Process for removing deposits from water-carrying systems and devices for water supply

ABSTRACT

Process for removing deposits from water-carrying systems and devices for water supply, or from their individual parts, in which the deposits are dissolved by means of an aqueous treatment solution and removed in dissolved form from the system or the device or their individual parts, wherein the deposits are dissolved by means of an aqueous treatment solution comprised of a combination of (i) a reducing agent, in particular in the form of a slat-like, reducing sulfur-oxygen compound, nitrogen-oxygen compound or phosphorous-oxygen compound, and (ii) a complexing agent having phosphonic acid groups or phosphonate groups or a complexing agent of the hydroxy acid type at pH values in the range of approximately 4.5 to 9.5, in particular from approximately 6.0 to 8.0.

INFORMATION

DETAILED DESCRIPTION OF THE INVENTION

EXAMPLE 1

Used Substances or Agents:

Used is a well filter gravel enveloped by a well ocher which forms a solid layer of mean width of approximately 2 mm about the gravel particles (present in a particle size fraction of 0.2 to 0.5 mm). The well ocher is composed in this example chemically primarily of Fe(III) compounds that are difficult to dissolve. The ocher-enveloped gravel particles have been pre-dried at 60° C. for constant weight.

Removal of the well ocher from the gravel particles is carried out by using a freshly prepared 10% solution of solid sodium dithionite in water (e.g. 100 g sodium dithionite per 1 kg solution).

Testing Method:

5.00 g of the dried gravel particles, enveloped by well ocher, are added in 5 ml freshly prepared 10% solution of sodium dithionite. The sample (pH value(beginning) approximately 7) is then left standing for 16 hours, without mechanical influence (agitating, ultrasound or the like) at 20° C.

After 16 hours, the sample is slightly shaken for peeling off loosely adhering well ocher, and the remaining ocher sample (gravel particles with enveloping well ocher) is separated from the liquid phase (remaining solution of sodium dithionite with blown off ocher particles).

The remaining, ocher-enveloped gravel particles are dried to constant weight and weighed again.

Result:

3.30 g ocher-enveloped gravel particles remain. This corresponds to a decrease of 34%, relating to the initially used filter gravel quantity. A significant, gravimetrically not registered amount of well ocher remains in the solution in the form of relatively small particles. These particles have been blown off the filter gravel particles during the test. The pH value has not changed during the reaction, or only insignificantly: pH(end) approximately 7.

Comparison to Conventional Processes:

A reaction solution containing 0.3 m HCl (pH(beginning) approximately 0.5) and 5% hydrogen peroxide, removes about 20% of the initially used filter gravel quantity at otherwise same test conditions (such as reaction time and reaction temperature). When considering the facts that the filter gravel particles consist of ocher envelope and gravel stone core and the gravel stone core does not dissolve under the selected solubilization conditions, the comparison of the de-ochering potential between both agents turns out even more clearly in favor of the dithionite solution according to the invention.

When operating with a solution of sodium dithionite of approximately 3% by weight and simultaneous use of approximately 20 mmol/l of phosphonobutane-1,2,4-tricarboxylic acid (PBTC) or citrate at a pH value of 6.4 (H2CO3/HCO3—buffer), even better results are realized.

EXAMPLE 2

Used Substances or Agents

Used is a well filter gravel enveloped by a well ocher which forms a solid layer of mean width of approximately 1 mm about the gravel particles (present in a particle size fraction of 0.2 to 0.5 mm). The well ocher is composed chemically in this example primarily of Mn(IV) compounds that are difficult to dissolve. The ocher-enveloped gravel particles have been pre-dried at 60° C. for constant weight.

Removal of the well ocher from the gravel particles is carried out according to the process of the invention by using a freshly prepared 10% solution of solid sodium dithionite in water (100 g sodium dithionite per 1 kg solution).

Testing Method:

5.00 g of the dried gravel particles enveloped by well ocher are added in 5 ml freshly prepared 10% solution of sodium dithionite. The sample (pH value(beginning) approximately 7) is then left standing for 16 hours without mechanical influence (agitating, ultrasound or the like) at 20° C.

After 16 hours, the sample is slightly shaken for peeling off loosely adhering well ocher, and the remaining ocher sample (gravel particles with enveloping well ocher) is separated from the liquid phase (remaining solution of sodium dithionite).

The remaining, ocher-enveloped gravel particles are dried to constant weight and weighed again.

Result:

2.60 g ocher-enveloped gravel particles remain. This corresponds to a decrease of 48%, relating to the initially used filter gravel quantity. No significant amount of small particles remains in the solution. Ocher removed from the filter gravel has thus, in fact, been dissolved after the reduction of the Mn(IV) to Mn(II). The blow-off effect observed in particular in the Fe(III) containing filter gravel according to Example 1, could not be observed here. The pH value has not changed during the reaction, or only insignificantly: pH(end) approximately 7.

Also in this case, the added use of complexing agents, such as PBTC, results in further improvements.

