Power Plant Condenser Online Chemical Cleaning: A Case Study

Abstract: A 300MW coal-fired power plant experienced condenser vacuum degradation from 95kPa to 89.8kPa due to copper tube scaling, increasing coal consumption by 3.8g/kWh. After scale analysis, LanXing QingXi implemented an online chemical cleaning program using Sulfamic Acid with BTA inhibitor. The half-side isolation cleaning was completed in 36 hours without unit shutdown, achieving a 97% descaling rate, restoring vacuum to 94.6kPa, and saving approximately 2,100 tons of standard coal annually.

1. Project Background & Equipment Overview

The power plant, located in East China, operates 2 × 300MW subcritical coal-fired generating units. The Unit 2 condenser is a dual-pass surface condenser (Model N-17000) with 17,000m² cooling area, featuring 19,680 HSn70-1A tin-brass tubes (Φ25×1mm). Circulating cooling water is sourced from a nearby surface water body, treated by clarification before entering the condenser.

The unit had been in continuous operation for 18 months since the last major overhaul cleaning. During the winter of 2025 through spring 2026, fluctuations in upstream water quality caused the circulating water concentration ratio to reach 4.2× (design limit ≤3.5×), with elevated carbonate hardness. Operating staff observed a gradual increase in condenser terminal temperature difference (TTD) and declining vacuum. By May 2026, condenser vacuum had dropped from the design 95kPa to 89.8kPa, and TTD had increased from the design 5℃ to 12.3℃, severely impacting unit economics.

The plant initially considered a shutdown for thorough cleaning. However, with the summer peak-load season approaching, grid dispatch could not approve an extended outage. After technical evaluation, the decision was made to adopt online chemical cleaning without shutdown, with LanXing QingXi contracted for the project.

2. Scaling Diagnosis & Deposit Analysis

Prior to cleaning, our technicians conducted systematic analysis of condenser operating data and collected tube-side deposit samples from the waterbox manhole. Visual inspection revealed: significant white to light-yellow hard scale deposits on the tube sheet surface and near tube inlets, with some tube openings blocked by more than 30% of the cross-sectional area. Scale thickness measured 0.8–1.5mm at tube inlets and 0.3–0.7mm in the mid-section.

Laboratory analysis of the deposit sample showed the following composition: CaCO₃ 62.4%, Mg(OH)₂ 12.8%, SiO₂ 8.3%, Fe₂O₃ 6.5%, phosphates and organic slime 9.4%, with trace CuO from the tube surface oxide layer. XRD diffraction confirmed the calcium carbonate was predominantly calcite crystal form — dense and strongly bonded to the tube wall.

Based on the deposit composition, the primary scaling mechanism was CaCO₃ supersaturation precipitation due to elevated circulating water concentration ratios, with microbial biofilm providing an adhesion substrate for inorganic salt deposition. The fouling thermal resistance was estimated at 0.00034 m²·K/W, causing the overall heat transfer coefficient to drop from the design 2,800 W/(m²·K) to approximately 2,100 W/(m²·K) — a 25% reduction.

3. Online Chemical Cleaning Program Design

Based on the deposit analysis, we designed an online chemical cleaning formulation using Sulfamic Acid as the primary cleaning agent and BTA as the copper-specific corrosion inhibitor. Sulfamic Acid was selected for the following reasons: first, its strong CaCO₃ dissolution capacity, producing soluble calcium salts without CaSO₄ precipitation risk (unlike H₂SO₄); second, its controllable corrosion rate on HSn70-1A tin-brass, which, combined with BTA inhibitor, can keep copper corrosion below 0.1g/(m²·h); third, effective reaction at ambient temperature without heating — ideal for online conditions.

Cleaning formulation system:

The cleaning process employed half-side isolation circulation: the condenser waterbox was divided into A/B sides, with one side undergoing cleaning while the other maintained normal operation. The cleaning side was connected via temporary piping to an acid-resistant circulation pump and cleaning solution mixing tank, forming a closed-loop circulation system. Total cleaning solution volume was approximately 18m³, with circulation flow controlled at 60% of the single-side design flow (approximately 5,400m³/h), ensuring the solution filled all tubes with adequate turbulence.

Key process control parameters: cleaning solution pH maintained at 1.5–2.0, temperature at 25–40℃ (utilizing waste heat from circulating water during low-vacuum operation), solution velocity ≥0.5m/s (ensuring turbulent flow in tubes), real-time Cu²⁺ monitoring (alarm ≤200mg/L), Fe³⁺ monitoring (alarm ≤500mg/L). Total cleaning cycle estimated at 36–48 hours in three phases: pre-cleaning (4h), main cleaning (24–30h), displacement and passivation (6–8h).

4. Cleaning Execution Process

Phase 1 — System Isolation & Pre-Cleaning (4 hours): Prior to cleaning, the B-side condenser was isolated on the water side by closing inlet/outlet butterfly valves and opening waterbox drain valves to empty residual water. A temporary circulation system was installed: 25m³ PE mixing tank, acid-resistant circulation pump (Q=600m³/h, H=30m), and DN300 temporary piping. After successful hydrostatic testing, pre-cleaning solution (0.5% Sulfamic Acid + 0.2% Surfactant) was injected and circulated for 2 hours before draining. This phase primarily removed loose surface deposits and biofilm from tube surfaces, providing a clean interface for the main cleaning stage. The discharged solution appeared pale yellow and turbid, containing significant suspended solids.

