Download - COMBUSTION ENGG

04/08/2304/08/23 Dr. G. N. Halder- NIT DurgapurDr. G. N. Halder- NIT Durgapur 11

COMBUSTION COMBUSTION ENGINEERINGENGINEERING

Paper Code: ChE-611Paper Code: ChE-611Credits: 3L+1T=4Credits: 3L+1T=4

Dr. G. N. HalderDr. G. N. Halder

Chemical Engg DepartmentChemical Engg Department

E-mail: [email protected]: [email protected]


Syllabus:Syllabus: IntroductionIntroduction Furnace: Role and EssenceFurnace: Role and Essence Classification of furnacesClassification of furnaces Heat Transfer Processes in FurnacesHeat Transfer Processes in Furnaces Estimation of heat transfer by conduction, Estimation of heat transfer by conduction,

convection & radiation, Problemsconvection & radiation, Problems Case study: Steel Plant & Chemical rxns Case study: Steel Plant & Chemical rxns Furnace design and theories, applicationsFurnace design and theories, applications Refractory and Insulating materialsRefractory and Insulating materials Flameless combustion and its significanceFlameless combustion and its significance


Syllabus:Syllabus: Beneficiation of CoalBeneficiation of Coal Clean Coal TechnologyClean Coal Technology Coal bed Methane and Carbon dioxide Coal bed Methane and Carbon dioxide

SequestrationSequestration Coal gasification technology, chemical rxns, Coal gasification technology, chemical rxns,

process conditions, Underground Coal process conditions, Underground Coal GasificationGasification

ASTM test techniques of solid, liquid and ASTM test techniques of solid, liquid and gaseous fuelsgaseous fuels


Text/Reference BooksText/Reference Books1.1. Modern Furnace Technology: Etherington & Modern Furnace Technology: Etherington &

Etherington, Charles Griffin & Company LtdEtherington, Charles Griffin & Company Ltd

2.2. Combustion Engg and Fuel Technology: A. K. Combustion Engg and Fuel Technology: A. K. Saha, Oxford & IBH Publishing Co.Saha, Oxford & IBH Publishing Co.

3.3. Science and Technology of Coal and Coal Science and Technology of Coal and Coal Utilization: Cooper and Ellingson, PlenumUtilization: Cooper and Ellingson, Plenum

4.4. Fuels and Combustion: Sharma & MohanFuels and Combustion: Sharma & Mohan

5.5. Fundamentals of Coal Combustion for Clean and Fundamentals of Coal Combustion for Clean and Efficient Use: L. D. Smoot, ElsevierEfficient Use: L. D. Smoot, Elsevier

FURNACE IN

COMBUSTIONDefinition: A furnace is an enclosed structure in which fuel is burned to produce heat to melt metals for casting or heat materials for change of shape (rolling, forging etc) or change of properties (heat treatment). The term ‘furnace’ is derived from the Latin word ‘FORNAX’ means oven.

Areas of application: Steel making industries, Oil refineries, Research laboratory, Chemical plants and allied process industries.

Essence of Furnace Technology In the process of combustion in the furnaces, the chemical

energy of fuel transforms into the thermal energy, which is used either directly, or through the agency of heat energy, is converted into mechanical power.

Chemical energy Thermal energy Power

Furnace technology comprises scientifically applied knowledge of combustion, thermodynamics, gas flow, heat transfer, and the properties of furnace materials. It includes the application of sound engineering principles to the construction and control of furnaces and related equipment.

Combustion in a furnace is the constant pressure process.

Continued… Efficient combustion of a fuel in a Furnace

largely depends upon the following stringent factors:

Geometry Design Shape of the inner shell Selection of Materials of construction Alignment of Refractory materials Proper Insulation Thermal conductivity of the materials Quantity of feed charged Air fuel ratio

Characteristics of an efficient furnace

Furnace should be designed so that in a given time, as much of material as possible can be heated to an uniform temperature as possible with the least possible fuel and labour.

