Chemistry: physical processes – Physical processes – Crystallization
Patent
1978-06-07
1980-12-16
Serwin, R. E.
Chemistry: physical processes
Physical processes
Crystallization
364500, 422 62, 422108, G05B 1302, G05D 2102
Patent
active
042394937
ABSTRACT:
The invention relates to a method and apparatus for controlling the pH in a continuous flow vessel into which process material is fed through a feed channel and controlling chemical solution is fed through a control channel and in which the pH is measured at an output part of the vessel in order to effect the control by controlling the control chemical feed according to the feedback method, the value of a reference variable being given by a pH number. According to the invention the result of the pH measurement as well as the reference value are transformed to the hydrogen ion concentration or to another concentration quantity unambiguously depending on said hydrogen ion concentration, a final feedback quantity is determined by means of an equation describing dissociation equilibria in the solution, said feedback quantity being a function of the concentration quantity derived from the pH measurement and eventually a function of an independent concentration quantity derived from an other measurement at the vessel output, a final reference value is determined by means of said equation, said final reference value being a function of the concentration quantity derived from the initial reference value, and, eventually, a function of the independent concentration quantity mentioned, a control deviation is formed as the difference between said final reference value and said final feedback quantity, and, finally the feed of the controlling chemical is controlled on the basis of said control deviation, typically using a linear controller and an actuator controlled thereby.
REFERENCES:
patent: 3791793 (1974-02-01), Friedmann et al.
patent: 3899294 (1975-08-01), Magiros
patent: 4053743 (1977-10-01), Niemi
Shinskey, et al., "Adaptive Feedback Applied to Feedforward pH Control," 1970 Phila. ISA Conf., Preprint, pp. 565-570.
Wilson, H. S. et al., ISA Preprint 11. 1-2-64, 10/12/64.
Jutila Pentti K.
Niemi Antti J.
Jutila Pentti
Serwin R. E.
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