Optimization of an Alkalinity Control Unit

Abstract: This master thesis project has been performed in cooperation with AGA, the well-known gas company which is a part of the German Linde group and the Department of Automatic Control, Lund Institute of Technology. Since summer 2000 AGA has developed and manufactured a fully automated reactor producing bicarbonate solution for stabilizing pH in papermaking processes. The reactor or ACU!22 (alkalinity control unit) is a part of a bigger application known as the ADALKA!22. Ever since that first installation of the ACU!22 the development has been going on and the aim of the thesis was, to check and improve the logics of the ACU!22 and the way the reactor is controlled. Since there are many ACU!22s running, but no test unit, only one ACU!22 has been examined in this thesis. If not other mentioned the ACU!22 refer to the mobile unit currently existing at the M-Real paper mill in Jyväskylä, Finland. The thesis resulted in a new control program, which included some new ideas based on more advanced control theory together with different logics. Modifications where made to the start up and stop sequences of the reactor as well as to the dilution part before the reactor. A different kind of pressure control for the reactor was implemented, tested and evaluated. The ACU!22 is operated from a panel, which was adjusted and fully configured to this new control program. The examination of the ACU!22's process image also contributed to the decision to change one of the control valves. This change had a big influence on the process. It became more stable. Since none of the control circuits were tuned prior to this work two of the most significant circuits were tuned.