Module - 3.pdf
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This document provides an overview of biomass conversion technologies, with an emphasis on lignocellulosic biomass. It discusses the basics of biomass structure and composition and compares different types of biomass feedstocks. It then outlines various options for thermochemical and biological conversion processes, including details on pretreatment technologies, enzymatic hydrolysis, and fermentation approaches. Challenges related to reducing costs, improving yields, and integrating processes are also summarized.
![MECHANISM AND PRODUCTS OF
BIOMASS PYROLYSIS
• Biomass Pyrolysis
Figure 4.51 illustrate the main stages and products of the reactions of biomass pyrolysis [82].
▪ Temperature:
Low T < 400 C < High T
▪ Pressure:
Low P < 75 kPa < High P
▪ Residence Time:
Fast < 0.1 second < Slow
PRIMARY
TAR
(LIQUID)
BIOMASS
(SOLID)
Low
Temperature
TRANSIENT
OXYGENATED
FRAGMENTS
(VAPOUR)
CO
CH4
H2
CO2
OLEFINS
VAPOUR PHASE
DERIVED TAR
(VAPOUR OR
LIQUID)
WATER SOLUBLE
OXYGENATED
COMPUNDS
(VAPOUR)
CARBONBLACK
(SOLID)
H2,CO,CH4,
CO2,H2O
High
Temperature
Slow
Low Pressure
High
Temperature
Slow
High Pressure
SECONDARY
TAR
(LIQUID)
PRIMARY
TAR
(VAPOUR)
High
Temperature
Fast
Low Pressure
High
Temperature
Fast
Low Pressure
High
Temperature
Slow
Low Pressure
Medium
Temperature
Slow
Medium Pressure
CHARCOAL
(SOLID)
CO2,H2O
High
Temperature
Fast
Low Pressure
Low
Temperature
Slow
High Pressure
High
Temperature
Slow
High Pressure
High
Temperature
Slow
High Pressure](https://image.slidesharecdn.com/module-3-230117122902-e7820617/85/Module-3-pdf-169-320.jpg)
![Energy Balances
∆𝐸 = ሶ
𝑄 − ሶ
𝑊 + ሶ
𝑚𝑖𝑛 ℎ𝑖𝑛 +
1
2
𝑣𝑖𝑛
2 + 𝑔𝑧𝑖𝑛 − ሶ
𝑚𝑜𝑢𝑡 ℎ𝑜𝑢𝑡 +
1
2
𝑣𝑜𝑢𝑡
2 + 𝑔𝑧𝑜𝑢𝑡 (1)
where, ∆𝐸 is the net change in energy within the control volume with respect to time (J/h or BTU/h), ሶ
𝑄 is the change in
heat added/removed with respect to time (J/h or BTU/h) , ሶ
𝑊 is the work added to the system with respect to time (J/h or
BTU/h), ሶ
𝑚 is the mass flowrate (kg/h or lb/h), ℎ is the specific enthalpy (J/kg or BTU/lb), 𝑣 is the velocity per mass
(m/sec.kg), 𝑧 is the height with respect to mass (m/kg or ft/lb).
In many bioprocesses, a steady state conditions are primary interest in determining the efficacy of a system. Under
steady state conditions, the rate of change in energy within a control volume become zero and the general energy
balance equation simplifies to
ሶ
𝑄 − ሶ
𝑊 = −[ ሶ
𝑚𝑖𝑛 ℎ𝑖𝑛 +
1
2
𝑣𝑖𝑛
2
+ 𝑔𝑧𝑖𝑛 − ሶ
𝑚𝑜𝑢𝑡 ℎ𝑜𝑢𝑡 +
1
2
𝑣𝑜𝑢𝑡
2
+ 𝑔𝑧𝑜𝑢𝑡 ] (2)
Further simplification can occur if we consider that in most cases, potential and kinetic energies are negligible, at least
in the case of bioenergy production. The energy balance equation reduces to :
ሶ
𝑄 − ሶ
𝑊 = −[ ሶ
𝑚𝑖𝑛 ℎ𝑖𝑛 − ሶ
𝑚𝑜𝑢𝑡 ℎ𝑜𝑢𝑡 ] (3)](https://image.slidesharecdn.com/module-3-230117122902-e7820617/85/Module-3-pdf-210-320.jpg)
Module - 3.pdf
- 1. Dr. Sourav Poddar Department of Chemical Engineering National Institute of Technology, Tiruchirappalli Tamil Nadu Pyrolysis and thermos-chemical conversion
- 3. Outline • Biomass Basics • Overview of Conversion Options • Details of Enzyme-based Technology • Biorefining Now and in the Future
- 4. Biomass Feedstock Types • “Starchy”: Grains (e.g., corn and wheat) • “Oily”: Seeds (e.g., soya and rape) • “Fibrous”: Lignocellulose (e.g., ag and forestry residues, grasses, trees, etc. Emphasis of today’s presentation will be conversion of lignocellulosic biomass – Comparison to illustrate the differences between starchy and fibrous feedstocks: corn grain versus corn stover
- 6. Biomass Basics • Grain contains – ≥80% carbohydrates, dry basis – Major component is starch • Lignocellulosic biomass contains – 60-70% carbohydrates, dry basis – Major components are cellulose, hemicellulose, and lignin • Biomass types exhibit differences in – Macro structure and cell wall architecture – Types and levels of lignins and hemicelluloses – Types and levels of minor constituents
- 12. Biomass Structure • Surface and structural property measurement are key to developing a sound understanding of recalcitrance and conversion mechanisms – Very difficult system to study • Extremely heterogeneous at both macro- and micro-scales (ultrastructure complexity) – Tools and techniques emerging • E.g., NREL’s Biomass Surface Characterization Laboratory, NMR Laboratory, etc.
