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Wind energy system with different examples.pptx
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- 2. Intro • Wind energyis a form of solar energy. Because it powers the winds used to generate wind power. • Wind is caused due to absorption of solar energy on the earth surface and rotation of earth about its own axis and around the sun. • Because of this alternate heating and cooling occurs and difference in pressure is obtained and the air movement is caused. • Wind energy describes the process by which wind is used to generate electricity. • Wind turbines convert the kinetic energy in the wind into mechanical power. A generator can convert mechanical power into electricity.
- 3. Wind energy conversion •When the wind strikes the rotor blades, blades start rotating. • The turbine rotor is connected to a high-speed gear box. Gearbox transforms the rotor rotation from low speed to high speed. The high-speed shaft from the gearbox is coupled with the rotor of the generator and hence the electrical generator runs at a higher speed. An exciter is needed to give the required excitation to the magnetic coil of the generator field system so that it can generate the required electricity.
- 5. Different parts ofWind Turbine
- 6. Wind speed • Theamount of energy in the wind varies with the cube of the wind speed, in other words, if the wind speed doubles, there is eight times more energy in the wind (23 = 2*2*2=8). • Small changes in wind speed have a large impact on the amount of power available in the wind.
- 7. Wind power density •The more dense the air, the more energy received by the turbine. Air density varies with elevation and temperature. Air is less dense at higher elevations than at sea level, and warm air is less dense than cold air. All else being equal, turbines will produce more power at lower elevations and in locations with cooler average temperatures.
- 8. Swept area ofthe turbine • The larger the swept area (the size of the area through which the rotor spins), the more power the turbine can capture from the wind. Since swept area is , where r = radius of the rotor, a small increase in blade length results in a larger increase in the power available to the turbine.
- 9. Efficiency Limit ForWind Energy Conversion • A German physicist Albert Betz has calculated & defined the efficiency limit for wind turbine. This theory is called Betz limit. As per this theorem, no wind turbine could convert more than 59.3% of the kinetic energy of the wind into mechanical energy turning a rotor. It is the theoretical maximum efficiency of any wind turbine. • In reality, turbines cannot reach the Betz limit, and common efficiencies are in the 25-45% range. Efficiency= 𝐸𝑙𝑒𝑐𝑡𝑟𝑖𝑐𝑎𝑙𝑝𝑜𝑤𝑒𝑟𝑡𝑟𝑎𝑛𝑠𝑓𝑜𝑟𝑚𝑒𝑑𝑏𝑦𝑤𝑖𝑛𝑑𝑡𝑢𝑟𝑏𝑖𝑛𝑒 𝑃𝑜𝑤𝑒𝑟𝑎𝑣𝑎𝑖𝑙𝑎𝑏𝑙𝑒𝑖𝑛 h 𝑡 𝑒𝑤𝑖𝑛𝑑
- 10. Types Of Converters •There are two types of wind turbines. One is fixed speed wind turbine and other is variable speed wind turbine. Variable speed wind turbines can operate with two types of power converters. • Partial-scale power converter • Full scale power converter
- 11. Partial-scale power converter •Doubly fed induction generator (DFIG) is adopted with partial scale power converter for variable speed controlled wind turbine. • This converter performs reactive power compensation and smooth grid interconnection. • Slip rings and protection schemes are used in case of grid faults.
- 12. Advantages of PartialScale Converter Cost Efficiency: • Since the converter is rated at only ~30% of generator capacity, it is smaller, lighter, and cheaper. Lower Losses: • Less power is processed electronically, leading to reduced conversion losses. Efficient Control: • Still allows for variable speed operation and reactive power control.
- 13. Limitations of Partial-ScaleConverters • Limited ability to handle grid faults or ride-through requirements, compared to full-scale converter systems. • Cannot completely decouple generator from grid during disturbances. • Less effective in weak grid scenarios.
- 14. Full scale powerconverter • The generator used for full rated power converter can be synchronous/asynchronous generators. • Elimination of slip rings , full power , speed controllability are the main advantages compared with DFIG concept. • There will be high power loss and switching loss in this converter.
