Firebrick is a kind of building material brick with thermal shock resistance, slag resistance, fire resistance and other properties.Although a lot of people do not know it, but it often appears in our life, such as building, coal stove, so how should firebrick be chosen?Below we on the "refractory brick design selection considerations and alumina refractory brick production process" to understand in detail.
1. Basic conditions for waste gas incineration
In order to determine whether the waste gas generated in a certain process can be purified by incineration, we must first analyze the basic conditions of incineration. We believe that the basic conditions of exhaust gas incineration include three elements: incineration temperature, residence time and air demand.
Burning temperature.Incineration temperature refers to the temperature required for the oxidation decomposition and destruction of harmful components in waste gas at high temperatures.The burning temperature is different from the ignition temperature (ignition point), which is much higher than the ignition temperature.
Generally speaking, increasing incineration temperature is beneficial to decomposition and destruction of harmful components in waste gas.However, too high incineration temperature will not only put forward higher requirements on lining material selection and process thickness, increase fuel consumption and environmental protection costs, but also increase the content of nitrogen oxide in incineration products, causing secondary pollution.
The appropriate incineration temperature is determined by experiment under a certain residence time. In production practice, most organic waste gas incineration temperature ranges from 800℃ to 1100℃, usually involving the selection of 800℃ to 900℃.
Stay time.Residence time refers to the time consumed for decomposition and combustion of harmful components into harmless components at incineration temperature.Residence time directly affects the perfection of incineration and is an important basis for determining the size of furnace volume.
The residence time is not the better for waste gas incineration.Because the residence time of the design is too long, it will not only cause the structure of the furnace is too large, increase the floor area and construction cost of the furnace, but also may cause the temperature of the furnace is not enough, so that the incineration cannot be completely decomposed.
The residence time of waste gas in furnace is determined by many factors.For the general waste gas produced in industry, the residence time is usually 1~2 seconds.
2. Design key points of incinerator chamber
The chamber size of waste gas incinerator is mainly determined by the volumetric thermal intensity of combustion and the residence time required by waste gas incineration in the high-temperature chamber. The thermal intensity value of waste gas volume is generally (20~25) X104Kcal/ (m ^ 3 ·h). The appropriate data should be determined according to different materials and the selection of appropriate lining firebrick.
3: selection of firebrick lining for incinerator
Furnace lining refractory brick should first choose according to the temperature of the furnace chamber can withstand the temperature of refractory materials and heat insulation materials, at the same time should consider the corrosion of burning waste gas on the furnace lining, is the choice of materials according to its acid and alkali resistance can be divided into three kinds: good resistance to acid refractory brick.
Such as silicon brick: to alkali resistance ability of strong fire brick, such as magnesia aluminum brick, magnesium brick, dolomite brick, acid and alkali resistance effect can be neutral fire brick such as: high aluminum brick, corundum brick, silicon carbide brick and carbon brick.According to its specific gravity fire brick is divided into light brick and heavy brick.
Light brick high porosity, slag resistance, low mechanical strength, poor stability, while heavy brick, on the other hand, for furnace temperature below 1200 ℃, in general, choose heavy level 3 high alumina brick, its load softening temperature can reach 1350 ℃, and the cost is relatively low, however, if the incinerator adopts the design of overhead, you will need to choose lightweight brick or fiber folding, in order to reduce body weight, decrease the cost of steel structure construction, increase the aesthetic.
In the process of treating waste gas, corrosion and damage will inevitably occur in the incineration furnace lining. Therefore, the design should consider the convenience of operation of the furnace lining. Usually, small maintenance is needed every 2-3 years.
1. Selection of binder
High alumina bricks are usually made with soft clay as a binder.The main function of clay in batching is to improve the molding performance of clay and make the formed and dried green body have certain strength.However, in the firing process, the free SiO2 in clay and the free A12O3 in high alumina clinker have a secondary mullite reaction, which intensifies with the increase of the amount of binding clay added.
The higher the secondary mullite reaction, the higher the porosity, the higher the strength and the higher the volume density.Starting from this point, the amount of bound clay in the ingredients should be reduced as much as possible.The amount of clay powder in the batching is generally 5%.
In order to produce volume-stable high alumina bricks, small powder of high alumina bauxite can be used as high alumina binding agent.Or synthetic mullite can be prepared by using high-alumina powder and clay powder in predetermined proportion.
2. Determination of particle composition
The grain composition of high alumina clinker has an important influence on molding operation, blank density, high alumina brick density and strength.Therefore, the determination of reasonable particle composition according to different molding methods is an important process factor to stabilize the process operation and improve the quality of high alumina bricks.
The principle of determining particle gradation is to form a good stacking density without any adverse effect on the properties and appearance quality of high alumina bricks.For xia and other bricks, the volume expansion produced by secondary mullite petrochemical reaction should also be considered.
High alumina bricks are usually made of three grades: coarse, medium and fine.However, secondary or secondary ingredients may also be used.When three grade ingredients are used, the critical size of each grain size is: coarse particle 3 -- 0.5mm, medium particle 0.5 -- 0.1mm, fine powder <0.1mm.
The production practice shows that increasing the size and quantity of coarse particles can increase the density of the mud, and it is easy to form.During sintering, the secondary mullite reaction around the material is weakened due to the small specific surface area of the large particle material, which is beneficial to the sintering of the green body.Furthermore, the gas binding rate of high alumina brick is reduced, the softening temperature under load and compressive strength are improved, and the thermal stability is improved.
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