lecture 11 - fuel calculation

8/11/2019 Lecture 11 - Fuel Calculation

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FUEL CALCULATIONS



Sources of CO2

Stationary sources Energy Industries

Manufacturing Industries andConstruction

Ferrous/Non-ferrous production

Chemical manufacturing

Pulp, paper and print

Food processing, beverages

and tobacco Commercial/Institutional

Residential

Agriculture/Forestry/Fisheries

Mobile Sources

Civil Aviation

Road Transportation

Cars

Light duty trucks

Heavy duty trucks and

buses

Motorcycles

Railways

Navigation

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Carbon flow for a typical combustion process

Most of the carbon is emitted as CO2 immediately

Small fraction emitted as non-CO2 gases

CH4, CO, non-methane volatile organic compounds(NMVOCs)

Ultimately oxidizes to CO2 in the atmosphere

Integrated into the overall calculation of CO2 emissions

Remaining part of the fuel carbon is unburnt

Assumed to remain as solid (ash and soot)

Accounted by using oxidation factorsQA



Non-CO2 emissions

Direct greenhouse gases

Methane (CH4)

Nitrous oxide (N2O)

Precursors and SO2

Nitrogen oxides (NOx)

Carbon monoxide (CO)

Non-methane volatile organic compounds (NMVOCs)

Sulfur dioxide (SO2)

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Methane (CH4)

CH4 emission is a function of:

methane content of the fuel

engine/boiler/kiln/stove type

hydrocarbons passing unburnt through theengine/boiler/kiln/stove

temperature in boiler/kiln/stove

post-combustion controls

Highest emissions in residential applications (e.g. small

stoves, open biomass burning, charcoal production)

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Nitrous oxide (N2O)

Lower combustion temperatures tend to lead to higher N2O emissions

Emission controls (catalysts) on vehicles can increasethe rate of N2O generation, depending on the: Driving practices (i.e. number of cold starts) Type and age of the catalyst

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Methods for estimating CO2



Reference Approach (Tier 1)

Estimates based on national energy balance (production +imports - exports) by fuel type without information onactivities

Performed quickly if basic energy balance sheet is available

A way of cross-checking emission estimates of CO2 withthe “Sectoral Approach”

Sectoral Approach (Tier 1)

Estimates based on fuel consumption data by sectoralactivity

Bottom-Up Approaches (Tier 2 or 3) More detailed activity and fuel data

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Fundamental equation

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Six basic steps

1. Collect fuel consumption data

2. Convert fuel data to a common energy unit

3. Select carbon content factors for each fossil fuel/product

type and estimate the total carbon content of fuelsconsumed

4. Subtract the amount of carbon stored in products for long periods of time

5. Multiply by an oxidation factor6. Convert carbon to full molecular weight of CO2 and sum

across all fuels

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1. Data collection

Focus on completeness and use judgment or proxy data to

allocate to various subsectors

Biomass combustion not needed for CO2 estimation, butreported for information purposes

Informal sector fuel use is an important issue if not

captured in energy statistics

Household kerosene use can be approximated based on

expert judgment or proxy data

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2. Common energy unit

Convert fuel data to a common energy unit

Production and consumption of solid and liquid fuels

in tons

Gaseous fuels in cubic meters Original units converted into energy units using calorific

values (i.e. heating values)

Reference approach: use different calorific values for

production, imports and exports

Calorific values used should be reported

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3. Estimate total carbon content of fuelsconsumed

Natural gas

Depends on composition (methane, ethane, propane, butaneand heavier hydrocarbons)

Typical: 15 to 17 tons C/TJ

Oil Lower carbon content for light refined petroleum products

such as gasoline

Higher for heavier products such as residual fuel oil

Typical for crude oil is 20 tons C/TJCoal

Depend on coal's rank and composition of hydrogen, sulfur,ash, oxygen and nitrogen

Typical ranges from 25 to 28 tons C/TJ

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4. Subtract non-energy uses

Oil refineries: asphalt and bitumen for road construction,naphthas, lubricants and plastics

Natural gas: for ammonia production

Liquid petroleum gas (LPG): solvents and synthetic rubber

Coking: metals industry

Attempt to use country-specific data instead of IPCC (Intergovernmental

Panel on Climate Change) default carbon storage factors.



5. Oxidation factor

Not all carbon is oxidized during combustion. Some may be

deposited in the combustion equipment and its exhaust flues

or be carried in its gases or remain in residues and ashes after

combustion. The fraction which is oxidized is termed theoxidation factor

Multiply by an oxidation factor to account for the small amount of

unoxidized carbon that is left in ash or soot.

Amount of carbon remaining unoxidized should be low for oil and

natural gas combustion… but can be larger and more variable for coal

combustion

When national oxidation factors are not available, use IPCC default

factors



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Oxidation factor values

Natural gas

Less than 1% left unburnt

Remains as soot in the burner, stack or environment IPCC default oxidation factor = 99.5%

Higher for flares in the oil and gas industry

Closer to 100% for efficient turbines

Oil

1.5 ± 1% left unburnt IPCC default oxidation factor = 99%

Recent research has shown 100% combustion in autos

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Oxidation factor values (cont.)

