1. Introduction: Why Is Spiral Plate Heat Exchanger Cleaning So Difficult?
Spiral plate heat exchangers are formed by winding two parallel metal plates into two concentric spiral channels, with hot and cold fluids flowing counter-currently in adjacent channels. With a heat transfer coefficient 2~3 times that of shell-and-tube heat exchangers, they are widely used in chemical, pharmaceutical, food, and wastewater treatment industries.
However, the structural characteristics of spiral plate heat exchangers also create significant cleaning challenges: the channel width is typically only 5~20mm, and the channels are curved arcs. Once fouling occurs, the channels become further narrowed or even completely blocked, rendering conventional cleaning methods ineffective. According to industry statistics, approximately 35% of spiral plate heat exchanger performance degradation is caused by fouling, and over half of these cases result in premature equipment scrapping due to inadequate cleaning.
This article, based on engineering practice, systematically analyzes the core challenges of spiral plate heat exchanger cleaning and provides proven synergistic chemical and physical cleaning solutions.
2. Four Major Challenges in Spiral Plate Heat Exchanger Cleaning
Challenge 1: Narrow, Curved Channels — Mechanical Tools Cannot Access
Spiral plate heat exchanger channel widths are typically 5~20mm with a spiral curved configuration. While shell-and-tube heat exchangers can be mechanically cleaned tube-by-tube and plate heat exchangers can be disassembled for individual plate cleaning, the channels of spiral plate heat exchangers are non-removable, enclosed curved passages — tube lancing machines, drills, scrapers, and other mechanical tools cannot advance along a spiral path. Once channels are blocked by hard scale, physical unclogging methods are nearly ineffective.
Engineering data: Taking a spiral plate heat exchanger with 100m² heat transfer area and 12mm channel width as an example, the total spiral channel length can reach 40~60m. If CaCO₃ scale accumulates to 3mm thickness, the effective channel cross-sectional area reduces by 50%, and the pressure drop increases to 3~4 times the design value.
Challenge 2: Complex Scale Composition — Single Cleaning Agents Are Ineffective
Spiral plate heat exchangers handle diverse media, and common scale layers are often mixed deposits rather than single components:
| Scale Type | Primary Components | Common Operating Conditions | Cleaning Difficulty |
|---|---|---|---|
| Carbonate Scale | CaCO₃, MgCO₃ | Cooling water systems, heating systems | ★★☆ |
| Sulfate Scale | CaSO₄, BaSO₄ | Chemical reaction cooling, desulfurization systems | ★★★★ |
| Silicate Scale | SiO₂, Calcium Silicate | Geothermal water, boiler feed water | ★★★★★ |
| Organic/Polymer Scale | Resins, Tar, PVA | Chemical polymerization, food processing | ★★★☆ |
| Mixed Scale | Organics + Inorganic Salts + Rust | Most common in actual operation | ★★★★★ |
Challenge 3: Insufficient Chemical Cleaning Flow Velocity — Incomplete Scale Detachment
The design flow velocity of spiral plate heat exchangers is typically 0.5~1.5 m/s (liquid media). However, the actual flow rate of the cleaning pump is limited by channel resistance — when scale has already caused partial blockage, the actual cleaning fluid velocity may drop to 0.1~0.3 m/s, far below the flow rate required for effective chemical cleaning (typically ≥0.5 m/s). Low velocity results in:
- Insufficient contact between cleaning agent and scale, slow reaction interface renewal
- Detached scale fragments cannot be carried out by the fluid flow, causing secondary accumulation at bends
- Formation of localized dead zones where cleaning agent cannot reach
Challenge 4: Material Sensitivity — High Risk of Acid Cleaning Corrosion
Common materials for spiral plate heat exchangers include 304, 316L stainless steel, and carbon steel. In areas of concentrated bending stress (weld seams, spacer stud weld points), the material is particularly sensitive to stress corrosion cracking (SCC). Especially when the medium contains Cl⁻, improper cleaning fluid selection (e.g., using HCl) can trigger pitting and intergranular corrosion within hours.
