E5 - Petrol must be 5% ethanol

B7 - Diesel must be 7% biodiesel

- Increasing fuel security in countries with limited petrol reserves (cause of a push in Brazil)

- Producing biofuels creates jobs and diversifies the economy

- Reliant on government policies, as production costs still greater than petrofuels.

Sugar cane - BE

Soya - BD

Rapeseed - BE

Wheat - BD

Agricultural Products

-Require significant areas of high-quality fertile land

- Vast amounts of fresh water required

- Competing with food crops brings up the "food vs. fuel" debate

Agricultural waste products

- Addresses arable land use

- Still the issue of water use, freshwater needed to sustain crops.

- Loss of biodiversity

1) Reduced waste, meaning more sustainability and reduced environmental impact.

2) Profitability is greater

3) More economically robust - more products means less vulnerability to market change

1) Well-defined chemicals, "speciality chemicals"

2) Transport Fuels

3) Feedstock chemicals - still require other processes

4) "Syngas" - Synthesis (not synthetic) gas, a mixture of H₂ and CO.

5) Heat & Power

Max. ethanol content is about 10%.

Distillation and subsequent processes necessary to increase this value.

Sugary - Sugar cane, sugar beet

Starchy - Maize, wheat

DDGS - Distiller Dried Grains -> Protein Animal Feed

CO₂ for the drinks/food industry

To prevent it from being drinkable

1) Safer

2) Not taxable

- Process takes 8-12 hours due to long reaction time

- Large vessels therefore needed

- This means high capital cost and areas of land taken up

- Get "beer" which is 7-10% ethanol

- Split into solids and liquids (separation by density) via centrifugation

- Solids are yeast cells that can be reused.

- Moves onto distillation

- Separation by boiling points is done

- For every litre of BE, there is 10 to 13 litres of stillage

- Stillage is other liquid and solid waste (goes to animal feed)

- Propanol and butanol are heavier with higher boiling points, also methanol.

What method is used for ethanol dehydration?

Pressure Swing Adsorption

- Separation by molecular size as H₂O is smaller than ethanol.

- Mixture pressurised to 600kPa, and fed into a 'bed'

- 3A Zeolites adsorb the water, well-defined pore structure means it can discriminate between the two compounds.

- Beds are switched intermittently to recharge pressure

- Output of 99.9% ethanol

Conversion of starches to sugars. 

Hydrolysis -> Water breaks up the molecules

Starch molecules need to be broken down into multiple individual sugar units

1) Acid-catalysed hydrolysis at high temperature

2) Enzyme-catalysed hydrolysis (preferred route)

1) High yield

2) Sugar not starch so less processing (no saccharification).

- Ethanol has lower calorific value, less than 70% of octane.

- Higher compression ratios can be used, and the required air needed for ethanol is less.

- Reduced emissions of carbon monoxide and hydrocarbons

- Oxygenated products like acetic acid are produced, but should be removed by the catalytic converter

- NO_x emissions are increased slightly due to higher combustion temperature and the oxygen in the fuel (unlike petroleum).

Used Cooking Oil.

Waste is repurposed. No land use change and feedstock production processes not considered.

- They are too viscous to flow through modern diesel engines or to atomise in the engine

- Leads to incomplete combustion causing problems like:

1) Formation of gums and lacquers on injection nozzles

2) Partial combustion products, such as acrolein.

- Transesterification

- Done to reduce molecule size, reducing viscosity.

- Reacted with methanol in the presence of a catalyst (usually an alkali)

- Fatty Acid Methyl Ester (FAME) or "Biodiesel" (flows and combusts better than triglycerides)

- Glycerol, a by-product

Sulphur (wt%) - PD: 0.05% and BD: 0%

- CO reduction of 48% with B100

 - 50% reduction in particulate matter 

- 67% reduction of un-burnt hydrocarbons

Negative:

- 10% increase in NOx emissions (due to higher temp combustion and oxygen availability)

BD has higher cetane number and greater oxygen content which means better combustion.

Less air required with BD combustion.

BD has higher cloud and pour points (°C) meaning B100 isn't viable in cold countries.

