CHE3163 Sustainable Processing I Case study

Sustainability Assessment of Biofuels

Sources

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Sustainable Development in Practice: Case Studies for

Engineers and Scientists, Adisa Azapagic & Slobodan Perdan (2011), Chapter 6

Other sources as noted Some images from other sources

Learning outcomes

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To understand biofuels production approaches and feedstocks To understand the environmental sustainability of biofuels

compared with fossil fuels To be aware of the importance of Land Use Change (LUC) in

assessing the sustainability of biofuels To appreciate the social and economic sustainability of

biofuels

What are biofuels?

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Any fuel derived from a biological feedstock Can be used for transportation, power generation, heating This case study will focus on fuels for transportation

Introduction

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The transport sector contributed 13% of global greenhouse gas (GHG) emissions in 2007(a)

Contributed 11.4% of Australias GHG emissions in 2009(b) In the EU the contribution is 25% and in the USA the

contribution is 29%(a)

In order to reduce global GHG emissions, significant cuts must be made in transport sector

Biofuels offer an alternative to fossil-based transport fuels (a) Azapagic, pp. 142-143. (b) Australian National Greenhouse Accounts 2009

Biofuel policies

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Many countries have implemented policies to encourage the production and use of biofuels for transport.

Principal objectives of these policies are: Reduce GHG emissions from transport Enhance security of supply (not reliant on fossil oil supplies

from politically unstable regions) Increase employment, especially in rural areas

Many countries require blending biofuels with conventional fuels: E.g. in New South Wales, 2% of total volume of petrol sold

must be ethanol

Biofuels - Feedstocks, Production and Products

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First generation biofuels

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Produced from conventional food crops such as corn, wheat, sugar cane, canola, sunflower seeds and palm oil.

Starches and sugars Bioethanol

Oils and fats Biodiesel

Advantages and disadvantages of first generation biofuels

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Advantages Disadvantages

Familiar feedstocks Competition with food crops (social / economic impacts)

Well-established production methods High cost feedstocks can lead to high production costs (exception is Brazilian sugarcane ethanol)

Scalable processes Modest reductions in fossil fuel use and GHG emissions (except for Brazil sugarcane ethanol) due to Land Use Change

Fuels compatible with fossil fuels (somewhat)

Production of by-products (Glycerine, DDGS) exceeds demand creates waste

Commercial production and use in many countries

Second generation biofuels

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Produced from non-food sources, including dedicated energy crops. Examples include: Perennial grasses Short-rotation coppice willow trees Waste biomass (agricultural, forestry, municipal solid waste)

Waste biomass generally preferred as no additional stresses are placed on environment from their use (e.g. water demand, land demand)

Main second gen biofuels are ethanol and biodiesel Others include biohydrogen, biomethanol, bio-dimethylfurant

(bio-DMF), biodimethylether (bio-DME), Fischer-Tropsch biodiesel, biohydrogen diesel and mixed alcohols

Second generation biofuels Processing routes

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Two main routes themo-chemical and bio-chemical Thermochemical carried out at high temperatures and sometimes high

pressures. Analogous to chemical/fossil fuel processing (e.g pyrolysis used for ethylene manufacture)

Biochemical route includes processes used in first generation biofuels (chemical conversion, biological conversion) but also includes anaerobic digestion to produce biogas (60% methane, 40% CO2)

Advantages and disadvantages of second generation biofuels

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Advantages Disadvantages

Similar processes to petroleum/chemical/bio industry

Unfamiliar feedstock with uncertain / fluctuating availability

No competition with food High capital and energy costs

Reduction in amount of waste that needs to be disposed of / treated (if waste is used as feedstock)

Processing not optimised for new feedstocks (e.g. tar formation, syngas cleanup)

Competition for land and water for some energy crops

For anaerobic digestion, only a fraction of the waste produced can be used

For non-liquid fuels, compatibility with existing transport vehicles is significant problem

