Regenerative Thermal Oxidizer Applications in the Petrochemical Industry
Regenerative Thermal Oxidizer (RTO) is currently one of the core technologies for VOCs waste gas treatment in the petrochemical industry. With its advantages of high efficiency, energy saving, and strong adaptability, it is widely used in various Organic Waste Gas Treatment applications. In response to the complex and variable waste gas compositions and increasingly stringent emission standards in the petrochemical industry, Regenerative Thermal Oxidizer technology can achieve ultra-low VOCs emissions and deep removal of characteristic pollutants through optimized design and process integration.
The petrochemical industry uses petroleum fractions, natural gas, and other raw materials to produce organic chemicals, synthetic resins, synthetic fibers, synthetic rubber, and other products. During petrochemical production processes, large amounts of VOCs waste gas are often generated. Organized emission sources generated during petrochemical production mainly include: PTA production unit tail gas, acrylonitrile production unit tail gas, rubber production unit tail gas, PO/SM production unit tail gas, heating furnace flue gas, waste gas incinerator flue gas, flare gas, etc.
To meet the requirements for ultra-low VOCs emissions and compliance with emissions of certain characteristic organic pollutants in the petrochemical industry, the following optimized combinations can effectively satisfy strict emission standards:
1. Optimized Design of Regenerative Thermal Oxidizer Equipment
To ensure high VOCs removal efficiency, the principle of “Three Ts and One O” must be satisfied.
The key to improving VOCs removal efficiency lies in the proper matching of residence time, combustion chamber temperature, turbulence intensity, and oxygen content, known as the “Three Ts and One O” principle. For rotary valve RTO systems, optimization should focus on residence time, combustion chamber temperature, and turbulence intensity to improve VOCs removal efficiency.
Based on experience and related technical data, when the residence time is ≥1.2 seconds, and the oxidation chamber temperature is 300°C higher than the highest ignition point temperature of the waste gas components, the oxidation chamber purification efficiency can exceed 99.5%.
Therefore, when designing the regenerative thermal oxidizer combustion chamber volume, the residence time should be ≥1.2 seconds, and the oxidation chamber temperature should be set at 300°C above the highest ignition point temperature among the combustible components. Meanwhile, through CFD simulation and optimization of the RTO's flow and temperature fields, the rotary valve's treatment capacity can be fully utilized, enabling RTO purification efficiency to exceed 99.5%.
The following are images of software simulation optimization:
a. Combustion chamber flow field optimization for efficient oxidation combustion
b. Regenerative chamber flow field and temperature optimization for sufficient waste gas preheating
2. Process Flow Design
>> 1. Tank Farm and Loading/Unloading Area Waste Gas
Characteristics of waste gas from tank farms and loading/unloading areas: the waste gas concentration is relatively high, while both the waste gas flow rate and concentration fluctuate significantly. If directly diluted with air, the resulting waste gas volume becomes excessively large after dilution.
Therefore, for waste gas from tank farms and loading/unloading areas, the process route of “low-temperature diesel washing + oxygen supplementation and air mixing + rotary valve RTO” or “low-temperature condensation + oxygen supplementation and air mixing + rotary valve RTO” is generally adopted to achieve compliant emissions.
A tank farm and loading/unloading area waste gas project of a Sinopec refining and chemical enterprise adopted the “low-temperature diesel washing + oxygen supplementation and air mixing + rotary valve RTO” process for treatment. After treatment, the exhaust gas achieved compliant emissions with NMHC ≤20 mg/m³.
>> 2. Large Air Volume Process Waste Gas
Waste gas from petrochemical process units is characterized by large air volume, high concentration, and the presence of characteristic pollutants. Due to the relatively high waste gas concentration and certain strictly controlled characteristic pollutants, it is generally difficult to achieve compliant emissions through a single treatment process. In particular, when additional dilution air is required for safety reasons, and oxygen content correction is involved, achieving compliance becomes even more difficult.
Therefore, for high-concentration waste gas, secondary incineration processes such as “flue gas recirculation + RTO reburning” or “RTO + RTO” are adopted to achieve compliant emissions of NMHC and characteristic pollutants.
① “Flue Gas Recirculation + RTO Reburning” Process
A PO/SM unit waste gas project of a PetroChina petrochemical enterprise adopted the “flue gas recirculation + RTO reburning” process to ensure compliant emissions with NMHC ≤20 mg/m³ after oxygen content correction.
② “RTO + RTO” Process
A synthetic resin plant waste gas project of a PetroChina petrochemical enterprise adopted the “RTO + RTO” process to achieve compliant emissions with NMHC ≤20 mg/m³ and meet the emission requirements for characteristic pollutants.
3. Conclusion
In summary, the application of RTO in the petrochemical industry is no longer limited to conventional VOCs reduction, but is developing toward higher efficiency, lower energy consumption, and coordinated control of multiple pollutants. For different waste gas sources and component characteristics, the reasonable selection of RTO design parameters and process combinations is the key to achieving ultra-low emissions.
Practical project experience has demonstrated that through refined simulation optimization and secondary incineration technologies, RTO can fully satisfy the increasingly stringent environmental protection requirements of the petrochemical industry, while also providing enterprises with a feasible balance between emission compliance and operational economy.