- 15. Advantages of Full-ScalePower Converters • Full Control Over Power Flow – Frequency, voltage, phase, and power quality can be controlled independently of the grid. • Low-Speed Operation – Ideal for direct-drive turbines without gearbox (reduces maintenance). • Ride-Through Capability – Handles grid faults, voltage dips, and frequency disturbances better. • Better Grid Code Compliance – Meets modern grid connection standards worldwide.
- 16. Limitations of Full-ScalePower Converters Higher Cost – Converter must be rated for 100% of turbine capacity, making it more expensive. Higher Losses – Since all power passes through the converter, conversion losses can be higher than in partial-scale systems.
- 17. Aerodynamics of WindRotors • Aerodynamics of wind rotors refers to the principles of airflow and forces acting on the blades (rotors) of a wind turbine that allow it to extract energy from the wind and convert it into mechanical energy, which is then transformed into electrical energy. • Understanding the aerodynamics is essential for maximizing efficiency, ensuring stability, and designing blades that can capture the most wind energy. Basic Principle • Wind turbines work on the principle of aerodynamic lift and drag, similar to an aircraft wing. When wind flows over the blade: • The shape of the blade (airfoil) causes a pressure difference. • The wind moves faster over the curved side of the blade (top) than the flat side (bottom). • This creates lower pressure on the upper surface, producing lift. • The lift force causes the blades to rotate.
- 18. Aerodynamic Forces ona Wind Rotor Lift (L) • Acts perpendicular to the wind direction. • Generated due to pressure difference on airfoil surfaces. • Helps in rotating the rotor blades. Drag (D) • Acts parallel to the wind direction. • It resists the motion of the blade. • Should be minimized for efficient performance. Maximize Lift-to-Drag ratio (L/D) for better efficiency.
- 19. Airfoil Design ofRotor Blades Wind turbine blades are shaped like airfoils, with: • Curved upper surface • Flatter lower surface • Twisted blade structure to maintain a favorable angle of attack along the length of the blade This design ensures: • Uniform power extraction along the blade • Prevention of stalling at higher wind speeds Angle of Attack (α) •It is the angle between the incoming wind and the chord line of the blade. •Small angles generate high lift with low drag. •Too high angle → stall occurs → lift drops → turbine performance reduces
- 20. Types of WindRotors Based on Aerodynamics • Horizontal Axis Wind Turbines (HAWT) •Rotor axis is parallel to the wind. •Lift-based design. •Higher efficiency, used in modern wind farms. •Needs yaw mechanism to face the wind.
- 21. Aerodynamics Of WindRotors • The primary application of wind turbines is to generate energy using the wind. • Hence, the aerodynamics is a very important aspect of wind turbines. Like most machines, there are many different types of wind turbines, all of them based on different energy extraction concepts. • Though the details of the aerodynamics depend very much on the topology, some fundamental concepts apply to all turbines. • Every topology has a maximum power for a given flow, and some topologies are better than others.
- 22. • The mostcommon topology is the horizontal-axis wind turbine. It is a lift-based wind turbine with very good performance. • Accordingly, it is a popular choice for commercial applications and much research has been applied to this turbine. • Despite being a popular lift-based alternative in the latter part of the 20th century, the Darrieus wind turbine is rarely used today. • The Savonius wind turbine is the most common drag type turbine. • Despite its low efficiency, it remains in use because of its robustness and simplicity to build and maintain.
- 23. Power ~ Speedcharacteristics of wind turbines • Here we have taken a Variable Speed Wind Turbine Generator (VSWTG). • We assume that the WTG consists of a wind turbine connected to a generator via a gearbox or direct-drive generator. • The output of the generator is connected to the utility via a power converter.
