NEW OPPORTUNITIES OF CERAMIC WELDING AT HOT REPAIR OF REFRACTORY LINING OF HYPER THERMAL INDUSTRIAL UNITS
The running time and operating efficiency of high-temperature industrial units depends on the level of their technical exploitation, timely fault diagnosis and quality of preventive maintenance. The first minor damage to brickwork laying can be observed in the early years of operation. From then on developmental character of defects becomes increasingly complex.
Aging and natural deterioration of ovens stock in coke and by-product industry inspire an intense interest in new advanced technologies of repair which provide long service life of thermal units. Service life of well maintained coke oven battery is 30-40 years (at depreciation guidelines 18 years). To date most coke oven batteries in Russia are either worn out or at the limit of their operating capacity. Thus, the mean age of the existing coke oven batteries in Russia today is 21.4 years. On the other hand, as the experience of domestic by-product coking industry shows, there are many examples of coke oven batteries working for 40-50 years due to correct operation and timely repair.
Before the appearance of ceramic welding technology well-worn coke oven batteries were repaired only by method of partial or complete rebricking of heating wall, while the majority of existing at that time wet, semi dry and jet guniting gave temporary and rather a cosmetic result. Restorative hot and cold repairs of industrial ovens with full or partial rebricking of heating walls until recently remained an important, much as expensive means of enhancement of service life of industrial ovens. Restoration of industrial units by means of rebricking has several disadvantages: it requires large-scale material and financial resources associated with a significant loss of production due to taking the chamber or the whole battery from the production cycle. The quality of the junction of old and new brickwork laying remained low because of different coefficients of linear expansion of refractory products and is particularly evident during heating and further operation of coke oven battery.
In these circumstances it was essential to find a repair method meeting the following conditions:
- no interruption to the production cycle;
- reliability: achievement of long-life performance of the repaired sections;
- cost effective: simple and time-saving.
Long-term research of «NPO MEGATEK» personnel in the field of targeted controlled synthesis of refractory material in the combustion wave, such as x-ray, morphological studies, theoretical and thermo chemical calculations including the study of the effect of the particle size distribution enabled to develop a world-class ceramic welding technology in Russia. This technology allows carrying out hot repair of practically any chemical composition. The technology provides maximum resistance of repaired areas with minimal negative impact on the brickwork.
Technological scheme of repair with the help of ceramic welding machine "MaKS" manufactured by «NPO MEGATEK» (Fig. 2) is as follows: repair material from the tank is fed from the bunker to the lance by a pneumatic transport and then on to the restored surface. Inflammation and synthesis of refractory material in the combustion wave occurs on the hot surface of refractory lining. As a result it became possible to eliminate various kinds of defects. Ceramic welding method can not only weld cracks and chips, but also large area defects, such as cavities. Furthermore, the technology allows for reliable welding of joints of old and new brickwork laying.
Currently, «NPO MEGATEK» produces all materials necessary for hot repair of coke oven batteries:
- "MEGA-K" - ceramic mixture intended for restoration of silica brickwork of coke ovens.
- "MEGA-SHAMOT" - ceramic mixture for repair of fireclay lining of industrial furnaces.
- "MEGA-KV" - ceramic mixture intended for restoration of industrial furnaces in the zones of major temperature oscillations.
- "NIKA" - ceramic mixture intended for restoration of ovens’ sole surface of coke oven batteries, heating furnaces, etc.
- "BARRIER" - ceramic mixture for hermetic sealing of micro cracks of heating walls of coke oven batteries.
Elimination of defects of lining with ceramic mixtures "MEGA-K", "MEGA- SHAMOT" and "MEGA-KV" is performed by method of ceramic welding.
Moreover, long-standing of repaired sites is achieved as a result of the following factors:
- affinity of chemical and mineral composition of repair materials to characteristics of restored brickwork lining;
- identity of the structural-phase composition of refractory material;
- strong interatomic (crystalline) linkage of welded layer and oven’s brickwork.
Ceramic mixture "MEGA-K" reproduces all properties of silica refractory after welding and is well-proven in coke and by-product plants.
Ceramic mixture "MEGA-SHAMOT" enables recovering fireclay refractories used in ovens’ lining subject to significant thermal and mechanical exposure.
Ceramic mixture "MEGA-KV" is designed to repair sections of brickwork adjacent to the armor and subject to significant temperature oscillations. This mixture can be used to restore lining of "cold" areas of coke chamber at temperature of 800ºC.
Unlike previous repair materials, ceramic mixture "NIKA" is applied in the form of suspension. "NIKA" is premixed with well-defined amount of water, the resulting suspension being uniformly poured on the oven’s sole, filling defects and irregularities. Exothermal reaction results in the inflammation and melting of ceramic mixture, submelting of silica brickwork of the oven’s sole chamber and filling of defects, forming a flat and smooth surface. When the temperature of the welded mixture is reduced to the temperature of the oven’s sole it hardens and gains necessary strength. The important fact is that almost immediately after the repair coking chambers can be charged with coke. Ceramic mixture "NIKA" for repair of ovens’ sole surfaces proved to be highly efficient repair material, resistant to thermal and mechanical exposure.
Sealant "BARRIER" eliminates small leakages in heating walls by sealing cracks, thereby ensuring stable operation of coke oven batteries and significantly reducing emissions of coke gases into the atmosphere. "BARRIER" is used at the final stage of lining restoration by method of dust injection after ceramic welding.
Ceramic welding is a widely recognized method of repair. Ceramic welding technology offers ample opportunities for repair of linings of various physical and chemical composition to increase service life of high-temperature units. Long-standing of repaired sites of coke ovens’ linings can be achieved based on the advanced ceramic welding technology using high quality materials.