You want kW, not kW/hr. kW is energy/time, kW/hr is esentially equivalent to acceleration but in terms of energy.
You need the heating value of the gas first. You then need to convert your gas flow (m3/hr) to the same basis as the heating value (standard conditions, normal conditions, whatever).
You might have to do some more conversions depending on your units.
For example, if your gas flow is 150,000 standard m3/hr and the heating value is 25,000 kJ per standard m3, the product is in kJ/hr and you just have to convert that to kW.
