Calculation of CO2 emissions

Document Sample
Calculation of CO2 emissions Powered By Docstoc
A carbon footprint is "the total set of greenhouse gases (GHG) emissions caused by an organization,
event or product" [1]. For simplicity of reporting, it is often expressed in terms of the amount of carbon
dioxide, or its equivalent of other GHGs, emitted.

The concept name of the carbon footprint originates from ecological footprint discussion. The carbon
footprint is a subset of the ecological footprint and of the more comprehensive Life Cycle Assessment .

Crude oil:
Crude oil is separated into fractions by fractional distillation. The fractions at the top of the fractionating
column have lower boiling points than the fractions at the bottom. The heavy bottom fractions are often
cracked into lighter, more useful products. All of the fractions are processed further in other refining

Raw or unprocessed crude oil is not generally useful. Although "light, sweet" (low viscosity, low
sulfur) crude oil has been used directly as a burner fuel for steam vessel propulsion, the lighter
elements form explosive vapors in the fuel tanks and are therefore hazardous, especially in
warships. Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a
refinery into components which can be used as fuels, lubricants, and as feedstock in
petrochemical processes that manufacture such products as plastics, detergents, solvents,
elastomers and fibers such as nylon and polyesters.

Petroleum fossil fuels are burned in internal combustion engines to provide power for ships,
automobiles, aircraft engines, lawn mowers, chainsaws, and other machines. Different boiling
points allow the hydrocarbons to be separated by distillation. Since the lighter liquid products are
in great demand for use in internal combustion engines, a modern refinery will convert heavy
hydrocarbons and lighter gaseous elements into these higher value products.

The oil refinery in Haifa, Israel is capable of processing about 9 million tons (66 million barrels) of crude
oil a year. Its two cooling towers are landmarks of the city's skyline.
Oil can be used in a variety of ways because it contains hydrocarbons of varying molecular
masses, forms and lengths such as paraffins, aromatics, naphthenes (or cycloalkanes), alkenes,
dienes, and alkynes. While the molecules in crude oil include different atoms such as sulfur and
nitrogen, the hydrocarbons are the most common form of molecules, which are molecules of
varying lengths and complexity made of hydrogen and carbon atoms, and a small number of
oxygen atoms. The differences in the structure of these molecules account for their varying
physical and chemical properties, and it is this variety that makes crude oil useful in a broad
range of applications.

Once separated and purified of any contaminants and impurities, the fuel or lubricant can be sold
without further processing. Smaller molecules such as isobutane and propylene or butylenes can
be recombined to meet specific octane requirements by processes such as alkylation, or less
commonly, dimerization. Octane grade of gasoline can also be improved by catalytic reforming,
which involves removing hydrogen from hydrocarbons producing compounds with higher octane
ratings such as aromatics. Intermediate products such as gasoils can even be reprocessed to break
a heavy, long-chained oil into a lighter short-chained one, by various forms of cracking such as
fluid catalytic cracking, thermal cracking, and hydrocracking. The final step in gasoline
production is the blending of fuels with different octane ratings, vapor pressures, and other
properties to meet product specifications.

Oil refineries are large scale plants, processing about a hundred thousand to several hundred
thousand barrels of crude oil a day. Because of the high capacity, many of the units operate
continuously, as opposed to processing in batches, at steady state or nearly steady state for
months to years. The high capacity also makes process optimization and advanced process
control very desirable.

Major products

Petroleum products are usually grouped into three categories: light distillates (LPG, gasoline,
naphtha), middle distillates (kerosene, diesel), heavy distillates and residuum (heavy fuel oil,
lubricating oils, wax, asphalt). This classification is based on the way crude oil is distilled and
separated into fractions (called distillates and residuum) as in the above drawing.[2]

      Liquified petroleum gas (LPG)
      Gasoline (also known as petrol)
      Naphtha
      Kerosene and related jet aircraft fuels
      Diesel fuel
      Fuel oils
      Lubricating oils
      Paraffin wax
      Asphalt and tar
      Petroleum coke
Common process units found in a refinery

