Your wording about clean-in-place and steam in place are somewhat confusing.
To sterilize in place (SIP) the unit using clean/pure steam you would heat it from 70 F to 250 F(121 C) and then hold at 250 F. Saturated steam pressure at 250 F is about 15 psig. You should use at least 20 psig steam, being careful not to exceed the pressure rating of the vessel.
The amount of steam you need to heat it up will depend on the weight of the vessel: weight x (250-70)/900 BTU per lb./heat capacity of vessel matl.= lb of steam. (assuming an empty vessel). The heat capacity of stainless steel is about 0.11 Btu/F/lb. The average rate of steam flow required will depend on the heat up time that you want. If time is an issue you might pick 5 minutes, if not you could pick 20 minutes or whatever. The lb.of steam divided by the time will give you an average steam rate. Add about 10% for losses during the heatup to get your generator output. (There will be some time lag between when the steam enters and when the vessel comes to temperature, so the heat up time based on the average rate will be pretty close) As you can see, the time you pick for the heatup time has the biggest impact the rate of steam that you need from the generator. The amount of steam needed will not vary significantly for different pressures of steam.
It is critical that air be efficiently removed from the vessel during heatup, and the right steam trap is used.
You will then hold the temperature for a given sterilization time, during which the rate of steam required is just equal to the heat losses to the room. These losses will be smaller than the heat up requirement, so will not dictate your generator size.
The “pureness” of the “clean” steam needs to be considered in terms of the process requirements for contamintation.
