The working environment and damage of the refractory lining of the circulating fluidized bed boiler can be summarized

  The construction and maintenance of refractory castables and anti-wear measures for circulating fluidized bed boilers are directly related to the stable operation of circulating fluidized bed boilers. This article comprehensively analyzes the construction of refractory materials, the overall and partial design of the refractory and wear-resistant structure, the operation mode and its special operation technology, the selection of refractory castables and wear-resistant materials, etc. , A series of anti-wear measures.

  The combustion technology of circulating fluidized bed boiler is currently recognized as a clean coal combustion technology. It has two major advantages of environmental protection and economy: (1) The combustion efficiency is high, the fuel is disturbed and stays in the furnace for a long time, and the fuel can be fully burned; (2) The combustion temperature is low, about 800~900℃, and it adopts staged air supply. , Make NO1, emissions greatly reduced: (3) Limestone powder can be added together with the fuel to reduce the sulfur in the fuel, so that the SO2 emissions are greatly reduced: (4) Inferior fuel can be used, due to the high thermal inertia of the circulating materials, the combustion temperature It is lower than the melting point of ash, so that inferior coal with high ash content and high humidity can burn stably.

  The material circulation path in the circulating fluidized bed boiler furnace is: pulverized coal (generally 0~10mm in size) and limestone powder (0~1mm in size) are fed into the fluidized bed combustion chamber (dense phase zone) through the feeder, where the fuel is Zone boiling and burning. The flue gas rises and enters the cyclone separator through the dilute phase zone to the separator inlet, and the coarse particles sink and return to the combustion chamber through the return valve to burn again. The flue gas entrains fly ash and rises through the convection flue and enters the external heat exchanger. Refractory materials are mainly lined in the combustion chamber, ceiling, separator inlet, high temperature cyclone separator and return valve.

  Taking a 220t circulating fluidized bed boiler as an example, the working conditions of refractories at each part are as follows: (1) Dense phase zone, the depth of this zone is 1220~1530mm, the length is 2100mm, sand-like medium (coal powder and limestone powder) boils here, this zone The pressure is 13818~20580Pa, the flue gas flow rate is about 1.2~1.8m·S-1, and the normal working temperature is 820~900℃: (2) The dilute phase zone, the area above the secondary tuyere is where the fine particles of fuel combustion are concentrated. The solid material concentration at the place is about 12~16Kg·m-3, the flue gas flow rate is 1.2~3m·g-1, the normal working temperature is 930~980℃: (3) The furnace top area, the normal working temperature is 850~1100℃, in the separator The flue gas flow rate at the inlet increases by 18m·S-1 (4) The cyclone separator, the normal working temperature is 850~930℃, and the flue gas flow rate at the cyclone outlet can reach 29m·g-1: (5) The cyclone separator outlet manifold, this The dust content of the flue gas is 70~530g·m-3, the normal working temperature is 850-930℃, and the maximum flue gas flow rate is 18m·S-1

  The working environment and damage of the refractory lining of the circulating fluidized bed boiler can be summarized as follows:

(1) At medium temperature, the working temperature of each part of the lining of the circulating fluidized bed boiler is 800~1100℃. From the point of view of refractory materials, this is a medium temperature range. The medium temperature physical and chemical properties must be considered first when selecting refractory materials. For fired products, the sintering temperature is generally higher than this temperature range, so its physical and chemical properties at high temperatures can be directly used as the basis for selecting refractory materials. For unshaped refractory materials and unburnt products, the temperature physical and chemical properties must be investigated. Organically bonded materials or hydration-bonded hydraulic materials have the worst strength at medium temperature. These materials produce ceramic bonding at high temperatures and greatly increase their strength. Therefore, their physical and chemical indicators at high temperatures cannot be used as a basis for selecting refractory materials.

(2) Thermal shock Under normal operating conditions, the circulating fluidized bed boiler must be started and stopped at least 2 to 4 times a year. The refractory lining will be subjected to a strong thermal shock every time it is put into operation. If the refractory material has poor thermal shock resistance, the spalling of the refractory material caused by thermal shock will become a fatal factor for its damage.

(3) Erosion and wear, the flue gas flow rate in the circulating fluidized bed boiler is large (up to 29m·S-1 or more), and the solid material concentration is high. The high-speed flue gas entrains a large number of solid particles at medium temperature and produces strong sand washing and abrasion on the refractory lining, especially in the impact area of the cyclone, where the erosion is the most serious. For the circulating fluidized bed boiler and cyclone separator with single-side material return, the refractory lining is strongly worn area caused by the circulating flow of materials. In addition, SO2, SO3, H2S and CO in the flue gas will corrode the refractory lining, and alkali metal infiltration and carburization will also deteriorate the refractory lining.

  The refractory lining of the circulating fluidized bed boiler is different because of the different working conditions of each part. The main structural forms are water-cooled walls and non-water-cooled walls. The typical monolithic refractory lining structure first uses lightweight heat-insulating castables, followed by high wear-resistant refractory working linings.

  Foreign companies have used different refractory materials in the impact area of the cyclone flue gas for comparative tests. It is found that silicon carbide bricks combined with silicon oxynitride have the best effect. The rest are in order: AL2O3 ＞95% corundum bricks, AL2O3 ＞90% phosphate bonded plastics, and SiC ＞80% phosphate bonded plastics. Al2O3—Cr2O3 combined with phosphate is the worst plastic.

  The future development trend of circulating fluidized bed boiler lining is: according to different furnace types and fuel types used, appropriate refractory materials are selected, construction is more convenient, and quality control is stricter in order to reduce costs and extend service life. The choice of refractory materials should not be one-sided pursuit of high-end products. According to the needs of the economic operation cycle of the circulating fluidized bed boiler, different materials and different performance refractory materials should be used in different parts of the boiler to achieve balanced corrosion loss of the lining to improve the comprehensive economic benefits of the boiler.