- 19. Outline • Biomass Basics • Overview of Conversion Options • Details of Enzyme-based Technology • Biorefining Now and in the Future
- 21. Biomass Conversion (or Fractionation) • Approaches – Mechanical • e.g., milling, comminution, decompression – Thermal • e.g., hot water, steam, heat – Chemical • e.g., acids, alkalis, solvents – Biological • e.g., cellulases, hemicellulases, ligninases Most processing schemes employ a combination of methods
- 22. Process Technology Options • Major categories of biomass conversion process technology – Sugar Platform • Dilute acid cellulose conversion • Concentrated acid cellulose conversion • Enzymatic cellulose conversion – Using any of a variety of different primary fractionation or “pretreatment” methods – Syngas Platform • Gasification followed by synthesis gas fermentation
- 24. Dilute Acid Hydrolysis • Driving Forces – Adapt existing infrastructure, use recycled equip. – Exploit recombinant fermentation technology for hexose and pentose sugar conversion • Strengths – Proven: oldest, most extensive history of all wood sugar processes, with the first commercial process dating back to 1898. • Active Companies/Institutions include – BC International – Swedish government
- 26. Concentrated Acid Process • Driving Forces – Cost effective acid/sugar separation and recovery technologies – Tipping fees for biomass • Strengths – Proven: large scale experience dates back to Germany in the 1930s; plants still may be operating in Russia today. – Robust: able to handle diverse feedstocks • Active Companies include – Arkenol – Masada Resources Group
- 29. Enzymatic Process • Driving Forces – Exploit lower cost cellulases under development – Conceptually compatible with many different fractionation/pretreatment approaches • Strengths – Potential for higher yields due to less severe processing conditions – Focus of USDOE’s core R&D • Active companies include – Iogen/PetroCanada, BC International, SWAN Biomass, and many others, including some of the recent Bioenergy Initiative solicitation awardees
- 32. Syngas Fermentation Process • Driving Forces – While unproven, may enable higher yields through conversion of non-carbohydrate fractions (e.g., lignin) to syngas components • Strengths – Build off previous gasification/clean up knowledge – Ability to process a diverse range of feedstocks to a common syngas intermediate • Active groups include – Bioresource Engineering Inc. – Oklahoma State – Mississippi State
- 33. Status of Conversion Options • Many options based on Sugar and Syngas Platform technology routes exist and are being pursued • Sugar Platform technologies are at a more advanced development stage because of their longer history • Recent programmatic emphasis has been on Enzymatic Hydrolysis route • Further information on process options is available at: – http://www.eere.energy.gov/biomass/sugar_platform.html • USDOE EERE Biomass Program web site
- 34. Process Development Challenges • Processing at high solids levels • Understanding process chemistries • Closing carbon, mass & energy balances – Requires accurate measurement/analysis methods • Identifying critical process interactions – Integration efforts must focus on key issues • Producing realistic intermediates and residues – Essential to evaluate potential coproduct values
- 35. Commercialization Challenges • Demonstrated market competitiveness – Compelling economics with acceptable risk • Established feedstock infrastructure – Collection, storage, delivery & valuation methods • Proven societal & environmental benefits – Sustainable – Supportive policies
- 37. Outline • Biomass Basics • Overview of Conversion Options • Details of Enzyme-based Technology • Biorefining Now and in the Future
- 40. Technical Barriers • Feedstock Valuation and Delivery – Analytical methods/sensors – Supply systems – Soil sustainability • Biomass Recalcitrance to Conversion – Pretreatment – Enzymatic hydrolysis – Pentose fermentation • Process Integration – Solids handling ➢Interactions – Process chemistry
- 46. Comparing the Attributes of SSF and SHF Process Configurations Simultaneous (SSF/SSCF) • Minimize enzyme inhibition by accumulating sugars • Achieve high cellulose conversion yields • Reduce process complexity via “one step” approach • Increase pentose utilization and fermentative strain robustness through sustained production and co-utilization of glucose • Minimize the potential for contaminant outgrowth by maintaining a low free sugar concentration Sequential (SHF) • Run enzymatic hydrolysis and fermentation at their respective temperature and pH optima – large benefits possible when optima are significantly different • Generate intermediate sugar product(s) – Upgrade for sale or use as substrates to manufacture other value-added products…enable multi-product biorefineries • Easier mixing in fermentation – Lower levels of solids in fermentation (or absence of solids if S/L separation used prior to fermentation)
- 48. Technical Barriers • Feedstock Valuation and Delivery – Analytical methods/sensors – Supply systems – Soil sustainability • Biomass Recalcitrance to Conversion – Pretreatment – Enzymatic hydrolysis – Pentose fermentation • Process Integration – Solids handling – Interactions ➢ Process chemistry
- 49. Biomass Chemistry and Ultrastructure • Our understanding of biomass chemistry and structure and of conversion mechanisms continues to grow, but many issues remain unknown – Further work needed to advance analysis tools and fundamental understanding of biomass ultrastructure and process chemistry during conversion processes
- 51. The Role of Technoeconomic Analysis • Quantify relative impacts of process Improvements • Identify research directions with largest cost reduction potential, or highest perceived benefit/investment ratio
- 55. Economic Modelling Highlights, cont’d • Estimated operating costs are becoming competitive, although capital costs remain high – Process intensification and the ability to produce additional value-added coproducts are both approaches being pursued to reduce the capitalization/financing burden ➢ There has been significant progress in reducing projected sugar platform costs through a variety of approaches, including co-location, feedstock valuation, enzyme cost reduction, high solids processing, etc. – Selected highlights follow….
- 57. Towards a Low Cost Feedstock Infrastructure • Reducing feedstock cost is a significant opportunity – Apply innovative harvesting & storage methods • Whole stalk harvest? • Dry or wet densification? – Value the feedstock based on its composition • In-field or point-of-delivery rapid compositional analysis, e.g., using calibrated Near InfraRed Spectroscopy (NIRS) ⇒ Application of NIRS shows that significant knowledge gaps remain about the magnitude and sources of feedstock compositional variability.
- 61. Reducing Cellulase Cost ➢ role: • Issue subcontracts to industry and facilitate their success • Supply “standard” pretreated feedstock • Develop cost metric to translate enzyme performance into economic terms, i.e., enzyme cost ($/gallon EtOH) • Experimentally validate key results • Review/Audit key results that can’t be independently validated • Provide supporting information, consultation, and guidance as requested or needed to facilitate subcontractor success Objective: Reduce cost of cellulases for biomass conversion applications to enable large volume sugar platform technology • The program’s enzyme cost target is $0.10/gallon ethanol or less NREL’s
- 64. Metrifying Enzyme Cost Reduction Where: – CE = Enzyme cost ($/gal ethanol) – EP = Enzyme price ($/L product) (subcontractor supplied) – EL = Enzyme loading (g protein/g cellulose entering hydrolysis) (measured) – BN = Enzyme concentration in product (g protein/L product) (measured) – Y = Ethanol Process Yield (gal EtOH/g cellulose entering hydrolysis) (calculated from process model
- 65. 1. . Measure enzyme concentration, BN • Use accepted protein measurement method (Pierce BCA) 2. Measure required enzyme loading on “standard” pretreated corn stover (PCS) substrate, EL • Use variation of traditional shake flask SSF digestibility test 3. Calculate CE using subcontractor supplied EP and metric Y 1. Measure enzyme concentration, BN • Use accepted protein measurement method (Pierce BCA) 2. Measure required enzyme loading on “standard” pretreated corn stover (PCS) substrate, EL • Use variation of traditional shake flask SSF digestibility test 3. Calculate CE using subcontractor supplied EP and metric Y Approach
- 67. Overall Improvement Matrix Benchmark Improved Lot 1 P010129 A mg/g A’ mg/g Lot 2 P020502 B mg/g B’ mg/g Enzyme Preparation Feedstock PCS Lot Enzyme related Improvements (Subcontractor) W X Substrate-related Improvements (NREL)
- 68. Industry-led Cellulase Cost Reduction • Similar Subcontracts set up with Genencor and Novozymes to reduce cost of commodity cellulases by tenfold or greater – 3 year periods of performance + 1 year extensions – 20% cost share by industry – Annual performance milestones with ultimate 3 yr 10X goal relative to benchmark established at start of subcontracts; in extensions, goal adjusted to reaching an enzyme cost of $0.10/gallon of ethanol or less • Status – Details proprietary. Both companies presented updates at a May ‘03 project review and have since issued press releases. See internet. • http://www.ott.doe.gov/biofuels/enzyme_sugar_platform.html • http://www.genencor.com • http://www.novozymes.com – Go to the companies press web site archives and search on “biomass” • Highlights/Summary of Reported Accomplishments – Both companies exceeded 3 yr 10X cost reduction goal, decreasing estimated enzyme costs from ~$5.00 to $0.30-0.40 per gal EtOH – Cost reduction efforts continuing •One year extensions finished in 11/04 (Genencor) or 1/05 (Novozymes)
- 72. Dilute Sulfuric Acid Pretreatment of Corn Stover Stover harvested from northeastern Colorado in the fall of 2002
- 73. High Solids Pre-treatment Performance Pilot-scale dilute acid pretreatment of corn stover at 25%-35% w/w solids Xylan Solubilization as a Measure of Hemicellulose Extraction/Hydrolysis Efficiency Enzymatic Digestibility of Pretreated Solids Monomeric Xylose Yield Total Xylose Yield Cellulose Digestibility
- 81. Combining Enzymatic Saccharification and Mixed Biomass Sugar Fermentation • Complex process integration issue influenced by – Characteristics of substrate, enzyme(s), and microbe • Substrate: What ranges of sugars and toxins are present after pretreatment, what enzyme activities are required to complete saccharification, and how reactive/susceptible is the substrate? • Microbe: What sugars can be fermented, and what temperatures and inhibitors tolerated? • What Enzyme: How effectively are pretreated solids hydrolyzed, how thermostable are enzymes, and how resistant is the enzyme system to end product inhibition? – Many potential substrates, enzyme preparations, and fermentation strain combinations are possible
- 83. Shakeflask SSF as a Predictor of Integrated SSCF
- 84. Pilot vs. Bench SSCF
- 85. Biomass Sugar Fermentation Needs • High Yield Requires Fermenting all Biomass Sugars – Glucose, Xylose, Arabinose, Mannose, Galactose • Resistant to toxic materials/chemicals in hydrolysates – Acids, phenolics, salts, sugar oligomers, … • Robust, able to out-compete contaminating microbes – Temperature, pH – High fermentation rates • Minimum metabolic byproducts
- 87. Incineration for safe disposal of hazardous waste
- 101. Hazardous Waste Incineration Techniques
- 107. Direct-Fired Biomass Residue System 134% carbon closure
- 108. Examples: Hydrothermal Processing, Liquefaction, Wet Gasification
- 109. Temperature
- 110. Pyrolysis Severity
- 112. Pyrolysis
- 113. Energy Efficiency • Conversion to 75 wt‐% bio‐oil translates to energy efficiency of 70% • If carbon used for energy source (process heat or slurried with liquid) then efficiency approaches 94%
- 115. Mohan D., Pittman C. U. Jr., and Steele P. H. “Pyrolysis of Wood/Biomass for Bio‐oil: A Critical Review” Energy & Fuels, 20, 848‐889 (2006)
- 118. • Advantages of bio‐oil: – Can be upgraded to drop‐in (hydrocarbon) fuels – Opportunities for distributed processing • Disadvantages of bio‐oil – High oxygen and water content bio‐oil inferior to makes bio petroleum‐derived fuels – Phase‐separation and polymerization and corrosiveness make long‐term storage difficult Applications of Bio‐Oil • Stationary Power • Commodity Chemicals • Transportation Fuels
- 125. CFB and Transported Beds • Good temperature control in reactor, • Larger particle sizes possible, • CFBs suitable for very large throughputs, • Well understood technology, • Hydrodynamics more complex, larger gas flows in the system, • Char is finer due to more attrition at higher velocities; separation is by cyclone, • Closely integrated char combustion requires careful control, • Heat transfer to bed at large scale has to be proven.