- 24. • Figure showsthe power curve of the VSWTG. Because the aerodynamic efficiency of a wind turbine is maximized at a specified tip-speed ratio, it is controlled so that it operates at that specific tip-speed ratio. This condition can be achieved when the ratio of rotor speed to wind speed is constant. • Two curves are shown in Figure 3. Below rated speed, the curves coincide. Above rated speed, however, the curves deviate. The thick line represents a controller that maintains constant power above rated speed; thus, above the rated speed, the torque is inversely proportional to the rotor speed. • The thin line represents a controller that maintains a constant torque above rated speed, so the power increases in proportion with the speed. • The constant torque capability above rated speed can better prevent the wind turbine from reaching runaway condition.
- 25. Torque ~ speedcharacteristics of wind turbines
- 26. Wind Turbine ControlSystem • A wind turbine is a revolving machine that converts the kinetic energy from the wind into mechanical energy. This mechanical energy is then converted into electricity that is sent to a power grid. • The turbine components responsible for these energy conversions are the rotor and the generator. The rotor is the area of the turbine that consists of both the turbine hub and blades. • As wind strikes the turbine’s blades, the hub rotates due to aerodynamic forces. This rotation is then sent through the transmission system to decrease the revolutions per minute. • The transmission system consists of the main bearing, high-speed shaft, gearbox, and low- speed shaft. The ratio of the gearbox determines the rotation division and the rotation speed that the generator sees. • For example, if the ratio of the gearbox is N to 1, then the generator sees the rotor speed divided by N. This rotation is finally sent to the generator for mechanical-to-electrical conversion.
- 27. • Figure hereshows the major components of a wind turbine: gearbox, generator, hub, rotor, low-speed shaft, high-speed shaft, and the main bearing. • The purpose of the hub is to connect the blades’ servos that adjust the blade direction to the low-speed shaft. • The rotor is the area of the turbine that consists of both the hub and blades. The components are all housed together in a structure called the nacelle.
- 28. Control Methods • Youcan use different control methods to either optimize or limit power output. You can control a turbine by controlling the generator speed, blade angle adjustment, and rotation of the entire wind turbine. Blade angle adjustment and turbine rotation are also known as pitch and yaw control, respectively. A visual representation of pitch and yaw adjustment is shown in Figures below.
- 29. • The purposeof pitch control is to maintain the optimum blade angle to achieve certain rotor speeds or power output. You can use pitch adjustment to stall and furl, two methods of pitch control. • By stalling a wind turbine, you increase the angle of attack, which causes the flat side of the blade to face further into the wind. • Furling decreases the angle of attack, causing the edge of the blade to face the oncoming wind. Pitch angle adjustment is the most effective way to limit output power by changing aerodynamic force on the blade at high wind speeds.
- 30. • Yaw refersto the rotation of the entire wind turbine in the horizontal axis. Yaw control ensures that the turbine is constantly facing into the wind to maximize the effective rotor area and, as a result, power. Because wind direction can vary quickly, the turbine may misalign with the oncoming wind and cause power output losses. You can approximate these losses with the following equation: • ∆P=α Cos(ε) • Where ∆P is the lost power and ε is the yaw error angle
- 31. Types of windturbines • Wind turbines can be separated into two basic types determined by which way the turbine spins. • Wind turbines that rotate around a horizontal axis are more common (like a wind mill), while vertical axis wind turbines are less frequently used (Savonius and Darrieus are the most common in the group).
- 32. HAWT(Horizontal Axis WindTurbine) • Horizontal axis wind turbines (HAWT) are the common style that most of us think of a wind turbine. • A HAWT has a similar design to a windmill, it has blades that look like a propeller that spin on the horizontal axis. • Horizontal axis wind turbines have the main rotor shaft and electrical generator at the top of a tower, and they must be pointed into the wind. • Small turbine are pointed by a simple wind vane placed square with the rotor (blades), while large turbines generally use a wind sensor coupled with a servo motor to turn the turbine into the wind. • Most large wind turbines have a gearbox, which turns the slow rotation of the rotor into a faster rotation that is more suitable to drive an electrical generator.
