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Energy competition is a challenge that the steel industry is facing. Reducing energy consumption and establishing environmentally friendly steel companies have become an important aspect of the sustainable development of the steel industry and an important foundation for the profit growth of the steel industry. The proposal of the Central Committee of the Communist Party of China on formulating the eleventh five-year plan for national economic and social development also proposes that the energy consumption per unit of GDP during the 11th Five-Year Plan period will be reduced by about 20% from the end of the 10th Five-Year Plan period. Energy conservation and consumption reduction in metallurgy, building materials, chemical, electric power and other industries.
The energy consumption of rolling steel heating furnace accounts for about 10% of the energy consumption of the metallurgical industry, and the rolling steel heating furnace accounts for 75 to 80%. There is still a certain gap between the steel rolling furnace of China's metallurgical industry in terms of output, furnace structure, mechanization, automation level and theoretical operation. The furnace has a high fuel consumption and low efficiency, resulting in a great waste of energy and thus heating. Furnace efficiency and energy-saving work of heating furnaces are one of the effective ways to reduce the cost of rolling steel production and achieve sustainable development of steel enterprises.
Reasonable furnace structure
The furnace type structure is the congenital condition for the energy saving of the heating furnace. Therefore, the energy saving of the heating furnace should be considered as much as possible when the heating furnace is newly built. The new or modified furnace structure should make the fuel combustion happen in the furnace as much as possible, reduce the heat loss of the flue gas from the furnace; recycle as much waste heat as possible from the flue gas to the furnace to improve the fuel utilization of the furnace. Coefficient; try to reduce the fixed heat loss of the furnace and improve the thermal efficiency of the furnace.
(1) Adopt step type furnace type. The practice of step-type heating furnace shows that it has many advantages compared with the traditional push-type heating furnace: because there is a gap between the billets, the billet is heated on all sides, the heating quality is good, the steel heating temperature is uniform; the heating speed is fast, the billet is The short residence time in the furnace is beneficial to reduce the oxidized burning loss of the billet, and is beneficial to the control of the depth of the decarburization layer by the easy decarburization steel; the operation is flexible, and the forward, backward or step can be changed, the charging interval can be changed, and the furnace output can be controlled. The production capacity is large, the furnace is not controlled by the thickness and shape of the billet, and the furnace is not arched; it is convenient for the production coordination of the hot billet of the continuous casting billet.
(2) Appropriately increase the length of the furnace. The length of the furnace is determined by the total heating capacity, but in order to reduce fuel consumption. To increase the heat utilization rate of the furnace, the length of the furnace body can be appropriately increased. The furnace body is short, high-temperature flue gas will not be fully utilized, and the exhaust gas will take away a lot of heat energy to run away from the flue. Therefore, proper extension of the exposed body can reduce the strength of the hearth and improve the thermal efficiency. Under certain heating conditions, the higher the hearth load, the lower the thermal efficiency and the higher the fuel consumption. Conversely, as the hearth load decreases, the heat loss from the exhaust gas will be significantly reduced. If the other conditions are the same, the furnace body is properly extended. Although the heat loss of the furnace is increased due to the increase of the bottom water pipe and the furnace body, it is far less than the saved fuel.
In general, for every 1 meter of furnace elongation, the billet temperature can be increased by 25 to 30 degrees Celsius, the exhaust gas temperature is reduced by about 30 degrees Celsius, and the unit heat loss is reduced by 1.5 to 1.8. Increasing the length of the furnace body mainly extends the length of the preheating section and reduces the exhaust gas temperature. Some domestic enterprises have adjusted the preheating section appropriately according to the length of the preheating section of 45 to 50% of the effective length of the whole furnace. Significant energy savings have been achieved.
(3) Reduce the furnace space. The height and length of each section of the furnace have a great influence on the heat transfer in the furnace, which directly affects the heating of the furnace and the utilization of fuel. When considering the height of the furnace, it is necessary to ensure the full combustion of the fuel and to fill the furnace with the furnace gas. .
(4) The partition wall inside the furnace. The partition wall in the furnace can play the role of stabilizing the furnace pressure, controlling the flow of the furnace gas, controlling the furnace temperature, reducing the flue gas overflow, reducing the exhaust gas temperature and reducing the suction of the burner. Therefore, according to the actual situation, the partition wall is added between the burner head, the furnace tail and each section, which has obvious effect on energy saving and consumption reduction of the furnace.
Reduce furnace heat loss
Furnace heat loss mainly includes heat loss such as water cooling, furnace door radiation, outgassing, and lining heat dissipation. Reducing this part of the heat can greatly reduce the unit consumption.
1. Reduce the heat loss of the bottom tube
(1) Insulation wrapping of the bottom tube. In order to eliminate the black mark of the heating furnace water pipe. Reduce heat loss, improve heating quality and product quality, reduce fuel consumption, heating furnaces generally use the bottom tube insulation insulation technology. Water heat loss generally accounts for about 10% of the total heat income of the furnace. This part of the heat loss is mainly caused by the vertical and horizontal pipes of the furnace bottom and the water-cooled parts of the furnace. In order to reduce this part of the heat loss, it is necessary to strengthen the heat insulation of the cooling water pipe, and the single-layer heat insulation wrap of the vertical cross-pipe of the original furnace can be changed into the double-layer dressing of the two materials, which can significantly reduce the heat loss of the water cooling. The furnace bottom pipe and the water-cooled slide rail insulation wrapping method of the domestic steel rolling furnace are refractory plastic dressing, ceramic fiber wrapping, silicon-aluminum refractory fiber felt wrapping and other unshaped refractory fiber preforms and refractory castables.
