The convertion cannot be done directly since with CFM you are talking of volumetric flow and with pounds per hour you are talking of mass flow. To make the convertion it is necesary to know the point caracteristics of steam (presure, temperature) and if the steam is saturated or superheated.
If you send me this data I can make the calculation for you.
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Assuming 0 gauge pressure (and that the "steam" you mention is from water), steam weighs 0.03732 lbs/cubic feet. So:

1 cfm = 0.03732 pounds/min, and
= 2.2392 pounds/hr

If the pressure changes, you will need a look-up table (or maybe there's an algorithm?). You can find one at: