SAS025 Final

Examples of finite resources for energy

supplies of fossil fuels, deposits of radioactive materials, productive sites for renewable energy generation, arable land for sufficient biofuel production

if fuel consumption continues at its 2024 rate, what will happen to known fossil fuel reserves?

Known reserves of petroleum will last approximately 53 more years, coal 113 more years, natural gas 55 more years, uranium 120 more years

why is it important to increase efficiency of light-duty vehicles?

they are one of the few sources of greenhouse gases that individuals have direct control over

Major factors that increase fuel efficiency

driving conditions, taxes on petroleum and vehicles, consumer preferences, use of diesel-powered vehicles, agreements with automobile manufacturers

why do fuel efficiencies decline at speeds above 50 mph?

the wind resistance of a vehicle is proportionate to the square of its speed

what is the most important factor to determining fuel efficiency?

driving behavior; quick acceleration and heavy braking diminish fuel economy by more than 30%

Causes of traffic congestion

Either recurring on non-recurring. Recurring is things like rush hour, holiday traffic, and routine road maintenace; non-recurring is unplanned, like accidents and weather

Strategies reduce traffic congestion

constructing new roads, eliminating choke points by building new intersections or lanes

Why are taxes on fuel a good source of revenue?

Amass a lot of money, 10.8% of revenues collected by governments. Easier to collect than other taxes because they are assessed at refineries or large wholesalers. People are less averse to paying these taxes because they see the money going towards infrastructure

What do consumers value in vehicles?

Larger vehicles with faster acceleration

How have cars in the US and Europe changed over time?

Bigger, more powerful engines, faster acceleration

Why are diesel engines more efficient than gasoline engines?

They operate at higher pressures and temperatures

How much more efficient are diesel engines than gasoline?

abt 40% higher fuel efficiency per volume of fuel

problems with small diesel engines

loud, more vibrations, harder to start, emit black smoke

solutions to issues w small diesel engines

computer-controlled electronic ignition and turbocharged direct fuel injection

Diesel vs gasoline - GHGs emitted

Diesel engines emit over 20x more NOXs, more particulates, less CO

Ways diesel and gasoline engines differ

Ability to accommodate alternative fuels. Diesel fuel contains abt 11% more energy per volume, but also emit 15% more CO2. Diesels weigh more. Diesels still emit around 5-30% less GHG per distance traveled

Gasoline engines built after 1980

can use mixtures of gasoline and up to 10% ethanol without modification. With modifications, they can use mixtures that are up to 85% ethanol or methanol

Today’s diesel engines

Can switch between petrodiesel and mixtures of petrodiesel and biodiesel

Benefits of higher fuel efficiencies

conserve limited natural resources, reduce dependence on unreliable sources of petroleum, improve balance of the trade for many countries, and mitigate air pollution and GHG emissions

Two general approaches for improving vehicle fuel efficiency

1. Focusing on the design of vehicle — engines, transmissions, or drivetrains — to get more energy out of the fuel combusted

2. Focusing on air conditioning, vehicle weight, aerodynamics, or rolling resistance to diminish the effort required to propel the vehicle

A central factor in transportation efficiency is

passenger occupancy

most travel in the US and Europe is via

private vehicles - including cars, small trucks, SUVs, bikes, motorcycles

How has ridership of public transport changed?

increasing on ground transport and public air travel

Alternative energy sources for transportation

Bioethanol, biodiesel, compressed and liquid natural gas, hydrogen, electric and electric-hybrid

Where is natural gas extracted from?

oil wells, coal beds, natural gas fields and landfills

Why compress natural gas?

Natural gas has a very low energy content at normal atmospheric pressures, and have to pressurize for transport.

Cons of natural gas

Still has a quarter or less of the energy content in gasoline and requires larger storage tanks at refueling stations and on the vehicles themselves; refueling is slow

Pros of natural gas

Costs less on the world market than gasoline or diesel fuel; produces fewer particulates, non-methyl hydrocarbons, and NOXs; less greenhouse gases than any fuel except hydrogen

Why is leakage of natural gas during the process a problem?

its main constituent is methane

Liquefied natural gas

has energy content similar to other liquid fuels, can be stored in smaller tanks and transferred more quickly than CNG; but such tanks require heavy duty insulation to keep LNG from boiling, which is hard

Hydrogen fuel cells

hydrogen reacts w oxygen to form water and generates electricity for an electric motor that moves a vehicle

