US 4,378,639 A · Method and apparatus for uniformly drying a continuous web of cellulosic fibers

Abstract

A method and apparatus used in the uniform drying of a continuous web, such as a sheet of paper or paperboard. A newly formed web of paper of wet cellulosic fibers and the necessary additives is initially directed through a press section where excessive water is squeezed from the web to reduce its moisture content to about 50-80 percent, by weight, for subsequent passage through a dryer section wherein the moisture content is further reduced to anywhere between 3 and 15 percent, depending on the quality of the paper being processed. The moisture content profile of the nearly dry web of paper is constantly monitored adjacent the discharge end of the dryer section for dry streaks which occasionally occur in the web. Moisture is added accordingly to the web when the web is relatively wet and has a moisture content of at least 25 percent to eliminate further dry streaks and provides a paper product which has a uniform moisture content.

Claims13

Dependent claims

A method of uniformly drying a continuous web of wet fibrous material as the web travels along a processing line, comprising:

(a) constantly monitoring the moisture content of the web to sense dry streaks therein below a certain desired moisture content, when the web is in a dry end of the line where the moisture content of the web is less than 20%, by weight, and
(b) adding moisture to the web in areas thereof which are spaced substantially upstream from the dry end and longitudinally aligned with any dry streaks sensed in the dry end of the line, the moisture being added in accordance with the moisture content of any such dry streaks, when the web is in a wet end of the line where the moisture content of the web is greater than 25%, and at least 50% greater than the moisture content thereof where monitored at the dry end of the line, and where the web moisture content is not less than 35% of its moisture content before drying is begun, the differential in moisture content between the area of moisture monitoring and the areas of moisture addition being at least 10%.

An apparatus used in the production of a continuous web of cellulosic fibers such as a sheet of paper or paperboard, comprising:

(a) means for forming wet cellulosic fibers into a continuous web;
(b) a press section for squeezing excess liquid from the web as it travels along a pathway;
(c) a dryer section through which the web travels along the pathway subsequent to passage through the press section, the dryer section including means for heating the web to reduce the moisture content thereof to a desired level where the moisture content is less than 10% to 15%;
(d) means for monitoring the web to sense dry streaks at a point along the pathway where the web has a moisture content less than 20%, a dry streak having a moisture content below a desired level whereat the web is monitored;
and
(e) means for adding moisture to the web at an area spaced substantially upstream from the dry end, and longitudinally aligned with a sensed dry streak at a point along the pathway where the web has a moisture content greater than 25% and at least 50% greater than the moisture content thereof where monitored at the dry end of the line, and where the web moisture content is not less than 35% of its moisture content before drying is begun, the difference in moisture content between the area of moisture monitoring and the areas of moisture addition being at least 10%.

3 more elements

Dependencies are inferred from the claim text.

Method and apparatus for uniformly drying a continuous web of cellulosic fibers

Life of this patent

Method and apparatus for uniformly drying a continuous web of cellulosic fibers

Life of this patent

Abstract

Claims13