The petrochemical industry is one of the world’s most concentrated sources of VOC emissions. From refining units and tank farms to loading and unloading systems and separation towers, VOCs permeate almost the entire production chain. These waste gases are typically complex in composition, fluctuate greatly in concentration, and are often flammable, posing a severe challenge to end-of-pipe treatment.
Among numerous control technologies, the Direct Fired Thermal Oxidizer (DFTO) has become one of the core methods for treating waste gas from petrochemical facilities worldwide, thanks to its high destructive removal efficiency of over 99%, strong adaptability to concentration fluctuations, and unique advantages in achieving self-heating operation under high concentration conditions.
Why Petrochemical Facilities Need VOC Control
VOC emissions from petroleum refining enterprises can be classified into 12 emission sources: leaks at sealing points, evaporation from storage tanks, emissions from loading and unloading vehicles, wastewater treatment systems, fugitive emissions from processes, organized emissions from processes, combustion flue gas, circulating water systems, sampling, flares, abnormal operating conditions, and accident emissions.
In recent years, countries around the world have imposed strict restrictions on air pollutant emissions. Among these, the three main emissions from process heating furnaces include particulate matter, sulfur dioxide, and nitrogen oxides, with nitrogen oxides being the most difficult to meet standards. Therefore, the petrochemical industry urgently needs to control VOC emissions.
What Is a Direct Fired Thermal Oxidizer(DFTO)?
Direct Fired Thermal Oxidizer (DFTO) is a waste gas treatment device that directly oxidizes and decomposes volatile organic compounds (VOCs) in exhaust gases into harmless substances using a high-temperature flame. It does not rely on catalysts or adsorption media, but rather utilizes the high-temperature environment generated by fuel combustion to achieve the destruction of organic matter.
Working principle of direct fired thermal oxidizer unit
The core logic of DFTO can be summarized as three steps: heating → retention → oxidation.
The process exhaust gas containing VOCs is first sent into the combustion chamber, mixed with auxiliary fuel (usually natural gas or fuel oil), and ignited under excess air conditions. The temperature inside the combustion chamber is usually maintained between 650 ° C and 1000 ° C, depending on the composition of the exhaust gas and the required destruction efficiency. High temperature breaks the chemical bonds of organic molecules and undergoes violent oxidation reactions with oxygen molecules, ultimately converting them into carbon dioxide (CO2) and water vapor (H2 O).
To ensure complete reaction, the residence time of exhaust gas in the combustion chamber is typically designed to be between 0.5 and 2.0 seconds—this parameter, along with temperature, constitutes the two most critical design parameters for DFTO. Too short a residence time leads to incomplete oxidation, while too long a time unnecessarily increases equipment size and energy consumption.
Combustion chamber
The combustion chamber is the “heart” of the DFTO (Flame-Dedicated Rotary Turbine). It typically employs a steel shell structure lined with refractory materials to withstand continuous high temperatures and thermal shock. The thermal oxidizer burner system, responsible for ignition and maintaining a stable flame temperature, is installed inside the combustion chamber. For high-concentration exhaust gases, when the calorific value of the exhaust gas itself is sufficient, the thermal oxidizer burner can automatically reduce or even shut off the auxiliary fuel supply, allowing the system to enter self-heating operation mode, significantly reducing operating costs.
Furthermore, the design of the combustion chamber must consider the uniformity of airflow distribution, avoiding “cold zones” or “short circuits,” ensuring that every portion of the exhaust gas undergoes a sufficient thermal oxidation process.
How Direct Fired Thermal Oxidizers Work in Petrochemical Facilities
In petrochemical production processes, refining units, storage tank areas, loading and unloading systems, and chemical reaction units continuously generate waste gases containing volatile organic compounds (VOCs). Direct emission of these waste gases without treatment not only causes environmental pollution but may also pose safety hazards and compliance risks.
