Ratio control: Ammonia synthesis reactor

Lecture notes for Advanced modeling and Control

Example 15.1 from (Seborg et al. 2016)

A ratio control scheme is to be used to maintain a stoichiometric ratio of H₂ and N₂ as the feed to an ammonia synthesis reactor Figure 1. Individual flow controllers will be used for both the H₂ and N₂ streams. Using the information given below,

1. Draw a schematic diagram for the ratio control scheme.
2. Specify the appropriate gain for the ratio station, $K_R$.

Available information:

1. The electronic flow transmitters have built-in square root extractors. The spans of the flow transmitters are 30 L/min for H₂ and 15 L/min for N₂.

2. The control valves have pneumatic actuators.

3. Each required current-to-pressure (I/P) transducer has a gain of 0.75 psi/mA.

4. The ratio station is an electronic instrument with 4–20 mA input and output signals.

Figure 1: Ammonia synthesis reactor

References

Seborg, Dale E., Thomas F. Edgar, Duncan A. Mellichamp, and Francis J. Doyle III. 2016. Process Dynamics and Control. John Wiley & Sons. https://books.google.com?id=ZZVFEAAAQBAJ.