The SOLVAir® bicarbonate solution process is based on the injection of dry, finely ground sodium bicarbonate into the gases to be cleaned.
The composition of the gases to be cleaned depends largely on the process generating them. Even so, very generally they contain:
- dust (fly ash)
- acid components: hydrochloric acid (HCl), sulphur dioxide (SO2), hydro-fluoric acid (HF) and nitrogen oxides (NO and NO2),
- heavy metals (lead, mercury, cadmium, etc.)
- dioxins and furans
Double step filtration
Initial dedustring (generally using an electrofilter) is carried out in certain cases prior to neutralisation : this eliminates the majority of the fly ash and a part of heavy metals and organics like dioxins. Where the gases are dedusted by an initial filter before injecting sodium bicarbonate, we talk of a double step filtration SOLVAir® bicarbonate process; in other cases, we talk of a single step filtration SOLVAir® bicarbonate process.
In case of double step filtration, the cake on the bag filter is more homogeneous for a better treatment of the gas, especially where there is a lot of dust. This process allows also a more economical recycling of RSC and of the fly ashes.
The sodium bicarbonate, stored in silos or in bigbags depending on the applications, is ground to an optimal granulometry and immediately injected into the gases.
The raw gases temperature at the injection point is more than 140°C.
If the residence time of the sorbent in the flue gas before the baghouse filter is less than 1 second, a contact reactor is used.
Residual sodium chemicals
The sodium bicarbonate neutralizes the acids present in the gases (in particular hydrochloric acid, sulphur dioxide, hydrofluoric acid) to form sodium salts (sodium chloride, sodium sulphate, sodium fluoride, sodium carbonate), known as the Residual Sodium Chemicals (RSC).
Recycling of the purification residues is facilitated by the fact that the different types of residues (residual salts and fly ash) are separated.
Double filtration is generally the most economical solution where it is possible to recycle the residues.