Pickling is the main method for removing a large amount of oxidizing substances and corrosion products inside a gas boiler, and it also has the effect of removing deposits. The pickling process is usually carried out 1–3 weeks after the boiler starts operating.

Firstly, cleaning equipment

Boiler economizer, steam drum, water wall, hydrochloric acid, ammonium bifluoride.

Secondly, cleaning method

1. First, at the beginning of the pickling operation, the boiler economizer, steam drum, and water wall are filled with demineralized water.

2. The boiler is ignited. When the boiler temperature reaches 70–80 °C, the boiler is shut down, and then the pickling operation can be carried out. Before the pickling process, the superheater must also be filled with demineralized water until water overflows into the steam drum to prevent acid or acid vapor from entering the superheater.

3. When acid is filled into the boiler, the boiler must not be ignited under any circumstances. To release the hydrogen generated from the reaction between acid and iron, the steam drum and other ventilation openings must be opened. Before ensuring that hydrogen has dissipated, avoid open flames or using electrical equipment that may produce sparks to eliminate the risk of hydrogen explosion.

4. Finally, after the acid filling is completed, allow the boiler and economizer to soak in the solution for about 6 hours, then drain the acid and rinse the superheater with demineralized water. The acid is drained. After draining the acid, the boiler feed water pump is started, and water from one economizer is supplied to the boiler to prevent leakage of the water supply shut-off valve.

Thirdly, matters requiring attention

The gas boiler can be pickled with 5% hydrochloric acid with the addition of 0.25% ammonium bifluoride inhibitor. The acid solution is injected into the boiler from the acid connection at the lower pipe of the steam drum, and the filling of the economizer with acid is carried out through the recirculation pipe. The filling of the acid solution should continue until the liquid level in the temporary water level measuring device of the steam drum rises significantly, reaching above the cyclone separator level. However, it must be ensured that the acid solution does not enter the superheater, otherwise it may cause serious damage.