Sunflower and rapeseed oil :)

Palm oil :(

- Similar boiling point to BE so no inlet manifold redesign needed.

- BD acts as a rubber solvent, so some seals need replacing with resistant materials.

- Some high pressure engines limited to B5, but B7 widely used.

Palm Oil (by far the most productive)

Rapeseed

Sunflower 

Soya

Triglyceride + 3 Methanol ↔ 3 FAME + Glycerol

Twice as much methanol is used than required to push the reaction to the product side and achieve a 95% conversion (only 70% without)

1) The reaction is much slower, typically 8-10hrs, (otherwise <1), and requires a large excess of methanol (20:1)

2) More expensive materials needed to tolerate the acid.

Necessary for "low-grade" oils such as UCO. "Yellow/brown grease" rather than pure, virgin oils. Required due to water and breakdown products in the oil, especially free fatty acids (FFAs).

- Dedicated energy crops (wood, shrubs)

- Agricultural residues (wheat stalks and leaves)

- Wood residues (sawdust)

- Waste paper

Bottom 3 are all waste materials

Biochemical - 2.6

Thermochemical - 5.0

Biochemical has more processing steps due to pretreatment and separation.

 What is cellulose?

Percentage of wood?

- Polysaccharide (starch polymer)

- Made up of C6 sugar units (such as glucose).

Typically about 40-50% of lignocellulosic material.

What is hemi-cellulose, downsides?

Percentage of lignocellulosic materials?

- Polymer made up of C5 sugar units ("xylose" normally). 

- Amorphous, and about 25-30% of lignocellulose

- As it is C5 not C6 it cannot be fermented into bioethanol.

Lignin provides strength to the plant by bonding with hemicellulose. 

Transports water through plant, typically about 15-20% of lignocellulosic material.

Made of phenols and aromatic alcohols. It isn't linear, and is highly branched. 

Difficult to make specific products from due to complex chemistry.

1) Combustion - Heat & Power

2) Gasification - Hydrogen, Alcohol, Olefins, Gasoline, Diesel

3) Liquefaction (Hydrothermal is a subset) - Hydrogen, Methane, Oils

4) Pyrolysis - Hydrogen, Olefins, Oils, Speciality chemicals

1) Break up the woody structure

2) Increase surface area for hydrolysis

More energy required for woody biomass

Conventional: Hot water, dilute acid or alkalis

Others:

a) Ammonia fibre explosion - contact with liquid ammonia at high pressure then release the pressure.

b) Steam explosion with catalyst - high pressure and temp (then release)

a) Feedstock composition (low/high lignin content)

b) Production of toxic compounds

c) Energy costs

d) Requires large-scale usually meaning significant capital investment

Used to convert somplex sugars to simple sugars:

- Cellulose to glucose

- Hemicellulose to xylose

Used in thermochemical conversion of lignocellulosics at demonstrator scale. 

Biomass is converted to syngas (CO + H₂) before synthesis.

During synthesis get an output of hydrocarbon fuels (and water).

1) Algae growth

2) Harvest and dewatering

3) Drying

4) Fuel production

Per ton:

- 1.82 tonnes of CO₂ absorbed

- 0.43 tonnes of water 

- 0.32 tonnes of nutrients

- 1.54 tonnes of O₂ produced (photosynthesis)

- 0.048 tonnes of calcium hydroxide produced

Open pond - 0.2 to 1g per litre (dry biomass)

Closed photo-bioreactor - 1 to 10g per litre

1) Mechanically capture wet algae via filtration

2) Heat until dry

3) Solvent extract the oil

4) React to make biodiesel

Issues:

- Drying is so energy-intensive that the NER is less than 1

- Hexane used for solvent extraction, large carbon footprint

- Biodiesel reaction is not water tolerant, need less than 0.5% water

1) In-situ transesterification (fast and needs excess methanol) -> biodiesel

2) Hydrothermal processing (requires much separation) -> produce "bio-oil"

- Production rates are potentially massive per sq. ha

- Can use a wide range of water sources: Wastewater and Seawater

- Can be used to sequestrate CO₂

- Produce lipids up to 77% of their total weight

- Water removal too energy intensive, requires many steps

- Not all lipids produced are easily transesterifiable; you want neutral lipids like triglycerides, but environmental conditions can cause complex growth

- Contamination by protozoa or bacteria can decrease production yields.

