Scrap iron is loaded to the reactors in batch operation.
Ferric chloride solution, coming from storage tank, is continuously fed to the first reactor in series. Its flow rate is automatically controlled by means of FIC.
Process water coming from distribution ring is continuously added to ferric chloride stream in automatic control by FIC. Its flow rate is adjusted by a flow rate ratio controller depending on the flow rate of ferric chloride solution in order to reach the desired concentration of the final product (40% w/w of FeCl3 aqueous solution).
The resulting FeCl2 aqueous solution overflows from the second reactor to the receiving tank.
A temperature of 45÷50 °C is needed in order to trigger the FeCl3 reduction, while in steady condition the reaction is exothermic with 150 Kcal/Kg FeCl3.
Consequently a double task has to be performed:
- heating of the FeCl3 solution every start-up;
- cooling of the reacting solution during normal operation.
This double task is carried out by the heat exchanger. A solution stream coming from the bottom of the reactors is heated/cooled through the heat exchanger and then recirculated into the reactors.
Low pressure steam is fed to the exchanger during start-up in order to heat-up the FeCl3 solution, while during normal operation cooling water cools-down the reacting solution.
Cooling water flow rate is automatically controlled by TIC.
Two basket filters (one in stand-by) are placed on pump suction line in order to avoid pump damage due to scrap iron entertainment.
All the draining and cleaning waters coming from this section are sent to the sludge pit, where solids are settled and clarified FeCl2 solution is recovered.
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