GASEOUS FUELS

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Gaseous fuels in common use are:• Liquefied petroleum gases• Natural gas• Producer gas• Blast furnace gas• Coke oven gas

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LPG

• LPG may be defined as those hydrocarbons, which are gaseous at normal atmospheric pressure, but may be condensed to the liquid state at normal temperature, by the application of moderate pressures.

• LPG includes:• Propane (C3H8)• Propylene (C3H6)• Normal & Iso-Butane (C4H10)• Butylene (C4H8)

• Although they are normally used as gases, they are stored and transported as liquids under pressure for convenience and ease of handling

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LPG - HAZARDS & PRECAUTIONS

• LPG vapor is denser than air, consequently, the vapor may flow along the ground and into drains sinking to the lowest level of the surroundings and be ignited at a considerable distance from the source of leakage. • Escape of even small quantities of the liquefied gas can give rise to large

volumes of vapor / air mixture and thus cause considerable hazard.

• To aid in the detection of atmospheric leaks, all LPG’s are required to be odorized.

• There should be adequate ground level ventilation where LPG is stored. • LPG cylinders should not be stored in cellars or basements, which have no

ventilation at ground level.

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NATURAL GAS

• Natural gas comprises of: • Methane (major constituent)• Ethane• Propane• Butane• Pentane• Nitrogen• Carbon Dioxide• Traces of other gases and sulphur compounds

• Natural gas is a high calorific value fuel• It mixes with air readily and does not produce smoke or soot• It is lighter than air and disperses into air easily in case of leak

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SYNTHESIS GAS

• Syngas, or synthesis gas, is a fuel gas mixture consisting primarily of Water gas (a mixture of carbon monoxide and hydrogen) and very often some carbon dioxide.

• Production methods include:• Steam reforming of natural gas or liquid hydrocarbons to produce

hydrogen• The gasification of coal or biomass• Waste-to-energy gasification facilities

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SYNGAS PRODUCTION

• When used as an intermediate in the large-scale, industrial synthesis of hydrogen, it is produced from natural gas (via the steam reforming reaction) as follows:

• In order to produce more hydrogen from this mixture, more steam is added and the water gas shift reaction is carried out:

• The hydrogen must be separated from the CO2 to be able to use it. This is primarily done by pressure swing adsorption (PSA), amine scrubbing, and membrane reactors.

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PRODUCER GAS

• Producer gas, also called suction gas, specifically means a fuel gas made from coke, anthracite or other carbonaceous material.

• Air is passed over the red-hot carbonaceous fuel and carbon monoxide is produced.

• The ideal reaction proceeds as follows:

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PRODUCER GAS CONSTITUENTS

• Under ideal conditions:• Carbon Monoxide (34.7%)• Nitrogen (65.3%)

• Under normal conditions:• Carbon Dioxide (5-15%)• Carbon Monoxide (15-30%)• Methane (2-4%)• Hydrogen (10-20%)• Water (6-8%)• Nitrogen (45-60%)

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BLAST FURNACE GAS

• Blast furnace gas (BFG) is a by-product of blast furnaces that is generated when the iron ore is reduced with coke to metallic iron.

• It consists of:• Nitrogen (~60%)• Carbon dioxide (18-20%) • Oxygen• Carbon monoxide

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COKE OVEN GAS

• Coke gas is created by high-temperature dry distillation of coking coals in the absence of oxygen. • The gas mainly consists of hydrogen (50-60%), methane (15-

50%) and a small percentage of carbon monoxide, carbon and nitrogen.

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OVERVIEW OF NATURAL GAS INDUSTRY

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THE WORLD PICTURE OF NATURAL GAS

• Russia• Iran• Qatar• Saudi Arabia• United Arab Emirates• United States

• Nigeria• Algeria• Venezuela• Iraq

Six countries possess two thirds of the world’s gas reserves, with almost half of the reserves located in Iran and Russia

Major gas producing countries:

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BENEFITS OF NATURAL GAS OVER COAL AND OILS

• Carbon dioxide production is 30 to 40% less in case of natural gas as compared to oil and coal

• Nitrogen Oxides production is 20% less in case of natural gas as compared to oil and coal