      Desalted unit washes out salt from the crude oil before it enters the atmospheric distillation
      Atmospheric distillation unit distills crude oil into fractions. See Continuous distillation.
      Vacuum distillation unit further distills residual bottoms after atmospheric distillation.
      Naphtha hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric distillation.
       Must hydrotreat the naphtha before sending to a Catalytic Reformer unit.
      Catalytic reformer unit is used to convert the naphtha-boiling range molecules into higher
       octane reformate (reformer product). The reformate has higher content of aromatics and cyclic
       hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst
       reaction. The hydrogen is used either in the hydrotreaters or the hydrocracker.
      Distillate hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric distillation.
      Fluid catalytic cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products.
      Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more valuable
      Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter, more
       valuable reduced viscosity products.
      Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulfides.
      Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual oils into
       gasoline and diesel fuel, leaving petroleum coke as a residual product.
      Alkylation unit produces high-octane component for gasoline blending.
      Dimerization unit converts olefins into higher-octane gasoline blending components. For
       example, butenes can be dimerized into isooctane which may subsequently be hydrogenated to
       form isooctane. There are also other uses for dimerization.
      Isomerization unit converts linear molecules to higher-octane branched molecules for blending
       into gasoline or feed to alkylation units.
      Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker.
      Liquified gas storage units store propane and similar gaseous fuels at pressure sufficient to
       maintain them in liquid form. These are usually spherical vessels or bullets (horizontal vessels
       with rounded ends.
      Storage tanks store crude oil and finished products, usually cylindrical, with some sort of vapor
       emission control and surrounded by an earthen berm to contain spills.
      Slug catcher used when product (crude oil and gas) that comes from a pipeline with two-phase
       flow, has to be buffered at the entry of the units.
      Amine gas treater, Claus unit, and tail gas treatment convert hydrogen sulfide from
       hydrodesulfurization into elemental sulfur.
      Utility units such as cooling towers circulate cooling water, boiler plants generates steam, and
       instrument air systems include pneumatically operated control valves and an electrical
      Wastewater collection and treating systems consist of API separators, dissolved air flotation
       (DAF) units and further treatment units such as an activated sludge biotreater to make water
       suitable for reuse or for disposal.[3]
      Solvent refining units use solvent such as cresol or furfural to remove unwanted, mainly
       asphaltenic materials from lubricating oil stock or diesel stock.
      Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum
       distillation products.
Flow diagram of typical refinery
Production of gasoline and diesel:

Gasoline or petrol is a petroleum-derived liquid mixture which is primarily used as a fuel in
internal combustion engines. It is also used as a solvent, mainly known for its ability to dilute

It consists mostly of aliphatic hydrocarbons obtained by the fractional distillation of petroleum,
enhanced with iso-octane or the aromatic hydrocarbons toluene and benzene to increase its
octane rating. Small quantities of various additives are common, for purposes such as tuning
engine performance or reducing harmful exhaust emissions. Some mixtures also contain
significant quantities of ethanol as a partial alternative fuel.

Gasoline is produced in oil refineries. Material that is separated from crude oil via distillation,
called virgin or straight-run gasoline, does not meet the required specifications for modern
engines (in particular octane rating; see below), but will form part of the blend.

The bulk of a typical gasoline consists of hydrocarbons with between 4 and 12 carbon atoms per
molecule(Commonly referred to as C4-C12).

Many of the hydrocarbons are considered hazardous substances and are regulated in the United
States by the Occupational Safety and Health Administration. The material safety data sheet for
unleaded gasoline shows at least fifteen hazardous chemicals occurring in various amounts,
including benzene (up to 5% by volume), toluene (up to 35% by volume), naphthalene (up to 1%
by volume), trimethylbenzene (up to 7% by volume), Methyl tert-butyl ether (MTBE) (up to
18% by volume, in some states) and about ten others.[6]

The various refinery streams blended together to make gasoline all have different characteristics.
Some important streams are:

      Reformate, produced in a catalytic reformer with a high octane rating and high aromatic
       content, and very low olefins (alkenes).
      Cat cracked gasoline or cat cracked naphtha, produced from a catalytic cracker, with a
       moderate octane rating, high olefins (alkene) content, and moderate aromatics level.
      Hydrocrackate (heavy, mid, and light) produced from a hydrocracker, with medium to low
       octane rating and moderate aromatic levels.
      virgin or straight-run naphtha, directly from crude oil with low octane rating, low aromatics
       (depending on the grade of crude oil), some naphthenes (cycloalkanes) and no olefins (alkenes).
      alkylate, produced in an alkylation unit, with a high octane rating and which is pure paraffin
       (alkane), mainly branched chains.
      isomerate (various names), which is obtained by isomerizing the pentane and hexane in light
       virgin naphthas to yield their higher octane isomers.

The terms above are the jargons used in the oil industry. The exact terminology for these streams
varies by refinery and by country.
Overall, a typical gasoline is predominantly a mixture of paraffins (alkanes), naphthenes
(cycloalkanes), and olefins (alkenes). The actual ratio depend on:

      the oil refinery that makes the gasoline, as not all refineries have the same set of processing
      crude oil feed used by the refinery;
      the grade of gasoline, in particular, the octane rating.

Currently, many countries set limits on gasoline aromatics in general, benzene in particular, and
olefin (alkene) content. Such regulations led to increasing preference for high octane pure
paraffin (alkane) components, such as alkylate, and is forcing refineries to add processing units
to reduce benzene content.

