Introduction

Dávid Havasi

• Assistant Professor

• Department of Chemical and Environmental Process Engineering

• havasi.david@mail.bme.hu

Recommended Literature:

• P. J. Chenier: Survey of industrial chemistry, VCH, N.Y. 1992.

• Ullmann’s Encyclopedia of Industrial Chemistry, Wiley, 2000.

• http://kkft.bme.hu/en/education/subjects/chemtech

Content:

• Introduction

• Basic equipments

• Natural gas, crude oil and coal

2018_19_2 semester

2 tests and a presentation:

• 1st test: 2019.03.04. time and place of lectures

(re-take of 1st test: next week, place and time later discussed)

• 2nd test: 2019.04.15. time and place of lectures

(re-take of 2nd test: next week, place and time of lectures)

• Last repeat (re-re-take) of one test

Group presentation:

• Small group of students will present a chemical technology

• Topics will be given in the first 3 weeks

• Dates for presentations:• 2019.04.29. and 2019.05.06.

• PPT-presentation and a small essay is required from each group

• Every group member has to speek for equal time

IntroductionChemistry is everywhere:

• Houses, cars, clothes, food, medicine, etc.

Nearly everything around us is related to chemical technologies.

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Definition of chemical technologies

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The chemical technology comprises all knowledge which enables theindustrial utilisation of chemical reactions.Chemical technologies are working in the chemical industry andoutside of it: energy production, metallurgy, building materials, foodindustry, transportation, water technologies, corrosion control.

The most important divisions of industry where chemicaltechnologies are working:• Paper and packing• Chemicals (fertilizers, plant protection, pharmaceuticals,

detergents, cosmetics, paints, dyestuffs)• Hydrocarbons, coal industry• Polymer and rubber• Silicates, building materials

Classification of chemicals

• Inorganic compounds (NaOH, Cl2, sulfuric acid)

• Monomers (ethylene, vinylchloride)

• Pharmaceuticals (acetyl salicylic acid, penicilline)

• Household chemicals (soap, detergent)

• Dyestuffs (indigo)

• Organic chemicals (methanol, acetic acid)

• Agrochemicals (fertilizers, herbicides, pesticides, fungicides)

• Miscellaneous (expolsives)

Coal, oil and natural gas (NG) are the primary raw materials for production of most bulk chemicals.

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Structure of the chemical industry

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Relative valueCrude oil 1Fuel 2Typical petrochemical 10Typical consumer product 50

Each stageadds value!

• Know-how: practical knowledge of how to accomplish/manufacture/dosomething.

• High tech: the most advanced available technology.Low technology: traditional or mechanical technology.

The 4 basic infrastructure required by the chemical industry:

• Water (drink, technolgical)

– Heat exchanging fluid (cooler, steam, etc.)

– Reagent

– Solvent

• Air (natural, technical and compressed)

– Heat exchanger

– Reagent (e. g. combustion)

• Energy (electric, steam, fuel)

• IT

– Design, process control

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Equipments in the chemical industry

• Operative units:– Alactors: Units performing physical conversions (mills, dryers, coolers,

drills, etc.)

– Reactors: Units performing chemical conversions (reactors, blast furnaces, boilers, etc.)

• Batch

• Continuous

• Logistical units:– Transporters: material and energy transporters (pipelines, vehicles,

conveyors, compressors, ventilators, pumps, etc.)

– Storages: Storing raw materials, products, etc. (tanks, warehouses, heaps, etc.)

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Crushers and grinders

• Mechanical process for reducing size

• A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust.

• A grinder is a machine for producing fine particle size reduction through attrition and compressive forces at the grain size level.

• Utilizing pressure and impact for breaking

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Gyratory and cone crushers

• Cone shaped crushing surface

• Eccentric movement

Jaw crusher

• Compressive force (pressure) for breaking

• Swing jaw moves quite small

• Heavy duty machines

• Soft to very hard materials

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Impact crusher

• Use of impact for crushing: Impact on the innersurface of the chamber

• Possible vertical and horizontal designs

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Ball mill

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• Used for grinding, both wet and dry

• Possible use in reactions

• Impact and attrition

• Hollow rotating shell with steel/ceramic/rubberballs

Cyclone/Hydrocyclone

• Remove dust/small particles from a fluid

• Exhaust gas purification

• Solid/liquid separation

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Centrifuge

• Uses rotation for separation. (e. g. decanter centrifuge, disc centrifuge)

• Denser substances move to outward in radial direction, while less dense particles move to the center.