• Particulate formation is significantly less in gas

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P R I M A RY S O U R C E S O F E N E R G Y I N T H E W O R L D I N 2 0 0 3 . T O TA L E N E R G Y U S E D WA S 4 0 5 Q U A D R I L L I O N B T U

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M A J O R P R O V E N N AT U R A L G A S R E S E RV E S B Y C O U N T RY. T O TA L P R O V E N R E S E RV E S E S T I M AT E D T O B E 6 , 0 4 0 T C F

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G A S P R O D U C T I O N ( T O P 5 C O U N T R I E S )

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SOURCES OF NATURAL GAS

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Conventional natural gas generally occurs in deep reservoirs, • Associated Gas• Associated gas is produced with the oil and separated at the

casing-head or wellhead • Gas produced in this fashion is also referred to as casing-

head gas, oil well gas, or dissolved gas.

• Non-associated gas• Non-associated gas occurs in reservoirs that contain little or

no crude oil• It is sometimes referred to as gas-well gas or dry gas.

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NATURAL GAS COMPOSITION

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TRADITIONAL NATURAL GAS

• Traditional natural gases, that is, associated and unassociated gas from wells, vary substantially in composition

• Water is almost always present at wellhead conditions

• Unless the gas has been dehydrated before it reaches the gas processing plant, the common practice is to assume the entering gas is saturated with water at the plant inlet conditions.

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IMPORTANT IMPURITIES

• Water• Most gas produced contains water, which must be removed. • Concentrations range from trace amounts to saturation.

• Sulfur species• If the hydrogen sulfide (H2S) concentration is greater than 2 to 3%,

carbonyl sulfide (COS), carbon disulfide (CS2), elemental sulfur, and mercaptans may be present.

• NORM. • Naturally occurring radioactive materials (NORM) may also present

problems in gas processing.

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• Mercury• Trace quantities of mercury may be present in some gases; levels reported

vary from 0.01 to 180 μg/Nm3. • Because mercury can damage the brazed aluminum heat exchangers used in

cryogenic applications, conservative design requires mercury removal to a level of 0.01 μg/Nm3

• Oxygen. • Some gas-gathering systems operate below atmospheric pressure. As a

result of leaking pipelines, open valves, and other system compromises, oxygen is an important impurity to monitor.

• A significant amount of corrosion in gas processing is related to oxygen ingress.

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NATURAL GAS - CLASSIFICATION

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Natural Gases commonly are classified:

• According to Liquid Content• Either lean or rich

• According to Sulfur Content• Either sweet or sour

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LIQUID CONTENT

• The more liquids, usually defined as C2+, in the gas, the “richer” the gas.• To quantify the liquids content of a natural gas mixture, the industry

uses GPM, or gallons of liquids recoverable per 1,000 standard cubic feet (Mscf) of gas.

• Determination of the GPM requires knowledge of the gas composition on a mole basis and the gallons of liquid per lb-mole.

• The rich and lean terms refer to the amount of recoverable hydrocarbons present. The terms are relative, but a lean gas will usually be 1 GPM, whereas a rich gas may contain 3 or more GPM

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SULFUR CONTENT

Sweet and sour refer to the sulfur (generally H2S) content. • A sweet gas contains negligible amounts of H2S• A sour gas has unacceptable quantities of H2S, which is both

odiferous and corrosive

• When present with water, H2S is corrosive. The corrosion products are iron sulfides, FeSX, a fine black powder.

• Sweet Gas < 4 ppmv of H2S• Allowable limit 4 – 16 ppmv of H2S

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PROCESSING AND PRINCIPAL PRODUCTS

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PROCESSING

• Purification. • Removal of materials, valuable or not, that inhibit the use of

the gas as an industrial or residential fuel• Separation. • Splitting out of components that have greater value as

petrochemical feedstocks, stand alone fuels (e.g., propane), or industrial gases (e.g., ethane, helium)

• Liquefaction. • Increase of the energy density of the gas for storage or

transportation

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G E N E R I C R AW G A S A N D P R O D U C T S L AT E

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SPECIFICATIONS OF PIPELINE QUALITY GAS

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MAJOR COMPONENTS AND VAPOR PRESSURES OF COMMON LIQUID PRODUCTS

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REFERENCES

• A. J. Kidney & W. R. Parrish, Fundamentals of Natural Gas Processing, CRC Press. 2006• Chapter no. 1, 2