Nozzle box for air-borne continuous paper sheet drying

Abstract

A nozzlebox for blowing hot gas in the convective drying zone of equipment for the continuous drying of air-borne paper sheets comprises at least one direct impingement nozzle for ejecting a jet of hot gas perpendicular to the average plane of the paper sheet to be dried. The nozzle box comprises a plurality of inclined jet nozzles for ejecting jets of hot gas under an inclined angle with respect to the average plane of the paper sheet to be dried. At least two inclined jet nozzles are provided for which the plane comprising the vector representations of the jet directions of the at least two inclined jet nozzles does not comprise the vector representing the jet direction of a direct impingement nozzle.

1 . Nozzle box for blowing hot gas in the convective drying zone of equipment for the continuous drying of air-borne paper sheets, the nozzle box comprises
 at least one direct impingement nozzle for ejecting a jet of hot gas perpendicular to the average plane of the paper sheet to be dried; and   a plurality of inclined jet nozzles, wherein inclined jet nozzles are provided for ejecting jets of hot gas under an inclined angle with respect to the average plane of the paper sheet to be dried;   
       wherein at least two inclined jet nozzles are provided for which the plane comprising the vector representations of the jet directions of the at least two inclined jet nozzles does not comprise the vector representing the jet direction of a direct impingement nozzle. 
     
     
         2 . Nozzle box as in  claim 1 , wherein the nozzle box comprises at least three inclined jet nozzles, wherein each of the at least three inclined jet nozzles has a vector representing its jet direction when in use; wherein each of the vectors of the at least three inclined jet nozzles has a different direction in the three-dimensional space. 
     
     
         3 . Nozzle box as in  claim 1 ,
 wherein the inclined jet nozzles comprise or consist out of a first set of inclined jet nozzles and a second set of inclined jet nozzles;   wherein the first set of inclined jet nozzles are provided for blowing in a first direction; and   wherein the second set of inclined jet nozzles are provided for blowing in a second direction;   and wherein the first direction is perpendicular to the second direction.   
     
     
         4 . Nozzle box as in  claim 1 , wherein the nozzle box comprises suction openings for the evacuation of gas. 
     
     
         5 . Nozzle box as in  claim 1 , wherein the nozzle box comprises a plurality of nozzle units over the nozzle box, wherein each of the units comprises
 at least one direct impingement nozzle for ejecting a jet of hot gas perpendicular to the average plane of the paper sheet to be dried; and   a plurality of inclined jet nozzles, wherein inclined jet nozzles are provided for ejecting jets of hot gas under an inclined angle with respect to the average plane of the paper sheet to be dried;   
       wherein at least two inclined jet nozzles of the nozzle unit are provided for which the plane comprising the vector representation of the jet directions of the at least two inclined jet nozzles does not comprise the vector representing the jet direction of a direct impingement nozzle of the nozzle unit. 
     
     
         6 . Nozzle box as in  claim 5 , wherein suction openings for the evacuation of gas are provided in the nozzle box between nozzle units. 
     
     
         7 . Nozzle box as in  claim 5 , wherein nozzle units are provided as nozzle heads mounted in the nozzle box. 
     
     
         8 . Nozzle box as in  claim 5 , wherein the at least one direct impingement nozzles are provided in the central section of the nozzle unit; and
 wherein the inclined jet nozzles surround the at least one direct impingement nozzles.   
     
     
         9 . Nozzle box as in  claim 8 ,
 wherein a first part of said inclined jet nozzles are provided for blowing inwards towards the at least one direct impingement nozzle;   and wherein a second part of said inclined jet nozzles are provided for blowing in the direction away from the at least one direct impingement nozzle.   
     
     
         10 . Nozzle box as in  claim 5 , wherein the inclined jet nozzles within a nozzle unit are provided so that when the inclined jet nozzles are in operation, the jets of the inclined jet nozzles are present in equi-angularly distributed planes perpendicular to the nozzle box 
     
     
         11 . Equipment for continuous air-borne drying of a paper sheet, comprising a nozzle box as in  claim 1 , wherein said nozzle box spans the width available in the equipment for the transport of the paper sheet. 
     
     
         12 . Equipment as in  claim 11 , wherein one or more than one nozzle box as in  claim 1  is provided such that the vector sum of the vectors representing the jet direction and having as magnitude the jet impulse of the inclined jet nozzles of the nozzle box points in the opposite direction of the direction of transport of the paper sheet through the drying equipment. 
     
     
         13 . Equipment as in  claim 11 , wherein the equipment comprises a multiple number of nozzle boxes as in  claim 10 ; and
 wherein at least two consecutive nozzle boxes comprise nozzle units that are staggered when comparing the positions of the nozzle units in the first nozzle box of the two consecutive nozzle boxes with the positions of the nozzle units in the second nozzle box of the two consecutive nozzle boxes.   
     
     
         14 . A method for continuous drying of a paper sheet,
 wherein an equipment for continuous drying is used as in  claim 11 ;   wherein a paper sheet is transported through the equipment in order to dry the paper sheet in the equipment for continuous drying;   wherein the paper sheet is air-borne in the equipment without the selvedge of the paper sheet being held by mechanical means;   wherein the paper sheet undulates in the direction of transport of the paper sheet through the drying equipment;   and wherein the paper sheet undulates in the direction perpendicular to the direction of transport of the paper sheet through the drying equipment.   
     
     
         15 . Method as in  claim 14 , wherein the vector sum of the vectors representing the jet direction and having as size the jet impulse of the inclined jet nozzles of the nozzle box, points in the opposite direction of the direction of transport of the paper sheet through the drying equipment.