To achieve this end, the following parameters can be considered:

Determination of the quantity of heat to be imparted to the material or charge.

Liberation of sufficient heat within the furnace to heat the stock and overcome all heat losses.

Equalization of the temperature within the stock

Continued… Transfer of available part of that heat from the

furnace gases to the surface of the heating stock.

Reduction of heat losses from the furnace to the minimum possible extent.

Classification of Furnaces A furnace is usually described considering its

structure consisting of three main portions: fireplace (where combustion of fuel takes

place) working chamber (where heat is transferred

from the products of combustion to the materials under heating)

the appliances for the removal of the flue gases

A furnace may be classified in several ways. I) Classification by HEAT SOURCE or TYPE

OF FUEL: Furnaces may be heated by combustion of

solid, liquid or gaseous fuels. Depending upon the kinds of fuel, it may be divided into: four classes :

a) solid fuel furnaces (coal-fired, coke-fired, wood-fired)

b) liquid fuel furnaces (oil-fired) c) gaseous fuel furnaces (producer-gas fired) d) mixed fuel furnaces (combination of any

two or three fuels may be used, e.g., CNG)

Continued… II) Classification by METHOD OF

CHARGING:

a) continuous type furnaces (e.g. rolling mill furnace)

b) batch type furnaces (e.g., glass pot, tank furnace)

Continued… III) Classification by DEVICES EMPLOYED

FOR REMOVAL OF FLUE GASES: All the existing furnaces may be divided into

two classes : a) natural draught furnaces (furnaces

operating either with chimneys or with open doors. It is also called self-draught furnace)

b) forced draught furnaces (here forced draught fans are used both for the removal of flue gases and introduction of air needed for combustion)

Continued… IV) Classification by MODE OF

OPERATION:

Depending upon this condition, furnaces may be divided into two classes :

a) periodical furnaces (e.g., coke-ovens, brick kilns, annealing furnaces)

b) continuous furnaces (e.g., glass tank furnaces, continuous gas retorts)

Continued… V) Classification by MODE OF HEAT

RECOVERY:

a) regenerative furnaces

b) recuperative furnaces


Some Common Industrial Furnaces1.1. Blast furnaceBlast furnace

2. Muffle furnace2. Muffle furnace

3. Coal-fired furnace3. Coal-fired furnace

4. Pot furnace4. Pot furnace

5. Gas-fired furnace5. Gas-fired furnace

6. Retort furnace6. Retort furnace

7. Direct-fired furnace7. Direct-fired furnace

8. Rotary kiln8. Rotary kiln

9. Recirculating furnace 9. Recirculating furnace

10. Regenerative furnace10. Regenerative furnace

BLAST FURNACEA blast furnace is a type of metallurgical furnace used for

smelting to produce industrial metals, generally iron.In a blast furnace, fuel (coke), ore, and flux (limestone) are

continuously supplied through the top of the vertical cylindrical furnace, while air (sometimes with oxygen enrichment) is blown into the bottom of the chamber for combustion of the fuel, so that the chemical reactions take place throughout the furnace as the material moves downward by gravity. The end products are usually molten metal and slag phases tapped from the bottom continuously or intermittently, and flue gases exiting from the top of the furnace.

Hearth Refractories

Tuyeres

Bustle Main

Refractory Lining

Throat Armour

Top Bins

Top Gas Mains

Above Burden Probe

Temperature Probe

Sub Burden Probe

Blast Furnace

Stock House

Hot Blast StovesGas Cleaning

Scrubber

Iron making in the Blast Furnace

Bell Less Top

Blower

Combustion Air Slag, Hot Metal

Gasholder

Enrichment Gas

Combustion Gas

Sinter Coke

Cast House

Chemical Reactions Involved: The main chemical reaction producing the molten iron is: Fe2O3 + 3CO → 2Fe + 3CO2 This reaction might be divided into multiple steps, with

the first being that preheated blast air blown into the furnace reacts with the carbon in the form of coke to produce carbon monoxide and heat:

2C(s) + O2(g) → 2 CO(g) The hot carbon monoxide is the reducing agent for the

iron ore and reacts with the iron oxide to produce molten iron and carbon dioxide. Depending on the temperature in the different parts of the furnace (warmest at the bottom) the iron is reduced in several steps. At the top, where the temperature usually is in the range between 200 °C and 700 °C, the iron oxide is partially reduced to iron (II,III) oxide, Fe3O4.

