At present, some domestic manufacturers conduct salt immersion treatment on the fired magnesia-chromium or magnesium-aluminum products in order to improve the corrosion resistance and the service life of the products. However, if the water brought in by salt immersion cannot be discharged in time, it will have a negative impact on the performance of the product.
Magnesium oxide, the main component of magnesia refractory bricks, easily reacts with water to form magnesium hydroxide. The chemical reaction equation is: MgO + H2 O = Mg (OH) 2 ↓. The surface of the hydrated magnesia refractory bricks is bulged, frosted, loose in structure and has radioactive star-shaped cracks. As the hydration reaction intensifies, the magnesia refractory bricks will eventually be completely pulverized and damaged. In order to prevent the hydration of magnesia refractory bricks, magnesia refractory bricks are immersed in salt in the industry. The magnesia refractory bricks after salt immersion need to be pushed into a heat treatment kiln for heat treatment to volatilize the water in the immersion salt.
1 The salt immersion heat treatment kiln for magnesia refractory bricks needs to solve the following problems:
1.1 Magnesium refractory bricks will accelerate hydration at 80-110 ℃. Therefore, magnesia refractory bricks often undergo hydration reaction in the lower temperature zone at the entrance of the heat treatment kiln. Therefore, it is required that the bricks should leave this temperature zone as soon as possible.
1.2 The product is heated continuously for several hours under the condition of 200 ℃, and the temperature fluctuation of the heat treatment kiln is required to be controlled within a small range, and every time the product enters the kiln or exits the kiln, the entrance of outside air will affect the temperature of the heat treatment kiln. And pressure have a greater impact, thereby affecting the quality of products.
1.3 The moisture content of the product at each position in the heat treatment kiln is different, and the heat treatment kiln requires different hot air volume. Therefore, the hot air volume in the kiln must be controlled in different areas to ensure the reasonable temperature distribution in the kiln.
2 Design of heat treatment kiln for magnesia salt-leaching refractory bricks
2.1 Technical scheme
In view of the problems that need to be solved in the heat treatment kiln for magnesia-based salt-leaching refractory bricks mentioned in the previous section, by setting up inlet and outlet preparation rooms, air volume partition control, hot air circulation devices, etc., the heat-treatment kiln is guaranteed to meet the requirements for heat treatment of salt-leaching magnesium products.
The specific technical scheme of the heat treatment kiln is as follows:
(1) An entrance preparation room and an exit preparation room are set before and after the heat treatment kiln. When the entrance kiln door or exit kiln door of the heat treatment kiln is opened, close the entrance preparation room or exit preparation room kiln door to prevent outside air from entering the heat treatment kiln and to avoid affecting the temperature in the kiln.
(2) There are several parking spaces in the kiln, and a hot air inlet and an exhaust gas outlet are set above each parking space. Both sides of the kiln body of the heat treatment kiln are provided with interlayers, which are the interlayer on the hot air inlet side and the exhaust gas outlet side respectively. There are partitions in the interlayers on both sides, and the partitions divide the air inlet and exhaust air of the heat treatment kiln into 3 areas. The air inlet and exhaust of each area can be adjusted independently without mutual interference. The hot air is sent into the hot air inlet through the fan, and is sent into the heat treatment kiln through the regulating air plate on the side of the hot air inlet, which undertakes the heating of a certain area and heat-treats the products in the kiln.
(3) Several circulating fans are installed on the top of the heat treatment kiln to ensure uniform temperature distribution in the kiln.
(4) The heat source required by the heat treatment kiln is hot air drawn from the product firing kiln, or hot air generated by a separate hot air furnace.
2.2 Kiln configuration and heat treatment process
(1) Furnace configuration
Figures a and b show the configuration of the heat treatment kiln for magnesia salt-leached refractory bricks.
①-Extrance Preparation Room ②-Heat Treatment Kiln Body ③-Exit Preparation Room
④~⑦-Kiln Gate (1#,2#,3#,4#) ⑧-Blower ⑨-Exhaust Fan ⑩-Circulation fan
(2) Heat treatment process of kiln
The kiln car enters the entrance preparation room via 1# kiln door, closes 1# kiln door and 4# kiln door, opens 2# kiln door and 3# kiln door, pushes the kiln car in the entrance preparation room into the heat treatment kiln body, and closes 2# kiln door, at the same time drag the last kiln car in the heat treatment kiln body to the exit preparation room, close 3# kiln door, open 1# kiln door and 4# kiln door, push the kiln car into the entrance preparation room and Pull out the kiln car in the exit preparation room, and the work cycle is over.
2.3 Furnace characteristics
The heat treatment kiln has the following salient features:
(1) The products in the heat treatment kiln have different moisture content in different areas, and the required drying speeds are also different. Through the sub-regional control of the temperature and air volume in different areas of the heat treatment kiln, the moisture drying speed of the products can be controlled, It solves the problem of slow volatilization of water in the entrance area of the heat treatment kiln, which is likely to cause product hydration.
(2) By setting the top circulation fan to make the temperature distribution in the heat treatment kiln uniform up and down, so that the quality of the products in the heat treatment kiln can be obtained effective protection.
(3) The heat treatment kiln is equipped with a preparation room to control the lifting sequence of the kiln door, which can ensure that the heat treatment kiln will not cause large fluctuations in temperature and pressure due to the entry and push of the kiln car.
(4) The heat treatment kiln adopts negative pressure operation, which is conducive to improving the condition of the kiln, reducing heat loss and protecting the environment.
(5) The heat treatment kiln adopts PLC control to realize the automation of the whole kiln mechanical equipment and the automatic adjustment of the thermal system.
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3 Conclusion
(1) The heat treatment kiln for magnesia-based salt-immersed refractory bricks is a type of heat treatment kiln specially developed. The heat treatment kiln fully meets the requirements of users, including the production capacity of the heat treatment kiln, thermal system, heating air conditions, technological process and plant supporting facilities, etc. The production and operation have been in good condition since it was put into production.
(2) The heat treatment kiln adopts mature, stable, practical and reliable technological process and equipment, and its technical equipment has reached the domestic advanced level, which is energy-saving and environmentally friendly.
(3) The heat treatment kiln has a high degree of automation, which can realize the different requirements of users for full-process automation, semi-automation and full manual operation near the machine.
(4) The heat treatment kiln has a compact structure and makes full use of the space above the kiln. The hot blast stove, blower, exhaust fan and other equipment are all arranged above the heat treatment kiln, and are equipped with an overhaul platform, which is convenient for overhaul and saves workshop space. The whole kiln adopts steel structure and light-duty heat insulation materials, with low investment and short construction period.
In summary, the heat treatment kiln is an ideal heat treatment equipment in the production of magnesia salt-leached refractory bricks. The company base on this kiln, heat treatment kilns of different types and scales can be designed according to the different requirements of users.