EXAMPLE 3

Used Substances or Agents

Used is a well filter gravel enveloped by a well ocher which forms a solid layer of mean width of approximately 1 mm about the gravel particles (present in a particle size fraction of 0.2 to 0.5 mm). The well ocher is composed in this example primarily of Fe(III) compounds that are difficult to dissolve.

The ocher-enveloped gravel particles were used in moist condition.

Removal of the well ocher from the gravel particles is carried out by using a freshly prepared 3% solution of solid sodium dithionite in water which further contains 0.1 mol/L PBTC in the form of its tetra sodium salt (commercial name “Bayhibit S” by Bayer AG) and 0.1 mol/L of an equimolar sodium hydrogen carbonate/carbonic acid buffer.

Testing Method:

13.00 g of the well ocher are affixed in the interior of plastic ring of 40 mm inner diameter and a height of 10 mm by means of two plastic nets with a mesh size of approximately 0.2 mm. The ocher-filled ring is secured approximately 15 mm above the bottom of a beaker glass. The ocher is removed from the particles by adding 80 mL of the above-stated dithionite solution to the well ocher. The solution is stirred at room temperature for 24 hours at 550 revolutions/min. 0.1 mL of the solution are withdrawn in time-controlled manner, filtered through a 0.2 μm filter and its iron content is analyzed.

Result:

After treatment for 2 hours, the maximum solubility of iron is reached. Hereby 4200 mg/L of iron are present in the solution. Already after one hour, 4100 mg/L have been measured, thereby confirming the rapid effect of the solution. Subsequently, the iron content drops again slightly in the solution (3900 mg/L after 24 hours). This drop can be explained by a precipitation of Fe-salts which can be attributed to the exhaustion of the dithionite solution.

The presence of an effective dithionite concentration can be simply checked through discoloration of a methylene blue solution—if too little dithionite is in the solution, methylene blue will not be discolored. Thus, methylene blue is suitable to monitor the regeneration process, when periodically testing, e.g. during well regeneration, a partial amount, pumped out for test purposes from the well.

While the invention has been illustrated and described as embodied in a process for removing deposits from water-carrying systems and devices for water supply, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of prior filed copending PCT International application no. PCT/DE00/04426, filed Dec. 11, 2000.

CLAIMS

1. A process for removing deposits precipitated from cold freshwater from water-carrying systems and devices for water supply, or from their individual parts, said process comprising the steps of dissolving the deposit to be removed from cold freshwater in water-carrying systems and devices for water supply by contacting the deposit with an aqueous treatment solution comprised of a combination of a reducing agent selected from the group consisting of dithionite, disulfite and mixtures thereof, and a complexing agent selected from phosphono butane-1,2,4-tricarboxylic acid and its alkali metal salts for a period sufficient to dissolve at least part of said deposit and removing spent treatment solution from the so treated water carrying system or the devices for water supply.

2. The process of claim 1, wherein the deposits are dissolved at pH values in the range of about 4.5 to 9.5.

3. The process of claim 2, wherein the deposits are dissolved at pH values an the range from about 6.0 to 8.0.

4. The process of claim 1, wherein the concentration of the treatment solution of dithionite, disulfite or their mixture is in the range from 0.5 to 25 percent by weight.

5. The process of claim 1, wherein the treatment solution further comprises at least a component selected from the group consisting of buffer salts, wetting agents and stabilizers, wherein the component is introduced in a state selected from the group consisting of dissolved state, emulsified state, and as suspended solids.

6. The process of claim 1, wherein the deposit is at least one compound selected from the group consisting of oxides, oxide hydrates, and hydroxides of iron metal or manganese.

7. The process of claim 1, wherein the contacting step in which the treatment solution is contacted with the deposit is carried out by at least one of spraying and washing off.

8. The process of claim 1, wherein the contacting step in which the treatment solution is contacted with the deposit is carried out by at least one of filling and rinsing the system or the device.

9. The process of claim 1, wherein the device for water supply includes at least one selected from the group consisting of water wells, drinking water reservoir, drinking water conduit, filter system, water preparation plant, plant sections and individual parts thereof.

10. The process of claim 1, wherein the device is a water well, said dissolving step including a) filling the well with the treatment solution, b) allowing the treatment solution to react with the deposit for a predetermined reaction time to dissolve the deposit in the treatment solution, a) subsequently emptying the well by pumping out its content together with the treatment solution with dissolved deposit, wherein an additional after-treatment step d) is carried out during which the treated well is subjected to an aqueous solution of an oxidant.

11. The process of claim 10, wherein steps a), b) end c) are repeated at least once, before carrying out step d).

12. The process of claim 10, wherein the oxidant is hydrogen peroxide.

13. The process of claim 2, wherein the water-carrying system includes one element selected from the group consisting of heat exchanger and cooling system and feed lines thereof, and the device for water supply includes one element selected from the group consisting of well, drinking water reservoir, drinking water conduit, filter system, water preparation plant, and plant sections and individual parts thereof.

COPYRIGHT

User acknowledges that Fairview Research and its third party providers retain all right, title and interest in and to this xml under applicable copyright laws. User acquires no ownership rights to this xml including but not limited to its format. User hereby accepts the terms and conditions of the License Agreement.