• E. g. separation of liquid from solid materials

• Isotope separation: uranium enrichment with gascentrifuges

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Heat exchangers

• Direct: direct contact of phases

• Cooling tower: hot water cooled by air, then collected at the bottom

• Phases can mix through heat exchange, e. g. condensate steam with waterdroplets

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Indirect exchangers

• Phases are separated, no mixing

• Paralell-flow, counter-flow and cross-flow

• Different desings:

– Shell/tube

– Plate

– Extended surface

– regenerative

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Absorber

• Absorption: when particles (atoms, molecules, ions) enter a bulk phase. Molecules are taken up by the volume.

• Physical and chemical absorption: depending on whether chemical reactions between the media and the absorbed particles occur.

• Gas scrubbers

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Adsorption

• Unlike absorption, particles interact with the surface of the adsorber. It is the adhesion of atoms, molecules, ions to a surface.

• Adsorption is a consequence of surface energy.

• Adsorbers have small pore diamaters – higher exposed surface

• Gas cleaning, removal of volatile organic content (gas-mask)

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Dryers

• Dryers use heat and hot air for removing liquid content (mainly water orsolvents)

• Rotary drum dryers: material is moving in rotating tube

• Conveyor dryer: moving by belt

• Rolling bed dryers

• Fluid bed dryer19

Evaporators and distillation units

• Evaporation: liquid content is removed by heating, concentrating solutions, preparing thermally sensitivematerials

• Distillation: separation of liquid mixtures by heating.

• Distillation units can have different trays, packings

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Tank reactor

• Batch reactor or continuous stirred-tank reactor

• Heat exchange via duplicated wall orspiral pipes

• Intense mixing21

Equipements for tank reactors

• Stirrers, baffles, heat exchangers (single external jacket, coil jacket, internal coils)

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Tubular reactors

• Continuous flow through filledtubes or

• Loop reactors

• Heating/cooling through walls

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Fixed bed and fluid bed reactors

• Fixed bed: catalyst on support interacts with reactants flowing through. Products and unreacted materials exit. (Tubular and column types)

• Fluidization: granular material is converted to fluid state by upward flow (gas/liquid)

• Fluid bed: reactant flow keeps particles in fluid state – high surface forinteraction. 24

Scale-up

• Laboratory scale: proving thatreactions can be performed toachieve the product. Parametersand catalyst can be tested. Alternative routes can be compared.

• Pilot plant: demonstration thatreaction can be performed atgreater volumes, withoutinvesting in full function plants. Full function plants cannot be designed based on laboratoryexperiments.

• Demonstration plant: is used tovalidate the industrial processfor commercialization.

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Issues of scaling up:

• Heat exchange

• Pressure control

• Effective mixing

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Le Chatelier - Braun

• Possible disturbances in a chemical reaction:

– Concentration

– Pressure

– Temperature

– Volume

– Adding inert gas

– Adding catalyst

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If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change.Generally: Any change in status quo prompts an opposing reaction in the responding system.

“ “ Z…………………

“ “ Y…………………..

Add more X…………………..

X(g) + 3 Y(g) 2 Z(g) + heat

Le Chatelier’s principle:

Disturbance Equilibrium Shift

no shift

1 mole of X reacts with 3 moles of Y and produces 2 moles of Z. The forwardreaction is exothermic while the reverse reaction is endothermic

Add a catalyst…………………

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Raising the temperature……favors the endothermic reaction (the reverse

reaction) in which the rise in temperature is

counteracted by the absorption of heat.

Increasing the pressure……favors the forward reaction in which 4 mol

of gas molecules is converted to 2 mol.

Decreasing the concentration

of Z…

…favors the forward reaction in order to

replace the Z that has been removed.

Catalyst

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Catalyst diminishes the activationenergy, accelaerates the reactionrate.

• Homogeneous

• Heterogeneous

• Enzymatic

In physisorption the bond is a van der Waalsinteraction. adsorption energy is typically 5-10 kJ/mol(much weaker than a typical chemical bond). Manylayers of adsorbed molecules may be formed.

For chemisorption the adsorption energy iscomparable to the energy of a chemical bond. Themolecule may chemisorp intact (left) or it maydissociate (right). The chemisorption energy is 30-70kJ/mol for molecules and 100-400 kJ/mol for atoms.

Heterogeneous/homogeneous

Heterogeneous: Active sites on the surface capable for bonding

• Silver forms too strong bonds – reactants cannot adsorb on surface

• Tungsten adsorbs too strongly – product cannot desorb from surface

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Homogeneous: Catalyst is present in the same phase as the reactants

• Separation is harder from the final product

Autocatalysis: the reaction is catalysed by one if its products

Fossil fuels

• Coal

• Crude oil

• Natural gas

• Formed by natural processes such as anaerobic decomposition of buried dead organisms.

