RU2190715C1 - Method for leveling pulp admitted onto papermaking machine screen - Google Patents

Abstract

FIELD: pulp-and-paper industry. SUBSTANCE: method involves distributing pulp over width of pressure box in collector pipe section; separating portion of pulp and providing flow of pulp over partition wall of air chamber; turbulizing pulp in turbulence section and regulating pulp admittance rate by deforming plank in admittance opening; dividing separated portion of pulp into number of local streams over the width of pressure box; providing flow of each stream over separate partition wall and regulating flow rate of local streams by moving respective partition walls. Pulp mass between collector pipe and turbulence sections may be divided into row of longitudinal flows over width of pressure box. Method allows paper web quality to be increased by improved pulp leveling. EFFECT: simplified method and increased efficiency. 2 cl, 6 dwg, 1 tbl

Description

 The invention relates to methods for leveling the pulp poured onto the grid of a paper machine, and can be used in the pulp and paper industry for the production of paper and cardboard.

 A known method of leveling the pulp poured onto the grid of a paper machine, including distributing the mass across the width of the headbox in the collector-tubular section, separating part of the mass with its overflow through the overflow baffle of the air chamber, turbulence of the mass in the turbulent section and adjusting the rate of its inlet by deformation of the bar in the inlet lip [Patent SU 694087, cl. D 21 F 1/02, publ. 10.25.79, BI 39].

 In the known method, the mass is distributed across the width of the headbox in the collector-tubular section and flows out of it with an uneven distribution over the width of the headbox and over time. Before the turbulent section, part of the mass is separated from the main stream by a single continuous flow, poured over the overflow partition of the air chamber and leaves the chamber through the side pipe. In this case, the total flow rate of the separated part of the mass is regulated by moving the overflow partition. When separating part of the mass into the air chamber, the uneven distribution of mass over time is suppressed, so that the main stream enters the turbulent section with a flow rate equal in time. In the turbulent section, the mass is turbulent, due to turbulent mixing, the unevenness of the flow when it enters the inlet lip decreases. The final alignment of the mass is made by adjusting the rate of its inlet by deforming the bar along the width of the headbox installed on the end of the inlet lip.

 The disadvantage of this method is the low quality of the formed web due to insufficient alignment of the mass that is poured onto the machine’s grid along the width of the headbox.

 A low degree of mass equalization is caused by the fact that when a part of the mass is separated by a single stream from the main stream with its subsequent overflow through the overflow partition, the flow does not equalize along the width of the headbox, so that the flow flowing into the turbulent section is aligned only in time, but not in time headbox width. The movement of the septum regulates the total percentage of the separated mass, but does not equalize the main flow. Local deformation of the strap does not completely compensate for the mass unevenness in the headbox and the mass goes to the machine grid with an insufficient degree of alignment, which leads to large deviations of the square meter mass from the set value.

 The invention provides an increase in the quality of the formed web due to a decrease in the unevenness of its mass per square meter by increasing the degree of alignment of the mass poured onto the machine’s grid along the width of the headbox.

 The essence of the invention lies in the fact that in the method of leveling the pulp poured onto the machine grid, including distributing the mass across the width of the headbox in the collector-tubular section, separating part of the mass with its subsequent overflow through the overflow partition of the air chamber, mass turbulence in the turbulent section and regulation of the rate of its inlet by deformation of the strap in the inlet lip, the detachable part of the mass is divided into a number of local flows along the width of the head box with the subsequent overflow of each flow h through a separate overflow partition and regulate the costs of local flows by moving the corresponding overflow partitions. In this case, the mass between the collector-tubular and turbulent sections is divided into a number of longitudinal flows along the width of the headbox.

 In the method of leveling the mass, increasing its degree of leveling is ensured by dividing the separated part of the mass into local flows and independently controlling the flow rate of each of them with high accuracy, so that the flow rate of the mass entering the turbulent section is the same in width of the headbox.

In figure 1, 2, 3 shows a diagram of mass flows by the proposed method:
in FIG. 1 - headbox that implements the proposed method;
in FIG. 2 and 3 are a cross-sectional view in FIG.

In FIG. 4, 5, 6 depict mass flow diagrams of the proposed method with dividing the mass between the collector-tubular and turbulent sections into a number of longitudinal flows:
in FIG. 4 - headbox that implements the proposed method;
in FIG. 5 and 6 are a cross-sectional view of FIG. 4.

