bio fuel production - fsu

Sustainable Energy Science and Engineering Center

Bio Fuel Production

Reference: Donald L. Klass, Biomass for Renewable Energy, Fuels and Chemicals, Academic Press, 1998.

http://www.energy.kth.se/compedu/webcompedu/media/Lecture_notes/S1B11C2.pdf

http://www.energy.kth.se/compedu/webcompedu/media/Lecture_notes/BiomassCombustionStudyPack.pdf

Source: Miroslav Petrov @ KTH


Conversion Methods


Fuel from the Forest?


Gasifiers Types

Source: Ohlström M. et al. “New concepts for biofuels in transportation”, VTT research notes 2074, Technical Research Center of Finland, Espoo 2001.


NG-based or Wood-based MethanolSynthetic methanol from natural gas or biomass:

Source: Ohlström M. et al. “New concepts for biofuels in transportation”, VTT research notes 2074, Technical Research Center of Finland, Espoo 2001.


Steam Reforming and Water-Gas-Shift

Gas mixture for fuel synthesis (syngas) can be produced from hydrocarbon reforming with steam, or from biomass gasification (preferably oxygen-blown gasification to avoid the presence of inert nitrogen).

steam-methane reforming: CH4 + H2O CO + 3H2 (very endothermic)

The product gas is in reality a mixture of CO, CO2, H2, water vapours, and traces of reactants. It has a high energy value.

Product gas from biomass gasification needs to be enriched with hydrogen to the required molar ratio CO/H2 for the methanation reaction to proceed. This is done by the “water-gas-shift” reaction, where a certain part of the CO in the product gas is sacrificed to produce H2.

water-gas-shift reaction: CO + H2O CO2 + H2 (slightly exothermic)


Methanol Synthesis

The syngas after the water-gas-shift reaction is fed to the methanol reactor vessel, where on the surface of catalysts the CO and CO2 react with H2 to form CH3OH mixed with water, also denoted as MeOH.

The methanol is then distilled out, which is an energy demanding process.

methanol synthesis: CO + 2H2 CH3OH (exothermic)CO2 + 3H2 CH3OH + H2O (slightly exothermic)

If hydrogen from additional source is added to the process, so that carbon is not sacrificed to produce hydrogen, the methanol yield can be doubled.


Problems with Methanol FuelMethanol is a perfect fuel for gasoline (Otto) engines or gas turbines. However, there are several major disadvantages with it:

• Very toxic

• Good solvent dilutes old deposits in the fuel system and washes them to the engine, destroys rubber hoses/gaskets/seals…

• Corrosive to certain steels

• Lower energy per mass/volume ratio compared to gasoline ( ~ two times lower energy value)

• Difficult cold start of the engine due to low vapour pressure


Dimethyl-ether

Dimethyl ether (DME), CH3OCH3, is a perfect fuel for diesel engines, allowing for high-efficiency energy conversion with very low pollution levels. DME is gaseous at normal conditions, but is a liquid at 6 bar pressure, similar to LPG (propane/butane). The absence of a direct C-C chemical bond in the molecule allows for clean combustion with very low CO emissions and almost without soot formation.

DME synthesis reaction: 2CH3OH CH3OCH3 (exothermic)


DME synthesisDME yield and conversion efficiency for a hypothetic DME production plant in Sweden, based on biomass gasification:


Fischer-Tropsch Reactions

Source: Mozaffarian, M., Zwart, R.W.R. “Feasibility of biomass/ waste-related SNG production technologies”, report nr: ECN-C--03-066, Dutch Ministry of Economic Affairs, 2003.


Methanation Reactions


(exothermic reactions)


Avoiding Formation of Pure Carbon



Biomass Pyrolysis

• Pyrolysis is the direct conversion of biomass to liquid (termed bio-oilor bio-crude), solid and gaseous fractions, by heating the biomass in absence of air to around 500°C

• Optimized fast pyrolysis (flash pyrolysis) can be used to produce predominantly bio-oil, enabling the conversion of biomass to liquid biofuel with an efficiency of up to 75%.

• The problems are the very unstable structure of the bio-oil, its water content, and certain corrosive activity.

C10H14O6 + heat energy aCO + bCxHy + cCnHmOq + dC gas partly condensible char residue


Biomass Pyrolysis Process

crushing<8 mm

drying< 10 % Heating

~ 1 s~ 500 C

Combustion of CO and char residue

Condensa-tion of productgases

Product: 60 -70 % per initialenergy and mass content

particle separation

Residues from the forest industries: wood chips, sawdust, bark, etc...

heat

FORESTERA™ - pyrolysis reactor

gases

non-condensiblegases

heat


SolvolysisSolvolysis, followed by catalytic hydrotreatment, is another thermochemical method, aiming at the direct production of liquid hydrocarbons of higher quality than the pyrolysis oil.

The solvolysis process comprises simple dissolving of the wood in acidified organic solvents, at certain temperature and pressure. After that the solvent is evaporated under vacuum and recycled.

