Method for controlling the pH and other concentration variables

• US 4,053,743 A
• Filed: 02/18/1976
• Issued: 10/11/1977
• Est. Priority Date: 02/18/1976
• Status: Expired due to Term

• Current Assignee: Antti Johannes Niemi
• Original Assignee: Antti Johannes Niemi
• Inventors: Niemi, Antti Johannes
• Primary Examiner(s): Ruggiero, Joseph F.
• Application Number:
  US05/658,897
• Time in Patent Office: 601 Days
• Field of Search: 235/151.12, 235/151.1, 235/150.1, 23/230 R, 23/230 A, 23/253 R, 23/253 A, 23/255 R, 23/255 E
• US Class Current: 700/267
• CPC Class Codes: G01N 31/00 Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
• CPC Class Codes: G05D 21/02 characterised by the use of electric means

Abstract

In a chemical reactor or analogous apparatus, a tank or similar system, pH and other concentration variables are controlled by a method wherein -- when at least one desired outlet concentration or a function dependent on outlet concentrations is given -- initially, the apparent output concentration of at least one feed component is calculated with the aid of the inlet concentration and the residence-time distributioned either the requisite feed concentration or flow of each control component with the aid of a control algorithm based on the residence-time distribution of said control component between its feed point and the outlet point of the reactor, or the control of each actuating variable that substantially affects a physical control, with the aid of an appropriate control algorithm; whereby other corresponding mathematical representations, e.g., time-variable and approximative representations are also considered as the said residence-time distributions, and the said residence-time distributions can also be equal and/or all but at least one of them can be replaced with a constant or flow-dependent time delay, or may even be overlooked; and finally, the corresponding control steps are effected. Said equilibrium dependences, from which the requisite apparent output concentration of each component is calculated, may preferably comprise a group of material balances and equilibrium equations, experimentally determined curves, or numerically expressed experimental dependences.

Claims

1. A method for controlling concentration variables of process material in a chemical reactor containing reactants which reach thermodynamic equilibrium substantially simultaneously, the reactor having at least one process inlet flow through the inlet, one process outlet flow through an outlet, and one control inlet flow, further at least one desired outlet concentration being provided, the method comprising the steps of:

a. measuring the concentration of at least one reactant of the process material in the process inlet flow, and the concentration of a reactant of a control material in the control inlet flow;

b. providing a residence-time distribution function for the process material flow from said inlet to said outlet, and a residence-time distribution function for the control material flow from said control inlet to said outlet;

c. calculating an apparent outlet concentration of said at least one reactant of the process material and an apparent outlet concentration of said reactant of the control material with the aid of the respective measured inlet concentration and the respective residence-time distribution function in accordance with the following relationship;

##EQU7## g = residence-time distribution (weighting function) C_i = concentration of component i in the outlet channel

C_in = inlet concentration

t,0 = time variables

d. assuming thermodynamic equilibrium and utilizing said provided desired outlet concentration of the preamble as well as said apparent outlet concentration of said at least one reactant of the process material in step (c), calculating a desired apparent concentration of said reactant of the controlled inlet flow at said outlet; and

e. controlling the control inlet flow by means of a feedback control, like a proportional, integral and derivative PID control, on the basis of the difference between said apparent outlet concentration of the control reactant in step (c) and said desired apparent outlet concentration of said control reactant in step (d).

2. The method according to claim 1 wherein the thermodynamic equilibrium from which the desired apparent outlet concentration of each reactant of the control inlet flow is calculated comprises a group of material balances and equilibrium equations.

3. The method according to claim 1 wherein the thermodynamic equilibrium from which the desired apparent outlet concentration of each reactant of the control inlet flow is calculated comprises experimentally determined dependencies.

4. The method according to claim 1 in which step (a) is carried out by measuring the pH of said process inlet flow from which is calculated the concentration.

5. A method for controlling concentration variables of process material in a chemical reactor containing reactants which reach thermodynamic equilibrium substantially simultaneously, the reactor having at least one process inlet flow through an inlet, one process outlet flow through an outlet, and one control inlet flow, further at least one desired outlet concentration being provided, the method comprising the steps of:

a. measuring the concentration of at least one reactant of the process material in the process inlet flow;

b. providing a residence-time distribution function for the process material flow from said inlet to said outlet, and a residence-time distribution function for the control material flow from said control inlet to said outlet;

c. assuming thermodynamic equilibrium and utilizing said provided desired outlet concentration of the preamble, calculating a constant factor equivalent to the coefficient of linear dependence between the concentrations of the process and control reactant; and

d. controlling the control inlet flow on the basis of the measured concentration of said reactant in step (a) multiplied by a control function, said control function being defined by its Laplace transformation being equivalent to the ratio of Laplace transformations of the residence-time distributions of the process material and of the control reactant in turn multiplied by said constant factor in step (c).

6. The method according to claim 5 wherein the thermodynamic equilibrium from which the desired apparent outlet concentration of each reactant of the control inlet flow is calculated comprises a group of material balances and equilibrium equations.

7. The method according to claim 5 wherein the thermodynamic equilibrium from which the desired apparent outlet concentration of each reactant of the control inlet flow is calculated comprises experimentally determined dependencies.

8. The method according to claim 5 in which step (a) is carried out by measuring the pH of said process inlet flow from which is calculated the concentration.

9. A method for controlling concentration variables of process material in a chemical reactor containing reactants which reach thermodynamic equilibrium substantially simultaneously, the reactor having at least one process inlet flow through an inlet, one process outlet flow through an outlet, and one control inlet flow, further at least one desired outlet concentration being provided, the method comprising the steps of:

a. measuring the concentration of a least one reactant of the process material in the process inlet flow;

b. providing a residence-time distribution function for the process material flow from said inlet to said outlet, and a residence-time distribution function for the control material flow from said control inlet to said outlet;

c. assuming thermodynamic equilibrium and utilizing said provided desired outlet concentration of the preamble, calculating a constant factor equivalent to the coefficient of linear dependence between the concentrations of the process and control reactant; and

d. controlling the control inlet flow on the basis of the measured concentration of said reactant in step (a) multiplied by a control function, said control function being defined by its Fourier transformation being equivalent to the ratio of Fourier transformations of the residence-time distributions of the process material and of the control reactant in turn multiplied by said constant factor in step (c).

10. The method according to claim 9 wherein the thermodynamic equilibrium from which the desired apparent outlet concentration of each reactant of the control inlet flow is calculated comprises a group of material balances and equilibrium equations.

11. The method according to claim 9 wherein the thermodynamic equilibrium from which the desired apparent outlet concentration of each reactant of the control inlet flow is calculated comprises experimentally-determined dependencies.

12. The method according to claim 9 in which step (a) is carried out by measuring the pH of said process inlet flow from which is calculated the concentration.