CME201 Fossil Fuels and Fossil Energy

8/2/2019 CME201 Fossil Fuels and Fossil Energy

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Fossil Fuels Fossil Fuel is a sold, liquid or gaseous substance

containing carbon that releases heat via chemical reaction

with air

CH4 + O2 = CO2 + H20

storehouse of chemical energy produced via decay of plant and/or animal remains over geological

times

Combustion = rapid reaction with oxygen that produces

heat via oxidation

equipment to produce combustion is via combustor

Biomass = carbon based fuel produced over 10-100 yr

timescales fuel


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Coal & Peat

Rock-like combustible substance formed by arresteddecay of remains if plant life that flourished millions of

years ago during prolonged periods of tropical climates

and abundant rainfall

exhibits substantial variability in chemical composition a ndmolecular structure

contains inorganic substances

Peat = coal precursor formed by bacterial and chemical

action on plant debris under action of heat and pressure


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Natural Gas/Petroleum/Shale

Natural Gas

Consists of mixture if simple hydrocarbon gases (mostly

methane)

CH4

C2H6 etc H2S, N2, CO2

Petroleum

hydrocarbon oily deposits in upper strata of Earths crust

complex mixture of many hydrocarbon fluids

impurities are S,N,O,Ni,V


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Tar Sands

Oil Shales fine grained mixture if sedimentary rock containing mixtures of

sand,clay in association with organic materials

Sand or sandstone impregnated with viscous crude asphalt-

like substances

mixture of sand , water, bitumen

recoverable by heating


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Heating Values of Fossil Fuels

Table 7.1(pg 299)


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Facts on Fossil Fuels

Gasoline costs are of the same order as bottled water

World crude production = 70 million bbl/day


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Fuel Properties

Heating value = maximum energy obtained by completecombustion of fuel to its end products + cooling all

products to RT

Higher Heating Value = includes any additional heat

released due to condensation

Lower Heating Value = does not include heat of

condensation

Adiabatic Flame Temperature = maximum temperature

that burns with no heat loss to the surroundings


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Resource Base for Fossil Fuels

Table7.2 (pg 303)

New technology liberates unrecoverable fuel stock

utility decided by depletion and current advances that open up new

sources


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Unconventional Fossil Fuels

Ultra-heavy Oils viscous dense mixture of hydrocarbons that cannot be recovered

by pumping

viscosity lowered by steam injection or via injecting hot air to

burn residual gases inside well

has a low H/C ratio

Gas Hydrates

crystalline water molecules surrounding natural gas (CH4) in a

cage

formed beneath ocean floor

must harvest natural gas that is locked up in molecule

must avoid emissions that lead to global warming


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Fossil Resources and Sustainability

Driving force for sustainability is: insurance against global warming

smooth transition to lower fossil dependency

diversification of global energy resources to prevent overreliance

one a single energy source


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Issues for Harvesting of Fossil Fuels

Harvesting Fossil Fuels based upon

exploration

discovery

extraction

transportation

Coal

extraction and transportation are major issues

Petroleum

locating additional deposits undersea development

offshore drilling

ANWR


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Fuel Storage and Transport

Safety Issues fires and explosions

careless handling causing ignition

electrical discharge

fuel spills (Exxon Valdez)

better training & technology

Transport Issues

high shipping costs

high gas-to-liquid conversion costs


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Fuel Conversion

We define conversion as: The chemical/physical transformation needed to improve

the quality of the fuel

leads to upgraded fuel products

yields feedstock for chemical manufacture

removes impurities from raw stocks

chemical cracking (I.e. thermal decomposition) of raw fuel to

produce more usable components

fractional distillation to separate out different components

yields higher quality fuels with higher H/C ratio via hydrogenadditions


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Products of Fuel Conversion

Fig. 7.1 (pg 308)


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Improvements in Processing

Improvements in fuel processing include: thermal and catalytic processing

petroleum refining

compartmentalization

conversion

cleaning

Compartmentalization

fractional distillation & separation into simpler components

Conversion

modification of chemical composition to obtain desired properties

catalytic cracking

Cleaning

removal of pollutants from fuel

S,N

, metals


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Refining Adjusts yield of specific products to meet fuel requirements

regional

time of year

quality regulations

Alternative Fuels

use natural gas and biomass as raw materials

use coal and oil shale to obtain cleaner fuels


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Pyrolysis of Coal

Thermal Decomposition of Coal

Fig. 7.2 (pg.311)


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Coal Liquefaction

Heat coal to a liquid via carbon rejection or addition ofhydrogen

further upgrade

React coal slurry (coal particals in oil) with hydrogen

CH.8 +H2 = CH 1.3-1.7 (liquids) + solids need good source of low cost H2

gasify coal containing N,S tp obtain H2S,NH3,HCN

remove solid by-products

inorganic silicates


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Coal Gasification Chemistry

Table 7.3 (pg 312)


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Hydrogen Generation

Water -Gas Shift CO + 2H 2O = CO2 + H2

Direct production

C + H 2 = CH4

C + H 2O = CH4 + 1/2 CO2 (500oC)

Methanation of Coal

CO + 3H 2 = CH4 + H2O

requires catalyst

requires lower Ts for higher yields

Synthesis Gas

C + H 2O = CO + H2

used to manufacture important fuels


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Range of Fuels Obtained form Synthesis Gas

Fig.7.4(pg315)


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Coal Gasification with Steam

Wide range of heating values obtainable

fig.7.3(pg.314)


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Basics of Fuel Combustion

Combustion = release of heat via chemical reaction of fuelwith oxidizer (air)

