YUHONG GROUP - Heat exchanger tube bundle cleaning steps and precautions

System isolation before cleaning: cut off the heat exchanger from the process system, close the inlet and outlet valves and add blinds, and empty the internal medium; and do a good job of safety protection: set up warning signs, wear protective equipment (anti-acid and alkali gloves, goggles, gas masks, etc.). Sample and analyse the scaling composition (e.g. carbonate, sulphate, biofouling, etc.), choose mechanical or chemical cleaning according to the type of scale layer, configure tools or reagents, and determine the cleaning programme.

Cleaning is carried out both mechanically and chemically.

Mechanical cleaning is divided into three main categories, high-pressure water jets, physical brushing and air pulse cleaning.

High-pressure water jet refers to the use of pressure 100-300 MPa high-pressure water gun flushing tube bundle by tube, the water pressure needs to be adjusted according to the hardness of the scale layer, to avoid damage to the pipe wall; Physical cleaning brush refers to the stubborn scale, the use of flexible shaft brush or sandblasting (quartz sand particle size 0.5-1.5 mm), pay particular attention to the cleaning of the U pipe elbow parts; and the air impulse cleaning refers to the use of compressed air to generate a pulse wave to peel off the The air pulse cleaning refers to the use of compressed air to generate pulse waves to strip off loose dirt, suitable for lightweight scale.

There are three types of chemical cleaning: acid cleaning, alkaline cleaning and neutralisation rinsing.
Acid cleaning method is mainly for carbonate scale, using 5-10% hydrochloric acid or 10-15% citric acid solution cycle cleaning, adding 0.5% corrosion inhibitor (such as urotropin) to protect the metal. Control temperature ≤ 60 ℃, time 2-4 hours. Alkaline rinsing method is mainly used to remove oil or organic matter, using 3-5% sodium hydroxide solution, heated to 80 ℃ cycle cleaning. Neutralisation rinsing means rinsing with water to PH neutrality after chemical cleaning, and then using 0.5% sodium carbonate solution to neutralise the residual acid.

After the cleaning is completed, a drying inspection should be carried out, using compressed air to blow dry the pipe bundle, endoscopic inspection of each pipe to confirm that there is no residual dirt or mechanical damage. And carry out pressure test: carry out 1.5 times the design pressure of the water pressure test, holding pressure for 30 minutes without leakage. Then carry out anti-corrosion treatment: spray passivation agent (such as sodium nitrite solution) on carbon steel pipe bundles, stainless steel pipe bundles need to carry out nitric acid passivation.

Test the heat transfer temperature difference after cleaning to ensure that it is restored to more than 90% of the design value to verify the heat transfer efficiency, while removing the blind plate, restoring the pipeline connection, and gradually increasing the pressure to the working pressure.