Spray drying and milling is one of the high energy consumption production processes in the ceramic industry.
Spray drying and milling is one of the high energy consumption production processes in the ceramic industry. The control of fuel is an important part of the cost control of raw material workshops. According to the ceramics energy audit data, the spray drying powder fuel accounts for 1/3 of the total energy consumption of the ceramics factory. With the energy crisis and fierce market competition, reducing the energy consumption of spray drying and milling has far-reaching and important significance for reducing the production cost of enterprises, improving the competitiveness of enterprises and promoting the sustainable development of the ceramic industry.
Main measures for energy saving and consumption reduction of spray drying tower
Since the energy consumption in the spray drying process directly affects the economic benefits and development prospects of the enterprise, ceramics and industry experts have put forward a lot of measures for energy saving and consumption reduction in the spray drying process. The summary is mainly as follows.
1. Control of drying medium
Increasing the temperature of the hot air into the tower: Under the condition that the temperature of the tower is constant, the higher the inlet temperature of the hot air (also known as the inlet air temperature), the higher the total heat brought in, and the hot air per unit mass is transferred to the mud droplets. The more heat there is, the more water is evaporated by the unit hot air. In the case of constant production capacity, the required hot air volume is reduced (ie, the heat taken away from the tower when the hot air is removed), the heat consumption of the spray drying powder is reduced, and the utilization rate and thermal efficiency of the hot air are improved. However, the temperature of the hot air entering the tower should not be too high (not more than 600 oC). If the temperature is too high, the top wind splitter will be burned out.
Decrease the temperature of the hot air out of the tower: Under the condition that the hot air temperature of the tower is constant, the lower the temperature of the hot air outlet tower, the larger the temperature difference between the inlet and outlet towers, and the greater the heat energy that the hot air transfers to the mud for drying, so the hot air utilization rate is higher. high. However, the exhaust air temperature should not be too low. When the temperature is lower than 75 °C, the powder is too wet, which affects normal drying.
Recycling of hot air (exhaust gas) from the tower: After the ceramic slurry is spray-dried and powdered, if the hot air of the tower is directly discharged into the atmosphere, this part of the heat loss will be considerable (about 10% to 20% of the energy consumption of the milling process). ). Therefore, this part of the residual heat should be fully utilized, for example, the hot air of the tower can be recycled to the preheating drying process. In addition to direct recycling, the tower hot air can also be stored by heat exchangers or exchanged for reuse.
2, spray drying tower itself factors
Choose the right specifications: Most manufacturers in the ceramic industry use the Model 6000 spray drying tower. Some ceramic factories use the 8000 and 10000 models, the Zui large has the 12000 model, and the nozzles have as many as 54. The larger the model, the greater the production capacity, the less energy is produced per ton of powder, and the manufacturer can choose the model according to the specific conditions.
Integral closed type control: Since the system uses negative pressure operation, if there is air leakage, it will increase energy consumption. Therefore, all parts of the equipment and the connecting flange, the thermocouple socket of the hot blast stove, the hot air duct and the exhaust duct, and the tower body The negative pressure measuring hole, as well as the outlet of the lower cone taper of the tower body, the portion of the cyclone dust removal and the material outlet must be sealed and air leakage is not allowed.
Control of hot blast stove: The hot blast stove is the hot air source for the drying of the spray tower. Its fuel consumption directly affects the level of drying cost, so it is a key part of the energy saving of the spray drying tower. The efficiency of the hot blast stove depends mainly on the fuel atomizing nozzle. When the fuel atomization is uniform and the combustion is sufficient, the thermal efficiency is high. For this reason, the atomizing air pressure, flow rate, fuel pressure and flow rate should be strictly controlled. In addition, the atomization angle, the spray height, and the angle of the spray gun of the atomizing nozzle should be controlled within a suitable range. Generally, the atomization angle (α) of the atomizing nozzle is 90o-120o, the spraying height is 4~4.5m, and the angle of the spray gun is maintained between 110o and 120o, so as to ensure sufficient heat exchange between the spray material and the hot air. The choice of hot blast stove fuel can directly affect the cost of fuel consumption. For example, clean petroleum gas and light diesel oil will greatly increase the cost. Heavy oil and mixed oil must be used to control the sulfur content. Otherwise, it is difficult to ensure SO2 in the exhaust gas. Emissions are up to standard. At present, many ceramic factories use coal-fired gas to separate coal ash (coal gas contains 10% to 20% of unburned carbon, and some are as high as 20% or more) to make coal water slurry and turn coal. The phenol water and tar produced in the gas are injected into the hot air furnace for combustion, which can eliminate the discharge of these harmful substances, and discharge them into harmless water and CO2 during high-temperature combustion. This not only can greatly reduce the cost of combustion, but also make full use of these waste residue and waste liquid to save energy and reduce consumption.
