Method and device for regeneration of hydrochloric acid

Abstract

The subject matter of the present invention is a method to extract or recover hydrochloric acid from hydrochloric acid solutions containing metal by means of pyrohydrolytic treatment, followed by absorption and/or condensation of the gaseous hydrogen chloride thus formed in order to form hydrochloric acid. According to the invention, a first partial flow of the hydrochloric acid solution containing metal undergoes pyrohydrolytic treatment and a second partial flow of the metal-containing solution is fed to the absorption column. A device for implementing the process according to the invention is also the subject of the present invention.

Claims

1. Method to extract or recover hydrochloric acid from hydrochloric acid solutions containing metal by means of spray roasting followed by one or both of absorption and condensation of gaseous hydrogen chloride thus formed in order to form hydrochloric acid, comprising providing an initial flow of hydrochloric acid solution containing metal; splitting the flow of the hydrochloric acid solution containing metal into a first partial flow and a second partial flow of hydrochloric acid solution containing metal; feeding the first partial flow of hydrochloric acid solution containing metal to a spray roaster to undergo pyrohydrolytic treatment, which releases gases; directly contacting the gases released from the pyrohydrolytic treatment with the hydrochloric acid solution containing metal, thereby cooling the gases released from the pyrohydrolytic treatment and concentrating the hydrochloric acid solution containing metal; feeding the second partial flow of hydrochloric acid solution containing metal directly to an absorption column without undergoing pyrohydrolytic treatment, thereby increasing a concentration of metal in the hydrochloric acid solution containing metal, wherein at least one of the initial flow or the first partial flow of hydrochloric acid solution containing metal is concentrated by evaporation such that the first partial flow of hydrochloric acid solution containing metal fed to the spray roaster for pyrohydrolytic treatment is a concentrated solution.

2. Method according to claim 1, wherein the step of cooling gases released from the pyrohydrolytic treatment via direct contact with the hydrochloric acid solution containing metal causes a concentration of hydrochloric acid solution containing metal to increase via evaporation prior to splitting the hydrochloric acid solution containing metal such that the first partial flow to the spray roaster and second partial flow to the absorption column are both a concentrated solution.

3. Method according to claim 2, comprising mixing the second partial flow of hydrochloric acid solution containing metal with rinsing water before being fed to the absorption column.

4. Method according to claim 1, comprising extracting hydrochloric acid from a ferrous solution and using the extracted hydrochloric acid in the hydrochloric acid solution containing metal.

5. Method according to claim 4, comprising extracting a regenerated hydrochloric acid with an iron content of more than 10 g/l after the second partial flow of hydrochloric acid solution containing metal passes through the absorption column.

6. Method according to claim 1, wherein the hydrochloric acid solution containing metal originates from a pickling process, comprising regenerating hydrochloric acid by extraction after the second flow of hydrochloric acid solution containing metal passes through the absorption column and recycling the regenerated hydrochloric acid containing metal to the pickling process.

7. Method according to claim 1, wherein the hydrochloric acid solution containing metal originates from a leaching process, comprising regenerating hydrochloric acid by extraction after the second flow of hydrochloric acid solution containing metal passes through the absorption column and recycling the regenerated hydrochloric acid containing metal to the leaching process.

8. Method according to claim 1, wherein the first partial flow of the hydrochloric acid solution containing metal is concentrated by evaporation prior to feeding to the spray roaster.

9. Method according to claim 1, wherein both the first partial flow of the hydrochloric acid solution containing metal and the second partial flow of hydrochloric acid solution containing metal are a concentrated solution.

10. Method according to claim 9, wherein the initial flow of hydrochloric acid solution containing metal is concentrated by evaporation prior to splitting into the first partial flow and second partial flow.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a diagram of the mass flows in a conventional pickling line with acid recovery; and

(2) FIG. 2 shows a diagram of the mass flows in a pickling line with acid recovery according to an embodiment of the invention.

DETAILED DESCRIPTION

(3) FIG. 1 shows a diagram of a pickling line 1 with an acid recovery plant 2 (ARP) according to the prior state of the art. In this pickling line, 1200 kg/h of iron are dissolved at a throughput of 2 million tonnes of low-alloy steel per annum, with a pickling loss of 0.4% (as Fe). Regenerated hydrochloric acid containing 194.6 g/l of free hydrochloric acid is pumped from the ARP (Acid Recovery Plant) 2 to the pickling line 1.