- 33. HAWT(Horizontal Axis WindTurbine) • Since a tower produces turbulence behind it, the turbine is usually pointed upwind of the tower. • Wind turbine blades are made stiff to prevent the blades from being pushed into the tower by high winds. • Additionally, the blades are placed a considerable distance in front of the tower and are sometimes tilted up a small amount. • Downwind machines have been built, despite the problem of turbulence, because they don‘t need an additional mechanism for keeping them in line with the wind. • Additionally, in high winds the blades can be allowed to bend which reduces their swept area and thus their wind resistance. • Since turbulence leads to fatigue failures and reliability is so important, most HAWTs are upwind machines.
- 34. Important point toremember regarding HAWT are: • Lift is the main force • Much lower cyclic stress • 95% of the existing turbines are HAWTs • Nacelle is placed at the top of the tower • Yaw mechanism is required
- 35. Advantages of HAWT •The tall tower base allows access to stronger wind in sites with wind shear. In some wind shear sites, every ten meters up the wind speed can increase by 20% and the power output by 34%. • High efficiency, since the blades always move perpendicular to the wind, receiving power through the whole rotation.
- 36. Disadvantages of HAWT •Massive tower construction is required to support the heavy blades, gearbox, and generator. • Components of horizontal axis wind turbine (gearbox, rotor shaft and brake assembly) being lifted into position. • Their height makes them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition. • Download variants suffer from fatigue and structural failure caused by turbulence when a blade passes through the tower‘s wind shadow (for this reason, the majority of HAWTs use an upwind design, with the rotor facing the wind in front of the tower). • HAWTs require an additional yaw control mechanism to turn the blades toward the wind. • HAWTs generally require a braking or yawing device in high winds to stop the turbine from spinning and destroying or damaging itself.
- 37. VAWT(Variable Axis WindTurbine) • Vertical wind turbines (VAWTs), have the main rotor shaft arranged vertically . • The main advantage of this arrangement is that the wind turbine does not need to be pointed into the wind. • This makes them suitable in places where the wind direction is highly variable or has turbulent winds. • With a vertical axis, the generator and other primary components can be placed near the ground, so the tower does not need to support it, also makes maintenance easier. • The main drawback of a VAWT is that, it generally creates drag when rotating into the wind.
- 38. VAWT(Variable Axis WindTurbine) • It is difficult to mount vertical-axis turbines on towers, meaning they are often installed nearer to the base on which they rest, such as the ground or a building rooftop. • The wind speed is slower at a lower altitude, so less wind energy is available for a given size turbine. • Air flow near the ground and other objects can create turbulent flow, which can introduce issues of vibration, including noise and bearing wear which may increase the maintenance or shorten its service life. • However, when a turbine is mounted on a rooftop, the building generally redirects wind over the roof and this can double the wind speed at the turbine. • If the height of the rooftop mounted turbine tower is approximately 50% of the building height, this is near the optimum for maximum wind energy and minimum wind turbulence.
- 39. Important point toremember regarding VAWT are: • Nacelle is placed at the bottom. • Drag is the main force • Yaw mechanism is not required • Lower starting torque • Difficulty in mounting the turbine • Unwanted fluctuations in the power output
- 40. Advantages VAWT • Noyaw mechanisms is needed • A VAWT can be located nearer the ground, making it easier to maintain the moving parts. • VAWTs have lower wind startup speeds than the typical HAWTs. • VAWTs may be built at locations where taller structures are prohibited. • VAWTs situated close to the ground can take advantage of locations where rooftops, means hilltops, ridgelines, and passes funnel the wind and increase wind velocity. •
- 41. Disadvantages VAWT • Incontrast to HAWT, all vertical axis wind turbines, and most proposed airborne wind turbine designs, involve various types of reciprocating actions, requiring airfoil surfaces to the wind leads to inherently lower efficiency. • Most VAWTs have an average decreased efficiency from a common HAWT, mainly because of the additional drag that they have as their blades rotate into the wind. Versions that reduce drag produce more energy, especially those that funnel wind into the collector area. • Having rotors located close to the ground where wind speeds are lower and do not take advantage of higher wind speeds above. • Because VAWTs are not commonly deployed due mainly to the serious disadvantage mentioned above, they appear novel to those not familiar with the wind industry. This has often made them the subject of wild claims and investment scams over the last 50 years. •
- 42. Dynamic control • Youcan achieve this dynamic control with power electronics, or, more specifically, electronic converters that are coupled to the generator. • The two types of generator control are stator and rotor. The stator and rotor are the stationary and non-stationary parts of a generator, respectively. In each case, you disconnect the stator or rotor from the grid to change the synchronous speed of the generator independently of the voltage or frequency of the grid. • Controlling the synchronous generator speed is the most effective way to optimize maximum power output at low wind speeds.