Third generation biofuels

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Main feedstock is microalgae. Still under development. Algae cultivated in purpose-built systems (e.g. fermenters, photo-reactors or

ponds) or harvested from oceans. Similar processing routes as for second gen biofuels Currently not cost competitive Other third gen biofuels could include bio-propanol or bio-butanol but not

expected to hit the market before 2050

Advantages and disadvantages of third generation biofuels

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Advantages Disadvantages

Microalgae has a high oil content Not commercially available yet

Can be cultivated in a range of systems, including in contaminated water

High initial costs to establish algae production systems

Wide spectrum of processing routes and biofuel products

High water content

If cultivated artificially could require large areas growth rates limited by rate of insolation

If exploited from the oceans, could impact on marine life and ecosystems

Sustainability assessment of biofuels

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Biofuels have emerged as potentially more sustainable alternative to fossil fuels particularly due to potential to reduce GHG emissions. This is because CO2 emissions from biomass are considered carbon neutral

Also attractive as may enhance security of supply and may stimulate rural development

However there are some disadvantages such as Additional land requirements and competition with food

production systems Additional GHG emissions due to Land-use Change (LUC) High capital and (sometimes) operating costs Various social issues such as health & safety, land-rights, child

labour

Sustainability assessment of biofuels

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Assessing these competing sustainability impacts should consider all relevant environmental, social, economic aspects

Should also avoid shifting burdens along supply chains Should therefore consider the full life cycle of biofuels including

Cultivation of feedstock Biofuel production processes Biofuel use

This assessment clearly lends itself to the LCA approach

Sustainability issues in the life cycle of biofuels

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Life cycle of fossil fuels

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Need to also consider fossil fuels such as distillate (diesel) and gasoline (petrol). This gives a basis for comparison with biofuels.

Global warming potential

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Global warming potential (GWP) measured in mass (g or kg) of CO2 equivalent Kyoto protocol GWP factors based on radiative forcing effects of each greenhouse gas

over 100 years in the atmosphere (if gas lasts that long)

You multiply each gas by its GWP factor to get its CO2-equivalent (all are on a mass basis). Then add up all these GWP (CO2-eq) values to get total GWP for a process or step in the life cycle

Greenhouse gas GWP (CO2-equivalent)

Kyoto Protocol(1997) IPCC AR4 (2007)

CO2 1 1

Methane (CH4) 21 25

Nitrous oxide (N2O) 310 298

HFC-23 11,700 14,800

HFC-134a 1,300 1,430

Sulphur hexafluoride (SF6) 23,900 22,800

Sources: IPCC 2nd Assessment Report (1995) IPCC 4th Assessment Report (2007)

GWP LCA approach

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To compare GWP for different fuels, each containing different Lower Heating Values (LHV) means GHG emissions are usually compared on an energy basis (kg CO2-eq / MJ fuel).

Hence the FUNCTIONAL UNIT in this LCA is 1 MJ of fuel GWPtotal = GWPproduction + GWPuse (g CO2-e / MJ) GWPuse for biofuels is zero as CO2 from combustion is simply returning

CO2 that was absorbed from atmosphere during biomass growth However GWPuse for fossil fuel use (combustion) must be considered

Life cycle GWP for different fuels

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Cultivation stage for wheat bioethanol

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Analysis of life cycle GWP for wheat ethanol

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Considerable fraction of total life cycle GWP for wheat ethanol comes from cultivation

Of this cultivation GWP impact, almost two-thirds comes from N2O emissions. Some N2O is produced as by-product of N fertiliser manufacture

N2O is also produced as nitrogen-based fertilisers break down after being sprayed on the soil (only 20-50% of fertiliser is actually taken up by plant)

As GWP factor for N2O is very high (298 in IPCC AR4) even small quantities of N2O emissions from nitrogen breakdown make a big difference.

Somewhat counter-intuitive result! Many people would expect that CO2 from fertiliser production or from use of fuels used for cultivation would be the biggest contributor.

