Cleaning Process For Removing Magnetite-Containing Deposits From A Pressure Vessel Of A Power Station
A cleaning method for removing deposits containing magnetite out of a pressure vessel of a power plant, during which the deposits are treated with an aqueous cleaning solution, which contains a reducing agent and which is heated to an elevated cleaning temperature above ambient temperature, in order to reduce iron III ions to iron II ions. The cleaning solution is introduced into the pressure vessel. This cleaning solution contains an initial substance that releases the reducing agent under the conditions existing during cleaning. Hexamethylenetetramine is preferably used as the initial substance.
1 - 19 . (canceled)
21 . A cleaning process for removing magnetite-containing deposits from a pressure vessel of a power station, the process comprising:
treating the deposits in a two-stage process, including:
a reduction stage, wherein the deposits in the pressure vessel are treated with a first cleaning solution I containing a presubstance configured to liberate a reducing agent under conditions prevailing during cleaning, and heated to an elevated cleaning temperature above room temperature, in order to reduce iron(III) ions to iron(II) ions; and
a subsequent complexation stage, wherein a second cleaning solution II is metered into the process, the second cleaning solution II containing triethylamine and a complexing agent configured to form a soluble complex with divalent iron ions.
22 . The cleaning process according to claim 21 , wherein the second cleaning solution II is saturated with EDTA and contains not more than 0.5 mol/l of triethylamine.
23 . The cleaning process according to claim 21 , which comprises employing a presubstance configured to liberate an aldehyde as the reducing agent.
24 . The cleaning process according to claim 23 , which comprises employing a presubstance configured to liberate formaldehyde as the reducing agent.
25 . The cleaning process according to claim 21 , which comprises carrying out the reduction stage in slightly acidic to slightly alkaline solution.
26 . The cleaning process according to claim 25 , which comprises maintaining a pH from substantially 5 to substantially 7 during the reduction stage.
27 . The cleaning process according to claim 26 , which comprises maintaining a pH from 5.0 to 7.0 in the reduction stage.
28 . The cleaning process according to claim 21 , which comprises adding a complexing agent to the first cleaning solution I in an amount corresponding to no more than 10% of an amount required for complexing an amount of iron(II) formed by the reduction.
29 . The cleaning process according to claim 28 , which comprises employing EDTA as the complexing agent.
30 . The cleaning process according to claim 21 , wherein the presubstance is hexamethylenetetramine.
31 . The cleaning process according to claim 21 , wherein the process is carried out at a temperature ranging from 90° C. to 200° C.
32 . The cleaning process according to claim 31 , wherein the process is carried out in a temperature range of from 140° C. to 200° C.
33 . The cleaning process according to claim 30 , which comprises employing a first cleaning solution I with hexamethylenetetramine and EDTA present in a molar ratio of from 3.5:1 to 2:1.
34 . The cleaning process according to claim 33 , wherein the first cleaning solution I contains from 0.6 to 0.7 mol/l of hexamethylenetetramine and from 0.17 to 0.36 mol/l of EDTA.
35 . The cleaning process according to claim 21 , which comprises employing a second cleaning solution II containing EDTA as a complexing agent.
36 . The cleaning process according to claim 35 , which comprises employing a second cleaning solution II with a complexing agent consisting exclusively of EDTA.
37 . The cleaning process according to claim 21 , which comprises carrying out the complexation stage in slightly acidic to slightly alkaline solution.
38 . The cleaning process according to claim 37 , which comprises maintaining a pH from substantially 6 to substantially 10 in the complexation stage.
39 . The cleaning process according to claim 38 , which comprises maintaining a pH from 6.5 to 9.3 in the complexation stage.