Evaporative Condenser Chemical Cleaning & Jetting

Direct answer: Traditional acid cleaning (such as HCl, H₂SO₄) has a strong corrosive effect on the zinc layer and can completely dissolve it within tens of minutes.

1. Structural Characteristics and Cleaning Challenges of Evaporative Condensers

Evaporative condensers utilize spray water that evaporates and absorbs heat on the surface of heat exchange coils, condensing the medium inside the tubes. The circulating water continuously evaporates and concentrates, causing calcium and magnesium ions to precipitate on the outer walls of the coils, forming scale. The coil base material is carbon steel, with an outer surface having a hot-dip galvanized layer (60μm–100μm) — this is the most critical anti-corrosion barrier. Once the zinc layer is damaged and the carbon steel substrate is exposed, rapid perforation and leakage will occur in humid environments, rendering the entire unit unusable.

Therefore, the core challenge of evaporative condenser cleaning is: effectively removing scale without damaging the galvanized layer. Traditional acid cleaning (such as HCl, H₂SO₄) has a strong corrosive effect on the zinc layer and can completely dissolve it within tens of minutes.

2. Zinc Corrosion Characteristics and pH Control

Zinc is an amphoteric metal that reacts with both acids and strong alkalis. Under static conditions at 25°C, the corrosion rate of zinc in solutions of different pH values is as follows:

Zinc Corrosion Characteristics and pH Control — pH, Type, Corrosion Rate (g/m²·h) and Assessment.
pH	Type	Corrosion Rate (g/m²·h)	Assessment
1~2	Strong Acid	>50	Prohibited
3~4	Moderately Strong Acid	5~50	Usable with inhibitor
5~6	Weak Acid	0.5~5	Safe with inhibitor
6~8	Neutral	<0.1	Safe
9~11	Weak Alkaline	0.1~1	Usable
>12	Strong Alkaline	>10	Prohibited

Conclusion: Zinc is most stable at pH 6~8; pH 5~6 weak acid and pH 9~11 weak alkaline are usable with inhibitor protection; strong acid (pH<3) and strong alkaline (pH>12) are unusable regardless of inhibitor type.

3. Cleaning Agent and Corrosion Inhibitor Selection

Cleaning Agents

Sulfamic Acid (5%~8%) is the preferred primary cleaning agent. Its corrosion rate on zinc is only 1/5 to 1/10 that of HCl, it contains no chloride ions, and it is solid at room temperature, making it convenient for storage and transport. Reaction: CaCO₃ + 2NH₂SO₃H → Ca(NH₂SO₃)₂ + H₂O + CO₂↑.

Citric Acid (2%~3%) serves as an auxiliary cleaning agent, dissolving iron oxides through chelation; its waste solution is biodegradable.

Strictly prohibited: HCl, H₂SO₄, HF, Concentrated NaOH (pH>12), high-concentration EDTA solutions.

Inhibitor Combination (Core Protection System)

BTA (0.15%~0.25%): A nitrogen-containing heterocyclic inhibitor that self-assembles on the zinc surface to form a dense hydrophobic protective film, blocking H⁺ attack.

MBT (0.05%~0.10%): Forms Zn-S chemical bonds with zinc through mercapto groups in acidic media, more robust than physical adsorption films. When used synergistically with BTA, inhibition efficiency can exceed 95%.

Sodium Molybdate (0.05%~0.10%): An anodic inhibitor that promotes the formation of a ZnO/Molybdate composite passivation film, providing dual "cathodic shielding + anodic passivation" protection.

Urotropine (0.10%~0.15%): Provides secondary protection for the carbon steel substrate, preventing acidic corrosion at localized zinc layer defects.

4. Combined Cleaning Process

Stage 1 — Chemical Softening: Prepare acidic cleaning solution with pH strictly controlled at 4.5~5.5, temperature 40~55°C (not exceeding 60°C to prevent inhibitor failure). Circulate for 4~8 hours, testing pH and calcium ion concentration every 30 minutes; end when two consecutive readings show no further change.