• Contains high percentage of carbon.

• Used for energy and chemical production.

• Combustion results high carbon-dioxide emission.

• Long reproduction time, resources are depleting.

https://sites.google.com/site/drnemessandor/home/kemiai-technologia

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Natural gas

• Natural gas is a naturally occurring, combustible mixture of hydrocarbongases. While natural gas is formed primarily of methane (CH4), it can alsoinclude ethane (C2H6), propane (C3H8), butane (C4H10) and pentanes (C5H12);and hydrogen sulfide (H2S), carbon dioxide (CO2), water vapor (H2O), andsometimes helium (He) and nitrogen (N2).

• Natural gas is an energy source often used for heating, cooking, andelectricity generation. It is also used as fuel for vehicles and as a chemicalfeedstock in the manufacture of plastics and other commercially importantorganic chemicals.

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Typical composition of natural gas

Methane CH4 70-90%

Ethane C2H6

0-20%Propane C3H8

Butane C4H10

Carbon Dioxide CO2 0-8%

Oxygen O2 0-0.2%

Nitrogen N2 0-5%

Hydrogen Sulphide H2S 0-5%

Rare gases Ar, He, Ne, Xe trace

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Sources of natural gas

• Raw natural gas comes primarily from one of three types of wells: crudeoil wells, gas wells, and condensate wells.

• Gas wells typically produce only raw natural gas, while condensate wellsproduce raw natural gas along with other low molecular weighthydrocarbons. Those that are liquid at ambient conditions (i.e., pentaneand heavier) are called natural gas condensate.

• The natural gas that comes from crude oil wells is typically termedassociated gas. This gas can have existed as a gas cap above the crude oilin the underground formation, or could have been dissolved in the crudeoil.

• Natural gas is termed sweet gas when relatively free of hydrogen sulfide;however, gas that does contain hydrogen sulfide is called sour gas. Naturalgas, or any other gas mixture, containing significant quantities of hydrogensulfide, carbon dioxide, or similar acidic gases is termed acid (sour) gas

• Raw natural gas can also come from methane deposits in the pores of coalseams, and especially in a more concentrated state of adsorption onto thesurface of the coal itself. Such gas is referred to as coalbed gas or coalbedmethane.

35https://www.youtube.com/watch?v=SfazJ6P_g7w&index=4&list=PL0gBJKv_mskxAz1I9BTa40aaotBq_CdNs

Natural gas terminology

• CNG: compressed natural gas, CNG is made by compressing natural gas, toless than 1% of its volume at standard atmospheric pressure.

• Condensates: general term for a group of liquid phase hydrocarbons inwhich light components dominate, and which are extracted at the surfaceby natural gas separation.

• LNG: liquefied natural gas.

• LPG liquid petroleum gas, or liquefied petroleum gas, or liquified propanegas. These days the motoric usage of LPG spreads. This fuel is the„autogas”.

• SNG synthetic natural gas, also referred to as substitute natural gas, is amanufactured form of natural gas. It is created through converting orreforming carbonaceous feedstocks (coal, biomass) and can be used inalmost every way that natural gas can be used.

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Natural gas processing

• Whatever the source of the natural gas, once separated from crude oil (if present) it commonly exists in mixtures with other hydrocarbons (other than methane); principally ethane, propane, butane, and pentanes, and heavier components. In addition, raw natural gas contains water vapor (H2O), hydrogen sulfide (H2S), carbon dioxide (CO2), helium (He), nitrogen (N2), and other compounds.

• Natural gas processing consists of separating all of the various hydrocarbons and fluids from the pure natural gas, to produce what is known as pipeline quality dry natural gas.

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• The processing of natural gas involves four main processes: 1. Oil Removal2. Water Removal3. Separation of Natural Gas Liquids 4. Hydrogen Sulfide and Carbon Dioxide Removal

Oil removal

• In order to process and transport associated dissolved natural gas, it mustbe separated from the oil in which it is dissolved.

• The most basic type of separator is known as a conventional separator. Itconsists of a simple closed tank, where the force of gravity serves toseparate the heavier liquids like oil, and the lighter gases, like natural gas.

• In certain instances, however, specialized equipment is necessary toseparate oil and natural gas. An example of this type of equipment is theLow-Temperature Separator (LTX). This is most often used for wellsproducing high pressure gas along with light crude oil or condensate.