Direct Fired Thermal Oxidizer (DFTO) uses high-temperature oxidation technology to decompose organic pollutants in waste gases into harmless substances, achieving stable and efficient VOC treatment. Its workflow typically includes the following steps:
1. Collection of VOC Exhaust Gas
VOC exhaust gas from process units, storage tank breather valves, loading systems, or other emission points is first collected centrally through a pipeline system. Depending on the characteristics of the exhaust gas, some systems are also equipped with filtration devices or pretreatment equipment to remove particulate matter, droplets, or other impurities that may affect equipment operation, ensuring the stability and reliability of subsequent treatment processes.
2. Exhaust Gas Enters the Thermal Oxidizer System
The collected exhaust gas enters the Direct Fired Thermal Oxidizer under the action of an induced draft fan. Before entering the combustion zone, the exhaust gas is evenly distributed according to the design flow rate to ensure that the subsequent high-temperature oxidation reaction can proceed fully. For high-concentration VOC exhaust gas, some organic components themselves have a high calorific value, which can provide some heat for system operation.
3. The burner heats the exhaust gas to the oxidation temperature.
The thermal oxidizer is equipped with an industrial burner that uses natural gas, liquefied petroleum gas, or other fuels as a heat source. The burner continuously provides heat, raising the exhaust gas temperature to the oxidation reaction range of 760°C to 1100°C. Within this temperature range, most organic pollutants can be rapidly decomposed. Simultaneously, the system automatically monitors the combustion chamber temperature to ensure the exhaust gas maintains a sufficient residence time at the set temperature, thereby achieving efficient treatment.
4. High-Temperature Oxidation of VOCs
When exhaust gas enters the combustion chamber, the VOCs within it undergo a high-temperature oxidation reaction with oxygen. Under sufficient oxygen and high temperature conditions, the complex organic molecular structure is completely destroyed, ultimately transforming into carbon dioxide and water vapor:
VOC + O₂ → CO₂ + H₂O + Heat
This process is similar to complete combustion, but its primary goal is to destroy pollutants rather than generate energy. After sufficient oxidation, the system can typically achieve a VOC destruction efficiency (DRE) of 95% to 99.99%.
5. Purified Gas Meets Emission Standards
After the oxidation reaction is complete, the purified gas leaves the combustion chamber. In some systems, the high-temperature flue gas can also recover some heat energy through a heat recovery device to improve overall energy efficiency. Subsequently, the treated gas is discharged into the atmosphere through a chimney. Since most VOCs have been converted into harmless substances, the emitted gas meets the requirements of relevant environmental regulations and emission standards.
Ruichang Direct Fired Thermal Oxidizer Solutions for Petrochemical Facilities
VOC treatment in the petrochemical industry often faces challenges such as complex waste gas composition, large concentration fluctuations, long continuous operation times, and stringent emission requirements. Therefore, waste gas treatment systems not only need to possess highly efficient pollutant destruction capabilities but must also ensure long-term stable operation and reasonable energy utilization efficiency.
Taking the specific operating conditions of different petrochemical projects, Ruichang offers customized Direct Fired Thermal Oxidizer (DFTO) solutions, which can be designed and equipment selected based on waste gas volume, VOC concentration, waste gas composition, and emission standards.
For medium- to high-concentration VOC emissions, the Ruichang Direct Fired Thermal Oxidizer employs high-temperature oxidation technology to convert organic pollutants into carbon dioxide and water vapor through complete combustion, achieving efficient VOC treatment and stable emission compliance. The system boasts a simple structure and reliable operation, making it particularly suitable for applications in oil refining units, chemical production units, tank farms, and loading/unloading facilities.
For projects involving large volumes of low-concentration VOC emissions, the system can also integrate an adsorption and concentration unit. This pre-treatment process, using adsorption and concentration technology to enrich low-concentration VOCs, allows the gas to be sent to the thermal oxidizer for high-temperature decomposition, effectively reducing fuel consumption, improving overall treatment efficiency, and lowering operating costs.
Furthermore, the Ruichang thermal oxidizer system utilizes an industrial-grade control system and reliable combustion technology, meeting the long-term continuous operation requirements of petrochemical enterprises and providing customers with safe, efficient, and environmentally compliant VOC treatment solutions.