- 44. Induction Generator InWind Power System & Concept of DFIG • Generally, there are two types of induction generators widely used in wind power systems – Squirrel-Cage Induction Generator (SCIG) and Doubly-Fed Induction Generator (DFIG). • The main component of a modern induction generator wind power system is the turbine nacelle, which generally accommodates the mechanisms, generator, power electronics, and control cabinet. • The mechanisms, including yaw systems, shaft, and gear box, etc., facilitate necessary mechanical support to various dynamic behavior of the turbine.
- 45. • The generatoris dedicated to the conversion between mechanical energy, which is captured by turbine rotor, and electrical energy. • The generated electrical energy then needs to be regulated and conditioned to be connected to the power grid for use. • The most promising classifications in induction generator wind systems are fixed-speed, limited-variable-speed, and variable-speed wind systems, according to the operations of induction generator speed.
- 46. Synchronous Generator InWind Power System • Synchronous generators are commonly used for variable speed wind turbine applications, due to their low rotational synchronous speeds that produce the voltage at grid frequency. • Synchronous generators can be an appropriate selection for variable speed operation of wind turbines . • They do not need a pitch control mechanism. The pitch control mechanism increases the cost of the turbine and causes stress on turbine and generator. Synchronous generators in variable speed operation will generate variable voltage and variable frequency power. • Using an AVR for the excitation of the field voltage, the output voltage of the synchronous generator can be controlled. • However, induction generators require controlled capacitors for voltage control. In addition, their operating speed should be over synchronous speed in order to operate in generating mode.
- 47. • AC synchronousWTGs can take constant or DC excitations from either permanent magnets or electromagnets and are thus termed PM synchronous generators (PMSGs) and electrically excited synchronous generators (EESGs), respectively. • When the rotor is driven by the wind turbine, a three-phase power is generated in the stator windings which are connected to the grid through transformers and power converters. • For fixed speed synchronous generators, the rotor speed must be kept at exactly the synchronous speed. Otherwise synchronism will be lost.
- 48. Grid Connected AndSelf Excited Induction Generator • Many types of generator concepts have been used and proposed to convert wind power into electricity. The size of the wind turbines has increased during the past ten years, and the cost of energy generated by wind turbine has decreased. • The asynchronous or an induction machine is sometimes used as a generator. Asynchronous generators are frequently used in wind power systems. They are often employed to supply additional power to a load in a remote area that is being served by a weak transmission line. Their advantages in this application are that they are rugged and relatively cheap, and that engine or windmill driving the generator is not required to operate precisely at the synchronous speed. The machine must be driven above the synchronous speed, however, and the mechanical drive must be equipped with a control to cause the speed to increase as the electrical load increases.
- 49. Operation • SCIG andDFIG are used almost exclusively in the energy conversion stage of the induction generator wind power system. The most commonly used system topologies are SCIG directly connected into the power grid and DFIG fed by back-to-back converter. • The first topology implies a constant frequency and voltage of the SCIG that establishes a fixed-speed operation. • In such system, the SCIG relies on the grid (or capacitor bank) to provide reactive power which is necessary to build electromagnetic excitation for rotary field. • The generating mode of SCIG is triggered by driven torque which acts opposite to the generator speed within the super-synchronous speed operation region. • Due to the absence of the power electronics interface, such system can only serve the grid support applications, wherein just limited control (pitch angle control) can be applied.
