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Cement is one of the most commonly used building materials in the construction industry. Due to its many advantages, cement concrete has become an indispensable material in the construction industry, further increasing the importance of cement. At present, my country's cement production process is relatively backward. Some areas still use the traditional cement production process, which is the traditional shaft kiln production process. Due to a large amount of investment and serious pollution, this production process is increasingly unable to meet the needs of social production. Energy consumption is an important indicator of the production cost of rotary kiln. The thermal efficiency of ordinary cement rotary kiln is about 30%, and the thermal efficiency of advanced cyclone preheater kiln is only about 50%.
Application of energy-saving technology
1.1 Frequency conversion control technology
The power generated by the main drive of the rotary kiln is mainly used to drive the frequency control technology motor. The characteristics of the work require that only the motor system with high starting torque and stable speed regulation performance can be adapted to the rotary kiln. In the 1970s, the rotary kiln was driven by the motor series resistance speed regulation. The development of transistor technology in the 1980s was very rapid, and the frequency of use of the DC motor speed control system in the rotary kiln was also increasing. Because of the high heat dissipation of the rotary kiln, the DC motor will quickly damage the carbon brushes and commutator heads, resulting in unstable low-speed operation and a large amount of power consumption. The rotary kiln motor drive system applies frequency conversion speed regulation technology to form an AC speed regulation drive system, which completely replaces the DC speed regulation system, and the energy saving effect is very obvious. The inverter and the AC motor form an AC speed control system. Inverters are passive inverters that convert commercial frequencies to each other. The driving task of the rotary kiln is completed by controlling the frequency converter and the variable frequency AC motor drive, and the traction frequency conversion control and synchronous control of the rotary kiln are realized. It can fully meet the high torque requirements of the rotary kiln. It is very stable in the process of speed regulation, and the energy saving effect is also very obvious. Technology can be used in all main drive systems of rotary kilns.
1.2 Improvement of combustion technology
1.2.1 New double-tube burner KBN series new double-tube pulverized coal burner is introduced. In addition to the advantages of the traditional multi-channel burner, the burner can eliminate the local high temperature phenomenon in the combustion area, and distribute the flame temperature more reasonably, which can make the kiln run for a long time. The main advantage of the new dual-pipe burner is that it can eliminate the inner pipe and adjust the swirl intensity of the swirler and the outer pipe. When the thickness of the annular jet is increased to three times the thickness of the duct burner, the combustion efficiency of the burner is greatly reduced. It can delay the ignition speed of air and pulverized coal, reduce the maximum temperature of the flame, and prolong the service life of the refractory bricks in the sintering area. The internal and external air regulating valve of the traditional multi-wind burner is omitted, which simplifies the system and saves about 30% of the primary fan. The shape of the flame is adjusted by the handwheel of the gearbox and prompted by the display on the gearbox. The flame can be controlled simply and accurately. The pulverized coal screw feeder is installed with the screw pump above. The fan sends the pulverized coal to the double-tube burner through the screw pump, and the high-pressure centrifugal fan provides the outside air.
1.2.2 Pulverized coal combustion technology At the same time, since the pulverized coal is completely burned in the sufficient oxygen zone, the chemical incomplete combustion loss of the pulverized coal is significantly reduced.
1.2.3 Reduce the heat loss of the kiln During the operation of the rotary kiln, the heat lost in the cylinder air accounts for more than 20% of the total heat. The surrounding air receives heat from the hot air flow in the rotary kiln through the liner and cylinder. The greater the thermal conductivity of the lining, the smaller the thermal resistance and the greater the heat loss. Therefore, improving the thermal resistance of the kiln lining, that is, the adiabatic effect, and reducing the heat loss of the kiln cylinder are important measures to improve the thermal resistance of the kiln lining.
energy saving measures
2.1 Decomposition and energy saving measures
2.1.1 Use CB20 single-layer moisture-proof brick. CB20 single-layer humidification and thermal insulation brick is a light-weight, high-strength, wear-resistant and high-temperature-resistant phosphating brick composed of a working layer and a thermal insulation layer. Due to the high strength of thermal insulation bricks, low thermal conductivity and good thermal shock resistance, the surface of the cylinder can be cooled to 70-90 °C. At the same time, the density of the brick body is lighter than that of ordinary clay bricks, which reduces the weight load of the kiln system and the energy consumption of the kiln. After the use of CB20 bricks, the material temperature, airflow and lining material in the decomposition zone are improved to a certain extent, and the decomposition reaction of the material is relatively complete.