- Way too expensive to produce atm, also NER is shit.

1) Plate tectonics

2) Volcanic eruptions and dust storms

3) Solar variations

4) Orbital variations

- Continental shift can influence climate at specific locations

- Can also influence global temperature by redistributing the collection of solar radiation and/or providing land masses on which continental glaciers can form 

Both release particles that can reflect radiation.

Volcanoes emit CO₂, H₂O and SO₂ that can get trapped in the upper parts of the atmosphere. These can react to create sulphates and aerosols. Aerosols lower surface temperature.

In lesser amounts emit CO, H₂S, CS₂, HCl, etc.

1) Eccentricity

2) Precession of the Equinox

3) Obliquity

Eccentricity is the extent to which an object's orbit around another body deviates from a perfect circle.

Earth's orbit changes with a period of 100k years, at the moment it is fairly circular but in 50k years it will be more eccentric.

Further from the sun = Colder

Axial precession is the gradual shift of Earth's axis of rotation in a cycle of approx. 26,000 years

Changes the time of year that seasons occur.

- 51% absorbed by land and oceans

- 19% absorbed by atmosphere

- 20% reflected by clouds

- 6% reflected by the atmosphere

- 4% reflected by the Earth's surface

- 55% radiated to space from the atmosphere

- 20% becomes latent heat as water vapour

- 13% of radiation is absorbed by the atmosphere

- 6% is conducted or becomes rising air

- 5% is radiation from Earth to space

Albedo is the percentage of incoming radiation that is reflected back into space.

The value is 31% for Earth

Nearly half of sunlight is in the visible light spectrum, the rest is in the ultraviolet and infrared ranges.

The radiation emitted by the Earth is infrared.

The change in net (down minus up) irradiance (in W/m²) due to the change in the amount of an agent, with surface temperature assumed constant.

Positive radiative forcing tends to warm the Earth's surface and lower atmosphere. Negative radiative forcing tends to cool them.

E.g. increase in greenhouse gases leads to positive forcing.

A measure of the future impact of emitting unit mass of a particular greenhouse gas today. It is normally measured relative to CO₂ and is calculated for a specific time horizon

GWP = time-integrated radiative forcing for the gas ÷ time-integrated radiative forcing for CO₂

It is assumed gas is released instantaneously and decays gradually.

CO₂ - 1, 1.5W/m²

CH₄ - 36, 0.48W/m²

N₂O - 300, 0.15W/m²

Refrigerants (CFC-12) - 10600, 0.17W/m²

- Found via bubble plume distribution analysis, in the

Cascadia Margin (in Pacific off the west coast of NA).

- Observed increased activity of methane emission 150-250m deep.

These reservoirs potentially causing warming of North Pacific, also pH increase and tsunami activity.

Perfluorocarbons (PFCs) and SF₆, only present in low amounts.

- Manufacture of aluminium and magnesium

- Semiconductor processing

Effects are complex and not fully understood and they

may decrease warming. Sources of aerosols include:

- Anthropogenic: smoke from burning fossil fuels, sulphates

- Natural: volcanoes, dust-storms

Pre 1750: 280ppm

1999: 367ppm

2020: 418ppm

Land sinks: Photosynthesis, respiration/decay, fossilisation over a long time schedule

Ocean sinks: Plankton, sedimentation of CaCO₃, becoming rock

- Large-scale ocean circulation driven by global density gradients (cold and more saline water is more dense)

- Created by surface heat and freshwater fluxes

- Has an important role in supplying heat to polar regions and thus in regulating sea ice.

- Could be changed due to large shifts in radiative forcing

- Likelihood is uncertain but impacts on climate could be catastrophic

1) Sea level rise (0.1-0.8m), destruction of habitat.

