Presented by :

Rishav Ghosh(163110029)Bidyut Dutta(163110032)

Kapildeb Mondal(163110035)Pramod Behera(163110036)

Shubham Mahajan(163110063)

Udit Kumar(163110065)

Furnaces and their atmosphere

Furnace

“An enclosed structure in which material can be heated to very high temperatures”

The principal objective of a furnace is to attain a higher processing temperature than can be achieved in the open air.

Basis For Classification of Furnaces

1. Furnace Classification by Heat Source2. Furnace Classification by Batch3. Furnace Classification by Fuel4. Furnace Classification by Recirculation5. Furnace Classification by Direct-Fired or Indirect-Fired6. Classification by Furnace Use7. Classification by Type of Heat Recovery8. Based of Atmosphere9. Other Furnace Type Classifications

Classification by Furnace Use

1. Industrial furnace2. Laboratory FurnacesIt can be further subdivided based on use but for the simplicity and scope of the presentation, it is best.

Laboratory Furnaces Muffle furnaces - for high temperature uses such as ignition tests,

gravimetric analysis, heat treating steel parts, and more Ashing furnaces - can be ideal for determining the amount of ash in

distillate and residual fuels, gas turbine fuels, crude oils, lubricating oils, waxes, and other petroleum products.

Tube furnaces - are great for educational, governmental, and industrial laboratories for purifications and syntheses.

Melting furnaces - safely melt silver, gold, brass and other metals without the potential hazards of torch melting or gas furnaces

Laboratory Furnaces Classification

Based on atmosphere

• Inert Gas• Endothermic• Hydrogen• Dissociated ammonia• Exothermic Gas• Steam

Based on temperature

control• Two-Position

Control• Proportional,

integral and derivative control

• Program Control

Generation of heat

• Combustion type(fuel-type)

• Electric type

Role of Furnace Atmosphere Purging air (oxygen) from a furnace Controlling the surface chemistry to prevent oxidation and/or

reduction reactions from occurring Controlling the surface chemistry to allow oxidation and/or reduction

reactions to take place Avoiding decarburization of the surface Allowing surface-chemistry reactions for the purpose of introducing a

chemical species such as carbon (carburizing) or nitrogen (nitriding)

REFRACTORIES

Refractories are inorganic nonmetallic material which can withstand high temperature without undergoing physico – chemical changes while remaining in contact with molten slag, metal and gases.

It is necessary to produce range of refractory materials with

different properties to meet range of processing conditions.

Why Required?

1. To minimize heat losses from the reaction chamber.

2. To allow thermal energy dependent conversion of chemically reactive reactants into products.

Refractory RequirementsThe refractory materials should be able to withstand--

• High temperature

• Sudden changes of temperature

• Load at service conditions

• Chemical and abrasive action of phases

The refractory material should not contaminate the material with which it is in contact.

Properties of refractories for high temperature applicationsRefractoriness

Refractoriness is a property at which a refractory will deform under its own load. The refractoriness is indicated by PCE (Pyrometric cone equivalent).

Refractoriness decreases when refractory is under load. Therefore more important is refractoriness under load (RUL) rather than refractoriness.

SpallingSpalling relates to fracture of refractory brick which may occur due to the following reasons:

• A temperature gradient in the brick which is caused by sudden heating or cooling.

• Compression in a structure of refractory due to expansion

• Variation in coefficient of thermal expansion between the surface layer and the body of the brick.

• Variation in coefficient of thermal expansion between the surface layer and the body of the brick is due to slag penetration or due to structural change.

Permanent Linear change (PLC) on reheating

In materials certain permanent changes occur during heating and these changes may be due to

• Change in the allotropic form

• Chemical reaction

• Liquid phase formative

• Sintering reactions

These changes determine the volume stability and expansion and shrinkage of the refractory at high temperatures.

Temperature: The reaction chamber temperatures may vary from 1200-1600° C in liquid state processing and 700-1200°C in various solid state processing operations.

Abrasion due to movement:

The refractory chamber should be able to withstand the erosion and corrosion caused by the movement of the phases (molten metal, slag, gases).

