At present, the heat exchanger with plate heat exchanger as the main body has been widely used
in the heating system.However, in the process of its use, due to the poor circulating water
quality in the system caused by plate heat exchanger plate scaling, resulting in the reduction of
heat transfer efficiency of the problem often occurs.Therefore, choosing a reasonable chemical
cleaning method has become a necessary means to improve the heat transfer efficiency and
extend the service life of the equipment.
1. Phenomena and causes of common operating failures of heating system
In the daily operation process of heating system, the circulating water system often appears
scaling, corrosion and biological mud phenomenon, resulting in the heat transfer efficiency of
plate heat exchanger decrease, circulating water flow rate, drop pressure drop increase.
If it is serious, it will affect the normal operation of the system, and lead to the increase of
operation cost, the shortening of heating equipment and even the early scrapping of
equipment.The main causes of these failures are:
1.1 In the heating system, especially in the secondary network system, the plate heat exchanger
water is generally used untreated tap water containing a large amount of Ca2+, Mg2+ and other
scale ions.
In the actual production process, the method of adding anti-corrosion scale inhibitor is often
used to reduce the hardness of tap water.But at the same time, often due to equipment,
operation management is not in place, resulting in the addition of anti-corrosion scale inhibitor
can not meet the requirements, resulting in a large number of Ca2+, Mg2+ from the water
saturated precipitation deposition in the heat exchanger and pipe network in the metal surface
to form scale;
1.2 After the sediment and all kinds of bacteria and algae in the water refill enter the circulating
water system, the microorganisms grow and multiply due to the appropriate temperature. A
large number of microbial mud is produced in the system, which is attached to the heat
exchanger and mixed with scale to form biological dirt;
1.3 Dissolved oxygen and salts in water will cause oxygen corrosion and chemical corrosion on
metal materials of heating system.Since the heating system is composed of a variety of metal
materials, in the water containing a lot of electrolytes and salts, galvanic couples and corrosion
batteries are formed between different metals, thus producing electrochemical corrosion of the
heating system metals.
2. Damage of scaling and corrosion to heating system
2.1 Energy consumption increases significantly and operation costs rise
After the heating system generates scale and biological slime, the heat transfer efficiency of heat
exchanger decreases, the circulation area of circulating water becomes smaller, and the
circulation resistance increases, which leads to a large increase in the energy consumption of the
whole system and the heating cost.
The above data show that the thermal conductivity of scale is much lower than that of carbon
steel and similar to that of brick. The generation of scale will seriously affect the heat transfer
efficiency of plate heat exchanger.
2.2 System working efficiency decreases, affecting the heating effect
The scaling of the heating system will reduce the heat exchange efficiency and the outlet
temperature of the medium, resulting in the reduction of the temperature difference between
the import and export medium and the decrease of the heating efficiency