Drying system

Abstract

A drier for drying boards (32) comprises at least one conduit (34, 40) for directing airflow towards one of the faces of the board (32). The drier is configured such that at least a portion of the airflow travels across the face of the board (32) along the longitudinal axis of the drier, the longitudinal axis of the drier being the axis along which the board (32) travels as it is dried.

Claims

1. A drier for drying a board, the board having two principal surfaces that are opposed to each other, the drier comprising: rollers for conveying the board along a longitudinal direction of the drier, the rollers further being for supporting the board in a support plane containing the longitudinal direction of the drier; air inflow means for directing airflow towards the principal surfaces of the board, the air inflow means comprising a lower conduit and a upper conduit, the lower and upper conduits each having a substantially rectangular cross-section and each extending transversely to the longitudinal direction of the drier, the lower conduit having a plurality of apertures for directing airflow towards an underside of the board and the upper conduit having a plurality of apertures for directing airflow towards an upper side of the board; wherein the combined cross-sectional area of the upper and lower conduits at their respective airflow inlets is at least 40% of the unit area of the drier, the unit area being a quadrilateral having: one side equal to the distance between the axis of the roller immediately preceding the lower conduit, in the direction of travel of the board, and the axis of the roller immediately following the lower conduit, in the direction of travel of the board; and another side equal to the distance between the uppermost portion of the upper conduit and the lowermost portion of the lower conduit; wherein the width of the lower conduit in the longitudinal direction of the drier is less than the width of the upper conduit in the longitudinal direction of the drier; and further wherein the cross-sectional area of the lower and upper conduits at a given distance along the transverse direction of the drier is the same.

2. A drier according to claim 1, wherein said lower and upper conduits each have a planar face facing towards the support plane, the plurality of apertures associated with each respective conduit being provided in the respective planar face of that conduit, the planar face of the lower conduit being narrower than the planar face of the upper conduit.

3. A drier according to claim 2, wherein the width of the lower conduit in the longitudinal direction of the drier is less than 90% of the width of the upper conduit in the longitudinal direction of the drier.

4. A drier according to claim 1, further comprising a panel that is aligned with the longitudinal direction of the drier and intersects the support plane, the panel being for enhancing airflow in the longitudinal direction of the drier.

5. A drier according to claim 3, wherein a panel is provided at the downstream end of the conduits, relative to the direction of airflow along the conduits.

6. A drier according to claim 1, wherein the cross-sectional area of at least one of the lower and upper conduits decreases in a transverse direction of the drier.

7. A drier according to claim 5, wherein at least one of the lower and upper conduits has a cross section that decreases continuously in a transverse direction of the drier, for at least part of the length of the at least one conduit.

8. A drier according to claim 1, wherein at least 90% of the plurality of apertures provided in the lower conduit are distributed within two bands extending along the length of the conduit, the bands being provided in the lateral portion of the conduit and each band having a width that is about 18% of the total width of the conduit.

9. A drying system comprising a drier according to claim 1, the system being configured such that the airflow directed by the air inflow means is heated using thermal energy recovered from an exhaust conduit provided within the system.

10. A drying system according to claim 8, the system comprising a heat pump for transferring thermal energy from the exhaust to the air inflow means.

11. A system according to claim 8, wherein an exhaust conduit provides an outlet for steam generated by a drying chamber located up-stream or downstream of said drier.

Description

(1) The invention will now be described by way of example with reference to the following Figures in which:

(2) FIG. 1 is a schematic plan view of a drying system according to a first embodiment of the second aspect of the invention;

(3) FIG. 2 is a schematic section view of part of a drier, according to a first embodiment of the first aspect of the invention;

(4) FIG. 3 is a schematic section view taken along the line A-A of FIG. 2 and including multiple drier levels.

(5) Referring to FIG. 1, a drying system 10 has multiple drying chambers 12 arranged in sequence. Gypsum boards to be dried pass along this sequence in turn, starting in a pre-drying region 14, before passing through a main drying region 16 and finally a finishing zone 18.

(6) The main drying region 16 is heated using gas burners, while the chambers in the pre-drying and finishing regions 14, 18 are heated through heat exchangers. The heat exchangers use heat that is recovered from the exhaust of the main drying region 16. Thermal energy may be recovered from the exhaust of the main drying region 16 using a heat pump 22.

