Energy Sources - Fuel & Energy Technologies Eng. PDF

Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. Thus the net volume of air required is: Constituent...

Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. Thus the net volume of air required is: Constituent The air required CO 0.0095*2.39 = 0.02 C2H4 0.0066*14.33 = 0.09 C2H6 0.0355*16.74 = 0.59 H 0.2195* = 0.53 CH4 0.7215*9.57 = 6.90 Total The net air per cubic feet = 8.13 Stoichiometric combustion It is the theoretical combustion of every drop of fuel when mixed with the correct amount of air (Oxygen) to yield exhaust products of only CO2 and H2O. Complete oxidation of simple hydrocarbon fuels forms carbon dioxide (CO2) from all the carbon and water (H2O) from the hydrogen, that is, for a hydrocarbon fuel with the general composition CnHm, However, Air is composed of oxygen, nitrogen, and small amounts of carbon dioxide, argon, and other trace species. Since the vast majority of the diluent in air is nitrogen, for our purposes it is perfectly reasonable to consider air as a mixture of 20.9% (mole basis) O2 and 79.1 % (mole basis) N2. Thus for every mole of oxygen required for combustion 3.78 mol of nitrogen must be introduced as well. Although nitrogen may not significantly alter the oxygen balance, it does have a major impact on the thermodynamics, chemical kinetics, and formation of pollutants in combustion systems. For this reason, it is useful to carry the "inert" species along in the combustion calculations. The stoichiometric relation for complete oxidation of a hydrocarbon fuel. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. Combustion Reactions: Combustion: -the rapid reaction of a fuel with oxygen- is perhaps more important than any other class of industrial chemical reactions, despite the fact that combustion products (CO2, H2O, and possibly CO and SO2) are worth much less than the fuels burned to obtain them. The significance of these reactions lies in the tremendous quantities of energy they release energy that is used to boil water to produce steam, which is then used to drive the turbines that generate most of the world’s electrical power. The job of designing power generation equipment usually falls to mechanical engineers, but the analysis of combustion reactions and reactors and the abatement and control of environmental pollution caused by combustion products like CO, CO 2, and SO2 are problems with which chemical engineers are heavily involved. In the sections that follow, we introduce terminology commonly used in the analysis of combustion reactors and discuss material balance calculations for such reactors. Combustion Chemistry Most of the fuel used in power plant combustion furnaces is either coal (carbon, some hydrogen and sulfur, and various noncombustible materials), fuel oil (mostly high molecular weight hydrocarbons, some sulfur), gaseous fuel (such as natural gas, which is primarily methane), or liquefied petroleum gas, which is usually propane and/or butane. When a fuel is burned, carbon in the fuel reacts to form either CO2 or CO, hydrogen forms H2O, and sulfur forms SO2. At temperatures greater than approximately 1800 ᵒC, some of the nitrogen in the air reacts to form nitric acid (NO). A combustion reaction in which CO is formed from a hydrocarbon is referred to as partial combustion or incomplete combustion of the hydrocarbon. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. # Examples: For obvious economic reasons, air is the source of oxygen in most combustion reactors. Dry air has the composition of N2, O2, Ar, co2, H2, He, Ne, Kr, Xe. In most combustion calculations, it is acceptable to simplify this composition to 78.1% N2, 20.9% O2. The term composition on a wet basis is commonly used to denote the component mole fractions of a gas that contains water, and composition on a dry basis signifies the component mole fractions of the same gas without the water. For example, a gas that contains 33.3 mole% CO2, 33.3% N2, and 33.3% H2O (wet basis) contains 50% CO2 and 50% N2 on a dry basis. The product gas that leaves a combustion furnace is referred to as the stack gas or flue gas. When the flow rate of a gas in a stack is measured, it is the total flow rate of the gas including water; on the other hand, common techniques for analyzing stack gases provide compositions on a dry basis. You must therefore be able to convert a composition on a dry basis to its corresponding composition on a wet basis before writing material balances on the combustion reactor. The procedure to convert a composition from one basis to another is similar to the one used to convert mass fractions to mole fractions and vice versa. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 1.11 Theoretical and Excess Air If two reactants participate in a reaction and one is considerably more expensive than the other is, the usual practice is to feed the less expensive reactant in excess of the valuable one. This has the effect of increasing the conversion of the valuable reactant at the expense of the cost of the excess reactant and additional pumping costs. The extreme case of an inexpensive reactant is air, which is free. Combustion reactions are therefore invariably run with more air than is needed to supply oxygen in stoichiometric proportion to the fuel. The following terms are commonly used to describe the quantities of fuel and air fed to a reactor. Theoretical Oxygen: the moles (batch) or molar flow rate (continuous) of O2 needed for complete combustion of all the fuel fed to the reactor, assuming that all carbon in the fuel is oxidized to CO2 and all the hydrogen is oxidized to H2O. Theoretical Air: the quantity of air that contains the theoretical oxygen. Excess Air: the amount by which the air fed to the reactor exceeds the theoretical air. If you know the fuel feed rate and the stoichiometric equation for complete combustion of the fuel, you can calculate the theoretical O2 and air feed rates. If in addition you know the actual feed rate of air, you can calculate the percent excess air from the Equation above. It is also easy to calculate the air feed rate from the theoretical air and a given value of the percentage excess: if 50% excess air is supplied, for example, then: #Homework One hundred mol/h of butane (C4H10) and 5000 mol/h of air are fed into a combustion reactor. Calculate the percent excess air. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 1.12 Manufactured Solid Fuels and their Characteristics The manufactured solid fuels include, charcoal, coke, briquettes, etc. They are obtained from the natural fuels, like wood, coal, etc. 1. Charcoal and its Characteristics Charcoal is a produce derived from destructive distillation of wood, being left in the shape of solid residue. Charcoal burns rapidly with a clear flame, producing no smoke and developing heat about 6,050 cal/kg. Charcoal is used for cooking purposes in most of the countries, such as India. 2. Coke and its Characteristics It is obtained from destructive distillation of coal, being left in the shape of solid residue. Coke can be classified into two categories: soft coke and hard coke. Soft coke is obtained as the solid residue from the destructive distillation of coal in the temperature range of 600-650⁰C. It contains 5 to 10% volatile matter. It burns without smoke. It is extensively used as domestic fuel. Hard coke is obtained as solid residue from the destructive distillation of coal in the temperature range of 1200-1400⁰C. It burns with smoke and is a useful fuel for metallurgical process. 3. Briquettes and their Characteristics The term briquettes are used in respect of the dust, culm, slack and other small size waste remains of lignite, peat, coke, etc. Good briquettes should be quite hard and as little friable as possible. They must withstand the hazards of weather, and must be suitable for storing and general handling in use. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 4. Bagasse and its Characteristics Bagasse is the residue of sugarcane, left as waste in the sugar mill after extraction of sugar juice. In weight, it is about 20% of virgin cane. By nature, it is fibrous fuel, which can be compared to wood. It contains 35-45% fiber, 7-10% sucrose and other combustible, and 45-55% moisture, and possesses an average calorific value of 2200 cal/kg. On moisture-fiber basis the average composition is: C = 45%, H2 = 6%, O2 = 46% and Ash = 3% Bagasse is the main fuel satisfying the needs of sugar industries and efforts are being made for decreasing the percent moisture of bagasse with the help of flue-gas waste heat dryers. Bagasse is a quick burning fuel with good efficiency. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 2.1 Hydrogen energy Introduction Hydrogen energy involves the use of hydrogen and/or hydrogen-containing compounds to generate energy to be supplied to all practical uses needed with high energy efficiency, overwhelming environmental and social benefits, as well as economic competitiveness. The world is presently experimenting the dawning of hydrogen energy in all sectors that includes energy production, storage, and distribution; electricity, heat, and cooling for buildings and households; the industry; transportation; and the fabrication of feedstock. Energy efficiency and sustainability are two important factors driving the transition from the present fossil fuel– based economy to a circular economy, that is, a renewable circular sustainable fuel utilization cycle that will characterize the highly efficient engineering and the energy technological choices of the 21st century. Hydrogen energy development continues to be an important research, development, and demonstration pathway for major economies around the world. 