1. Structural Characteristics of Different Heat Exchanger Types
Heat exchangers are critical equipment for heat exchange in industrial production, widely used in chemical, petroleum, power, food, and pharmaceutical industries. Based on structural form, common heat exchangers include plate heat exchangers, shell-and-tube (tubular) heat exchangers, spiral plate heat exchangers, and double pipe heat exchangers. Each type of heat exchanger has significant differences in cleaning method selection due to its unique structural design.
Plate heat exchangers consist of a stack of corrugated metal plates, forming narrow flow channels between the plates where fluids flow on both sides for heat exchange. Their advantages include high heat transfer coefficient and compact structure, but the plate spacing is small (typically 2–6mm), the flow path is tortuous, and clogging is likely. Plate heat exchangers can be disassembled for cleaning; gasket materials are typically NBR (nitrile butadiene rubber) or EPDM (ethylene propylene diene monomer), with temperature resistance generally not exceeding 150°C.
Shell-and-tube heat exchangers consist of a shell, tube bundle, tube sheet, and head. One fluid flows inside the tubes while another flows in the shell side. Tube diameters generally range from 19–38mm, and tubes may be straight or U-shaped. Shell-and-tube heat exchangers feature robust construction and high pressure tolerance, suitable for high-temperature and high-pressure conditions, but cleaning is relatively difficult, especially on the shell side.
Spiral plate heat exchangers are formed by rolling two parallel steel plates into spiral channels, creating two independent spiral flow paths. Their advantages include strong self-cleaning capability, resistance to clogging, and high heat transfer efficiency. However, due to narrow and long channels (width 5–20mm), once severe fouling occurs, cleaning is extremely challenging and the unit cannot be disassembled.
2. Comparative Analysis of Cleaning Methods
| Cleaning Method | Applicable Heat Exchanger Types | Advantages | Disadvantages | Applicable Fouling Types |
|---|---|---|---|---|
| Chemical Circulation Cleaning | Shell-and-tube, spiral plate, double pipe | Thorough cleaning, reaches dead zones, no disassembly required | Requires cleaning solution preparation, waste liquid treatment needed, gasket compatibility required | Scale, rust scale, oxide scale, silicate scale |
| High-Pressure Water Jetting | Shell-and-tube (tube side), plate (after disassembly) | High efficiency, no chemical pollution, low cost | Cannot clean shell side, limited effect on hard scale, requires disassembly | Soft fouling, sludge, loose scale, coke deposits |
| Ultrasonic Cleaning | Plate (individual plates), small tubular | Fine cleaning, no surface damage, environmentally friendly | High equipment investment, limited throughput, requires disassembly | Fine particulate fouling, oil fouling |
| Mechanical Cleaning | Shell-and-tube (tube side) | Effective on hard scale, simple operation | May damage tube walls, slow speed, high labor intensity | Hard water scale, coking layer |
| Online Sponge Ball Cleaning | Shell-and-tube condensers | Online operation, continuous cleaning | Only suitable for soft fouling prevention, cannot address existing hard scale | Soft fouling, microbial slime |
3. Recommended Cleaning Solutions by Heat Exchanger Type
Plate heat exchanger cleaning: High-pressure water jetting or chemical immersion cleaning after disassembly is recommended. When disassembling, mark the plate sequence to avoid incorrect reassembly order. For scale fouling, immerse in 3%–5% nitric acid or sulfamic acid solution for 2–4 hours at 40–50°C. For oil fouling, perform alkaline degreasing first, followed by acid cleaning. After cleaning, inspect gaskets and promptly replace aged or deformed ones.
Shell-and-tube heat exchanger cleaning: Tube-side cleaning can use high-pressure water jetting or mechanical cleaning (using rotary tube cleaners). For severely scaled tube sides, perform chemical circulation cleaning first to soften the scale layer, then high-pressure water flushing. Shell-side cleaning is more complex and generally uses chemical circulation cleaning. Set up a temporary cleaning loop at the shell-side inlet and outlet, using 5%–8% hydrochloric acid with corrosion inhibitor for circulation cleaning at a flow rate of 0.5–1.0m/s.
Spiral plate heat exchanger cleaning: Chemical circulation cleaning is the preferred method. Since spiral plate units cannot be disassembled and have long flow paths, the cleaning solution must have sufficient flow rate and circulation time. It is recommended to use acidic cleaning agents (hydrochloric or nitric acid, 5%–8% concentration) with high-efficiency corrosion inhibitors, circulated at 50–60°C for 8–12 hours. For organic fouling, alkaline and acid cleaning can be alternated. After cleaning, thorough rinsing and passivation treatment should be performed.
Double pipe heat exchanger cleaning: The inner tube typically uses chemical circulation cleaning, while the annular space can use chemical or mechanical cleaning. Due to the narrow annular gap, special attention must be paid during chemical cleaning to prevent air locks and ensure the cleaning solution fills the entire annular space.
4. Cleaning Method Selection Principles
When selecting a heat exchanger cleaning method, the following factors should be comprehensively considered: heat exchanger type and structural characteristics, fouling type and thickness, equipment material corrosion resistance, on-site construction conditions, environmental requirements, and economic cost. For complex operating conditions, a combination of multiple cleaning methods is often needed to achieve optimal cleaning results. Danyang Blue Star Anti-corrosion Cleaning Co., Ltd. can provide tailored cleaning solutions based on the specific conditions of different heat exchangers. Please call for consultation.
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