Key constraint: For 304 stainless steel in acidic environments above 60°C with Cl⁻ concentration >50ppm, the risk of stress corrosion cracking increases dramatically. This requires cleaning formulations that balance both scale removal efficiency and material protection.
3. Cleaning Solution System
3.1 Chemical Cleaning Formulations (Selected by Scale Type)
| Scale Type | Primary Cleaning Agent | Concentration (wt%) | Temperature | Circulation Time | Corrosion Inhibitor System |
|---|---|---|---|---|---|
| Carbonate Scale | Sulfamic Acid | 5%~8% | 50~60°C | 4~8h | BTA 0.3% + Urotropine 0.2% |
| Sulfate Scale (CaSO₄) | NaOH Alkaline Boil + EDTA | NaOH 3%~5% → EDTA 5%~10% | 80~90°C → 60~70°C | Alkaline boil 12h + Chelation 8h | Na₂CO₃ 1% + Sodium Molybdate 0.1% |
| Silicate Scale | NH₄HF₂ + Citric Acid | NH₄HF₂ 3%~8% + Citric Acid 3%~5% | 40~60°C | 6~12h | BTA 0.5% + Surfactant 0.1% |
| Organic Scale | NaOH + Surfactant | NaOH 2%~5% + Surfactant 0.5%~1% | 70~85°C | 8~24h | — |
| Mixed Scale (Standard Protocol) | Sulfamic Acid + Citric Acid | Sulfamic Acid 5% + Citric Acid 3% | 50~65°C | 6~10h | BTA 0.3% + Urotropine 0.2% + Surfactant 0.1% |
3.2 Chemical Cleaning Process Flow
- Pre-inspection Analysis and Coupon Testing: Collect scale samples for XRF/XRD composition analysis to determine primary scale components; use material-matched coupons to perform 24h corrosion rate testing in candidate formulations (requirement: ≤2 g/(m²·h)).
- Water Flush and Flow Test: Circulate ambient-temperature clean water for 30min, record initial flow rate and pressure differential to assess blockage severity.
- Alkaline Wash/Solvent Wash (if organic scale present): NaOH 3% + Surfactant 0.5%, circulate at 70~80°C for 8~12h to remove oil and organic deposits. Drain and flush with clean water until pH≤9.
- Main Acid Cleaning Circulation: Select the appropriate formulation from the table above based on scale type, alternate forward and reverse circulation (switch flow direction every 2h), maintain flow velocity ≥0.3 m/s. Sample and test Ca²⁺/Fe²⁺ concentration and pH in the cleaning solution every 1h; determine endpoint when concentrations stop rising for 2 consecutive measurements.
- Passivation Treatment: After acid cleaning, drain and neutralize with Na₂CO₃ 1.5% solution to pH 6~7; switch to passivation solution (NaNO₂ 1% + Na₃PO₄ 0.5%), circulate at 60°C for 4h to form a protective film on the stainless steel surface.
- Final Water Rinse and Acceptance: Rinse with clean water until pH=7, compare pre- and post-cleaning flow rate/pressure differential data — Acceptance criteria: flow rate restored to ≥90% of design value, pressure drop ≤120% of design value.
3.3 High-Pressure Water Jet Assisted Cleaning
For thick scale accessible at the channel inlet end (within 200~500mm from the inlet), high-pressure water jetting can serve as a pre-treatment step before chemical cleaning:
| Parameter | Recommended Value | Notes |
|---|---|---|
| Working Pressure | 500~1000 bar | Select based on scale hardness; upper limit applicable when stainless steel plate thickness ≥2mm |
| Flow Rate | 30~60 L/min | High flow rate helps flush away detached scale fragments |
| Nozzle Type | Rotary Nozzle | Fan-shaped coverage of spiral channel cross-section |
| Spray Angle | 15°~25° | Narrow angle focus for deep channel penetration |
| Safety Distance | ≥50mm | Prevent high-pressure water from directly impacting spacer stud weld points |
Limitations: High-pressure water jetting can only clean the channel inlet section; it is ineffective against scale in the mid-to-rear curved sections. Therefore, it must be combined with chemical cleaning — inlet high-pressure water breakthrough + full-length chemical circulation dissolution is currently the most effective combined approach.
