Process for regulating a screw press

Details Process for regulating a screw press Process for regulating a screw press

1999-02-10

2001-04-17

Silverman, Stanley S. (Department: 1731)

Paper making and fiber liberation

Processes and products

With measuring, inspecting and/or testing

C162S198000, C162S252000, C162S254000, C162S262000, C162S263000, C162S264000, C162SDIG004, C100S110000, C100S145000

Reexamination Certificate

active

06217710

ABSTRACT:

BACKGROUND OF THE INVENTION
The invention relates to a process for regulating a screw press, particularly for dewatering a pulp suspension.
In current screw presses, the level is measured in the feed box. If the level rises, either the screw press speed is increased or the infeed of suspension to be dewatered is reduced. This is primarily the case in sludge dewatering presses because they have very long retention times and any change in the filling level does not have any effect until after this retention period, which is in the range of 20 minutes.
In pulp screw presses, a torque controller is normally used. This keeps the torque at a constant level regardless of speed and throughput. On the other hand, the regulating efficiency is relatively poor, as is then reflected in the power consumption by the subsequent mixer. The reason for substantial fluctuations in the power consumption is the varying outlet dry content, which is lower at high speed and higher at low speed.
SUMMARY OF THE INVENTION
The aim of the invention is always to obtain a constant final dry content, also at fluctuating feed conditions. In addition, the invention should provide constant operating conditions without any build-up of operating parameters.
The invention is thus characterised by the speed being varied as a function of the torque, where the regulating process can be applied according to a torque characteristic curve. This ensures that the dry profile of the pulp suspension remains even along the screw axle, even at different production rates.
A favourable further development of the invention is characterised by the nominal speed being increased when the torque rises. If the amount of pulp fed to the press increases, the screw has a higher filling level and the torque increases. The result would be a higher outlet concentration. By raising the nominal speed of the press, the filling level drops accordingly and the outlet concentration remains constant.
A favourable configuration of the invention is characterised by the speed being maintained at a constant level if the torque changes within a pre-set range. As a result, any build-up of operating parameters as a result of the regulating process can be prevented.
An advantageous configuration of the invention is characterised by the counter-pressure being reduced if the torque is rising. This means that constant operations can be achieved quickly, particularly in the starting phase.
An advantageous further development of the invention is characterised by the torque being varied in the range of 1 to 6, preferably 1 to 3. The regulating process is particularly stable within this torque range.
A favourable further development of the invention is characterised by the speed being varied in the range of 1 to 4, preferably 1 to 2.5. As a result, a constant regulating process can be achieved even if production fluctuates erratically, which means that the power consumption by a subsequent mixer is also very constant.


REFERENCES:
patent: 3548743 (1970-12-01), Pikel
patent: 3938434 (1976-02-01), Cox
patent: 4041854 (1977-08-01), Cox

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