DE599998C - Method of dehydration of water - Google Patents

Description

It is known that water can be completely removed. harden by treating the hardeners with trialkali phosphates, especially trisodium phosphate, as insoluble compounds in good filterable form precipitates.

It has also already been proposed to precipitate the hardness constituents of the water by treatment with alkali fluorides, such as insoluble alkaline earth fluorides. It has now been found that water can be completely softened in an excellent manner by using it to precipitate the hardness builders with fluorine-containing alkali metal phosphates, in particular sodium phosphate fluorides, such as sodium phosphate-sodium fluoride (2Na ₃ PO ₄ * NaF * 19H ₂ O), in the present Corresponding amounts of hardness constituents are added. It is advisable not to remove the total hardness of the water with fluorine-containing alkali metal phosphates, but rather before treating the water with:. carry out a pre-softening of these substances and first remove the residual hardness of the pre-softened water with the fluorine-containing alkaline phosphates. The pre-softening. the water can in a known manner, for example by treatment with soda, ^caustic: soda, lime, base exchangers ο. Like., take place. The Vorent- is particularly advantageous; Hardening with alkaline reacting boiler sludge water or boiler return water, because a complete softening can then be achieved with only very small amounts of fluorine-containing alkali metal phosphates. If you use fluorine-containing alkali metal phosphate to remove the residual hardness of the water, the chemical reactions that take place during softening result in boiler water that reacts alkaline, so that this boiler water, which from the residual softening reacts alkaline with fluorine-containing alkali metal phosphates, is obtained. can be used to pre-soften the water before the subsequent softening according to the invention with sodium phosphate fluorides or the like is carried out.

Compared to the well-known softening of water with alkali fluorides, the new process the advantage that the apatite-like properties that arise from the constituents of hardness in the water Compounds are practically completely insoluble and are coarsely flaky and easily filterable while precipitating in the case of softening with alkali fluorides alone in slimy, poorly filterable Form, which is probably the main reason that the alkali fluoride hardening of water has not been introduced in practice.

Compared to the known softening of water with Trinatriumphösphat o. The like. Has the new process has the advantage that the fluorine

*) ^V on the patent searcher has been given as the inventor:

'. . 'Dr.-Ing. Guido Hedrich in Budenkeim,

containing alkali metal phosphates, for example sodium phosphate-sodium fluoride, according to more recent Methods (according to patent 595 235) can be produced more cheaply than the trisodium phosphate. Another major advantage of the new process compared to the well-known trisodium phosphate softening of Water is that the precipitation reactions proceed faster, so that one already Better results are achieved at a lower temperature than when softening with pure Trisodium phosphate. If you work at higher temperatures, you will succeed while working according to the invention due to the

> 5 properly rapid course of the precipitation reactions to carry out the softening with smaller equipment than is necessary for a softening with trisodium phosphate are.

Execution example

i. A water with 8.8 ° lime hardness and y, J ° magnesia hardness, i.e. 16.50 ° total hardness, of which io.6 ° sulfate hardness, is at a temperature

a5 temperature of 18 ⁰ C with 0.75 kg of crystallized trisodium phosphate in the form of a concentrated solution to the cubic meter. After ^{stirring for 1} Z for ₄ hours, the water is freed from the precipitates which have flooded out by filtration. The filtrate has a total hardness of 5.8 °. If, in addition to 0.75 kg of crystallized trisodium phosphate, 0.0413 kg of sodium fluoride is added to the same water or this mixture is replaced by the corresponding _{double salt 2Na 3} PO ₄ 'NaF «19H ₂ O in an amount of 0.703 kg, the filtrate under the same conditions 2 , 8 ° hardness. From the schematic equations for the softening processes, namely

2 Na ₃ PO ₄ + 3 CaO = Ca ₃ (PO ₄ ), + 3 Na ₂ O

and

2 NaF + CaO = CaF ₂ + Na ₂ O

It can be seen that _^2/3 mole of Na ₃ PO ₄ are equivalent to 2 moles of NaF. The above 0.0413 kg of NaF correspond to 0.124 kg of crystallized trisodium phosphate if the reaction takes place quantitatively in the sense of the right-hand side of the equation.

If you soften water instead of 0.75 kg of trisodium phosphate, it crystallizes and 0.0413 kg of NaF crystallized with 0.75 kg of trisodium phosphate and 0.124 kg of trisodium phosphate crystallized, the filtrate has a hardness of 4.7 ° compared to 2.8 ° when used of sodium phosphate-sodium fluoride. If you wanted the same softening effect to reach 2.8 ° only with crystallized trisodium phosphate, one would have to 1.17 kg of trisodium phosphate for the above water apply crystallized, which, however, increases the alkalinity of the water considerably because a A multiple of the amount of alkali metal phosphate is required than theoretically corresponds to the equation.

2. In the same water as under 1, 1.15 kg of double salt 2 Na ₃ PO ₄ · NaF · 19 H ₂ O are added at 18 ° C. After the flakes have separated out, the filtrate has a hardness of o °. This complete softening can be achieved even with considerable surpluses of precipitating chemicals, which are not considered in practice, when other softening methods are used, ζ. Β. the alkali phosphate method, soda or lime-soda softening, cannot be achieved.

3. The same experiment as under 2 is ^{carried out at a temperature of 5 °} C .; the filtrate has a hardness of 0.1 °.

4. Raw water with a total hardness of 12.2 °, which is composed of 8.4 ° carbonate hardness and 3.8 ° sulfate hardness, is mixed with 0.445 kg of 2Na ₃ PO ₄ * Na F · 19 H ₂ O per cubic meter at 70 ° C softened; After the filtration, a steam boiler is fed with this water. When the boiler is full, the boiler is heated and the boiler water recirculation is put into operation in such a way that the rüdigef ührte boiler water, which is _{alkaline due to the reaction products of carbonate hardness and precipitants due to the formation of Na 2} CO ₃ , pre-softens the raw water to be softened. However, since soda is partially split into caustic soda and carbon dioxide in the steam boiler, the boiler return water contains caustic soda as well as sodium carbonate that has not yet been decomposed. The backwater falls out of the sulphate hardness, insofar as it is bound to lime, and the total magnesia hardness, but also a considerable part of the carbonate hardness, because the caustic soda has bound the bicarbonate carbonic acid, which is necessary to keep the calcium carbonate hardness in solution. The water pre-softened by the boiler water return then only has a residual hardness of 1.5 °. By adding 0.055 kg of 2 Na ₃ PO ₄ · NaF · 19 H ₂ O per cubic meter of the pre-softened water to be softened, it is continuously post-softened to 0 °.

Claims (3)

Patent claims: i. Process for softening water, characterized in that the water to precipitate the hardness builders with the corresponding amount of fluorine-containing Alkali phosphates, especially sodium phosphate fluorides, such as sodium phosphate-sodium fluoride, is moved. 2. The method according to claim i, characterized in that the water in known Way pre-softened and only the residual hardness is removed by treatment with fluorine-containing alkali metal phosphates. 3. The method according to claim 2, characterized characterized in that the pre-softening by returned boiler water or Boiler sludge water is caused, the alkaline reactions from the subsequent softening with fluorine-containing alkali metal phosphates Has.