(2) Minimum tube bottom ratio. The tube bottom ratio of China's rolling steel heating furnace is generally larger. In order to minimize the tube bottom ratio, the methods used nowadays mainly include: increasing the spacing of the horizontal pipes, reducing the number of horizontal pipes and increasing the spacing within the allowable range of longitudinal pipe strength. ; Change the vertical and horizontal water pipe support structure, using waterless cold longitudinal pipe and T-shaped horizontal pipe support. This can reduce the heat taken away by the cooling water, reduce the tube bottom ratio, and improve the heating quality of the metal.
(3) Application of special slide rails. In recent years, new technologies such as waterless cold slides, hot slides, and metal semi-thermal slides have been gradually adopted, and the quality of heated billets has been significantly improved, and energy consumption has also been reduced.
2. Strengthen the insulation of the furnace body, reduce the heat dissipation and heat storage of the furnace body
The polycrystalline refractory fiber felt is attached to the top of the furnace and the top of the heating section, and the furnace steel plate is added outside the furnace wall, which not only reduces the heat storage of the lining but also reduces heat dissipation. Since the surface area of ​​the furnace body is relatively large, the continuous heating furnace with an average production time of 60 tons/hour generally has a heat dissipation surface area of ​​300 to 400 cubic meters.
3. Reduce the outgas and radiation of the hole
On the furnace, in addition to the necessary openings, the hole settings should be reduced as much as possible to reduce the heat loss caused by radiation and outgassing. Infrared photography found that if the temperature of the gas ejected reaches 700 degrees Celsius or more, the amount of open space per square meter can save 11 times and 104 kilojoules per hour per hour.
Recycling of flue gas waste heat
The main cause of a large amount of heat loss is the heat loss of the flue system and the heat transfer efficiency of the heat exchanger.
(1) Reform of the flue gas system. There are still quite a few furnaces that use underground exhaust and underground brick flue, and the flue gas is sent to the chimney through underground or semi-underground brick flue. Such smoke exhausting makes it easy for the flue gas to be emitted from the tailgate loading gate to the atmosphere, and its heat loss accounts for 15 to 30% of the total flue gas heat. In addition, the flue gas and the groundwater often infiltrate, so that the flue gas volume and the flue gas temperature have been seriously lost before reaching the heat exchanger, affecting the use of the heat exchanger. In order to make good use of flue gas waste heat, the flue system must be modified to minimize the flue before the heat exchanger. At the same time, there must be strict operation of the furnace door and Zhuang discharge door and flexible flue gate, paying attention to the tightness of the flue, so that the heat preservation rate of the flue gas before the heat exchanger is not less than 90 to 95%, Conducive to the full recovery of waste heat.
(2) Application and selection of heat exchangers. The heat exchanger is an efficient energy-saving device for recovering waste heat from flue gas. The rolling steel heating furnace adopts flue gas waste heat exchanger, which can recycle 60 to 70% of the residual heat in the flue gas, shorten the heating time, save fuel consumption by 20 to 30%, and increase the furnace output by 15 to 30%. There are many types of heat exchangers. In addition to the old-fashioned clay heat exchangers that have been eliminated, the new type of metal heat exchangers developed in the past decade have sheet-like tube heat exchangers, tubular insert-type heat exchangers, and jets. Heat exchangers, etc.
Reasonable choice of heat exchanger
As a heating device, the burner has been paid more and more attention. The technical progress of the burner has also developed rapidly. The application is widely used. The burners with better heating quality and energy saving effect are mainly as follows:
(1) Coal burner high-speed burner. The high-speed burner has the advantages of uniform temperature in the furnace, rapid increase of furnace temperature and heating speed of the billet. At the same time, since the burner has a high combustion regulation ratio, the temperature of the jetted gas can be adjusted within the range of 200 to 1,700 degrees Celsius, so its application range is wide. The disadvantage is that the noise is large and the life of the lining is short.
(2) Gas sub-high speed burner. Gas sub-high-speed burner is a kind of energy-saving low NOx new burner developed in the early 1980s to meet the requirements of modern continuous heating for large energy, wide furnace type, high Fengwen and long flame. It is especially suitable for flat flame. The burner is used in combination for lower heating. Its main feature is to adapt to the requirements of Gao Fengwen and full hot air. The wind temperature can reach 800 degrees Celsius; the burner has large energy and wide application range; the structure is simple, the maintenance and repair is convenient; the adjustment range is large, and the adjustment ratio can reach 1:10, the flame ejection speed High, low noise, strong furnace gas agitation, uniform furnace temperature.
(3) Flat flame burner. The flat flame burner has the advantages of fast heating, uniform heating, lower furnace height, reduced oxidation loss and reduced fuel consumption. At the same time, it can also improve the furnace pressure, reduce the cold air from the discharge port, and eliminate the burning phenomenon of the charging port.
(4) Radiant tube burner and regenerative burner. The radiant tube burner has the advantages of uniform heating and no pollution of the steel slab, but generally the heating temperature is low and is mostly used for the heat treatment furnace. The regenerative burner is an energy-saving burner that has been developed in recent years. It uses the mutual heat storage between a pair of burners to increase the air temperature, reduce the exhaust gas temperature, and efficiently burn low-oxygen. However, the regenerative type The control of the burner is complicated and expensive.
The domestic steel rolling furnace has high fuel consumption and low efficiency, which causes great waste of energy. Under the national energy conservation and emission reduction policy, it is necessary to do a good job of heating furnace energy saving, improve furnace thermal efficiency, and reduce rolling steel production cost.