A PROCESS FOR CLEANING A TANK

PROCEDE POUR NETTOYER UN RESERVOIR

English Abstract

The present invention relates to a process for cleaning a tank, in particular a steam boiler.
Using this process, copper and copper compounds present in deposits are dissolved out. To
this end, a complexing agent and a strong organic agent, preferably guanadine carbonate, are
introduced into the tank. Soluble copper complexes form in aqueous solution. After this, the
tank is emptied.

French Abstract

La présente invention se rapporte à un procédé pour nettoyer un réservoir, plus particulièrement une chaudière à vapeur. Ce procédé vous permet de faire dissoudre le cuivre et les composés du cuivre présent dans des dépôts pour les retirer de ces derniers. Pour ce faire, il faut introduire un agent chélatant et un agent organique puissant, de préférence de la guanadine carbonate, dans le réservoir. Des complexes de cuivre solubles se forment dans une solution aqueuse. Ensuite, le réservoir est vidé.

Claims

Claims
1. A process for cleaning a tank, in particular a steam boiler, whereby in order to dissolve
copper and copper compounds out of deposits within the tank, a complexing agent and
an alkalyzing agent are added to the tank in order to form soluble copper complexes in
aqueous solution, after which the tank is emptied, characterized in that a strong
organic base is used as the alkalyzing agent.
2. A process as defined in Claim 1, characterized in that guanidine carbonate is used as
the strong organic base.
3. A process as defined in Claim 1 or Claim 2, characterized in that ethylenediamine is
introduced into the tank as the complexing agent.
4. A process as defined in Claim 1 to Claim 3, characterized in that the temperature is
between 20° Celsius and 100° Celsius.
5. A process as defined in Claim 1 to Claim 4, characterized in that the pH value is
greater than 10.
6. A process as defined in Claim 1 to Claim 5, characterized in that during the formation
of copper complexes, pressurizing gas with an oxygen concentration of up to 100 per

cent is introduced into the tank in order to bring about a mixing effect and/or to modify
the pressure.
7. A process as defined in Claim 6, characterized in that the pressurizing gas is removed
from the tank.

Description

CA 02207406 1997-06-10
A Process for Cleaning a Tank
The present invention relates to a process for cleaning a tank, in particular a steam boiler,
whereby a complexing agent and an alkalyzing agent are introduced into the tank in order to
dissolve copper and copper compounds that are present in deposits within the tank and form
5 soluble copper complexes in aqueous solution, after which the tank is emptied.
A process for cleaning a tank, in which copper compounds are dissolved out of deposits by
forming copper complexes is described in EP 0 198 340 B1. In this case, ethylene~ mine is
used as the complexing agent, and ammonia is used as the alkalyzing agent. Ammonium
lo carbonate can also be added in order to accelerate the chemical reaction. In this process, the
ammonia can be replaced by ammonium carbonate.
In such a process, the ammonia must be added continuously in the case of processes that last
a longer time, since it leaves the cleaning solutions in the form of gas.
If soluble iron compounds are present, even at the trace level, in the presence of ammonia
these can act on the materials consisting of iron-copper alloy used in the tank and dissolve
copper out of the tank material.
20 It is the task of the present invention to describe a process for cleaning a tank, in which the
tank, which is of an iron-copper alloy or contains such an alloy, is not attacked.
According to the present invention, this problem has been solved in that a strong organic base
is used as the alkalyzing agent.

CA 02207406 1997-06-10
It is more advantageous if an alkalyzing agent that can the replace the ammonium completely
be used. The strong organic base does not attack the container material that is of an
iron-copper alloy, so that metallic copper and copper compounds that are present in deposits
within the tank can be removed from tanks made of such a material, particularly steam boilers.
Furthermore, a strong organic base does not leave the cleaning solution in the form of gas, so
that it is not necessary to add it continuously. As a consequence, smaller quantities of
chemicals can be used and process-technology costs can be reduced, which means that the
cleaning process is particularly economical.
Using a strong organic base as opposed to a strong inorganic base, for example, NaOH, one
achieves the advantage that the strong organic base does not form any salts that could attack
the material used for the tank.
5 As an example, guanidine carbonate can be introduced into the tank as the strong organic
base. This is a crystalline substance, and for this reason it is easy to handle. In particular,
guanadine carbonate is a strong organic base that is inexpensive, so that the cleaning process
can be completed very economically by using it.
20 As an example, ethylenediamine is introduced into the tank as the complexing agent. A
suitable temperature for the cleaning process lies, for example, between 20~ and 100~ Celsius.
The pH value can be adjusted to a value greater than 10 by addition of the alkalyzing agent.

CA 02207406 1997-06-10
Using these measures, that are cited as examples, is possible to further improve the cleaning
process.
As an example, during the formation of copper complexes, pressurizing gas with an oxygen
5 concentration of up to 100 percent is introduced into the tank in order to bring about a mixing
effect and/or to modify the pressure. The pressurizing gas can also be released from the tanks
for the same purpose.
Using the process according to the present inventionone achieves the advantage that the
o iron-copper alloys that can be used for the tank or part of the tank are not attacked.