SU872509A1 - Method of producing chrome-magnesial refractory materials - Google Patents

Description

(54) METHOD FOR OBTAINING CHROMMAGNESIAL REFRACTORY MATERIALS

one

The invention relates to the production of refractory chromium-containing materials, in particular magnesium chromite and compositions based on it, and can be used in the technology of manufacturing highly resistant refractory materials.

Methods are known for producing magnesium chromate refractory materials by thermal decomposition of magnesium chromate in high-temperature spray reactors at 850 C. Highly dispersed powders with a loose particle structure and a low bulk density are produced by such methods by using high thermal evaporation of the original solution, high evaporation rate of water, and oxygen evolution. 3

However, the capture, cooling, transport and storage of such products is fraught with significant technological difficulties.

and lead to material losses and deterioration of working conditions.

A known method for producing chromium magnesium materials in the form of granules by thermal decomposition of 5 chromate or magnesium dichromate. The granules of these intermediates are obtained by thermal granulation of the corresponding production solutions in the fluidized bed apparatus. At 130-160 ° C with a temperature pressure of 500 ° C (the temperature difference between the temperature under the grate and the layer). After the thermal decomposition stage at 800-1300s, the granules are subjected to

S cooling and packing. Cooling is performed in a fluidized bed apparatus with a stream of cold air of 2 J.

This method, however, is not universal, since it gives

The ability to obtain only coarse components for the manufacture of refractories. To obtain a fine particulate fractions as

for refractories, and for merkel, the fracture of cooled granules is required. Due to the high strength of magnesium chromite granules (hundreds of kg / cm), the grinding operation requires high energy costs. In addition, when obtained at the specified temperature head, their strength is low and a large dust content is observed during the granulation process. This phenomenon is explained by a very large temperature difference between the coolant inlet zones (630-660 s) and the main fluidized bed zone (30-160 ° С). Due to the intensive and repeated circulation of granules between these temperature zones, thermal stresses accumulate in the bulk of the granules and their strength decreases to the limits lower than the dynamic forces of the layer on the granules. As a result, they are destroyed into several fragments (mainly 2-3). The sharp edges of the fragments are subject to intensive accumulation and abrasion, which leads to a sharp growth of the pyeunos.

The purpose of the invention is to reduce the dust extraction, simplify the production technology and reduce the energy costs of grinding the chromium-magnesium granules to a powdery state of a given dispersion.

The goal is achieved by the fact that upon receipt of chromagnese refractory materials by granulation of chromate and dichromate in a fluidized bed at 130-160 ° C, heat treatment of the granules at 800-1300 ° C and subsequent cooling in the fluidized bed as well, thermal granulation in the layer is carried out at a temperature head 250–450 ° C, and the calcined pellets are cooled with a pulsed flow of a liquid refrigerant, for example, water, the flow takes place at a frequency of 0.5–2 pulses per minute and with a pulse duration of 0.

The essence of the invention is that during thermal granulation of solutions of magnesium chromate or magnesium dichromate in a fluidized bed, optimum crystallization conditions are selected to obtain given sizes of steel that are bound by crystallization bridges in granules (at a level of 30-60 microns. Upon cooling, after the stage high temperature decomposition, these connections are superimposed

powerful thermal stresses that contribute to the destruction of granules into elementary crystals.

Since the size of the crystals is determined primarily by the rate of evaporation of water from solutions, the parameter regulating the size of the elementary crystals in the granules is the temperature difference that is realized in the fluidized bed apparatus. For the process of thermal granulation of chromate and sodium bichromate, the sizes of elementary crystals within 30-60 µm are achieved in the range of temperature differences 250-450 C.

At L - 250 ° C, the size of the crystals increases to 65-70 µm, and at L 450c, the process of thermal crushing of the granules in the dryer-granulator dramatically increases due to the intense accumulation of thermal stresses during repeated circulation of the granules between the heat-transfer and drying zones. As a result of the destruction of the granules, the dust particles increase to 30-40%.

Temperature in

The layer is maintained at 130-160 ° C and determines

only the limits of the steady operation of the apparatus.

During the thermal decomposition of magnesium chromate and bichromate granules with SOO-nOO C, the granules are hardened sharply, due to the chemical transformation of these compounds into magnesium chromite. However, the dimensions of the original crystals are practically unchanged.

When magnesium chromite is supplied to the layer of granules in a fluidized bed refrigerator, a coolant, for example, water, the granules are rapidly cooled to 40-60 C.

Stationary refrigerant injection, as a rule, leads to the destruction of the granules into several parts, without a significant weakening of the bonds between the individual crystals. The pulsed coolant supply with a certain alternation of cooling and heating periods of the granules, optimizing the rates of the cooling and heating processes imposes thermal fatigue stresses on the connection between the crystals, drastically reducing the strength of the granules. For magnesium chromite granules, the optimal frequency is the pulse frequency in the range of 0.5–2 pulses per minute and the pulse duty cycle (ratio of refrigerant delivery times and idle mode) is 0.2–0.05. With a frequency of less than 0.5 and a duty cycle of less than 0.2,

Claims (1)

Claim The process for producing refractory materials hrommagnezialnyh by granulation chromate or bichromate magnesium in a fluidized bed at 130-160 ^{° C,} heat treating the granules at 800-1300 C and then cooling them in order to simplify kiotlichayuschiys tehpyaschem layer with I that, nology and reduce energy costs , the process of thermal granulation is carried out at a temperature head of 250-450 ^σ 0, and the calcined granules are cooled by pulsed supply of liquid refrigerant to the layer with a frequency of 0.5-2 pulses per minute and with a duty cycle of 0.05-0.2.