Chemical Industry Equipment Cleaning: Reactors & Heat Exchangers

1. Introduction

The chemical industry is one of the sectors with the greatest demand for industrial cleaning. Reactors and heat exchangers, as core chemical production equipment, operate long-term in high-temperature, high-pressure, and corrosive media environments, where scaling and corrosion issues directly affect product quality, energy consumption levels, and production safety. According to industry statistics, heat transfer efficiency decline caused by heat exchanger scaling can increase energy consumption by 15%–30%, and for every 1 mm increase in reactor inner wall coking layer thickness, the vessel heat transfer coefficient drops by approximately 8%–12%. In fine chemicals, petrochemicals, and coal chemicals sub-sectors, equipment scale composition varies significantly — fine chemical reactors are dominated by organic polymers, while coal chemical heat exchangers primarily feature mixed inorganic salt and tar scale — requiring cleaning solutions that are tailored to the specific scale type. Regular, standardized equipment cleaning is an essential measure for chemical enterprises to ensure continuous production. This article systematically describes professional cleaning solutions for reactors and heat exchangers based on chemical industry equipment scaling characteristics, providing technical reference for chemical enterprise equipment management personnel.

2. Analysis of Chemical Industry Equipment Scaling Characteristics

2.1 Reactor Scaling Types

Reactor inner wall scale formation has complex causes, mainly divided into three categories: polymer coking — during high-temperature polymerization reactions, monomers or oligomers deposit on the vessel wall forming dense organic scale layers, commonly seen in resin synthesis workshops of chemical groups; inorganic salt crystallization — Ca²⁺, Mg²⁺ and other ions in the reaction system combine with CO₃²⁻, SO₄²⁻ to form CaCO₃, CaSO₄ and other hard scales, frequently observed in neutralization reaction processes; catalyst residues — metal catalyst or support particles deposit on vessel walls and agitator surfaces, particularly prone to enrichment at glaze defects in glass-lined reactors.

2.2 Heat Exchanger Scaling Mechanisms

Scaling in chemical industry heat exchangers is predominantly mixed type, typically containing a three-layer structure of organics, inorganic salts, and corrosion products. The tube side (cooling water side) is primarily water scale (CaCO₃, Mg(OH)₂), while the shell side (process medium side) is dominated by organic coking and polymer scale. The hazard of heat exchanger scale layers extends beyond reduced heat transfer efficiency — the metal surface beneath the scale layer is also prone to forming oxygen concentration cells, triggering severe localized corrosion, which is the root cause of premature perforation and leakage of heat exchanger tubes in many chemical enterprises. Below is a comparison of common scaling types and cleaning strategies in the chemical industry:

3. Reactor Cleaning Solutions

3.1 Safe Cleaning of Glass-Lined Reactors

The cleaning challenge for glass-lined reactors lies in protecting the glaze layer. The glass lining is sensitive to HF and strong alkalis (NaOH concentration > 10%), and fluoride-containing cleaning agents are strictly prohibited. Recommended cleaning procedure: first soak with organic solvent (such as acetone or specialized degreaser) for 2–4 hours to soften the polymer coking layer; then circulate Na₂CO₃ solution (concentration 3%–5%, temperature 60–70°C) for 2 hours to remove residual organics; finally flush with fresh water to neutral. A chemical group's glass-lined reactor (5000L, 5 years in service) achieved 92% recovery of jacket heat transfer coefficient after adopting this solution. Throughout cleaning, the reactor internal temperature must not exceed 80°C to prevent thermal stress cracking of the glass lining.

3.2 Stainless Steel Reactor Pickling-Passivation Solution

The cleaning priority for stainless steel reactors is integrated descaling and passivation. For Cr-Ni series stainless steels (304/316L), a Sulfamic Acid (concentration 5%–8%) + Citric Acid (concentration 2%–3%) composite formulation is recommended, with pickling temperature controlled at 50–65°C and circulation time 4–6 hours. Sulfamic Acid has strong CaCO₃ scale dissolution capability with low corrosion rate on stainless steel substrate (< 1.0 g/m²·h), while Citric Acid provides iron ion chelation functionality and simultaneously acts as a passivation promoter, naturally forming a dense passivation film in the later cleaning stage. For reactors with welded joints or dissimilar metal connections, Sulfamic Acid's low Cl⁻ characteristic (inherently chloride-free) effectively reduces intergranular corrosion and crevice corrosion risks, making it the preferred acid agent for cleaning austenitic stainless steel equipment.

4. Heat Exchanger Cleaning Solutions

4.1 Shell-and-Tube Heat Exchanger Comprehensive Cleaning

Shell-and-tube heat exchangers are the most common heat exchange equipment in the chemical industry. Their cleaning must address both tube side and shell side, with differentiated cleaning parameters for different tube bundle materials. The tube side (cooling water side) is dominated by CaCO₃ water scale; HCl (concentration 5%–8%) or Sulfamic Acid (concentration 8%–10%) circulation cleaning is recommended, with BTA corrosion inhibitor (concentration 0.3%–0.5%) added to protect carbon steel tube sheets. The shell side (process medium side) has complex scaling; when organics and polymers are present, alkaline boiling (NaOH 2%–3% + Na₂CO₃ 1%–2%, 80–90°C, 4 hours) or solvent circulation must be performed before acid cleaning. For heat exchangers with small tube diameters (≤ 19 mm) or severe scaling, high-pressure water jet cleaning (pressure 40–80 MPa) should be added after acid cleaning for tube-by-tube unblocking, ensuring every heat exchanger tube is clear.

