Optimisation of deacidification control


Optimisation of deacidification control.

Result: 80% reduction in pressure variations
When producing cokes for ironmaking, furnace gases escape that must be cleaned. One of the installations to clean the gas is a deacidification/stripping process that involves multiple destillation columns, fed by the cokes gas and steam. The process engineers of this particular plant discovered that reducing the pressure variations in the steam feed would lead to improved process stability which, in turn, would lead to major cost reductions. DotX was assigned to improve the stability of the pressure control loop(s). First, the existing control system was analysed and the steam process was modelled carefully. The steam pressure was controlled mainly by two seperate control systems, each acting on one valve. One for exhausting steam, and one to feed steam. Each valve showed a nonlinear characteristic (i.e. a nonlinear relation between valve opening and flow). Then, a new model based control system was designed, and implemented over three PLCs, communciating witch each other. The new controller showed a remarkable improvement in pressure stability, see the figure below (showing scaled measurements): as soon as the DotX Control solution is activated, the pressure is almost constant; as soon as it is deactivated, the old controller takes over and the pressure shows increased variations. This DotX controller has been activated in August 2012 and since then, the deacidification/stripping process now runs much more stable

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