Classification of atmospheres for heat treatment and other purposes

Atmosphere type Preparation ApplicationExothermic base (AGA 100) Prepared either by partial or by

complete combustion of gaseous fuel with air

Bright annealing of steel, copper, sintering of non ferrous metal powders, and iron powders

Prepared nitrogen base (AGA 200)

Produced by combustion of a mixture of air and fuel gas

Used to heat treat low-carbon, medium-carbon and high carbon steels

Endothermic base atmospheres (AGA 300)

Prepared by using a lean mixture of hydrocarbon fuel with air

Bright annealing of steel of any carbon content without decarburization or carburization

Charcoal base atmospheres (AGA 400)

It is produced by following reaction

2C+O2 + 3.76 N2=2CO + 3.76 N2

Used for hardening, annealing and normalizing high carbon steels without scale formation

Exothermic-Endothermic base atmospheres (AGA 500)

Prepared by combusting a mixture of air and fuel. The mixture is made to react in presence of a catalyst.

Carburizing and carbo-nitriding

Ammonia base atmospheres (AGA 600)

Ammonia dissociation is used to prepare highest purity nitrogen which is free from oxygen.

Ferrous and non ferrous metals are bright annealed in ammonia atmosphere

Composition (vol%)Atmosphere N2 CO2 CO H2 CH4 Dew

Point(oC)Applications

Lean exothermic

86.8 10.5 1.5 1.2 - 4.5 Bright annealing of Cu, sintering of ferrites

Rich exothermic

71.5 5.0 10..5 12.5 5 10 Bright annealing low C steel, silicon steels/Cu brazing, sintering

Dissociated NH3

25 - - 75 - -50 to +60 Brazing sintering bright annealing

Endothermic 40-45

0-0.5

20 34-40

0.51 -10 to +10 Hardening, carburizing with CH4, sintering brazing

Nitrogen 99.9 - - - - -60 Natural for annealing

Hydrogen - - - 99.9 - -68 Reducing, sintering

Ar or He : These are pure and inert gases and are used to prevent oxidation during welding of stainless steel , aluminum etc. and heat treatment of special steels.

Atmospheric Control

THE PURPOSE of atmosphere control is to –

maintain consistent levels of the various constituents that make up the atmosphere,and

determine if changes in those levels are required in order to produce a desired result under a given set of conditions

Atmosphere Control Devices

Oxy-probes

Infrared Analysers

Dew Point Instrument

Oxy-Probes

The oxygen probe is an in situ type device; i.e. it directly samples the atmosphere to be measured.

Control of Carburising furnaces- The electrical signal generated by an oxygen probe is directly proportional to the carbon potential of the atmosphere.

Solid-state sensors have found uses in a wide range of applications, including, control of atmosphere in materials processing and control of air-to-fuel ratio in combustion.

Solid State Oxy-sensors Commerical oxy-probes are based on the concept of solid-state

electrochemical cell. Solid-state electrolyte : Yttria-stabilised ZrO2

Electrodes :-Platinum electrodes deposited on the inner and outer surfaces

The output of the oxygen probe is a direct measurement of the oxidation potential of the atmosphere at the process temperature of the furnace.

Infrared Analyser Infrared control measures a sample drawn from the furnace.

Infrared control is usually used to measure carbon monoxide and/or carbon dioxide levels.

Carbon dioxide control and/or dew point control can be used for determining carbon potential in carburizing atmospheres.

Infrared analyzers can also be used to monitor ammonia in nitriding atmospheres and carbon monoxide in other applications.

Working Principle of Infrared Analyser• The infrared gas analyzer involves two chambers--reference chamber and

sample chamber; allowing for measurement of the type of gas and quantity.

• Infrared light of a particular frequency is emitted from one end of the chamber through to a series of gas chambers that contain given concentrations of different gases.

• As the photons from the infrared source pass through the gas chamber, the gas of interest will absorb some of the infrared radiation

• The detector converts the amount of infrared radiation absorbed by the gas into a voltage signal.

Dew Point Measurement

Dew point is the “temperature at which a given concentration of water vapor in air will form dew.”

Dew point of a furnace atmosphere is an indication of : carbon potential moisture content

Working Principle The instrument consists of an Al2O3

sensor which consists of an aluminum base material with an aluminum oxide etched on its surface.

The oxide is then covered with a thin permeable gold layer. The inner aluminum base and the gold layer form a capacitor.

Moisture passes through the outer metal layer and is absorbed on the oxide. This changes the capacitance of the entire assembly proportionally to the moisture content in the atmosphere

FUTURE SCOPE REQUIRMENTS:

Energy efficient Absolute safety High throughput Low capital investment Low Running and maintenance cost Easy to handle

RECENT DEVELOPMENTS

Hydrogen as protective gas. High capacity base fans Better design diffusers Inner cover Furnace insulation Change in burner design Advanced cooling covers

Other possible scope

Electron beam heating furnace Laser heating furnace Open door furnace Solar heating Plasma heating Infrared melting Microwave heating