Sugar cane requires less fertiliser and hence produces less N2O and has lower GWP during cultivation (cf. wheat) and over full life cycle

Demonstrates you cannot always rely on intuition when dealing with LCA

Life cycle GHG emissions for biofuels compared with conventional transport fuels

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Life cycle GHG emissions for biofuels compared with conventional transport fuels

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Best performing biofuel from food crops is Brazilian ethanol from sugar cane However best overall is 2nd generation ethanol from biological waste (derived

from municipal solid waste MSW) Notice that US corn ethanol actually has worse life cycle emissions that

petrol! However these results are controversial and rely heavily on the assumptions

used in the estimation of GHG emissions Significant variation in life cycle emissions results can be seen depending on

assumptions used Does however call into question the emissions benefits for some (not all)

biofuels Note that its generally the feedstock and not the biofuel product that affects

the life cycle GWP Demonstrates the power of a full LCA to make rational decisions

Land use change (LUC)

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LUC probably most controversial issue with biofuels

Additional GHG emissions when carbon stored in soil or natural vegetation is disturbed and released through LUC

Direct LUC conversion of existing land from current use to cultivation of biomass for biofuel production

Indirect LUC displacement of existing agricultural activity due to biofuel crop cultivation

Direct LUC relatively easy to assess for GWP impact

Indirect LUC much harder Highly dependent on particular land and its

existing use being changed to biomass production

Land use change (LUC)

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GHG emissions (g CO2-eq./MJ)

GHG savings relative to distillate (diesel)

Total without LUC 45.2 -

Direct LUC 32.8 47.5

Total with LUC 78.0 9.5

Influence on GHG emissions with/without direct LUC for biodiesel from rapeseed (canola) oil (Fehrenbach et al., 2007)

In some cases conversion of land (managed or wild grassland, forest) to biofuel production will result in GHG emissions large enough to cancel out potential benefits of biofuels. Hence LUC must be included in LCA for biofuels

Default values for land use change for bioethanol (UK Dept. of Transport, 2008)

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GWP from LUC for bioethanol all figures in g CO2-eq. / MJ biofuel All impacts calculated over 20 year period from when LUC occurs Feedstock Origin Land originally covered by

Cropland Forestland Grassland

Wheat Canada 0 977 126

France 0 329 83

UK 0 438 116

Sugar beet UK 0 228 60

Sugar cane Brazil 0 319 88

South Africa 0 220 14

E.g. converting Brazilian rainforest to sugar cane LUC GWP = 319 g CO2-eq/MJ. Over 20 years total GWP = 20 x 319 = 6380 g CO2-eq / MJ. GWP for ethanol from Brazilian sugar cane is 24.1 g CO2-eq / MJ. GWP for petrol is 84.8 g CO2-eq / MJ. So bioethanol GHG saving = 84.8-24.1=60.7 Payback time for LUC GWP is 6380/60.7 = 105 years! Not a good thing to do!

Other life cycle environmental impacts

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Economic sustainability of biofuels

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Over the life cycle, costs of biofuels consist of: Costs of feedstock cultivation, preparation, delivery Capital costs for biofuel manufacturing plants to convert

feedstock into biofuels Other costs such as labour, utilities, maintenance, insurance

etc.

Feedstock costs vary widely from place to place and over time E.g. Europe 21 to 180 per tonne of dry matter (2006) Average in Europe around 60 per tonne of dry matter

Economic sustainability of biofuels

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Capital costs uncertain due to many factors Thermochemical plants (involving gasification and Fischer-

Tropsch synthesis) appear to be most economically sustainable option

Integration of biofuel facility with existing refinery or chemical plant can be the most cost effective option

Biochemical plants have much more uncertainty around costing

Some figures provided in Azapagic table 6.7 and 6.8 Also competition from fossil fuels is very significant rising

crude oil prices making biofuels more economically attractive

Social sustainability of biofuels

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One stated aim of biofuels is to increase rural development improve welfare, infrastructure, reduce poverty etc.

Biomass production has range of social impacts including Human health Human rights and labour rights Land ownership Impact on food security / affordability Community development Impact on indigenous peoples

The areas of high biomass production are often areas of low wealth/earnings, so socio-economic benefits from biofuels can be significant

Ethical biofuel certification programmes, such as the UKs Renewable Fuel Transport Obligation programme (started 2008), can help