2) Mass extinctions, potentially 1/3rd of species

3) More intense hurricanes

4) Atlantic conveyor shut down

1) Time delays: Greenhouse gases have lifetimes of many years and the ocean reacts to atmospheric changes over decades

2) Improvements in energy efficiency and cleaner energy sources will be offset by population growth and industrialisation in developing countries.

The capture of carbon dioxide and storage.

- Removed from flue gases such as at power stations, before storage in underground reservoirs.

Biological sequestration

Geological sequestration

Marine sequestration

Mineral sequestration

- Reforestation

- Alternative agricultural methods

- Plants can provide biofuels :)

- Requires significant land use :(

- Bury CO₂ in rocks or aquifers

- Can be used to capture CO₂ before it reaches the atmosphere :)

- May leak out over time :(

- Seed oceans with chemicals that increase CO₂ intake.

- Could be an effective an easy fix :)

- Science not fully established, side effects on ecosystem?

:(

The formation of carbonates using captured carbon dioxide.

Example is the potential use of sea urchins which can naturally complete this process.

Urchins are pollutant sensitive, reproducible

Liquefied petroleum gas (LPG) is propane which can work to replace CFCs to reduc damage to the ozone layer. It burns with no soot and low sulphur emission.

Provides electricity and heating. 

• 1. The Sun

• 2. The motion and gravitational potential of the Sun, Moon and Earth

• 3. Geothermal energy from cooling, chemical reactions and radioactive decay in the Earth

• 4. Human induced nuclear reactions

• 5. Chemical reactions from mineral sources (batteries, dry cells etc.)

1) Stand-alone system

2) Grid-connected system

The dilution of solar radiation when it touches the top of the atmosphere.

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Any object when heated above absolute zero emits energy in the form of electromagnetic radiation.

The rate at which energy is emitted increases with temperature, according to the formula for a grey body:

S_b = ε*σ*T⁴ (W/m²)

Where ε is emissivity (between 0 and 1), depends on material and surface finish.

Stefan-Boltzmann Constant: σ = 5.67x10^-8 Wm^-2K^-4

A black body absorbs all light that falls on it (absorbance, α = 1)

Kirchoff's Law states that α = ε.

Meaning that it also emits the maximum possible amount of radiation.

Therefore for a black body:

S_bb = σ*T⁴

E = hf

Where h is Planck's constant (6.63*10^-34)

and f is frequency

E can be measured in joules but is more commonly measured in eV, the energy needed to raise 1 electron through a potential of 1 volt.

1eV = 1.60*10^-19 J

λ_maxT = γ

Where γ = 2.8977729x10^-3 mK

The rate at which radiant energy arrives at a specific area of surface during a specific time interval.

Typically W/m²

Dilution factor = (r/r₀)²

r = Distance from centre of emitter (Sun) to the measured surface (Earth's atmosphere).

r₀ = Emitter radius (Sun radius)

Value for Earth is 46500

S is the irradiance just outside the Earth's atmosphere on a plane facing the Sun.

It is not a true constant as ellipticity of Earth's orbit leads to variation of ±3.5%. The 11 year sunspot cycle of the Sun also leads to variation of about 0.1%

G₀ = S*cosθ

Where: 

S = Solar Constant

θ = Zenith Angle

It is the angle between the sun and the vertical (perpendicular to the Earth's radius at a particular point).

[image]

cosθ = (sinδ*sinφ)+(cosδ*cosφ*cosω)

Where θ = Zenith angle

δ = Angle of declination: sinδ = 0.4sin(2πn/365)

φ = Latitude

n = Day number counted from spring equinox (21st March), when declination is zero

ω = Solar hour angle, propertional to time of day. ω=0 at solar noon and advances 15° every hour.

Global irradiance on a surface, G = B + D + R

Where R = Albedo

B = Direct radiation

D = Diffuse radiation

Albedo, R, is a measure of the reflectivity of the Earth's surface at a certain point.

Albedo irradiance can be neglected for most photovoltaic applications because it is only worth factoring in on polar caps or icy mountains.

Direct component:

B_h = B*cosθ

Where θ is Zenith angle

Direct component, B:

B_s = B*cosβ

Where β is the angle between the Sun and the perpendicular of the tilted surface.

