Wuxi Zechuan Environment, a professional manufacturer of RTO incinerators, RTO, RCO, and VCU equipment, reports on September 2, 2024: Good technical articles are worth reading carefully! As key equipment in the RTO system, whether the design and selection of the fan and the fan system are correct determines the safe production of the entire system and the economic benefits of the enterprise. Today, this article will elaborate and explain in detail from the perspectives of the classification, principle, explosion-proof and other aspects of the fans required in the RTO system, hoping to provide a certain degree of guidance and suggestions for our fellow industry partners.
For RTO systems, the commonly used fans include centrifugal medium and high-pressure induced draft and ventilator fans and axial flow medium and high-pressure induced draft and ventilator fans. According to the material, fans can be classified into metal fans and non-metal fans. Among them, commonly used metal fans are mostly carbon steel, SS304, SS316L, duplex steel, etc., while non-metal fans are generally made of FRP, electrostatic conductive FRP, PP, etc. In the RTO system, fans are classified into the following types: fans that come into contact with exhaust gas and fans that do not. Among them, fans that come into contact with exhaust gas include main pipeline exhaust and supply fans as well as relay fans. Fans that do not come into contact with exhaust gas include combustion-supporting fans, reverse purging fans, and leak-proof fans, etc. For general fans that come into contact with waste gas, material selection and design should be based on the components and characteristics of the waste gas. For fans that do not come into contact with waste gas, design and selection only need to be carried out according to the total pressure and air volume of the fan.
Fans are the general term for gas compression and gas conveying machinery. They convert the mechanical energy of rotation into the pressure energy and kinetic energy of gas and convey the gas out. They usually have the following parameters that need to be determined
1. Flow rate, including air volume and standard air volume;
2. Pressure, static pressure at intake and exhaust, static pressure of the fan, total pressure, and pressure increase;
3. Gas medium, including temperature, humidity, density, dust content and the composition of the gas, etc.
4. Rotational speed;
5. Output power is generally expressed in KW.
In the RTO system, we usually calculate the pressure loss of the pipelines and equipment within the system first as the total pressure of the fan. The air volume is then calculated based on the exhaust gas flow rate of the entire plant's exhaust gas collection system. This way, the total pressure and air volume of the RTO system's induced draft fan can be determined. Of course, when choosing a fan, a margin of 1.05 to 1.2 needs to be considered. Because the selected fan must meet the system requirements in terms of total pressure and air volume when operating at full load. However, some first-line domestic fan manufacturers have already taken this factor into account and integrated it into the selection software. You only need to input the environmental conditions and process conditions.
So, exactly how to determine the air volume and pressure? First, the upper limit of wind speed or air change rate needs to be determined in accordance with the HVAC standards of the relevant industry. After determination, the exhaust gas flow rate should be determined based on the exhaust gas emission volume of the pollution source emission point and the size of the pollution source space, which is what we call the fan air volume. Secondly, the pressure of the fan should be determined based on the pressure loss of the equipment and pipelines. Here, let's introduce what the pressure of the fan is.
In the RTO system, in order to normally draw the organic waste gas (VOCs) to the RTO treatment boundary area and convey the treated clean air to the chimney for discharge, it is necessary to overcome the pressure loss of the entire system's pipelines and equipment. The fan must generate these pressures. The fan pressure is divided into three forms: static pressure, dynamic pressure, and total pressure. The pressure that overcomes the aforementioned air supply resistance is called static pressure. Static pressure is the pressure exerted by a gas on the surface of an object parallel to the gas flow. It is measured through holes perpendicular to its surface. Dynamic pressure is the form of converting the kinetic energy required in gas flow into pressure.
Pt=pv2/2
In the formula, Pd represents dynamic pressure
ρ- Density of gas (kg/m³)
v- Velocity of gas (m/s)
The total pressure Pt is the algebraic sum of dynamic pressure and static pressure, that is
Pt=Pd+Ps
In fact, in the RTO system, apart from paying attention to the fan pressure and air volume, the explosion-proof of the fan is another top priority. This is because the RTO is a high-temperature oxidation device, and the media it processes are all flammable, explosive, toxic and harmful organic compounds, which pose certain dangers. Therefore, the explosion-proof of the fan becomes one of the most fundamental safety measures. The fan motors used in the RTO system are generally selected as flameproof motors. Besides the motor being explosion-proof, the fan itself needs to be treated to be spark-free. For instance, the impeller of a metal fan should be made of alloy material, and the outlet should be treated to be spark-free. For non-metal fans, the non-metallic materials must be electrostatic conductive materials; otherwise, static electricity will pose a significant risk.
The fans in the RTO system are basically in continuous operation. Attention should be paid to lubrication and cooling, and regular lubrication and maintenance should be carried out. Taking the lubrication cycle and inlet and outlet water volume of a certain brand of fan as a reference, it is necessary to ensure the stable and continuous efficient operation of the RTO induced draft fan to guarantee the economic benefits of the enterprise.
In RTO systems, when fans convey high-concentration VOCs, explosive gases, high-concentration dust, ultrafine particle materials, toxic gases, and gases with pungent odors, to prevent the leakage of these gases, it is recommended to select low-leakage or zero-leakage ones. At the same time, it is necessary to choose shaft seals above packing seals. For zero-leakage, it is best to use compressed air seals and ensure proper shaft seals. In the active pharmaceutical ingredient (API) industry, due to the characteristics of the exhaust gas components, we recommend that the system be designed under negative pressure. This can prevent the escape of toxic and harmful gases and avoid the potential safety hazards to operation and maintenance personnel and enterprises as a result.
In summary, the RTO system mainly consists of the main fan, the rear induced draft fan, the combustion-supporting fan, the reverse purging fan, as well as the drying fan and the adsorption fan. Both the main fan and the rear induced draft fan of the RTO are equipped with frequency converters. The fans are linked with the pressure inside the pipeline to ensure that the fans maintain the pressure inside the pipeline to meet the process requirements. The fan adopts explosion-proof fan and variable frequency motor, with the rated frequency of the motor being 50Hz. During operation, the system can automatically adjust the fan frequency and air volume according to the changes in air volume and the pressure in the pipeline before the fan, saving energy and reducing consumption, and ensuring the stability of the production line within the user's range. In addition, RTO operation and maintenance inspection personnel need to regularly maintain and service the fans based on the on-site usage conditions. It is essential to ensure that the most reasonable fan air volume and total pressure are selected according to the process conditions of the client, supplemented by regular maintenance operations. Only in this way can the entire system operate safely, stably and efficiently.
Waste Gas Treatment, RTO, CO