Using improved control schemes to utilise the buffering capacity in gas headers to absorb upstream disturbances
A spectral element method (SEM) model was developed and validated using measurements from a real process for simulation and control applications. The figures show that model is complex enough to represent a real header process accurately, but simple enough to be implemented practically.
The importance and optimal placement of pressure measurement locations on the gas headers for buffering control is determined through the combined use of the SEM model collocation points, an extended kalman filter (EKF), and a staggered pressure control scheme in a self-optimising control (SOC) framework. The figures show that the optimal pressure measurement location was found to be dependant on the distance from the flow disturbances and final control elements as well as the individual importance of consumer flow stability, expensive supplier use and gas emissions.
Suitable control strategies to reduce gas emissions and improve flow stability for consumers were investigated and compared using the SEM model and a Monte Carlo simulation.The figures show the effect of variance in the gas properties on the total cost using the Sobol method. A chosen buffering control scheme was implemented on a real gas header and compared with standard PI control. The figures show that the chosen scheme (CLMPC) reduced emissions and improved consumer stability by intelligently utilising the available pressure buffering capacity in the industrial gas headers.
All these figures therefore show that: it is possible and beneficial to mitigate flaring and improve consumer stability in industrial gas headers through the use of suitable pressure buffering control strategies, that the pressure measurement location impacts the performance of the control strategy and can be provided through a SOC framework using the combination of suitable state estimators and the SEM model developed, and that the SEM model accurately represents real industrial gas header dynamics and is suitable for use in practical control and simulation applications.