Types And Characteristics Of Wear-resistant Refractories For Circulating Fluidized Bed Boilers
The circulating fluidized bed boiler has a high operating temperature, and the temperature in the furnace changes frequently, resulting in thermal shock. At the same time, there are many high temperature solid particles in the furnace, which constantly erode the heating surface, so it is necessary to lay wear-resistant refractory materials for maintenance. Types and characteristics of wear-resistant refractories for circulating fluidized bed boilers:
1.1 Types of wear-resistant refractories
Introduction of wear-resistant refractories for circulating fluidized bed boiler
Wear-resistant refractories can be divided into fixed materials and non-fixed materials according to their delivery conditions, and can be divided into: wear-resistant refractories (including bricks, castables, plastics, mortar) according to their functions; Refractory materials (including bricks, castables, mortar); Refractory insulation materials (including brick, castable and mortar).
Composition material
1) wear-resistant refractory (dense refractory) : silica-aluminum brick (silica brick, refractory clay brick, high aluminum brick), zirconia-silicon brick, non-composite brick (carbon brick, silica-carbon brick), magnesia-calcium chromium brick and electrosoluble magnesium product category (magnesium brick, chrome-magnesium brick, chrome brick, dolomite brick).
2) Thermal insulation materials: refractory thermal insulation brick, thermal insulation brick, thermal insulation block, ceramic fiber.
Amorphous material
Amorphous materials include castable, plastering material, plastic, repair material, spray gun material, castable, vibrating material, wipe fabric, etc., can be divided into powder, mud, clay.
1.2 Characteristics of wear-resistant refractory materials
Wear-resistant refractory is a special product that is not easily damaged and deformed at high temperatures. In order to avoid damage from soot and fly ash, wear resistant materials are laid inside some easily damaged parts. The correct selection and installation of this wear-resistant material is particularly important. It guarantees the long-term characteristics of the system and reduces the frequency of wear-resistant material shedding and maintenance.
Henan refractory brick manufacturers, refractory ball manufacturers, light insulation bricks, Sun Hung Kai Refractory Co., LTD
The chemical composition of wear-resistant refractories is mainly composed of aluminum and silicon compounds, accounting for 80%-95% of the total content.
In order to withstand the environmental hazards of CFB boilers, wear-resistant refractories must have certain fire resistance, compressive strength, flexural strength, thermal shock resistance and a small enough linear change rate. The main physical and chemical indexes of wear-resistant refractories are as follows:
A Refractory
Refractoriness refers to the possibility of wear-resistant refractory materials resisting melting at high temperatures without external force. Refractoriness is also usually expressed by the highest service temperature, that is, the linear rate of change of the material after 5h of calcination does not exceed 1.5% of the temperature.
B volume density
Bulk density, also known as bulk density, refers to the mass of the unit volume of the wear-resistant refractory, which can reflect the density of the refractory, the unit is kg/m3.
C Heat transfer coefficient
Heat transfer coefficient refers to the heat of wear-resistant refractories in unit temperature gradient per unit time per unit vertical area, w/(M.K). The heat transfer coefficient of refractory is not only related to its use, but also a key factor that directly endangers the thermal shock stability of handicrafts.
D Thermal shock stability
Thermal shock stability refers to the potential of wear-resistant refractory products to resist large temperature changes without damage, also known as thermal shock resistance, temperature change resistance and rapid cooling and heating resistance. During the use of refractory materials, they are often harmed by the sharp change in working temperature, resulting in cracking, falling off and even collapse of the material. The factors affecting thermal shock stability include thermal deformation rate, heat transfer coefficient, material structure, product shape and particle composition.
Electronic circuit change rate
The linear rate of change refers to the ratio of the irreversible variable of the length change of the wear-resistant refractory material at unit temperature to the original length, expressed as a percentage, also known as the linear expansion coefficient. It is one of the bases for the overall design of refractory materials and the arrangement of expansion joints.
Alpha = (L2 - L1)/L1
Where: L1 is the length of the sample at room temperature, mm; L2 is the length of the sample heated to the experimental temperature T, mm.
F Constant temperature compressive strength and flexural strength
Compressive strength, generally refers to the compressive strength at room temperature, is the ultimate pressure that wear-resistant refractory materials can withstand per unit area at room temperature. If this value is exceeded, the material will be destroyed. The calcination, melting state and the properties related to the structure of the refractory are the key manifestations of its compressive strength. It is a common item for testing wear-resistant refractory materials, also known as cold pressing strength. Calculation method of compressive strength:
CCS= Fixed assets
Where: CCS is compressive strength, unit is mpa; F is the ultimate pressure that the material can withstand; a is the force area of the material.
In the application of wear-resistant refractories, in addition to compressive stress, tensile stress, bending stress and shear stress are also subjected. The flexural strength generally refers to the flexural strength at room temperature, which refers to the ultimate stress of the specimen under bending load at room temperature, and the unit is MPa.
The compressive strength and flexural strength depend on the type and amount of flux and admixture, and are also affected by the purity of raw materials, the ratio, the total amount of mixed liquid, the construction method and the curing method.
G Wear index
A pound of quartz sand is sprayed on the wear-resistant material at a certain speed, and the amount of wear-resistant material is called the wear-resistant index, and the unit is g/cm2. Comprehensive wear resistance index is the key index to measure the wear resistance of castable and brick.
In order to meet the safe operation of the unit, the wear-resistant refractories of CFB boiler should have the following characteristics: high constant temperature and heat strength; Low wear rate; Excellent corrosion resistance; Excellent high temperature volume stability.
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