- 126. Rotating Cone (BTG) Centrifugation drives hot sand and biomass up rotating heated cone; Vapors are condensed; Char is burned and hot sand is recirculated.
- 127. Vacuum Moving Bed ➢ Developed at Université Laval, Canada, scaled up by Pyrovac ➢ Pilot plant operating at 50 kg/h ➢ Demonstration unit at 3.5 t/h ➢ Analogous to fast pyrolysis as vapor residence time is similar. ➢ Lower bio-oil yield 35-50% ➢ Complicated mechanically (stirring wood bed to improve heat transfer)
- 128. Auger Reactor • Developed for biomass pyrolysis by Sea Sweep, Inc (oil adsorbent) then ROI (bio-oil); • 5 t/d (200 kg/h) mobile plant designed for pyrolysis of chicken litter; • Compact, does not require carrier gas; • Lower process temperature (400ºC); • Lower bio-oil yields • Moving parts in the hot zone • Heat transfer at larger scale may be a problem
- 129. Char Removal • Char acts as a vapor cracking catalyst so rapid and effective removal is essential. • Cyclones are usual method of char removal. Fines pass through and collect in liquid product. • Hot vapor filtration gives high quality char free product. Char accumulation cracks vapors and reduces liquid yield (~20%). Limited experience is available. • Liquid filtration is very difficult due to nature of char and pyrolytic lignin.
- 130. Liquid Collection • Primary pyrolysis products are vapors and aerosols from decomposition of cellulose, hemicellulose and lignin. • Liquid collection requires cooling and agglomeration or coalescence of aerosols. • Simple heat exchange can cause preferential deposition of heavier fractions leading to blockage. • Quenching in product liquid or immiscible hydrocarbon followed by electrostatic precipitation is preferred method.
- 132. Bio-oil Properties The complexity and nature of the liquid results in some unusual properties. Due to physical-chemical processes such as: 1. Polymerization/condensation 2. Esterification and etherification 3. Agglomeration of oligomeric molecules Properties of bio-oil change with time: 1. Viscosity increases 2. Volatility decreases 3. Phase separation, deposits, gums
- 133. Upgrading of Bio-oils Physical Methods 1. Filtration for char removal, 2. Emulsification with hydrocarbons, 3. Solvent addition, Chemical Methods 1. Reaction with alcohols, 2. Catalytic deoxygenation: Hydrotreating, Catalytic (zeolite) vapor cracking
- 135. Bio-oil Cost Different claims of the cost of production: • Ensyn $4-5/GJ ($68-75/ton) • BTG $6/GJ ($100/ton) Cost = Wood cost/10 + 8.87 * (Wood throughput)-0.347 $/GJ $/dry ton dry t/h
- 136. Why Is Bio-oil Not Used More? • Cost : 10% – 100% more than fossil fuel, • Availability: limited supplies for testing • Standards; lack of standards and inconsistent quality inhibits wider usage, • Incompatibility with conventional fuels, • Unfamiliarity of users • Dedicated fuel handling needed, • Poor image.
- 139. Indian Policy on Biofuels *An indicative target of 20% blending of Biofuels both for biodiesel and bioethanol by 2017. *Biodiesel production from non-edible oilseeds on waste, degraded and marginal lands to be encouraged *A Minimum Support Price (MSP) to be announced for farmers producing non-edible oilseeds used to produce biodiesel. *Financial incentives for new and second generation Biofuels, including a National Biofuels Fund *Setting up a National Biofuels Coordination Committee under the Prime Minister for a broader policy perspective *Setting up a Biofuels Steering Committee under the Cabinet Secretary to oversee policy implementation *Several ministries are involved in the promotion, development and policy making for the Biofuels sector *The Ministry of New and Renewable Energy is the overall policymaker, promoting the development of biofuels as well as undertaking research and technology development for its production *The Ministry of Petroleum and Natural Gas is responsible for marketing biofuels and developing and implementing a pricing and procurement policy *The Ministry of Agriculture’s role is that of promoting research and development for the production of Biofuels feedstock crops *The Ministry of Rural Development is specially tasked to promote Jatropha plantations on wastelands *The Ministry of Science & Technology supports research in Biofuels crops, specifically in the area of biotechnology
- 140. Salient features of the National BioDiesel Policy : 1. An indicative target of 20% by 2017 for the blending of biofuels (Bioethanol and BioDiesel) was proposed. (Even 1% is not achieved) 2. BioDiesel production will be taken up from non-edible oil seeds grown in waste / degraded / marginal lands. (This has Failed) 3. The focus would be on indigenous production of BioDiesel feedstock and import of Free Fatty Acid (FFA) of oils, such as palm oil etc. would not be permitted. (Due to this, raw material is not available) 4. BioDiesel plantations on Community / Government / Forest waste lands would be encouraged while plantation in fertile irrigated lands would not be encouraged. (This has Failed) 5. Minimum Support Price (MSP) with the provision of periodic revision for oil seeds for BioDiesel manufacture, would be announced to provide fair price to the growers. The details about the MSP mechanism, enshrined in the National Biofuel Policy, would be worked out carefully subsequently and considered by the BioDiesel Steering Committee. (This has Failed due to non remunerative price offered by the oil marketing companies) 6. Minimum Purchase Price (MPP) for the purchase of bio-ethanol by the Oil Marketing Companies (OMCs) would be based on the actual cost of production and import price of bio-ethanol. In case of BioDiesel, the MPP should be linked to the prevailing retail diesel price. (This was not done) 7. The National Biofuel Policy envisages that bio-fuels, namely, BioDiesel and Bioethanol may be brought under the ambit of “Declared Goods” by the Government to ensure unrestricted movement of biofuels within and outside the States. It is also stated in the Policy that no taxes and duties should be levied on bio-diesel.