Liquefied hydrogen

contains nearly double the energy content per volume of hydrogen gas, but only 40% of that of LNG; energy losses occur when liquefying it and during storage and refueling

Fuel cell costs

Very high! Nearly all electrode/catalysts for hydrogen fuel cells contain platinum

Catalyst

a substance that promotes a chemical reaction without being consumed itself

Cons of hydrogen fuel use

fragile because of thin membranes and high surface area makes them vulnerable to contamination. water and temperature management is complex. we don’t have the infrastructure

methods for producing hydrogen

either produced from fossil fuels or electrolysis

Electrolysis

electric current passes through water and releases hydrogen and water

potential future methods of hydrogen production

direct splitting of water and oxygen, biological production from photosynthesis

2 strategies for supplying hydrogen to a network of refueling stations

a few large stations to produce hydrogen and then ship it further through special pipelines or truck or ship transport, or have many small facilities produce it locally; large stations could produce hydrogen at much lower production and social costs but shipping is hard

Problems with electric vehicles

battery technology limits the amount of energy that a vehicle can carry and thus its speed, range, and recharge time; lead-acid batteries are heavy and have low energy per size and weight

Advantages of electric vehicles

often achieve 90% conversion efficiency, emit no GHGs, recharge at night, don’t need gears or torque convertors, operate at temperatures near ambient, need less maintenance, regenerative braking

Most of the locomotives and many of the ships built in last 50 years are

diesel-electric hyrbids

how do diesel-electric hybrids work?

large diesel engine turns a generator that recharges batteries, which in turn power small electric motors connected to wheels or propellers

Pros of diesel-electric hybrids

operates diesel engines at optimized fuel efficiency, eliminates need for complex drive trains between engine and wheels/propellers, makes cars smoother and quieter

Today’s hybrid cars:

connect gasoline-powered engine and electric motors to the wheels; sometimes electric motors assist gasoline engine, in others vice versa. Gasoline engine shuts down when vehicle stops. Regenerative braking

cons of today’s hybrids

nickel-metal hydride batteries have small capacities, are difficult to recycle, and only guaranteed for 8 years; replacements are expensive

Biofuels

those that are produced from living materials, including bioethanol, biomethane, and biodiesel

what contributes most GHGs emitted during biomass production?

manufacture, distribution, and application of nitrogen fertilizer

the promise of biofuels

expanded cultivation of crops that require lower inputs of nitrogen, other chemicals and water and less use of mechanical equipment to produce high, sustainable yields of biomass rich in organic compounds that can be turned into biofuels

why is sugarcane a promising source of biofuel?

tissues host nitrogen fixing bacteria, maintains high level of productivity under low nitrogen fertilization

Well established procedures for converting biomass into biofuels:

Direct burning of biomass, fermentation of sugars to ethanol, and cellulose purification

Biofuel processing facilities are located

near biomass production sites - mostly the Corn Belt. transport to the processing facility, even over short distances, contributes between 2-4% to total GHG emissions during bioethanol production

Are biomass plantations sustainable in the long term?

doubtful w/o restoration of soils

Energy density of fuels from highest to lowest

 gasoline, biodiesel, ethanol, starch, switchgrass shoots

Distillation separates chemicals by

their differences in boiling temperature

Brewer’s Yeast

used to convert glucose/fructose in plant juices to ethanol

Efficiency to sugar to ethanol

87% of energy in sugar converted to energy in ethanol

Fermentation followed by distillation and dehydration results in a product that is

better than 99% ethanol

Efficiency of starch to ethanol

66% of energy in starch converted

Cellulose

a polymer composed of glucose subunits. These subunits alternate in direction, forming strong chem bonds between adjacent cellulose chains

First step of cellulosic ethanol processing is to

release cellulose and hemicellulose from cell walls; done via hydrolysis

Hydrolysis

to decompose/dissolve cellulose and hemicellulose into sugars 

The second step of cellulosic ethanol processing is

fermentation; microbes convert sugar into ethanol

Drying biomass does not

reduce its energy density

Cellulose chains interact w e/o to

increase strength

Vegetable oil is extracted by

a mechanical press or chemically with organic solvents like hexane

FAME

Reaction of extracted veg oils or animal fat w methanol or ethanol in presence of base and separation from alcohol, base, and glycerol

