Fermentation tank titanium heating tubes have two mainstream cleaning modes: online CIP circulation cleaning (no disassembly, daily/monthly routine maintenance) and offline full disassembly immersion cleaning (semi-annual major overhaul deep cleaning). The two methods differ greatly in cleaning thoroughness, labor cost, production shutdown time, passive film protection degree and applicable scale type. This article compares their advantages, defects, applicable working conditions and standardized operation key points, providing a combined cleaning cycle matching scheme for production lines.
1. Basic definition and applicable scenarios of two cleaning modes
1.1 Online CIP circulation cleaning
Process: The acid-base cleaning liquid is circulated in the closed tank system through a dedicated CIP pipeline, the heating tube is immersed in the liquid for circulating scouring without disassembling the tube bundle, and the cleaning liquid is discharged after the cycle is completed. Applicable scenarios:
Routine daily sterilization cleaning, monthly regular descaling maintenance;
Thin organic grease, light sugar carbon deposits, a small amount of loose inorganic salt scale;
Continuous production lines that cannot stop production for a long time, large-volume fermentation tanks with complex tube bundle layout.
1.2 Offline disassembly immersion cleaning
Process: Empty the tank, disassemble the entire titanium heating tube assembly, transport it to an independent cleaning tank, and fully immerse it in composite cleaning liquid for static soaking + soft water high-pressure flushing. After cleaning, passivate and reinstall. Applicable scenarios:
Semi-annual major overhaul deep maintenance;
Thick coked carbon scale, hard calcium-magnesium mineral scale that cannot be removed by online circulation;
Tube surface with weld black oxide layer, deep scratch dirt accumulation, serious local pitting blind area dirt;
Tubes with passive film potential continuously lower than the standard value after multiple online passivations.
2. Multi-dimensional comprehensive performance comparison table
表格
| Comparison Dimension | Online CIP Circulation Cleaning | Offline Disassembly Immersion Cleaning |
|---|---|---|
| Production shutdown loss | Short shutdown (1~4h), can be arranged between batches, low broth scrapping risk | Long shutdown (1~2 working days), tank emptying, sterilization rework, high production loss |
| Labor & auxiliary cost | Low, automatic pipeline circulation, only regular reagent configuration | High: disassembly, handling, reinstallation labor consumption; extra cleaning tank, passivation liquid consumption |
| Cleaning scale removal ability | Medium, only removes loose surface scale; blind areas such as support gaps, upper bubble stagnation zone cannot be fully cleaned | Excellent, full-surface all-round contact with cleaning liquid, manually scrub dead corners, thoroughly remove thick hard coking scale |
| Passive film protection degree | Mild cleaning liquid, controllable temperature, less damage to TiO₂ film; continuous aeration during circulation can synchronously complete preliminary passivation | Long-time soaking in high-efficiency composite cleaning liquid may slightly thin the outer loose layer of the passive film; mandatory independent chemical passivation after cleaning to repair |
| Bubble stagnation blind area cleaning effect | Poor, bubbles gather on the upper arc of the tube, liquid cannot fully contact the bubble coverage area, residual scale easily forms pitting source | Perfect, the heating tube is flipped regularly during immersion, no gas retention dead angle, uniform cleaning of upper and lower tube walls |
| Weld oxide cleaning effect | Weak, circulating liquid has limited erosion ability for thick weld black oxide | Strong, long-term soaking combined with local citric acid spot cleaning completely removes weld oxidation layer |
| Frequency limit | Can be implemented weekly/monthly, frequent execution has little impact on production | Only suitable for semi-annual overhaul, frequent disassembly easily scratches tube surface and damages PTFE insulation accessories |
| Subsequent passivation convenience | After cleaning, directly switch to aerated passivation liquid circulation, one-line completion | Need to transfer to a separate passivation tank for full immersion film formation, extra independent operation steps |
3. Advantages and defects detailed analysis
3.1 Online CIP cleaning core advantages
Minimal production interruption: The cleaning window is arranged during the tank emptying interval between fermentation batches, no long-term shutdown loss, suitable for 24h continuous mass production.
High degree of automation: The CIP system automatically completes liquid feeding, circulation, flushing and liquid discharge, reducing manual operation errors.
Integrated cleaning and preliminary passivation: After acid-base descaling, the pipeline can directly switch to hydrogen peroxide passivation liquid circulation, without secondary handling of the tube bundle.
Less mechanical damage risk: No disassembly and handling, avoiding scratches on the titanium tube surface caused by collision, friction with brackets and tools.
Online CIP cleaning inherent defects
Dead corner cleaning blind areas exist: Support contact gaps, upper bubble retention areas, weld concave areas cannot be fully scoured by circulating liquid, and scale accumulates year by year.
Limited capacity for thick hard scale: Carbonized coking scale formed by long-term high-power heating cannot be completely decomposed by short-term online circulation, and residual scale triggers under-deposit crevice corrosion.