Gasoline can also contain other organic compounds such as organic ethers (deliberately added),
plus small levels of contaminants, in particular sulfur compounds such as disulfides and
thiophenes. Some contaminants, in particular thiols and hydrogen sulfide, must be removed
because they cause corrosion in engines. Sulfur compounds are usually removed by
hydrotreating, yielding hydrogen sulfide, which can then be transformed into elemental sulfur via
the Claus process.

Petroleum is used mostly, by volume, for producing fuel oil and gasoline (petrol), both important
"primary energy" sources.[9] 84% by volume of the hydrocarbons present in petroleum is
converted into energy-rich fuels (petroleum-based fuels), including gasoline, diesel, jet, heating,
and other fuel oils, and liquefied petroleum gas. The lighter grades of crude oil produce the best
yields of these products, but as the world's reserves of light and medium oil are depleted, oil
refineries increasingly have to process heavy oil and bitumen, and use more complex and
expensive methods to produce the products required. Because heavier crude oils have too much
carbon and not enough hydrogen, these processes generally involve removing carbon from or
adding hydrogen to the molecules, and using fluid catalytic cracking to convert the longer, more
complex molecules in the oil to the shorter, simpler ones in the fuels.

Synthetic diesel can be produced from any carbonaceous material. This include biomass, biogas,
natural gas, coal and many others. The raw material is gasified into synthesis gas which after
purification is converted by the Fischer-Tropsch process to a synthetic diesel.

The process is typically referred to as biomass-to-liquid (BTL), gas-to-liquid (GTL) or Coal-to-
liquid (CTL) depending on the raw material used.

Paraffinic synthetic diesel generally have a near zero content of sulfur and very low aromatics
content, reducing unregulated emissions of toxic hydrocarbons, emissions of nitrous oxides and
emissions of PM.
Production of hydrogen:
Hydrogen fuel does not occur naturally on Earth and thus is not an energy source, but is an
energy carrier. Currently it is most frequently made from methane or other fossil fuels. However,
it can be produced from a wide range of sources (such as wind, solar, or nuclear) that are
intermittent, too diffuse or too cumbersome to directly propel vehicles. Integrated wind-to-
hydrogen plants, using electrolysis of water, are exploring technologies to deliver costs low
enough, and quantities great enough, to compete with traditional energy sources.[1]

Many companies are working to develop technologies that might efficiently exploit the potential
of hydrogen energy for mobile uses. The attraction of using hydrogen as an energy currency is
that, if hydrogen is prepared without using fossil fuel inputs, vehicle propulsion would not
contribute to carbon dioxide emissions. The drawbacks of hydrogen use are low energy content
per unit volume, high tankage weights, the storage, transportation and filling of gaseous or liquid
hydrogen in vehicles, the large investment in infrastructure that would be required to fuel
vehicles, and the inefficiency of production processes.

The molecular hydrogen needed as an on-board fuel for hydrogen vehicles can be obtained
through many thermochemical methods utilizing natural gas, coal (by a process known as coal
gasification), liquefied petroleum gas, biomass (biomass gasification), by a process called
thermolysis, or as a microbial waste product called biohydrogen or Biological hydrogen
production. 95% of hydrogen is produced using natural gas,[47] and 85% of hydrogen produced is
used to remove sulfur from gasoline. Hydrogen can also be produced from water by electrolysis
or by chemical reduction using chemical hydrides or aluminum.[48] Current technologies for
manufacturing hydrogen use energy in various forms, totaling between 25 and 50 percent of the
higher heating value of the hydrogen fuel, used to produce, compress or liquefy, and transmit the
hydrogen by pipeline or truck.

at present not economically competitive with steam reforming of natural gas (CH4).

On a large, industrial scale, steam reforming of natural gas (SMR—steam methane reforming)
water vapor reacts with methane to yield carbon monoxide and H2 at high temperatures (700 –
1000 °C),

       CH4 + H2O → CO + 3 H2.

This process takes place under 3-25 bar pressure (1 bar = 100 kPa = 0.987 atm) in the presence
of a nickel oxide catalyst. SMR is endothermic—that is, heat must be supplied to the process for
the reaction to proceed. The product mixture is known as synthesis gas ("syngas") because it is
often used directly for the production of methanol and related compounds. Hydrocarbons other
than methane can be used to produce synthesis gas

       CxHy + x H2O → x CO + (x + 0.5y) H2,

but steam reforming of heavier hydrocarbons has the problem that it gives pure carbon (coke) as
a contaminating byproduct. The steam reforming of methane is by far the largest source of
hydrogen gas today.

With the use of an iron oxide catalyst it is possible to generate hydrogen by the water-gas shift
reaction, which is slightly exothermic,

       CO + H2O → CO2 + H2

and removes the carbon monoxide from the gas mixture. The carbon dioxide can be frozen out
from the product mixture or can be washed out by a solution of KCO3 in water.
Production of electricity:
Elecricity is mainly poduced by burning fuel,coal,nalural gas, nuclear energy,hydro electric
conventional and other renewable sources.

