Chemical cleaning in steam boiler is performed prior to a new boiler is put in service; the internal surface of the steam generating section should be cleaned to remove oil, grease and protective coatings. The overall chemical cleaning procedures in steam boiler contains of two steps as follow cold degreasing and passivation.
Preliminary to boiling out:
- The intent of degreasing is to remove the oils, grease and the other hydrocarbon or preservation oils.
- The intent of passivation is to get a final passive film on the waterside heating surface.
Preparation of chemical cleaning in steam boiler as follow:
- All pressure parts must be carefully inspected for obstruction and the necessary hydrostatic test made. Steam drum blowdown line and chemical feed line should be checked to be certain that they are free and clear.
- Mechanically remove as much oil and grease as possible from drums and headers before boiling out. Check all drums internal for tightness of bolted parts.
- Prepare all recommended chemical ready on site.
- Check the leaks of the temporary lines flanges and fitting by circulating the water using circulating pump.
The procedure of chemical cleaning in steam boiler as follow:
- Make up the closed circuits system with de-mineralized or condensate water.
- Reduce the water level to allow the total amount of chemical entering the system with no over flow (assume 1 kg chemical is approximately equal to 1 liters).
- Add the cold degreasing chemical as recommended.
- Do a multi sampling system to ensure that the solution has fully mixed.
- Perform continuous circulation for 8 hours to get sufficient contact time and satisfactory grease removal.
- The oils sign should appears in the solution and add the de-mineralized water to make the oils sign overflow from the closed system.
- If the final solution pH less than 9.5, so adjust the pH using the Trisodium Phosphate.
- If the oil signs on the water surface has disappeared, cold degreasing is considered completed.
- Drain the solution in the boiler system, flush the boiler using condensate de-mineralized water until the pH less than 9.
Recommended water quality during perform chemical cleaning in steam boiler:
- After degreasing is finished, drain the water solution inside the system.
- Flush the system with de-mineralized water to ensure that the turbidity has been lower than 10 NTU and the iron concentration has less than 2 ppm.
- Inject the passivation chemicals as recommended.
- Adjust the pH with amine to get the pH range of 9.5 – 11
- Circulate for 4 – 6 hours.
- Passivation is complete.
- The solution should be maintained in the system until the boiler is ready to be started. Do not allow the boiler is in empty condition for a long time.
- Use trisodium phosphate to increase pH.