In chemical plants multiple machines are combined into complex machine trains, to achieve the conditions for complex chemical reactions. An example are machine trains for production of nitric acid, used in fertilizer production.
To achieve a stable, efficient chemical reaction all parts of the machine train need to be coordinated by complex control algorithms. The power turbine requires a speed control, to drive the compressors at the required flows and pressures. After the process is started the expander will contribute to the drive power. Its power output needs to be coordinated with the turbine. The compressors need to keep specific flow and pressure conditions to keep the chemical reaction stable. During production they need to be protected against compressor surge.
In addition to control functions independent safety functions are required to protect against hazardous incidents on the plant.