2.2 Methods of hydrogen generation There are four main sources for the commercial production of hydrogen: natural gas, oil, coal, and electrolysis; which account for 48%, 30%, 18% and 4% of the world's hydrogen production respectively. Fossil fuels are the dominant source of industrial hydrogen. Carbon dioxide can be separated from natural gas with a 70–85% efficiency for hydrogen production and from other hydrocarbons to varying degrees of efficiency. Specifically, bulk hydrogen is usually produced by the steam reforming of methane or natural gas. 2.2.1 Steam reforming (SMR) Steam reforming is a hydrogen production process from natural gas. This method is currently the cheapest source of industrial hydrogen. The process consists of heating the gas to between 700–1100 °C in the presence of steam and a nickel catalyst. The resulting endothermic reaction breaks up the methane molecules and forms carbon monoxide CO and hydrogen H2. The carbon monoxide gas can then be passed with steam over iron oxide or other oxides and undergo a water gas shift reaction to obtain further quantities of H2. The downside to this process is that its major byproducts are CO, CO 2 and other greenhouse gases. Depending on the quality of the feedstock (natural gas, rich gases, naphtha, etc.), one ton of hydrogen produced will also produce 9 to 12 tons of CO2, a greenhouse gas that may be captured. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. For this process high temperature (700–1100 °C) steam (H2O) reacts with methane (CH4) in an endothermic reaction to yield syngas. 𝑪𝑯𝟒 + 𝑯𝟐 𝑶 → 𝑪𝑶 + 𝟑 𝑯𝟐 In a second stage, additional hydrogen is generated through the lower-temperature, exothermic, water gas shift reaction, performed at about 360 °C: 𝑪𝑶 + 𝑯𝟐 𝑶 → 𝑪𝑶𝟐 + 𝑯𝟐 Essentially, the oxygen (O) atom is stripped from the additional water (steam) to oxidize CO to CO 2. This oxidation also provides energy to maintain the reaction. Additional heat required to drive the process is generally supplied by burning some portion of the methane. 2.2.2 Methane pyrolysis The thermal decomposition of methane, which is the main component of natural gas, is a suitable technology to provide clean hydrogen when renewable power is not sufficient to fulfill the hydrogen demand. This process is usually referred to as methane pyrolysis. Methane pyrolysis splits CH4 directly into its components, i.e., hydrogen and carbon. Unlike other technologies that use fossil resources, such as coal gasification or steam methane reforming, the greatest benefit of methane pyrolysis is the production of CO2‐free hydrogen. Solid carbon is the only by‐product resulting from the thermal decomposition of methane, so neither a CO2 separation step nor its subsequent storage is needed. The process is conducted at higher temperatures (1340 K, 1065 °C or 1950 °F). CH4(g) → C(s) + 2 H2(g) ΔH° = 74 kJ/mol The industrial quality solid carbon may be sold as manufacturing feedstock or landfilled. 2.2.3 Partial oxidation Partial oxidation (POX), or gasification, is a chemical reaction that occurs when a mixture of a hydrocarbon feedstock and a sub-stoichiometric amount of pure oxygen (O2) are reacted together, producing a syngas stream with a typical H2/CO ratio range of 1.6 to 1.8. The hydrocarbon feedstock is fed into the POX reactor (see figure below), where the carbon in the feedstock is reacted with oxygen in an exothermic reaction, forming carbon monoxide (CO). Since there is a lack of oxygen, the reaction does not complete to form carbon dioxide (CO2). C + ½ O2 → CO Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. Typically, all or a portion of the CO then flows to a water shift reactor, where the CO reacts with steam, forming a mixture of CO and H2: There are two primary types of POX systems: 1) Thermal POX (TPOX), which occurs at >2200°F and is used with high sulfur feedstocks. 2) Catalytic POX (CPOX), which uses low sulfur feedstocks with a sulfur-sensitive catalyst, allowing the reactions to occur in a lower temperature range of 1475-1650°F, which reduces energy consumption. The chemical reaction takes the general form: 𝑪𝒏 𝑯𝒎 + 𝒏⁄𝟐 𝑶𝟐 → 𝒏 𝑪𝑶 + 𝒎⁄𝟐 𝑯𝟐 Idealized examples for heating oil and coal, assuming compositions C12H24 and C24H12 respectively, are as follows: C12H24 + 6 O2 → 12 CO + 12 H2 C24H12 + 12 O2 → 24 CO + 6 H2 Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 2.2.4 Plasma reforming The plasma reforming method can be used in the production of hydrogen and hydrogen-rich gases from a variety of fuels. It is for the production of hydrogen and carbon black from liquid hydrocarbons (CnHm). Of the available energy of the feed, approximately 48% is contained in the hydrogen, 40% is contained in activated carbon and 10% in superheated steam. CO2 is not produced in the process. A variation of this process is presented in 2009 using plasma arc waste disposal technology for the production of hydrogen, heat and carbon from methane and natural gas in a plasma converter. 2.2.5 Coal Gasification Chemically, coal is a complex and highly variable substance that can be converted into a variety of products. The gasification of coal is one method that can produce power, liquid fuels, chemicals, and hydrogen. Specifically, hydrogen is produced by first reacting coal with oxygen and steam under high pressures and temperatures to form synthesis gas, a mixture consisting primarily of carbon monoxide and hydrogen. Coal gasification reaction (unbalanced): 𝑪𝑯𝟎.