How to calculate the quantity of oxygen required for gas cutting operation?

 We know that, for gas cutting operation generally we use combination of oxygen and LPG or Oxygen and acetylene.But now a days for some industry LPG is banned for safety point of view.

 

Following table gives the difference between Oxy-acetyle and Oxy-LPG gas cutting

COMPARISON BETWEEN ACETYLENE AND LPG FUELS FOR GAS CUTTING OPERATION
SL No.	Acetylene	LPG (Propane)
1	Highest flame temperature up to 3100 Deg C	Flame temperature up to 2800 Deg C
2	Flame speed up to 7.5 m/sec	Flame speed up to 3.3 m/sec
3	Most of the heat released is in inner cone	Most of the heat released is in outer cone
4	Higher flame GCV of inner cone (4500 kcal/M3)	Lower flame GCV of inner cone (2500 kcal/M3) as compared to acetylene
5	Stoichiometric air fuel ratio1.2:1 (Requires 2.5 to 3 Oxygen cylinders for burning one Acetylene cylinder)	Stoichiometric  air fuel ratio 4.3:1 (Requires 7 to 8 Oxygen cylinders for burning one LPG cylinder)
6	Can be used in gas welding, as acetylene when burning with air creates reducing zone that cleans the steel surface	Cannot be used in gas welding as it does not create reducing zone
7	Acetylene has Specific gravity 0.9 kg/m3, so if it leaks it will raise in air without harming much	Propane  has Specific gravity 1.6 kg/m3,which is heavier than air.So if it leaks it will concentrate in deck level or any other closed/corner area
8	Acetylene requires less air for complete combustion	Propane requires more air for complete combustion, so there may be chances of formation of carbon monoxide (CO) in case of incomplete combustion. This incomplete combustion may result into poisoning of working area, as CO is poisonous gas
9	Can be used for cutting & welding applications in industry	Used only for domestic applications

 

Calculate the number of Oxygen cylinders required to consume 1 no.of industrial LPG cylinder for gas cutting operation

Commercial LPG (C3H8) has 19 kg weight that is 19 kg of propane

Combustion equation of propane

C3H8 + 5O2 = 3CO2 + 4 H2O

44 + 160 = 132 + 72 (Molecular weight of C = 12, O = 16, H = 1)

 Divide equation by 44

1 + 3.63 = 3 +1.63

 From above result it is clear that 3.63 kg of Oxygen is required to burn 1 kg of Propane to achieve 100% combustion.

So for burning 19 kg of commercial LPG, need 19 X 3.63 = 68.97 Kg of oxygen

 Volume of oxygen cylinder in cylinder = 6.9 M3 compressed at 140-150 kg/cm2

Convert 6.9 to kg by dividing oxygen density, we get weight of O2 in cylinder = 9.1 kg

 So total O2 cylinders required = 68.97 / 9.1 =7.58 Nos for consuming 1 LPG cylinder

Calculate the number of Oxygen cylinders required to consume 1 no.of dilute acetylene cylinder for gas cutting operation

DA (C2H2) cylinder has 8 m3 of acetylene

 Convert volume to kg by multiplying the density of the gas

8 X 0.899 = 7.192 kg

Combustion equation of propane

2C2H2 + 5O2 = 4CO2 + 2H2O

52 + 160 = 176 + 36 (Molecular weight of C = 12, O = 16, H = 1)

 Divide equation by 52

1 + 3.07 = 3.38 +0.69

So for burning 7.192 kg of DA, need 7.192 X 3.07 = 22.07 Kg of oxygen

So total O2 cylinders required = 22.07 / 9.1 =2.42 Nos

 Read Powerplant maintenance calculations

Note:

DA (Dilute Acetylene): OD 265 mm X Height 1 meter (Appx) and thickness 4.0 mm.Volume of acetylene in cylinder is 8.5 m3

 Oxygen cylinder size : OD 235 mm X Height 1.34 meter (Appx) and thickness 4.0 mm.Volume of O2 in cylinder is 6.9 m3

 

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