The development and application of refractory materials in heating furnaces

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The development and application of refractory materials in heating furnaces www.baowen88.com 2009.02.26 The roof types of steel rolling heating furnaces are arched roofs and flat roofs. The dome is constructed using refractory bricks; generally, there is a layer of refractory bricks with a thickness of 232 mm or 300 mm on the inner side, with an insulating layer placed on the outside. This design is used only in small furnaces whose furnace width is less than 3 meters. Large furnaces all use flat furnace roofs. Previously, the flat roofs were supported by special-shaped refractory bricks, but since the widespread use of unfired refractory materials, the roofs of steel rolling heating furnaces are now almost entirely made of refractory castables or refractory plastics. There are two typical types of roof structures made from refractory castables. It is a monolithic cast structure. During construction, the formwork is first set up, and the anchors are fixed to the steel structure of the furnace roof; thereafter, the refractory layer is poured, making sure to leave expansion joints in place ； The insulation layer above the fire-resistant layer is made of lightweight cast material. The second type is the precast block structure, which appeared in the early days of the use of unfired refractory materials. Its advantage lies in its ease of construction and maintenance, but it requires more materials and provides poor insulation for the furnace roof; it has gradually been replaced by the monolithic casting structure. 3. Applications of refractory materials in regenerative heating furnaces: Since the late 1990s, there have been fast-drying castables, fast-drying self-flowing castables, and fast-drying slag-resistant castables for use in heating furnaces. Such materials not only ensure the excellent performance of low-cement, ultra-low-cement, and cement-free castables but also enable rapid construction; in particular, they allow for fast drying, enabling the entire castable furnace body to be dried within 3 to 5 days. In addition to these features, fast-drying slag-resistant castables also possess excellent resistance to oxidation and corrosion by iron scales. A regenerative heating furnace is a new type of heating furnace that has been developed in recent years. The greatest advantage of regenerative heating furnaces is their high efficiency and energy savings; the average energy-saving rate is increased by 30% compared to existing systems, and they also reduce pollutant emissions, especially NOx emissions. As a result, such heating furnaces have received significant attention from the metallurgical industry. Regenerative heaters mainly include channel-type heaters, regenerative heaters with external refractory materials, and burner-type heaters. Compared with ordinary heating furnaces, regenerative heating furnaces experience significant changes in aspects such as combustion methods, heat exchange methods, and heat exchange media, and the structure of the furnace itself also changes. 3.1 Self-flowing castables Self-flowing castables are low-cement or ultra-low-cement refractory castables that can flow, level themselves, and release gas on their own without the need for vibration. Appropriate raw materials and particle size distributions are selected based on the different application areas, along with composite ultra-fine powders and high-efficiency dispersants, to achieve good construction properties and performance at high temperatures. Self-flowing castables are suitable for areas where construction is difficult, such as locations with narrow spaces or complex shapes; they are useful for wrapping the water pipes at the bottom of steel rolling heating furnaces, as well as for the furnace walls of regenerative heating furnaces with special structures. They are also convenient to use in areas that require local repair and filling. The furnace body of a channel-type heating furnace contains numerous mutually isolated regenerative chambers, as well as many intersecting gas pipes or air pipes. Regenerative chambers cast using traditional vibration-compacted refractory castables suffer from shortcomings such as reduced strength at medium temperatures, high linear shrinkage, and poor volume stability, due to the unsuitable gradation of ordinary refractory castables and the use of cement as a binding agent. After some time of use, cracks tend to appear in these refractory materials, resulting in air leakage from the regenerative chambers during operation and affecting the efficiency of heat exchange and energy savings. In particular, air leakage in the gas regenerative chambers can pose safety risks to production. In the construction of ordinary castables, vibration equipment is used to make the material flow and achieve the desired filling effect. However, in areas such as regenerator furnace walls where the space is limited, the refractory materials are scarce, and the shape is complex (the furnace wall has a multi-layer structure built layer by layer, with each layer being only about 100 mm thick), vibration equipment cannot be used; self-flowing castables solve this problem effectively. Quick-drying self-flowing casting material is used for wrapping the water-cooling tubes. In the area where refractory material is used to wrap the water-cooling tubes, the thickness of the material is generally low, ranging from 40 to 60 mm. If castable material is used, it is difficult to vibrate it thoroughly, which affects the integrity and strength of the material. The use of fast-drying, self-flowing castable not only allows the material to fill the space densely on its own, ensuring its integrity and strength, but also simplifies the construction and baking processes.