Chlor-alkali diaphragm electrolysis process and relevant cell

In a process of chlor-alkali electrolysis carried out in a diaphragm cell, comprising pairs of interleaved anodes and cathodes, said cathodes are provided with openings and coated with a porous diaphragm resistant to corrosion, said diaphragm dividing the cell into a cathodic compartment and an anodic compartment, the anodes are either expandable or non-expandable said cell having inlets for feeding fresh brine, and outlets for removing produced chlorine and hydrogen and caustic where the caustic includes a concentration of chlorine and chlorate, the improvement comprising controlling oxygen content in the chlorine and chlorate concentration in the caustic independently from the flow rate and the concentration of the said fresh brine by equipping each anode with hydrodynamic means and downcoming ducts and by adding an aqueous solution of hydrochloric acid to the brine in the anodic compartment of the cell through distributors positioned over said hydrodynamic means.