4.2 Plate Heat Exchanger Disassembly Cleaning

Plate heat exchangers are sensitive to blockage due to small plate spacing (typically 2–5 mm). Recommended solution: after disassembling the plates, soak in Citric Acid (concentration 3%–5%, 50–60°C) in an immersion tank for 2–3 hours, supplemented with soft brush gentle scrubbing of plate surfaces. Steel brushes or hard tools are strictly prohibited to prevent damage to plate sealing surfaces. After cleaning, flush with fresh water, inspect gasket aging condition, and replace if necessary. A chemical enterprise's BR0.2 plate heat exchanger (heat transfer area 20 m²) achieved a reduction in inlet-outlet pressure differential from 0.38 MPa to 0.12 MPa (design value 0.10 MPa) after cleaning with this solution, with heat transfer efficiency recovering to 96% of new equipment.

4.3 Online vs. Offline Cleaning Selection

Another critical decision in chemical industry heat exchanger cleaning is choosing between online cleaning (CIP) and offline cleaning (shutdown overhaul). Online cleaning is suitable for scenarios with mild scaling (scale thickness < 1 mm) and continuous production that cannot be shut down, using low-concentration cleaning agents with extended circulation (12–24 hours), achieving approximately 60%–70% of offline cleaning efficiency but avoiding production loss. Offline cleaning is suitable for severe scaling cases or when high-pressure water jet and mechanical unblocking are needed, providing thorough descaling and allowing simultaneous completion of gasket replacement, tube bundle inspection, and other overhaul items. A chemical enterprise with an annual 300,000-ton synthetic ammonia plant adopted a combined strategy of "one offline deep cleaning per year + one online maintenance cleaning per quarter" for critical heat exchangers, extending the equipment continuous operation cycle from 8 months to over 24 months and reducing annual comprehensive maintenance costs by approximately 40%.

5. Engineering Cases

Case 1: Chemical Group Stainless Steel Reactor Cleaning

Equipment parameters: 316L stainless steel reactor, volume 8000L, jacketed heating, operating temperature 180°C, medium: organic acid esters. After 3 years of operation, inner wall coking layer thickness approximately 3–5 mm, jacket heat transfer efficiency dropped by approximately 35%, single-batch production cycle extended from 8 hours to 11 hours.

Cleaning process: Alkaline wash (Na₂CO₃ 4%, 80°C, 3h) → Water flush → Acid cleaning (Sulfamic Acid 7% + Citric Acid 2.5%, 55°C, 5h) → Rinse → Passivation (NaNO₂ 1.5%, pH 9.5, 4h).

Cleaning results: Inner wall coking layer completely removed, metal surface formed uniform silver-white passivation film. Jacket heat transfer efficiency recovered to 94% of original, single-batch production cycle restored to 8.2 hours. Annual steam cost savings approximately CNY 180,000.

Case 2: Chemical Enterprise Shell-and-Tube Heat Exchanger Online Cleaning

Equipment parameters: Carbon steel shell-and-tube heat exchanger, heat transfer area 120 m², tube side: circulating cooling water, shell side: organic solvent vapor. Tube-side scale thickness approximately 2–3 mm (mainly CaCO₃), heat transfer approach temperature deteriorated from design 8°C to 22°C.

Cleaning process: Under non-shutdown conditions, tube-side Sulfamic Acid (concentration 8%, with BTA 0.4% inhibitor) circulation cleaning for 8 hours, flow velocity controlled at 0.5–1.0 m/s, temperature 45–50°C. Real-time Fe²⁺ concentration monitoring throughout for corrosion control.

Cleaning results: Descaling rate > 95%, heat transfer approach temperature recovered to 9–10°C. Annual circulating water electricity savings approximately 60,000 kWh, equipment operating cycle extended from 6 months to 12 months.

6. Summary and Recommendations

The core principle of chemical industry equipment cleaning is "one equipment, one solution" — developing targeted cleaning processes based on equipment material, scaling type, and process requirements. Reactor cleaning focuses on material protection: glass-lined equipment must avoid HF and strong alkalis, while stainless steel equipment should adopt integrated pickling-passivation solutions. Heat exchanger cleaning must address differentiated tube/shell side strategies, with combined chemical cleaning and physical cleaning (high-pressure water jet) delivering optimal results. For continuous production units, implementing a dual-track system of "periodic deep cleaning + routine online maintenance" can significantly extend equipment operating cycles and reduce comprehensive maintenance costs.

It is recommended that chemical enterprises establish equipment cleaning records, documenting each cleaning's chemical formulation, process parameters, and performance data to provide a basis for subsequent cleaning cycle optimization. For equipment with stress corrosion cracking risk (such as austenitic stainless steel in Cl⁻ environments), material testing and risk assessment should be conducted before cleaning. Additionally, cleaning waste liquid disposal must comply with environmental regulations: acidic waste liquid requires neutralization treatment (pH 6–9) before discharge, and organic waste liquid must be handed over to qualified hazardous waste treatment facilities.