Method and apparatus for controlling wood chip digester level

Paper making and fiber liberation – Processes of chemical liberation – recovery or purification... – Continuous chemical treatment or continuous charging or...

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162 49, 162 52, 162238, 162243, 162246, 162262, 162263, 364110, 364116, 364509, 364551, 364562, D21C 706, D21C 708, D21C 712

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041417844

ABSTRACT:
A control system and a process is disclosed for a continuous wood chip downflow digestion system. The system maintains chip level in the top of the digester and maintains a consistency in the ratio of chips to liquor in the blowline thus allowing the system to run without constant operator attention. The system comprises a means for measuring the level of chips at the top of the digester and producing a level index over a predetermined time. This level index is compared with a preset level index and an error signal produced which operates a speed control means within preset limits for a rotating scraper feeding into the blowline. There is also provided a means for measuring the feed rate of chips to the digester, and a summating means for adding a predetermined ratio setpoint for the feed rate of chips against a flow in the blowline, to an integral of the error signal above or below a preset range to produce a summated ratio. The blowline flow is then controlled within preset limits to proximate the summated ratio to the feed rate of chips.

REFERENCES:
patent: 2938824 (1960-05-01), Richter
patent: 3617717 (1971-11-01), Smith
patent: 3650890 (1972-03-01), Kamio
patent: 3746843 (1973-07-01), Wesner
patent: 3898124 (1975-08-01), Olson
Fuchs et al., "Advances in Computer Control of Kamyr Continuous Digesters," Tappi; vol. 59, No. 2, Feb. 1976, presented Sep. 9-1975, (pp. 96-99).
Fuchs et al., "Blow Flow Control of Continuous Digesters," Tappi, vol. 54, No. 3; Mar. 1971, (pp. 368-371).
Fox; "Control Strategy;" Tappi, May 1966; vol. 49, No. 5, (pp. 87A-89A), May 1966.

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