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FINAL REPORT

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FINAL REPORT

  1. 1. Design and fabrication of small scale continuous flow type bio mass gasifier By Fahad Atiq (BENG/F10/0123) K.M. Ahsan Rajput (BENG/F10/0106) Sameer Sohail Asim (BENG/F10/0115) 2016 Faculty of Engineering Sciences and Technology Hamdard Institute of Engineering and Technology Hamdard University, Main Campus, Karachi, Pakistan
  2. 2. Design and fabrication of small scale continuous flow type bio mass gasifier By Fahad Atiq (BENG/F10/0123) K.M. Ahsan Rajput (BENG/F10/0106) Sameer Sohail Asim (BENG/F10/0115) Under the supervision of Engr. Syed Nadeem Mian 2016 Faculty of Engineering Sciences and Technology Hamdard Institute of Engineering and Technology Hamdard University, Main Campus, Karachi, Pakistan
  3. 3. Design and fabrication of small scale continuous flow type bio mass gasifier By Fahad Atiq (BENG/F10/0123) K.M. Ahsan Rajput (BENG/F10/0106) Sameer Sohail Asim (BENG/F10/0115) A project presented to the Facultyof EngineeringSciences and Technology Hamdard Institute of Engineering and Technology In partial fulfillment of the requirements for the degree of Bachelors of Engineering In Energy Faculty of Engineering Sciences and Technology Hamdard Institute of Engineering and Technology Hamdard University, Main Campus, Karachi, Pakistan
  4. 4. Faculty of Engineering Sciences and Technology Hamdard Institute of Engineering and Technology Hamdard University, Main Campus, Karachi CERTIFICATE This project “Design and fabrication of small scale continuous flow type bio mass gasifier” presented by Fahad Atiq, K.M. Ahsan Rajput, Sameer Sohail Asim under the direction of their project advisor’s and approved by the project examination committee, has been presented to and accepted by the Hamdard Institute of Engineering and Technology, in partial fulfillment of the requirements for Bachelor of Engineering (Energy). ___________________ _________________ Engr. Syed Nadeem Mian (Member) (Project Supervisor) _________________ ___________________ Prof. Dr. Abdul Hameed Memon Prof. Dr. Pervez Akhtar (Chairman Energy Engineering) (Director, HIET
  5. 5. I ABSTRACT The title of our project is ‘’Designing and fabrication of small scale continuous flow bio mass gasifier’’. The objective of this project is to design and construct a gasifier which is capable of producing flammable gas (producer gas) using bio-mass as a fuel. The idea is to produce flammable gas by designing a system which is mechanically simple, cheap, easily available, reliable, safe and environmental friendly. For the development of small scale gasifier we have selected fixed bed gasification system which is easy to design. In fixed bed systems we have chosen to construct an up-draft gasifier which can be operated in different feeds and different particle sizes and it has also the ability to produce results with fuels with greater moisture content in them. Three bio masses were used as a feed during our performances and observations namely; Babul wood, Bagasse, Guava wood. The design of our project was altered few times and after that noticeable improvements were noted.
  6. 6. II ACKNOWLEDGEMENT All praises and thanks to Al-Mighty” ALLAH”, the most merciful, the most gracious, the source of knowledge and wisdom endowed to mankind, who conferred us with the power of mind and capability to take this project to the exciting ocean of knowledge. All respects are for our most beloved Holy Prophet “Hazrat MUHAMMAD (Peace Be Upon Him)”, whose personality will always be source of guidance for humanity. Acknowledgement is due to Hamdard Institute of Engineering and Technology for support of this Project, a highly appreciated achievement for us in the undergraduate level. We wish to express our appreciation to our project supervisor Assistant Professor Engr. Syed Nadeem Mian who served as our major advisor. We would like to express our heartiest gratitude for his keen guidance, sincere help and friendly manner which inspires us to do well in the project and makes it a reality. Many people, especially our classmates and team members itself, have made valuable comment suggestions on this proposal which gave us an inspiration to improve our project. Our thanks extends to our Head of department Prof. Dr. Abdul Hameed Memon and all faculty members who have provided help and inspiration for the completion of the project particularly Lab Engineer Sir Hassan Jafri and to the technician of the workshop for his assistance during the fabrication and performance of experiments. A special thanks to the Fuel Research Center of Pakistan Council of Scientific and Industrial Research (PCSIR), whose management has been so co-operative to us. Scientific Officer Sir Amanat Ali supervised us in the fabrication of the project his assistance and guidance were very helpful in all the areas, we are very much grateful to him for his active co-operation and valuable inputs throughout the project and to the technical staff of the workshop as-well.
  7. 7. III At last but not the least we are thankful, from the bottom of our hearts to our parents who are always the source of inspiration and helped us in difficult moments.
  8. 8. IV TABLE OF CONTENTS Abstract…………………………………………………………………………………...IV Acknowledgement...............................................................................................................II Table Of Contents............................................................................................................. IV List Of Figures.................................................................................................................VII List Of Tables.................................................................................................................... IX List Of Abbreviation ..........................................................................................................X Chapter 1 Introduction .....................................ERROR! BOOKMARK NOT DEFINED. 1.1 Motivation....................................................................................................................2 1.2 Aims And Objective ....................................................................................................2 1.3 Environmental Aspects................................................................................................3 Chapter 2 Gasification And Gasifiers................................................................................4 2.1 Biomass Gasification...................................................................................................4 2.2 Bio Gas ........................................................................................................................6 2.3 Syn Gas........................................................................................................................7 2.4 Gasifiers.......................................................................................................................7 2.4.1 Down-Draft Or Co-Current Gasifier ........................................................................8 2.4.2 Cross Draft Gasifier................................................................................................10 2.4.3 Fluidized Bed Gasifier............................................................................................11 2.4.4 Eentrained Flow Gasifier........................................................................................13 2.4.5 Up-Draft Or Counter Current Gasifier ...................................................................14 2.5 Mechanism.................................................................................................................16 2.5.1 Drying/De-Hydration..............................................................................................17
  9. 9. V 2.5.2 Pyrolysis .................................................................................................................18 2.5.3 Reduction................................................................................................................19 2.5.4 Combustion.............................................................................................................19 2.6 Factors Influencing Gasification Process ..................................................................20 2.6.1 Energy Content .......................................................................................................20 2.6.2 Bed Temperature ....................................................................................................20 2.6.3 Moisture Content In Feed .......................................................................................20 2.6.4 Bed Height ..............................................................................................................20 2.6.5 Fluidization Velocity..............................................................................................21 2.6.6 Particle Size ............................................................................................................21 2.6.7 Equivalence Ratio...................................................................................................21 Chapter 3 Bio-Mass Feed Study........................ERROR! BOOKMARK NOT DEFINED. 3.1 Gasifier Fuel Characteristics......................................................................................22 3.2 Bio Masses Used........................................................................................................26 3.3 Chemical Composition ..............................................................................................29 Chapter 4 Designing, Calculations And FabricationERROR! BOOKMARK NOT DEFINED. 4.1 Internal Components of Gasifier …………………………………………………..30 4.1.1 Fire Tube.................................................................................................................30 4.1.1.1 Finding The Diameter Of The Reactor ‘D’.......................................................31 4.1.1.2 Height Of The Reactor ‘H’ ...............................................................................32 4.1.1.3 Volume Of The Reactor....................................................................................33 4.1.2 Out-Let Pipe ........................................................................................................34 4.1.2.1 Finding Diameter Of Outlet Gas Pipe...............................................................35 4.1.3 The Feed Pipe ......................................................................................................36
  10. 10. VI 4.1.4 Grate/Hearth ...........................................................................................................37 4.1.4.1 Fuel Settling......................................................................................................39 4.1.4.2 Ash filtration.....................................................................................................39 4.1.4.3 Air introduction ................................................................................................39 4.1.5 Shaker Assembly/Agitator......................................................................................39 4.1.6 Ash Disposal Unit...................................................................................................40 4.1.7 Supporting Rods .....................................................................................................42 4.1.8 Housing...................................................................................................................43 4.2 External Components of A Gasifier………………………………………..……….44 4.2.1 Blower.....................................................................................................................46 4.2.2 Burner .....................................................................................................................47 4.3 Result…...……………………………………………………………………….49 4.4 Operation Procedure ..................................................................................................51 4.5 Precautions.................................................................................................................51 CHAPTER 5 TESTING AND OBSERVATIONSERROR! BOOKMARK NOT DEFINED. 5.1 Testing Methodology.................................................................................................52 5.2 Bio-Mass Feed Type Vs Temperature.......................................................................54 5.3 Air Flow Rate V/S Temperature................................................................................55 5.4 Inlet Flow Rate V/S Outlet Flow Rate.......................................................................58 5.5 Particle Size V/S Temperature...................................................................................59 5.6 Ash Production ..........................................................................................................60 5.7 Time V/S Temperature ..............................................................................................61 CHAPTER 6 CONCLUSION AND RECOMMENDATIONSERROR! BOOKMARK NOT DEFINED.