Difficult to inspect the tube surface in real time: The tube bundle is sealed in the tank, and the scaling and pitting status can only be judged through the sight glass, which cannot achieve full visual inspection of all surfaces.
3.2 Offline disassembly cleaning core advantages
Thorough full-surface decontamination: The tube bundle is completely exposed, and manual auxiliary soft brush cleaning can eliminate all dead-angle scale, fundamentally eliminate hidden dangers of crevice corrosion.
Synchronous comprehensive inspection of tube body: After disassembly, high-light inspection, wall thickness measurement, weld flaw detection and passive film potential test can be completed at one time to find early pitting and thinning defects.
Targeted local treatment: Weld black oxide, deep scratch dirt and local thick scale can be treated with targeted spot soaking and polishing, which cannot be realized by online circulation.
Eliminate bubble blind area interference: Flipping the tube bundle regularly during immersion ensures that all tube surfaces are continuously contacted by cleaning liquid without gas isolation.
Offline disassembly cleaning inherent defects
Huge production shutdown loss: The tank needs to be completely emptied, sterilized and re-prepared for culture medium, which greatly reduces the annual production batch quantity of the workshop.
High risk of mechanical damage during disassembly and assembly: Hoisting, handling and bolt disassembly easily scratch the titanium passive film, and frequent disassembly accelerates aging and cracking of PTFE gaskets and insulating sleeves.
Increased comprehensive labor and material costs: Additional manpower is required for disassembly and reinstallation, and a large amount of composite cleaning and passivation reagents are consumed for independent tank soaking.
4. Standard matching cycle scheme for mixed use of two cleaning modes
Combined with the production load of fermentation tanks, a hierarchical cleaning system of "routine online cleaning + periodic offline deep cleaning" is formulated, which balances production efficiency and equipment anti-corrosion protection:
Low-load intermittent fermentation tank (≤16h daily operation, low-sugar medium): Online CIP cleaning once a week; offline disassembly deep cleaning and full passivation once a year.
Conventional medium-load continuous food fermentation tank (24h operation, biweekly CIP): Online alternating acid-base cleaning every two weeks; offline disassembly cleaning and overhaul every six months.
High-load pharmaceutical sterile fermentation tank (daily mild alkali CIP, high-viscosity high-sugar medium): Daily short-term online alkali circulation sterilization, monthly online citric acid deep descaling; offline full disassembly cleaning, flaw detection and integral passivation every 6 months.
High-corrosion industrial wastewater heating tank (high TDS salt, easy hard mineral scale): Weekly online pickling descaling; offline disassembly immersion cleaning, hydrogen removal baking and re-passivation every 4 months.
5. Key protective operation specifications to reduce passive film damage
Unified control rules for online CIP cleaning
Strictly limit alkali liquid temperature ≤60℃, acid liquid temperature ≤45℃, single circulation time in accordance with Article 66 standards;
Maintain circulating flow velocity ≥1.0m/s to reduce bubble stagnation and local scale residue;
After each acid-base circulation, mandatory 2h warm aerated water pre-passivation circulation to repair the thinned outer passive film.
Unified control rules for offline disassembly cleaning
Before disassembly, wrap the tube bundle with soft PTFE foam to avoid scratch friction during hoisting and handling;
Composite cleaning liquid soaking time shall not exceed 8h, and timely transfer to deionized water multi-stage flushing after scale removal to prevent excessive etching of the titanium matrix;
After cleaning, the whole tube must be immersed in hydrogen peroxide passivation liquid for 6~8h integral film formation, and reinstalled after natural air-drying and film maturation for 24h.
6. Judgment standard for mandatory offline deep cleaning
When any of the following conditions occur, online cleaning alone cannot eliminate hidden dangers, and offline disassembly cleaning must be arranged during the next overhaul window:
Thick black carbon coking layer visible on the tube wall through the sight glass, which cannot be removed after two consecutive online deep descaling cycles;
Quarterly detection shows that the upper arc wall thickness of the tube is significantly thinner than the lower part, accompanied by bubble stagnation pitting spots;
Weld potential is continuously lower than +120mV after two online passivations, and the surface has obvious black oxidation discoloration;
More than 1 year without offline disassembly inspection and cleaning, cumulative scale blind area hidden risk.
Brief Summary
Online CIP circulation cleaning is the main routine maintenance method for titanium heating tubes, with the advantages of low shutdown loss and automatic operation, but it has unavoidable cleaning dead corners such as bubble stagnation zones and support gaps. Offline disassembly immersion cleaning has thorough decontamination and full inspection capabilities, but it brings high production and labor costs. Enterprises should adopt a combined maintenance system of frequent online routine cleaning + regular offline deep overhaul cleaning according to the tank production load and medium corrosion degree, and implement standardized temperature and time control during all cleaning processes, matched with post-cleaning passivation repair, to minimize cumulative damage to the titanium dioxide passive film and extend the overall service life of heating tubes.
