Citric Acid Process in Boiler Pickling

The process flow for citric acid-based boiler descaling typically includes the following steps:

1. Preparation

① System inspection: Conduct a comprehensive inspection of the boiler and its associated systems to ensure that all equipment is in good condition, with no leaks or other abnormalities. Close valves not involved in the acid‑washing process and connect the acid‑washing piping to verify the integrity of the acid‑washing system.

② Chemical formulation: Based on the boiler’s volume and the extent of scale formation, calculate and prepare the required amounts of citric acid, corrosion inhibitor, solubilizing agent, and other chemicals. The typical concentration of citric acid is 2% to 4%, while the dosage of the corrosion inhibitor should be determined according to its specific type and the manufacturer’s instructions, generally ranging from 0.1% to 0.3%.

③ Water Quality Testing: Conduct water quality tests on the water used to prepare the acid solution to ensure it meets the required standards, thereby preventing impurities from compromising the pickling process or causing damage to the boiler.

2. Water flushing

① Start the flushing pump: Inject an adequate amount of deionized or softened water into the boiler, then start the flushing pump to circulate the water throughout the boiler system for flushing. The purpose of this flushing is to remove dust, silt, and other loose contaminants from the boiler, as well as to verify the system’s water flow and sealing integrity.

② Water Quality Monitoring: During the flushing process, water samples should be collected at regular intervals for analysis, monitoring parameters such as turbidity and pH. Flushing is considered satisfactory when the turbidity of the water sample meets a specified threshold (e.g., less than 10 NTU) and the pH remains stable near neutral.

3. Pickling

① Acid solution preparation: Add citric acid, a corrosion inhibitor, and water to the cleaning tank according to the calculated proportions, and stir thoroughly until homogeneous to prepare the acid‑pickling solution. Then, slowly inject the acid solution into the boiler system, ensuring uniform distribution throughout the boiler.

② Circulating Acid Cleaning: Start the acid‑cleaning pump to circulate the acid solution throughout the boiler system. During circulation, maintain the acid‑solution temperature at approximately 80–90°C to enhance cleaning efficiency. At the same time, regularly monitor the acid‑solution concentration and pH, and promptly replenish citric acid as needed to ensure stable acid‑solution strength. The typical cleaning duration is 3–6 hours; the exact length should be determined based on the thickness and characteristics of the scale deposits.

③ Monitoring the pickling process: During pickling, the condition inside the boiler should be observed through inspection ports or sampling taps, noting changes in the acid solution’s color and the extent of scale dissolution. If slow scale dissolution or a rapid drop in acid concentration is detected, the underlying causes should be promptly investigated and appropriate corrective measures implemented.

4. Rinsing after pickling

① Acid Solution Discharge: After pickling is completed, the acid solution remaining in the boiler shall be discharged into a dedicated waste‑acid treatment pond for proper treatment. During the discharge process, strict precautions must be taken to prevent acid leakage and avoid environmental contamination.

② Water flushing: Immediately after acid cleaning is completed, inject deionized water or softened water into the boiler for flushing. During flushing, start the flushing pump to circulate water throughout the boiler system until the pH of the discharge water reaches 6–7 and the citric acid content in the water falls below the specified limit (e.g., less than 0.1%); at that point, the flushing is considered satisfactory.