Talking about the Energy Saving Measures of Spray Drying Tower

Summary

The energy-saving methods of spray drying towers were discussed from the aspects of drying medium, spray drying tower structure and ceramic mud properties. The energy-saving measures commonly used in spray drying towers were summarized.

Key words spray drying tower, energy saving, drying medium, mud performance

In recent years, China's ceramic industry has developed rapidly. In 2006, the output of China's daily-use ceramics and building sanitary ceramics ranked the world*, of which the output of daily-use ceramics reached 17 billion pieces, accounting for about 65% of the world's total output; the annual output of building ceramic tiles was about 3.5 billion – about 55% of the world's total production. At the same time, China is also a major energy consumer, and the building sanitary ceramics industry is a major fuel consumption and power consumption. At present, the energy utilization rate of China's ceramic industry is only 28% to 30%, and the energy utilization gap between 50% and 57% in developed countries is still relatively large.

Spray drying and milling is one of the high energy consumption production processes in the ceramic industry. According to the ceramics energy audit data, the energy consumption of spray drying and milling accounts for 10-20% of the total energy consumption of ceramics. 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.

1 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 main conclusions are as follows: The performance of the spray drying tower itself is adjusted; the other is the nature of the dry matter itself, fuel problems, drying medium properties and other factors.

1. 1 control of drying medium

1. 1. 1 　 Increase the temperature of the hot 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 more heat per unit mass of hot air transferred to the mud droplets, the unit hot air The more moisture that is evaporated. 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 exceeding 600 °C). If the temperature is too high, the top wind splitter will be burned out.

1. 1. 2 　 Reduce the temperature of the hot tower

When the temperature of the hot air entering 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. 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.

1. 1. 3 　 Recycling of hot air ( exhaust gas )

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 or exchanged for reuse by using a heat exchanger.

1. 2 spray drying tower itself factor

1. 2. 1 　 Pick the right specifications

Most manufacturers in the ceramic industry use the Model 4000 spray drying tower. Some ceramic factories use the 5000 and 6000 models. The Zui has the 12000 model developed by SACMI and has up to 48 nozzles. 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.

1. 2. 2 　 Integral closed control

Since the system uses negative pressure operation, if there is air leakage, it will increase energy consumption. Therefore, the various 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 negative pressure measuring hole on the tower body And the outlet of the lower cone taper of the tower body, the part of the cyclone dust removal and the material outlet must be sealed and the air should not be leaked.

1. 2. 3 　 Hot blast stove control

The hot blast stove is a hot air source for the drying of the spray tower, and 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 and flow rate as well as the 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 90° to 120°, the spraying height is 4 to 4. 5 m, and the angle of the spray gun is maintained between 110° and 120° to ensure that the spray material and the hot air can be fully performed. Heat exchange. The choice of hot blast stove fuel can directly affect the cost of fuel consumption. For example, clean petroleum gas, light diesel oil, etc. will greatly increase the cost. It is necessary to control the sulfur content of heavy oil and mixed oil. 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.

1. 2. 4 　 Use of linear burners

Conventional spray drying tower hot air devices generally use a fuel (gas) hot blast stove, a boiler steam heat exchanger, a heat transfer oil heat exchanger or an electric heating heating system. The above conventional heating systems all use heat exchangers, and the efficiency of the heat exchanger determines the heat utilization efficiency of the conventional heating system; and the heat exchanger has a limited service life and high maintenance cost. Direct-fired hot air device with a linear burner as the core. The linear burner is relatively small in size and is directly installed in the duct. The drying medium can be directly contacted and rapidly raised to the required temperature. The direct-fired hot air device with the linear burner as the core has two characteristics of energy saving and environmental protection. Firstly, the linear burner has a reasonable combustion mechanism, and the combustion zone maintains a certain amount of excess air, which can ensure complete combustion and inhibit the formation of nitrogen oxides. The direct-fired hot air device directly contacts the air without a heat exchanger, ensuring efficient heat transfer to the air and high thermal efficiency. In addition, the ease of use is another feature of the linear burner, which can be changed by adjusting the gas regulating valve.

1. 3 mud quality control

1) Reducing the moisture content of the ceramic slurry, the heat required for drying is less, but the mud 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. The author and the Guangdong New Pearl Group cooperated with the composite water reducer, the mud moisture was reduced from 39.5 % to 36%, the ball milling time was shortened by 5 h, the electricity consumption per ton of powder was 16.5 yuan, and the output increased by 18.8 %. The annual cost savings amounted to more than 1.5 million yuan.

2) 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.

2 Conclusion

In addition to the above measures, the energy saving of the spray drying tower can also find solutions in energy, such as developing and utilizing new energy sources and rationally controlling the combustion process. Of course, many problems need to be discovered and solved in actual production. In order to improve the energy efficiency of spray drying towers, ceramic enterprises can improve the economic and social benefits of enterprises with the purpose of sustainable development.