  11. 11. VII 6.1 Recommendations And Improvement .......................................................................65 6.2 Conclusion.................................................................................................................66 LIST OF FIGURES Figure 1 Products of Producer gas........................................................................................3 Figure 2 Syn gas and Producer gas.......................................................................................6 Figure 3 Downdraft Gasifier .................................................................................................8 Figure 4 Cross draft Gasifier ...............................................................................................10 Figure 5 Fluidized bed Gasifier...........................................................................................11 Figure 6 Entrained flow Gasifier.........................................................................................13 Figure 7 Updraft Gasifier ....................................................................................................14 Figure 8 Showing Reaction Zones in Gasifier ....................................................................17 Figure 9 Producer gas constituents......................................................................................26 Figure 10: Old Fire tube ......................................................................................................30 Figure 11: New fire tube......................................................................................................31 Figure 12: Outlet pipe..........................................................................................................34 Figure 13: The feed pipe......................................................................................................37 Figure 14: Grate...................................................................................................................38 Figure 15: Grate front view .................................................................................................38 Figure 16: Agitator ..............................................................................................................40 Figure 17: Ash Disposal Door.............................................................................................42 Figure 18: Supporting Rods.................................................................................................43 Figure 19: Housing of the Gasifier......................................................................................44 Figure 20: 3d AutoCAD design showing Updraft Gasifier.................................................45 Figure 21: Centrifugal fan showing inlet and Outlet of gas ................................................46 Figure 22: Blower................................................................................................................46 Figure 23: Burner .................................................................Error! Bookmark not defined. Figure 24: Final Shape of Gasifier ......................................................................................50
  12. 12. VIII Figure 25: Anemometer.......................................................................................................52 Figure 26: Stop watch..........................................................................................................53 Figure 27: Weighing Machine.............................................................................................53 Figure 28: Infra-red thermometer........................................................................................53 Figure 29: Regulator............................................................................................................53 Figure 30: Flow Rate v/s Combustion Zone Temperature for Babul wood ........................56 Figure 31: Flow Rate v/s Combustion Zone Temperature for Bagasse ..............................57 Figure 32: Flow Rate v/s Combustion Zone Temperature for Guava wood …………… 58 Figure 33: Inlet Flow Rate of Air Vs Outlet Flow Rate of Gas ..........................................59 Figure 34: Ash Production for Babul Wood for Guava Wood & Bagasse .........................61 Figure 35: Time v/s Combustion Zone Temperature for Babul wood ................................62 Figure 36: Time v/s Combustion Zone Temperature for Bagasse ......................................63 Figure 37: Time v/s Combustion Zone Temperature for Guava wood ...............................64 Figure 38: Gasifier Future Work Diagram..........................................................................67
  13. 13. IX LIST OF TABLES Table 1: Producer gas composition ………………………………………………………………..25 Table 2: Proximate analysis of Babul wood …………………………………………………....27 Table 3: Ultimate analysis of Babul wood ……………………………………………………....27 Table 4: Proximate analysis of Bagasse ………………………………………………………….28 Table 5: Ultimate analysis of Bagasse …………………………………………………………….28 Table 6: Results of important dimensions calculated …………………………...…………49 Table 7: Bio mass v/s reduction zone temperature …………………………………………54 Table 8: Bio mass v/s Combustion zone temperature ……………………..………………54 Table 9: Bio mass v/s Outlet pipe temperature ………………….……………………………54 Table: 10: Air flow rate v/s Combustion Zone Temperature for Babul wood……..55 Table: 11: Air flow rate v/s Combustion Zone Temperature for Bagasse…....…….55 Table: 12: Air flow rate v/s Combustion Zone Temperature for Guava wood…...55 Table 13: Inlet Flow Rate of Air Vs Outlet Flow Rate of Gas ……………………….........56 Table 14: Ash Production for Babul Wood ……………………………………………………….60 Table 15: Ash Production for Babul Wood for Guava Wood & Bagasse …………….60 Table 16: Time v/s Combustion Zone Temperature for Babul wood ……………..…61 Table 17: Time v/s Combustion Zone Temperature for Bagasse ………………………62 Table 18: Time v/s Combustion Zone Temperature for Guava wood ……………..…63
  14. 14. X LIST OF ABBREVIATION M.a.f Moisture and Ash Free Syn Synthetic CO Carbon mono Oxide CO2 Carbon di Oxide H2 Hydrogen NH3 Ammonia H2O Water m Meter mm Mili Meter DAF Dry Ash Free
  15. 15. 1 CHAPTER 1 INTRODUCTION The basic need of renewable and alternative means of energy is that they are never ending. Fossil fuels are big source of pollution around the world and recent facts & figures shows that their availability is temporary. Due to the inevitable coming to end for the fossil fuel sources at some point or if you see from the environment point of view, there is a desperate need for some alternate source of energies to at least gradually substitute the conventional sources of energies. Gasification is one such technology on which work has been done for nearly a century now. At present this technology has been widely used to produce commercial fuels and chemicals as well as for heating and power generation. Gasification is, although the technology exists already for decades, it is still being developed for advanced uses of biomass and waste. The gas which can be produced this way, a syngas, is a well-known commodity in the energy generation and chemical process industry and offers excellent options for high efficiency large scale electricity production and chemicals. Current developments in the chemical manufacturing and petroleum refinery industries show that use of gasification facilities to produce synthesis gas will continue to rise. A striking feature of the technology is its ability to produce a reliable, high-quality syngas product that can be used for energy production. In addition, it includes the ability to house a wide variety of gaseous, liquid, and solid feed stocks. Conventional fuels such as coal and oil, as well as low- or negative-value materials and wastes such as petroleum coke, heavy refinery residuals, secondary oil-bearing refinery materials, municipal sewage sludge, and chlorinated hydrocarbon byproducts have all been used successfully in gasification operations. Biomass and crop residues also have been gasified successfully. Gasification of these materials has many potential benefits over conventional options such as combustion or disposal by incineration.
  16. 16. 2 1.1 Motivation Biomass contributes as the world’s fourth largest energy source today up to 14% of the world’s primary energy demand. In developing countries it can be as high as 35% of the primary energy supply. Biomass is a versatile source of energy in that it can be readily stored and transformed into electricity and heat. It has also the potential that it is used as a raw material for production of fuel and chemical feedstock. Production units range from small scale up to multi-megawatt sizes. Whereas it’s source or feed is easily available worldwide in abundance and that to at a very cheap cost. 1.2 Aims and Objective The main objective of doing this project is to focus on the designing of an efficient and cost effective bio-mass gasifier which is able to generate producer gas for basic cooking and thermal use of people in rural area. Besides the main objective, this project also aims to bring awareness to world about the good of a renewable energy over pollution. The gasifier designed by us would have the potential to produce flammable gas for hours using almost nothing external power; this gas can be used for cooking and heat purposes. Such a process would need to have some precautions to be followed. In many rural areas of Pakistan the natural gas is not available. They have being finding alternate ways to cook their foods and other thermal uses since past many decades. The major advantage of this type of system in rural areas is that it uses bio-mass as fuel that bio-mass could be any wood , crop waste , seeds , sugarcane waste , rice husk , coconut shell or any similar sort of biological crop or wood from plants. This system provides a facility of wide range of bio-mass feed what are very easily available in rural areas with almost no cost to the owner. The rising prices of oil has favored and will favor the development of systems in the future that are environmentally friendly due such a deadly threat of global warming looming above our head and at the same time economically competitive.
  17. 17. 3 1.3 Environmental Aspects Environmental and climate change. CO2 is the main gas responsible for climate change, and it is observed that the gas emissions from road transport are the main contributors to the increase of the total level of emission in recent years, in spite of leveling off or even reduction of CO2 emissions from other activities worldwide. If we use bio mass which is a waste such as manure, municipal waste or unusable crops/vegetables then there will be no need for them to dispose in the landfills polluting. The life cycle of biomass as a renewable material has a neutral effect on CO2 emission. It also offers the possibilities of a closed mineral and nitrogen cycle. The environmentally hazardous sulphur dioxide (SO2), which is produced during combustion of fossil fuels, leading to acid deposition, is not a major problem in biomass systems due to the low sulphur content of biomass. Figure 1 Products of Producer gas
  18. 18. 4 CHAPTER 2 GASIFICATION AND GASIFIERS 2.1 Biomass Gasification The gasification process is a well-known technology. Between 1920 and 1940, compact gasifier systems for automotive applications were developed in Europe. In the 1970’s the oil crisis renewed the interest in gasification, as a relatively cheap indigenous alternative for small- scale power generation in developing countries. In the early 1980’s European manufacturers offered small-scale wood and charcoal-fueled power plants up to 250 kW of electricity. Currently the development of gasification systems is directed to the production of bio fuels (automotive fuels) and of electricity and heat in advanced gas turbine based cogeneration units (commercialized heat and power generation). The main feed for bio gasification is bio mass which is present in huge amount everywhere. The main biomass resources include the following: short rotation forestry (Willow, Poplar, Eucalyptus), wood wastes (forest residues, sawmill and construction/industrial residues, etc.), sugar crops (Sugar beet, Sweet Sorghum, Jerusalem Artichoke), starch crops (Maize, Wheat), herbaceous lignocellulose crops (Miscanthus), oil crops (Rapeseed, Sunflower), agricultural wastes (straw, slurry, etc.), municipal solid waste and refuse, and industrial wastes (e.g. residues from the food industry). At present, however, wastes, either in the form of wood wastes, agricultural wastes, municipal or industrial wastes, are the major biomass sources and, consequently, the priority fuels for energy production. There is also an additional environmental benefit in the use of residues such as municipal solid waste and slurry as feedstocks as these are withdrawn from polluting land filling. The gasification is a thermo-chemical process that converts any carbon-containing material into a combustible gas by supplying a restricted amount of oxygen (under typical gasification conditions, oxygen levels are restricted to less than 30% of that required for
  19. 19. 5 complete combustion)i.e. an organic or fossil fuel based carbonaceous materials such as coal, natural gas or biomass, is broken down into carbon monoxide (CO) and hydrogen (H2), plus carbon dioxide (CO2) and possibly hydrocarbon molecules such as methane (CH4). C + ½ O2 → CO CO + ½ O2 → CO2 H2 + ½ O2 → H2O C + 2H2 ↔ CH4 Raw producer is not an end product, but requires further processing. Gasification adds value to low- or negative-value feedstocks by converting them to marketable fuels and products. In utilization of gases from biomass gasification, it is important to understand that gas specifications are different for the various applications. Furthermore, the composition of the gasification gas is very dependent on the type of gasification process, gasification agent and the gasification temperature. Based on the general composition and the typical applications, two main types of gasification gas can be distinguished as producer/bio gas and syngas.
