FR2554594A1 - IMPROVED DEVICE FOR MEASURING THE CONCENTRATION OF OXYGEN IN HIGH TEMPERATURE FLUID MEDIA - Google Patents

Abstract

IN AN OXYGEN BATTERY WHOSE UNKNOWN PARTIAL OXYGEN PRESSURE IS DERIVED BY MEASURING THE F.E.M. OF A CONCENTRATION BATTERY, THE GENERATION OF THE KNOWN PARTIAL OXYGEN PRESSURE IS CARRIED OUT BY USING A SUBSTANCE WHICH REACTS WITH OXYGEN TO FORM COMPOUNDS WHICH ARE EASILY ELIMINATED FROM THE REACTION SITE. THIS ELIMINATES THE PROBLEM OF POLARIZATION OF THE BATTERY WHOSE USEFUL LIFE IS EXTENDED AND THE SIGNAL REMAINS EXTREMELY ACCURATE IN THE LONG TERM.

Description

IMPROVED DEVICE FOR MEASURING THE

  CONCENTRATION OF OXYGEN IN A FLUID MEDIA

HIGH TEMPERATURE.

  The present invention relates to an improvement

  oxygen stacks and, in particular, addresses the problem of the long-term reliability of the measurement for the determination of the

  oxygen of fluid media at high temperature.

  Measuring the oxygen content of media

  High temperature fluids are becoming more and more

  for the control and regulation of a large number of industrial processes such as the production of metals

  and alloys in the molten state, annealing and cementation.

  metals, the agglomeration of ores, the burning of

  tion, etc. For this type of measurement, it is known to use

  bury oxygen cells consisting essentially of a chamber whose walls are made of compounds, such as zirconium oxide, suitably stabilized, which have the property of becoming permeable to oxygen ions beyond a certain temperature, by

example around 500C.

  If one creates in these devices, inside the chamber, a known partial pressure of oxygen, one

  obtains a concentration stack whose electro-

  motor (e.m.) is expressed by the well-known Nernst equation: RT P02r E - ln nF P02x where E denotes the cell fme, P02r the known oxygen partial pressure and PO2x the pressure

  partial oxygen which one wishes to measure. The problem

  consists in obtaining a P02r which remains known in the long term in order to allow a precise control to be

any time.

  There are basically two ways to get the known oxygen partial pressure: - The first way is to send Inside

  of the chamber a continuous flow of gas of composition

  naked. This supposes that the walls of the measuring chamber

  re and the gas supply ducts are perfect-

  leakproof or that, in any case, they do not allow

  the entry into the chamber of contaminants likely to

  to alter the composition of the reference gas.

  Given the thermal and mechanical shocks that these

  probes should normally be subjected to the above condition

  is very difficult to respect and in fact increases

  the price, while still leaving some doubt as to the long-term effectiveness of the measures that have been taken. In addition, the current technical and economic requirements prevent the use of gas supply pipes exceeding a certain length, for example 70 to 100 cm, which considerably limits the

  scope of this kind of devices.

  - The second way is to place inside of

  the chamber of complex mixtures of metal + oxide which

  at equilibrium, partial pressures of known oxygen at various temperatures. Such devices

  have the disadvantage of not being able to function cor-

  only for limited periods of time, as oxygen passing through the walls of the chamber reacts with the metal at the interface causing

  the polarization of the battery. As a result, the response

  of the pile undergoes a drift the magnitude of which is

naked.

  There is therefore a problem with the reliability of

  long-term measurement of A cell measurements

  oxygen and this problem has so far resulted in the replacement

  frequently these batteries. However, this solution

  is not satisfactory as well for interrup-

  possible processes of the process under control and for

  intrinsic difficulties due to replacement operations

  than for the cost of these devices, which, although not huge, is nevertheless

types A gas supply.

