Acid gas treatment and dust removal

Acid gas treatment and dust removal

For the treatment of acid gases such as SOx, HCl, and HF, PROSSERGY has developed dry/semi-dry processes,
with or without recirculation and reactivation, using calcium or sodium sorbents.

The addition of activated carbon or coke injection also allows for the treatment of PCDD/F (dioxins and furans), Hg (mercury), and other metallic pollutants. Each solution is specifically tailored to the client’s needs and the installation’s characteristics, considering:
  • The types of gases to be reduced and their respective concentrations.
  • Required efficiencies.
  • Sorbent cost.
  • The cost of disposal for residues.
  • Integration into the overall flue gas treatment and the thermal design of the unit (reaction temperature and energy consumption).
Reagent selection must be based on the specific pollutants to be captured to achieve optimal economic performance.

Sodium Bicarbonate or Sodium
Carbonate (Na₂CO₃ or NaHCO₃)

Sodium Bicarbonate or Sodium Carbonate (Na₂CO₃ or NaHCO₃) must be ground to reduce particle size before being injected into the flue gas. It can also be supplied already ground to the optimal grain size.

In the case of using bicarbonate, the first step is to convert it into carbonate.
2NaHCO3 ⇒ Na2CO3 + H2O + CO2

The capture reactions are as follows:
NaHCO3+ HCl ⇒ NaCl + H2O + CO2
2 NaHCO3+ SO2 + ½O2 ⇒ Na2SO4 + 2 CO2 + H2O
NaHCO3 + HF ⇒ NaF + H2O + CO2

Lime (Ca(OH)₂)

Lime (Ca(OH)₂) can be used without grinding but with various qualities (standard lime or high specific surface lime) depending on the process used and the expected economic and technical performance.

The capture reactions are as follows:

Ca(OH)2 + 2HCl ⇒ CaCl2 + 2H2O
Ca(OH)2 + SO2 + ½O2⇒ CaSO4 + H2O
Ca(OH)2 + 2HF ⇒ CaF2 + 2H2O

When using lime as a reagent, residue recirculation can be implemented to limit its consumption.

It is also possible to carry out dual injection of lime/sodium bicarbonate to combine the best of both reagents, achieving optimal efficiency and operating costs. La sélectivité de captation des deux réactifs est différente :

The two reagents have different capture selectivity:

Optimal reaction temperatures also vary. Generally, for the commonly encountered temperature ranges in these treatments, sodium bicarbonate offers good capture efficiency above 150°C, while the efficiency of hydrated lime increases at lower temperatures.

The optimal capture efficiencies and temperatures differ depending on the pollutants to be treated.

When combining several processes for capturing multiple pollutants, temperature selection is crucial to achieve optimal techno-economic results. In some cases, the addition of a heater and heat exchanger can improve treatment operation and optimize the energy efficiency in the installation.

As with all other processes, PROSSERGY pays close attention to the compatibility and combination of different treatments (DeNOx, dust removal, acid gas, metals, etc.) and their energy integration.