Online Non-Stop Chemical Cleaning Technology Principles

1. Introduction

In continuous-production industries such as petrochemical, power, metallurgy and chemical processing, heat exchangers inevitably accumulate calcium carbonate scale, iron oxide scale and biological slime on heat transfer surfaces during long-term operation. The thermal conductivity of scale is only one-tenth to several tenths of that of carbon steel, so even a thin layer significantly reduces heat transfer efficiency and raises energy consumption. Industry statistics show that for every 0.5mm of condenser scaling, the terminal temperature difference rises, vacuum drops, and coal consumption increases by about 1%–2%; cooling water heat exchanger fouling directly raises outlet temperature and reduces cooling capacity.

Conventional cleaning requires shutdown, draining and disassembly, causing production loss, long overhaul periods and complex cross-operations. Online non-stop chemical cleaning was developed precisely to address this contradiction: while equipment remains running, cleaning agents are injected into the circulating medium using the system's own circulation power or an added bypass pump, dissolving and peeling scale and corrosion products to restore heat transfer. It is especially suitable for condensers, cooling water heat exchangers and central AC chillers that have circulation loops and light scale, and is an important preventive maintenance measure.

2. Mechanism of Online Cleaning

2.1 Triple Mechanism of Scale Dissolution

Online cleaning removes scale through the combined action of acid pickling, chelation and dispersion. Acid pickling, represented by Sulfamic Acid, reacts with calcium carbonate scale to form soluble calcium salts; it is milder and less corrosive to metals than HCl, making it a common agent for online condenser copper-tube cleaning. Chelation, represented by Citric Acid and EDTA, forms stable water-soluble complexes with rust and calcium/magnesium ions, especially suitable for iron scale and mixed scale. Dispersion relies on surfactants and dispersants to suspend and disperse stripped scale particles in the circulating medium so they are carried out with the fluid, preventing secondary deposition or blockage.

The essential difference from shutdown cleaning is that, limited by non-stop safety conditions, the cleaning agent concentration is lower than in shutdown cleaning, so descaling efficiency must be compensated by longer circulation time and higher flow velocity. Therefore the success of online cleaning depends more on circulation dynamics design and process monitoring than on agent concentration alone.

2.2 Circulation Dynamics and Mass Transfer Enhancement

Descaling efficiency is closely related to circulating flow velocity, Reynolds number and contact time. The flow velocity must exceed the settling velocity of scale particles, typically 0.5–1.5 m/s in the tube, keeping the fluid turbulent to strengthen mass transfer, continuously delivering agent to the scale surface and carrying reaction products away. The waste heat of running equipment accelerates the reaction rate, but the temperature must be kept within the allowable upper limit for the agent and material to prevent accelerated inhibitor decomposition or local corrosion.

2.3 Corrosion Inhibition

During non-stop cleaning, agents inevitably contact carbon steel, copper and copper alloys, so corrosion inhibitors must be added. BTA (benzotriazole) provides excellent protection for copper and copper alloys by forming a dense adsorption film on the copper surface; MBT (mercaptobenzothiazole) protects both copper and carbon steel; Sodium Molybdate provides anodic passivation, synergistically reducing metal corrosion. Inhibitor selection and combination are the core guarantee of online cleaning safety.

3. Key Process Parameters

Typical parameters for online non-stop chemical cleaning are shown below; actual values should be adjusted based on scale sample analysis and equipment material.

4. Online Cleaning Process

4.1 Circulation Loop Design

There are two loop design modes: for equipment with an existing circulation system (such as cooling water heat exchangers and chillers), directly use the system circulation pump and piping, dosing chemicals into the circulation basin or sump; for condensers without an existing loop, add a bypass circulation pump and temporary piping, drawing from the water chamber and returning to it to form an independent cleaning loop. The loop design must ensure all tube passes are evenly covered by cleaning solution, with reserved sampling and drain ports.