  20. 20. 6 Figure 2 Syn gas and Producer gas …………………. (xiii) The energy derived from gasification and combustion of the resultant gas is considered to be a source of renewable energy, if the gasified compounds were obtained from biomass. Similarly the gas from which the energy is derived is called bio gas or syn gas depending on the process of obtaining the gas. Because the inputs and technology to produce biogas and syngas are different, the resulting gas output is also different. For example, using the latest technology transportation fuels can be obtained using wood syngas, but methane is a less concentrated fuel it is better suited for other purposes. 2.2 Bio Gas Biogas or producer gas typically refers to a mixture of gases produced by the breakdown of organic matter in the absence of oxygen. Biogas can be produced from regionally available raw materials such as recycled waste, manure, municipal waste, plant material, sewage, green waste or food waste. It is a renewable energy source and in many cases Low temperature gasification (800 – 1000 C) Producer Gas CO, H2, CH4, CXHY Syngas CO, H2 High temperature (1200 – 1400 C) or catalytic gasification BIOMASS Thermal cracking or reforming EndUseApplication
  21. 21. 7 exerts a very small carbon footprint which very good for controlling the pollution resulting in global warming. 2.3 Syn Gas The process we are using creates Synthetic Gas or Syn Gas for short. Syngas, or synthetic gas, is a gas composed of carbon monoxide, carbon dioxide and hydrogen (It will also contain other compounds, such as sulfur and nitrogen oxides, depending on the chemical composition of the fuel),that is created when coal or biomass is gasified (gasification is a thermo-chemical process). This is achieved by reacting the material at high temperatures (>700 °C), with partial combustion (controlled amount of oxygen).The resulting gas mixture is called syngas (from synthesis gas or producer gas), and is itself a fuel. Syngas has 50% of the energy density of natural gas. It cannot be burnt directly, but is used as a fuel source. The other use is as an intermediate to produce other chemicals. The production of syngas for use as a raw material in fuel production is accomplished by the gasification of coal or municipal waste. In these reactions, carbon combines with water or oxygen to give rise to carbon dioxide, carbon monoxide, and hydrogen. 2.4 Gasifiers The process of gasification occurs in a machine called gasifier. There are many types of gasifiers present in modern world for us to use. Among them some are available extensively for the commercial uses which are as under. Gasifier designing is a mandatory task before carrying out gasification. The purpose is to study designing of gasifier is to find out: What would be the composition of the gas. Calculate how much steam you can produce. What type of gasifier to use? What would be size of gasifier? How much steam, air or oxygen is needed? Types  Down-draft or co-current gasifier.  Cross draft gasifier.  Fluidized bed gasifier.
  22. 22. 8  Up-draft or counter current gasifier. 2.4.1 Down-draft or Co-current Gasifier Figure 3Downdraft Gasifier In this type of gasifier primary gasification air is introduced at or above the oxidation zone in the gasifier. The producer gas is removed at the bottom of the apparatus, so that fuel and
  23. 23. 9 gas move in the same direction, as schematically shown in Fig. 3. On their way down the acid and tarry distillation products from the fuel must pass through a glowing bed of charcoal and therefore are converted into permanent gases hydrogen, carbon dioxide, carbon monoxide and methane. The main advantage of downdraught gasifiers lies in the possibility of producing a tar-free gas suitable for engine applications. Because of the lower level of organic components in the condensate, downdraft gasifiers suffer less from environmental objections than up draft gasifiers. A major drawback of downdraught equipment lies in its inability to operate on a number of unprocessed fuels. In particular, fluffy, low density materials give rise to flow problems and excessive pressure drop, and the solid fuel must be pelletized or briquetted before use. Downdraft gasifiers also suffer from the problems associated with high ash content fuels (slagging) to a larger extent than updraft gasifiers. Minor drawbacks of the downdraft system, as compared to updraft, are somewhat lower efficiency resulting from the lack of internal heat exchange as well as the lower heating value of the gas. Besides this, the necessity to maintain uniform high temperatures over a given cross-sectional area makes impractical the use of downdraft gasifiers in a power range above about 350 kW (shaft power).
  24. 24. 10 2.4.2 Cross Draft Gasifier Figure 4 Cross draft Gasifier Cross-draft gasifiers, schematically illustrated in Figure 4 are an adaptation for the use of charcoal. Charcoal gasification results in very high temperatures (1500 °C and higher) in the oxidation zone which can lead to material problems. In cross draft gasifiers insulation against these high temperatures is provided by the fuel (charcoal) itself. Advantages of the system lie in the very small scale at which it can be operated. Installations below 10 kW (shaft power) can under certain conditions be economically feasible. The reason is the very simple gas-cleaning train (only a cyclone and a hot filter) which can be employed when using this type of gasifier in conjunction with small engines.
  25. 25. 11 A disadvantage of cross-draft gasifiers is their minimal tar-converting capabilities and the consequent need for high quality (low volatile content) charcoal. It is because of the uncertainty of charcoal quality that a number of charcoal gasifiers employ the downdraft principle, in order to maintain at least a minimal tar-cracking capability. 2.4.3 Fluidized Bed Gasifier Figure 5 Fluidized bed Gasifier The operation of downdraft gasifiers is influenced by the morphological, physical and chemical properties of the fuel. Problems commonly encountered are: lack of bunker flow, slagging and extreme pressure drop over the gasifier
  26. 26. 12 A design approach aiming at the removal of the above difficulties is the fluidized bed gasifier illustrated schematically in Fig. 5. Air is blown through a bed of solid particles at a sufficient velocity to keep these in a state of suspension. The bed is originally externally heated and the feedstock is introduced as soon as a sufficiently high temperature is reached. The fuel particles are introduced at the bottom of the reactor, very quickly mixed with the bed material and almost instantaneously heated up to the bed temperature. As a result of this treatment the fuel is pyrolysed very fast, resulting in a component mix with a relatively large amount of gaseous materials. Further gasification and tar-conversion reactions occur in the gas phase. Most systems are equipped with an internal cyclone in order to minimize char blow-out as much as possible. Ash particles are also carried over the top of the reactor and have to be removed from the gas stream if the gas is used in engine applications. The major advantages of fluidized bed gasifiers, as reported by Van der Aarsen (44) and others, stem from their feedstock flexibility resulting from easy control of temperature, which can be kept below the melting or fusion point of the ash (rice husks), and their ability to deal with fluffy and fine grained materials (sawdust etc.) without the need of pre- processing. Problems with feeding, instability of the bed and fly-ash sintering in the gas channels can occur with some biomass fuels. Other drawbacks of the fluidized bed gasifier lie in the rather high tar content of the product gas (up to 500 mg/m³ gas), the incomplete carbon burn-out, and poor response to load changes. Particularly because of the control equipment needed to cater for the latter difficulty, very small fluidized bed gasifiers are not foreseen and the application range must be tentatively set at above 500 kW (shaft power).
  27. 27. 13 2.4.4Entrained Flow Gasifier Figure 6 Entrained flow Gasifier In entrained-flow gasifiers, fine coal feed and the oxidant (air or oxygen) and/or steam are fed co-currently to the gasifier. This results in the oxidant and steam surrounding or entraining the coal particles as they flow through the gasifier in a dense cloud. Entrained- flow gasifiers operate at high temperature and pressure—and extremely turbulent flow— which causes rapid feed conversion and allows high throughput. Some fuels have ashes with very high ash fusion temperatures. In this case mostly limestone is mixed with the fuel prior to gasification. Addition of a little limestone will
  28. 28. 14 usually suffice for the lowering the fusion temperatures. The fuel particles must be much smaller than for other types of gasifiers. This means the fuel must be pulverized, which requires somewhat more energy than for the other types of gasifiers. By far the most energy consumption related to entrained flow gasification is not the milling of the fuel but the production of oxygen used for the gasification. 2.4.5 Up-draft or Counter Current Gasifier Figure 7 Updraft Gasifier The oldest and simplest type of gasifier is the counter current or updraft gasifier shown schematically in Fig. 7. We are using this type of gasifier for the production of producer gas.