3, the quality control of the mud
The water content of the ceramic slurry is lowered, and the heat required for drying is small, but the fluidity with low moisture content is not good, and the atomization effect is poor. In order to solve this contradiction, a suitable diluent (water reducing agent) or electrolyte (such as water glass, soda ash, humic acid, etc.) is usually added to the production to adjust the fluidity of the slurry while reducing the moisture content of the slurry.
Increasing the temperature of the ceramic slurry can effectively reduce the viscosity of the mud, improve the atomization performance of the mud, and prevent the atomizing nozzle from being blocked by the crystallization of the mud. Therefore, the waste heat recovered by the tower hot air can be used to preheat the mud, which is an effective way for energy recycling.
Popularization and application of dry milling
In the dry milling process, it is generally said that the raw material formulation is relatively simple, so that the delamination of the raw material during the processing can be avoided. Because the raw material impurities are difficult to remove in the dry process, relatively pure raw materials are generally used. In the pulverization of raw materials, various raw materials are pulverized separately according to their own characteristics, so that the pulverization efficiency can be improved, and the fineness of each raw material can be ensured.
The dry milling process generally consists of: raw material coarse, medium and fine crushing → batching → fine grinding → sieving → humidification → granulation → drying → sieving iron removal → stale → dry pressing. After the raw materials are pulverized (particle size ≤ 40mm), they are placed in the feeding hopper respectively. The raw materials are removed from the bottom by the weight of the raw materials, and are transported to the vertical mill through the electronic belt scale and the feeding belt conveyor placed at the bottom of the feeding hopper. After grinding, the qualified powder after grinding is transported by wind, collected by a cyclone collector and a pulse bag collector, and then conveyed to the storage bin through the airflow conveying system. The powder in the storage bin passes through the screw conveyor at the bottom of the warehouse, and the powder is added into the weighing and measuring bucket. When the weight of the powder into the weighing bucket reaches the set weight, the screw conveyor stops feeding and measuring. The outlet at the bottom of the bucket is opened for the granulator and the granulator begins to granulate. The pellets formed by the granulator are discharged through the bottom of the granulator, optimized by the optimization machine, and the optimized powder is introduced into the dry fluidized bed. After drying, the optimized granules are passed through the large dip belt conveyor. Direct access to the silo, used after stale.
The equipment used for dry milling is mainly granulators and vertical mills. The granulator consists of a straight section and a curved cylinder. The cylinder can be rotated. The rotation speed is adjusted according to the performance of the required powder. There is a special humidification and water adding device in the cylinder. When rotating at high speed, the centrifugal force acts. The water is atomized and combined with the powder. At the same time, the device acts as a stirring to form water-bonded particles, and rolls through the curved section of the cylinder to achieve the purpose of granulation.
The vertical mill is used to replace the traditional ball mill, and the powder conveying system is changed, which greatly improves the efficiency of grinding and saves the consumption of electric energy. Vertical mills have been used in the cement, chemical and other industries in the past, and the vertical mills have been introduced into the ceramic wall and floor tile milling process, as a grinding equipment for the dry process of the new process of powdering. The new fine powder pneumatic conveying system is adopted in the powder conveying, which effectively avoids secondary pollution during the fine powder conveying process and increases the cleanliness in production. The principle is as follows: the raw material with good ratio is added to the inside through the inlet of the vertical mill, the reducer drives the grinding disc to rotate, and the raw material on the grinding disc is pressed into fine powder by the relative rotary extrusion of the grinding disc and the grinding roller. The fine powder is blown to the separator of the vertical mill through the high-pressure fan, and the powder with the particle size is passed into the silo through the pneumatic conveying system, and the unqualified large-particle powder is returned to the vertical mill for two. The secondary grinding, according to this cycle work.
The dry milling production process reduces the coal-fired and powder-making process of the drying tower, and solves the environmental pollution and impact caused by the dust, smoke, sulfide and other aspects caused by the drying tower in the tile production process. It not only protects the environment well, but also makes effective use of raw materials.
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