- 141. First Generation Biofuels - 'First-generation Biofuels' are Biofuels made from sugar, starch, vegetable oil or animal fats using conventional technology. The basic feedstock's for the production of first generation Biofuels are often seeds or grains such as sunflower seeds, corn or soybeans which are pressed to yield vegetable oil that can be used for producing biodiesel. These feedstock's could instead enter the animal or human food chain, and as the global population has risen their use in producing Biofuels has been criticised for diverting food away from the human food chain, leading to food shortages and price rises. Second Generation Biofuels - Second-generation Biofuels use non-food crops as the feedstock; these include waste biomass, the stalks of wheat, corn, wood, and special-energy-or-biomass crops (e.g. Miscanthus). Second generation (2G) Biofuels use biomass to liquid technology, including cellulosic Biofuels. Many second generation Biofuels are under development such as biohydrogen, biomethanol, DMF, Bio-DME, Fischer-Tropsch diesel, biohydrogen diesel, mixed alcohols and wood diesel. Cellulosic ethanol production uses nonfood crops or inedible waste products and does not divert food away from the animal or human food chain. Lignocelluloses is the "woody" structural material of plants. This feedstock is abundant and diverse, and in some cases (like citrus peels or sawdust) it is in itself a significant disposal problem. Third Generation Biofuels - Algae fuel, also called oilgae or third generation Biofuels, is a Biofuels from algae. Algae are low-input, high-yield feedstock's to produce Biofuels. Based on laboratory experiments, it is claimed that algae can produce up to 30 times more energy per acre than land crops such as soybeans, but these yields have yet to be produced commercially. With the higher prices of fossil fuels (petroleum), there is much interest in alga culture (farming algae). One advantage of many Biofuels over most other fuel types is that they are biodegradable, and so relatively harmless to the environment if spilled. Algae fuel still has its difficulties though, for instance to produce algae fuels it must be mixed uniformly, which, if done by agitation, could affect biomass growth.
- 142. Common Second Generation Feedstock
- 146. TYPES OF PYROLYTIC REACTORS • System Configuration • A pyrolysis system unit typically consists of the equipment for biomass pre-processing, the pyrolysis reactor, and equipment for downstream processing. • Can be classified as units that produce heat and biochar (using slow pyrolysis) or units that produce biochar and bio-oils (using fast pyrolysis), (a) Biochar and bio-oil production (b) Biochar and heat production Air Pyrolysis vapors Combustion Chamber Combustion Gases Biomas s Char Heat PYROLYSIS REACTORS Bio-oil Condensers Pyrolysis vapors Biomas s Char PYROLYSIS REACTORS Gas
- 147. TYPES OF PYROLYTIC REACTORS • Classification based on solid movement • Reactors used for biomass pyrolysis is most commonly classified depending on the way the solids move through the reactor during pyrolysis. ✓Type A: No solid movement through the reactor during pyrolysis (Batch reactors) ✓Type B: Moving bed (Shaft furnaces) ✓Type C: Movement caused by mechanical forces (e.g. rotary kiln, rotating screw etc.) ✓Type D: Movement caused by fluid flow (e.g., fluidized bed, spouted bed, entrained bed etc.)
- 148. TYPES OF PYROLYTIC REACTORS • Classification based on method of heat supplied • Pyrolytic reactor can also be classified depending the way heat is supplied to biomass: ✓Type 1: Part of the material burnt inside the reactor to provide the heat to carbonize the remainder ✓Type 2: Direct heat transfer from hot gases produced by combustion of the pyrolysis products or any other fuel outside the reactor. ✓Type 3: Direct heat transfer from inert hot material (hot gases or sand introduced into the reactor). ✓Type 4: Indirect heat transfer through the reactor walls (i.e. external heat source due to combustion of one or more pyrolysis products or any other fuel).
- 149. TYPES OF PYROLYTIC REACTORS • Variations in the Process and Reactors • Many different combinations of modes of solid movement and modes of heat transfer are possible in practice. • Accordingly, the type of a pyrolytic reactor can probably be best specified by denoting it as type XI where X stands for type of solid movement and I indicates the type of heat transfer. • Different names are often used to describe specific type of pyrolytic reactors. ✓The term “kiln” is used for devices producing only charcoal. ✓The terms “retort” and “converter” are used for equipments capable of recovering by-products. ✓The term “converter” normally refers to devices used for pyrolysing biomass of small particle size and the term “retort” refers to equipment for pyrolysing log reduced in size to about 30 cm length and 18 cm diameter.
- 150. TYPES OF PYROLYTIC REACTORS • Types of Pyrolysis Reactor Designs • A number of different pyrolysis reactor designs are available. • These include Fluidized bed, Re-circulating fluidized bed, Ablative, Rotating cone, Auger (or screw), Vacuum, Transported bed, and Entrained flow. Fluidized bed Rotating cone
- 151. TYPES OF PYROLYTIC REACTORS • Types of Pyrolysis Reactor Designs Re-circulating fluidized bed Vacuum
- 152. TYPES OF PYROLYTIC REACTORS • Types of Pyrolysis Reactor Designs • As pyrolysis is a precursor to gasification and combustion, the same reactors used for gasification can be used for pyrolysis. • Bubbling fluidized bed reactors are simpler to design and construct than other reactor designs, and have good gas to solids contact, good heat transfer, good temperature control, and a large heat storage capacity. • Circulating fluidized bed pyrolysis reactors are similar to bubbling fluidized bed reactors but have shorter residence times for chars and vapors which results in higher gas velocities, faster vapor and char escape, and higher char content in the bio-oil. • They have higher processing capacity, better gas- solid contact, and improved ability to handle solids that are difficult to fluidize.
- 153. TYPES OF PYROLYTIC REACTORS • Heat Transfer Modes and features of various reactors: Reactor type Mode of heat transfer Typical features Fluidized bed 90% conduction; 9% convection; 1% radiation High heat transfer rates; Heat supply to fluidizing gas or to bed directly; Limited char abrasion; Very good solids mixing; Particle size limit < 2 mm in smallest dimension; Simple reactor configuration Circulating fluidized bed 80% conduction; 19% convection; 1% radiation High heat transfer rates; High char abrasion from biomass and char erosion; Leading to high char in product; Char/solid heat carrier separation required; Solids recycle required; Increased complexity of system; Maximum particle sizes up to 6 mm; Possible liquids cracking by hot solids; Possible catalytic activity from hot char; Greater reactor wear possible Entrained flow 4% conduction; 95% convection; 1% radiation Low heat transfer rates; Particle size limit < 2 mm; Limited gas/solid mixing Ablative 95% conduction; 4% convection; 1% radiation Accepts large size feedstocks; Very high mechanical char abrasion from biomass; Compact design; Heat supply problematical; Heat transfer gas not required; Particulate transport gas not always required
- 154. PARAMETERS INFLUENCING PYROLYSIS PROCESS • The basic phenomena that take place during pyrolysis: • Heat transfer from a heat source, leading to an increase in temperature inside the fuel; • Initiation of pyrolysis reactions due to this increased temperature, leading to the release of volatiles and the formation of char; • Outflow of volatiles, resulting in heat transfer between the hot volatiles and cooler unpyrolysed fuel; • Condensation of some of the volatiles in the cooler parts of the fuel to produce tar; and • Autocatalytic secondary pyrolysis reactions due to these interactions.
- 155. PARAMETERS INFLUENCING PYROLYSIS PROCESS • Pyrolysis process control parameters: • Important pyrolysis process control parameters include: ✓ Heat rate (length of heating and intensity), ✓ Prevailing temperature and pressure ✓ The presence of ambient atmosphere ✓ The chemical composition of the fuel (e.g., the biomass resource), ✓ Physical properties of the fuel (e.g. particle size, density), ✓ Residence time and the existence of catalysts. • These parameters can be regulated by selection among different reactor types and heat transfer modes, such as gas–solid convective heat transfer and solid–solid conductive heat transfer.
