1. Wuxi Industrial Heat Equipment Overview
Located on the shores of Lake Tai, Wuxi is a major manufacturing base in China, hosting over 8,000 above-designated-size industrial enterprises across textile dyeing, precision machinery, chemical new materials, and food processing sectors. A significant proportion of these enterprises rely on industrial steam boilers and thermal oil heaters as production heat sources.
Wuxi's municipal water supply has moderate-to-high Ca2+ and Mg2+ content, with total hardness ranging from 120 to 180 mg/L (as CaCO3). In some areas, Lake Tai water receives only basic treatment before makeup feed into boilers, leading to substantial hardness fluctuations. Boilers using insufficiently softened makeup water inevitably develop scale — the thermal conductivity of scale (0.5-0.7 W/(m·K)) is approximately 70 times lower than carbon steel (45 W/(m·K)). Meanwhile, thermal oil systems in Wuxi's textile dyeing and chemical fiber sectors, operating continuously at 280-320°C, undergo thermal cracking and polymerization, forming coke and carbon deposits on tube walls with thermal conductivity as low as 0.1 W/(m·K). Each millimeter of coke deposit can elevate tube wall temperatures by 80-120°C and reduce heat transfer efficiency by 20-40%, posing serious safety risks including tube creep and perforation.
2. Common Scale Types and Coking Characteristics
2.1 Carbonate Scale
The most prevalent scale type in Wuxi boilers is a CaCO3 and Mg(OH)2 mixed deposit, appearing grayish-white to pale yellow with a relatively loose texture. When makeup water is untreated or inadequately softened, Ca(HCO3)2 decomposes into CaCO3 at high temperatures and deposits on heating surfaces. A mere 1 mm of scale raises tube wall temperatures by 50-100°C, increases exhaust gas temperature by 15-25°C, and raises fuel consumption by 5-8%.
2.2 Silicate Scale
Enterprises using surface water sources often encounter silicate scale in boilers. Silicate scale is hard, tightly bonded to metal surfaces, and resistant to acid cleaning alone — it requires fluoride-based solubilizing agents such as NH4HF2 for effective removal.
2.3 Thermal Oil Coking
Coke and carbon deposits in thermal oil systems appear as black asphalt-like or hard coke crust, primarily composed of high-molecular-weight polymers and carbonized material. In Wuxi chemical fiber enterprises, thermal oil typically reaches end-of-life after 3-4 years, with inlet-outlet temperature differentials expanding from the design value of 15-20°C to 35-50°C — a clear indicator of severe coking.
3. Technical Solutions
3.1 Boiler Chemical Descaling Process
| Step | Chemicals & Parameters | Purpose |
|---|---|---|
| Alkaline boil-out | Na₂CO₃ 2-3%, NaOH 0.5-1%, 80-90°C, 4-6h | Remove grease, loosen scale layers |
| Acid cleaning | Sulfamic Acid 5-8%, Citric Acid 1-2%, BTA 0.3%, 50-65°C, circulation 6-8h | Dissolve scale, chelate Fe ions |
| Neutralization | Na₂CO₃ 1-2%, pH 7-8 | Neutralize residual acid |
| Rinse | Citric Acid 0.5%, pH 3.5-4, ambient temperature | Remove secondary flash rust |
| Passivation | NaNO₂ 1-2% + Na₃PO₄ 0.5%, pH 9-10, ambient, 4h | Form Fe₃O₄ protective film |
Sulfamic Acid provides high calcium scale dissolution efficiency without acid mist, while Citric Acid's Fe-ion chelation capability removes both scale and rust. BTA offers excellent corrosion inhibition for carbon steel and copper alloys in acidic media, controlling the corrosion rate below 6 g/(m²·h) — well under the Chinese national standard GB/T 25146-2010 limit of 20 g/(m²·h). For silicate-bearing scales, NH₄HF₂ at 1-2% is added to the acid cleaning solution as a solubilizer. After cleaning, passivation forms a dense Fe₃O₄ protective film that suppresses secondary corrosion upon boiler restart.