  29. 29. 15 The air intake is at the bottom and the gas leaves at the top. Near the grate at the bottom the combustion reactions occur, which are followed by reduction reactions somewhat higher up in the gasifier. In the upper part of the gasifier, heating and pyrolysis of the feedstock occur as a result of heat transfer by forced convection and radiation from the lower zones. The tar and volatiles produced during this process will be carried in the gas stream. Ashes are removed from the bottom of the gasifier. The gasifier construction is robust and relatively easy in operation. The gasifier can use fuel with moisture content up to 60 % (wet basis). However, the higher the moisture content, the lower the gasification efficiency. The gasifier accepts size variations in the feedstock. The fuel must have high mechanical strength and must be non-caking so that it will form a permeable bed. The possibility of channeling in the fuel bed can lead to oxygen break through and the possibility of explosions. As pyrolysis takes place at rather low temperature, tar and methane production are significant. As the pyrolysis gases do not pass a combustion zone, instead leaving with the product gas, the tar content of the product gas is high. Char conversion is high, as the char reacts with oxygen as a last sub-process and char combustion reaction is faster than the char gasification reactions. The gasification efficiency is high due to high char conversion and due to that the gas exit temperature is relatively low (300 - 400°C). The major advantages of this type of gasifier are its simplicity, high charcoal burn-out and internal heat exchange leading to low gas exit temperatures and high equipment efficiency, as well as the possibility of operation with many types of feedstock (sawdust, cereal hulls, etc.). Major drawbacks result from the possibility of "channeling" in the equipment, which can lead to oxygen break-through and dangerous, explosive situations and the necessity to install automatic moving grates, as well as from the problems associated with disposal of the tar-containing condensates that result from the gas cleaning operations. The latter is of
  30. 30. 16 minor importance if the gas is used for direct heat applications, in which case the tar are simply burnt. The gas has relative high heating value compared to other gasification technologies as for the high tar content in the product gas. The gas is suitable for direct combustion applications, such as a small steam boiler or for ceramic industry. Using the gas in an IC- engine requires extensive gas cleaning. We have chosen ‘’updraft gasifier’’ because the major advantage of updraft type of gasifier are its simplicity, high charcoal burn out and internal heat exchange leading to low temperature of exit gas and high equipment efficiency. This gasifier can work with several kind of feedstock ranging from Coal to Biomass. Main disadvantage for not using other are that downdraft gasifier cannot be operated with range of different feedstocks. Other disadvantage is it gives lower efficiency, since there is no provision internal exchange compare to updraft gasifier. The product stream also has low calorific value. And cross draught gasifier is their minimal tar-converting capabilities and the consequent need for high quality (low volatile content) charcoal. 2.5 Mechanism Gasification is made up for four discrete thermal processes: Drying, Pyrolysis, Reduction and Combustion. All of these processes are naturally present in the flame you see burning off a match, though they mix in a manner that renders them invisible to eyes not yet initiated into the mysteries of gasification. Gasification is merely the technology to pull apart and isolate these separate processes, so that we might interrupt the “fire” and pipe the resulting gases elsewhere. Processes  De-hydration (120oC)  Pyrolysis (180-400oC)  Reduction (300-700oC)
  31. 31. 17  Oxidation(Combustion) (700-1000oC) ………………………………(xiv) Figure 8 Showing Reaction Zones in Gasifier 2.5.1 Drying/De-hydration In this zone the water within the fuel is removed by evaporation. The water content within a particle is bound in several ways:  It can be enclosed in cavities, ƒ Drying zone Pyrolysis Zone Reduction Zone Combustion Zone Ash Zone Biomass Air Producer gas
  32. 32. 18  It can be capillary, ƒ  It can be chemically bound with the particle substance. The chemically bound water requires more energy to vaporize. During the drying process, water leaves dry fuel behind through vaporization. The vaporization takes place at almost constant temperature (100ºC at atmospheric pressure), but some water will leave at temperatures lower than the vaporization temperature due to the fact that water within the fuel has a higher partial pressure than the atmosphere. The drying process is endothermic i.e. it requires heat. This heat is obtained from the combustion step. The higher is the humidity content, the more heat is needed to dry the fuel. When drying takes place at normal conditions, the vaporization heat is approximately 2256 kJ/ kg of water (latent heat). 2.5.2 Pyrolysis Pyrolysis is an endothermic process where the particle structure decomposes due to heating. The decomposition products come out in gas form and are called volatile gases. Pyrolysis takes place after the drying has finished. Pyrolysis takes place in the temperature range of 250 ºC to 900 ºC. During pyrolysis a particle decreases in volume and mass. The volatile products are mainly CO, CO2, CH4, CnHm, NH3, some H2 and tars (also called pyrolysis oils). In biomass the volatile content is about 70-80 wt% (m.a.f.), while coal has 10-30 wt% (m.a.f.). The solid residue left after pyrolysis is called char, which mainly consists of elemental carbon and ash. Charcoal for barbequing is pyrolysed wood. To start a particle pyrolysis, an external heat source is needed, as pyrolysis is an endothermic process. When pyrolysis gases leave the particle and meet an oxidant (e.g. air), they will ignite. After ignition, the pyrolysis is self-sustained with heat from the combustion (exothermic reactions).
  33. 33. 19 2.5.3 Reduction In the reduction sub-process, char is converted into product gas by endothermic reactions with the hot combustion gases in absence of oxygen. The reducing atmosphere is obtained since the oxidant was supplied in deficit. Specifically, char reacts with steam forming hydrogen and with carbon dioxide forming carbon monoxide. The gasification reactions are very slow (compared to pyrolysis and combustion), and this sub-process is the “bottleneck” of a gasifier. The residence time for char is of large importance, as well as zone temperature and char reactivity to obtain high char conversion. The temperature is kept constant (800 ºC -900ºC depending on gasifier). The higher the reduction temperature, the faster is the gasification reaction. The product gas is a mix of H2, H2O, CO and CO2 in different proportions. 2.5.4 Combustion In the combustion sub-process, pyrolysis gases and char will react with provided oxygen or air. In a gasifier, the oxidizing agent is supplied in deficit; m = 0.2 – 0.4. For stoichiometric conditions, m = 1. For common combustion processes, oxidant is supplied in excess, m>1. The reactions, in which the reactants and products are in the same phase, are called homogeneous reactions. The reactions, in which there are both solid and gas phases of reactants and products, are called heterogeneous reactions Combustion of gases (homogeneous reactions): H2 + ½ O2 H2O CO + ½ O2 CO2 CH4 + 2O2 2H2O + CO2 C2H4 + 3O2 2H2O + 2CO2 Total and partial combustion of char (heterogeneous reactions):
  34. 34. 20 C + O2 CO2 C + ½ O2 CO Methane production: CO + 3H2 CH4 + H2O C+ 2H2 CH4 2.6 FACTORS INFLUENCING GASIFICATION PROCESS 2.6.1 Energy Content Fuel with high energy content provides easier combustion to sustain the endothermic gasification reactions because they can burn at higher temperatures. 2.6.2 Bed Temperature The gasification rate as well as the overall performance of the gasifier is temperature dependent. All gasification reactions are normally reversible and the equilibrium point of any of the reactions can be shifted by changing the temperature. 2.6.3 Moisture Content in Feed The moisture content of feed material affects reaction temperature due to the energy required to evaporate water in the fuel. It is found that there is a direct correlation between high moisture content and high volumes of produced char. This results in a decrease in gasifier temperature with increase in fuel moisture content. 2.6.4 Bed Height At a given reactor temperature, a longer residence time (due to higher bed height) increases total gas yields.
  35. 35. 21 2.6.5 Fluidization Velocity Fluidization velocity plays an important role in the mixing of particles in the fluidized bed. 2.6.6 Particle size The feed particle size significantly affects gasification results. The coarser the particles, the more char and less tar they produce. The rate of thermal diffusion within the particles decreases with increased particle size, thus resulting in a lower heating rate. 2.6.7 Equivalence Ratio The equivalence ratio (actual fuel-air ratio divided by the stoichiometric fuel-air) has the strongest influence on the performance of gasifiers because it affects bed temperature, gas quality, and thermal efficiency.