- 156. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Overall Mechanism • On heating, the constituents of biomass materials decompose following different pathways and yielding a variety of products, each of which has its own kinetic characteristics. • In addition, secondary reaction products result from cross-reactions of primary pyrolysis products and between pyrolysis products and the original feedstock molecules. Overall mechanism of biomass pyrolysis
- 157. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Pyrolysis of main constituents • To understand pyrolysis of wood, it is interesting to consider first the pyrolysis of the main wood constituents - cellulose, hemicellulose and lignin. ✓Cellulose: C6H10O5; Lignin: C9H10O3(OCH3)0.9-1.7; Hemicellulose: C5H8O4 • On an average hardwood contains 43% cellulose, 35% hemicellulose and 23% lignin while softwood contains 43% cellulose, 28% hemicellulose and 29% lignin. • On heating, the constituents of wood decompose following different pathways and yielding a variety of products.
- 158. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Pyrolysis of main constituents Figure 4.48: Thermal stability regimes for cellulose, hemi-cellulose and lignin 100 150 200 250 300 350 400 Drying A Glass transition/ softening B A Depolymerization and recondensation C Limited devolatitization and carbonization D Extensive devolatitization and carbonization E A (1) C D C D E E Temperature (℃) Thermal stability regimes for cellulose, hemi-cellulose and lignin
- 159. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Cellulose Pyrolysis • Upon heating to temperatures below 250C cellulose undergoes a drop in the degree of polymerization and pyrolysis takes place slowly, the major products being H2O, CO2, CO and a carbonaceous residue. • At temperatures above 250C cellulose begins to pyrolyse rapidly producing condensable “tar” along with gases and leaves a charred residue. • The pyrolysis of cellulose proceeds very rapidly at around 350C and above 500C the volatile products begin to undergo gas-phase pyrolysis.
- 160. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Cellulose Pyrolysis • Following figure provides a simplified reaction scheme of cellulose pyrolysis. temperature but takes place over a much wider temperature range and produces less char. Figure 4.49: Reaction scheme for cellulose pyrolysis
- 161. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Hemicellulose Pyrolysis • Compared to cellulose, hemicellulose pyrolysis begins at a lower temperature but takes place over a much wider temperature range and produces less char. • Lignin Pyrolysis • Lignin is regarded as the most stable of the major biomass components. • Below 200C its rate of thermal degradation is very slow. • Lignin decomposes between 280C and 500C and produces more char compared to cellulose. • At low heating rates the char yield from lignin exceeds 50% by weight.
- 162. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis • Behavior of biomass during pyrolysis depends on the behavior of its major components. • Products of biomass pyrolysis can be regarded as a linear combination of products expected from the separated pyrolysis of the three major components. • Cellulose and hemicellulose are the major sources of volatiles and tar while lignin is the major source of char. • The biomass is decomposed by a number of parallel primary reactions into primary products, which are acted upon by a number of secondary reactions. • Char is formed as a product of the primary reactions and as solid material deposited due to the secondary reactions.
- 163. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis Moisture (drying) Extractives (Terpenes, lipids) Acids (acetic acids) Furans (furfural) Anhydrosugars (levoglucosan) Hydroxymethylfurfural Phenols, methanol Charcoal Use of catalysts 100 ℃ 200 ℃ 300 ℃ 400 ℃ 500 ℃ 600 ℃ Overlapping thermochemical stability Complicates selective products devolatilisation! Torrefaction for enhanced wood fuels (250 – 290 ℃) Fast pyrolysis for bio-diesel (450 – 550 ℃) carbonization for charcoal 100 ℃ 200 ℃ 300 ℃ 400 ℃ 500 ℃ 600 ℃ Lignin Drying Cellulose Hemicellulose Overview of the thermal fractionation of biomass by a step-wise pyrolysis approach.
- 164. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis • The chemistry and products of biomass pyrolysis are summarized in the following table. Type Feature and Process Products and their characterizations Pyrolysis of holocellulose General effects: Colour changes from brown to black, Flexibility and mechanical strength are lost, size reduced, weight reduced Processes: Dehydration – also known as char forming reactions produces volatile products and char. Depolymerization – produces tar Effect of temperature: At low temperatures dehydration predominates, at 630K depolymerization with production of levoglucosan dominates. Between 550 and 675K products formed are independent of temperature. Volatile products: Readily escape during pyrolysis process, 59 compounds are produced out of which 37 have been identified CO, CO2, H2O, acetal, furfural, aldehydes, ketones. Tar: Levoglucosan is principal component. Char: As heating continues there is 80% loss of weight and remaining cellulose is converted to char, prolonged heating or exposure to higher temperature (900K) reduces char formation to 9%.
- 165. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis • The chemistry and products of biomass pyrolysis are summarized in the following table. Type Feature and Process Products and their characterizations Pyrolysis of lignin Conventional (Carbonization): At 375-450 K endothermic reaction From 675 K exothermic reaction Maximum rate occurring between 625 and 725 K Fast and Flash pyrolysis: High temperature of 750K, rapid heating rate, finely ground material, less than 10% moisture content, rapid cooling and condensation of gases, yields in 80% range, char and gas used for fuel Char: Approximately 55% Distillates: 20%, methanol, methoxyl groups, acetone, acetic acid Tar: 15%, phenolic compounds and carboxylic acid Gases: CO, methane, CO2, ethane Bio-oil: Will not mix with hydrocarbon liquids, cannot be distilled, substitute for fuel oil and diesel in boilers, furnaces, engines, turbines, etc. Phenols: Utilizes a solvent extraction process to recover phenolics and neutrals, 18-20% of wood weight, secondary processing of phenol pharmaldehyde resins, adhesives, injection molded plastics. Other chemicals, extraction process: Chemical for stabilizing the brightness regression of thermochemical pulp (TMP) when exposed to light , food flavorings, resins, fertilizers, etc.
- 166. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis • Mathematical modeling of biomass pyrolysis process is a complicate one, in particular for large biomass particles. • Small particles offer negligible resistance to internal heat transfer and their temperature can be assumed to be uniform during pyrolysis. • Further, in the case of rapid heating (e.g. in fluidized beds), the biomass particles are rapidly heated to the temperature of the reactor, which remains essentially constant during pyrolysis.
- 167. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis • However, pyrolysis of large biomass is a complicate process and involves following steps: ✓Transfer of heat to the surface of the particle from its surrounding usually by convection and radiation ✓Conduction of heat through the carbonized layer of the particle ✓Carbonization of the virgin biomass over a range of temperature inside the particle ✓Diffusion of the volatile products from inside to the surface of the particles, and ✓Transfer of the volatile products from the surface of the particle to the surrounding inert gas.
- 168. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis • Thus the rate of expression for pyrolysis in this case will incorporate heat and mass transfer terms in addition to kinetics terms of biomass decomposition reactions. • The overall pyrolysis process is further complicated by ✓Secondary pyrolysis of the volatile products while diffusing out through the particle, ✓Heat transfer by convection to the volatile products while diffusing out through the particle, ✓Shrinkage of the biomass particle as it undergoes pyrolysis, etc.