In the headbox that implements the proposed method, the mass enters the manifold-tubular section 1, where it is distributed across the width of the headbox and flows out of it with an uneven distribution in width and time of flow Q _to . In front of the turbulent section 2, part of the mass is separated from the main stream and divided into a number of local flows between the separation walls 3 installed in the air chamber 4. Local mass flows are poured through separate overflow partitions 5, which can be moved using mechanisms 6 (for example, in a straight line in Fig. 1 or around the circumference of Fig. 4). Merging into the general flow, the mass is removed from the air chamber through the side pipe 7. When separating part of the mass into the air mass, the non-uniformity of the flow rate Q _about in time of the mass flow entering the turbulent section is suppressed. The movement of the overflow partitions controls the height Z _{i of the} overflow of mass for each local flow, counted from the horizontal bottom of the headbox. The flow rate Q _{pi of} each separated local stream, with a change in height Z _i , changes in accordance with the Bernoulli equation and the flow rate balance.

ΔP / (ρ • g) = Z _i + C _in • Q $\genfrac{}{}{0ex}{}{\text{2}}{\text{pi}}$ ;
Q _pi = Q _ki -Q _oi ,
where ΔP is the same across the width of the headbox of the difference in mass pressure before entering the air chamber and air pressure in the air chamber;
C _in - the input impedance of the air chamber that is the same across the width of the headbox
О _кi , Q _oi - respectively, the local mass _flow rate in front of the air chamber and after it before entering the turbulent section in the zone located opposite the i-th overflow partition.

When leveling the mass by controlling the flow rate Q _{pi of} local flows, the flow Q _oi should be the same across the width of the headbox in all n-zones
Q _o1 = Q _o2 ... = Q _oi ... = Q _on ,
where n is the number of overflow partitions.

From the differentiation of the first two equations, taking into account the last equality, it follows:
ΔZ _i = -2 • C _in • • (Q _t / n) • ΔQ _ki
ΔQ _ki - uneven distribution of mass flow over the width of the headbox in front of the air chamber in the area located opposite the i-th overflow partition;
ΔZ _i - change in overflow height when moving the i-th overflow partition, eliminating the unevenness ΔQ _ki ;
Q _t - average flow rate of the mass removed from the air chamber through the side pipe.

From the last equality it follows that a linear dependence of the change in the position of the regulatory body (ΔZ _i - overflow partition) on the degree of uneven flow ΔQ _ki in each zone of the headbox with a width approximately equal to the width of the overflow partition is ensured. This ensures high accuracy of the alignment of the mass entering the turbulent section.

 For more accurate flow equalization, the mass between the collector-tubular and turbulent sections is divided into a number of longitudinal flows along the width of the headbox using longitudinal partitions 8 (Figs. 4, 5, 6). This avoids the occurrence of cross-flows, which can occur in adjacent controlled areas when the local flows are separated from the main flows into the air chamber.

 Aligned with a sufficient degree of accuracy, the mass enters the turbulent section, is turbulent in it and enters the inlet lip 9, further leveled by turbulent mixing. The final alignment is done by adjusting the speed of its inlet onto the paper machine grid by deforming the bar 10 mounted on the end of the inlet lip. Since the strip completely compensates for the residual unevenness of the flow, and the mass enters the grid with a uniform flow, which ensures high quality of the formed web.

 Example. Molded paper with a given mass per square meter of 100% sulfite bleached pulp used in the production of printed types of paper, in a laboratory setting using a headbox according to the method of the prototype and the same headbox (figure 1, 2, 3) with installed in it air chamber dividing and mobile partitions according to the proposed method. Additionally, longitudinal partitions were installed between the collector-tubular and turbulent sections, dividing the mass into a number of longitudinal flows between them.

 During the tests, the minimum deviation of the square meter mass from the set value was achieved by deforming the strap in the inlet lip according to the prototype method and according to the proposed method by simultaneously deforming the strap and moving the overflow partitions. The test data are shown in the table.

 From the presented data it follows that the proposed method provides, in comparison with the known, reducing the unevenness of the mass of sq.m. molded web.

Claims (2)

 1. A method of leveling the pulp poured onto the paper machine grid, including distributing the mass across the width of the headbox in the collector-tubular section, separating part of the mass with its subsequent overflow through the overflow baffle of the air chamber, turbulizing the mass in the turbulent section and adjusting the rate of its inlet by deformation straps in the inlet lip, characterized in that the detachable part of the mass is divided into a number of local flows along the width of the head box with subsequent overflow of each flow h through a separate overflow partition and regulate the costs of local flows by moving the corresponding overflow partitions.  2. The alignment method according to claim 1, characterized in that the mass between the collector-tubular and turbulent sections is divided into a number of longitudinal flows along the width of the headbox.

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