4. Engineering Case Studies
Case 1: Calcium Sulfate Hard Scale Cleaning in a Chemical Plant Spiral Plate Heat Exchanger
Equipment parameters: Heat transfer area 80m², channel width 14mm, material 316L, in service 6 years without cleaning.
Fouling condition: Medium contained CaSO₄ reaction liquid; scale thickness at the inlet end (within 200mm) reached 8~10mm, Mohs hardness 3.5, channel cross-sectional area reduced by approximately 65%.
Cleaning protocol:
- High-pressure water jet (800bar × 40L/min) to remove inlet hard scale, 3h duration
- NaOH 4% alkaline boil for 12h (85°C), to soften and partially convert CaSO₄ scale
- EDTA 8% chelation cleaning for 10h (65°C), alternating forward and reverse circulation
- Citric Acid 3% + BTA 0.5% passivation for 4h
Cleaning results: Post-cleaning flow rate restored to 93% of design value, pressure drop reduced from pre-cleaning 4.2 bar to 1.1 bar (design value 0.9 bar). 316L coupon corrosion rate 1.2 g/(m²·h), well below the standard limit.
Case 2: Organic Mixed Scale Cleaning in a Pharmaceutical Plant Spiral Plate Heat Exchanger
Equipment parameters: Heat transfer area 50m², channel width 10mm, material 304, medium contained resin-type organics and CaCO₃ mixed scale.
Cleaning protocol:
- Surfactant 1% + NaOH 3% alkaline wash for 8h (75°C), to remove resin adhesive layer
- Sulfamic Acid 6% + Citric Acid 3% + BTA 0.3% acid cleaning for 6h (55°C)
- NaNO₂ passivation treatment
Cleaning results: Flow rate restored to 91%, organic removal rate (TOC test) >95%, 304 coupon showed no pitting traces.
5. Preventive Maintenance Recommendations
- Regular online cleaning: It is recommended to perform a mild chemical circulation cleaning every 3~6 months (Sulfamic Acid 3%~5%, ambient temperature ~40°C, circulation 2~4h) to prevent scale accumulation from reaching the hard scale stage.
- Pre-filtration: Install Y-type strainers (100~200μm precision) at the media inlet to intercept large particulate impurities and reduce channel blockage risk.
- Operating parameter monitoring: Establish pressure differential and outlet temperature trend records — when the pressure differential increases by 20% or heat exchange efficiency decreases by 15%, immediately schedule cleaning to avoid scale hardening.
- Material-appropriate selection: For high fouling tendency operating conditions, prioritize models with channel width ≥18mm, or consider removable spiral plate heat exchangers (end covers can be opened for mechanical unclogging).
- Cleaning record management: After each cleaning, document scale type, cleaning formulation, circulation parameters, and performance data to provide a basis for subsequent cleaning optimization.
6. Summary
The core challenges of spiral plate heat exchanger cleaning lie in non-removable channels, narrow curved passages, and complex scale composition. A successful cleaning solution must achieve:
- Analyze first, then formulate: Determine the cleaning agent system through scale sample analysis, avoiding blind trial-and-error
- Physical + chemical synergy: High-pressure water for inlet sections, chemical circulation for the full length
- Protection first: Strictly control cleaning temperature, concentration, and corrosion inhibitor ratios to prevent stress corrosion
Danyang Blue Star Cleaning has 20 years of industrial equipment cleaning experience and has independently developed specialized cleaning processes and corrosion inhibitor formulation systems for spiral plate heat exchangers. If your spiral plate heat exchanger presents cleaning challenges, please contact us for a technical solution.