3.2 Thermal Oil System Decoking Process
| Step | Method | Parameters |
|---|---|---|
| Solvent soaking | Specialized thermal oil cleaning agent | 80-120°C circulation, 12-24h |
| High-pressure water jetting | High-pressure water jet | 500-800 bar, 40-60 L/min |
| Chemical fine cleaning | Alkaline cleaner + Surfactant | 60-80°C circulation, 4-6h |
| Nitrogen purge | N₂ protection | Dew point ≤ -40°C |
Post-cleaning, the tube wall temperature differential should recover to within ±5°C of design value, with system thermal efficiency gains of 15-30%. Replacement of thermal oil and installation of bypass filtration is recommended after cleaning.
4. Full Wuxi Coverage
Lanxing Qingxi provides industrial boiler and thermal oil system cleaning services across all Wuxi districts:
Urban districts: Liangxi, Xishan, Huishan, Binhu, Xinwu
County-level cities: Jiangyin, Yixing
Located just 80 km from Wuxi city center, we offer 2-hour response and 24-hour on-site technical assessment. Standard boiler cleaning projects are completed in 3-5 working days; thermal oil system cleaning in 5-7 working days. Six months of complimentary follow-up monitoring is included post-cleaning.
5. Local Case Studies
Case 1: Textile dyeing enterprise steam boiler descaling
A Wuxi textile dyeing enterprise operated a DZL10-1.25-AII steam boiler (10 t/h) for 5 years without chemical cleaning. Boiler water hardness consistently exceeded limits (0.2-0.5 mmol/L). Scale thickness at the drum bottom reached 3-5 mm (85% CaCO₃, ~5% silicates). Exhaust gas temperature rose from the design 160°C to 230°C, reducing thermal efficiency by ~18% and increasing annual fuel costs by approximately ¥400,000.
Results after Sulfamic Acid + Citric Acid composite cleaning with BTA inhibition: scale removal rate ≥95%, exhaust gas temperature recovered to 168°C, annual natural gas savings of ~120,000 m³. No pitting or intergranular corrosion observed. The Fe₃O₄ passivation film remained intact with no secondary corrosion. The enterprise saved ~¥360,000 in annual fuel costs, with cleaning investment recouped in under 3 months.
Case 2: Chemical fiber enterprise thermal oil heater decoking
A Wuxi chemical fiber enterprise operated a 6-million kcal thermal oil heater with 4-year-old thermal oil. The inlet-outlet temperature differential expanded from the design 15°C to 42°C, fuel consumption increased 35%, and local overheating oxidation appeared on tube outer walls.
Results after 18-hour solvent soaking at 80°C, 600-bar high-pressure water jetting tube-by-tube, and 4-hour alkaline Surfactant fine cleaning: temperature differential recovered to 18°C, system thermal efficiency improved 22%, annual natural gas savings of ~250,000 m³, and tube wall oxidation risk eliminated.
6. Summary & Recommendations
Industrial boiler scale and thermal oil coking are two pervasive challenges affecting production efficiency and energy consumption across Wuxi's manufacturing base. Scientifically designed chemical cleaning programs can efficiently remove deposits without compromising equipment integrity, while standardized passivation establishes long-term corrosion protection.
We recommend Wuxi enterprises establish routine cleaning and maintenance schedules: steam boiler chemical cleaning every 2-3 years, hot water boilers every 3-4 years, and thermal oil systems based on dynamic monitoring of carbon residue (>1.5%) and temperature differential (>30°C). Combined with water quality management and periodic thermal oil analysis, this approach sustains high equipment thermal efficiency while supporting energy conservation and operational safety.
7. Why Choose Lanxing Qingxi?
Danyang Lanxing Anti-Corrosion Cleaning Co., Ltd. is a member of the China Industrial Cleaning Association, founded in 2001, holding Grade B industrial chemical cleaning certification with over 20 years of service across the Yangtze River Delta. Located only 80 km from Wuxi, we offer inherent rapid-response advantages.
- Technical expertise: Proven boiler chemical cleaning and thermal oil decoking processes tailored to Wuxi water quality and scale characteristics
- Rapid response: 2-hour response, 24-hour on-site, full Wuxi coverage
- Safety assurance: BTA corrosion inhibition throughout, corrosion rate <6 g/(m²·h)
- Environmental compliance: Cleaning wastewater neutralized and treated to meet Lake Tai basin discharge standards
- After-sales guarantee: 6 months complimentary follow-up monitoring and operational guidance