- 169. MECHANISM AND PRODUCTS OF BIOMASS PYROLYSIS • Biomass Pyrolysis Figure 4.51 illustrate the main stages and products of the reactions of biomass pyrolysis [82]. ▪ Temperature: Low T < 400 C < High T ▪ Pressure: Low P < 75 kPa < High P ▪ Residence Time: Fast < 0.1 second < Slow PRIMARY TAR (LIQUID) BIOMASS (SOLID) Low Temperature TRANSIENT OXYGENATED FRAGMENTS (VAPOUR) CO CH4 H2 CO2 OLEFINS VAPOUR PHASE DERIVED TAR (VAPOUR OR LIQUID) WATER SOLUBLE OXYGENATED COMPUNDS (VAPOUR) CARBONBLACK (SOLID) H2,CO,CH4, CO2,H2O High Temperature Slow Low Pressure High Temperature Slow High Pressure SECONDARY TAR (LIQUID) PRIMARY TAR (VAPOUR) High Temperature Fast Low Pressure High Temperature Fast Low Pressure High Temperature Slow Low Pressure Medium Temperature Slow Medium Pressure CHARCOAL (SOLID) CO2,H2O High Temperature Fast Low Pressure Low Temperature Slow High Pressure High Temperature Slow High Pressure High Temperature Slow High Pressure
- 170. THE CHARCOAL MAKING PROCESS • Basics • Charcoal is made in many different ways depending on the type of reactor employed. • However, the basic steps by which wood is transformed to charcoal are the same. • Three distinct phases can be distinguished: drying, pyrolysis, and cooling. • In practice, and particularly when the charcoal is made in large kilns, there is often a considerable overlap between these. • Thus, pyrolysis may be well advanced in one area of the kiln before drying is complete in another.
- 171. THE CHARCOAL MAKING PROCESS • The Drying Phase • Before wood can be carbonized, the water it contains must be driven off. This happens in two distinct stages: ✓The first is when the water in the pores of the wood, sometimes called the free water, is expelled. While this is happening, the temperature of the charge of wood remains at about 110C. The wetter the wood, the longer this process takes and the greater is the amount of energy consumed during it. ✓When all the water in the pores has been driven off, the temperature rises. When it reaches about 150C, water which is more tightly bound or absorbed into the cellular structure of the wood (bond water) begins to be released. This continues as the temperature rises to around 200C. ✓When the charcoal is made in a kiln, the water is released to the air in the form of water vapour. This is the principal constituent of the white smoke characteristic of the early stages of carbonization.
- 172. THE CHARCOAL MAKING PROCESS • The Pyrolysis Phase • With the continued application of heat, the temperature of the wood rises further. • Around 280C, the pyrolysis reaction begins to occur. The breakdown of biomass results in the evolution of a complex series of chemical substances referred to as the pyrolysis products. • Because most of these are driven off in the form of gas or vapour, they are often described as the volatiles. • The presence of the volatiles causes the colour of the smoke coming from a charcoal kiln to darken thus indicating that pyrolysis is under way. • It also gives rise to the characteristic heavy smell of wood-tar normally associated with charcoal making.
- 173. THE CHARCOAL MAKING PROCESS • The Pyrolysis Phase • Once the pyrolysis is under way, the need for a heat supply to maintain the reaction is very much less than that needed to drive off the water during the drying phase. • When using a kiln, the need to continue burning part of the charge is reduced and the air supply is usually restricted at this stage. • The temperature reached during pyrolysis depends on the size of the charge of wood being carbonized, the geometry of the kiln, the degree to which the manufacturing process is insulated against heat loss, the ambient temperature, the original moisture content of the wood, and a variety of other factors.
- 174. THE CHARCOAL MAKING PROCESS • The Pyrolysis Phase • In most small-scale traditional methods of manufacture, the maximum temperature reached tends to be about 400-500C. But in some types of kilns, temperatures of up to 600-700C are attained. Higher temperatures normally require the use of retorts. • During pyrolysis, there is a considerable loss of volume in the wood. Across the grain this can be as much as 30-40%, though it is much less along the grain. • A kiln in which the wood has been laid horizontally thus tends to collapse down wards during charcoal making, whereas on in which the wood has been stacked vertically has a much smaller change in volume.
- 175. THE CHARCOAL MAKING PROCESS • The Cooling Phase • As the pyrolysis reaction draws to its completion, the temperature in the charge of wood begins to fall. • The amount of smoke given off from a charcoal kiln drops substantially and its colour changes to a pale blue and in some cases the smoke emission stops completely. • The kiln or retort must be kept tightly sealed at this stage. If air is admitted before the charcoal has fallen below its ignition temperature, there is a danger of the whole load bursting into flame. • Even when it has been allowed to cool thoroughly, care must always be taken as the charcoal is being unloaded from the kiln. High temperature pockets often remain and these can ignite spontaneously as they come into contact with air.
- 176. THE CHARCOAL MAKING PROCESS • The Cooling Phase • Once it has been released to the open air, charcoal is usually left for a period of about 24 hours for ‘seasoning’ to occur. • During this time, the charcoal cools to air temperature and some of the remaining volatiles escape. Some moisture and a small amount of oxygen are also absorbed. • Once thee danger of spontaneous combustion disappears and the charcoal is ready for packing and transport.
- 177. FACTORS INFLUENCING THE CHARCOAL YIELD • Factors • A number of factors affect the yield of charcoal obtained from a particular manufacturing method. • Two of the most important of these are the maximum temperature reached during carbonization and the moisture content of the wood • Carbonization Temperature • The carbonization temperature affects the yield as well as the fixed carbon content. • The extreme case is where the carbonization temperature is 200C, with maximum yield and lowest fixed carbon content. • This is sufficient to produce little more than a through drying and light charring of the wood (low quality).
- 178. FACTORS INFLUENCING THE CHARCOAL YIELD • Carbonization Temperature • Effect of Carbonization Temperature on Yield and Fixed Carbon Content of Charcoal Carbonization Temperature C Yield of charcoal as % of oven dry weight of original wood Fixed carbon as % of dry weight of charcoal 200 91.8 52.3 250 65.2 70.6 300 51.4 73.2 500 31.0 89.2 600 29.1 92.2 700 27.8 92.8 800 26.7 95.7 900 26.6 96.1 1000 26.3 96.6 1100 26.1 96.4
- 179. FACTORS INFLUENCING THE CHARCOAL YIELD • Water Content • The water content of the wood also affects the final yield because it determines the proportion of the charge which has to be burned during the drying phase. • For example, for green wood with a moisture content of 56% on a wet basis, 17.4% of the original dry weight of the wood is lost in driving off the water. • If the wood is pre-dried to a moisture content of 17%, then the proportion required to drive off the water falls to 2.7%. • This means that 14.3% of the original wood charge, which would otherwise have been burned to drive off the water, is available for turning into charcoal.
- 180. FACTORS INFLUENCING THE CHARCOAL YIELD • Water Content • High initial water content also reduces the maximum temperature reached during carbonization. • In addition, it extends the carbonization time. • Therefore influence of moisture content on the final yield is very complex. • When charcoal with a high fixed carbon content is required, the use of dry wood leads to a higher yield. • It reduces the time needed for carbonization, which is a particularly important factor when charcoal making equipment with a high capital cost is being used. • In such cases, it usually makes considerable technical and economic sense to reduce the water content of wood before making it into charcoal.
- 181. DIFFERENT TYPES OF CHARCOAL KILN • Classifications Systems for Carbonizing Wood Internal source of heat to dry and heat wood achieved by burning part of the charge External source of heat to dry and heat wood, by burning wood, gas, coal or oil and tars Pits; Mounds Brick Kilns Metal Kilns Indirect heating through retort walls Direct heating by recirculation of neutral hot gas through wood to be carbonized Metal Retorts Brick Kilns Metal Kilns Portable Fixed Portable Fixed
- 182. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits / Mounds • Using earth as a shield against oxygen and to insulate the carbonising wood against excessive loss of heat is the oldest system of carbonization. • There are two distinct ways to use an earth barrier in charcoal making: ✓one is to excavate a pit, put in the charge of wood and cover the pit with excavated earth to seal up the chamber. ✓The other is to cover a mound or pile of wood on the ground with earth. • The earth forms the necessary gas-tight insulating barrier behind which carbonization can take place without leakage of air.
- 183. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits • A stratum of deep soil is needed for this method. Figure shows a large pit of about 30 m³ gross volume. It will hold a charge of about 26 m³.
- 184. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits • A sandy loam is preferred with adequate depth. • About three man days are needed to dig the pit and a day to add the channels for lighting and for smoke exist. • The pit is loaded with logs measuring 2.4 m or less, which will fit easily across the pit. • To ensure that the wood is properly heated for carbonization, the hot gas is allowed to pass along the floor of the pit by placing the charge on a crib of logs. • First, about five logs, cut to the width of the pit, are laid evenly spaced along the length; then four logs each equal to the length of the pit are evenly spaced on top of the first layer.
