Normal Cubic Meter

Hey;

I want to know why do gas flow rate in cement industry measure by Nm3 (normal cubic meter) not by m3?

This is the conversion formula:

Ideal Gas Law: PV = nRT,

Let n= 1

R = P_act.V_act/ T_act                      At given temp & pressure

R = P₀.V₀/ T₀                            At normal condition (0 °C & 1.0 atm)

P_act.V_act/T_act = P₀.V₀/T₀

è V₀ = V_act . (P_act/ P₀) . (T₀/ T_act)

OR:

Q₀ = Q_act . (P_act/ P₀) . (T₀/ T_act)

Let;

Q₀ = Q_N = Gas flow rate at normal condition (0 °C & 1.0 atm)

Q_act = Measured flow rate in m³/h

P_act = P_measured + P_ambient

P_ambient = 1.01325 bar

P₀ = Pressure at normal condition (1.0 atm

T₀ = Temperature at normal condition (0 °C = 273°K)

T_act = Measured Temperature in °K

Then;

Q_N = Q_act . ((P_measured + P_ambient)/ P₀) . (T₀/ T_act)       [Nm³/h]

Significant deviation from ideal gas behaviour appears when the empty space between molecules is reduced as e.g. high pressures or low temperatures. Compressibility factor (Z) uses to determine how much a gaseous system deviates from ideality. For ideal gas Z=1.0, any deviation of the compressibility factor from 1.0 is a non-ideality (real gas).

Z is not a constant factor for real gas but changes with pressure and temperature and can be determined from the Compressibility Factor table (or graphic) where K (compressibility number) = 1/Z.

Then;

Q_N = Q_act . ((P_measured + P_ambient)/ P₀) . (T₀/ T_act) . (1/K)       [Nm³/h]

Example: (Incoming Natural Gas)

Q_N =? Nm³/h

Q_act = 2956 m³/h

P_measured = 5.4 bar

T_act = 1.3°C+273 = 274.3 °K

Z (=1/K) = 1/0.99 = 1.01

Best Regards;

Saprina