(7) Referring to FIGS. 2 and 3, a drier has rollers 30a, 30b that support a gypsum board and cause it to move through the drier (e.g. from left to right in FIG. 2). The rollers are provided in multiple sets 30, each set of rollers defining a different plane for supporting a respective board. A group of four rollers 30a, 30b, 30c, and 30d defines a unit area against which the cross-sectional area of the nozzle boxes is compared.

(8) Lower nozzle boxes 34 provide airflow conduits for supplying heated air to the underside of a respective gypsum board 32 via apertures 36, 38. Upper nozzle boxes 40 provide airflow conduits for supplying heated air to the upper side of a respective board 32 via apertures 42, 44. The apertures are provided in the surface of the respective nozzle box that faces the board to be dried. The upper and lower nozzle boxes are aligned with the rollers 30a, 30b, such that they extend in a transverse direction of the drier (that is, into the plane of FIG. 2).

(9) The terms lower nozzle box and upper nozzle box denote the position of the nozzle box relative to the board that experiences airflow from that nozzle box.

(10) The upper and lower nozzle boxes 34, 40 are each provided with a set of multiple apertures, the set of multiple apertures extending along the length of the respective nozzle box. The apertures are provided in the face of the nozzle box that is opposed to the respective board.

(11) The nozzle box further has sides that extend away from the respective board, towards the back face of the nozzle box.

(12) At least 90% of the apertures provided on the lower nozzle box 34 are located within 30 mm of the sides of the nozzle box. Thus, at least 90% of the apertures are located within two bands extending adjacent to the sides of the nozzle box, and each band having a width that is about 18% of the total width of the nozzle box. This arrangement helps to ensure that air exiting the apertures 36, 38 flows towards the rollers and down the sides of the nozzle box. That is, air exiting the apertures of the lower nozzle box 34 initially flows in a generally longitudinal direction of the drier, rather than along the length of the nozzle boxes.

(13) The upper nozzle boxes are about 40% wider than the lower nozzle boxes, and thus extend over a greater area of the respective gypsum board 32. This arrangement helps to ensure that air exiting the apertures 42, 44 flows towards the closest edge of the upper nozzle and up the sides of the nozzle. That is, air exiting the apertures of the upper nozzle initially flows in a generally longitudinal direction of the drier, rather than along the length of the nozzle boxes.

(14) The width of the lower nozzle boxes 34 is such they each fit between an adjacent pair of rollers 30, 30b.

(15) The height of the upper nozzle boxes 40 is less than that of the lower nozzle boxes 34, with the result that the cross-sectional area of the upper and lower nozzle boxes is the same. This helps to ensure a homogenous air distribution to both the upper and lower faces of the board.

(16) Referring to FIG. 3, the upper and lower nozzle boxes 40, 34 are aligned with the rollers 30, and hence extend transversely to the direction of travel of the gypsum boards 32. Air enters the nozzle boxes at an air inlet 50, travels along the nozzle boxes and is directed towards the gypsum boards 32 by a plurality of apertures located on the face of the nozzle that is opposed to the respective gypsum board. The upper and lower nozzle boxes taper in a direction away from the air inlet 50, that is, in a downstream direction. However, the face of the nozzle box that is opposed to the respective gypsum board remains aligned with the gypsum board.

(17) The taper of the upper and lower nozzle boxes 34, 40 helps to reduce the pressure differential along the length of the nozzle boxes, so as to reduce the extent to which air exiting the nozzle apertures tends to flow along the external length of the nozzle box. By reducing this effect, the configuration promotes airflow in a generally longitudinal direction of the drier.

(18) The drier comprises an air inflow means 31 for directing airflow towards the principal surfaces of the board 32, the air inflow means 31 comprises a lower conduit 40 and a upper conduit 34, the lower and upper conduits 40,34 each having a substantially rectangular cross-section and each extending transversely to the longitudinal direction of the drier.

(19) The rollers 30a,30b,30c,30d further being for supporting the board 32 in a support plane 33 containing the longitudinal direction of the drier.

(20) A panel 54 extends in the direction of travel of the gypsum board, that is, into the plane of FIG. 3 and transversely to the nozzle boxes 34,40, and is provided at the downstream end of the nozzle boxes. The panel 54 helps to prevent air leaving the drier in the longitudinal direction of the rollers 30. Thus, the presence of the panel helps to reduce airflow along the length of the nozzle boxes and increase airflow in a generally longitudinal direction of the drier. Preferably, the panel is a mask.