  36. 36. 22 CHAPTER 3 BIO MASS FEED STUDY 3.1 GASIFIER FUEL CHARACTERISTICS Almost any carbonaceous or biomass fuel can be gasified under experimental or laboratory conditions. However the real test for a good gasifier is not whether a combustible gas can be generated by burning a biomass fuel with 20-40% stoichiometric air but that a reliable gas producer can be made which can also be economically attractive to the customer. Towards this goal the fuel characteristics have to be evaluated and fuel processing done. Many of the gasifier manufacturers claim that a gasifier is available which can gasify any fuel. There is no such thing as a universal gasifier. A gasifier is very fuel specific and it is tailored around a fuel rather than the other way round. Thus a gasifier fuel can be classified as good or bad according to the following parameters: 1) Energy content of the fuel 2) Bulk density 3) Moisture content 4) Dust content 5) Tar content 6) Ash and slagging characteristic A. Energy content and Bulk Density of fuel The higher the energy content and bulk density of fuel, the similar is the gasifier volume since for one charge one can get power for longer time. B. Moisture content In most fuels there is very little choice in moisture content since it is determined by the type of fuel, its origin and treatment. It is desirable to use fuel with low moisture content
  37. 37. 23 because heat loss due to its evaporation before gasification is considerable and the heat budget of the gasification reaction is impaired. For example, for fuel at 25 0 C and raw gas exit temperature from gasifier at 300 0 C, 2875 KJ/kg moisture must be supplied by fuel to heat and evaporate moisture. Besides impairing the gasifier heat budget, high moisture content also puts load on cooling and filtering equipment by increasing the pressure drop across these units because of condensing liquid. Thus in order to reduce the moisture content of fuel some pretreatment of fuel is required. Generally desirable moisture content for fuel should be less than 20%. C. Dust content All gasifier fuels produce dust. This dust is a nuisance since it can clog the internal combustion engine and hence has to be removed. The gasifier design should be such that it should not produce more than 2-6g/mof dust. Figure 7 shows dust produced as a function of gas production for wood generators used during World War II. The higher the dust produced, more load is put on filters necessitating their frequent flushing and increased maintenance. D. Tar Content Tar is one of the most unpleasant constituents of the gas as it tends to deposit in the carburetor and intake valves causing sticking and troublesome operation. It is a product of highly irreversible process taking place in the pyrolysis zone. The physical property of tar depends upon temperature and heat rate and the appearance ranges from brown and watery (60% water) to black and highly viscous (7% water). There are approximately 200 chemical constituents that have been identified in tar so far. Very little research work has been done in the area of removing or burning tar in the gasifier so that relatively tar free gas comes out. Thus the major effort has been devoted to cleaning this tar by filters and coolers. A well-designed gasifier should put out less than 1 g/mof tar. Usually it is assumed that a downdraft gasifier produces less tar than other gasifiers. However because of localized inefficient processes taking place in the throat of
  38. 38. 24 the downdraft gasifier it does not allow the complete dissociation of tar. More research effort is therefore needed in exploring the mechanism of tar breakdown in downdraft gasifiers. E. Ash and Slagging Characteristics The mineral content in the fuel that remains in oxidized form after complete combustion is usually called ash. The ash content of a fuel and the ash composition has a major impact on trouble free operation of gasifier. Ash basically interferes with gasification process in two ways: a) It fuses together to form slag and this clinker stops or inhibits the downward flow of biomass feed. b) Even if it does not fuse together it shelters the points in fuel where ignition is initiated and thus lowers the fuel’s reaction response. Ash and tar removal are the two most important processes in gasification system for its smooth running. Various systems have been devised for ash removal. In fact some fuels with high ash content can be easily gasified if elaborate ash removal system is installed in the gasifier. Slagging, however, can be overcome by two types of operation of gasifier; 1) Low temperature operation that keeps the temperature well below the flow temperature of the ash. 2) High temperature operation that keeps the temperature above the melting point of ash. The first method is usually accomplished by steam or water injection while the latter method requires provisions for tapping the molten slag out of the oxidation zone. Each method has its advantages and disadvantages and depends on specific fuel and gasifier design.
  39. 39. 25 Keeping in mind the above characteristics of fuel, only two fuels have been thoroughly tested and proven to be reliable. They are charcoal and wood. They were the principal fuels during World War II and the European countries had developed elaborate mechanisms of ensuring strict quality control on them. Table 1: Producer gas composition………..….(xv)
  40. 40. 26 Figure 9 Producer gas constituents ………………………….. (xvi) 3.2 Bio masses used We have primarily used three different bio-masses during our experiments and observations which are mentioned below. 1) Babul wood 2) Bagasse 3) Guava wood All the three above mentioned fuels are easily available in Pakistan. Gaur et al (1998) provides a proximate analysis of many types of wood. The study concluded the composition of the various woods was not different enough to cause variation in gasification characteristics, if the wood feedstocks were gasified at similar moisture contents. ………………………………………………….. (xvii)
  41. 41. 27 After the operation of the gasifier it was noticed that difference in gasification characteristics were due to the difference in the sizes of the babul and guava wood otherwise they both had produced similar physical and chemical properties. The particle size of babul wood is 1’ * 0.5’ whereas particle size of guava wood is around 3’ * 1’ which is too big for updraft gasification. The proximate and ultimate analysis of babul wood, guava wood and bagasse are shown under. Table 2: Proximate analysis of Babul wood These are the proximate analysis of babul wood sample obtained from the experiments performed in Pakistan Council of Scientific and Industrial Research Table 3: Ultimate analysis of Babul wood Elements Percentage Carbon 43.62 As Determined Dry Dry free ash Moisture % 7.383 ___ ___ Ash % 5.090 5.496 ___ Volatile matter % 66.110 71.380 75.531 Fixed carbon % 21.417 23.124 24.469 Total 100.00 100.00 100.00
  42. 42. 28 Hydrogen 5.26 Nitrogen 0.56 Oxygen 46.5 Others 4.06 Table 4: Proximate analysis of Bagasse Table 5: Ultimate analysis of Bagasse As determined Dry Dry free ash Moisture % 10.39 ___ ___ Ash % 2.19 2.44 ___ Volatile matter % 76.72 85.61 87.75 Fixed carbon % 10.71 11.95 12.25 Total 100.00 100.00 100.00 Elements Percentage Carbon 47 Hydrogen 6.5 Nitrogen 0 Oxygen 44 Others 2.5
  43. 43. 29 The proximate and ultimate analysis of guava wood was not available on internet so they are not included. 3.3 Chemical Composition Though wood composition varies according to species and growing conditions etc, wood is essentially composed of cellulose, hemicelluloses, lignin, and extractives. According to Reed and Desrosiers (1979), generic formulas are sufficient for many gasification calculations. It further states that biomass is a mixture of ~50% cellulose, 25% hemicellulose and 25% lignin, and all biomass can be approximated with CH1.4O0.6. ........................ (xviii) & (xix)
  44. 44. 30 CHAPTER 4 DESIGNING, CALCULATIONS AND FABRICATION 4.1 INTERNAL COMPONENTS OF OUR GASIFIER Basic components of an up-draft gasifier are. a) Fire tube b) Outlet pipe c) Feed pipe d) Grate/Hearth e) Shaker assembly or agitator f) Ash disposal unit g) Supporting rods h) Housing 4.1.1 FIRE TUBE The fire tube is the reactor of the gasifier; here all the chemical and thermo-chemical reactions take place. The material of the fire tube is generally stainless Steel (SS) or Galvanized Iron (GI) whereas in some cases ceramic made fire tubes are also used. The material of the fire tube is mostly steel because of the fact that it has to bear the temperature range of 200-1400°C which in fact is just below the melting point of steel. Figure 10: Old Fire tube
  45. 45. 31 Figure 11: New fire tube The first one is the old fire tube which due do some practical limitations had proven to be a failed choice while the second one is the new and improved form of the old one and that too has been chosen after some detailed examination and calculations shown as under. 4.1.1.1 Finding the diameter of the reactor ‘D’ Helpful conversion 1m=100cm=39.37inch
  46. 46. 32 Reactor diameter has been found by the formula D=√ 𝟏.𝟐𝟕×𝑭𝑪𝑹 𝑺𝑮𝑹 …………. (iv) Where; FCR -fuel consumption rate, SGR -specific gasification rate In the run it was observed that reactor could have a maximum of 3kg of guava wood chips within itself with a big particle size of 2.5*1 inch and 0.5 inch thickness for one hour. Therefore the Fuel consumption rate is 3kg/hr SGR –specific gasification rate of biomass, (90kg h-1/m2for Babul Wood) ….. (iv) D==√ 1.27×5𝑘𝑔/ℎ𝑟 90kg h−1/m2 =√0.04233𝑚2 =0.2057m or 8.1 inch ≈ 8 inch Diameter of fire tube is 0.2057m 4.1.1.2 Height of the reactor ‘H’ Height of the reactor has been found by the formula
  47. 47. 33 H = 𝑺𝑮𝑹×𝑻 𝛒 ……. (iv) Where; SGR -specific gasification rate T –time required to consume biomass, hr ρ - Biomass density, kg/m3 The time required for the complete combustion or the consumption time was observed 1hr; The density of the bagasse = 160kg/m3 ……. (v) H= 90kg h−1/m2×1ℎ𝑟 160 𝑘𝑔/𝑚3 = 0.5625m or 21.8 in Height of the fire tube is 0.5625m 4.1.1.3 Volume of the reactor Volume of the reactor has been found by the formula 𝑽 = 𝝅𝒓 𝟐 h Where; r = radius of the reactor h = height of the reactor  The diameter of reactor as calculated is 0.205m d = r×2 0.205m = r×2
  48. 48. 34 Radius of the reactor is 0.1028m  Height of the reactor as calculated is 0.5625m Therefore, V= 𝝅 × (0.1028m)2× 0.5625𝑚 = 0.0185m3 Volume of the reactor is 0.0185m3 4.1.2 OUT-LET PIPE The outlet pipe is the one hoisted at the top of the gasifier feed pipe in updraft gasifiers whereas in the downdraft the outlet pipe is at the bottom of the gasifier. It is the one responsible of carrying away all the flue gases and volatiles out from the gasifier where the useful producer gas can be collected or used directly by burning it through a gas burner and other volatiles like water vapors, CO2, Nitrogen can be separated by gas separation techniques or filtration. Figure 12: Outlet pipe
  49. 49. 35 4.1.2.1 Finding diameter of outlet gas pipe The diameter of the outlet gas has been found by the formula Q=AV Where; Q is the flow of the gases coming out of the pipe in m3/s A is the area of the pipe in m2 V is the velocity of the gases in m/s  The velocity of the gases was found to be 4m/s by the help of a primitive method using anemometer.  The flow of the gases was derived in the following pattern. We have gas production rate = 2.65 m3/Kg..………. (vi) & (xv) Feed rate = 3 kg/hr or 0.0008333 kg/sec Q= 2.65m3/kg *0.0008333kg/sec = 0.002208m3/s As, 𝑨 = 𝝅𝒓 𝟐 for circle A= π ( 𝑑 2 )2 Therefore; Q=AV 0.0022m3/s = π ( 𝑑 2 )2×4m/s d= √ 0.0022m3/s×4 4𝑚/𝑠×𝜋
