Invariant System for Automatic Control of Low-Temperature Separation Process

The low-temperature separation (LTS) process is widely used for moisture and condensate removal in natural gas treatment and is typically controlled using local automation systems. However, the process is inherently multivariable, with strong cross-couplings between inputs and outputs, and is significantly affected by external disturbances. This study defines the control inputs as actuator signals on the gas and condensate outlet lines, while the outputs are the gas pressure and condensate level in the separator. Disturbances include variations in inlet gas pressure and condensate line pressure. A linearized mathematical model of the LTS process is developed, based on input–output and disturbance–output relationships. Using this model, an invariant automatic control system is synthesized, incorporating cross-coupling and disturbance compensators. The cross-coupling compensator ensures decoupling of control loops, while the disturbance compensator reduces the impact of external disturbances. The effectiveness of the proposed system is verified through simulation, confirming the validity of the theoretical approach and demonstrating improved control performance.