As a heat exchange system using water as the heat carrier, scale easily adheres to the surface of the heat exchange tubes. If descaling is not performed for a long time, the scale formed on the surface of the heat exchange tubes will become increasingly thick, affecting heat transfer efficiency and causing damage to the fully automatic heat exchanger. Therefore, when using afully automatic heat exchanger, regular descaling is required. So, what are the commonly used descaling methods?
Manual or mechanical methods. When pipes are slightly clogged and fouled, they can be cleaned using manual or mechanical methods such as scraping and wire brushing, combined with compressed air, high-pressure water, and steam for cleaning. When pipes are severely fouled or completely blocked, a pipe water drill (also known as a pipe auger) can be used.
There are two flushing methods. The first is countercurrent flushing, typically used during operation or during short periods of downtime. The equipment does not need to be disassembled, but a countercurrent bypass line must be pre-installed. This method is more effective when scaling is not severe. The second is high-pressure water jet flushing. Different rotating water jet heads are used for different heat exchangers, either rigid or flexible, with adjustable pressures from 10 MPa to 200 MPa. High-pressure water jets are suitable for removing contaminants between pipes, within pipes, and on the shell. High-pressure water jet flushing of heat exchangers is highly effective and widely used.
1. Preliminary preparation (clarifying scale characteristics and equipment status)
Scale sampling and analysis: Determine the main components through laboratory testing and select the cleaning solution.
Equipment status inspection: Check whether the heat exchange tubes are corroded, leaking or blocked, which can be judged by the pressure gauge difference;
Develop a cleaning plan: Determine the cleaning method based on the analysis results and develop an emergency plan.
2.Core cleaning method: chemical cleaning
|
Scale type |
Recommended cleaning agents |
Applicable materials |
Precautions |
|
Carbonates (accounting for more than 80%) |
Hydrochloric acid (5%-10% concentration), citric acid (8%-12%) |
Carbon steel, stainless steel |
Hydrochloric acid needs to be added with a corrosion inhibitor (such as hexamethylenetetramine) to avoid corrosion; citric acid is suitable for acid-sensitive materials. |
|
Sulfate/Silicate (stubborn) |
Sulfamic acid (10%-15%) + fluoride (auxiliary) |
Stainless steel, copper alloy |
Fluoride concentration must be strictly controlled (≤2%) to prevent silica scale from solidifying |
|
Mixed scale |
Compound cleaning agent (such as hydrochloric acid + citric acid + corrosion inhibitor) |
Carbon steel, stainless steel |
A small test is required to verify the corrosion resistance (coupon test: corrosion rate ≤ 0.1mm/year is qualified) |
3.Physical cleaning (suitable for mild scale or sensitive materials)
Physical cleaning does not require chemical agents and is suitable for scenes where the scale is loose or the material is not acid-resistant. (High-pressure water jet cleaning, mechanical scraper cleaning, and ultrasonic cleaning are optional)
4.Acceptance after cleaning and daily anti-scaling measures
Acceptance of cleaning effect (visual inspection, performance test)
Daily anti-scaling measures (reduce scale regeneration, install a water softener at the water inlet of the unit)
Scaling in heat exchanger tubes is primarily caused by poor water quality, which results in the formation of scale and grease, which forms in the form of coking, precipitation, and adhesion. Chemical descaling methods require first analyzing and testing the scaling substances. Understanding the nature of the scaling substances will help determine the appropriate solvent for cleaning. Alkaline cleaning is generally used for sulfate and silicate scale, while acid cleaning is used for carbonate scale. Grease and coking can be removed using a cleaning solution composed of sodium hydroxide, sodium carbonate, laundry detergent, liquid detergent, sodium silicate, and water in a specific ratio.
To remove scale from the interior of a fully automatic heat exchanger, different descaling methods can be used. Each descaling method has different characteristics, so you can choose the appropriate descaling method based on your actual situation. Furthermore, when maintaining and servicing a fully automatic heat exchanger, in addition to regular descaling, other maintenance measures are also required to reduce the failure rate of the fully automatic heat exchanger and extend its service life.