𝟖 + 𝑶𝟐 + 𝑯𝟐 𝑶 → 𝑪𝑶 + 𝑪𝑶 𝟐 + 𝑯 𝟐 + 𝒐𝒕𝒉𝒆𝒓 𝒔𝒑𝒆𝒄𝒊𝒆𝒔 After the impurities are removed from the synthesis gas, the carbon monoxide in the gas mixture is reacted with steam through the water-gas shift reaction to produce additional hydrogen and carbon dioxide. Hydrogen is removed by a separation system, and the highly concentrated carbon dioxide stream can subsequently be captured and stored. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 2.2.6 From water An electric current splits water into its constituent parts. If renewable energy is used, the gas has a zero-carbon footprint, and is known as green hydrogen. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. 2.3 Hydrogen storage Hydrogen can be stored physically as either a gas or a liquid. Storage of hydrogen as a gas typically requires high-pressure tanks (350–700 bar [5,000–10,000 psi] tank pressure). Storage of hydrogen as a liquid requires cryogenic temperatures because the boiling point of hydrogen at one atmosphere pressure is −252.8°C. Hydrogen can also be stored on the surfaces of solids (by adsorption) or within solids (by absorption). In addition to separate compression or cooling, the two storage methods can be combined. The cooled hydrogen is then compressed, which results in a further development of hydrogen storage for mobility purposes. The first field installations are already in operation. The advantage of cold or cryogenic compression is a higher energy density in comparison to compressed hydrogen. However, cooling requires an additional energy input. Currently it takes in the region of 9 to 12 % of the final energy made available in the form of H2 to compress hydrogen from 1 to 350 or 700 bar. By contrast, the energy input for liquefaction (cooling) is much higher, currently around 30 %. The energy input is subject to large spreads, depending on the method, quantity and external conditions. Work is currently in progress to find more economic methods with a significantly lower energy input. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. Materials-based H2 storage An alternative to physical storage methods is provided by hydrogen storage in solids and liquids and on surfaces. Most of these storage methods are still in development, however. Moreover, the storage densities that have been achieved are still not adequate, the cost and time involved in charging and discharging hydrogen are too high, and/or the process costs are too expensive. Materials-based hydrogen storage media can be divided into three classes: first, hydride storage systems; second, liquid hydrogen carriers; and third, surface storage systems, which take up hydrogen by adsorption, i.e. attachment to the surface. Hydride storage systems In metal hydride storage systems, the hydrogen forms interstitial compounds with metals. Here molecular hydrogen is first adsorbed on the metal surface and then incorporated in elemental form (H) into the metallic lattice with heat output and released again with heat input. Metal hydrides are based on elemental metals such as palladium, magnesium and lanthanum, intermetallic compounds, light metals such as aluminum, or certain alloys. Palla-dium, for example, can absorb a hydrogen gas volume up to 900 times its own volume. Liquid organic hydrogen carriers Liquid organic hydrogen carriers represent another option for binding hydrogen chemically. They are chemical compounds with high hydrogen absorption capacities. They currently include, in particular, the carbazole derivative N-ethylcarbazole, but also toluene Surface storage systems (sorbents) Finally, hydrogen can be stored as a sorbate by attachment (adsorption) on materials with high specific surface areas. Such sorption materials include, among others, microporous organometallic framework compounds (metal-organic frameworks (MOFs)), microporous crystalline aluminosilicates (zeolites) or microscopically small carbon nanotubes. Adsorption materials in powder form can achieve high volumetric storage densities. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. Biomass energy The term biomass encompasses a large number of materials of an extremely heterogeneous nature. We can state that everything that has an organic matrix is a biomass. Plastics and fossil materials have been excluded, even though they belong to the family of carbon compounds, because they do not have anything in common with the characterization of the organic materials discussed here. In scientific terms, the word biomass includes every kind of material of biological origin; it is so linked to carbon chemistry which directly or indirectly derives from the chlorophyllian photosynthesis. The biomass is the most sophisticated storage of solar energy. In fact, through the photosynthesis process vegetables are able to convert the radiant energy into chemical energy and to stock it as complex molecules with high energy content. For this reason, the biomass is considered renewable and unexhaustive, if appropriately used as a resource; that is, if the use tax of the same does not exceed the regeneration capacity of the vegetable forms. The biomass is also an energy source that considers as neutral the aim of the greenhouse gas emissions increment. In fact, vegetables, through photosynthesis, contribute