Chain Grate Burnout Issues And How To Fix Them

This Chain grate we study is an important part of the industrial boiler, and its role is to stack solid fuel and make it burn effectively. The horizontal chain grate stoker is composed of a fixed grate bar and a movable heating fire grate bar in a staggered manner. The grate bars of each group are on the same horizontal plane.

Its advantage is clear that the quality of coal is not high, so the cost is low, and its fire is automatically dialed. However, the shortcomings are also obvious. At present, we often encounter serious burn-through and deformation of the horizontal network during the regular inspection of industrial boilers. Some even have to be replaced after a few months of operation. The grate is directly related to the production of the enterprise.

It has an impact and consumes a lot of manpower and material resources. Here we analyze the large-area burning loss and deformation of a horizontal chain grate of an SZL10-1.0-AII double-drum industrial steam boiler and analyze the causes and countermeasures.

CHAIN GRATE STOKER (2)
SZL15TON

Chain Grate Stoker Boiler Case Introduction

We can see it is a boiler plant made in Dec, the year 2019, when Dec 2021 gets into operation. All instrument installation inspections before commissioning showed that the furnace was in good condition, and the traveling grate stoker was very normal. Its furnace has been in operation for more than two years, but the grate has been problematic.

The occurrence of large-area burning deformation has seriously affected production. The shortest replacement interval for the grate is three months. We rushed to the scene and saw that the dismantled grate pieces were severely corroded. Some grate slices are only 2/3 or shorter along the length.

chain grate stoker burn out
chain grate stoker burn out

Chain Grate Stoker Combustion Influencing Factors

The practice has proved that it affects the life of the film. There are probably four factors, the first aspect of Choice of fuel, the second is chain grate stoker design, the third aspect of fire grate bars manufacturing technology, and the fourth aspect of boiler operation management. Below we respectively elaborate on the case.

  • Choice Of Fuel

The chain grate is suitable for low to medium bituminous coal, low-quality coal, lignite, biomass fuel, etc. With a low calorific value of less than 5000kcal/kg.

Here is an explanation of what is the low calorific value. The low calorific value refers to a sample of unit mass that is burned in excess oxygen under constant volume conditions. The combustion products are composed of oxygen, nitrogen, carbon dioxide, sulfur dioxide, carbon water, and solid ash.

LHV is a constant low calorific value and high calorific heat minus water vaporization heat. The water here refers to the original water and the water produced by the combustion of hydrogen in the coal.

After laboratory analysis, it is calculated that the low calorific value of the coal used in the boiler is about 5500kcal/KG, and the high and medium coal is not suitable for horizontal chain grates.

Burning bituminous coal with strong slagging (coking) properties, causing the grate to overheat. When buying coal, pay attention to screening and investigating the type of coal suitable for your boiler. Generally, there are some coal types in industrial production.

For example, coking coal, gas coal, lean coal, weakly caking coal, long flame coal, and lignite are prone to coking. Fat coal has the strongest cohesiveness and is one of the basic coals in coking coal blending in China. The volatile content of coking coal is medium, and the shrinkage and shrinkage speed of the semi-coke is slower.

Therefore, the cock coal not only has high abrasion resistance, but also has large lumpiness, fewer cracks, and good crushing strength. Gas coal has poor cohesiveness but has the characteristics of high volatile content and large shrinkage, and it has abundant reserves in China.

Chain grate stoker design is very important. It directly affects the fuel by the following aspects.

  1. Fire grate bar material

According to the purchased material list, RQTSi5 is not used for the main dyeing and grate bars of RQTAI5Si heat-resistant cast iron. Instead, the HT150 material is used, and it can not bear the maximum operating temperature of 900 ℃.

  1. Grate bars Size

Observe the geometric dimensions of the disassembled grate bars, the shape, height, and head shape lap methods comply with the regulations, and there is no abnormality.

Follow are grate bars of different model

  1. Chain Grate Furnace Ventilation

In consideration that the reasonable distance between the grate bars and the moderate coal size, there is no situation that carbon particles are blocked on the gaps of the grate pieces, hindering the cooling effect of the one-time seal. Follow is normal chain grate ventilation.

