Method for controlling drying of a web-formed material
First Claim
1. A method for controlling drying of a web-formed material moving through a drying plant having a plurality of upper and lower blow boxes arranged in a plurality of drying decks, the web-formed material floating above the lower blow boxes, which at their upper sides blow out hot process air against the web-formed material, thereby drying the web-formed material, comprising:
- detecting water content in the web-formed material downstream of the blow boxes;
blowing process air on the web-formed material, wherein water escaping from the web-formed material is mixed with and discharged by the process air;
re-circulating at least part of the process air, whereas the a non-circulated part of the process air is discharged as exhaust air, replacing the discharged exhaust air with a corresponding portion of supply air controlling the temperature of the process air, determining a deviation from a desired water content of the dried web-formed material by comparing the desired water content to the sensed water content;
changing the volume flow of the process air in accordance with the deviation, whereby the volume flow of the process air is increased when the water content in the web-formed material is too high, and the volume flow of the process air is decreased when the water content in the web-formed material is too low, thereby rapidly regaining the desired water content of the dried web-formed material.
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0 Petitions
Accused Products
Abstract
A web-formed material (1), preferably a pulp web (1), is passed through a drying plant, comprising blow boxes arranged in a plurality of drying decks, floating above lower blow boxes, which at their upper sides blow out hot process air against the web-formed material (1). Water, in the form of steam, escaping from the web-formed material (1) is discharged by the process air, at least part of which is recirculated (43) whereas the non-recirculated process air is discharged as exhaust air (41) and is replaced by a corresponding portion of supply air (42) with a low water content. The temperature of the process air is controlled (4). If a deviation from the desired dry content of the dried web-formed material (1) is detected (6), the volume flow of the process air (40) is changed by increasing the volume flow of the process air (40) at too low a dry content in the web-formed material (1), and by decreasing the volume flow of the process air (40) at too high a dry content in the web-formed material, for the purpose of rapidly regaining the desired dry content of the dried web-formed material (1).
20 Citations
12 Claims
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1. A method for controlling drying of a web-formed material moving through a drying plant having a plurality of upper and lower blow boxes arranged in a plurality of drying decks, the web-formed material floating above the lower blow boxes, which at their upper sides blow out hot process air against the web-formed material, thereby drying the web-formed material, comprising:
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detecting water content in the web-formed material downstream of the blow boxes;
blowing process air on the web-formed material, wherein water escaping from the web-formed material is mixed with and discharged by the process air;
re-circulating at least part of the process air, whereas the a non-circulated part of the process air is discharged as exhaust air, replacing the discharged exhaust air with a corresponding portion of supply air controlling the temperature of the process air, determining a deviation from a desired water content of the dried web-formed material by comparing the desired water content to the sensed water content;
changing the volume flow of the process air in accordance with the deviation, whereby the volume flow of the process air is increased when the water content in the web-formed material is too high, and the volume flow of the process air is decreased when the water content in the web-formed material is too low, thereby rapidly regaining the desired water content of the dried web-formed material. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A method for controlling the moisture content of a web-formed material comprising the steps of:
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moving the web-formed material through a drying section;
supplying the drying section with process air at a predetermined flow rate selected to dry the web-formed material sufficiently to achieve a desired moisture content;
sensing moisture content of the web-formed material as it leaves the drying section;
determining deviations from the desired moisture content based on a difference between the desired moisture content and the sensed moisture content;
changing the flow rate of the process air in accordance with the deviations from the desired moisture content, such that the flow rate is increased when the deviation is such that the sensed moisture content is higher than the desired moisture content, and the flow rate is decreased when the deviation is such that the sensed moisture content is lower than the desired moisture content; and
increasing the temperature of the process air when the flow rate is increased, thereby increasing the drying capabilities of the process air, and decreasing the flow rate of the process air as the sensed moisture content decreases.
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Specification