- 50. Commonly used windpower system topologies ((a) DFIG with partial/matrix converter; (b) PMSG/SCIG with full converter; (c) direct drive; (d) PMSG with full converter and less stage gearbox; (e) EESG direct drive)
- 51. Constant Voltage AndConstant Frequency Generation With Power Electronic Control • The fundamental superiority of an IG is its ability to generate power at constant voltage constant frequency (CVCF) when driven by a variable speed source. • Therefore, in the wind power applications, most of the generators are IGs, which are grid connected.
- 52. Variable Speed ConstantFrequency Generator • Variable Speed Constant Frequency Generator (VSCF) involves generation of electrical power at fixed frequency and fixed voltage from a variable speed prime mover coupled to the generator shaft. Wind generator is one such example. • Speed of rotor varies with velocity and pressure of the wind, but power delivered to the supply mains must be at 50Hz and constant voltage.
- 53. Reactive Power Compensation Thereactive volt-ampere (VAR) requirements of the IG and the load are supplied by means of VAR Generator connected to the stator terminals. There are various possibilities to generate reactive power; • Synchronous Condenser • The combination of capacitors and saturated reactors • Static exciters
- 54. Characteristics Of WindPower plant Introduction of wind power generation has been increasing in the world, which has the following characteristics: • No CO2 emission. • Wind is a safe energy source existing everywhere, and there is no need to worry about depletion like fossil fuel. • Simple equipment and easy operation. • Few affection to nature environment.
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- 56. What is Biomass? •The residues of agriculture and forestry, animal waste and discarded material from food processing plants are known as Biomass. • The energy released by the use of biomass is known as Biomass energy.
- 57. Classification of Biomass Biomass EnergyCrops Natural vegetable growth Organic wastes & residues Forest residue Agricultral crop residue Animal waste Urban waste Municipal solid waste Sewage liquid waste Industrial waste
- 58. Forests • Forests area rich source of timber , fuel , wood , charcoal and raw materials for paper mills and other industries. • Forests also provide foliage and logging residues. • One important characteristics of forest residue is its caloric value which is 4399 to 4977 kcal/kg for softwood foliage and 3888 to 5219 kcal/kg for hard wood species.
- 59. Energy crops • Energyfarming refers to the cultivation of fast growing plants which supply fuel wood, biomass that can be converted into gaseous and liquid fuels like biogas, vegetable oil and alcohol. • To harvest biomass for power generation, energy plantation is done.
- 60. Vegetable oil crops •Oil can be extracted from fertile area crops such as sunflower, cotton seed,ground nut,palm and coconut. • These oils after purification can be blended with diesel oil suitable as engine fuel. • There is an arid area shrub “jajoba” its seeds provide oil which is an important renewable source of energy.It is cultivated in Orissa,Gujarat,Rajastan under hot arid condition. • It is also used as transformer oil due to its good insulating property.
- 61. Aquatic crop • Itconstitutes three water plants namely algae , hyacinth and sea weed. • These plants grow abundantly in water bodies and provide organic matter for biogas plants.
- 62. Animal waste • Animalwaste, an organic material with combustible property, is a rich source of fuel. • Dung cake prepared with animal waste are used for cooking in rural and semi urban areas.
- 63. Urban waste • Itis of two types • MSW(Municipal solid waste) that includes human excreta, household garbage and commercial waste. • Sewage liquid waste: from domestic sewage and effluents from institutional activities. • As per the report about 42 million tonnes solid waste and 6000 million cubic metres of liquid waste are generated every year in urban areas.
- 64. Industrial waste • Pulp& paper industry effluent, starch and glucose industry waste, palm oil industry, distillery waste. • Each project is aimed to treat its waste for the production of bio- energy which can be used for power generation.
- 65. Biomass Conversion Technology Thefollowings are the biomass conversion technologies: • Densification of biomass • Combustion and incineration • Thermo-chemical conversion • Bio-chemical conversion
- 66. Densification • Bulky biomassis reduced to a better volume to weight ratio by compressing in a die at a high temperature and pressure. • It is shaped into briquettes or pellets to make a more compact source of energy which is easier to transport and store than the natural biomass. • Pellets and briquettes can be used as clean fuel in domestic chullhas, bakeries and hotels.