- 185. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits • This crib structure supports the charge and yet allows hot gases once the pit is lit at one end, to pass beneath the charge, heating it as they travel to the flue at the opposite end. • These hot gases produced by partial burning of the wood charged slowly dry out the earth and heat up the rest of the wood to the carbonization point, about 280°C. • Spontaneous decomposition of the wood, with evolution of heat, then occurs to form charcoal. Copious volumes of water vapour, acetic and other acids, methanol and tars, are produced at the same time.
- 186. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits • These also transfer their heat to the drying wood charge on their way to the outlet. • Finally, the last of the wood is dried out, heated to carbonization point, and transforms itself into charcoal. • The carbonization stage may take 20 to 30 days to complete and it is accompanied by a marked volume reduction of the wood charge to 50-70% of its initial volume. • The earth covering the pit slowly sinks during the carbonization and any cracks or holes which form must be closed to prevent air leakage.
- 187. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits • When the covering of the pit has sunk from one end to the other, the burn is considered complete and openings are sealed and the pit allowed to cool, which can take 40 days approximately, depending on the weather. • After cooling, the pit is opened and the charcoal unloaded, taking care to separate it from earth and sand and partially carbonized wood. Forks and rakes are useful for this.
- 188. DIFFERENT TYPES OF CHARCOAL KILN • Earth Pits • Earth pit during burning
- 189. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • Earth mound is an alternative to digging a pit, where the wood is stacked above the ground and covered with earth.
- 190. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • Essentially the process is the same as the pit - the wood to be carbonized is enclosed behind an air-tight well made from earth. • The earth mound is preferred over the pit where the soil is rocky, hard or shallow, or the water table is close to the surface. • By contrast the pit is ideal where the soil is well drained, deep and loamy. • The mound is also more practical in agricultural zones where fuel wood sources may be scattered and it is desirable to make the charcoal near a village or other permanent site.
- 191. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • A mound site can be used over and over again, whereas pits tend to be used a few times and then new ones dug to follow the timber resource. • The repeated digging of pits also disrupts cultivation for crops or pasture. • The fuel wood to be carbonized, in a mound can also be gathered slowly over a period of months, stacked in position and allowed to dry out well before covering and burning. • This fits in well with the life style of a small farmer who may gather scrap wood, branches and logs and stack them carefully to form the mound.
- 192. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • The typical village type charcoal burning mound is about 4 m in diameter at the base and about 1 to 1.5 m high, approximately a flattened hemisphere. • About six to ten air inlets are made at the base and an opening at the top about 20 cm in diameter allows exit of smoke during burning. • All openings must be sealed with earth when burning is complete and the mound is allowed to cool. • A hybrid system containing elements of the earth mound and the pit could also be used.
- 193. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • The above type of mound has been modified by inserting a central chimney made of old oil drums welded together. • The chimney improves gas circulation which reduces the amount of brands (partially carbonized wood pieces) and speeds up the carbonization. Less brands means an improved yield of charcoal. • The mound is covered with grass and shrubs and then sand or loam. • The chimney is placed at the edge of the pile as in the diagram, with its base opening connected to the base of the pile.
- 194. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • This modified earth kiln, called a Casamance kiln, is shown in the figure.
- 195. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • The charcoal iron industry of Sweden brought the design and operation of large mound type kilns to a high stage of perfection. • The main improvements were the use of an external chimney connected to a flue constructed beneath the pile and adoption of a circular ground plan for the pile which reduced heat loss during carbonization and improved gas circulation. • The bottom of the base is covered with logs forming a grate or crib on which the wood is piled vertically. • The grate forms a free space between the bottom and the wood charge through which the air necessary for the carbonization process passes.
- 196. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • The piled wood is covered with leaves and grass and then earth about 20 cm thick. • The pile has an outside stack made of steel drums, which is connected to the pile through a flue cut into the ground, running under the pile and covered with round loge. • The pile has a number of air vents located around the circular base.
- 197. DIFFERENT TYPES OF CHARCOAL KILN • Earth Mounds • The Swedish earth kiln with chimney
- 198. DIFFERENT TYPES OF CHARCOAL KILN • Brick Kilns • Properly constructed and operated brick kilns are one of the most effective methods of charcoal production. • They have proved themselves over decades of use to be low in capital cost, moderate in labour requirements and capable of giving good yields of quality charcoal suitable for all industrial and domestic uses. • The ability of the brick kiln to conserve the heat of carbonization is an important factor in its high conversion efficiency of wood to charcoal.
- 199. DIFFERENT TYPES OF CHARCOAL KILN • Brick Kilns • There are many designs of brick kilns in use throughout the world. • The designs of traditional brick kilns have been refined over many hundreds of years but there are other types of brick kiln in use which have been subject in recent years to systematic experiment to improve them. ✓Brazilian beehive kilns, ✓Argentine half-orange kiln, ✓European Schwartz kiln ✓Missouri kiln of the U.S.A.
- 200. DIFFERENT TYPES OF CHARCOAL KILN • Brick Kilns • Argentine half orange or beehive brick kiln.
- 201. DIFFERENT TYPES OF CHARCOAL KILN • Brick Kilns • Argentine half orange or beehive brick kiln.
- 202. DIFFERENT TYPES OF CHARCOAL KILN • Brick Kilns • Brazilian beehive kiln.
- 203. DIFFERENT TYPES OF CHARCOAL KILN • Brick Kilns • Brazilian beehive kiln.
