ATMOSPHERE SAFETY

Why atmosphere?

• Protection from scaling

• To diffuse carbon into steel surface to develop strength and wear resistance

What does the atmospere contain?

• Carbon Monoxide

• Hydrogen

• LPG

All these are highly inflammable, highly toxic and form explosive mixtures rapidly.

Knowlegde and training is necessary to so that they can be handled safely.

Carbon Monoxide

Carbon monoxide is a colorless and odorless gas that cannot be detected through sense of smell or taste. Exposure to carbon monoxide may cause you to experience any or all of these symptoms:

• Headaches, tightness across the forehead and temples

• Weariness, weakness, dizziness and vomiting • Loss of muscular control • Watering and smarting of the eyes

Propane

• When produced, propane is colorless and odorless. For safety and detection purposes, a chemical odorant (ethyl mercaptan) is added to propane. The presence of the odorant alerts you of a potential propane gas leak.

• Propane vapor is heavier than air. As such, in the event of an unintended release of propane vapor, the vapor will migrate to the lowest point. For example-furnace pits.

Properties of Hydrogen…

Areas being covered

1. Difference between inert and combustible gases

2. Hazards involved3. Procedure for gassing the furnace4. Procedure for removing the atmosphere5. Procedure for purging chambers and

vestibules6. What to do when power fails7. Precautions in handling various gases and

liquids

Fire triangle

combustion engine

Source of ignition.(Spark) > 600 deg.C

Fue( petrol)l

oxygen

Absence of any one of them combustion cannot occur and they must be within combustible limits. For petrol it is 1.3 -6.0%.If engine is flooded with Petrol engine will not start.

Furnace atmosphere

Ignition – auto ignition

Fuel-CO, H2, LPG AIR ( Oxygen <0.002)

HEAT ABOVE FUEL MIN OXYGEN LIMIT

flamability limit,LCL

falamability limit,UCL

>530 deg C Natural gas CH4 18.1 5.5 13.6

>580 deg C Hydrogen 6.59 9 68.6

>650 deg C Carbon Monoxide 4.7 13 77.6

Petrol 1.3 6.0

Oxygen is the problem

1. To avoid explosion from occuring we should prevent oxygen from entering the furnace.

2. This is done by flame curtains, pilots , exlosion hatches.

3. Atmosphere is allowed to enter the furnace only its temperature is above 815 deg C

Safe handling of gases points to remember• Inert gases do not burn and are safe.Combustible gases are unsafe

and they burn/explode• Endothermic gas contains 20% CO, 40 %H2 and 40%N2. this is

much higher than the their lower combustible limit• Minimum ignition temperature for hydrogen and hydrogen is close to

595 deg C.• Introduction of endothermic atmosphere into furnace below 760

degree C constitues explosion hazard.• It is safe to introduce atmophere above 815degree C• To purge furnaces require ata least 5 times its volume is required.• Before entering any furnace for repairs ,disconnect gas lines,freshly

purge the furnace with air and blow air continuously.• Carbon monoxide is extreemly toxic , unburnt furnace atmosphere

should not be exhausted into a room• If power or gas fails feed bottled nitrogen at the rate no more than

the flow rate of endothermic gas and light the gas curtains at all doors till emergency power is restored.

Procedure for gassing the furnace

1. Heat furnace uniformaly to above 815 degree C2. Open the vestibule door/s3. Place a lit flare in the vestibule/s close to the furnace door4. Start feeding endo thermic gas5. When flame appears at the furnace door/s the oxygen inside the

furnace is completely purged from the furnace.6. Lower the vestibule door partially, take out the lit flare and keep at

the bottom of the vestibule door to ignite the gases escaping from the door

7. Shut the vestibule door/s.8. Make sure that door pilots and purge stack pilots are lit and

endogas is burning at the purge stack

Procedure for removing the atmosphere

• Make sure that furnace temperature is above 815 degree C.• Open vestibule door/s and keep a lit flare in the vestibule close to

the inner furnace door/s.• Open the furnace doors and allow the atmosphere to burn at the

furnace door/s• Turn off endothermic gas.• When the endothermic gas stops burning at the furnace

door/s ,furnace is purged. • Keep furnace door/s open for a minimum of 30 minutes after the gas

stops burning at the door/s to ensure that any accumulation combustible gases in the brick work alsos gets burnt.