(4) In pickling line 1, the hydrochloric acid reacts substantially according to the following reaction:
FeO+2HClFeCl.sub.2+H.sub.2O
and is thus spent and converted into iron chloride.

(5) At an iron content of approximately 121 g/l and a free acid content of 47 g/l, the pickling solution is spent and fed to the acid recovery plant (ARP) 2. For such content, the required capacity of the ARP is 10 m.sup.3/h, and the fuel gas requirement is 27896 MJ/h. For absorption and/or condensation of the gases coming from the roasting reactor, 11.11 m.sup.3 of water per hour are fed to the absorption column in the acid recovery plant 2. In addition, 1200 kg of iron are discharged from the spray roasting reactor as Fe.sub.2O.sub.3.

(6) Similarly, a waste gas flow of 10.99 tonnes of water vapor leaves the ARP hourly.

(7) FIG. 2 shows a diagram of a pickling line 1 with an acid recovery plant 2 according to an embodiment of the invention. In this embodiment, regenerated hydrochloric acid containing 194.6 g/l of free hydrochloric acid is pumped from the ARP 2 to the pickling line 1. Due to the fact that a part 6 of the spent pickling solution is fed to the absorption column together with rinsing water, the regenerated acid has an iron content of 39.9 g/l. In the pickling line 1, the same amount of iron is dissolved as in FIG. 1, and the hydrochloric acid is spent.

(8) At a free acid content of 47 g/l, the pickling solution is spent and fed through the feed line 3 to the acid recovery plant 2. In this scenario, the iron content is 161 g/l.

(9) The feed line 3 to the ARP has a branch piece 4 through which a partial flow 5 of the spent pickling solution is fed to the pyrohydrolysis reactor (spray roaster), and another partial flow 6 of the spent pickling solution is fed to the rinsing water in the absorption column.

(10) Thus, a smaller amount of spent pickling solution, compared to FIG. 1, is fed to the pyrohydrolysis in order to extract the same amount of iron (1200 kg/h). In this scenario, only 7.52 m.sup.3/h are fed to the pyrohydrolysis stage of the ARP, and the remaining 2.48 m.sup.3/h are fed to the absorption column, together with the water. Thus, the fuel gas requirement is only 21319 MJ/h.

(11) As a result, 23.6% of the fuel gas is saved.

(12) In addition, electrical energy is also saved, mainly due to the exhaust air fan, because the volume of process gas drops by the same proportion as the saved fuel gas. Thus, only 8.2 tonnes of water vapor per hour leave the ARP with the waste gas.

(13) In both described embodiments of the present invention, both the regenerated and the spent acid each have approximately the same free HCl content. The process according to the invention does not have any negative influence on the pickling effect.

(14) In another embodiment of the invention, the concentration of the spent acid is first increased in a cooling unit for the hot waste gases, e.g. in a Venturi loop. The concentrated, metal-containing solution (concentrate) is then split into a first and second partial flow. The first partial flow is fed to the pyrohydrolysis reactor and the second partial flow from the concentrated waste pickling liquor is fed to the absorber or to the rinsing water flowing to the absorber.

(15) The results of some calculations are summarized in Table 1:

(16) TABLE-US-00001 TABLE 1 Roaster Spec. energy Fe (g/l) in Fe (g/l) in feed consumption Fuel waste picking regenerated Fe (g/l) quantity (kcal/l waste saving liquor acid in concentrate (m.sup.3/h) pickling liquor) (%) 1 Conventional 120 0 202 6.64 666 process (FIG. 1) 2 Waste pickling 160 40 270 4.99 509 23.6 liquor to absorber 3 Waste pickling 170 50 284 4.68 479 28.0 liquor to absorber 4 Concentrate to 160 40 237 5.65 570 14.4 absorber 5 Concentrate to 170 50 245 5.45 550 17.4 absorber

(17) The comparison in Table 1 shows that the energy-saving potential is greater if the waste pickling liquor is fed to the absorber, rather than its concentrate. The metal content in the regenerated acid is controlled via the amount of metal-containing solution mixed into the rinsing water for feeding to the absorber. Rinsing water consumption diminishes accordingly.

(18) In an HCl regeneration for 5.3 m.sup.3/h waste pickling liquor (for an annual pickling capacity of approximately 1 million tonnes), this results in savings of >200 k/year, based on European energy prices.

(19) The investment costs for a new plant are also lower.

(20) Similarly, in existing plants, the invention can be used to achieve a significant increase in performance.