Boiler tube cleaning methods

The necessity of cleaning the boiler tube
After long-term operation of the boiler tube, scale and rust problems are inevitable. Scale is the main cause of the service life of boiler tubes.
 
Causes of scale formation in boiler tubes
The main reason for the scale formation of the boiler is that the water has a hardness component. After continuous evaporation and concentration by high temperature and high pressure, a series of physical and chemical reactions occur in the furnace, and finally a hard and dense scale is formed on the heated surface.

1.The damage of scale to boiler tubes:
Because the thermal conductivity of scale is only a few tenths of that of steel, when the heating surface is fouled, the heat transfer will be blocked. In order to maintain a certain output of the boiler, it is necessary to increase the temperature of the fire side, so that the radiation and smoke are radiated outward. Cause heat loss. Due to the different working pressure of the boiler, the type and thickness of the scale are different, and the amount of fuel wasted differently. According to the test and calculation, the thickness of the scale and the fuel loss have the following proportions: When the scale thickness (S) ≥ 1 mm, the fuel is wasted 5~ 13%; ≥ 2mm, waste fuel 13~18%; ≥3mm, waste fuel 18~26%.

2. It is easy to burn the steel plate and boiler tube due to overheating.
Because the boiler tube is fouled, and must maintain a certain working pressure and evaporation, only increase the temperature of the fire side, but the thicker the scale, the lower the thermal conductivity of the boiler tube, the higher the temperature on the fire side. Generally speaking, the temperature on the fire side of the boiler tube is around 900 °C, and the temperature on the water side is around 190 °C. When there is no scale, the temperature of the steel sheet is about 230 ° C. Once the scale is about 1 mm, the temperature of the steel sheet is increased by about 140 ° C than when the scale is not.

Take the 20# boiler tube as an example.
When the temperature of the Gr 20 boiler tube reaches 315 °C, the plasticity index of the metal begins to decrease. When it reaches 450 °C, the boiler tube will creep and deform due to overheating. Therefore, boiler fouling is very easy to burn the boiler tube.
 
3. Increased maintenance costs of boiler tubes and reduced service life of boiler tubes
Accidents caused by scale in boiler tubes are about one-third of the total number of boiler accidents, or an upward trend, which not only causes damage to equipment, but also threatens personal safety. Therefore, in the case of qualified water supply, the boiler should be strictly controlled to control the water in the boiler tube during operation; and prevent the formation of scale during operation, and after scaling, it must be treated in time, and the scale and control in the boiler tube must be completely prevented and removed. Water quality.
 

Boiler tube cleaning
At present, the most scientific method is to add a comprehensive performance and comprehensive cleaning agent cleaning and descaling in the boiler tube operation.

1. Boiler tube pickling agent selection
Boiler pickling agent For different scales and metal materials, suitable pickling and cosolvent should be used. The general choices are as follows:
(1) For carbonate scale, generally washed with hydrochloric acid
(2) For silicate scale, it can be washed by adding hydrofluoric acid or fluoride to hydrochloric acid.
(3) Mixing scale with sulfate scale or sulfate and silicate should be pre-alkali-transformed and then washed with hydrochloric acid or hydrochloric acid.
(4) For iron oxide scale, fluoride may be added to hydrochloric acid or washed with nitric acid.
(5) For power station boilers, when the iron content in the iron oxide scale is high (CuO>5×10-2), measures should be taken to prevent copper plating on the surface of the boiler tube. Generally, hydrochloric acid plus fluoride and sulfur can be selected. Cleaning aids such as urea compounds and thiourea.
(6) For the cleaning of austenitic boiler tubes, hydrochloric acid should not be used as a cleaning agent. For the cleaning of boiler parts containing chromium materials, an organic mixed acid such as hydrofluoric acid, citric acid or formic acid or acetic acid may be generally used as a cleaning agent.
 
Boiler tube descaling agent
[Applicable objects] Various boilers, electric boilers
[Main components] food acid, penetrant, accelerator, metal material protectant
[Product Function] Quickly and thoroughly remove scale attached to the inner wall of the boiler tube
[Product Function] It can dissolve scale components such as calcium carbonate, magnesium carbonate, calcium sulfate, calcium silicate and iron oxide; it is non-corrosive, non-toxic, odorless, and quickly and completely removes the scale attached to the inner wall of the boiler.
[Product Advantages] Food grade raw materials can be used directly after cleaning; no corrosion to boiler inner wall, sealing rubber ring, plastic parts, etc.; green environmental protection formula, cleaning liquid can be directly discharged; powerful and efficient, descaling effect can be intuitively monitored .

2. Boiler tube descaling agent use method
(1) Open the boiler tube inlet;
(2) diluted into a boiler tube at a ratio of 1:10;
(3) Fill the water to the highest water level, wait 2 hours, and make the detergent solution fully react with the scale;
(4) Open the drain and drain the cleaning solution;
(5) Inject with water to rinse again, cleaning and descaling work is completed.
 
Note:
(1) The water is heated to about 50 degrees, and the descaling effect is better. It is recommended to clean once every six months.
(2) During the process of cleaning the boiler, it takes time to react the boiler tube cleaning agent with the scale. When the scale is not completely dissolved in the water, please extend the time as much as possible to 8-24 hours.
[Importance of Maintenance] After the boiler is deactivated, the outside air will enter the furnace system in a large amount, and the water film attached to the metal surface of the boiler tube will form an oxygen solution with the air to reach the bubble state and cause dissolved oxygen corrosion. The corrosion rate is the running time. Ten times, plus residual scale, is more corrosive. Practice has proved that the production of severely corroded boilers is caused by multiple shutdowns, so maintenance measures must be taken for decommissioning.