Calculation of CO2 emissions
Fuel type                                      Kg of CO2 per unit of consumption
Grid electricity                               43 per kWh
Natural gas                                    3142 per tonne
Diesel fuel                                    2.68 per litre
Petrol                                         2.31 per litre
Coal                                           2419 per tonne
LPG                                            1.51 per litre

Transport conversion table
Vehicle type                                   Kg CO2 per litre
Small petrol car 1.4 litre engine              0.17/km
Medium car (1.4 – 2.1 litres)                  0.22/km
Large car                                      0.27/km
Average petrol car                             0.20/km
Small diesel car (>2 litres)                   0.12/km
Large car                                      0.14/km
Average diesel car                             0.12/km
Articulated lorry, diesel engine               2.68/km (0.35litres fuel per km)
Rail                                           0.06 per person per km
Air, short haul ( 500km)                       0.18 per person per km
Air, long haul                                 0.11
Shipping                                       0.01 per tonne per km

It makes sense to perform this calculation on oil that is of average quality (i.e. not some kind of
heavy sulphuric sludge or tar-sand) to make it more generally useful. we know that the average
barrel (~159 litres) of crude oil to pass through U.S. refineries in 1995* yielded the following

1. Gasoline: 44.1% (70.12 litres)
2. Distillate fuel oil: 20.8% (33.07 litres)
3. Kerosene-type jet fuel: 9.3% (14.79 litres)
4. Residual fuel oil: 5.2% (8.27 litres)**

Percentage values from Riegel’s Handbook of Industrial Chemistry, 2003 edition (Page 515, Fig. 15.6).
Litre values based upon conversion rate of 159 litres per barrel.
All of the other products*** of refined crude have sufficient alternative uses to make it possible
(even if not entirely probable) that they will not end up as atmospheric CO2. Of the four grades
of fuel listed above, however, it’s fair to say all of it is destined to be burnt. It’s worth noting,
therefore, that our final result will represent a minimum CO2 per barrel.

Now, the litre values are no good to us by themselves. Each of the fuels has a different specific
gravity (a different weight per litre), and it’s the weight of carbon we’re looking for, not the
volume. Once we’ve multiplied the volume of each fuel by the relevant specific gravity we’ll
have a rough “kilogram per barrel” number for each fuel. So:

1. Gasoline: 70.12 litres x 0.74 = 51.89kg
2. Distillate fuel oil: 33.07 litres x 0.88 = 29.10kg
3. Kerosene-type jet fuel: 14.79 litres x 0.82 = 12.13kg
4. Residual fuel oil: 8.27 litres x 0.92 = 7.61kg****

Overall, this suggests that the average barrel of crude refined in the United States in 1995 yielded
a shade over 100kg of liquid fuels (that’s an uncannily round number… 100.73kg to be exact).
Now, we know that a carbon-based fuel will emit 3.15 times its own weight in CO2 when burnt.

When fuel oil is burned, it is converted to carbon dioxide and water vapour. Combustion of one
kilogram of fuel oil yields 3.15 kilograms of carbon dioxide gas. Carbon dioxide emissions are
therefore 3.15 times the mass of fuel burned.

This may seem anti-intuitive at first glance, but it’s a result of each atom of carbon reacting with
two atoms of oxygen to produce CO2. The “extra” weight is being drawn from the air (hence
why a fuel fire will die out if deprived of oxygen).

Using the 3.15 multiplier, we see that the combined liquid fuels from an average barrel of
crude oil will produce a minimum of 317kg of CO2 when consumed.

From the above discussion it is clear that the carbon footprint in each case follows the following order

electricity > diesel > hydrogen.

Process involved:                                                                   carbon footprint:

Crude oil > Distillation > Hydro-processing > Diesel                        2.68 kg of CO2 per lt

Crude oil > Distillation > Naphtha > Steam reforming > Hydrogen             3.9 kg of CO2 per kg

Crude oil > Distillation > Fuel Oil > Power generation unit >               5.1 kg of CO2 per kwh
Taking the efficiencies of each fuel in to consideration:
Fuel consumption of a car to run 100 km is as follows:
Diesel: 3 lt
Hydrogen: 1 kg
Electricity: 12KWh

Now relating the above two aspects finally we get the following results:

Diesel: 3 x 2.68 =8.04kg of carbon footprint

Hydrogen: 1 x 3.9 = 3.9 kg of carbon footprint

Electricity: 5.1 x 12 =61.2 kg of carbon footprint

Thus we can draw the conclusion that hydrogen is the best fuel for use which has lower carbon
foot print value.


y.chalapathi kumar,

jntu college of engineering ananthapur.

Shared By: