Controlling (feedback loop) steam rate

[cymeryss]

I have the following problem and would appreciate any input on the subject. I have a recirculating (low preassure) CO2 system, driven by a blower, and at one point am adding steam through a nozle into the main tube (d = 2.5in). I am using a small (2kW) steam (sauna) generator. At this point the unit, and I, have no controll over the steam rate. I am adding steam to increase the RH, and my goal is to be able to controll and keep a steady humidity level, at let say 80%. I am looking at several small steam generator units (2-4kW) which have sufficient power output, but non of them have the ability to control their steam rate. I am planning on using a "smart controller", ex. PID - self learning unit that would look at the humidity sensor, have a setpoint, and be able to control the steam rate via a low voltage signal ex. (0-5V), not an ON/OFF signal. I forgot to mention that the humidity in the system is decreased after the CO2 passes through the element which needs a high RH, that is why based on its load - temperature, the steam rate has to be controlled to keep a constant RH. Any ideas on how this can be done, or suggestions on steam generator units would be greatly appreciated. Thank you for reading the post.

 

[ilan7]

Think you will have problem controlling directly the RH.
The way I would recommanded to do it is adding steam flow Transmitter and RH transmitter. Controlling the steam flow to have a constant flow (Steam Flow Control loop). Then use the RH transmitter as a cascade to adjust the flow loop setpoint. (When the RH is too low, the cascade system will increase the steam flow setpoint). This way you will have a steady control loop controlling system RH