  50. 50. 36 d= 0.0264 m or 1inch The diameter of the outlet gas pipe is 1 inch 4.1.3 THE FEED PIPE The feed pipe is the one through which the bio-mass enters the gasifier. The diameter of the feed pipe should be of certain width that it allows the feed to easily enter into the reactor without any barrier or blockage. This was the massive flaw in our own gasifier design as our feed pipe was acting as the reactor itself, meaning; there was a single pipe which had to perform both the jobs, one of conveying the feed and other of the fire tube. The old design pipe had another flaw that its diameter was not thick enough to allow the feed to have enough space to move and move down into the grate; this in particular was the major reason of chocking in the reactor which increased the heat and pressure losses and hence resulting in low efficiency of the gasifier itself and of the producer gas as well. The old design of our gasifier had lot many flaws but on the top of all was the placement of the outlet gas pipe, the pipe was at the top of the drum and it was welded and attached to the body of the drum only which in fact allowed all the gases produced in the drum to escape out from the outlet pipe keeping in mind not all the gases produced during gasification are useful and they effect on the efficiency of the produced producer gas as- well. The design also had the limitation of extracting less gas from the gasifier as the most of the gas used to get settle down at the bottom of the gasifier body near ash zone and stay there for some time, further, when the gas would get extracted by the effect of the blower it was noticed that its characteristics and physical properties were different from that of the producer gas like the color of the gas was different and it had more CO2 then CO (instead of burning the gas was behaving as fire extinguisher) and the gas contained more amount of flue ash because of its unnecessary residence time in the ash chamber. The new proposed design of the fire tube reduced nearly all the losses in the gasifier. It was done in the sensible and economical way; the old pipe was used as the feed pipe only
  51. 51. 37 coming out from the top of the drum and the new fire tube of 8΄΄ replaced the previous of 4΄΄. The size of the bio-mass feed was also adjusted to reduce the feeding time and losses. Figure 13: The feed pipe 4.1.4 GRATE/HEARTH The grate of the gasifier is one of the most important parts of the gasifier it is the one where the bio-mass sits and gets itself into a process of gasification and combustion. The designing of the grate is quite sensitive job as the maximum temperature in the gasifier is on the grate. The grate was firstly designed to stay at some distance from the fire tube (3΄΄) but that in the end appeared to be a wrong choice as all the gases use to skip away from the fire tube and scatter all over in the gasifier. As the change in design was the only available choice so we attached the grate to fire tube so that all the produced gases will remain in the fire tube only and will go through all the chemical process and can then be extracted from the top of the feed pipe. There are three major tasks of the grate.  To settle down and position the bio-mass properly
  52. 52. 38  To allow the ash particles move down into the ash zone  To allow the proper amount of air get into fire tube Figure 14: Grate Figure 15: Grate front view
  53. 53. 39 4.1.4.1 Fuel Settling Fuel setting is the primary job of the grate. Particle size highly influences the design of the grate’s mesh. The particle size is directly proportional to the distance between the mesh. Bigger the particle size bigger will be the distance between the grate’s mesh. The design of the grate’s mesh is such that the particles easily sit on it and do not fall down. The gap between the mesh is set in accordance with the particle size. 4.1.4.2 Ash filtration After pyrolysis and gasification the bio-mass comes and settles at the grate for the final thermo-chemical process called combustion. After the combustion of the bio-mass when almost all the moisture, volatiles and other flue gases have been released the ash from the fuel remains unburned which is of very small size and density so that it gets through the mesh of the grate and goes down into the ash chamber. The distance between the grate’s mesh is such that it allows the ash particles to easily get filtered and get collected down at the base of the drum. 4.1.4.3 Air introduction The air enters the drum body from the bottom of the gasifier right below the combustion chamber. The distance of the grate and the air inlet is 2.5’’. However the air is introduced to the bio-mass through the grate, the air that gets into the drum goes directly to the grate where it is allowed to meet the bio-mass. The air plays an important role in the gasification as it the primary medium of the heat transfer by forced convection in the reactor zones. 4.1.5 SHAKER ASSEMBLY/AGITATOR The shaker assembly is yet another important component of the gasifier. Two problems arise during the whole process one while designing the assembly itself and one at the installation and attachment of it with the gasifier’s grate. The insulation of the assembly with the drum is yet another tough task during the installation of the assembly.
  54. 54. 40 For the initial design of the gasifier and the position of the grate the shaker assembly system was used, as the grate was moveable and not fixed so the movement of the shaker assembly manually from outside of the gasifier would move the grate in to-n-fro motion allowing the ash to get through the mesh properly. After the change of the fire tube design when the grate was fixed to the fire tube we came to know that shaker assembly system was now useless as the shaker assembly could not shake the fixed grate; we had to come up with an alternate plan so we decided to go for an agitator. The purpose of the an agitator is the same as of the shaker assembly, to allow the ash to get through off the grate properly and provide the gasifier with clean ash free fuel for better gasification and combustion but, fortunately the agitator comes up with additional advantage of its great design that it intermixes the bio-mass in the reactor so the unnecessary agglomerated bio-mass would move downwards and get into the process by the movement of the blades of the agitator. Figure 16: Agitator 4.1.6 ASH DISPOSAL UNIT The Ash disposal unit is the area where all the ashes are collected. Ash is the residue powder left after the combustion of the wood
  55. 55. 41 The basic wood ash composition is as follows Ash composition Calcium carbonates _ 25-45% Calcium oxide _ Iron oxide _ 3-10% Potash > 10% Phosphate _ 0-1% Other elements include Mg, Mn, S, Oxides, Iron, Zinc, Calcium, Cu and some heavy metals. However all these compositions may vary as the combustion temperature plays a vital role in determining the composition of wood ash. At the bottom of the gasifier we have placed an ash disposal door which can be accessed anytime for the ash cleaning and maintenance purposes. The maximum ash produced by our bio-masses was found to be 4%. The mass of the ash was calculated by the primitive manner, for the operation 3kg of wood was required and the end of the operation when the system was allowed to cool for hours we accessed the ash door took all the ash out and weighed. The weight of the ash including some unburned fuel particles too was around 100gm making it 3% of the wood inlet.
  56. 56. 42 Figure 17: Ash Disposal Door 4.1.7 SUPPORTING RODS Supporting rods are the ones responsible of carrying almost the entire system load and failure in any one of these would ultimately result in system break down. The material for supporting rods is steel undoubtedly as it has the highest strength in comparison with other available metals. The rods are welded onto the drum and the reactor too, in such a way that the reactor remains at the very center. We had to be very much precise in measurement and calculation during the whole scenario of welding the rods and then fitting the fire tube inside, because, the fire tube has to remain at the very center of the drum applying equal forces on the rods. If incase the reactor is not in the center then as a result the rod facing the unwanted weight would bend permanently which could lead to system break down in future. To keep the fire tube in the exact center of the gasifier we had to measure the length of the three equal rods which would be the distance from the inner part of the drum to the outer part of the fire tube. For this particular thing the formula calculated was. L = r2 –r1 Where; r2is the radius of the drum 11.5’’
  57. 57. 43 r1 is the radius of the reactor 4’’ L = 11.5’’ – 4’’ L = 7.5 ‘’ or 0.1905m The length of the supporting rods each is 0.1905m Figure 18: Supporting Rods 4.1.8 HOUSING The housing is the body of the gasifier it is the protective casing or covering that works as a shield. The housing on the gasifier has to be of certain material that is solid, does not change its shape and the one which can resist very high temperatures up to 1300°C. As our design is small scale so we have selected oil drum as our gasifier’s body. The oil drum was selected for this very purpose because it is very easy to weld it and make certain holes and spaces in it for the attachment of pipes and different ports.
  58. 58. 44 Figure 19: Housing of the Gasifier While having a first look at this drum one thing comes at mind is will it be able to resist the temperatures and won’t explode?? The only answer to the question is the drum is made up of steel whose melting point is 1370oC whereas, the maximum temperature drum has to face is 700oC.
  59. 59. 45 Figure 20: 3d AutoCAD design showing Updraft Gasifier
  60. 60. 46 4.2 EXTERNAL COMPONENTS OF OUR GASIFIER 4.2.1 BLOWER Figure 21: Centrifugal fan showing inlet and Outlet of gas Figure 22: Blower A centrifugal fan is a mechanical device for moving air or other gases. The term "blower" is frequently used as synonyms. These fans increase the speed of air stream with the rotating impellers. They use the kinetic energy of the impellers or the rotating blade to increase the pressure of the air/gas stream which in turn moves them against the resistance caused by ducts, dampers and other components. Centrifugal fans accelerate air radially, changing the direction (typically by 90°) of the airflow. They are sturdy, quiet, reliable, and capable of operating over a wide range of conditions, since it is the centrifugal force that creates the pressure. The blower can tolerate, and in fact will remove, a certain amount of tar and
  61. 61. 47 particulates, but a means for draining and cleaning the blower should be provided. Blowers can be used either to push the air into the gasifier or to pull the hot gas through the system at negative pressure. Considerably more power is required to pull the gas through the system than to push air because there is necessarily more mass to manipulate and the gas is less dense. In addition, suction fans must be capable of handling a higher temperature than fans pushing air into the gasifier. Most blower breakdowns occur due to deposits on shaft seal and impeller or erosion of the case. Reliability is limited by deposits. The blower could produce a maximum volume flow rate of 2.8m3/min with 16000 rpm. 4.2.2 BURNER Figure 23: Burner Burner is a mechanical device that burns a gas or liquid fuel into a flame in a controlled manner. Updraft producer gas is an excellent fuel for high quality heat applications. The high tar content does not need to be removed, and adds to the heating value. Furthermore, the sensible heat of the gas adds to the flame temperature and overall heat output.
  62. 62. 48 The classification of Burners is a detailed study itself and cannot be explained in this context. The Burner we have used in our project is a ‘Nozzle Mix Burner’. Nozzle-Mix Burners Air and gas are mixed at the burner nozzle in nozzle-mix burners. Some nozzle-mix burners keep the air and gas separated until the point of ignition, whereas others mix some of the primary air prior to the point of ignition. Sealed-nozzle mixed burner systems depend entirely on primary air. By contrast, secondary air is supplied to the flame after it is ignited and is brought in at the burner. An example of both types is in atmospheric burners, which use about 70% primary air and 30% secondary air.
  63. 63. 49 4.3 RESULT By design parameters the calculations carried out helped to determine critical dimensions. The critical dimensions of various components are Table 6: Results of important dimensions calculated Components Critical Dimensions Diameter of Reactor 0.2057m Height of Reactor 0.5625 Volume of Reactor 0.0185m3 Diameter of Outlet Pipe 0.0264m Length of Supporting Rods 0.1905m
  64. 64. 50 FINAL SHAPE Figure 24: Final Shape of Gasifier
  65. 65. 51 4.4 OPERATION PROCEDURE 1) Burn some pieces of coal and when they get red hot put them inside the fire tube from the top. 2) Fill the fire tube with the bio-mass feed and also fill up till 1/4th of the feed pipe. 3) Now cover and seal all the ports and openings. 4) Now switch on the blower and set it to 0.11m3/min in the beginning. Do not exceed the pressure of the blower more than 0.23m3/min. 5) After 25 minutes of continuous and stable operation attach the burner to the outlet pipe and ignite it. 6) After 50 minutes open the top opening of the feed pipe and refill the gasifier with the feed. 4.5 PRECAUTIONS 1) The gasifier should be operated in open atmosphere. 2) The person operating must always use oxygen mask as the gases released in gasification are dangerous to inhale. 3) Use hand gloves in opening the caps or getting into any physical contact with the plant. 4) Use helmet as there could be any system failure and a blast could also happen. 5) Unnecessary contact with the gasifier should be avoided. 6) After the operation the gasifier should be allowed to cool down in open atmosphere for at least 4 hours.
  66. 66. 52 CHAPTER 5 TESTING AND OBSERVATIONS 5.1 TESTING METHODOLOGY The testing of the continuous type up-draft gasifier was done at Hamdard University Karachi. The parameters measured were following: 1) Flow in m3/s 2) Temperature in K 3) Velocity in m/s 4) Mass in kg Following apparatus were used for measuring the above parameters: a) Anemometer b) Stop Watch c) Weighing machine d) Infra-red thermometer e) Regulator Figure 25: Anemometer
  67. 67. 53 Figure 26: Stop watch Figure 27: Weighing Machine Figure 28: Infra-red thermometer Figure 29: Regulator
  68. 68. 54 5.2 BIO-MASS FEED TYPE VS TEMPERATURE The temperatures in the gasifier were measured with the help of an infra-red temperature sensor. The change in temperatures of the combustion zone, reduction zone and the out-let gas pipe by the change of bio-mass feed is shown in the following tables. Table 7: Bio mass v/s reduction zone temperature Table 8: Bio mass v/s combustion zone temperature Number Feed type Combustion zone temperature in Kelvin 1st run 2nd run 3rd run Mean 1 Bagasse 763 773 781 772 2 Guava 653 653 671 659 3 Babul 893 873 881 882 Mean 770 766 778 771 Table 9: Bio mass v/s outlet pipe temperature Number Feed type Outlet pipe temperature in Kelvin 1st run 2nd run 3rd run Mean Number Feed type Reduction zone temperature in Kelvin 1st run 2nd run 3rd run Mean 1 Bagasse 531 536 541 538 2 Guava 459 467 463 463 3 Babul 596 603 610 603 Mean 528 535 538 534
  69. 69. 55 1 Bagasse 380 374 386 386 2 Guava 321 327 334 329 3 Babul 433 443 449 441 Mean 378 381 389 385 5.3 AIR FLOW RATE V/S TEMPERATURE The inlet air flow was measured with the help of a blower and regulated by a regulator attached to the blower. The change in temperature by the change in air flow rate for the different bio-mass feed is shown in the following tables. Table: 10 Air flow rate v/s Combustion Zone Temperature for Babul wood Number Flow rate (m3 /min) Combustion zone temperature in K 1st run 2nd run 3rd run Mean 1 0.11 763 743 753 753 2 015 858 861 866 862 3 0.19 840 835 840 839 4 0.23 773 783 779 778
  70. 70. 56 Figure 30: Flow Rate v/s Combustion Zone Temperature for Babul wood Table 11: Air flow rate v/s Combustion Zone Temperature for Bagasse Number Flow rate (m3 /min) Combustion zone temperature in K 1st run 2nd run 3rd run Mean 1 0.11 673 677 681 677 2 015 703 718 712 711 3 0.19 683 690 686 686 4 0.23 564 559 542 555 720 740 760 780 800 820 840 860 880 0 0.05 0.1 0.15 0.2 0.25 Temperature(K) Flow (cbm/min) Flow rate v/s combustion zone temperature Series1
  71. 71. 57 Figure 31: Flow Rate v/s Combustion Zone Temperature for Bagasse Table 12: Air flow rate v/s Combustion Zone Temperature for Guava wood Number Flow rate (m3 /min) Combustion zone temperature in K 1st run 2nd run 3rd run Mean 1 0.11 576 572 581 576 2 015 613 621 623 619 3 0.19 608 621 633 620 4 0.23 560 556 562 560 0 100 200 300 400 500 600 700 800 0 0.05 0.1 0.15 0.2 0.25 0.3 Temperature(K) Flow rate(cbm/min) Flow rate v/s combustion zone temperature Series1
  72. 72. 58 550 560 570 580 590 600 610 620 630 0 0.05 0.1 0.15 0.2 0.25 Temperature(K) Flowrate(cbm/min) Flowrate v/s combustionzonetemperature Figure 32: flow rate v/s Combustion Zone Temperature for Guava wood 5.4 INLET FLOW RATE V/S OUTLET FLOW RATE The outlet flow rate was measured by the general flow equation. The diameter of the pipe was derived already the velocity of the gases were measured by a primitive method using anemometer. The variations in outlet flow rate by varying inlet flow rate are shown in the following tables. Table 13: Inlet Flow Rate of Air Vs Outlet Flow Rate of Gas Number Inlet flow rate (m3 /min) Outlet flow rate (m3 /min) Difference 1 0.11 0.09 0.02 2 0.15 0.17 -.0.02 3 0.17 0.22 -.0.05 4 0.19 0.15 0.04 5 0.23 0.16 0.07
  73. 73. 59 The table shows that in the limited range of the inlet air flow rate the best is 0.17m3/min 0 0.05 0.1 0.15 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 outletflowrate(cbm/min) inlet flow rate(cbm/min) INLETFLOW RATE V/S OUTLET FLOW RATE Series1 Figure 33: Inlet Flow Rate of Air Vs Outlet Flow Rate of Gas 5.5 PARTICLE SIZE V/S TEMPERATURE The size of the particle plays an important role in the temperatures of the all the zones in the gasifier. Apparently, the particle size is also an important element in the design of the combustion chamber and hearth. The bigger the particle size the tougher will it get for the wood to diffuse thermally We have used three different bio mass feed for our experiments and the sizes of each of them are different from one another. The detailed study of the chemistry and size of the particles is done in chapter number 3.
