Kul-14.4700 Transport Biofuels, Combustion and Emission Control Lecture 7: Alternative fuel basics 4.11.2015 Aki Tilli
LEARNING OBJECTIVES: After this lecture, you should be able to......write down, what is meant by the terms biofuel, biodiesel, alternative fuel, renewable fuel and renewable diesel...list the most important alternative fuels and describe and compare their chemical and physical characteristics list the some of the characteristics effects on engine operation...list the feedstocks for different alternative fuels...compare and list the pros and cons of the use, production and environmental impacts of different fuels
Terms... Biofuel?
Terms... Biofuel? Fuel, whose feedstocks are (short carbon cycle) organic materials Renewable fuel?
Terms... Biofuel? Fuel, whose feedstocks are (short carbon cycle) organic materials Renewable fuel? Larger category! A fuel is renewable, if its energy source is replaced by natural processes at a rate comparable or faster than its rate of consumption by humans For instance, hydrogen from water, if the energy to produce the hydrogen is from a renewable source Alternative fuel?
Terms... Alternative fuel? A fuel seen as an alternative for traditionally produced (fossil) fuels Not necessarily renewable! Biodiesel?
Terms... Alternative fuel? A fuel seen as an alternative for traditionally produced (fossil) fuels Not necessarily renewable! Biodiesel? Defined by legislation: FAME!!! Controversy in literature For more developed diesels: bio-based diesel, renewable diesel, green diesel (another controversy...)
Alternatives to fossil gasoline (in SI-engines)?
(Bio)Ethanol (C2H5OH) added to gasoline Almost all the world s grain ethanol used as gasoline additive EN228: maximum ethanol 10% (E10) 10 % => possible VERY slight consumption increase (depends on engine and its parameters) 10-25 % => changes needed (seals, tanks...) E85 = max. 85 % ethanol gasoline needed for cold starts (25% in very cold) FFV Differences: tanks, hoses, seals, nozzles, control, valve sockets oil change ~twice as often E85: ~40 % greater fuel consumption Ethanol must be 99,7 % pure! 9 Source: VTT
Ethanol Traditional fermentation process Uses foodstuffs (sugar) to produce fuel => food price, land use problems In many cases inefficient in decreasing GHG emissions! Source: Castle Rock Renewable Fuels
Ethanol Cellulosic ethanol From cellulose into fermentable sugars via heat and/or chemicals (...like sulfuric acid) and/or enzymes...or via gasification and synthesis. production emerging, tech: development stage Still high investment, operation costs (enzymes etc.)
Ethanol Cultivation cycle emissions => inefficient in decreasing GHG! Fertilizer industry emissions; carbon dioxide (CO2 ), nitrous oxide (N2O) Cultivation CO2, N2O, grain drying energy VTT, MTT 2006: negative grain ethanol GHG balance Presumptions + boundary conditions = huge impact on LCA results! Reductions in CO, HC, PM, NOx and aromatics (vs. fossil) Increase in acetaldehyde, evaporative emissions, cold start emissions Source: US Environmental Protection Agency 12
Butanol Commonly produced using fossil fuels Biobutanol production emerging Fermentation, same feedstocks as ethanol corn etc. Can also be produced from cellulosic raw materials. Energy density only 10% 20% lower than gasoline. Lower vapor pressure => lower evaporative emissions. Butanol is being studied, less (of the same) problems in gasoline engines than ethanol (up to 15%-vol) Production entirely with solar energy and nutrients, from algae? (Current yield is very low )
Methanol Synthesis gas => reactor+catalyst => methanol+water Many feedstocks, natural gas the most economical. Low production costs (vs. other alternative fuels) Low flammability (vs. gasoline), toxic,corrosive (eg. aluminium) High heat of vaporization Now not preferred as gasoline component Energy carrier? Fuel cells?