Coal Range from 0.6% to 6.6% unburnt Primarily in the form of bottom and fly ash IPCC default oxidation factor = 98%

Biomass Can range widely, especially for open combustion For closed combustion (e.g. boiler), the range is from

1-10% No IPCC default

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6. Convert to full molecular weight and sum

Convert carbon to full molecular weight of CO2 and

add across all fuels

To express the results as CO2, multiply the quantity

of carbon oxidized by the molecular weight ratio of

CO2 to C (44:12)

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* Biomass fuels

CO2 emissions from biomass fuels should not be included

in national emission totals from fuel combustion

Account for mixed fuels (e.g. ethanol blends)

Non-CO2 emissions from biomass combustion should be

estimated and reported under the Energy Sector!

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Methods for non-CO2 emissions

Tier 1

Multiply fuel consumed by an average emission factor

Rely on widely available fuel supply data which assumes anaverage combustion technology in use

Tiers 2/3

Multiply fuel consumed by detailed fuel type and technology-specific emission factors

Tier 2 methods use data that are disaggregated according totechnology types

Tier 3 methods estimate emissions according to activitytypes (km traveled or ton-km carried) and specific fuelefficiency or fuel rates

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Fundamental equation

= Σ( × )

Where,a = fuel type

b = sector activity

c = technology type including emissions controls

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Stationary combustion

Default emission factors for CH4, N2O, NOx, CO and NMVOCs by major technology and fuel type are presented in the IPCC Guidelines

Most notable: CH4 emissions from open burning and biomass combustion

Charcoal production is likely to result in methaneemissions at a rate that is several orders of magnitudegreater than from other combustion processes

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Mobile combustion

Major transport activity

Road

Air

Rail

Ships

Most notable: N2O emissions from roadtransportation, affected by the type of emission

control technologies

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Mobile combustion (cont.)

Road transport activity data

Assume vast majority of motor gasoline used for

transport

Check data with equipment counts or vehiclesales/import/export data

Base assumptions of vehicle type and emission control

technology on vehicle vintage data (i. e. model year of

sale) and assumed activity level (i.e. vehicle) Consider national emission standards, leaded gasoline

prevalence, and compliance with standards

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Quality control and completeness checks

All gases (CO2, CH4 and N2O)

All source and sub-source categories

All national territories addressed

Bunker fuels and military operations

All fossil-fuel-fired electric power stations

Blast furnaces and coke production

Waste combustion with energy recovery Black market fuels

Non-metered fuel use for pipelines by compressor stations

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Combustion of Gaseous Fuels

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1- Flammability Limits

Mixtures of dispersed combustible materials (such as

gaseous or vaporized fuels, and some dusts) and air will

burn only if the fuel concentration lies within well-defined

lower and upper bounds determined experimentally,referred to as flammability limits or explosive limits

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Flammability limits can be experimentally determined to a high

degree of repeatability in an apparatus developed by the US

Bureau of Mines.

The apparatus consists of a flame tube with ignition electrodesnear to its lower end

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Intimate mixing of the gas/air mixture is obtained by

recirculating the mixture with a pump.

Once this has been achieved, the cover plate is removed and a

spark is activated.

The mixture is considered flammable if a flame propagates

upwards a minimum distance of 750 mm.

The flammability limits are affected by temperature and

pressure but the values are usually quoted as volume

percentages at atmospheric pressure and 25℃.

Fuel Lower Explosion

Limit (LEL) %

Upper Explosion

Limit (UEL) %Methane 5 15

Propane 2 10

Hydrogen 4 74

Carbon Monoxide 13 74



2- Burning Velocity

Burning velocity is the speed at which a flame front

propagates relative to the unburned gas.

When burning in aerated mode, the flame has a

distinctive bright blue cone sitting on the end of the

tube.

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Estimation of Burning Velocity

A simple method of measuring the burning velocity is to

establish a flame on the end of a tube similar to that of a

laboratory Bunsen burner.

The flame front on the gas mixture is travelling inwardsnormally to the surface of this cone

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If U represents the mean velocity of the gas-air mixture at

the end of the tube and α is the half-angle of the cone at

the top of the tube, then the burning velocity S can be

obtained simply from:S = U sin (α)

This method underestimates the value of S for a number of

reasons, including the velocity distribution across the endof the tube and heat losses from the flame to the rim of the

tube.

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More accurate measurements are made with a burner

design which produces a flat, laminar flame.

Some typical burning velocities are:

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Fuel Burning Velocity (m/s)

Methane 0.34

Propane 0.40

Town gas 1.0

Hydrogen 2.52

Carbon Monoxide 0.43



3- Wobbe Number

The Wobbe index or Wobbe number is an indicator of the

interchangeability of fuel gases such as natural gas,

liquefied petroleum gas (LPG), and town gas and is

frequently defined in the specifications of gas supply andtransport utilities.

If is the higher heating value, or higher calorific value,

and is the specific gravity, the Wobbe Index, , isdefined as

=

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The Wobbe index is used to compare the combustion

energy output of different composition fuel gases in an

appliance (fire, cooker etc.). If two fuels have identical

Wobbe Indices, then for a given pressure and valvesettings, the energy output will also be identical.

In spite of its usefulness, Wobbe index alone is not a good

indicator of the interchangeability of two or more gases, ormixtures of them.

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References

Tim Simmons, CO2 emissions from stationary combustion of

fossil fuels, Good Practice Guidance and Uncertainty

Management in National Greenhouse Gas Inventories, Avonlog

Limited, UK

Calculating Emissions for Stationary Fuel Combustion,

retrieved from:

http://www.rsc2lc.com:8080/archibus/help/user/Subsystems/webc/

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THANK YOU

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lecture 11 - fuel calculation

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