Water generated during the solvolysis is also evaporated. The solvolysisproduct is very viscous and has about 22% O2 content. It is then subjected to catalytic hydrotreatment (hydrodeoxyge-nation) at about 350-370oC under pressurised H2 atmosphere.

The final product is composed of a mixture of hydrocarbons with very low oxygen content, the heavy fractions prevailing. Further development and optimization of the process is necessary.


Biogas production



Farm-scale Biogas Plant

Source: Nordic Folkecenterfor Renewable Energy, Kammersgaardsvej 16, 7760 Hurup Thy, Denmark.


Biogas YieldTypically around 50-60% of the initial energy content in the material will be converted to biogas in a well-designed and properly operated digester. The resultant product gas mixture consists of CH4 (60-65%), CO2 (the rest), and small amounts of water vapours, H2S, NH3, and some organics that give bad odour. The gas is a ready fuel for stationary CHP boilers or piston engines, but should be cleaned and upgraded to minimum 95% methane if used as automotive fuel.

Source: Nordic Folkecenter for Renewable Energy, Kammersgaardsvej 16, 7760 Hurup Thy, Denmark.


Biogas Yield from Various Bio-material

Unofficial figures for typical average biogas yield from various biowaste types


For CH4

1Nm3 ~10.54 kWh


Biogas Production Example



Biogas Production ExampleThree different digester cases for different raw material mixtures:



Horizontal Biogas DigesterThe typical horizontal biogas digester for smaller-scale applications:



Vertical biogas digesterVertical biogas digesters are usually used for larger-scale centralized biogas plants:



Biogas from agricultural productsFresh grass can be digested for biogas production together with organic wastes:

Crops

Organic residues

Quality control and separation of unwanted material

Outsortedmaterial

Sterilizing at 70 oC for 1 hour

Pretreatment, mixing, and separation of inert material

Sand, etc.

Biogas to cars and buses

Cleaning & upgrading of biogas to fuel quality

Digestion at 37 oC for 20 days

Biogas from sewage treatment

Surplus gas to heat and power generation

Sludge to the fields as fertilizer

Crops

Organic residues

Quality control and separation of unwanted material

Outsortedmaterial

Sterilizing at 70 oC for 1 hour

Pretreatment, mixing, and separation of inert material

Sand, etc.

Biogas to cars and buses

Cleaning & upgrading of biogas to fuel quality

Digestion at 37 oC for 20 days

Biogas from sewage treatment

Surplus gas to heat and power generation

Sludge to the fields as fertilizer


Upgrading of Biogas Quality

Scrubbing of acidic gases (H2S):

• Dry oxidation process – adding air in the biogas to oxidise the hydrogen sulphide to elementary sulphur;

• Adsorption using iron oxides;

• Liquid phase oxidation process: physical absorption by solvents (NaOH), or chemical absorption and forming or precipitates (FeCl3).


Upgrading of Biogas Quality

Scrubbing of CO2:

Physical absorption – using water at high pressures;

Chemical absorption – using mono-ethanolamines (MEA) or alkaline solutions;

Adsorption on solid surfaces – using silica, alumina, activated carbon, etc.;

•Membrane separation;

•Cryogenic separation;

•Chemical conversion method.


Ethanol Energy

Source: Michael Wang, Argonne National Laboratory


Starch and Sugar based feedstock: Corn and Barley and food processing waste streams such as potato and brewery waste

Cellulosic feedstock: Agricultural crop residues, forestry wood wastes, mill residues, urban wood waste, paper manufacturing wastes, waste paper and energy crops.

Cellulosic biomass ethanol provides about four units of energy for every unit of fossil fuel energy used to produce it – a significantly higher ratio than for other renewable fuels, such as corn ethanol. The large positive net energy balance for cellulosic biomass ethanol compared to corn ethanol is due to the fact that relatively little fossil energy is used in the creation of cellulosic biomass and in the biomass to ethanol conversion process. However, unlike starch based crops, such as corn, this biomass waste is often burned (ethanol production solves this problem), and does not have market value other than as feedstock for energy production. In addition, biomass resources such as wood waste, and certain dedicated biomass ethanol crops (such as switch grass) are not nearly as energy intensive to produce as starch crops.

Ethanol Production


Ethanol Production via FermentationMicroorganisms responsible for ethanol production are facultative, i.e. they can grow with or without oxygen. These are of the saccharomyces type, similar to common yeast cultures.

The ethanol-producing process is actually anaerobic, where fermentable carbon sources (hexose/pentose sugars like glucose/fructose) are oxidised, and excess electrons are transferred to organic acceptor molecules instead of to oxygen. Ethanol is thereby produced as a waste product instead of water.

If air is allowed to enter the fermentation process in sufficient quantities, the microbial metabolism will switch to aerobic (more efficient) process, and ethanol production will stop.

Thus, microorganisms produce ethanol when growth parameters do not support an oxidative metabolic process, thereby requiring a less efficient pathway resulting in ethanol as a waste product.