Stage 2 — High-Pressure Water Jetting: After acidic wastewater is discharged to a neutralization tank for treatment, use 300~500 bar high-pressure water with a 25° fan nozzle, positioned 30~40cm from the coils, flushing layer by layer from top to bottom to remove loosened scale debris remaining after chemical cleaning.

Stage 3 — Rinse and Neutralization: Rinse with clean water until pH ≥6, then circulate 0.3%~0.5% Sodium Carbonate solution for 30 minutes to neutralize residual acid, followed by final fresh water rinse until conductivity returns to normal.

5. Acceptance Criteria and Engineering Case Study

Acceptance Criteria: ① Visual inspection: galvanized layer intact, uniform silver-gray appearance, no blackening or rust spots; ② Residual scale ≤0.1mm; ③ Zinc layer thickness loss rate ≤5%; ④ Condensing pressure reduced to nameplate range or decreased by ≥15% compared to pre-cleaning.

Engineering Case Study: In summer 2025, three evaporative condensers at a large chemical enterprise in Jiangsu experienced continuously rising condensing pressure and frequent shutdowns due to fouling (scale thickness 3~5mm, approximately 85% CaCO₃). Danyang Blue Star Cleaning adopted a customized solution using Sulfamic Acid + Citric Acid combined cleaning with BTA + MBT + Sodium Molybdate triple protection, with pH controlled at 5.0±0.3 and temperature at 48~52°C. After 6.5 hours of circulation cleaning, 400 bar high-pressure water jetting was applied. Post-cleaning inspection: galvanized layer intact and undamaged; average zinc layer thinning at 5 sampling points was only 4.1μm (loss rate 5.3%); condensing pressure decreased from 1.65 MPa to 1.32 MPa (20% reduction); system returned to normal operation.

6. Evaporative Condenser Cleaning FAQ

Q1: How often should evaporative condensers be cleaned?

Twice a year is the usual baseline for open evaporative units, once before the cooling season and once at its end, because the coil is simultaneously wet, warm and exposed to air, which suits scale and biofilm. Bring the work forward when condensing pressure rises above the commissioning figure at unchanged load, when spray distribution looks uneven, or when the basin holds sediment. In hard-water areas, quarterly inspection of the coil surface is sensible even if cleaning stays twice yearly. Danyang Lanxing Anticorrosion Cleaning Co., Ltd. sets the interval from measured condensing pressure and water analysis.

Q2: Can galvanised surfaces be cleaned without stripping the zinc layer?

Yes, provided the chemistry and contact time are controlled. Zinc is amphoteric, so it dissolves in both strong acid and strong alkali. The practical route is a mild organic-acid system held in a narrow pH band with a dedicated zinc inhibitor, plus continuous monitoring of dissolved zinc so circulation stops before measurable loss occurs. Field checks after cleaning compare zinc thickness at several sampling points against the pre-cleaning reading. In one project the average thinning came to 4.1 micrometres, about five percent of layer thickness. Danyang Lanxing Anticorrosion Cleaning Co., Ltd. reports that thickness data at handover.

Q3: How is evaporative condenser cleaning verified?

Three measurements: condensing pressure at a fixed load before and after, zinc layer thickness at marked sampling points, and a visual check of coil fins, fill and basin photographed from the same angles. A documented case on this site saw condensing pressure fall from 1.65 MPa to 1.32 MPa, a 20 percent reduction, after circulation cleaning followed by high-pressure water jetting. Where chemical cleaning is used, acceptance records follow GB/T 25146-2010, and jetting work follows the GB/T 26148-2025 safety requirements. Danyang Lanxing Anticorrosion Cleaning Co., Ltd. issues the complete verification record.

Evaporative Condenser Chemical Cleaning and High-Pressure Water Cleaning Technology