A feedback loop is used top maintain continuous

combustion of fuel and oxygen via mixing two species fir

temperatures and times needed to sustain reaction recirculate flow of hot combustion peoducts in unignited fuel/air

mix

electrical ignition of fuel/air mixture

Basic Combustion Reaction

fuel + oxidant+ diluent = desired combustion products + heat +diluent + undesired products


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Combustion Technology Issues

Is dominant means of converting fossil fuel into useful

form of energy Major source of CO2 emission into the atmosphere

Generates diverse pollutants

NOx, Sox

Current engineering design allows efficient burning offuels

Technology continues to improve in an evolutionary

manner


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Role of Diluents

Does not participate chemically in the combustion reaction Can influence the temperature, efficiency and

environmental performance of the combustion reaction

Can serve as a sink for energy liberated by combustion

waste heat Can become a source of adverse emissions

NOx


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Requirements for Combustion

Must have sufficient oxidant to combust fuel completely CO2 + H2O

Must release energy fast enough to heat up fuel and

oxidant to a minimum temperature for reaction

Must generate enough energy to compensate for work ofgas expansion or heat losses form combustion environment

Provide intimate physical contact between molecules of

fuel and oxidant

micromixing turbulence of mixed flow

momentum transfer

heat transfer


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Requirements for Combustion

Fast reacting needed to achieve desired heat release Rates pressure and temperature dependent

Mixing times must be sufficient to achieve complete

combustion


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Combustion of Fuel Droplet

Fig. 7.5 (pg.321)


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Temperature -Time History of Fuel Droplet

Fig. 7.6 (pg.321)

heating rates = 10,000-15,000/sec for coal

Times for combustion = 0.1sec


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Combustion of Atomized Oil Spray

Fig. 7.7 (pg.322)

particles vaporize in a fuel-rich flame


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Control NOx Emissions

Reduce peak temperatures Use dilute fuel feed

Useful fuel injection scenario to produce N2 (g)

Adverse emissions due to :

products of incomplete combustion too low temperatures or pressures

inadequate oxygen supply

excess fuel/oxygen

inadequate mixing times

Fuel Impurities

soot & smoke

polycyclic hydrocarbons

CO and metallic impurities


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Gas Turbine- Steam Turbine Combustion Plant

Fig. 7.8 (pg323)

generate electric powerlow capital cost

low cost electricity

efficiency= 60%


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Coal -fired Power Plant

Fig. 7.9 (pg 323)

Operating efficiency= 35%

Advanced designs = 50%


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How Do We Control Pollution Sources ?

Improve design for better

mixing fuel + oxidant

optimize temperature for minimum NOx production and polycyclic

aromatics

use improved materials for combustor

increase combustor volume


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Carbon Management

Fig. 7.16 (pg 334)

avg CO2 generation/capita = 3.7 tons CO2/yr


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Sequestration Options for CO2

Fig. 7.5 (pg335)


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Geopolitical Factors

50 % of Us consumption of fossil fuels comes fromexternal sources

To reduce the effects of CO2, international accords on

carbon management must be accepted by all produces and

consumers

Sustainability requires measures to prevent social,

economic and political instabilities in fossil fuel exporters

Sustainability requires an orderly transition in social and

political institutions as alternative technologies become

available


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Geopolitical Factors

Sustainability must prevent economic terrorism by oilexporter

prevent takeovers by radical idealogic groups

we must pay close attention to political developents in exporter

countries

Reducing dependency on fossil fuels must win popular

support

con only be done by education of public on importance of global

warming to their welfare


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Equitable Access

Emerging economics must receive financing from

developed countries to encourage sustainable development

Higher energy taxes on fossil fuels face tough resistance

due to public opposition to higher energy prices

Fossil fuel taxes are a large cash cow for many

governments

resistance to sustainability comes from govt desire to collect and

maintain high taxes on fossil fuels

Use of inefficient technologies in many developingcountries may reflect their need to concentrate resources

on health care, sanitation, nutrition etc.

Sustainability must take into account in-grained cultural

habits such as Americas lover for fossil fueled engines


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Economics of Fossil Energy Fossil fuels have a 100 yr history that has developed a

global fuel supply infrastructure

discovery

transport

upgrade

distribute utilize

Fossil fuels are often subsidized by tax incentives and

govt regulations that are favorable to fossil fuel industry

lobbystists in Congress and White House

Sustainable technologies do not have this advantage


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Comparison of Fuel Prices with Other Consumables

Fig. 7.18 (pg343)


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Fossil Fuel Costs and Consumption

Petroleum Avg. US consumption = 2.5 gal/day

prices fluctuate considerably

Natural Gas

$2.00-$5.00/106 BTU

Coal

$1.00-$1.50/ 10 6 BTU

Nuclear Power

$4.60/ 106 BTU


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Principles for Evaluation of Fossil Energy Option Energy Balances

1st/2nd laws ofThermodynamics

Thermal efficiency

Capital costs ~ energy efficiency

Material Balances

Accounts for raw materials used mass balances must account for all species input and output

Technical Feasibility

Must satisfy basic laws od physics

must obtain acceptable efficiency

must have acceptable kinetics

materials must available and have acceptable lifetimes

safety risks considered

economics must favorable


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Why Are Fossil Fuels Important to Sustainable Energy

Sustain economic progress Provide enabling technology to transition from non=fossil

alternatives

Avoid economic disasters until suitable alternatives come

on stream Indispensable to social and economic progress in the

developed world

Essential to the economics of both developed and

developing countries

Improvements in efficiency can prolong the transition

period to sustainable society

can have both positive and negative effects

Documents

CME201 Fossil Fuels and Fossil Energy