Therefore:

B_s = (B_h*cosβ)/cosθ

Diffuse component, D:

D_s = ½(1+cosγ)D_h

Where γ is the angle between the horizontal and the tilted surface.

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A phenomenon where light is scattered by particles that are larger than or comparable in size to the wavelength of light.

Occurs with aerosols (clouds) and dust.

A greater value for air mass (AM) leads to a decrease in irradiance on the ground. 

Remember that air mass is proportional to Zenith angle.

1) Direct measurements:

- Only available in some locations and may not go back enough years. 

-Usually only gives G_h

2) Number of hours of sunshine measurement on a given location

3) Stochastic modelling: Markov Chain

4) From satellite observations

- The global radiation flux on a horizontal surface on Earth, divided by the extra-terrestrial irradiance on the horizontal.

K = G_h/G₀

In general can't be predicted due to dependence on atmospheric conditions. 

Must be in the range 0-1.

Used to represent a ratio of total radiative energies received over a period of time (e.g. day/month period).

How can sunshine hours be correlated to clearness index?

How is sunshine hours measured?

K = 0.18 + 0.62(N_S/N_D)

Where K = Clearness Index

N_S = Number of hours of sunshine per day

N_D = Number of hours in the day (sunrise to sunset)

Would sum over months of interest

Hours of sunshine per day is measured using a Campbell-Stokes recorder

Diffuse fraction - expresses diffuse radiation as a fraction of global radiation on the horizontal.

K_D = D_h / G_h

Where D_h is diffuse radiation on the horizontal

and

G_h is total radiation on the horizontal.

A process whose future probabilities are determined by recent values.

Needed as sometimes short-term variations are needed but due to storage requirements, this data is often not available, and so random chains need to be generated.

[image]

Database of historical time series of irradiation, temp, humidity etc.

Has hourly data since 2010.

Uses weather station data. Uses interpolation and a stochastic model (along with hourly values of D_h) to resolve direct, diffuse and albedo.

Donor elements have one extra electron than the silicon, acceptor's have one less.

Donor:

- P, As, Sb 

- The additional electron is now free to move through the lattice

Acceptor:

- B, Al, In

-One less bond means neighbouring Si left with an empty state.

Majority carrier: The carrier that exists in higher population

Minority carrier: The carrier that exists in lower population

Valence band - the lower filled band

Conduction band - The upper band (partially filled or empty), free to move and can contribute to electrical conductivity.

For donor atoms in the valence band, the energy level is higher, making it easier for an electron to leave to the conduction band.

In the conduction band, acceptor atoms have a lower energy level, meaning only a small amount of energy is required for an electron from the valence band to move to their energy level.

Diffusion occurs towards the material where that particular donor is the minority carrier (e.g. electron diffusion towards the p-type material)

Carrier drift occurs in the opposite direction. 

Charged particle motion in response to an electric field.

Holes move in the direction of the electric field (+ to -).

Electrons move against the field (- to +).

Average net motion is described by drift velocity, v_d with units cm/second. Net motion gives rise to current.

J_n,drift = q*n*v_d 

Where:

J = Electron drift current density

q = Charge

n = Concentration of electrons

v_d = Drift Velocity

When electric field value is low:

J_n,drift = q*n*v_d

Where:

μ is "mobility" of the semiconductor material.

Max value for v_d is v_sat (saturation vel.)

Within intermediate values of electric field strength there will be a peak value of drift velocty that can be achieved. Want to ensure the system works near this value for faster operation.

[image]

Ohm's Law states: J=σE=E/ρ

Integrating equations for electron & hole drift currents at low electric fields:

σ = q(μ_nn+μ_pp) and ρ = 1/[q(μ_nn+μ_pp)]

However minority carriers changes very little and so can become:

[image]

What is Fick's Law?

Rewritten for electrons and holes in semiconductors?

A description of diffusion:

F = -D∇η

Where η is the concentration and D is the diffusion coefficient.

J_n|diffusion = -qD_n∇n

or 

J_p|diffusion = -qD_p∇p