Chemical Reactions Involved: 3 Fe2O3(s) + CO(g) → 2 Fe3O4(s) + CO2(g) At temperatures around 850 °C, further down in the

furnace, the iron(II,III) is reduced further to iron(II) oxide:

Fe3O4(s) + CO(g) → 3 FeO(s) + CO2(g) Hot carbon dioxide, unreacted carbon monoxide, and

nitrogen from the air pass up through the furnace as fresh feed material travels down into the reaction zone. As the material travels downward, the counter-current gases both preheat the feed charge and decompose the limestone to CaO and CO2 at 900 0C :

CaCO3(s) → CaO(s) + CO2(g)

Chemical Reactions Involved: As the iron(II) oxide moves down to the area with

higher temperatures, ranging up to 1200 °C degrees, it is reduced further to iron metal:

FeO(s) + CO(g) → Fe(s) + CO2(g) The carbon dioxide formed in this process is re-

reduced to carbon monoxide by the coke: C(s) + CO2(g) → 2 CO(g) The temperature-dependent equilibrium controlling

the gas atmosphere in the furnace is called the Boudouard reaction:

2CO → CO2 + C

Chemical Reactions Involved: The decomposition of limestone in the middle zones of

the furnace proceeds according to the following reaction: CaCO3 → CaO + CO2 The calcium oxide formed by decomposition reacts with

various acidic impurities in the iron (notably silica), to form a slag which is essentially CaSiO3:

SiO2 + CaO → CaSiO3 The “pig iron" produced by the blast furnace has a

relatively high carbon content of around 4–5%, making it very brittle, and of limited immediate commercial use. Some pig iron is used to make cast iron. The majority of pig iron produced by blast furnaces undergoes further processing to reduce the carbon content and produce various grades of steel used for construction materials, automobiles, ships and machinery.

Composition of Produced Iron: Iron : 93.5 - 95.0% Carbon : 4.1 - 4.4%

(partly in the form of graphite) Manganese : 0.55 – 0.75% Silicon: 0.3 - 1% Phosphorous: 0.03 - 0.09% Sulphur: 0.025 - 0.050% Titanium: 0.02 - 0.06%

Drawback in Steel making: One of the biggest drawbacks of the blast

furnaces is the inevitable carbon dioxide production as iron is reduced from iron oxides by carbon and there is no economical substitute – steelmaking is one of the unavoidable industrial contributors of the CO2 (greenhouse gas) emissions in the world.

How can it be utilized?


MUFFLE FURNACEMUFFLE FURNACE It consists of a refractory container or muffle It consists of a refractory container or muffle

supported in a surrounding combustion chamber. supported in a surrounding combustion chamber. The charge is placed in the muffle and is heated by The charge is placed in the muffle and is heated by conduction through the walls of the muffle.conduction through the walls of the muffle.

Muffle furnaces are used when it is desired to Muffle furnaces are used when it is desired to control the atmosphere in contact with the charge, control the atmosphere in contact with the charge, to avoid contamination by furnace gas, or to assure to avoid contamination by furnace gas, or to assure a uniform high temperature.a uniform high temperature.


Muffle FurnaceMuffle Furnace There are few muffle furnaces constructed to There are few muffle furnaces constructed to

receive containers in which the charge is sealed or receive containers in which the charge is sealed or otherwise separated from the flame.otherwise separated from the flame.

After advancement in materials for heating After advancement in materials for heating elements, such as molybdenum disilicide, offered elements, such as molybdenum disilicide, offered in certain models, can now produce working in certain models, can now produce working temperatures up to 1800 degrees Celsius, which temperatures up to 1800 degrees Celsius, which facilitate more sophisticated metallurgical facilitate more sophisticated metallurgical applications.applications.


