[Case Study]Optimization Of Refractory Lining For Overhaul Of 2500m³ Blast Furnace

Masteel No.2 2500m3 blast furnace was designed at the beginning of this century, from the view of the blast furnace, compared with today's high-efficiency production of blast furnace internal type requirements, there are gaps, mainly reflected in the small diameter of the furnace cylinder, the safety of the iron capacity is low, high diameter ratio is high. Therefore, the overhaul of the second generation of the furnace service needs to maintain the steel flange of the top of the furnace and the elevation of the iron mouth unchanged, how to ensure the success of the design of the furnace has become the key.

Furnace type is good or bad for the production of stable and smooth, a generation of furnace service life and gas utilization, etc. have a significant impact, therefore, the producers of the furnace type design are very important. Although there are empirical formulas for the design of blast furnace, and there are a lot of researches on the design of furnace by scholars, but in fact, it is almost impossible to copy and follow the formula for different sizes of blast furnaces and different external conditions. In order to obtain the successful furnace type in this design, we compare and analyze the database of production indexes of the same type of blast furnace and the database of furnace type of the same type in the last three years, and combine with the existing operation experience of No.2 blast furnace, and finally determine the second generation furnace type of No.2 blast furnace. The schematic diagram of blast furnace inner type is shown in Fig. 1, and the comparison of the first generation and second generation furnace type is shown in Table 1.

The mainstream design of today's blast furnace body lining structure adopts thin-wall lining, furnace belly, furnace waist and furnace body in the lower part of the basic use of cooling wall full coverage, inlaid with silicon nitride combined with silicon carbide bricks, phosphate impregnated clay bricks in the middle and upper part of the body of the furnace, and then covered with internal spraying layer. The key to the service life of a generation of blast furnace depends on the bottom of the furnace cylinder, therefore, the bottom of the furnace cylinder structural design and material selection is particularly important. A lot of domestic research on this, on the bottom of the furnace cylinder lining structure, summarized in "carbon brick and ceramic cup program", "carbon brick and ceramic mat program". Charcoal briquettes with ceramic cup program can be divided into "charcoal briquettes with free cup" and "charcoal briquettes with inlaid cup"; charcoal briquettes cylinder with molded small charcoal block program and large charcoal block program. Different furnace bottom cylinder structure have realized long life examples, there are also cases of cylinder burn through, long life type furnace bottom cylinder must be the result of the combined effect of design, construction and operation

The overhaul of No.2 2500m³ blast furnace requires a generation of furnace service life of more than 15 years. Masteel No.2 blast furnace first generation of furnace service of the furnace bottom cylinder structure and material configuration program has been nearly 14 years of safe operation, fully proved that the design of this furnace bottom cylinder structure is completely successful. Therefore, the overhaul of No.2 blast furnace retains the original form of the furnace bottom cylinder structure, for the current blast furnace enhanced smelting under the requirements of high life, the material of carbon brick, cooling wall and shell gap casting material to improve. Comparison of materials selected for the structure of furnace bottom cylinder in the first and second generation of furnace service is shown in Table 2.

This overhaul was combined with the conversion of the furnace body to soft water cooling and the complete renewal of the cooling walls and furnace shell. The cooling wall configuration scheme is shown in Table 3.The main features of this cooling structure design are:

(1)the furnace body adopts full cooling wall structure;

(2)the key parts of the furnace belly, waist and lower part of the furnace body using copper cooling wall;

(3)the middle part of the furnace body using double water pipe to strengthen the cooling;

(4)the iron mouth area using shaped cooling wall to meet the requirements of piping and maintenance;

(5) in the case of following the conditions of the furnace shell openings specification for the cooling strength of the requirements of the place, as far as possible, to increase the specific surface area of the cooling.

The previous generation of the blast furnace service all use industrial net loop water cooling system, the overhaul design of the blast furnace body cooling wall, furnace bottom water cooling tube, direct blowing pipe, air vent center sleeve and hot stove valve using soft water closed loop cooling system. The soft water system is divided into primary and secondary cycle: the cooling wall of the blast furnace body, the bottom of the furnace water-cooled pipe for the primary cycle, the total water volume of 5200m³/h; a part of the primary cycle of the water back to the diversion of the pressurized again for the cooling of the hot stove valves and the air outlet in the middle set of the secondary cycle, the total water volume of 1400m³/h. Secondary cycle of the water back to the top of the furnace at the large platform and the primary remaining cycle of the water combined, and then through the degassing tank, expansion tank into the main The secondary circulating water returns to the big platform at the top of the furnace and merges with the primary residual circulating water, and then enters the main circulating pump room through degassing tank and expansion tank to be cooled and then circulated. Cooling wall soft water cooling through the water supply loop pipe directly into the first section of the cooling wall of the water inlet pipe, has been strung to the 17th section of the cooling wall, and then were connected to the four sub-areas of the 16 return collector, and then converge to the return of the total loop pipe. The overhaul design of the large set of wind mouth is not cooled, the wind mouth of the middle set, small set of cooling. 30 wind mouth of the small set is still used in high-pressure net circulating water, which is based on the following considerations: First, to ensure the stability of the cooling system of the blast furnace body, taking into account the wind mouth of the small set of easy to damage caused by leakage, resulting in frequent fluctuations of the water softener system replenishment, the softener system of the leakage detection brought about by the interference; Second, to simplify the cooling system, as a large-scale blast furnace, the high pressure cooling water system is usually the only cooling water system. Usually high pressure cooling water system is essential, such as cross temperature measurement, furnace top airtight box, furnace top camera and furnace top hydraulic station, etc., all need to provide high pressure industrial net loop water, in the case of meeting the production requirements, all the high-pressure water into a net loop system, which can make the cooling system simplified.

In order to realize the requirement of "visual operation" for the blast furnace, this overhaul design is equipped with furnace cylinder erosion model, heat load model and fabric model, and perfect testing instrument and primary testing components, forming an all-round monitoring of the furnace body.

(1)Configured with infrared imaging at the top of the furnace and infrared imaging at each air outlet, and the furnace throat is equipped with "cross temperature measurement device".

(2)The bottom of the furnace cylinder charcoal briquettes with oxygen enrichment of 2.5%, the top pressure of 212kPa, iron ore into the furnace grade of 58%. From the feedback of on-site operation, the operation of the body is all normal, and the new furnace type shows good maneuverability in terms of stable and smooth operation. The high specification configuration and complete monitoring means of the blast furnace body, together with the rich operation experience of Masteel, it can be expected that the new generation of Masteel No.2 2500m³ blast furnace production will become a new benchmark of "high efficiency, long life and low consumption".