Chain Grate Stoker Chamber Furnace
Chain grate stoker chamber furnace at the bottom

 

  • Fire Grate Bars Manufacturing Process And Strength

  1. The level of casting technology.

In the past, the casting process was complicated and the yield of finished products was low. After several product technological innovations, at this stage, the manufacturer has been able to achieve a good pass rate, high surface finish, and no trachoma pores caused by casting.

  1. The link of the grate slices, considering that the grate slices are all standardized production, and there is no complicated process required for the linking of the white side of the road, so there is no problem on the link that will shorten the life.
  2. Furnace pressure.

The furnace pressure also has an impact on the life of the grate. In many cases, the blasting air volume is not properly proportioned, resulting in a large blast and a small amount of air, and the positive pressure of the furnace is burning seriously, which affects the life of the furnace wall itself. Second, long-term positive pressure combustion.

The primary winding is increased by the resistance of the coal seam. As a result, the temperature at the contact between the coal seam and the grate is too high, and the natural cooling is not good, resulting in a reduction in the life of the grate.

However, in this study case, the outer wall of the boiler has been seriously smoked, and there are several cracks in the furnace arch.

Following the operation, the condition is easy to happen coking matters.

  1. Coal seam thickness and grate travel speed during operation. Your coal seam is not easy to be too thin, nor should it be too thick. Your FD fan can directly cause the primary wind to cool down. If the coal seam is too thick and the chain grate stops during operation, the heat cannot be effectively dissipated, and your chain grate will be burnt at this time. But once your coal is too thin, economic performance cannot be guaranteed under the same grate travel speed.
  2. The fine ash gathered in the grate middle air chamber was not discharged in time.
  3. These fine ash contained a lot of combustible carbon particles. When the blast was stopped, due to excessive fine ash, high-temperature particles would fall from the grate again. Ignites combustible particles.
  4. When your chain grate stoker is running, the grate is denser due to the coal seams. Poor ventilation and poor cooling effect of the grate.
  5. Traveling grate stoker in the high-temperature zone is poorly ventilated, or when the furnace temperature is high, the air is stopped without opening the ash door for natural ventilation
  6. The positive pressure of the furnace is too large or the reflection of the arch is too strong;
  7. When the boiler was temporarily shut down, the fire suppression work was not done well, so coal was burned on the grate.

Chain Grate Stoker Problem Conclusion

In summary, we believe that the main reasons for the boiler grate burnout of the plant are the following three points.

  1. Selection of the material of fire grate bars. The material of RQTSi5 is not used in the main transfer area. It can not withstand the long-term burning of high temperatures, and the chain grate stoker life expectancy is reduced.
  2. The coal quality LHV ( low heating value ) is selected to be too high and is not suitable for reciprocating grate.
  3. The furnace is burning under positive pressure, and the iron sheet outside the furnace wall has been blackened. If there are several cracks, it can be seen that the furnace has a long positive pressure and the situation is more serious. Affect the cooling effect of primary air and grate.

As a result, the temperature at the contact between the coal seam and the grate is too high. Affect the life of the fire grate bars.

Several problems exist at the same time, influence and interact with each other, and create a vicious circle. Eventually, the life span of the real estate is drastically reduced, which brings unnecessary economic losses to the enterprise.

DZL COAL FIRED BOILER WORKING PRINCIPLE

How To Solve Chain Grate Stoker Burnout Problems?

  1. We suggested that the fire grate bars of the main combustion zone of the boiler of this production should be replaced with RQTSi5 material. Improve the heat-resistant temperature of the grate bars.
  2. For operation and management, bituminous coal with a low calorific value of 4000 kcal and about per kilogram is used.
  3. Medium coal sub-coals are mixed and burned, or mixed with a certain proportion of slag. It can significantly improve the burning of the grate. Keep the furnace small and burn under negative pressure.
  4. Ensure that the grate can be sufficiently cooled, the thickness of the coal seam, and the speed of the grate stroke are moderate.

Ultimately improve the service life of the grate and ensure the safe and stable operation of the boiler.

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