• Close the furnace door and drop the temperature.

Safety Instructions Do’s and Dont’s

Safety Instructions

SL NO. PARTICULARSBOMBAY HIGH SR

GRADE ( URAN)

1 Liquid Density @15deg, gms/cc 0.553

2 apecific gravity ( Air=1.0) approx 1.8

3 vapour pressure @100deg F, lbs/sq inch gauge 120

4 chemical composition %vol  

  Propane 38.7

  Propylene 0.0

  Butylene 0.0

  N-Butane 37.1

  Iso -Butane 24.2

  Total C5 and higher 0.0

5 Caloriefic Value  

  Gross K.Cal/kg 12500

  Nett K.cals/kg 10950

6 Air needed for complete combustion(Vols.Air/One vol.gas) 27.5

7 Sulphur, wt % <0.004

8 Exlosive limits,(% gas in air/gas ixture)  

  Lower 1.5

  Upper 9.0

9 Liquid /gas Ratio 1/120

10 Flame Temp.  

  In Air Deg.C 2000

  In Oxygen,deg.C 2850

     

SR. NO. CHARACTERISTICS UNIT REQUIREMENT

RESULT,Straight run LPG,HPCL USSAR,MUMBAI

RESULT, Mangalore LPG

1 Vapour Pressure @ 40° C K Pa 1050 (max) 938.18 700

2 Volatility for 95% by volume evaporation ° C 2.0 (max) 1.61 2

3 Copper Strip Corrosion for 1 Hr at 38° C  Not worse than

ASTM No. 1 ASTM No. 1 a 1

4 H2S   Pass Pass Pass

5 Free Water Content   None None Nil

6 Mercaptan ppm 20(min) More than 20Not in the

report

7 C2 Hydrocarbons (Ethane) Mole(%) Report 2.23 3.52

8 C3 Hydrocarbons (Propane) Mole(%) Report 53.45 23.83

9 i-C4 Hydrocarbons (Iso-Butane) Mole(%) Report 18.74 20.3

10 n-C4 Hydrocarbons (N-Butane) Mole(%) Report 23.75 51.4

11 i-C5 Hydrocarbons Mole(%)} 2.5 (Max)

1.61

0.9512 n-C5 Hydrocarbons Mole(%) 0.22

13 Density @ 15 ° C gms/cc Report 0.5384 0.5537

14 Total Volatile Sulphur PPM, max 150 NIL 20

Endothermic gas

It is a mixture of 20% carbon monoxide, 40%hydrogen and 40% nitrogen.

It is highly inflammable and highly toxic.

But it is a friend of heat treaters, because it supplies the carbon monoxide required

for gas carburising .

Principal components

Principal components of an endo gas generator are:1. a heating chamber to supply heat by combustion or

electric heating elements,2. one or more cylindrical retorts (usually vertical) in the

heating chamber with3. numerous small, porous ceramic pieces, impregnated

with nickel as a catalyst for the reaction. 4. a cooling heat exchanger to rapidly cool the reaction

products to a temperature that will not allow the reaction to proceed further.

5. the control system that maintains the reaction temperature and adjusts the gas/air ratio to provide desired dew point.

Endoe generator at AAL

Endo generator-line diagram

Air –gas ratio

Carbon content vs dew point

Dew point vs air gas ratio

reactions

1. C3H8+3O2 6CO+8H2

2. C3H8 3C+4H2

3. 2CO CO2 +C

4. C3H8+5O2 3CO2 +4H2O

5. C3H8 +3CO2 6CO +4H2

6. 2H2O 2H2 +O2Reaction 1 and 5 to be encouraged and 2 to 4 to be discouraged.This

is done by the

Nickel oxide catalyst and temperature of 1050degC

LPG quality

• Sulphur in LPG poisons the catalyst. Therefore LPG must be free from sulphur.

