Analysis And Life Prediction Of Corrosion Damage On Heating Surface Of Alkali Recovery Boiler

The alkali recovery boiler is an indispensable core equipment for the papermaking process.It can not only fully recover the alkali in the black liquor,but also can produce industrial steam by burning and heat exchange of the black liquor in the alkali recovery boiler to generate secondary economic benefits.Unlike general boilers,alkali recovery boilers have special fuel and poor operating conditions.Therefore,the alkali recovery boiler often has a heated surface squib which is caused by corrosion,erosion and wear on each heated surface,and has to be shut down for maintenance.Therefore,it is necessary to analyze the cause of corrosion damage on the heating surface of the alkali recovery boiler and predict its life,which is of great significance for ensuring the safe and economic operation of the alkali recovery boiler.For the 2200tds/d alkali recovery boiler of a certain plant,according to the operation of the alkali furnace and the damage of the heated surface,during the maintenance of the alkali furnace,the thickness of the wall of each heated surface was tested several times,and at the same time,the damage was serious.The water-cooled wall with the squib was subjected to sampling analysis of the tube;the SEM analysis of the water-cooled wall tube was carried out and compared with the new water-cooled wall tube to analyze the change of the material of the tube wall;the steam tube screen of the alkali recovery furnace was collected.XRD elemental composition analysis was performed on the inner wall of the superheater tube.Based on the detection and analysis data,the wall thickness reduction,internal and external corrosion and wear characteristics of each heating surface of the alkali furnace were analyzed to study the damage of the heated surface.According to the actual operation of the boiler,the pipes of each heating surface were carried out.Stress analysis,the ultimate stress of the pipeline and the ultimate thinning amount are calculated;the remaining life of the heated surface is predicted by the thinning rule of the wall of each heated surface and the limit thinning amount since the alkali recovery boiler is put into operation.The results of the analysis show that:(1)The quality of feed water is the main cause of corrosion in the heated surface tube.Since the sodium ions,chloride ions and phosphate ions in the feed water exceed the standard,the surface of the heated surface tube is thinned due to,for example,soda corrosion,chlorine corrosion,scale corrosion,etc.in the heating surface pipe;(2)When the black liquor burns,it causes corrosion outside the heated surface tube.The gases and compounds of the black liquor during the combustion process directly corrode or react with each other to form other compounds to cause corrosion to the pipe wall;(3)High smoke and dust content,local smoke corridor and uneven flow field in the furnace will cause the wear of the heated surface to be aggravated,thus affecting the thinning of the pipeline;(4)By calculating the remaining life of the heated surface,the remaining life of the water wall tube is the shortest,wherein the left water wall has only 4 years of life;and the remaining life of the superheater and economizer of each level is more than 10 years.