How to convert gas flow from M3/hr to Nm3/hr and Sm3/hr???

 

How to convert M3/hr to NM3/hr and Sm3/hr

How to convert Nm3/hr to SM3/hr and M3/hr

 

In order to understand the above, need to understand the basics of STP & NTP

STP - Standard Temperature and Pressure

STP is commonly used to define standard conditions for temperature and pressure of air or gases.

As per IUPAC STP is  air at 0 ^oC (273.15 K, 32 ^o F) and 10 ⁵ pascals (1.03 kg/cm2).

 As per  Imperial and USA system of units STP is air at 60 ^o F (520 ^o R, 15.6 ^oC ) and 14.696 psia (1 atm,  1.01325 bara)

Note! The earlier IUAPC definition of STP to 273.15 K and 1 atm (1.03kg/cm2) is discontinued. 

NTP - Normal Temperature and Pressure

NTP is commonly used  as a standard condition  for testing and documentation of fan capacities:

NTP - Normal Temperature and Pressure - is defined as air at 20 oC (293.15 K, 68 o F) and 1 atm ( 101.325 kN/m2, 101.325 kPa, 14.7 psia, 0 psig, 29.92 in Hg, 407 in H2O, 760 torr). Density 1.204 kg/m 3 (0.075 pounds per cubic foot)

 

In order to convert M3/Hr to NM3/hr, we use below formula

PaVa/Ta = PnVn/Tn

Vn = PaVaTn / TaPn

Where, Pa, Va & Ta are air parameters at actual condition

Pn,Vn & Tn are air parameters at Normal condition

In order to convert M3/Hr to SM3/hr, we use below formula

PaVa/Ta = PsVs/Ts

Vs = PaVaTs / TaPs

Where, Pa, Va & Ta are air parameters at actual condition

Ps,Vs & Ts are air parameters at Normal condition

In order to convert NM3/Hr to SM3/hr, we use below formula

PnVn/Tn = PsVs/Ts

Vs = PnVnTs / TnPs

Pn,Vn & Tn are air parameters at Normal condition

Ps,Vs & Ts are air parameters at Normal condition

Solved examples:

1-A 25 m3/sec capacity forced draft fan  discharges air at 250 mmwc static pressure and 30 deg C temperature, calculate the air flow at Nm3/hr and Sm3/hr

Pa = 250mmwc = 250/10000 = 0.025 kg/cm2

Va = 25 m3/sec

Convert it into M3/hr = 25 X 3600 = 90000 m3/hr

Ta = 30 + 273.15 = 303.15 K

Tn = 20 + 273.15 = 293.15 K

Ts = 15.6 + 273.15 =288.75 K

We have the formula

PaVa/Ta = PnVn/Tn

Vn = PaVaTn / TaPn

Vn = 0.025 X 90000 X 293.15 / (303.15 X 1.033)

Vn =2106.27 NM3/hr

Similarly

PaVa/Ta = PsVs/Ts

Vs = PaVaTs / TaPs

Vs =0.025 X 90000 X 288.75 / (303.15 X 1.033)

Vs = 2074.65 Sm3/hr

Now convert Nm3/hr to SM3/hr to cross check the flow

PnVn/Tn = PsVs/Ts

Vs = PnVnTs/TnPs

Vs =1.033 X 2106.27 X 288.75 / (293.15 X 1.033)

Vs = 2074.66 Sm3/hr

2-A boiler of 100 TPH produces flue gas 27 MT/hr of flue gases at pressure 350 mmwc (ID fan inlet) and 145 deg C temperature, calculate the flue gas flow in Nm3/hr  and Sm3/hr

Given data,

Flue gas flow = 27MT/hr = 27 X 1000 = 27000 kg/hr

Convert to M3/hr

Density of flue gas at 145 deg C temperature = 1.293 X 273.15 / (273.15 + 145) = 0.84 kg/m3

Flue gas flow in M3/hr = 27000 kg/hr / 0.84 kg/m3 = 32142.85 M3/hr

Pa = 350 mmwc = 350 / 10000 = 0.035 kg/cm2

Ta = 273.15 + 145 = 418.15 K

We have,

PaVa/Ta = PnVn/Tn

Vn = 0.035 X 32142.85 X (20 + 273.15) / (418.15 X 1.033)

Vn = 763.50 Nm3/hr

Similarly,

PaVa/Ta = PsVs/Ts

Vs =0.035 X 32142.85 X (15.6 + 273.15) / (418.15 X 1.033)

Vs = 752.04 Sm3/hr

Now convert Nm3/hr to SM3/hr to cross check the flow

PnVn/Tn = PsVs/Ts

Vs = PnVnTs/TnPs

Vs =1.033 X 763.50 X 288.75 / (293.15 X 1.033)

Vs = 752.04 Sm3/hr

 

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