Basis of this process is the separation of the free acid from the metals in a resin bed (retardation). The solution containing metal salts and deficient in acid is disposed in the waste water treatment plant, in a second step the acid absorbed in the resin bed is eluted again with water and returned to the pickling line. The retardation process is implementable for all pickling solutions such as HF/HNO3, H2SO4, HF/H2SO4 etc..
In order to guarantee the longterm and safe application of the Steuler Acid Purification Unit (SAPU) it is necessary to pretreat the hot, solid containing pickling solutions. In principal a complete solid removal is always required e. g. by Steuler Acid Microfiltration (SAM), ensuring that no particles at all permeate into the resin bed thus causing blockings, increased pressure loss and reduced capacity. According to the temperature, kind of pickling acid and concentrations, it is necessary to provide a cooling before the Steuler Acid Purification Unit (SAPU) in order to adjust the optimal operating temperature. This concerns, in particular, the recovery of hot sulfuric acid and the mixed acid purification. The cooling is designed like the one for the Steuler Acid Microfiltration (SAM), as cost-efficient single-stage cooling or two-stage cooling by heat recovery. The Steuler Acid Purification Unit (SAPU) use an ion exchange resin that has the ability to reversible adsorb strong acids from solution, metal salts pass the resin. The acid can be desorbed from the resin with water once again. By alternately passing metal containing acid and water through a bed of resin it is thus possible to separate the free acid from the metal salts. There are two steps in the basic Steuler Acid Purification Unit (SAPU) process - the upstroke and the downstroke. During the upstroke, filtered, metal containing acid is pumped into the bottom of the resin bed. Acid is adsorbed by the resin and the remaining de-acidified metallic salt solution is collected from the top of the bed. During the following downstroke water is pumped into the top of the bed, desorbing the purified acid from the resin, and is returned to the pickling line as regenerated acid. The total cycle lasts a few minutes and is automatically controlled. The waste acid from the regeneration is collected together with the concentrated sludge from the pre-filtration/sedimentation in the sump pit and conveyed to the waste water treatment plant. |
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