Liquid gasoline alternative properties
Biogas and natural gas Mainly methane: in end use, chemically the same! colourless, non-toxic, weight ~ half of air Need to be cleaned before use in transport CO2, N2, water, oil, mud, CO2, H2S, mercury Raw biogas Raw natural gas Dry (purified) gas Gas composition %(vol.) Methane 50-75 70 98 90 98 Higher alkanes ~0 0-20 0 3 Carbon dioxide 25-50 1 8 0 0,5 Nitrogen 0-30 1 5 0 1,5 Hydrogen sulphide 0-5 0-5 ~0 Properties Lower Heating value (MJ/kg) ~35 30 50 ~50 Density (kg/nm^3) ~1,15...1,3 0,73...1,1 0,73 Ignites well with spark => Mainly in Otto engines logistics, fuel injection differences! Dual-fuel: diesel gas engine, diesel fuel ignition energy mainly (cars 90%, ships 99%) from gas Performance can be enhanced by adding hydrogen. 16
Biogas & Natural gas Biogas: Life cycle GHG ~ the best option available production may in some cases lessen GHG in atmosphere! 17
Biogas & Natural gas: local emissions Very low PM emissions (vs. diesel vehicles) NOx emissions depend on technology (very low with stoichiometric combustion and 3-way-Cat) Unregulated emissions extremely low; methane slip problem 18 OECD/IEA 2010 The contribution of natural gas vehicles to sustainable transport
Biogas production Sewage treatment sludges, landfill gas, agricultural (easily decomposed) biomasses, food industry byproducts. Biogas reactor: anaerobic (fermentation): Pfeifer, B. 2008. Basics of the biogas process. International training course 1519 September 2008. 19
CNG, LNG, LPG CNG: compressed natural gas compressed to < 1% of the volume store and distribute p = 200 248 bar LNG: liquefied natural gas ~1/600 vol, low p (atm), ~ 162 C. The reduction in volume: cost efficient in long distance transport. specially designed vessels and tankers. LPG: liquefied petroleum gas propane, butane, or both from refining crude oil or oil/gas fields Gaseous in atmospheric T and p; vapour pressures: butane 2.1 bar, propane 8,1 bar at 20 LPG is heavier than air 20
Alternatives to fossil diesel (in CI-engines)?
Renewable diesel fuels Term biodiesel in legislation: traditional fatty acid ester diesels FAME = fatty acid methyl ester Synthetic diesel: paraffinic hydrocarbons Produced from any carbon-based combustable matter Fischer-Tropsch (FT) diesel Biomass-to-liquids BTL Gas-to-liquids GTL Coal-to-liquids CTL Hydrotreated vegetable oil (HVO) Feedstocks like FAME End-product like synthetic diesel DME Different fuel, from methanol or FT-synthesis * Place your footnotes / notes here 22
Trad biodiesel = FAME Thermodynamically ~ trad. diesel Non-toxic and biodegradable Improves lubricity when blended with other diesel fuels High density, viscosity, low compressibility Faster and bigger p-changes, higher max p in fuel injection system, faster start of injection Bigger droplets, narrower opening angle, longer penetration, decreased mixing in fuel sprays Chemical properties: as such problematic for fuel injection systems, may require material changes
Trad biodiesel = FAME Less emissions than with regular diesel particulate matter (PM), HC, CO; oxygen content important!...but NOx increase in most cases in engines: cold property problems, oil dilution, rubber part brittlement, corrosion, carbon deposits LCA s: no lower CO2 always oil plant cultivation vs. food production storage problems (biodegradable, water...) EU: max. 7% in any diesel Source: US EPA
Trad biodiesel = FAME Production: simple and easy process
Hydrotreated vegetable oil: HVO Neste oil: NEXBTL As an anwer to the demand for high quality renewable diesel produced at refinery volumes Production integrated with a trad. oil refinery => hydrogen, heat, infrastructure
Hydrotreated vegetable oil: HVO T, p control => chain length, isomerization => properties Catalysts e.g. NiMo/Al2 O3, CoMo/ Al2 O3
Hydrotreated vegetable oil: HVO Lower density, more compressible => injection later (in older engines) HC chain length and branching (= cold properties) adjustable (process T ja p => isomerization) Chemistry: combustion, ignition easier => Less PM; Lower adiabatic flame T = >lower NOx Paraffinic HC => high CN => possibilities to decrease NOx with technologies lowering T and worse combustion conditions (EGR, Miller) lower density, viscosity, faster vaporization => increased spray angle, decreased penetration, smaller droplets good mixing, no wall interactions => PM, NO, HC decrease Low lubricity => need of additives (as usual)
