Abstract: A technique for controlling the amount of dissolved material in a slurry liquid stream containing dispersed particulate solids which is being continuously processed in a zone of countercurrent particulate solids separation and washing. Flow rates and conductivity measurements are made on streams entering such zone which are then used to estimate the amount of dissolved material in a starting slurry liquid. Preferably, conductivity measurements are made with electrodeless conductivity measuring probes. The technique is well adapted for use in a brown stock washing system employing a plurality of counterflow washers. The technique can be used for measurement of the quantity of gas in an agitated process stream in such a zone.

Abstract: A method and apparatus are provided for automatically and simultaneously controlling the solution viscosity and degree of brightness of a pulp during a bleaching process which employs a sequence of chlorination, hypochlorite and chlorine dioxide bleaching reagents. The pulp is monitored during the bleaching sequence by employing an optical device utilizing reflected light of one or two wavebands. The optical monitoring device electronically feeds a control signal to a regulator or computer which regulates the input of one or more of the bleaching reagents. The amounts of reagents added are based upon and made possible by relationships which have now been determined between the light reflectance values of the pulp at various stages of the process and desired viscosity and brightness values. The viscosity is controlled by controlling the hypochlorite addition and the brightness of the fully bleached pulp is controlled by chlorine dioxide addition.

Abstract: In a multi-stage bleaching system in which respective bleaching chemicals are added to the stock in various stages, apparatus in which in the first stage in which chlorine is added to the brown stock, the first of a pair of sensing units associated with the stage comprises a source of red light directed onto the incoming brown stock and a suitable detector for sensing light scattered from the stock to produce a first signal representative of the brightness of the incoming stock and the second similar sensing unit of the pair senses the brightness of the stock immediately following the addition of chlorine to produce a second signal. The first and second signals are compared to produce a difference signal indicative of the change in brightness independently of the condition of the incoming stock and this difference signal is compared with a set point standard to provide a control signal for regulating the addition of the chlorine to the brown stock.

Abstract: To achieve constant brightness from the chlorine stage of a wood pulp bleaching system, the chlorine addition rate is controlled by two white light photosensors positioned, respectively, 1-5 minutes downstream of the chlorine addition point and immediately prior to the chlorine washers. A relative error signal from the late photosensor is cascaded upon the set-point of a signal differentiator for the early photosensor to generate a chlorine valve control signal. The photosensors comprise selenium photocells positioned against a transparent stock conduit window and reflection illuminated by a low power white light source positioned more remotely from the window than the photocell at a discreet offset angle relative thereto. The white light is directed past the photocells, through the windows and into the flow stream; the photocells being responsive to the relative magnitude of white light reflected from the wood pulp. The power generated from the photocell is correlated to the pulp brightness.

Abstract: A method is provided for controlling the amount of oxidizing bleaching agents in liquors used within the cellulose industry, as in the bleaching of sulphite, sulphate, mechanical, chemimechanical, semichemical or similar cellulose pulps, and in related industries, and particularly for controlling the addition of oxidizing bleaching agents to the system during the bleaching of cellulose pulp by mixing such liquor with at least one chemiluminescent reagent which reacts with the oxidizing bleaching agents in a manner to emit light. The amount of oxidizing bleaching agents in the liquor is then determined by comparison of the light intensity thus obtained with the light intensity for previously measured calibration values corresponding to known quantities of such oxidizing bleaching agents, and then from such determination controlling the addition of such oxidizing bleaching agents to the liquor.