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Industrial steam boiler scaling is unavoidable.Even if there is a good water treatment, with the growth of running time, it is difficult to ensure that the boiler does not scale.Boiler scaling will cause many hazards,it will affect the normal operation of the boiler.
In order to reduce the influence of industrial steam boiler scaling on boiler operation, EPCB specially summarizes the reasons, hazards and boiler scaling removal methods, hoping to help you solve the problem of boiler scaling, so that the boiler can operate more safely and stably.
Containing a certain hardness of water into the boiler, in the heating process, some calcium, magnesium salts due to thermal decomposition, from the water soluble substances into water soluble substances, attached to the metal surface of the boiler, forming scale.
With the increase of boiler water temperature, the solubility of some salts in boiler water decreased, such as Casd4 and Casio3 salts.These salts precipitate the solid phase from the water and deposit the scale on the evaporating surface.
After the reaction of salt and other salt and alkali with greater solubility in the boiler feed water, generate the compound insoluble in water , and the formation of water scale.
When the water slag in the boiler is too much, and sticky, if the sewage is not timely, it is easy to convert from sludge to scale.
When the boiler scales, the heat transfer performance of the heating surface becomes worse, the heat released by the fuel combustion can not be quickly transferred to the pot water, a large amount of heat is taken away by the flue gas, the thermal efficiency of the boiler is reduced.
In this case, in order to maintain the rated parameters of the boiler, it is necessary to add more fuel, improve the furnace and flue gas temperature, resulting in a waste of fuel.
After scaling, the heat transfer performance of the boiler becomes worse, and the heat of fuel combustion cannot be transferred to the pot water quickly, which will lead to the increase of temperature difference on both sides of the heating surface.The type and thickness of scale are different, and the heating surface metal temperature is different, which causes great damage to the heating surface, and then causes the damage and scrap of industrial boiler.
After scaling, the heat transfer performance of the boiler becomes worse. In order to achieve the rated evaporation or rated heat production of the boiler, it needs to consume more fuel.With the increase of scaling thickness, furnace volume and grate area are certain, fuel consumption is limited, therefore, boiler output will be reduced.
The scale on the heating surface of the boiler must be completely removed to ensure the safety and economic operation of the boiler.Whether mechanical, artificial, or the use of activating agents will affect the service life of the boiler.
After the boiler stops, put off the furnace water, rinse with clean water, you can use hammer, shovel, steel wire brush and electric pipe washer and other tools for descaling.This method is relatively simple, and is mostly used for small cast iron boilers with simple scaling.But the labor intensity, descaling effect is poor, easy to damage the boiler body.
Chemical descaling is generally divided into pickling descaling and alkali boiling descaling:
Usually refers to the use of hydrochloric acid solution to clean the scale;
There are three main principles of descaling:
1.Solubility: Hydrochloric acid and carbonate scale produce soluble oxides;
2.Peeling effect: hydrochloric acid can dissolve the oxides on the metal surface, thus destroying the combination between the metal and scale, so that scale is peeled off;
3.Air lifting and loosening effect: hydrochloric acid reacts with sulfate scale to produce a large amount of carbon dioxide gas, which has lifting power for scale, promotes scale falling off, and is easy to be washed down;
Acid lotion is composed of hydrochloric acid plus corrosion inhibitor or nitric acid plus corrosion inhibitor.This pickling solution can not only eliminate the scale in the boiler (to remove nitrate scale, need to add hydrofluoric acid), but also rarely corrode the boiler.
The agents used for pickling should adopt different agents according to different scale components:
Hydrochloric acid is suitable for carbonate scale
Hydrofluoric nitrate is suitable for silicate scale
In addition, now for boiler cleaning, citric acid and ethylenediaminetetraacetic acid (EDTA) can also be used to clean the various metal oxides in the sediment.
The silicate scale can be dissolved in the furnace under certain temperature and pressure by using some alkaline agents, and it mainly plays a loose role in other scale.
The effect of alkali boiling descaling method is worse than that of acid washing descaling method. However, the scale is loose after alkali boiling, so the scale that is difficult to be removed by hydrochloric acid can also be treated by alkali boiling method once before acid washing.The alkali boiling method is simple to operate and has less side effects.The disadvantage is that the cooking time is longer, the consumption of agents is more, and the effect is poor.
Sodium hydroxide, trisodium phosphate and sodium carbonate are commonly used in alkali cooking.
Carry out chemical supervision→put in Pickling solution and dilute with plenty of water,and neutralization with flake alkali→Flush the drum with water until neutral→Open the manhole and handhole to clean the scale in the boiler→Check the effect of chemical cleaning of boiler→close the manhole and handhole→Preparation of passivation medicine→The boiler began to passivation→Check the effect of chemical cleaning.
It is an important means and measure to prevent accidents, save fuel and prolong boiler life to prevent and remove scale in boiler operation.Therefore, the use of furnace units and furnace personnel must pay attention to, and can correct skilled operation, to ensure the safety and stability of the boiler for a long time.
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