- 204. DIFFERENT TYPES OF CHARCOAL KILN • Metal Kilns
- 205. Runs CGT:CM Operating Temp Bio Oil Bio Char Gas Gas Bio Oil Bio Char Losses Gas Char Bio Oil Yield (grams) Yield (%) HHV (MJ/KG) 1 1.86 550 76.29 123.59 36.05 11.51 27.25 44.14 17.10 4.44 20.18 29.41 2 4.00 450 107.80 102.44 37.29 13.32 38.50 36.59 11.60 29.14 18.73 36.40 3 2.33 600 43.31 186.72 36.37 10.82 15.47 66.69 7.03 0.87 20.87 26.75 4 1.50 600 69.67 108.95 34.88 15.42 24.88 38.91 20.78 2.26 14.64 32.58 5 4.00 500 117.74 108.29 50.99 17.66 42.05 38.68 1.62 18.20 14.99 31.48 6 3.00 550 107.75 113.72 37.21 14.65 38.48 40.61 6.26 7.79 16.86 28.41 7 1.86 450 57.15 164.40 36.79 12.07 20.41 58.71 8.81 1.40 20.97 31.31 8 1.50 500 69.49 127.25 46.52 16.06 24.82 45.45 13.68 7.49 15.90 31.08 9 1.50 400 98.02 103.57 38.62 13.79 35.01 36.99 14.21 27.77 13.93 33.25 10 2.33 500 101.24 104.08 62.65 21.92 36.16 37.17 4.75 16.28 16.73 30.22 11 4.00 400 42.70 183.92 32.47 10.45 15.25 65.69 8.62 1.53 21.66 23.24 12 2.33 400 99.64 108.13 38.51 13.83 35.59 38.62 11.96 29.43 12.98 28.41 13 3.00 450 111.21 112.35 38.67 13.89 39.72 40.13 6.27 27.80 14.65 26.57 14 4.00 600 121.97 104.16 39.83 14.83 43.56 37.20 4.41 26.55 16.49 26.25 15 4.00 400 61.46 170.36 34.96 11.51 21.95 60.84 5.70 1.29 22.05 22.21 16 2.33 600 115.50 107.39 32.29 15.97 41.25 38.35 4.43 3.89 14.74 35.59 17 1.50 600 115.74 111.30 37.57 13.44 41.34 39.75 5.48 28.96 15.65 32.40 18 1.50 400 64.05 124.76 40.48 14.04 22.88 44.56 18.53 12.77 17.96 25.77 19 4.00 600 42.80 155.73 30.18 8.84 15.29 55.62 20.26 0.17 20.80 35.61 CGT= Cotton Gin Trash, CM = Cow Manure Hanif MU, Capareda SC, Iqbal H, ArazoRO, Baig MA (2016) Effects of Pyrolysis Temperatureon Product Yields and Energy Recovery from Co-Feeding of Cotton Gin Trash, Cow Manure, andMicroalgae: A Simulation Study. PLoS ONE 11(4):e0152230. doi:10.1371/journal.pone.0152230
- 206. Mass Balances Matter both entering and exiting through the defined boundaries is accounted for using the general mass balance equation:
- 207. Example:
- 208. Solution:
- 210. Energy Balances ∆𝐸 = ሶ 𝑄 − ሶ 𝑊 + ሶ 𝑚𝑖𝑛 ℎ𝑖𝑛 + 1 2 𝑣𝑖𝑛 2 + 𝑔𝑧𝑖𝑛 − ሶ 𝑚𝑜𝑢𝑡 ℎ𝑜𝑢𝑡 + 1 2 𝑣𝑜𝑢𝑡 2 + 𝑔𝑧𝑜𝑢𝑡 (1) where, ∆𝐸 is the net change in energy within the control volume with respect to time (J/h or BTU/h), ሶ 𝑄 is the change in heat added/removed with respect to time (J/h or BTU/h) , ሶ 𝑊 is the work added to the system with respect to time (J/h or BTU/h), ሶ 𝑚 is the mass flowrate (kg/h or lb/h), ℎ is the specific enthalpy (J/kg or BTU/lb), 𝑣 is the velocity per mass (m/sec.kg), 𝑧 is the height with respect to mass (m/kg or ft/lb). In many bioprocesses, a steady state conditions are primary interest in determining the efficacy of a system. Under steady state conditions, the rate of change in energy within a control volume become zero and the general energy balance equation simplifies to ሶ 𝑄 − ሶ 𝑊 = −[ ሶ 𝑚𝑖𝑛 ℎ𝑖𝑛 + 1 2 𝑣𝑖𝑛 2 + 𝑔𝑧𝑖𝑛 − ሶ 𝑚𝑜𝑢𝑡 ℎ𝑜𝑢𝑡 + 1 2 𝑣𝑜𝑢𝑡 2 + 𝑔𝑧𝑜𝑢𝑡 ] (2) Further simplification can occur if we consider that in most cases, potential and kinetic energies are negligible, at least in the case of bioenergy production. The energy balance equation reduces to : ሶ 𝑄 − ሶ 𝑊 = −[ ሶ 𝑚𝑖𝑛 ℎ𝑖𝑛 − ሶ 𝑚𝑜𝑢𝑡 ℎ𝑜𝑢𝑡 ] (3)
- 211. The mass and energy balance equation for a combustion of biomass: 𝐶𝑥𝐻𝑌𝑂𝑧 + 𝑝 𝑂2 + 3.762𝑁2 → 𝑗𝐶𝑂2 + 𝑘𝐻2𝑂 + 𝑚𝑂2 + 𝑛𝑁2 (4) Where x, y, and z represent the different ratios of carbon, hydrogen, and oxygen found in the biomass respectively, and the coefficients p, j, k, m and n respect values that balances the overall equation. Simple algebra can be implemented by conducting a mass balance on the elemental species present in this reaction. C: x= j H: y= 2k O: z+2p=2j+k+2m N: (2)(3.762)p = 2n Now equation 5 is similar to equation 2 and 3, except that the work ( ሶ 𝑊) and heat ( ሶ 𝑄) terms are excluded so that the equation can be represented as, ∆𝐻𝑟𝑥𝑛 = σ 𝑛𝑐 ℎ𝑐 − 𝑛𝑝 ℎ𝑝 (5) Where n represents the number of moles of a particular species, h represents the heat of combustion and the subscripts p and c represent production and reactants respectively.
- 212. If equation 5 is written in terms of mass (instead of moles), it can be substituted into equation 3 as shown in equation 6. This assumes steady state ( ∆E = 0) and that kinetic and potential energy are negligible. −∆𝐻𝑟𝑥𝑛 = ሶ 𝑄 − ሶ 𝑊 (6) Problem: Bioenergy feedstocks are known as lignocellulosic biomass because they are made up of three primary components, lignin, cellulose, and hemicellulose. Both cellulose and hemicellulose are polysaccharides of great interest due to their importance in bioenergy production. Concentrated sulfuric acid serves as a catalyst to promote the following hydrolysis reaction and release glucose from the homogeneous polysaccharide, cellulose: 𝐶6𝐻10𝑂5 3 + 𝐻2𝑂 → 𝐶6𝐻12𝑂6 This process is critical for quantifying how much glucose is available in a particular feed-stock for biofuel production. Is this reaction endothermic or exothermic at 25oC? If you were to supply 2 kJ/mol of work to agitate the solution, would you also need to supply heat? If so, how much?
- 213. Step - 1 𝐶6𝐻10𝑂5 3 + 3𝐻2𝑂 → 3𝐶6𝐻12𝑂6 Step - 2 Balance the equation Calculate the heat of reaction (∆𝐻𝑟𝑥𝑛) using the respective heats of combustion at 25oC. “Δ You need to remove 7 kJ/mol of heat to promote the hydrolysis reaction in the forward direction.
- 214. Units of Measurement
- 218. Useful Units and Conversions
- 226. Energy and Heat British Thermal Unit (Btu) Calorie
- 227. Power Power is defined as a rate of energy consumption Heating Value
- 229. below)
- 230. Heat Capacity
- 233. Ideal Gas Law
- 234. Henry’s Law A law stating that the mass of a dissolved gas in a given volume of solvent at equilibrium is proportional to the partial pressure of the gas.
- 236. Problem - Determine the concentration (mg/L) of carbon dioxide in the upper liquid layer in a closed algal bioreactor operating at 30 oC and 1 atmosphere pressure, if the headspace CO2 concentration is 44%. Solutions : =570 mg/l OR 576 mg/l or 570.5 mg/l
- 238. Problems (Assignment) Solution 1: 287 gal, 99.26 gal, 106.16 gal, 393.38 l, 403.52 l, 401 l, 0.39338 m3, 0.40352 m3, 0.401 m3, 393380 cm3, 403520 cm3, 40100 cm3, 13.89 ft3, 14.21 ft3, 14.16 ft3
- 240. 11. a Consider the system shown in Figure 1. Write a mass balance for the system assuming steady state. Figure- 1. b. In Problem 11. a., assume that N2 and H2 are completely converted to NH3 via the following reaction: N2 +3H2 2NH3 What would be the mass flow rate of NH3 exiting the system at steady state? 12. Freshly harvested feedstock must be completely dried before being stored for later use in bioenergy production. You have been assigned to estimate the amount of energy required to dry this biomass. Which property do you need to consider, latent or sensible heat? Why?
- 241. 13. In Figure 2, an aqueous solution of glucose enters the reactor via Stream 1 at a mass fraction of 40%.Additional water is supplied continuously through Stream 2. Analyses of the output stream found that it contained 5% glucose. Assuming that all of the glucose was converted into ethanol by microorganisms inside of the reactor, what is the mass fraction of ethanol in the output stream? Figure 2. 14. a. There appears to be a problem with the fermentation unit shown in Figure 3. What control volume could be drawn to best conduct a mass/energy balance for this unit operation? Based on what you know about fermentation, is this diagram complete? How many output streams should cross the system boundary for the fermenter? How many inputs should there be? b. Using a appropriate balance Equation, balance the chemical reaction used to combust lignin if its elemental constituents were found to be C11H14O4. Figure 3.
- 242. Thank You