Reactor Chemical Cleaning: Glass-Lined & Steel

Direct answer: Professional reactor cleaning not only requires thorough deposit removal but also passivation treatment to protect the equipment substrate and prevent re-contamination.

I. The Importance of Reactor Cleaning

Reactors are core equipment in chemical, pharmaceutical, food and other industries for material mixing, reaction, crystallization and other process operations. During long-term use, the inner walls of reactors accumulate various types of fouling, including reaction residues, polymers, crystals, and corrosion products. These deposits not only affect heat transfer efficiency and reduce product quality, but in severe cases can also lead to safety incidents.

Fouling inside reactors typically exhibits strong adhesion and chemical stability. In particular, cross-linked polymer scale layers produced by polymerization reactions are difficult to remove with conventional cleaning methods. Furthermore, many reactor working media are corrosive, flammable, explosive, or toxic, requiring strict adherence to safety procedures during cleaning operations. Professional reactor cleaning not only requires thorough deposit removal but also passivation treatment to protect the equipment substrate and prevent re-contamination.

II. Standard Reactor Cleaning Process

Step 1: Safety Isolation and Preparation. Disconnect the reactor from upstream and downstream equipment, close all feed and discharge valves, and install blind flanges for isolation. Completely drain the reactor, and use nitrogen or steam to purge toxic and hazardous gases from the vessel. For flammable and explosive media, combustible gas concentration must be tested to ensure it is within safe limits before proceeding with subsequent operations. Obtain hot work permits, confined space entry permits, and other safety documentation.

Step 2: Manual Pre-Cleaning. For large lump residues, perform manual cleaning first. Operators must wear full protective equipment including positive-pressure respirators and chemical protective suits, using non-metallic tools (such as wooden or copper scrapers) to remove loose scale layers, preventing sparks from metal tools striking the vessel wall. Explosion-proof lighting must be used during manual cleaning, and adequate ventilation inside the reactor must be maintained.

Step 3: Solvent Soaking. Select appropriate solvents for soaking based on the nature of the deposits. For organic deposits, use ketones (such as acetone, methyl ethyl ketone), esters, or aromatic hydrocarbon solvents for 4 to 12 hours to swell and soften the polymer scale layer. Solvent soaking is performed at ambient temperature, and the solvent level inside the reactor should remain above the scale layer to ensure full contact.

Step 4: Chemical Cleaning. After solvent soaking, drain the waste liquid and proceed with chemical cleaning. Select the cleaning formulation based on vessel material and scale type: For polymer scale in stainless steel reactors, commonly use 5% to 10% sodium hydroxide with 0.5% surfactant, boiled at 80 to 100°C for 4 to 8 hours. For carbon steel or stainless steel composite scale (including water scale and rust), use 5% to 8% nitric acid or 3% to 5% citric acid with specialized corrosion inhibitor, circulating at 50 to 60°C for 4 to 6 hours.

For glass-lined reactors, chemical cleaning requires extra caution — fluorine-containing cleaning agents must not be used to avoid damaging the glass lining. Cleaning solution temperature should be controlled below 80°C, and alkaline solution concentration should not exceed 5%. During cleaning, sample and test the metal ion concentration in the cleaning solution every 30 minutes, plotting a concentration-time curve. When the curve plateaus, the cleaning endpoint has been reached.

Step 5: HP Water Flushing. After chemical cleaning, perform high-pressure water jet flushing. Water pressure is generally 50 to 100 MPa. Use a rotating nozzle for comprehensive flushing of the reactor walls to remove loosened scale layers remaining after chemical cleaning. Protect internal components such as agitators and thermowell sleeves during flushing.

Step 6: Rinsing and Neutralization. Repeatedly rinse the reactor with clean water until the discharged water pH is 6 to 7. Deionized or softened water should be used for rinsing to avoid introducing Ca²⁺, Mg²⁺, and Cl⁻. For acid-cleaned reactors, use 0.5% sodium carbonate solution for neutralization treatment, then rinse again until the discharge water is neutral.

