Acid washing heat exchanger

A heat exchanger is a solid surface that prevents the interference of two fluids with different temperatures. It enables the heat exchange between these two hot and cold fluids moving in parallel, opposite, or cross currents.
Due to its impurities, water contains some salts. These salts, such as calcium carbonate and magnesium carbonate, have temporary hardness, which forms deposits due to stagnant water or increased heat in the walls of the pipes. In other words, sedimentation results from the supersaturation of high salts on the surface. It is worth mentioning that the lower the temperature of the area and the higher the water flow, the lower the hardness of the water, which results in a significant reduction in the amount of sediment in the exchanger.
These salts, which are formed inside the tubes of shell and tube exchangers or welded plate and gasket (gasket) exchangers, are descaled by standard acids.
Descaling improves heat transfer in systems, including heat exchangers, in many ways. In shell-and-tube type heat exchangers, deposits increase the thickness of the pipe wall, which causes a decrease in the speed and flow rate of the passing water, which results in a reduction of the heat exchange between the two fluids. On the other hand, sediment increases the roughness inside the pipes and causes a drop in fluid flow pressure, which results in a decrease in heat exchange. Also, sediment reduces the heat transfer coefficient of lines. The result of all the above is a significant decrease in system efficiency and an increase in cost. Besides, deposits cause heat exchanger failure due to chemical and mechanical corrosion. So it should be fixed.

What acid should we use for acid washing the heat exchanger?

Acids in the form of anhydride or solution are not suitable for descaling. Descaler acids, available in concentrations of 30% and above, are the most suitable descaling acids on the market. The use of household scale removers, which are used by some services to descaling small converters, is not recommended.
Depending on the type and dimensions of the converter, it is possible to use different kinds of such hardeners as magnetic hardeners, resin, reverse osmosis, polyamide, etc. The use of a hardener for descaling includes the two advantages of increasing the system's life and reducing the costs of descaling.

How to descale and acid wash the heat exchanger

The first method:
In small heat exchangers such as instant water heater exchangers and welded plate exchangers in packages (secondary exchangers) or the primary exchanger of packages, we enter the acid by gravity into the exchanger. The way acid washing works in these converters is that after removing the converter from the device, we put it in a container like a basin and pour water halfway up the converter. We enter the acid from the output side of the converter. The acid washes in reverse of the water flow.
• The point that should be noted is that to do this, you must use gloves, a mask, and a shield to protect your hands, face, and eyes; Because the combination of acid with water and sediment may lead to acid splashing around.
• This method is also effective for descaling the outer part of the copper coil of coil converters.

The second method:
This method is used with the help of acid wash pumps with a pump housing and a plastic impeller compatible with acid. These portable pumps use an acid tank whose volume varies depending on the working volume or pump power. The small size of these pumps is used for packages with flexible hoses with clip or nut connections. The large size of these pumps uses hose-shaped and flexible pipes that are easily connected to the converter. In this method, descaling should be done patiently and for a long time with dilute acid. If the speed of the operation is important, acid washing can be done with more concentrated acid in a short period.

The time required for acid washing of the heat exchanger

An experimental method is to take a sample from the acid return pipe from the converter to the pump tank with a plastic container and pour it on the floor (for example, mosaic or paving stones). It needs to be better mixed with sediment, and you must wait for a little. The combination of acid with sediment will lead to a decrease in the properties of the acid. The result of sampling the next time should be less foam and less acid on the ground. The basic method is to measure the pH of the acid solution inside the converter.
• Acid washing of gasketed and welded converters is specialized and requires high skill. It is recommended to leave their descaling to experts.
• If you use acid with an inappropriate concentration or more acid than needed for acid washing, it will damage the plates or holes in them.

Significant cases after acid washing of the heat exchanger

Always wash the heat exchanger with an alkaline solution after descaling by emptying the acid. The acid in the exchanger will damage the pipes and plates, and the alkaline solution will neutralize the remaining acid. Will remain. After washing it with an alkaline solution, it is better to wash the converter once with plenty of water.
• Washing powder and water also have an alkaline composition. Make sure the powder is completely dissolved in the water.
Since in the heat exchanger, a plate is filled with copper and nickel welding between the plates, and acid is corrosive to these two metals, if the acid remains in the exchanger, it will lead to a hole in the exchanger, and its repair will be difficult. It comes with many issues, and the perforated converter should be abandoned, and a new converter should be used; It is recommended to use experienced and expert people for acid washing of such converters.

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final word

You can visit Damatajhiz.com, the specialized site of Damatajhiz.com, which started its activity in 2013 and is the first store site of the country and specializes in the field of installation equipment; View and buy different types of heat exchangers in different brands with different capacities and if necessary, use the specialized advice of the company's sales experts.

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