Washing water preparation in dip painting with complete return of used water into the washing water system

摘要

The method for obtaining desalinated water from rinse water of dip coating and recirculating the water into feed water of rinse water system, comprises transporting partial volume of the rinse water system in a coagulation container containing the rinse water, dosing coagulation agent and then adjusting the pH value, guiding the partial volume of the treated rinse water from the coagulation container over an activated carbon filter and then discharging from the coagulated coating residues, and guiding the filtrate of the filtration step over an ion exchanger system. The method for obtaining desalinated water from rinse water of dip coating and recirculating the water into feed water of rinse water system, comprises transporting partial volume of the rinse water system in a coagulation container containing the rinse water, dosing coagulation agent into the container and then adjusting the pH value, guiding the partial volume of the treated rinse water from the coagulation container over an activated carbon filter and then discharging from the coagulated coating residues, and guiding the filtrate of the filtration step over an ion exchanger system and recirculating the partial volume of the desalinated permeates of the ion exchanger system into the rinse water system of the dip coating. The reception of the partial volume of the rinse water and the recirculation of the treated rinse water are adjusted so that the conductivity of the rinse water in the rinse water system does not exceed 40mu S/cm, and are continuously carried out in all single steps and over an equally large volume stream. The coagulation container consists of two reactors separated from one another. The partial volumes of the rinse water system are fed exclusively into a reactor in which the coagulation agent is added and the pH value is adjusted. The partial volume of the treated rinse water is guided over the filter from the another reactor until a change in the operation mode of the both reactors is carried out. One of the reactors is evacuated or filled to 80%, so that the another reactor is fed with partial volume of the rinse water system, the coagulation agent is dosed and then the pH value is adjusted, and/or the partial volume of the treated rinse water is guided over the filter from the another reactor. In the partial volume of the rinse water to be obtained, 1 mmol of cationic equivalent of the coagulation agent per liter is dosed. The reception of the partial volume and the addition of the coagulation agent in the coagulation container are carried out in such a way that the pH value is 9.5 to each point of time before the adjustment of the pH value. The pH value in the coagulation agent after dosing is adjusted to 7.5. The pore size of the filter material in the filtration step is greater than 1 mu m. The ion exchanger system consists of a series arrangement of cation- and anion exchanger.