2.1.2 Masonry technology In order to slow down the moving speed of the material in the decomposition zone, prolong the heating time of the material, and improve the decomposition speed, the anti-stripping high and low brick tee fixing rings can be used to strengthen the function of the decomposition zone. After laying the high and low bricks, the layers of material are agitated, which increases the chances of supplying material to the surface. The heat transfer of the inner layer of the material is also increasing, the moving speed of the material is also slowed down, the decomposition speed of the material is accelerated, and the temperature difference between the air flow, the refractory brick and the material is continuously increasing, which prepares the conditions for improving the heat transfer capacity. The preheating capacity of the material is increased, the production is increased, and the heat consumption is reduced.
2.2 Exhaust system using heat pipe technology
The flue gas has a higher temperature and a large volume, and takes away about 33% of the heat, which is the largest heat loss. Use waste heat to improve furnace thermal efficiency and reduce the key to energy consumption. The heat carried away by the exhaust gas is proportional to the product of the exhaust gas temperature and the exhaust gas volume. In recent years, the heat pipe technology has been widely used in the waste heat recovery of flue gas, and the effect obtained is also obvious. Heat pipe technology can be used to reduce the exhaust gas temperature and thus reduce heat loss from the exhaust gas. The heat pipe is a high-efficiency heat transfer element developed according to the needs of heat transfer technology. There are many types of heat pipes. In order to save investment, gravity heat pipes have been widely used in China. A heat pipe is a sealed, clean, evacuated vacuum tube filled with a certain amount of working medium. The medium can be pure water, acetone, ethanol or organic compounds and inorganic potassium, sodium, alkali metals, etc. When the low temperature and high temperature heat sources transfer heat into the tube, when the liquid medium at the lower end of the tube is heated, it evaporates rapidly and rises to the upper end of the heat tube. Due to the endothermic effect of the low-temperature cooling source outside the upper casing, the steam condenses into water droplets and emits latent heat of vaporization. According to its own gravity, the droplets flow back along the tube wall and heat up and evaporate again. The process is continuous and accomplishes the task of heat recovery very quickly.
2.3 Energy consumption for ash and water removal
2.3.1 Reduce energy consumption for ash and slag removal
The heat removed by kiln dust accounts for about 1%-4% of the heat consumption. Although the weight of kiln dust is small, it is also a raw material that cannot be ignored. It avoids the opening and closing of the electrostatic precipitator, improves the efficiency of the precipitator, and selects the appropriate kiln air speed, raw material particle weight and heat exchange equipment to reduce the amount of kiln dust and reduce the heat taken away by the kiln dust.
2.3.2 Reducing energy consumption for dehumidification
The higher the water content of the slurry, the greater the heat consumed for evaporation. In order to reduce the heat of evaporation of the muddy water, it is necessary to reduce the muddy water and reduce or eliminate the external pumping. The use of thin slurry to improve the fluidity of the slurry is the key to reducing the evaporation heat of the slurry, and it is an economical and convenient way to achieve energy saving and increase the output of the wet kiln. Theoretically, for every 1% reduction of slurry moisture, the heat consumption of clinker can be reduced by 1%-2%, and the yield of clinker can be increased by 1.5%-2.5%.
With the development of my country's economy, the strengthening of economic globalization, the increasingly fierce competition among enterprises, coupled with environmental and resource problems, is an urgent problem faced by the development of modern enterprises. The development of enterprises must change the tradition. The direction of enterprise development. The traditional concept is to strengthen management while maximizing the economic benefits of the enterprise while introducing advanced technology and equipment.