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Water removal

• In addition to separating oil from the wet gas stream, it is necessary to remove most of the associated water. This treatment consists of dehydrating the natural gas, which usually involves one of two processes: either absorption, or adsorption.

• Absorption occurs when the water vapor is taken out by a dehydrating agent.

• Adsorption occurs when the water vapor is condensed and collected on the surface.

• An example of absorption dehydration is known as Glycol Dehydration. In this process, a liquid desiccant dehydrator serves to absorb water vapor from the gas stream. Glycol, the principal agent in this process, has a chemical affinity for water.

• Solid-desiccant dehydration is the primary form of dehydrating natural gas using adsorption, and usually consists of two or more adsorption towers, which are filled with a solid desiccant. Typical desiccants include activated alumina or a granular silica gel material.

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Natural gas liquids

• In most instances, natural gas liquids (NGLs) have a higher value as separate products, and it is thus economical to remove them from the gas stream.

• There are two basic steps to the treatment of natural gas liquids in the natural gas stream.

1. The liquids must be extracted from the natural gas.

2. These natural gas liquids must be separated themselves, down to their base components.

• In NGL absorption, absorbing oil is used. This absorbing oil has an affinity for NGLs.

• As the natural gas is passed through an absorption tower, it is brought into contact with the absorption oil which soaks up a high proportion of the NGLs. The absorption oil exits the absorption tower through the bottom. The rich oil is fed into lean oil stills, where the mixture is heated to a temperature above the boiling point of the NGLs, but below that of the oil.

• In the refrigerated oil absorption method (=cooled lean oil absorptionmethod), propane recovery can be upwards of 90 percent, and around 40percent of ethane can be extracted from the natural gas stream. Extractionof the other, heavier NGLs can be close to 100 percent using this process.

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Hydrogen sulfide and Carbon Dioxide Removal

• The process for removing hydrogen sulfide from sour gas is commonlyreferred to as sweetening the gas.

• Amine solutions are used to remove the hydrogen sulfide. This process isknown simply as the amine process.

• Amine solutions will absorb sulfur compounds from natural gas as itpasses through. The effluent gas is virtually free of sulfur compounds, andthus loses its sour gas status. The amine solutions used can beregenerated (that is, the absorbed sulfur is removed), allowing it to bereused to treat more sour gas.

H2S + (HO-C2H4)3N → (HO-C2H4)3NH+ HS-

H2S + (HO-C2H4)2NH → (HO-C2H4)2NH2+ HS-

H2S + (HO-C2H4)NH2 → (HO-C2H4)NH3+ HS-

• Sulfur can be recovered by the Claus process.

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Processing of natural gas

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Crude oil (Petroleum)

• A naturally occurring flammable liquid consisting of a complex mixture of hydrocarbons of various molecular weights and other liquid organic compounds.

• An oil well produces predominantly crude oil, with some natural gas dissolved in it. Because the pressure is lower at the surface than underground, some of the gas will come out of solution and be recovered (or burned) as associated gas.

• The proportion of hydrocarbons in the crude oil varies greatly among different oil fields, ranging from as much as 97 percent by weight in the lighter oils to as little as 50 percent in the heavier oils.

• The hydrocarbons in crude oil are mostly alkanes, cycloalkanes and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium.

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1.Carbon - 83 to 87%

2.Hydrogen - 10 to 14%

3.Nitrogen - 0.1 to 2%

4.Oxygen - 0.05 to 1.5%

5.Sulfur - 0.05 to 6.0%

6.Metals - < 0.1%

Oil wells

• After drilling, the higher pressure in the reservoirpumps the oil and natural gas out.

• Artificial lift: downhole pumps, gas lift or surfacepump jacks.

• Enhanced recovery: pumping gas (CO2) or water tothe reservoir.

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Physical and chemical processes

• The processing of crude oil involves :

– the purification of crude oil (desalting, desulfurization)

– the separation of components

– the chemical conversion of compononents to required products.