  The object of the present invention is to solve this problem by providing an improved type of oxygen battery which is absolutely reliable in the long term and, in addition, very sensitive, capable of being placed at any position relative to the measuring instruments and

  signal, while at a low cost.

  moth. According to the present invention, in a device for measuring the concentration of oxygen in high temperature fluid media, wherein said concentration is derived as an unknown oxygen partial pressure, by measuring the foemode. of a stack At concentration, one brings the improvement consisting of

  in that the known partial pressure of oxygen, ser-

  of reference, is generated by using a substance

  which, reacting with oxygen, gives composites

  which can easily be removed from the reaction site. It is preferable that this substance gives oxygen with reaction products in the gaseous state or that it is liquid at the temperature of use.

  and gives strong reaction products but which

try on the liquid.

  Examples of such substances are all elements capable of reacting with oxygen to give

  products that are volatile or that

  solid reaction products- have a lower melting point

  the temperature at which one must work, such as aluminum, antimony, bismuth, carbon, lead, alkali metals, phosphorus, sulfur, tin, etc. Obviously. in practice0 the

  choice is reduced for a variety of reasons, such as

  excessive activity of the element, its contaminating effect or the hazards of the element itself or its

reaction products.

  The invention will now be described with reference to

  to one of his achievements given as an example.

  non-limiting and illustrated in the accompanying drawing. The figure shows a wall chamber 1 in zirconium oxide, provided with a lid 2 and filled with reactive substance 3, as described above. e On the wall 1 are arranged the electrodes 8 and

  6, respectively on the outer face and the inner face

  dull, facing each other, these electrodes carrying their insulated conductors 7 and 5. The inner conductor exits the chamber Through the small hole 4 (which serves

  also the evacuation of the reaction products

  zeux) practiced in the lid 2 which is also preferably provided with a second passage 11 through which

  pass the wires 9 and 10 of a thermocouple whose junction

  12 is placed as close as possible to the electrode

6 and wall 1.

  This arrangement of the thermocouple is useful to ensure the best possible measurement of the temperature of the oxidation reaction that occurs in the vicinity

  electrodes. At each reaction temperature cor-

  responds to a precise partial pressure of oxygen which is used as reference value P02r in the equation

from Nernst mentioned above.

  In use, between the electrodes 6 and 8 a f is established. E. M. due to the difference between P02r and P02x; by measuring this f.e.m. At the terminals of conductors 5 and 7, and knowing the temperature, P02x is determined. Various prototypes of oxygen probes according to the present invention were constructed and tested in

  industrial conditions. The tests were carried out

  killed successfully for three months without interruption and

they continue.

  In use it has been found that the signal emitted by the battery is completely independent of the age of the probe and it has also been observed that there are no particular constraints between the respective positions of the battery or batteries. and measurement recording instruments. Among the many elements that have been used for the generation of the reference oxygen partial pressure, lead, tin, carbon and sulfur have given the best results. However, until

  present, we have obtained the greatest reliability and ab-

  complete absence of any problems as well as the

  better sensitivity by using tin and carbon

  not, obtaining as lower limit of concentration

  measured 1.10-18 atmosphere, value obtained with the

  mass trometer and with gaseous mixtures H2 / H20 A

known oxygen content.

Claims (5)

  1. Advanced device for measuring the   concentration of oxygen in fluid media with   high temperature, constituted by a concentration stack   of oxygen in which an electromotive force is generated   between two electrodes, one of which is   tact with the fluid medium at high temperature   with an unknown concentration of oxygen and whose   be placed in an environment with a concentration   known oxygen supply, generated by reaction between oxygen and a reactive substance in a chamber   with permeable walls with oxygen ions,   in that the substance that reacts with oxygen   by this reaction products that are easily   eliminated from the place of reaction.   S15 2. Improved device according to the claim   characterized in that said substance consists of an element which forms gaseous products by reaction with oxygen.   3. Advanced device according to the claim   characterized in that said substance is liquid   from the temperature at which the fluid medium is   of and gives, by reaction with oxygen, products solids easily sifted.   4. Improved device according to the claim   characterized in that said substance is chosen between carbon and sulfur.   5. Improved device according to the claim   characterized in that said substance is chosen between lead and tin.