DOES THE REFRACTORY CASTABLE FOR THE IGNITION DUCT OF THE CFB BOILER ALWAYS FALL OFF? YOU NEED TO DO THIS!

The fall of refractory castable at the ignition air duct of circulating fluidized bed boiler is a common boiler lining quality accident. This part is a refractory structure. According to the structure, it is divided into non-pressure part refractory structure, and according to the design purpose, it is heat insulation, heat preservation and refractory structure.
The refractory material is designed as a composite casting material, fixed with Y-pins, and divided into two layers of casting materials. The thickness of the thermal insulation casting material near the innermost metal plate is 140mm. It is mainly made of ceramsite, floating beads, cement, fine powder, additives and other materials. ; The second layer is refractory castable with a thickness of 60mm, and the main materials are refractory aggregates, micro-floaters, cement, fine powder, additives, etc.).
Analysis on the Causes of the Castable Falling of the Ignition Air Channel
(1) During the construction of the ignition air duct, the top construction did not consider the influence of the vaporization of the castable water to release the vapor, and the vapor accumulation during the construction could not be eliminated in time. After the vapor is heated and expanded, it will cause the insulation layer and the refractory layer. There are gaps between the castables, causing the two layers of castables to be improperly joined
(2) Due to the problems of the oven and the air distribution in the ignition process, the local high temperature is caused, which exceeds the softening temperature of the refractory material and causes the collapse.
(3) The castable collapses due to the lack of pins at the corners where the ignition air duct and the primary air duct are connected.
(4) Failure to properly match the air volume during ignition causes local over-temperature in the ignition air duct to carbonize the pins, which will not work and cause the refractory castable to fall off.
(5) The pin used for the ignition air duct is 1Cr18Ni9Ti and its operating temperature is 1050-1150℃. Therefore, when the temperature in the ignition air duct exceeds 1300℃, the refractory material itself is not thermally insulated, and the temperature in the pin area is also 1200-1250℃. The service temperature of the pin has been exceeded, causing the pin to be carbonized, causing the castable to fall off.
(6) In the design, it must have an expansion gap, generally 3mm. Because the expansion coefficients of refractory materials and steel are different, if the control is not good during start-up, the temperature in the ignition duct will rise suddenly, causing local expansion joints to crack. The flame is allowed to enter the heat preservation material, and the heat preservation material is burned out, causing a gap between the heat preservation material and the refractory material. Due to the gap, the pin is directly contacted with the flame, causing overfire and carbonization and causing it to fall off. The temperature of the thermal insulation castable is 600-800℃, and the flame temperature is 1200-1500℃.
improvement measures
Develop a rectification plan by analyzing the reasons. The specific method is as follows:
(1) Replace refractory materials
The refractory material used in the original design has a refractoriness of 1670℃. In this area, the theoretical combustion temperature of fuel is about 1900℃. If the hot flue gas cannot be taken away in time, it will cause the refractory material to over-temperature and collapse. For this reason, replace it with refractory Refractory materials with a temperature of 1900°C, and are constructed in strict accordance with the process standards.
(2) Reasonable configuration of pin construction spacing
During construction, the pin spacing at the lower part of the ignition air duct was reduced, and the lower part was changed from 230mm to 300mm. Increase the top pin spacing from 230mm to 150mm from the original design.
(3) Use 1Cr18Ni9Ti steel bars with a diameter of 6mm at the top pin of the ignition air duct to form a mesh with a spacing of 300×300 to strengthen its rigidity.
(4) In the construction, to prevent the flame from entering between the thermal insulation castable and the refractory castable, a 40mm thick high-temperature aluminum silicate rock wool blanket and high-temperature ceramic fiber paper were added. This prevents high-temperature flue gas from entering the thermal insulation castable from the reserved expansion joints, and prevents the thermal insulation castable from over-temperature failure and causing gaps to cause the castable to fall off.
(5) When drying the ignition air duct castable, drill the exhaust holes reasonably. The spacing of the holes is generally determined according to the requirements of the castable manufacturer. After medium temperature sintering, before high temperature sintering, each hole should be blocked to prevent high temperature. Stringing fire during sintering also ensures that the heat-preserving castable and pins do not exceed the service temperature.
(6) Reasonably distribute the air, reduce the primary air volume as much as possible in the initial stage of ignition, increase the ignition air volume and the peripheral wind in the ignition air duct, and prevent the flame from deviating from the center of the ignition air duct and causing local overheating.
(7) Strictly control the temperature in the ignition air duct and keep it within 1200°C as much as possible, thus preventing the problem of pin carbonization.
in conclusion
Through the improvement of the construction technology of the ignition air duct insulation castable and refractory materials, and the sintering process, the temperature rise is strictly controlled according to the temperature rise curve required by the manufacturer. During the start-up process, the flame temperature in the ignition duct is strictly controlled and monitored and the reasonable air distribution is effective. This effectively prevents the occurrence of refractory falling off in the ignition air duct.