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Physical

Chemical

Thermal Catalytic

Distillation

Solvent extraction

Propane deasphalting

Solvent dewaxing

Blending

Visbreaking

Delayed coking

Flexicoking

Hydrotreating

Catalytic reforming

Catalytic cracking

Hydrocracking

Catalytic dewaxing

Alkylation

Polymerization

Isomerization

Corrosive components in crude oil

• Salts present in crude are mainly chlorides

• Water-content of crude appears in the overhead

• At higher temperatures Ca/Mg chlorides can form HCl and oxides

• HCl dissolves in the condensed water droplets in the overhead

• HCl can react with Fe to FeCl3 which can react with H2S to regenerate HCl

• Organic chlorides (phantom chlorides) can also decompose to HCl, but they cannot be washed by water

• Carbon-dioxide present in crude oil – efficient water removal required

• Lower fatty acids (e. g. formic-, acetic-, propionic- and butanoic acid) appear in overhead where they can contact with water, increasing corrosion potential – attacking Fe

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Desalting

• Ca/Mg/Na chlorides – dissolved or in crystalline form

• Removal by washwater

• Emulsion formation is reduced by emulsion breaking chemicals and electrostatic grids

• Salt content of the treated oil should be below 1 ppm

• Additionally NaOH or NH3 can be added to react with HCl – this resultsdeposits 48

Catalytic Hydrodesulfurization Process• Hydrotreating for sulfur removal is called hydrodesulfurization.

• In a typical catalytic hydrodesulfurization unit, the feedstock is deaerated andmixed with hydrogen, preheated in a fired heater (315°-425° C) and then chargedunder pressure (up to 70 bar) through a trickle-bed catalytic reactor.

• In the reactor, the sulfur and nitrogen compounds in the feedstock are convertedinto H2S and NH3.

• The reaction products leave the reactor and after cooling to a low temperatureenter a liquid/gas separator. The hydrogen-rich gas from the high-pressureseparation is recycled to combine with the feedstock, and the low-pressure gasstream rich in H2S is sent to a gas treating unit where H2S is removed.

• The clean gas is then suitable as fuel for the refinery furnaces. The liquid stream isthe product from hydrotreating and is normally sent to a stripping column forremoval of H2S and other undesirable components.

• Hydrodesulfurized products are blended or used as catalytic reforming feedstock.

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HDS Unit

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Distillation

• Pre-treated Crude is heated in an oven (~400 °C).

• Inserted in the bottom of the column.

• The temperature at the bottom is provided by a reboiler.

• The condenser at the top provide the reflux against the vapor streams on the trays.

• The two streams provide temperature and stream gradient along the stages.

• On the trays, different hydrocarbon compositions will be created.

• The heaviest fractions are further processed in a vacuum unit, where reduced pressure is applied.

• The residue of the second column is bitumen.

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Produts of crude distillation

Distillation units for crude oil

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Car engines

Gasoline engines (Otto-engine):

• Fuel mixed with air and compressed

• Ignition by electric spark

Diesel engines:

• Air compression

• Separate fuel injection

• Spontaneous ignition by compression

• Direct injection of fuel53https://www.youtube.com/watch?v=rlK7JIAz9WY

Two-stroke engine Wankel engine

Four-stroke engines:• Intake• Compression• Power• Exhaust

Turbocharger

• A centrifugal compressor powered by a turbine, that is driven by the engine's exhaust gases.

• The compressor increases the amount (mass) of air entering the engine –forced unduction –, thus elevating the performance

• Air is heated during compression – intercooler is required

• More cool air to the engine than by naturally aspirated engines – smaller, more efficient engines

• Turbochargers require efficient lubrication – heating, high speed.

• Turbocharged petrol engines require high pressure fuel injection

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• Unconverged hydrocarbons may remain in the exhaust gas stream

• Incomplete combustion results carbon-monoxide

• Air is composed of ~78% Nitrogen and ~21% Oxygen

• Great amount of nitrogen is injected to the engine

• The high temperature results nitrogen-oxide (NOx) formation

• The treatment of exhaust gases is required – catalytic converter

Catalytic converter

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Fuel quality indicatorsGasoline: Octane number (RON, MON)

Measure of the ignition quality of gas (gasoline or petrol). Higher this number,the less susceptible is the gas to 'knocking' (explosion caused by itspremature burning in the combustion chamber) when burnt in a standard(spark-ignition internal combustion) engine. Octane number denotes thepercentage (by volume) of iso-octane (a type of octane) in a combustiblemixture (containing iso-octane and normal-heptane) whose 'anti-knocking'characteristics match those of the gas being tested.

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Diesel: Cetane number (CN)Measure of the ignition quality of diesel fuel; higher this number, the easier it is tostart a standard (direct-injection) diesel engine. It denotes the percentage (byvolume) of cetane (chemical name Hexadecane) in a combustible mixture(containing cetane and 1-methylnapthalene) whose ignition characteristics matchthose of the diesel fuel being tested.