Hydrotreated vegetable oil: HVO LCA s (according to Neste Oil): CO2 emissions -33%...-90% indirect land-use changes (deforestration) hard to calculate, not taken into account! palm oil => deforestration? =>?? Feedstocks are oils; competition with food industry; however, wider feedstock possibilities (good quality fuel) than with FAME Emission studies (VTT, Scania): standard high duty engine, no optimization for new properties! regulated not regulated NOx -0...-20% Aldehydes -40...-45% Particles -17...-30% Benzene -40...-45% CO -45...-55% PAH less HC -45...-55% Mutagens less
Fischer-Tropsch (FT) -diesel Biomass to liquids (BTL), Gas to liduids (GTL), Coal to Liquids (CTL) = same end-product as HVO, same properties raw material gasification => CO ja H2 (Synthesis gas, Syngas ) => Cleaning (BTL: problem with tar) => FT-process => (iso)paraffinic HC:s
Fischer-Tropsch-diesel High-grade fuel (~HVO), but costs ~ 3x trad diesel Small volumes, raw material production scattered (BTL) Costly technology (catalysts etc.) Energy efficiency? GTL or CTL has been in production stage already very long ago (China, South Africa, WW II germany) Research and development ongoing GTL produced already: Sasol, Shell, BTL: Choren, (Neste Oil+Stora Enso)
DME dimethyl ether Structurally the simplest ether one component => more controllable in-cylinder phenomena Production from methanol or straight syngas synthesis Compatible to diesel process: high CN Very low exhaust emissions (comparable with biogas) No particulate matter (PM); very low NOx; no SOx) Low CO2 emissions Low engine noise High fuel economy High WTW efficiency Thermal efficiency and ignition like diesel Sivu 32 Source: Volvo
DME dimethyl ether Use as a heating fuel and as an aerosol propellant already widespread production! Gaseous in normal conditions, pressurized (like LPG) logistics and storage properties: like LPG, infra exists in many places! Already eg. Sweden (Volvo) has BioDME-trucks Problems High compressibility, vapour pressure => cavitation problem? Low viscosity (=> leaks), incompatible with some materials (elastomers) => need for new materials in fuel injection density, heating value low need of longer injection for same power Need of pressurized tanks Sivu 33 Japan DME Forum
Biobased diesel fuel comparison
Biobased diesel fuel comparison FAME HVO BTL Process route Transesterification Hydrotreatment Gasification, FT Feed Product Vegetable oils Oils, fats Biomass Product (type) Product quality CO2 emissions (LCA) Fatty acid methyl esters Consistency and stability issues 1.6-2.3 kg CO2/kg oil equivalent Isomerized paraffinic hydrocarbons High 0.5-1.5 kg CO2/kg oil equivalent Isomerized paraffinic hydrocarbons High 0.3-1.5 kg CO2/kg oil equivalent Note: Fossil diesel fuel value reported as 3.8 kg CO2 / kg oil equivalent (Bown D. 2007)
Biobased diesel fuel comparison NExBTL GTL FT FAME (RME) Typical diesel Diesel Typical Typical fuel EN 590 Density at +15 C (kg/m3) 780-785 770-785 n. 885 n. 835 820-845 Viscosity at +40 C (mm2/s) 3.0-3.5 n. 3.2-4.5 n. 4.5 n. 3.5 2.0-4.5 Cetane number 98-99 n. 73-81 n. 51 n. 53 >51 10 % distillation ( C) n. 260-270 n. 260 n. 340 n. 200 90 % distillation ( C) 295-300 325-330 n. 355 n. 350 Cloud point ( C) n. - 15 n. 0... +3 n. 0... - 5 n. - 5 Heating value (MJ/kg) n. 44 n. 43 n. 38 n. 43 Heating value (MJ/l) n. 34,5 n. 33,8 n. 34 n. 36 Polyaromatic content (wt- %) n. 0 n. 0 n. 0 n. 4 <11 Oxygen content (wt-%) n. 0 n. 0 n. 11 0 Sulfur content (mg/kg) < 10 < 10 < 10 < 10 <50
GHG and cost of GHG avoided
Bio-based diesels, in short FAME Production: oil+alcohol => fatty acid ester (+glycerol) simple production, low emissions quality, food vs. fuel, enough feedstocks? NOx? HVO oils/fats + hydrotreatment => paraffin HC quality, emissions low, production at refinery levels food vs. fuel, enough feedstocks?, deforestration, price? BTL Biomass => gasification => syngas (CO +H2) => (Fischer Tropsch synthesis) => paraffin HC quality, emissions, any biomass ok! price, development stage, difficult process, small production scale so far DME From syngas or direct synthesis from methanol quality, emissions, any biomass ok, existing production, no new logistics solutions (vs. LPG)! Logistics and production in a new scale, requires pressurized systems, engine adaptation requirement, difficult process * Place your footnotes / notes here 39
Thank you! Trad diesel vs. synthetic diesel