Non-renewable energy source It emits some quantity of greenhouse gases Q10) Define Catalytic Cracking? A10) Catalytic CrackingIn this process large hydrocarbon molecules are broken into smaller and more useful molecules, the reaction takes place in the presence of a catalyst, that promotes breakage of large molecules in a way that forms gasoline as maximum yield. The feed in the catalytic reaction is gas oil or naphtha, the residue formed in the catalytic reaction is recycled back into the feed stream. This recycling is called recycling of extinction.ReactionThe first step is the cracking reaction, where the hydrocarbon feed combines with the catalyst at 900F and 482 OC, the cracking reaction takes place and coke is formed, the coke that is formed coats the catalyst preventing the catalyst from burning off and promote the cracking reaction. Renewal of the catalyst takes place by burning off the coke deposits from the catalyst surface during regeneration. The resulting hydrocarbons are separated using conventional fractionating equipment. AdvantagesCatalytic cracking is a controlled process The reaction takes place at low temperatures and pressure (3000C-400OC) and 1-5kg/cm2 The catalytic activity produces a higher yield of branched-chain, unsaturated and aromatic hydrocarbons Sulphur content of products is low Product yield and octane numbers are high.
Fuel + O2 CO2 + H2O + Energy Q2) Explain Calorific Value and its Types? A2) Calorific value: Efficiency of combustible fuels can be measured in terms of their calorific value. It is the heat evolved on combustion of a unit quantity of fuel.Types of calorific value (Higher and lower)Higher Calorific Value
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