Phase 2 — Main Cleaning Circulation (28 hours): Fresh main cleaning solution was prepared by sequentially adding Sulfamic Acid, Citric Acid, BTA, and auxiliary agents per the formula. Samples were collected and analyzed every 2 hours for pH, Ca²⁺, total iron, and Cu²⁺ concentrations, with online pH and conductivity meters installed on the circulation return line for real-time monitoring. During the early stage (0–8h), Ca²⁺ concentration rose rapidly from an initial 12mg/L to a peak of 1,850mg/L, indicating substantial CaCO₃ dissolution from the deposit layer. pH gradually increased from 1.6 to 2.8, with timely Sulfamic Acid replenishment to maintain pH below 2.0. During the middle stage (8–20h), Ca²⁺ concentration growth decelerated and pH stabilized at 1.8–2.1, indicating the bulk of the deposit had dissolved. During the late stage (20–28h), Ca²⁺ concentration plateaued with fluctuations below 5% over three consecutive samples, total iron stabilized below 380mg/L, and Cu²⁺ remained consistently below 80mg/L (well under the 200mg/L alarm), confirming the cleaning endpoint was reached.

Phase 3 — Displacement, Passivation & System Restoration (6 hours): The circulation pump was stopped, and cleaning waste liquid was drained to the plant wastewater treatment station (neutralized with NaOH to pH 6–9 before compliant discharge). The cleaning side was then flushed three times with demineralized water, each cycle lasting 15 minutes, until discharge conductivity dropped below 50μS/cm. Finally, passivation solution (0.3% NaNO₂ + 0.1% Na₂CO₃, pH 9–10) was circulated for 2 hours to form a protective film on tube surfaces before draining. Temporary piping was dismantled, and the B-side condenser was restored to normal operation by opening the inlet/outlet butterfly valves. Total B-side isolation time was 38 hours, with the A-side maintaining normal operation throughout and unit load factor remaining above 85%.

5. Cleaning Results & Economic Benefits

After cleaning completion and B-side return to service, the overall condenser vacuum rapidly recovered from 89.8kPa to 94.2kPa. After 48 hours of stable operation, vacuum further improved to 94.6kPa, with TTD decreasing from 12.3℃ to 5.8℃ — approaching design values. One week later, borescope inspection through the waterbox manhole revealed smooth tube inner surfaces with no significant residual deposits; visual descaling rate was estimated above 95%. Quantitative testing of three extracted sample tubes using gravimetric method confirmed an average descaling rate of 97.2%. No pitting, dezincification, or other abnormalities were observed on tube surfaces, confirming effective BTA protection.

Operating parameter comparison:

Economic benefit estimation: Based on 5,000 annual operating hours at 300MW, the 3.8g/kWh coal consumption reduction equates to approximately 2,100 tons of standard coal saved annually. At 800 RMB/ton standard coal, annual fuel cost savings reach approximately 1.68 million RMB. Total cleaning project cost (including chemicals, labor, and temporary facilities) was approximately 120,000 RMB — a payback period of under one month. Additionally, vacuum recovery enables the unit to return to rated output, avoiding generation losses from low-vacuum load limiting, with substantial indirect economic benefits.

6. Summary & Technical Insights

This condenser online chemical cleaning case validates the feasibility and economic benefits of the Sulfamic Acid + BTA formulation for copper tube condensers without shutdown. Compared to outage cleaning, online cleaning avoids startup/shutdown costs (approximately 150,000–200,000 RMB per cycle), compresses the schedule from 7–10 days to 38 hours, and does not impact grid dispatch planning.

Key technical insights:

First, deposit analysis is the foundation of cleaning program design. The precise determination that CaCO₃ comprised over 60% of the deposit confirmed Sulfamic Acid suitability. If silicate or sulfate content were higher, formulation adjustment or supplemental high-pressure water jetting would be required.

Second, BTA inhibitor is the cornerstone of copper tube cleaning safety. Throughout this project, Cu²⁺ concentration remained below 80mg/L — far surpassing the copper corrosion rate requirements in Chinese national standard GB/T 25146-2010. The BTA-Cu protective film formed on tube surfaces post-cleaning provides ongoing corrosion protection.

Third, online monitoring is critical for ensuring cleaning quality and safety. Real-time pH monitoring and scheduled sampling analysis tracked cleaning progress, preventing both over-cleaning and under-cleaning. Future projects should incorporate online Ca²⁺ ion-selective electrodes for automated cleaning endpoint determination.

Fourth, circulation velocity control is essential. Insufficient velocity fails to effectively remove deposits at tube bottoms, while excessive velocity increases pump energy consumption and may cause tube vibration. The 60% single-side design flow used in this project balanced cleaning effectiveness with operational safety.

Condenser online chemical cleaning is a mature, economically significant maintenance practice, particularly suitable for thermal power units that cannot tolerate frequent shutdowns. LanXing QingXi brings over 20 years of power plant equipment cleaning experience, offering customized cleaning solutions for various tube materials (copper, titanium, stainless steel) and deposit types (carbonate, phosphate, silicate scale).

Service Coverage: Jiangsu (Nanjing, Suzhou, Wuxi, Changzhou, Zhenjiang, Yangzhou) · Zhejiang (Hangzhou, Ningbo) · Shanghai · Anhui (Hefei) · Shandong · Henan

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