Date post: | 14-Apr-2017 |
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MANUFACTURE OF BIOGAS FROM AGRICULTURAL WASTES
PRESENTED BY-SUDIPTA GHOSH
& PALLAVI JHA
NIT DURGAPURPAPER NO.- AISEC/16/T-1/16
WHY WE NEED RENEWABLE ENERGY SOURCES?
Do not lead to emission of greenhouse gases.
Environment friendly
Available in abundant quantity and are free to use
BIOGAS
Biogas typically refers to a mixture of different gases produced by the breakdown of organic matter in the absence of oxygen. Biogas is primarily methane (CH4): 50-75% and carbon dioxide(CO2): 25-50% and may have small amounts of hydrogen sulphide (H2S), H2, O2, N2.
BIOGAS UTILIZATION
Domestic &
Industrial Fuel
Automobile
Fuel
Fuel Cells for
Electricity Generatio
n
Production of
various chemicals
like methanol
DIFFERENT SOURCES OF BIOMASS
ANAEROBIC DIGESTION
Anaerobic digestion is a series of biological processes in which microorganisms breakdown biodegradable materials in the absence of oxygen to produce biogas.OPTIMUM CONDITIONS FOR ADAbsence of OxygenTemperature: Mesophilic Range- 20 to 45°C pH: 6.4 to 7.2Carbon to Nitrogen Ratio(C:N) : 20-30Retention Time: 15 to 30 daysSlow Mixing
STAGES OF ANAEROBIC DIGESTION
Carbohydrates
Fats
Proteins
Sugars
Fatty Acids
Amino Acids
Carbonic Acids & Alcohol
Hydrogen Carbon dioxide
ammonia
Methane
Carbon dioxide
HydrogenAcetic Acid
Carbon dioxide
Hydrolysis
AcidogenesisAcetogenesisMethanogenesis
SINGLE BATCH AD REACTOR SYSTEM
The concrete reactor with integrated heating system is loaded with biowaste and closed, starting the anaerobic degradation. High organic content leachate is producedThe leachate is stored, heated and continuously redistributed in the reactor to increase the biogas yield. The waste is kept in the reactor from 20 to 40 days, until the biogas production stops or drops
BIOGAS YIELD FROM DIFFERENT SUBSTRATES
REFERENCE: J ranjhita et al. Production of biogas from flowers and vegetable wastes using anaerobic digestion, International Journal of Research in Engineering & Technology
LIGNOCELLULOSIC BIOMASS
PRETREATMENT
THE MAIN PURPOSE OF PRETREATMENT:Increase porosityDestroy lignin shell protecting cellulose and hemicelluloseDecrease crystallinity of celluloseMust break the shell for enzyme to access substrate(sugar)
PRETREATMENT METHODS:ChemicalPhysicalBiological
CHEMICAL PRETREATMENTALKALINE PRETREATMENT:Alkali used are mainly lime and NaOHCauses swelling of lignocelluloses & partial lignin solubilizationProcess Conditions- relatively mild, long reaction timeHigh Cost of Chemicals
REFERENCE: Mohsen Taherdanak & Hamid Zilouei, Improving biogas production from wheat plant using alkaline pretreatment, Elsevier
CHEMICAL PRETREATMENTDILUTE ACID PRETREATMENT:Breaks down hemicellulose, disrupts ether bonds between lignin and hemicellulose & increases p0rosity of cell wallTypical conditions: Acid used: Dilute H2SO4 Concentration: low(<2%, w/w) Temp: 160-200°CDemerits: i) Removal of lignin is insignificant(<70%) ii) Corrosive to the metal of the reactor iii) Forms furfural & HMF which is inhibitory to fermentation
CHEMICAL PRETREATMENTOXIDATIVE PRETREATMENT:Oxidizing agents used are H2O2, O3, O2 & airEffectively removes lignin & does not produce toxic residuesOzonolysis occurs at room temperature & pressureExpensive
ORGANOSOLV PROCESS:Uses organic solvents like ethanol, acetone, carboxylic acid etc.Temp: 200°C, high pressureRemoves lignin, hydrolyses hemicelluloseIncreased risk of combustion & explosion in case of use of flammable organic solventSolvent recovery is difficult
PHYSICAL PRETREATMENT
MECHANICAL PRETREATMENT:Carried out by mills which breaks open the cellulose structure & increases the specific surface area of the biomassMills divided into hammer or knife millsGreater possibility for enzyme attack Particle size- 1 to 2 mm(effective hydrolysis)Repair cost of mills is large
The figure above shows that knife milling slices the fibers & hammer milling grinds the fibers
PHYSICAL PRETREATMENTTHERMAL PRETREATMENT:Temperature- 125 to 190°C under pressure, time-1 hrCarried out in pressure cooker, autoclave or microwave heaterWater is added to the dry substrate. Presence of heat & H2O disrupts H2 bonds that holds together the cellulose & lignocellulose complexEffective for crops upto 190°CLarge scale application – TDH developed at ATZ Entwicklungszentrum in Germany, increase in biogas yield by 20-30%
COMBINED PRETREATMENTSTEAM EXPLOSION:Most applied process, low use of chemicals & limited energy consumptionDemerit: Long retention time & high temperature can decrease CH4 yield REACTOR
FILLED WITH BIOMASST=160-260°C
High Pressure Sat. Steam
Sudden pressure reduction
Hemicellulose
degradation & lignin
matrix disruption
BIOLOGICAL PRETREATMENT
Wood degrading microbes like white, brown & soft rot fungi & bacteria are usedModifies the chemical composition & structure of the lignocellulosic biomass.The modified biomass is more amenable to enzyme digestion
ADVANTAGES: •No chemical requirement•Low energy input•Mild environmental Conditions•Environment friendly working manner
DISADVANTAGES:•Slow•Requires careful control of growth conditions•Large space requirements
CONCLUSION
Biogas is being watched with keenest interest as environment-friendly, alternative energy source instead of petroleum.The major shortcoming is the presence of H2S in biogas which can be overcome by biogas cleanup process like biological desulphurization and biofiltration.It is not possible to define the best pretreatment method as it depends on many factors such as type of lignocellulosic biomass and desired products. Research has shown that it is possible to increase the methane yield by over 1,000 % and therefore, cost effective commercial application is possible if the correct techniques are applied.