Fuel additives

• Oxygenates – to elevate octane number:– Alcohols (e. g. methanol, ethanol)

– Ethers (MTBE – methyl tert-butyl ether, TAME – tert amylmethyl ether)

• Antioxidants – to inhibit the oxidation in the fuel tank

• Antiknock agents – reduce engine knocking and elevate octane number:

– Tetraethyllead (banned in most countries)

– Toluene

• Lead scavengers – lead and lead-oxide tend toaccumulate in the engine – scavengers remove them

• Fuel dyes – achive consistent fuel color, deifferentiatefuels

• Nitro – nitromethane, nitrous oxide

• Buthyl rubber – detergent to prevent the fouling of injectors

• Biofuel components:– Ethanol

– Biodiesel

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Lubricants

• To minimize the friction, heat and wear between mechanical parts

• Mineral (from crude oil) and synthetic (polyalphaolefins)

Prodution of mineral lubricants:

• After the fractioning towers lube oils are filtered, to remove impurities.

• Aromatic-content can affect viscosity – removal by solvent extraction

• Aromatics dissolve in selective solvent.

Synthetics:

• Derived from crude oil or byproducts through chemical process (more consistent molecular size, more uniform properties)

• Polymer (poly-alpha-olefin)

• Esters

Solid lubricants: e.g. PTFE, graphite, boron nitride, alloys.

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Effects: https://www.youtube.com/watch?v=117yJz1f9ogEngine lubrication system: https://www.youtube.com/watch?v=mmmcj53TNic

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http://www.acpaegypt.com/lubricant-additives.html

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• Residuum from the atmosphericdistillation tower is heated (425-510 °C)at atmospheric pressure and mildlycracked in a heater.

• It is then quenched with cool gas oil tocontrol over-cracking, and flashed in adistillation tower.

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• Visbreaking is used to reduce the pour point of waxy residues and reduce theviscosity of residues used for blending with lighter fuel oils. Middle distillatesmay also be produced, depending on product demand.

• The thermally cracked residue tar, which accumulates in the bottom of thefractionation tower, is vacuum-flashed in a stripper and the distillate recycled.

• Alternatively, vacuum residue can be cracked. The severity of the visbreakingdepends upon temperature and reaction time (1-8 min).

• Usually < 10 wt% of gasoline and lighter products are produced.

Delayed Coking

• Coking is a severe method ofthermal cracking used to upgradeheavy residuals into lighterproducts or distillates.

• Coking produces straight-rungasoline (Coker naphtha) andvarious middle-distillate fractionsused as catalytic crackingfeedstock.

• The process completely reduceshydrogen so that the residue is aform of carbon called "coke."

• Three typical types of coke areobtained (sponge coke,honeycomb coke, and needle coke)depending upon the reactionmechanism, time, temperature,and the crude feedstock.

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Delayed Coking

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In delayed coking the heated charge (typically residuum from atmosphericdistillation towers) is transferred to large coke drums which provide the longresidence time needed to allow the cracking reactions to proceed to completion.

Catalytic Cracking• Main incentive for catalytic cracking is

the need to increase gasoline production.

• Feedstocks are typically vacuum gas oil.

• Cracking is catalyzed by solid acids whichpromote the rupture of C-C bonds. Thecrucial intermediates are carbocations(+ charged HC ions) formed by the actionof the acid sites on the catalyst.

• Besides C-C cleavage many otherreactions occur:

- isomerization- protonation and deprotonation- alkylation- polymerization- cyclization and condensation

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The formation of coke is an essential feature of the cracking process and this cokedeactivates the catalyst.Catalytic cracking is one of the largest applications of catalysts: worldwide crackingcapacity exceeds 500 million t/y.Catalytic cracking was the first large-scale application of fluidized beds which explainsthe name fluid catalytic cracking (FCC).

Fluid Catalytic Cracking (FCC)• Oil is cracked in the presence of a finely divided catalyst, which is maintained in an

aerated or fluidized state by the oil vapours.

• The fluid cracker consists of a catalyst section and a fractionating section that operatetogether as an integrated processing unit.

• The catalyst section contains the reactor and regenerator, which, with the standpipe andriser, form the catalyst circulation unit. The fluid catalyst is continuously circulatedbetween the reactor and the regenerator using air, oil vapors, and steam as the conveyingmedia.

• Preheated feed is mixed with hot, regenerated catalyst in the riser and combined with arecycle stream, vapourized, and raised to reactor temperature (485-540°C) by the hotcatalyst.

• As the mixture travels up the riser, the charge is cracked at 0.7-2 bar.