Efficiency of FAME

89; economic viability depends on value of 38%-97% of biomass remaining after oil extraction

biomass-to-liquids process

gasification of carbon from natural gas, biomass, or coal with steam under heat and pressure to produce CO and H

Hydrotreated vegetable oil process

uses hydrogen to remove oxygen from vegetable oils or animal fats and produces long-chain reactions

Many heavy industries have moved to developing countries like China and India

 to take advantage of low labor costs and avoid stringent environmental regulations

Abatement of greenhouse gases may be relatively slow even after wide-scale adoption of new technologies because

electric power plants in the US have median age of 30 yrs - replacement of old power plants is slow

Energy generation in China and India have

increase exponentially over the last few decades, but are now slowing down

Coal is attractive to China, India and the US because

they have bigger stores of coal than gas, oil or uranium

Fluidized bed combustion

Burns coal in a layer of heated particles suspended in flowing air. The bed acts as a fluid that mixes coal particles with air. This fluidizing action completely combusts the coal at relatively low temps

Power plants of all types have a lifespan of

30-50 yrs

Pulverized coal steam-generating system

crush pieces of coal into powder. Hot air blows coal powder into furnace, combusts at high temps. Converts water to steam in tubing that lines walls of furnace. Steam passes thru turbines connected to common shaft that spins a generator

Major advantage of fluidized bed combustion

it can use almost any grade of coal - often burns coal rejected from pulverized coal power plants

IGCC System

Does not combust coal directly, but converts coal into gas - syngas, CO and hydrogen. Water gas shift converter changes carbon monoxide in steam to carbon dioxide in hydrogen. Hydrogen produced combusts directly in gas turbine that spins an electric generator

Advantages of an IGCC system

produce less sulfur dioxide and nitrous oxides in the flue gas, and high fuel efficiencies – 38%-49%

Disadvantage of an IGCC system

high construction costs

Conversion of chem energy into mechanical energy becomes

more efficient at higher temps and pressures. Diesel engines run at higher temps and pressures than gasoline engines and therefore are more efficient

Efficiencies of coal-fired power plants increase and GHG emissions per unit decrease

at higher units and temperatures

Water at temperatures above 374 degs C at pressures above 218 atmospheres

becomes a supercritical fluid

Supercritical fluid

properties of both gas and water. Has a density that changes with temperature and pressure in a continuous manner

Advantages of using supercritical fluid in a coal fired power plant

power plants designed to operate under supercritical conditions scale to higher temps and pressures w/o having to accommodate two phases of water (liquid and gas) in various locations; more efficient, and lower fuel costs may eventually compensate for higher construction and maintenance costs

Disadvantages of using supercritical fluid in a coal fired power plant

higher temps and pressures are more high maintenance, and supercritical water is very corrosive. These restrictions add 7% to cost of building and maintaining

Advantages of natural gas power plants

have lower costs, high fuel efficiency, operating flexibility, rapid deployment, and low GHG emissions

Carbon capture and storage (CCS)

collecting CO2, concentrating it, transporting it, and storing it in a manner that prevents it from mixing freely w atmosphere

Storage options for captured carbon

diversion into industrial processes, conversion into mineral carbonates, pumping to depths of oceans, and burial in geo formations

Power plants may capture during

fuel processing, before combustion, or from flue gas after combustion

ways to remove CO2 from gas streams

Physical separation, chemical separation, or a combo

Physical methods of removing CO2

cryogenic separations and membrane separations

How does cryogenic separation work?

Based on differences in temperatures at which gases condense to a liquid or freeze directly to a solid dry ice – cooling large volumes of flue gas to very low temps. More efficient to do it before combustion. Only adds 15% to fuel use of power plant

How does membrane separation work?

depends on differences in partial pressures to transfer CO2 or H2 across a gas-permeable membrane to screen impurities out

Chemical methods for removing CO2

liquid solvents and solid sorbents

Liquid solvent method

chem substances (solvents) r isolated from main gas stream and exposed to high temps or lower pressures to release CO2 and regenerate capacity for CO2 removal from gas streams. Forms a solution that, when heated, expels the CO2

Solid sorbent method

Molecular sieves and activated carbons; materials filled w pores of the exact size that let CO2 molecule enter and absorb on surface but excludes larger molecules. Release CO2 and regenerate when subjected to large temperature or pressure swings

Oxy-fuel

combust coal, syngas, or natural gas in nearly pure O2 and produce exhaust gases that are over 95% CO2