  74. 74. 60 5.6 ASH PRODUCTION The production of the ash content from our sample of babul wood extracted from the premises of Hamdard University Karachi is discussed in the below. The wood samples were taken to Pakistan Council of Scientific and Industrial Research (PCSIR) for the testing purpose, there we after close examination discovered the Proximate Analysis of the wood and its calorific value. The Ash content in our sample of Babul wood was 5.09%. Before the operation of the gasifier we first weighed the babul wood and a total of 5kg was fed to the gasifier’s fire tube. After the operation the wood was gasified in an hour and the gasifier was allowed to cool down for 5 hours in open air. Then the ash door was accessed and all the ash was collected and filtered and weighed. The mass of the ash was 155gm making it 3.1 of the total bio-mass inlet, hence proved the ash content in babul wood is less than 5% which is acceptable for updraft gasification. Table 14: Ash Production for Babul Wood Number Ash content theoretical Ash content practical 1 5.09 % 3.1% Ash content in Guava wood is 3.25% ………………………………………………. (x) Ash content in Bagasse is 4% ………………………………………………………......(xi) Table 15: Ash Production for Babul Wood for Guava Wood & Bagasse Number Bio-mass type Ash (theoretical) % Ash (practical) % 1 Babul 5.09 3 2 Guava 3.25 2.3 3 Bagasse 4 2.5
  75. 75. 61 5.09 4 3.25 3 2.5 2.3 babul bagasse guava ASHPERCENTAGE ash theo. ash prac. Figure 34: Ash Production for Babul Wood for Guava Wood & Bagasse 5.7 TIME V/S TEMPERATURE The temperatures, as mentioned earlier were measured by the infra-red temperature sensor. The function of change in temperature by the change in time by keeping the air flow constant at 0.15m3/m is described under. Table 16: Time v/s Combustion Zone Temperature for Babul wood Number Time (mins) Temperature of combustion zone (K) 1 10 483 2 20 623 3 30 863 4 40 773 5 50 870
  76. 76. 62 6 60 883 7 70 751 Figure 35: Time v/s Combustion Zone Temperature for Babul wood Table 17: Time v/s Combustion Zone Temperature for Bagasse Number Time (mins) Temperature of combustion zone (K) 1 10 379 2 20 496 3 30 697 4 40 595 5 50 661 0 100 200 300 400 500 600 700 800 900 1000 0 20 40 60 80 Temperature(K) Time(min) TIME V/S TEMPERATURE Temp
  77. 77. 63 6 60 774 7 70 586 For Bagasse 0 100 200 300 400 500 600 700 800 900 0 10 20 30 40 50 60 70 80 Temeperature(K) Time(min) TIMEV/S TEMPERATURE Temp Figure 36: Time v/s Combustion Zone Temperature for Bagasse Table 18: Time v/s Combustion Zone Temperature for Guava wood Number Time (mins) Temperature of combustion zone (K) 1 10 294 2 20 399 3 30 581 4 40 327 5 50 528
  78. 78. 64 6 60 620 7 70 379 0 100 200 300 400 500 600 700 0 10 20 30 40 50 60 70 80 Temperature(K) Time(min) TIME V/S TEMPERATURE Temp Figure 37: Time v/s Combustion Zone Temperature for Guava wood
  79. 79. 65 CHAPTER 6 RECOMMENDATIONS AND CONCLUSION 6.1 RECOMMENDATIONS AND IMPROVEMENT There are many places where improvements can be made in this project which will increase the overall efficiency of the system as well as the cost of the system. Some of the improvements are proposed below:  The feed hoper could be used instead of feeding manually the feeding system could be made automatic.  Proper insulation of the system can be done by using a thick insulation coating this would minimize the distance between the reactor and the drum thus increasing the system efficiency as well.  A small blower could be used which will consume less external power and will surely be cheaper.  Cyclone tar removal system can be used for the removal of tar content this will surely increase the efficiency of the producer gas and the system.  The produced gas should go through a gas filtration unit (Scrubber) through which only the desired producer gas could be obtained.  The design of the agitator should be improved.  Agitation should be automatic instead of manual; it will surely minimize the risk of any serious damage to the operator.  The particle size should be small, proper and definite. The particle size has a big impact on the system operation and efficiencies of both system and produced gas.  A bulk amount of feed should always be available and that too be dried.  Ash removal gate could be made down at the very bottom of the drum this would make ash removing very much easy.  The gas cooling techniques should be applied to the gas.
  80. 80. 66  A flew gas analyzer should be used which could detect the type and amount of different gases present in the producer gas. This would be very helpful in deciding which bio-mass could be used and what parameters could be set in obtaining the required amount and type of gases.  A bomb calorimeter should be used in finding the calorific value of the producer gas. Later, the cold gas efficiency could easily be found.  For this design (updraft gasification) the certain bio-mass should be used which has ash content less than 6%.  This project can be used as a measurement instrument, instrument to measure calorific values of the producer gas produced by bio-masses. 6.2 CONCLUSION Pakistan is a country which is blessed with huge Renewable Energy resources but unfortunately Pakistan is facing a severe Energy crisis at present. As an Energy Engineer it is our duty to exploit its natural resources of renewable energy and help our country toward a better Future. This project focuses on providing an efficient, simple design, cheap, locally made gasification system which can provide a solution for the existing energy crisis situation of Pakistan. The recommendations and improvements discussed above would lead to an efficient, capable of producing tar free gas which not only be used for cooking and heating purposes but can directly be used in a generator as-well. Meaning, this project can meet the energy crises in Pakistan specifically rural areas where electricity is abandon and they are deprived from all the necessary resources. Gasifier as a measuring instrument: Having the improvements made in the design and configuration of the gasifier and making sure all the desired apparatuses are available the system would then act as a measuring apparatus itself and could then be used as a measurement device of the Calorific values of both bio-mass and the producer. The theoretical ash component of various bio-masses can easily be found what can be then
  81. 81. 67 compared with the actual values. The gasifier would also have the tendency to let differentiate between the good fuels and bad fuels. Usage of the gas in ICE engine: After proper filtration of the producer gas, separation of unwanted components specifically tars by the introduction of cyclone filtration and scrubbers and finally the cooling of the gas; obtained producer gas can then be used directly into the ICE engine. GASIFIER SYSTEM SHOWING MEANS OF MOVING SOLIDS AND GASES AND POSITIONS FOR THERMOCOUPLE. Figure 38: Gasifier Future Work Diagram
  82. 82. 68 References I. www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8& ved=0CB0QFjAAahUKEwjmzceS883HAhXJshQKHXnlDn0&url=https%3A%2F%2 Fwww.ecn.nl%2Ffileadmin%2Fecn%2Funits%2Fbio%2FOverig%2Fpdf%2FBiomass a_voordelen.pdf&ei=uXDhVaaNPMnlUvnKu- gH&usg=AFQjCNEfMaCo44G7fdLIskuh__P6LxHiXw&sig2=Uq8tzXxZvwMgPeL7i WBBzw II. www.fao.org/docrep/t0512e/t0512e0a.htm III. www.netl.doe.gov/research/coal/energy-systems/gasification/gasifipedia/entrainedflow IV. inpressco.com/special_edition/design-and-development-of-household-gasifier-cum- water-heater/ V. www.psst.org.pk/papers2012/m.iqbal.ppt VI. scholar.google.com.pk/scholar?q=Industrial+Application+of+Biomass+Based+Gasific ation+System&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwjZnID YkLvJAhUECywKHek2CvwQgQMIGDAA VII. shareok.org/bitstream/handle/11244/7965/Rowland_okstate_0664M_11051.pdf?seque nce=1 VIII. www.nariphaltan.org/gasbook.pdf IX. www.nrel.gov/docs/legosti/old/3022.pdf X. www.ncbi.nlm.nih.gov/pmc/articles/PMC4553883/figure/T1/
  83. 83. 69 XI. matiari-sugar-mills-ltd.pakbd.com/ XII. https://www.google.com.pk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja &uact=8&ved=0ahUKEwi- vMrLuZrKAhXB1BoKHTFWAakQFggZMAA&url=http%3A%2F%2Fwww.agri- techproducers.com%2Fupload%2FThermodynamic%2520analysis%2520of%2520bio masss%2520gasification%2520and%2520torrefaction.pdf&usg=AFQjCNE_y8agwbK YZ5kv8k6LaPd0KTI1qA&bvm=bv.110151844,d.d2s XIII. http://www.unep.org/ietc/ XIV. http://www.biomassenergycentre.org.uk/portal/page?_pageid=75,17504&_dad=portal &_schema=PORTAL XV. https://www.comsats.edu.pk/ XVI. http://cturare.tripod.com/pdc.htm XVII. (Gaur et al, 1998) XVIII. Reed and Desrosiers (1979) XIX. https://www.google.com.pk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja &uact=8&ved=0ahUKEwjz1- rG46XKAhUMbRQKHbXNAWMQFggdMAA&url=http%3A%2F%2Fwww.nrel.gov %2Fdocs%2Flegosti%2Fold%2F3022.pdf&usg=AFQjCNGAC0xKc2MYSyWx7Jm- xGlxpGuxrA&sig2=_eUWIUYLHPnvSygaGltocA
  84. 84. 70 Appendix A: Bulk Density of Various Fuels Bulk Density of Various Fuels Grading Density Kg/m3 Sawdust Sawdust Peat Loose briquettes 100 rnrn long 75 rnrn diameter dust 177 555 350-440 briquettes 45x65x60mm 350·620 hand cut 180-400 Charcoal (10% moisture) beech 21 0-230 birch 180-2003 softwood blocks 150-170 softwood slabs 130-150 mixed 60% hard/40% soft 170-190 Wood hardwood 330 softwood 250 mixed SO/50 290 Straw loose 80 bales 320 Alfalfa seed straw cube 30 x 30 x 50 mm. 7% moisture 298 Barley straw cube 30 x 30 x 50 mm. 7% moisture 300 Bean straw cube 30 x 30 x 50 mm, 7% moisture 440 Corn cobs 11 % moisture 304 Corn stalks cube 30 x 30 x 50 mm 391 Cotton gin trash 23% moisture 343 Peach pits 11 % moisture 474 Olive pits 10% moisture 567 Prune pits 8% moisture 514 Rice hulls cube 30 x 30 x 50 mm 679 Safflower straw cube 30 x 30 x 50 mm 203 Walnut shells cracked 336 8 mm pellets 559 Wood, blocks 17% moisture 256 chips 10% moisture 167 Coal anthracite 830-900 bituminous 770-930 Coke hard 380-530 soft 360-470 Brown coal air dry lumps 650-670

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