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• In modern FCC units, all cracking takes place in the riser and the "reactor" merely serves asa holding vessel for the cyclones. Cracked product is then charged to a fractionatingcolumn where it is separated into fractions, and some of the heavy oil is recycled to theriser.

• Spent catalyst is regenerated to get rid of coke that collects on the catalyst during theprocess.

• Spent catalyst flows through the catalyst stripper to the regenerator, where most of thecoke deposits burn off at the bottom where preheated air and spent catalyst are mixed.

• Fresh catalyst is added and worn-out catalyst removed to optimize the cracking process.

Chemical technology of coal

• Coal is a combustible black or brownish-black sedimentary rock. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure. Coal is composed primarily of carbon along with variable quantities of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.

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Types of coal

As geological processes apply pressure to dead biotic material over time, under suitableconditions it is transformed successively into:

• Peat, considered to be a precursor of coal, has industrial importance as a fuel in someregions. In its dehydrated form, peat is a highly effective absorbent for fuel and oil spillson land and water. It is also used as a conditioner for soil to make it more able to retainand slowly release water.

• Lignite, or brown coal, is the lowest rank of coal and used almost exclusively as fuel forelectric power generation.

• Sub-bituminous coal, whose properties range from those of lignite to those ofbituminous coal, is used primarily as fuel for steam-electric power generation and is animportant source of light aromatic hydrocarbons for the chemical synthesis industry.

• Bituminous coal is a dense sedimentary rock, usually black, but sometimes darkbrown, often with well-defined bands of bright and dull material; it is used primarily asfuel in steam-electric power generation, with substantial quantities used for heat andpower applications in manufacturing and to make coke.

• „Steam coal”; is a grade between bituminous coal and anthracite, once widely used asa fuel for steam locomotives.

• Anthracite, the highest rank of coal, is a harder, glossy black coal used primarily forresidential and commercial space heating.

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Carbon: The aromaticity increases from 40 –50% C in subbituminous coals to 70– 80% C in bituminous coals and is over 90% C in anthracites.

Hydrogen: Aromatic bonding to carbon and as aliphatic hydrogen in, e.g.,methylene (–CH2–) and methyl (–CH3) groups occurs.

Oxygen: Major functional groups are hydroxyl (– OH), carboxyl (– COOH),carbonyl (=C= O), etheric (–O–) and heterocyclic oxygen.

Sulfur: Bonding is predominantly as thiophenes, also in the thiolic form (R – SH),decreasing with higher rank coals; up to ca. 25 % S is present as aliphatic sulfides(R–S–R). Heterocyclic sulfur compounds are also known to exist.

Nitrogen: Very little information on organic nitrogen bonding is available. Itappears to occur in heterocycles.

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Contents of coal

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Surface mining

Coal is near to the surface.

• Strip mining: removing coal abovethe coal seam.

• Contour mining: The contour mining method consists of removing overburden from the seam in a pattern following the contours along a ridge or around the hillside.

• Mountaintop removal: practice involving removal of mountaintops to expose coal seams.

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Underground miningCoal seams are too deep underground for opencast mining.

• Longwall mining: continuous mining machine with movable roof supports (~300 m long).

• Shortwall mining: continuous mining machine with movable roof supports (40-60 m long).

• Room and pillar mining: cutting a network of 'rooms' into the coal seam and leaving behind 'pillars' of coal to support the roof of the mine.

• Continuous mining: room and pillar miningwith continuous miner machine.

• Retreat mining: the pillars that were left behind initially are removed, the roofcollases as retreating to the entrance.

• Blast mining: older practice, using explosion(dynamite) for breaking coal seam. 76

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Coking of coal

• Coke is a solid carbonaceous residue derived from low-ash, low-sulfurbituminous coal from which the volatile constituents are driven off bybaking in an oven without oxygen at temperatures as high as 1100°C, sothe fixed carbon and residual ash are fused together.

• C (as Coal) → coke + coal tar + coke-oven gas (H2, CO, CH4, CO2, N2) + H2O

• Metallurgical coke is used as a fuel and as a reducing agent in smeltingiron ore in a blast furnace. The result is pig iron, and is too rich in dissolvedcarbon, so it must be treated further to make steel.

• In the process of low-temperature coking, coal is coked at temperaturesbetween 360 and 750°C. These temperatures optimize the production ofcoal tars richer in lighter hydrocarbons than normal coal tar. The coal tar isthen further processed into fuels.