Muffle FurnaceMuffle Furnace


Muffle Furnace: Application Muffle Furnace: Application AreasAreas Fusing glass in Glass and Ceramic industries Creating enamel coatings in Paint industries Heat treatment in Ceramics Soldering and brazing articles in Fabrication

of metal body: Steel industries Also used in many research facilities, for

example, in order to determine what proportion of a sample is non-combustible and non-volatile (i.e., ash).

http://en.wikipedia.org/wiki/Glass

http://en.wikipedia.org/wiki/Vitreous_enamel

http://en.wikipedia.org/wiki/Ceramic


Pot furnacePot furnace

Pot furnace is a circular furnace containing a Pot furnace is a circular furnace containing a metal or refractory pot or crucible in which metal or refractory pot or crucible in which glass is melted glass is melted for change of shape. It can be . It can be used for annealing, normalizing & salt- bath used for annealing, normalizing & salt- bath solution treatment.solution treatment.

It may be regenerative or recuperative. The energy consumption is low but the efficiency is high.


Illustration of Pot furnace

Pot furnacePot furnace


Charging to a Pot furnaceCharging to a Pot furnace

Double pot furnaceDouble pot furnace


Coal-fired furnace A pulverized coal-fired furnace is an industrial or

utility furnace that generates thermal energy by burning pulverized coal (also known as powdered coal or coal dust). Coal is pulverized and carried into the furnace through a burner by an air-stream. This type of boiler dominates the electric power industry, providing steam to drive large turbines. Pulverized coal provides the thermal energy which produces about 50% of the world's electric supply.

http://en.wikipedia.org/wiki/Thermal_energy

http://en.wikipedia.org/wiki/Coal_dust

Coal-fired furnace


http://www.watertubeboiler.org/wp-content/uploads/2011/03/coal-fired-boiler1.jpg

Regenerative furnace

The regenerative furnace was first invented by Robert Stirling in 1816 and was applied to glass melting by Fredrick Siemens.

A furnace in which gas is used as fuel and air is for supporting combustion. The incoming air is heated by regenerators. By a direct furnace having a regenerator, we can save energy upto 75%.

Regenerative furnace


Direct-fired FurnaceDirect-fired Furnace The operation in a direct-fired furnace is very

simple. The burners are spaced along one side of the furnace near the roof, and vertical flues are constructed in the opposite wall with ports inside the furnace at hearth level. The products of combustion from the flame cross the furnace in a downward direction to the ports and pass up through the flues. In a long furnace, burners and flues are located on both sides in staggered positions. The material to be heated lies on the hearth directly exposed to the flame and hot gases.

Recirculating FurnacesMany furnace operations, such as, stess releiving of weldments and tempering of hardened steel parts, require heating at closely controlled temperatures upto 650C. Direct combustion products are usually much hotter than the required temperature and it may be difficult to control the temperature of the product without local overheating.

A recirculating furnace includes an external recirculating duct, with a high temperature fan used to draw off and recirculate the furnace atmosphere. The furnace gases are maintained only slightly above the desired temperature by burning fuel and mixing the high-temperature products with furnace gases before they are returned to the furnace.


Recirculating Furnace Maximum operating temperature

650°C Chamber capacities of 22, 112 &

324 litres Heating is provided by resistance

wire elements on both sides of the chamber

Powerful centrifugal fan and air guide system forces air over the elements & back through the chamber to ensure good thermal uniformity

Easy clean stainless steel inner chamber

Applications in general industry include:Low temperature ferrous metal heat treatment processes; # annealing # tempering # normalising and # stress relieving

Applications:

Rotary Kiln: A Rotary kiln is a device used to raise materials

to a high temperature (calcination) in a continuous process. Materials produced using rotary kilns include:

Cement Lime Refractories Titanium dioxide A alumina Vermiculite Iron ore pellets In rotary kilns, the entire kiln rotates and is

inclined at a slight angle, the movement of material by gravity from one end to other is assisted by the rotation.