4.2 Process Workflow

1. Pre-wash: flush with clean water to remove loose deposits and sediment, recording initial parameters as baseline.
2. Acid pickling: dose cleaning agent and corrosion inhibitor into the circulating medium, maintaining velocity and temperature during continuous circulation.
3. Neutralization: after the pickling endpoint, add neutralizer to bring pH to neutral.
4. Rinsing: displace with large volumes of clean water to drain residual solution and stripped scale.
5. Passivation: dose passivating agent as needed to form a protective film on metal surfaces.

Throughout the process, pH meter, conductivity meter and chemical sampling monitor simultaneously; when acidity no longer drops and iron or calcium ion concentrations stabilize, the cleaning endpoint is reached.

5. Case Study

Equipment overview: A power plant condenser accumulated calcium carbonate scale and biological slime on the inner walls of copper tubes after long-term operation, with terminal difference rising about 3℃ above design and vacuum dropping, increasing coal consumption. Due to grid dispatch constraints, the unit could not be shut down for long.

Treatment plan: Online non-stop chemical cleaning was adopted, using Sulfamic Acid as the main cleaning agent and BTA as the copper-tube inhibitor, establishing an independent cleaning loop through a bypass circulation pump, maintaining tube velocity around 1.0 m/s, and circulating continuously for about 12 hours using the unit's circulating water waste heat, with pH and copper ion monitored throughout.

Cleaning result: After cleaning, condenser terminal difference dropped by about 2.5℃ and vacuum clearly recovered, with descaling rate up to standard and no copper tube corrosion thinning. The unit restored its design heat transfer capacity without shutdown, and coal consumption subsequently fell, achieving significant economic benefit.

6. Summary and Recommendations

Online non-stop chemical cleaning removes scale through the combined action of acid pickling, chelation and dispersion, restoring heat transfer without affecting production through circulation dynamics design, corrosion inhibition and real-time monitoring — a cost-effective preventive maintenance approach for continuous-running equipment. Its technical difficulty lies not in the agents themselves but in rational loop design, precise parameter control and timely endpoint determination.

Enterprises are advised to build a fouling and performance ledger for heat exchange equipment, judging the best cleaning timing by terminal difference, vacuum and temperature difference, and to incorporate online cleaning into periodic preventive maintenance. For equipment with overly thick or severe blockage, shutdown cleaning should still be chosen to fully restore performance. Specific process plans should be finalized after on-site scale analysis and material confirmation.

FAQ

Will online non-stop cleaning damage the equipment?

No, when operated properly. Corrosion inhibitors (BTA, MBT, Sodium Molybdate) are added throughout, and pH, iron ion and copper ion concentrations are monitored in real time to keep corrosion rates within standard limits, far below normal operating wear. DanYang LanXing Cleaning performs scale and material analysis before construction to ensure safety.

Which equipment suits online cleaning, and which must be shut down?

Power plant condensers, cooling water heat exchangers and central AC chillers with circulation power and light scale (about 1.5mm or less) suit online cleaning; equipment with very thick or hard scale, or needing seal replacement, must be shut down. Whether online cleaning is feasible should be confirmed by scale sample analysis.

How often should online cleaning be performed?

Generally judged by terminal temperature difference, vacuum or water quality. Cooling water systems are typically cleaned online every 6–12 months; condensers depend on the rise in terminal difference. Keeping a periodic ledger helps catch the best timing and avoids excessive scale thickness.

How do you judge the effect of online cleaning?

Mainly by comparing terminal difference, vacuum, temperature difference, turbidity and iron ion concentration before and after cleaning. Qualified online cleaning should clearly lower terminal difference and restore vacuum. Call 18952832843 for acceptance criteria details.

How much does online non-stop cleaning cost?

The cost depends on equipment scale, scale thickness, chemical usage and duration, and is usually lower than the production loss of a shutdown. DanYang LanXing Cleaning offers free on-site inspection and quoting, hotline 18952832843.

All acceptance criteria follow GB/T 25146-2010 Quality acceptance specifications of chemical cleaning for industrial equipment.

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