Step 7: Passivation Treatment. Immediately after cleaning, the reactor should undergo passivation treatment to prevent rapid oxidation and rusting of metal surfaces in the atmosphere. Use 1% to 2% sodium nitrite solution or 0.5% to 1% phosphoric acid solution, circulating at 40 to 50°C for 2 to 4 hours. After passivation, the reactor wall should exhibit a uniform silver-gray or steel-gray appearance, free of rust spots and color variation.

III. Safety Precautions

1. All personnel entering confined spaces must undergo specialized safety training and hold certified qualifications. Toxic and hazardous gas testing and oxygen content testing (oxygen content must be between 19.5% and 23.5%) must be performed before work begins.

2. Emergency rescue equipment must be available on site, including lifelines, safety ladders, and positive-pressure respirators. A safety attendant must be stationed outside the reactor, maintaining continuous communication with personnel working inside.

3. Chemicals used in chemical cleaning must be properly stored and labeled, with eyewash stations and emergency showers available on site.

4. HP water jet operators must undergo professional training and wear impact-resistant face shields and protective clothing. High-pressure hoses should be inspected regularly, and safety chains should be used to secure connections.

5. Cleaning waste liquids must be collected separately and not mixed for discharge. Organic waste liquids and acid/alkaline waste liquids should be collected separately and entrusted to qualified units for treatment.

IV. The Importance of Passivation Treatment

After chemical cleaning, the metal surface of the reactor is in a highly activated state and readily reacts with oxygen and moisture in the air, forming secondary rust. Passivation treatment forms a dense oxide film or chemical conversion film on the metal surface, effectively isolating it from corrosive media and significantly improving the equipment's corrosion resistance.

Particularly for stainless steel reactors, nitric acid passivation treatment can produce a chromium-rich oxide layer on the surface, improving pitting resistance by 5 to 10 times. Carbon steel reactors can use the sodium nitrite alkaline passivation approach. Therefore, passivation treatment is not optional — it is an essential step in reactor chemical cleaning.

V. Reactor Cleaning FAQ

Q1: Can a reactor be cleaned without entry into the vessel?

For most deposits, yes. Closed-loop circulation of an inhibited solvent followed by rotating high-pressure water jetting at 50-100 MPa through the manway and top nozzle reaches the whole wetted surface, so personnel stay outside the vessel. Entry is reserved for large lumps of polymer or hardened residue that no circulation can lift. Where entry is unavoidable, the job runs under a confined space permit with continuous gas testing, an oxygen level of 19.5-23.5%, positive-pressure breathing apparatus and a standby attendant outside. Danyang Lanxing Anticorrosion Cleaning Co., Ltd. plans every reactor job on that basis.

Q2: Why is passivation required after reactor cleaning?

Cleaning leaves the metal surface chemically active, and a reactor exposed to humid air after descaling can flash-rust within hours. Passivation builds a dense oxide or conversion film that isolates the substrate, and the effect on stainless steel is measurable: chromium-rich film formation raises pitting resistance several fold against an untreated surface. It is treated as a mandatory final step, carried out immediately after rinsing to neutral pH and before the vessel is dried, inspected and returned to service. Danyang Lanxing Anticorrosion Cleaning Co., Ltd. records the passivated surface condition in the acceptance report.

Q3: What acceptance standard applies to reactor chemical cleaning?

Acceptance follows GB/T 25146-2010, the quality acceptance specification for chemical cleaning of industrial equipment. Three checks decide the result: the corrosion rate measured on coupons of the same material as the vessel wall, the achieved descaling rate against the agreed target, and a visual inspection of the cleaned and passivated surface, which must be uniform silver-gray or steel-gray without rust spots or colour banding. Rinsing is signed off when the discharge reaches pH 6-7. Danyang Lanxing Anticorrosion Cleaning Co., Ltd. issues the written acceptance report before handover.

Reactor Cleaning Technology