Main Reasons For Abrasion Of Refractories In CFB Boiler

August 08, 2018

The lining of circulating fluidized bed boiler is made of refractory material. The purpose of refractory material is to prevent high temperature oxidation and wear of high temperature flue gas and material to metal components of boiler, and to have heat insulation effect. The damage and wear of the material first occurred on the refractory material, so as to ensure the service life of the metal structure, which is one of the main measures to ensure the long term safe operation of the circulating fluidized bed boiler, and is one of the main features of the circulating fluidized bed boiler.

The main areas of using refractory materials in CFB boilers are combustion chamber,high temperature separators, external heat exchanger, flue and material pipeline etc.

Main reasons for the wear of boiler combustion chamber lining:

One of the main advantages of CFB boiler is their strong load regulation performance. In a circulating fluidized bed boiler, the combustion chamber temperature reaches 900℃~1000℃ during normal operation. In order to adapt to the load change or peaking demand, the heat and temperature cycle changes often occur in the load fluctuation, or start or shut down due to the peak demand.For example, the change of the temperature in the combustion chamber can reach 500℃ in a few minutes. Sometimes there maybe ten times of starting and shutdowns in a week,which will cause thermal shock and thermal stress to the refractory material of the combustion chamber, which will damage the refractory material.

The furnace section is made up of a thick lining,which is made up of a dense wear resistant castable refractory or plastic refractory(75~150mm) covering a similar thickness of insulation material, usually caused by excessive cracks and extursion and exfoliation. Shrinkage during drying, thermal shock and plastic deformation under stress are the main causes of cracks. Stainless steel fiber helps to reduce cracks, but it does not solve the problem completely. When the material is caught by the crack, there will be squeeze spalling when the lining temperature changes again and again.

Lining material commonly used in combustion chamber

Phosphate bonded mullite refractory plastic are durable in the combustion area, mainly due to its volume stability (thermal expansion and shrinkage resistance) and its good anti-wear properties. Since phosphate binders work well with ready made materials, they are often used to repair defective areas. When used,make sure that the area being repaired is supported, and at least two pins should be used. Ceramic or cast alloy pins should be used for plastic lining exposed to ultra-high temperatures. In addition, pins can be used alone to support the insulation layer.

Located in the dilute phase of the upper part of the furnace,silicon carbide tiles are commonly used to reduce the wear of the water wall tubes. Emery mortar is used behind the tile to improve heat transfer to the tube. The tile is usually supported by welded support on the pipe. In the design of the water wall tube down to the bottom of the combustor, the lining usually includes a thin, dense, high thermal conductivity, wear resistant plastic refractory or castable refractory.

Silicon carbide based castables refractory are usually used on the welded tubes, because these castables refractory can be repaired with phosphate bonded plastics, especially the high thermal conductivity of the silicon carbide. If the bed material or circulating ash contains high alkali content,because calcium aluminate cement is destoryed at high temperature and after alkali action.