• Straight run gas (from Uran) contains less than 3 ppm sulphur, where as catalyst craked LPG from Mangalore contains more than 20ppm

• Uran LPG only is procured in AAL.

Properties of LPG

SR. NO. CHARACTERISTICS UNIT REQUIREMENT

RESULT,Straight run LPG,HPCL USSAR,MUMBAI

RESULT, Mangalore LPG

1 Vapour Pressure @ 40° C K Pa 1050 (max) 938.18 700

2 Volatility for 95% by volume evaporation ° C 2.0 (max) 1.61 2

3 Copper Strip Corrosion for 1 Hr at 38° C  Not worse than ASTM No. 1 ASTM No. 1 a 1

4 H2S   Pass Pass Pass

5 Free Water Content   None None Nil

6 Mercaptan ppm 20(min) More than 20Not in the

report

7 C2 Hydrocarbons (Ethane) Mole(%) Report 2.23 3.52

8 C3 Hydrocarbons (Propane) Mole(%) Report 53.45 23.83

9 i-C4 Hydrocarbons (Iso-Butane) Mole(%) Report 18.74 20.3

10 n-C4 Hydrocarbons (N-Butane) Mole(%) Report 23.75 51.4

11 i-C5 Hydrocarbons Mole(%)} 2.5 (Max)

1.61

0.9512 n-C5 Hydrocarbons Mole(%) 0.22

13 Density @ 15 ° C gms/cc Report 0.5384 0.5537

14 Total Volatile Sulphur PPM, max 150 NIL 20

SL NO. PARTICULARSBOMBAY HIGH SR GRADE ( URAN)

1 Liquid Density @15deg, gms/cc 0.553

2 apecific gravity ( Air=1.0) approx 1.8

3 vapour pressure @100deg F, lbs/sq inch gauge 120

4 chemical composition %vol  

  Propane 38.7

  Propylene 0.0

  Butylene 0.0

  N-Butane 37.1

  Iso -Butane 24.2

  Total C5 and higher 0.0

5 Caloriefic Value  

  Gross K.Cal/kg 12500

  Nett K.cals/kg 10950

6 Air needed for complete combustion(Vols.Air/One vol.gas) 27.5

7 Sulphur, wt % <0.004

8 Exlosive limits,(% gas in air/gas ixture)  

  Lower 1.5

  Upper 9.0

9 Liquid /gas Ratio 1/120

10 Flame Temp.  

  In Air Deg.C 2000

  In Oxygen,deg.C 2850

     

Maintenace.

Daily:

1. Visually examine all instrumentation to assure that operation is normal.....without

incident. Determine that control outputs are within the expected range of operation.

2. Check temperature of water discharged from heat exchanger.

Weekly:

1. Regenerate ( burn out ) carbon in generator using air

2. After regeneration and readjustment of generator to proper condition, check the carbon potential.

3. Clean the air filter

• Monthly:1. Clean air-gas mixing valve (carburetor )

thoroughly.2.Check carbon potential by shim stock

analysis.3. Inspect thermocouples and protection

tubes and replace every 3 to 4 months.4. Check LPG pressure after the regulator to

maintain balance to the carburetor.5. Verify correct operation of over

temperature controls.

Semi- annually:1. Replace heat exchanger with standby, clean and

refurbish them for next service.2. Inspect catalyst in retort and fill to proper level or

replace.3. Inspect and clean all burners.4. Clean endo delivery lines to furnaces.5. Inspect cooling water thermostats, solenoids.6. Perform complete instrument calibration and service,

including safety controls.7. Have oxygen probe ( carbon sensor ) refurbished,

inspected and certified.Annually:• 1. Check compressor blades.• 2. Check motor and compressor bearings.

Carbon potential control

• Due point control

• Carbon di-oxide control

• Oxygen potential control

Oxygen probe control

• More reliable.

