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Thesis for the Degree of Master of Science

 

Year 2000
Valtteri Mustonen

Control Strategies of the Continuous Pressurised Three Phase Separating Tank


The continuous pressurised CTO-production (Crude Tall Oil) process developed in Rintekno Oy consists of a CSTR-type (Continuous Stirred Tank Reactor) acidification reactor and a separating tank. After the acidification reaction of solvent-bearing soap, the reaction mixture, which consists of three phases, is decanted. Raw tall oil is obtained as a product. The process has been implemented in the Kaukas research facilities of Sterol Technologies Oy. It has been noticed that the functioning of the process control is unsatisfactory. Control loops stabilise the controllable variables poorly and require the operator’‘s constant supervision.

The objective of this thesis is to study the dynamics of the process and to improve the controls in such a way that the process is better controlled. The work aims to find basic control loops and a solution which would reduce the constant supervision of the process. One objective was also to assess the instrumentation of the process.

The literature part of the thesis reviews the physical phenomena of the pressurised CTO-production process and the theory of the separatory event. In this part the dynamic modelling and development methods of dynamic models of similar processes were examined. The literature concerning basic controls and higher-level controls of similar processes was studied.

In the applied part of the thesis, a dynamic model of the process was developed. Modelling was based on step tests. With the help of the dynamic model, optimal control loops and control parameters were selected. In the process control system, higher-level pressure control was developed to reduce routine setpoint value changes made by the process operator. An informative expert system was included in the system.

It was observed that the basic controls had already been selected in the optimal manner. The obstacle to functionality was process technical deficiencies. The higher-level pressure control reduces the setpoint value changes made by the process operators. It gives information to operate the process at the correct pressure. This information was previously unavailable. It was noticed that the information system contains the right elements to automate the process. To develop the information system into a process supervision system more research is required. Suggestions for addition and change in the instrumentation of the process are given.


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