Method of operating an electrical heating arrangement

Abstract

A method of operating an electrical heating arrangement of considerable length using a heating line having at least one heating conductor surrounded by an insulation resistant to high temperatures. A metal tube ( 4 ) abutting against the insulation ( 3 ) is formed around the heating line ( 1 ) and the heating line ( 1 ), which is equipped with the metal tube ( 4 ) is inserted into a metallic tube ( 5 ) which has a diameter larger than the metal tube ( 4 ) and encloses, in addition to the heating line ( 1 ), an axially continuous clearance space ( 6 ). A non-combustible gas having a lower kinematic viscosity compared with air is inserted into the clearance space ( 6 ), the gas completely filling the latter and being kept permanently under pressure.

1 . A method of operating an electrical heating arrangement of considerable length using a heating line having at least one heating conductor surrounded by an insulation resistant to high temperatures, characterized in that
 a metal tube bearing against the insulation is formed around the heating line,   the heating line equipped with the metal tube is introduced into a metallic tube which has a diameter larger than the metal tube and encloses, in addition to the heating line, an axially continuous clearance space, and   a non-combustible gas having a lower kinematic viscosity compared with air is introduced into the clearance space, said gas completely filling the latter and being kept constantly under pressure.   
   
   
       2 . The method according to  claim 1 , characterized in that a gas having a kinematic viscosity of at most 90×10 −6  m 2 /sec at 500° C. is used. 
   
   
       3 . The method according to  claim 2 , characterized in that an inert gas is forced into the clearance space. 
   
   
       4 . The method according to  claim 3 , characterized in that argon is forced into the clearance space. 
   
   
       5 . The method according to  claim 4 , characterized in that the gas pressure is monitored. 
   
   
       6 . The method according to  claim 5 , characterized in that the gas pressure is regulated to a constant value. 
   
   
       7 . The method according to  claim 6 , characterized in that the gas is fed from the remote end via a small tube which is fastened to the metal tube of the heating line. 
   
   
       8 . The method according to  claim 7 , characterized in that the outer surface of the metal tube of the heating line is roughened, preferably by sand blasting. 
   
   
       9 . The method according to  claim 1 , characterized in that the gas pressure is monitored. 
   
   
       10 . The method according to  claim 9 , characterized in that the gas pressure is regulated to a constant value. 
   
   
       11 . The method according to  claim 10 , characterized in that the gas is fed from the remote end via a small tube which is fastened to the metal tube of the heating line. 
   
   
       12 . The method according to  claim 1 , characterized in that the outer surface of the metal tube of the heating line is roughened, preferably by sand blasting. 
   
   
       13 . An apparatus comprising:
 a heating line having at least one heating conductor surrounded by an insulation resistant to high temperatures,   a metal tube bearing against the insulation and formed around the heating line,   wherein the heating line with the metal tube is positioned in a metallic tube which has a diameter larger than the metal tube and encloses, in addition to the heating line, an axially continuous clearance space, and   a non-combustible gas having a lower kinematic viscosity compared with air completely filling the clearance space, said gas having a constant pressure.   
   
   
       14 . The apparatus according to  claim 13 , wherein the gas has a kinematic viscosity of at most 90×10 −6  m 2 /sec at 500° C. 
   
   
       15 . The apparatus according to  claim 13 , wherein said non-combustible gas is an inert gas. 
   
   
       16 . The apparatus according to  claim 15 , wherein said inert gas is argon. 
   
   
       17 . The apparatus according to  claim 13 , further comprising means to monitor the pressure of said non-combustible gas. 
   
   
       18 . The apparatus according to  claim 17 , further comprising means for regulating the pressure of said non-combustible gas so as to maintain the pressure of said non-combustible gas at said constant pressure. 
   
   
       19 . The apparatus according to  claim 13 , further comprising means for feeding said non-combustible gas from a remote end of said clearance space via a small tube which is fastened to the metal tube of the heating line. 
   
   
       20 . The apparatus according to  claim 19 , wherein an outer surface of the metal tube of the heating line is roughened.