They are also used for roasting a wide variety of sulfide ores prior to metal extraction.



Rotary Kiln

Rotary Kiln: Operation Principle The kiln is a cylindrical vessel, inclined slightly to the

horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner. The fuel for this may be gas, oil or pulverized coal.

Dr. G. N. Halder- NIT DurgapurDr. G. N. Halder- NIT Durgapur04/08/2304/08/23 4747

Components of Rotary Kiln

KILN SHELL: This is made from rolled mild steel plate, usually between

15 and 30 mm thick, welded to form a cylinder which may be up to 230 m in length and up to 6 m in diameter. This will be usually situated on a east/west axis to prevent eddy currents.

Upper limits on diameter are set by the tendency of the shell to deform under its own weight to an oval cross section, with consequent flexure during rotation. Length is not necessarily limited, but it becomes difficult to cope with changes in length on heating and cooling (typically around 0.1 to 0.5% of the length) if the kiln is very long.


Components of Rotary KilnDRIVE GEAR: The kiln is usually turned by means of a single Girth Gear

surrounding a cooler part of the kiln tube, but sometimes it is turned by driven rollers. The gear is connected through a gear train to a variable-speed electric motor. A 6 x 60 m kiln requires around 800 kW to turn at 3 rpm. The speed of material flow through the kiln is proportional to rotation speed, and so a variable speed drive is needed in order to control this. In many processes, it is dangerous to allow a hot kiln to stand still if the drive power fails. Temperature differences between the top and bottom of the kiln may cause the kiln to warp, and refractory is damaged. It is therefore normal to provide an auxiliary drive for use during power cuts. This may be a small electric motor with an independent power supply, or a diesel engine. This turns the kiln very slowly, but enough to prevent damage.


Components of Rotary Kiln Refractory Lining: The purpose of the refractory lining is to insulate the

steel shell from the high temperatures inside the kiln, and to protect it from the corrosive properties of the process material. It may consist of refractory bricks or cast refractory concrete, or may be absent in zones of the kiln that are below around 250°C.

The refractory selected depends upon the temperature inside the kiln and the chemical nature of the material being processed. In some processes, such as cement, the refractory life is prolonged by maintaining a coating of the processed material on the refractory surface. The thickness of the lining is generally in the range 80 to 300 mm. A typical refractory will be capable of maintaining a temperature drop of 1000°C or more between its hot and cold faces.


Components of Rotary Kiln TYRES and ROLLERS Tyres, sometimes called riding rings, usually consist of a single

annular steel casting, machined to a smooth cylindrical surface, which attach loosely to the kiln shell through a variety of "chair" arrangements. These require some ingenuity of design, since the tyre must fit the shell snugly, but also allow thermal movement. The tyre rides on pairs of steel rollers, also machined to a smooth cylindrical surface, and set about half a kiln-diameter apart. The rollers must support the kiln, and allow rotation that is as nearly frictionless as possible. A well-engineered kiln, when the power is cut off, will swing pendulum-like many times before coming to rest. The mass of a typical 6 x 60 m kiln, including refractories and feed, is around 1100 tonnes, and would be carried on three tyres and sets of rollers, spaced along the length of the kiln. The longest kilns may have 8 sets of rollers, while very short kilns may have only two. Kilns usually rotate at 0.5 to 2 rpm, but sometimes as fast as 5 rpm. The Kilns of most modern cement plants are running at 4 to 5 rpm. The bearings of the rollers must be capable of withstanding the large static and live loads involved, and must be carefully protected from the heat of the kiln and the ingress of dust. In addition to support rollers, there are usually upper and lower "retaining (or thrust) rollers" bearing against the side of tyres, that prevent the kiln from slipping off the support rollers.


http://en.wikipedia.org/wiki/File:LDRotaryKilnTyre.jpg

Download - COMBUSTION ENGG

Top Related