Single-double filtration

RECYCLING OF RESIDUAL SODIUM CHEMICALS IN THE MANUFACTURING OF SODIUM CARBONATE: SOLATECH^®/NEUTREC^® PROCESS

In the case of municipal and hospital waste incineration, and where the single filtration is used for flue gas cleaning, the Flue Gas Cleaning Residues collected in the bag filter are made up of the fly ash and the RSCs themselves, the latter consisting mainly of sodium chloride, sodium sulphate and sodium carbonate. These residues also contain impurities such as activated carbon, heavy metals, etc.

REVATECH, subsidiary of SITA BELGIUM (previoulsy WATCO), and SOLVAY have developed a process which combines the solidification of the sodium residues (based on the SOLATECH^® treatment and solidification process) and the recycling of their soluble saline fraction in the manufacturing of sodium carbonate.

The sodium residues are mixed with hydraulic binders, then placed in an aqueous solution with certain additives. The suspension formed in this way passes through a filter press which separates out the insolubles (containing in particular most of the heavy metals). The resulting products are a brine and a filtration cake.

The brine is then further purified so that it may be reused in the manufacture of sodium carbonate.

The filtration cake containing hydraulic binders solidifies into an inert matter (according for example to French standards) which is appropriate for tipping on a landfill site.

The process does not produce any aqueous effluent: the only outgoing flows are the recyclable brine and the filtration cake.

Other possibilities:

Direct recycling of flue gas cleaning residues (single filtration).

Recycling of Residual Sodium Chemicals in the production of sodium carbonate (double filtration).

Valorisation of all the flue gas cleaning residues: REVASOL pilot.