Ethanol from Complex Sugars

Starch (a glucose polymer) must be broken down into simple sugars - maltose and glucose - before the fermentation process can be applied. This can be accomplished by microorganisms of the amylases type, which are produced by the germinating seeds during malting of barley, or added artificially in fungal form. This is the way to produce ethanol from cereals, corn, potatoes, etc.

Cellulose and its derivatives (also a glucose polymer) can also be broken down into simple sugars, however with some difficulties. Lignin remains as a residue. The cellulose can be treated by twomain methods: acid hydrolysis and enzymatic hydrolysis. Acid hydrolysis is a well-developed method, however expensive, low-efficient and polluting. Enzymatic hydrolysis is promising, but needs further development and cost reduction.


Integrated Ethanol ProductionThe IBUS concept from Elsam A/S in Denmark:


Ethanol from Agricultural CropsEthanol can be produced from starch via the following process:

wheatmilling

Water and enzymes

yeastcarbon dioxide

Malting and saccharifi-cation

Fermen-tation

Ethanol 99.5%

absolutisation distillation Fodder drying

Fodder for animals

wheatmilling

Water and enzymes

yeastcarbon dioxide

Malting and saccharifi-cation

Fermen-tation

Ethanol 99.5%

absolutisation distillation Fodder drying

Fodder for animals


Ethanol Production Steps


Breaking Complex SugarsLiquefaction and saccharification of cellulose into C5-C6 sugars, which can undergo fermentation:


Cellulose Ethanol Production


Ethanol as Automotive FuelEthanol is a perfect fuel for Otto engines and gas turbines. There are though some small problems, like:

• Difficult cold start of the engine due to low vapour pressure,

• Might be aggressive to certain steels and rubbers,

• Energy per mass/volume ratio lower than gasoline, but slightly better than methanol!

The Brazilian example The Brazilian example –– fuel from sugar cane: fuel from sugar cane:

• 5x106 ha of sugar cane production 24.106 t of sugar and 14x106 m3 of ethanol

• 4 million cars driving on pure ethanol, the rest of the countryfleet uses gasoline with 24% ethanol mixed in it

• 600 000 direct jobs related to ethanol production (from agriculture to final fuel distribution)


Vegetable Oils

Vegetable oils (plant oils) are a ready liquid fuel produced by nature, replacement to fossil diesel.

They can be directly extracted from the seeds of the oil-producing plants by simple extraction methods:

• Cold pressing followed by filtration, or

• Warm pressing followed by extraction by organic solvents (methanol, gasoline, etc.) and purification.

Examples of plants with high oil content are: oil palm, sunflower, canola (raps), soy, peanuts, linseed, hemp, jojoba, and many others.


The Oil Palm


Oil Palm Plantations

Source: Fedepalma - Colombia

World production of palm oil – thousands of hectares:


Palm Oil Extraction Process

Source: www.fao.org


12991012121019olives

12789311901000rapeseed

1248731163978opium poppy

1137951059890peanuts

1107711026863cocoa (cacao)

102714952800sunflowers

100705940790tung oil tree

83585779655safflower

74522696585sesame

61430572481mustard seed

57402536450coriander

57401534449pumpkin seed

56393524440euphorbia

51362482405hazelnuts

51359478402linseed (flax)

US gal/acrelbs oil/acrelitres oil/hakg oil/haCrop

Highest Vegetable Oil Yields


Highest Vegetable Oil Yields

Source: http://journeytoforever.org/

US gal/acrelbs oil/acrelitres oil/hakg oil/haCrop

635446559505000oil palm

287201826892260coconut

282198026382217avocado

255179523922010brazil nuts

240168522461887macadamia nuts

202142018921590jatropha

194136518181528jojoba

191134417911505pecan nuts

151106114131188castor beans


The Canola (raps) Plant

The canola (rape seed, raps, colza) is the oil plant of the northern climate, with yields of around 1 – 2 m3 of oil per hectare.

Source: www.svenskraps.se

http://www.svenskraps.se/svenskraps/index.asp

http://www.svenskraps.se/oljevaxt/odlamerraps_2006.asp


Straight oils or biodiesel?

Plant oils can be used in two different forms:

• Raw straight vegetable oils (SVO), the only treatment is filtering;

• Chemically converted into esters = biodiesel.

Use of SVO in burners or engines is difficult due to high viscosity, danger of polymerization, wax sedimentation, coking at fuel injectors, etc.

Biodiesel avoids all these by having physical properties very close to those of fossil diesel, however the presence of residues of methanol and alkali might be a problem.


BiodieselBiodiesel production is a chemical process for trans-esterification of the complex triglyceride molecule of the vegetable oil. The result is a mixture of fatty esters with properties close to fossil diesel. The biggest disadvantage of biodiesel is its high cost!


Well-to-Wheels AnalysisTypical efficiencies for different powertrain alternatives:

Source: http://ies.jrc.cec.eu.int/

bio fuel production - fsu

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