Lecture 18: Biofuels 2

Question 1

dedicated biofueld crops: ‘energy’ grasses

Answer 1

• C4 Miscanthus
• C4 Switch Grass
• C3 Reed Canary Grass

Question 2

dedicated perennial energy crops: how to pick

Answer 2

• select cultivars for increased biomass, rapid growth
• Grow an easily processes form while minimising external inputs (fertilisers & pesticides)
• should be renewable - the biomass sources that provide firewood to the worlds poor are not being replaced

Question 3

miscanthus as a perennial energy crop

Answer 3

• 2 years for establishment
• harvest annually in winter, nutrients, recycled from leaves to rhizomes
• low external inputs of nitrogen, herbicides, ash returned to fields

Question 4

perennials have high ____

Answer 4

PRODUCTIVITY

• longer period of light interception, much of the biomass is used
• particularly suitable for developing countries with long tropical growing seasons

Question 5

2 forms of thermal conversion from combusted biomass

Answer 5

• pyrolysis

- gasification

Question 6

pyrolysis:

Answer 6

-thermal conversion (destruction) of organics in the absence of oxygen at lower temperatures producing liquids as the primary product

Question 7

gasification:

Answer 7

thermal conversion of organic materials at elevated temperatures and reducing conditions primarily to produce gases

Question 8

is production of biofuels efficient? burning Switchgrass

Answer 8

burning switchgrass yield 14.6-fold more energy than inputs

-converting Switchgrass to ethanol consumes 45% more energy than is produced

Question 9

production of each biofuel requires a :

Answer 9

Life cycle assessment (LCA)

Question 10

what is a life cycle assessment?

Answer 10

LCA is an evaluation of the environmental burdens associated with a product, process, or activity by identifying energy and materials used and wastes released to the environment.

Question 11

nitrogen fertilisers: The industrial Haber-Bosch process:

Answer 11

N2 + 3H2 —> 2NH3

• requires high temperature (300-600 degrees C)
• high pressures (20-80MPa)
• and has a low yield

Question 12

The industrial Haber-Bosch process: carbon footprint?

Answer 12

LARGE

-2 tonnes of oil are needed to produce 1 tonne of fertiliser

Question 13

how do we get away of using lots of nitrogen fertilisers?

Answer 13

• use crops with low fertiliser demand (perennial grasses like Miscanthus that move nutrients underground in winter) or legumes such as soybean, that fix N2
• recycle nutrients

Question 14

dedicating all US corn and soybean production to biofuels would meet

Answer 14

only 12% of gasoline demand and 6% of diesel demand

Question 15

do we have enough land in the UK for bioenergy?

Answer 15

• one hectare of land can support 30 people with food, but fuel on 2.5 cars
• basically no!

Question 16

are biofuels already competing with crops for food use?

Answer 16

YES

Question 17

half the worlds population lives in ___ where pressure on food production is high and increasing

Answer 17

SE Asia

-urbanisation is increasing and agricultural land being lost

Question 18

Environmental impacts of biofuels: Rainforest Destruction for Oil Palm

Answer 18

FARGIONE (2008), KOH et all 2011
-• EU’s aim of cutting greenhouse gas emissions by 20% by 2020, partly by demanding that 10% of vehicles be fuelled by biofuels, will increase palm oil demand.
• Within a few years, 98% of the rainforests of Indonesia and Malaysia will be destroyed, reducing biodiversity (including Orang‐utan, many plants).
• Burning forests releases large amounts of CO2, exacerbated by release of CO2 from peat lands.

Question 19

2 methods to create third generation biofuels

Answer 19

• Algal ‘Raceway’ Pond

- bioreactors

Question 20

possible industrial production of algae

Answer 20

• need to isolate useful species
• Inputs: large quantities of N and H2O, plus energy inputs for mixing -temperatures may limit growth in winter, particularly at night. Power stations could keep ponds warm at night
• high growth rate, but algae shade each other
• wild strains may invade ponds
• -algae may not grow as fast outdoors as they would in labs
• Harvesting: filters are not effective and centrifugation is energy expensive and even then dehydration is required
• can use marginal land

Question 21

algal biomass productivity: algal oil productivity:

Answer 21

• Algal oil productivity not yet well defined, but certainly not as high as often claimed. Oil yield is ~ 5 t.ha‐1.year‐1 from oil palm (soybean 0.4, rapeseed 0.7)
• At present, most promising algal cases would be economically competitive at market prices around $2 per L for crude oil