FERTILIZER INDUSTRY
How a major fertilizer industry solved exhaust elimination issue
How a large fertilizer industry solved the problem of exhaust gas elimination
A large fertilizer industry was facing a complex problem, consisting of numerous concomitant aspects.
To remove the exhaust gases produced during the acidification process of rocks and phosphate minerals, a reactive absorption unit (scrubber) was installed, in which a caustic soda solution (NaOH) was fed to the recirculated water to neutralize acids such as HCl, HF and H₂S. However, the exhaust gases also carried other contaminants, including dust and a significant amount of CO₂.
The results of the absorption were therefore largely disappointing, since the neutralization process conducted at a high pH (about 9) by caustic soda generated other problems at the same time:
| Cause |
Effect |
| Excessive absorption of carbon dioxide during acid abatement with caustic soda |
Excessive consumption of caustic soda |
| Formation of sodium fluorosilicates during acid absorption in the presence of silica |
Severe fouling of sensitive parts of the system, such as spray nozzles, packing media, instrumentation sensors, drip trays, etc. |
| Unwanted Solid Sodium Bicarbonate (SBC) Formation Due to Cause 1 |
Need for large quantities of system water to avoid exceeding the solubility limit of the SBC |
Despite the control efforts made by the operators to correct the problems, the results were disappointing, and continuous cleaning of the scrubber interior had to be carried out to ensure continuity of production due to dust consisting of sodium fluorosilicates and process sand residues. In addition, soda consumption was unsustainable.
The solution adopted by Industrious Global Technologies was a two-section system:
- First section: Dust removal by means of WDCS, wet collection system
- Second section: Absorption unit (3-stage scrubber)
In the first section, caustic soda is injected and the formation of sodium fluorosilicates (SFS) is promoted at this stage, so that SFSs can be removed from the exhaust gases before reaching the scrubber and creating occlusive adherent deposits on the fillers.
Caustic soda is also fed into the scrubber, but together with a strong oxidizing agent, to promote the neutralization of H₂S at a relatively low pH (7,3), with the formation of sodium sulfate as an end product instead of sodium sulfide, which at low pH could convert back into H₂S. At the same time, the low pH regime minimizes the reactive absorption of CO₂.
This solution was successfully tested using a small-scale pilot unit during two years of testing and achieved all objectives, solving the initial complex problem:
- No abnormal consumption of caustic soda due to the unwanted reaction with the CO2 present in the gaseous emission;
- No fouling of the packing bed and other internal parts of the scrubber;
- Very small amount of liquid discharge compared to the previous solution adopted by the customer.