to the subtraction of atmospheric carbon oxide and carbon fixation in the textures (a total of 2 × 1011 tons of carbon are fixed in a year, with an energy content of the order of 70 × 103 MTep, which is equivalent to ten times the world’s energy requirements). The quantity of carbon oxide released during the decomposition of biomasses, if it happens both naturally and through energy conversion processes (even if it is through combustion), is equivalent to that absorbed during the growth of the same biomass. Biogas naturally occurring gas that is generated by the breakdown of organic matter by anaerobic bacteria and is used in energy production. Biogas differs from natural gas in that it is a renewable energy source produced biologically through anaerobic digestion rather than a fossil fuel produced by geological processes. Biogas is primarily composed of methane gas, carbon dioxide, and trace amounts of nitrogen, hydrogen, and carbon monoxide. It occurs naturally in compost heaps, as swamp gas, and as a result of enteric fermentation in cattle and other Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. ruminants. Biogas can also be produced in anaerobic digesters from plant or animal waste or collected from landfills. It is burned to generate heat or used in combustion engines to produce electricity. The use of biogas is a green technology with environmental benefits. Biogas technology enables the effective use of accumulated animal waste from food production and of municipal solid waste from urbanization. The conversion of organic waste into biogas reduces production of the greenhouse gas methane, as efficient combustion replaces methane with carbon dioxide. Given that methane is nearly 21 times more effective in trapping heat in the atmosphere than carbon dioxide, biogas combustion results in a net reduction in greenhouse gas emissions. Additionally, biogas production on farms can reduce the odours, insects, and pathogens associated with traditional manure stockpiles. Animal and plant wastes can be used to produce biogas. They are processed in anaerobic digesters as a liquid or as a slurry mixed with water. Anaerobic digesters are generally composed of a feedstock source holder, a digestion tank, a biogas recovery unit, and heat exchangers to maintain the temperature necessary for bacterial digestion. Small-scale household digesters containing as little as 757 litres (200 gallons) can be used to provide cooking fuel or electric lighting in rural homes. Millions of homes in less-developed regions, including China and parts of Africa, are estimated to use household digesters as a renewable energy source. BIOGAS UTILIZATION Biogas systems enable the recovery and productive use of methane to generate renewable energy from the decomposition of organic materials, reducing direct emissions into the atmosphere and reducing GHGs by replacing fossil fuels (e.g., coal, natural gas) used for traditional energy generation. Biogas from anaerobic digesters is utilized in many situations where operations produce a significant organic waste stream. The biogas can be utilized from the following sources: – Agriculture: In agriculture, animal and crop wastes are typically used as a feedstock for anaerobic digesters. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department Mr. Hesham J. alnoor 3RD YEAR DEP.: Fuel & Energy Technologies Eng. – Industrial: Organic waste generated by industrial processes, particularly waste from the food processing industry, can be used as a feedstock for an anaerobic digester. – Wastewater treatment plants (WWTP): Wastewater treatment facilities employ anaerobic digesters to break down sewage sludge and eliminate pathogens in wastewater. Often, biogas is captured from digesters and used to heat nearby facilities. – Households: The biogas can be used as a clean source of cooking fuel while the slurry from the digester is a very good fertilizer. Biodiesel Made from an increasingly diverse mix of resources such as recycled cooking oil, soybean oil and animal fats, biodiesel is a renewable, clean-burning diesel replacement that can be used in existing diesel engines without modification. It is the nation’s first domestically produced, commercially available advanced biofuel. Producing Biodiesel Biodiesel is made through a chemical process called transesterification whereby the glycerin is separated from the fat or vegetable oil. The process leaves behind two products – methyl esters and glycerin. Methyl esters is the chemical name for biodiesel and glycerin is used in a variety of products, including soap. Biodiesel production spans across the US and has grown to more than 125 plants with the capacity to produce 3 billion gallons. In 2018, the US biodiesel industry produced 2.6 billion gallons of biodiesel. Production isn’t only about gallons produced, but also about the economic benefits to the US. The biodiesel industry supports nearly 60,000 jobs and generates billions of dollars in GDP, household income and tax revenues. Address: Southern Technical University – Engineering Technical College/Basrah – Fuel and Energy Department