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Coke Flow Diagram

One Metric Ton of Coal Yields:

Blast Furnace Coke:

600 - 700 kg

Coke Breeze: 50 - 100 kg

Coke Oven70%

Solids

30% Gas + Liquid

Tar 35 - 50 L

Ammonium Sulphate 10 - 15 kg

Ammonia Liquor 60 - 145 L

Light Oil 10 - 15 L

Coke Oven Gas300 - 360 m3

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Gasification

• Coal gasification can be used to produce synthesis gas (syngas), a mixture of carbon monoxide (CO) and hydrogen (H2) gas. This syngas can then be converted into transportation fuels, such as gasoline and diesel, through the Fischer-Tropsch process. This technology is currently used by the Sasol chemical company of South Africa to make motor vehicle fuels from coal and natural gas. Alternatively, the hydrogen obtained from gasification can be used for various purposes, such as powering a hydrogen economy, making ammonia, or upgrading fossil fuels. Coal gasification:

• C (as Coal) + H2O → H2 + CO

• If hydrogen is the desired end-product, however, the syngas is fed into the water gas shift reaction, where more hydrogen is liberated.

• CO + H2O → CO2 + H2

• In the past, coal was converted to make coal gas (town gas), which was piped to customers to burn for illumination, heating, and cooking.

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Gasification Chemistry

Gasification with Oxygen

C + 1/2 O2 CO

Combustion with Oxygen

C + O2 CO2

Gasification with Carbon Dioxide

C + CO2 2CO

Gasification with Steam

C + H2O CO + H2

Gasification with Hydrogen

C + 2H2 CH4

Water-Gas Shift

CO + H2O H2 + CO2

Methanation

CO + 3H2 CH4 + H2O

Coal

Oxygen

Steam

Gasifier Gas

Composition

(Vol %)

H2 25 - 30

CO 30 - 60

CO2 5 - 15

H2O 2 - 30

CH4 0 - 5

H2S 0.2 - 1

COS 0 - 0.1

N2 0.5 - 4

Ar 0.2 - 1

NH3 + HCN 0 -0.3

Ash/Slag/PM

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FEEDS GASIFICATION GAS CLEANUP END PRODUCTS

Alternatives:• Asphalt• Coal• Heavy Oil• Petroleum Coke• Orimulsion• Natural Gas• Wastes• Clean Fuels

Alternatives:• Hydrogen• Ammonia• Chemicals• MethanolMarketable

Byproducts:

Sulfur

Gas & SteamTurbinesSulfur

Removal

Syngas

ElectricitySteam

Combined CyclePower Block

Byproducts:

Solids (ash)

Gasifier

Oxygen

Source: ChevronTexaco

Characteristics of a Gasification Process

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Gasifiers

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• Oxygen Blown– Entrained Flow– Fluidized Bed– Moving Bed– Transport Reactor

• Air Blown– Fluidized Bed– Spouting Bed– Entrained Flow– Transport Reactor– Hybrid

Underground Coal Gasification (UCG)

• In-situ gasification of non-mined coal, via injecting oxidants and steamunderground through a drilled well.

• The product gas surfaces through a production well.

• The reaction parameters are provided by hydrostatic pressure and theunderground temperature.

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Liquefaction

• Coal can also be converted into synthetic fuels equivalent to gasoline or diesel.

• The indirect process involves gasification and using syngas for chemicalproduction. This is called the Fischer-Tropsch process.

• In the direct liquefaction processes, the coal is hydrogenated. Hydrogenation process is the Bergius process.

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Indirect (Fischer-Tropsch process)

• Typically carbon number is between 10 and 20

• Methane is unwanted

• Temperature range of 150-300 °C

• Catalyst: Co, Fe, Ru or transition metals 86

Direct (Bergius process)

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• Temperature between 400-500 °C, Hydrogen pressure: 20-70 Mpa

• Catalyst: Iron-sulfides, W- or Mo-sulfides, Sn- or Ni-oleate.

• Heavy-, middle oils, gasoline and gases – high in naphtanes and aromatics, low in paraffins and olefins

• About 97% of the inlet carbon can be converted

Production of chemicals

• Coal is used extensively as feedstock to produce chemicals using processeswhich require substantial quantities of water. In coal-to-chemicals,synthesis gas (syngas) — a gaseous mixture of primarily carbon monoxideand hydrogen — is produced by gasification of coal (note: other feedstocksare also capable of gasification to produce syngas).

• The syngas can then be fashioned into a number of useful chemicalbuilding blocks, like methanol.

• Ammonia and urea are significant products of coal-to-chemicals for use infertilizers. The syngas composition — specifically, the ratio of hydrogen tocarbon monoxide — is important for some downstream processes.

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