Method and apparatus for estimating relative proportion of wood chips species to be fed to a process for producing pulp

Abstract

Improved methods and apparatus for estimating and controlling relative proportion of wood chips originating from a plurality of sources characterized by various wood species, in a mass of wood chips to be fed to a process for producing pulp, use light reflection-related and density-related properties as input in a model characterizing a relation between such wood chip properties and species information. This principle allows efficient monitoring of the variation in wood species composition characterizing the wood chips to be processed, for the purpose of stabilizing chip feeding control and optimizing process parameters adjustment.

Description

FIELD OF THE INVENTION [0001] The present invention relates to the field of pulp and paper process automation, and more particularly to methods and apparatus for estimating and controlling relative proportion of wood chips originating from a plurality of sources characterized by various wood species, in a mass of wood chips to be fed to a process for producing pulp. BACKGROUND OF THE INVENTION [0002] Wood chips being one of the main raw materials entering into pulp production processes such as chemical (Kraft) and thermomechanical pulping (TMP) processes, variations in their physical properties have a direct impact on process control performance as well as on pulp and paper qualities. In the particular case of TMP processes, the quality of wood chips being fed to the refiners is of a great importance, since it is known to affect, along with process operating parameters, the rate of wear affecting refiner plates, as discussed by Myllyneva, J. et al. in “Fuzzy Control of Thermomechani...

AI Technical Summary

Benefits of technology

The present invention provides improved methods and apparatus for estimating and controlling the relative proportion of wood chips in a mass of wood chips to be fed to a process for producing pulp. The methods involve estimating the wood chip properties of the mass, such as light reflection-related properties and density-related properties, and using a model to characterize the relation between these properties and the wood chips of each source. The estimated relative proportion of wood chips is then used to control the discharge rate of the wood chip sources to optimize the process. The invention allows for efficient monitoring of wood chip composition and optimizes process parameters, resulting in improved production of pulp.

Problems solved by technology

While specific energy can in theory be kept constant through adjustments to motor load or production rate, in practice the absence of online data about dry wood chip / fibre volume and moisture content means that the control of this variable will be subjected to instability, as mentioned by Cluett, W. R., et al. in “Control and Optimization of TMP Refiners”, Pulp &Paper Canada, 96:5 (1995) pp.

Any variation in chip quality will be considered as disturbance in process control.

In fact, chip quality changes quite rapidly, and known control strategies cannot efficiently eliminate its influence, which prompts fluctuations of the three operational variables of the refining process mentioned above.

Wood species variation is an important factor that can negatively impact pulp quality.

The lack of wood chip quality data can cause operators to conclude that the problem is caused by refiner plate wear.

Although chip aging can be observed from chip brightness, it is only useful for substantially unvaried wood species.

However, these techniques cannot be used to evaluate a mixture involving more than two wood species.

However, it has been observed that such approach provides an estimation of the proportion of each species within a range of only about ±10%, which is generally insufficient to allow an efficient control over species variation in wood chips fed to the pulping process.

These off-line measurements are neither representative nor accurate.

Online direct pulp yield measurement is very difficult as stated by Hatton J. V in the above-cited paper.

This method is time consuming and requires well-trained operators and scientists, as well as ancillary equipment.

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