• Insitu probe.

• Very quick ,real time data gets captured

• Zirconium oxide sheath acts as an electolyte(solid)

• Reference is air

• Measures the potential difference between atmosphere and reference air.

Electroplating cell

Schematic Diagram Carbon Sensor

Formula

• E=0.0496Tlog pO2/pO2ref.

T- Temp in deg K,

E-Emf imillivolts

Heat resistance alloy castings

• Contain more than 12% Chromium• Capable of performing satisfactorily above

650 deg C• Have good surface film stability in various

atmopsheres and the temperatures they are subjected

• Have sufficient mecahnical strength and ductility to meet high temerature survice conditions.

Role of Nickel

• Designated as HA, HC,…..HT,HU etc.• First letter denotes “ heat resistance alloy”• Second letter indicates nominal nickel content,

increasing from A to X.• Nickel is present in cast alloys in amounts up to 70%• Function of Nickel is to strengthen and toughen the

matrix,increase resistance to oxidation,carbusrisation ,nitriding and thermal fatigue.

• Nickel promotes formation of Austenite which is stronger and more stable at elevated temperatures than ferrite

Role of Chromium

• Chromium content varies from 10- 30%• It imparts resistance to oxidation(scaling)

at elevated temperature and to sulphur containing atmospheres.

• Chromium carbides precipitatein the matrix and contibute to high temperature creep and rupture strength.

• It also increases resistance to carburisation.

Role of Carbon and Silicon

• Carbon content ranges from 0.20 to 0.75%.• Increasing the carbon improves the high

temperature strenth and creep resistance at the expence of ductility.

• Silicon has beneficial effect on the high temerature corrosion resistance and on resistance to carburisation.

• Silicon in amounts >2%,lowers the high temperature creep . Therfore it is limited to 1.5% in castings intended for service higher than 815 deg C.

Grouping of Heat resistance alloys

• Chromium- Iron Alloys : HA, HC, HD

• Cromium - Nickel –Iron Alloys : HE, HF, HH,HI,HK,HL

• Nickel-Chromium – Iron Alloys : HN,HP,HT,HU,HW,HX

Properties of 3 groups

TYPE OF ALLOY PROPERTIES.

HA,HC,HD

Chromium up to 30%, Nickel up to 7%.They are ferritic and poor hot strength. Not used in critical load bearing application beyond 760 deg.c

HE,HF,HH,HI,HK,HL

Contain 18-24% Chromium , 8-22% nickel. Either partial of completely austenitic. Good high temperature strength, hot and cold ductility and resistance to oxidising and reducing conditions. They are useful in deducing atmospheres high in sulphur

HN,HP,HT,HU,HW,HX

Contain 25-70% nickel, 10-26% chromium. Fully austenitic. Good weldability,Can be used satisfactorily up to 1150 deg.C.Good hot strength,resistanmce to carbusrisation and thermal fatigue. Can be used for load bearing applications and cyclic heating and large temperature differentials.

Properites of HT and HU

HT

Contains 35% nickel, 17% chromium.About 1/7th of total production of HR ALLOYS is HT grade because of its value insesisting thermal shock, resistance to oxidation and carburisation at high temperatures.Except in high sulphur gases,it performs satisfactorily up to 1150 deg C in oxidising atmopsheres and up to 1100 deg C in reducing atmospheres.It is used for load bearing membersin furance applications such as retorts, radient tubes,cyanide and salt pots,hearth plates and trays quenched with work.

HU

Contains 39% nickel,18% chromium. Has exceptionally high combination of creep strength and ductility up to 110 deg C. Used where high hot strength is required. It is used in applications involving high stress and rapid thermal cycling.It hsd good resistance to corrosion by either oxidising or reducing hot gases containing moderate amounts of sulphur.Typical uses are salt pots, Quenching trays, fixtures and gas dissociation equipment.

Fan casting

Base Tray –all case furnace

CCF base tray

Top tray-allcase Furnace

Gear spacer

Pinion top tray

PEG