Oxygen heat exchanger

Abstract

The present invention relates to a heat exchanger for the supply of oxygen or of a gas mixture containing at least 50% oxygen, the temperature at the outlet of the exchanger not being below 300° C., it preferably being above 400° C., the oxygen or the oxygen-rich gas feeding one or more burners of a glass melting furnace, the heat of the combustion gases being used directly or indirectly to heat the oxygen or the oxygen-rich gas in the exchanger, in which the exchange power is between 20 and 300 kW, preferably between 40 and 250 kW and particularly preferably between 80 and 170 kW.

1 . A heat exchanger for supplying oxygen or a gaseous mixture composed of at least 50% oxygen, the temperature of which at the outlet of the exchanger is not less than 300° C., wherein the oxygen or gas rich in oxygen supplies one or more burners of a glass melting furnace, and the heat of the combustion gases is used directly or indirectly to heat the oxygen or gas rich in oxygen in the exchanger, in which the exchange power is in the range of between 20 and 300 kW. 
     
     
         2 . The exchanger according to  claim 1 , in which the power per unit area of exchange in contact with the oxygen or gas rich in oxygen is in the range of between 5 and 15 kW/m 2 . 
     
     
         3 . The exchanger according to  claim 1  supplying at most three burners of the furnace. 
     
     
         4 . The exchanger according to  claim 1  of tubular configuration, in which the oxygen or gas rich in oxygen circulates in the tubes, the internal walls of which are in contact with a heat transfer gas. 
     
     
         5 . The exchanger according to  claim 4 , in which the total cross-section of the tubes carrying the oxygen or gas rich in oxygen provides the highest circulation rate in these tubes so long as the rate does not exceed 120 m/s. 
     
     
         6 . The exchanger according to  claim 1 , in which the pressure of the oxygen or gas rich in oxygen is kept below 3 bar, preferably below 2 bar. 
     
     
         7 . The exchanger according to  claim 1 , in which the surfaces in contact with the oxygen or gas rich in oxygen are polished so that their roughness does not exceed 6μ. 
     
     
         8 . The exchanger according to  claim 7 , in which the tubes in which the oxygen or gas rich in oxygen circulates are substantially straight and their walls have a thickness that is not more than 3 mm. 
     
     
         9 . The exchanger according to  claim 4 , in which the chamber enclosing the tubes is formed from several elements joined by flanges, wherein tightness is assured at these flanges by composite seals, the sealing element of which is made of material that is inert with respect to oxygen. 
     
     
         10 . The exchanger according to  claim 9 , in which the sealing element is a ring composed of compressible mineral material. 
     
     
         11 . The exchanger according to  claim 1 , in which the oxygen or gas rich in oxygen is heated indirectly by the combustion gases, wherein a first exchange between these is effected with an intermediate heat transfer gas, which is then passed to the exchanger to heat the oxygen or gas rich in oxygen, wherein the heat transfer gas is formed by a gas that is inert with respect to oxygen. 
     
     
         12 . The exchanger according to  claim 11 , in which the heat transfer gas is air, nitrogen, CO 2  or steam. 
     
     
         13 . The exchanger according to  claim 11 , in which the heat transfer gas is formed from combustion gases diluted by means of at least one of the gases: air, nitrogen, CO 2  and steam. 
     
     
         14 . The exchanger according to  claim 11 , in which the heat transfer gas is firstly heated in a recuperator, which has been heated by the combustion gases beforehand. 
     
     
         15 . The exchanger according to  claim 1 , in which the material of the surfaces in contact with the oxygen or gas rich in oxygen is made from a metal alloy of which a sample exposed to the hot gas does not exhibit a weight gain of more than 0.1 mg/cm 2  after 1000 cycles of exposure, wherein each cycle includes increasing the temperature to a value equal to or higher than 400° C., maintaining this phase temperature for one hour and returning to ambient temperature. 
     
     
         16 . The exchanger according to  claim 15 , in which the alloy complies with the condition of a weight gain of less than 0.1 mg/cm 2  of exposed surface when the phase temperature is at least 500° C. in the test in oxidising atmosphere. 
     
     
         17 . The exchanger according to  claim 15 , in which the alloy in contact with the oxygen or oxygen-based gaseous mixture resists the spontaneous combustion test according to standard ASTM G 124 at least up to a pressure of 3 bar. 
     
     
         18 . The exchanger according to  claim 15 , in which the alloy in contact with the oxygen or oxygen-based gaseous mixture is a ferritic steel alloy containing a percentage by weight of Cr of 12 to 30% and an Al content of 1 to 8%. 
     
     
         19 . The exchanger according to  claim 15 , in which the alloy in contact with the oxygen or oxygen-based gaseous mixture, for an oxygen temperature not exceeding 500° C., is an alloy containing a percentage by weight of chromium in the range of between 10 and 20% weight. 
     
     
         20 . The exchanger according to  claim 15 , in which the alloy has an Ni content higher than 25% and a Cr content from 10 to 30%. 
     
     
         21 . The exchanger according to  claim 20 , in which the alloy is one of those commercially available under the names “Inconel 600 H”, “600L”, “601”, “617”, “625”, “Incoloy 800H” or “800HT”. 
     
     
         22 . The exchanger according to  claim 1 , in which the elements are in contact with the oxygen or the oxygen-based mixture, are brought to a temperature in the range of between 300° and 900° C. 
     
     
         23 . The exchanger according to  claim 1 , in which an oxygen detector is placed in contact with the heat transfer gas, which is connected to an alarm when the oxygen content is more than 1% higher than that of the heat transfer gas.