- 67. Combustion • Direct combustionis the main process adopted for utilizing biomass energy. • It is burnt to produce heat utilized for cooking, space heating, industrial processes and for electricity generation. • This method is very inefficient with heat transfer losses of 30-90% of the original energy contained in the biomass.
- 68. Incineration • It isthe process of burning completely the solid biomass to ashes by high temperature oxidation. • The term incineration and combustion are synonymous. • But the process of combustion is applicable to all fuels i.e. solid, liquid and gaseous. • Incineration is a special process where the dry Municipal Solid Waste is incinerated to reduce the volume of solid refuse(90%) and to produce heat, steam and electricity.
- 69. Fermentation • It isa chemical process by which molecules such as glucose are broken down anaerobically. More broadly, fermentation is the foaming that occurs during the manufacture of wine and beer, a process at least 10,000 years old. • The frothing results from the evolution of carbon dioxide gas, though this was not recognized until the 17th century. • French chemist and microbiologist Louis Pasteur in the 19th century used the term fermentation in a narrow sense to describe the changes brought about by yeasts and other microorganisms growing in the absence of air (anaerobically); he also recognized that ethyl alcohol and carbon dioxide are not the only products of fermentation.
- 70. Thermo-Chemical Conversion (Pyrolysis) • Itis a thermo-chemical treatment in the absence or little presence of oxygen in order to produce a hydro-carbon, rich in gas mixture(H2, CO2, CO, CH4), an oil like liquid and a carbon rich solid residue. • There is no waste product, the conversion efficiency is high(82%) depending upon the feedstock used, process temperature in reactor and the fuel/air ratio during combustion.
- 71. • The wordPyrolysis is coined from the Greek words "pyro" which means fire and "lysis" which means separating. • Pyrolysis is commonly used to convert organic materials into a solid residue containing ash and carbon, small quantities of liquid and gases. • Extreme Pyrolysis, on the other hand yields carbon as the residue and the process is called carbonization. • Unlike other high-temperature processes like hydrolysis and combustion, Pyrolysis does not involve reaction with water, oxygen or other reagents. • However, as it is practically not possible to achieve an oxygen- free environment, a small amount of oxidation always occurs in any Pyrolysis system.
- 72. Types of Pyrolysis •Slow Pyrolysis • Flash Pyrolysis • Fast Pyrolysis
- 73. Slow Pyrolysis • SlowPyrolysis is characterized by lengthy solids and gas residence times, low temperatures and slow biomass heating rates. In this mode, the heating temperatures ranges from 0.1 to 2°C (32.18 to 35.6°F) per second and the prevailing temperatures are nearly 500°C (932°F). The residence time of gas may be over five seconds and that of biomass may range from minutes to days. • During slow pyrolysis, tar and char are released as main products as the biomass is slowly devolatilized. Re-polymerization/recombination reactions occur after the primary reactions take place.
- 74. Flash Pyrolysis • Flashpyrolysis occurs at rapid heating rates and moderate temperatures between 400 and 600°C (752 and 1112°F). However, vapor residence time of this process is less than 2s. • Flash pyrolysis produces fewer amounts of gas and tar when compared to slow pyrolysis.
- 75. Fast Pyrolysis • Thisprocess is primarily used to produce bio-oil and gas. • During the process, biomass is rapidly heated to temperatures of 650 to 1000°C (1202 to 1832°F) depending on the desired amount of bio- oil or gas products. • Char is accumulated in large quantities and has to be removed frequently.
- 76. Gasification • It isthe conversion of a solid biomass at a high temperature with controlled air into a gaseous fuel. • The output gas is known as producer gas, a mixture of CO2(9-12%), CH4(1-5%), H2(15-20%), CO(10-20%) and N2(45-55%). • It can be burnt to produce process heat and steam, or used in internal combustion engines or gas turbines to generate electricity. • Gasification is more versatile than solid biomass. • It is relatively clean and acceptable in environmental terms.