It is a dangerous phenomenon that cracks occur after pouring material of light powder fired boiler is built. This situation must be dealt with in time to avoid accidents. The causes of cracks are as follows:

1: the construction technology is unreasonable.

(1) when the castables are stirred, the control of ash to water ratio is not good. Excessive water addition, high porosity, low strength, long natural solidification time and long curing time of castable after moulding. Too little water is added, material fluidity is not good, vibration is not compact, easy to leave pores, caves, etc., strength will be greatly reduced.

(2) mixing time and vibration time are not well controlled. The mixing time is too short, the material mixing is not uniform, the density is not compact, and the strength decreases. The castable should be poured by layered vibrating rammer. If the vibration time is too long, the material is easy to be delaminated, the fine powder floats on the surface, and the aggregate sinks at the bottom, which leads to the decrease of material strength and easy peeling. When the castables are used in 30min after mixing, they should be poured to the required thickness and height once. Castable construction should be carried out under the environment above 5 C, because the temperature is too low, the material is not easy to solidify, even solidification, it is also a pseudo-solidification phenomenon, castable should generally be continuously poured, before the first layer of castable initial solidification, the next layer of castable should be poured. If the construction clearance exceeds its initial setting, it should be treated according to the requirements of construction joints.

(3) the release time is not well controlled. The castable is striped without hardening. The strength of the castable can be guaranteed and its edges and corners should not be demolished because of demolishing. The bearing formwork should be demoled only when the castable reaches 70% of the strength. To facilitate demoulding, all the surfaces of all molds should be coated with oil before pouring.

(4) the casting time is not well controlled. After the boiler is built, there must be enough natural drying period, so that most of the water in the refractory layer can be precipitated, so as to prevent a large amount of water from being discharged in time and make the refractory layer burst and fall off.

(5) drying oven quality control is not good. Drying oven is to remove free water and crystalline water which can not be excluded by natural drying of lining materials, and curing castables at high temperature to achieve a certain strength.

Before firing, the lining material must have certain natural strength (enough health period) to carry out. The principle of oven drying should be long rather than short, slow and fast. The heating rate should be uniform and stable, the constant temperature time and temperature should be controlled well, and the fluctuation of temperature should not be more than (+20 C). To prevent excessive heating, water can not be discharged in time, breaking through the wear-resistant and refractory layer; secondly, to prevent the temperature gradient in the fire-resistant and wear-resistant layer from being too large, resulting in huge thermal stress, so that the wear-resistant and refractory layer cracks, bulges and falls off.

It is also an important factor that the number of exhaust holes in the steel shell outside the wear-resistant refractory layer (such as the return leg and the cone of cyclone separator) is too small.

Light burning powder

Two: unreasonable structural design and poor quality of castables.

2.1 the design of fireproof and abrasion resistant structure for light firing powder is unreasonable.

(1) the design of expansion joints for fire-resistant and wear-resistant materials is unreasonable. The number of circumferential and longitudinal expansion joints is not enough. After the boiler is run, the wear-resistant refractory is heated, and the volume expands, squeezing and cracking. The expansion joints of wear-resistant refractory castables and refractory bricks in the inlet flue of cyclone separator were changed from 5 mm to 10 mm, and sufficient clearance was reserved to meet the expansion requirements. The expansion joint is changed to Z shape to prevent the ash from passing through the boiler and wash the insulation layer. Expansion joint filling material requires calf skin layer fireproof fiber felt on both sides to prevent fireproof slurry from being immersed in filling material. The design interval of circumferential expansion joints is changed from 1500mm to 1000mm. In large areas such as the outlet flue of separator and the cone of separator, the pouring surface is changed from (2.5 x 2.5 m) to small area (1.5 x 1.5 m) by one-time forming and masonry, and expansion joints are set at the same time. The width of expansion joints is less than 3 mm. The filling material requires rigid plywood to prevent deformation during vibration. After the boiler runs, the plywood is burned at high temperature and the space becomes an expansion joint.

(2) The cyclone separator cylinder is equipped with brick-lined bracket along the height direction to achieve the purpose of layered unloading of brick wall. By calculating the actual weight of refractory bricks in the cylinder, the design of one-layer bracket can not achieve the purpose of unloading, and the bracket is replaced by two-layer arrangement according to the actual situation in the field. The bracket of wear-resistant and refractory castable for the riser of the reclaimer was changed from three to four layers, and the spacing was reduced to 2.5m, so that the castable could be unloaded in layers.

(3) the shape of the Y nail should be improved and the heat resistance of the material is strong. The optimum angle is 60-80 degrees. Only by ensuring the top shape of the screw can the screw grasp the castable more effectively.

Grab nails, air distributor, slag discharge pipe and air duct are metal materials. The expansion coefficient after heating is much larger than that of refractory. If not pretreated, the interface between metal and refractory will form net cracks, leading to cracking and falling off. On the surface of refractory metal, oil and dirt should be removed and 1mm bitumen should be applied evenly. To ensure the consistency and thickness of asphalt, we must resolutely eliminate bitumen paint instead of asphalt.

2.2 the quality of fire-resistant and wear-resistant materials is not good enough.

(1) Matching and bonding between aggregate and matrix of wear-resistant materials have important influence on wear resistance of materials. The mismatch between aggregate and matrix will lead to cracks in the material body after forming, and the poor bonding between aggregate and matrix will lead to the matrix being eroded first, then the aggregate will be isolated, and then fall off. Thus, even if the aggregate has excellent wear resistance, it is useless. The best wear resistant materials are matrix and aggregate worn at the same speed.

(2) Wear-resisting refractories have passed the storage period, the materials are invalid, some materials are improperly preserved and deteriorated by moisture, which can also cause the quality of boiler masonry to be unqualified.