Application of Regenerative Thermal Oxidizer in PVC Paste Resin Industry
In the current field of industrial VOCs (waste gas) treatment, RTO (Regenerative Thermal Oxidizer), as a mature and highly efficient technology, has been widely applied across various industries. RTO decomposes organic waste gas into CO₂ and H₂O through high-temperature oxidation, featuring high treatment efficiency (≥99%), wide adaptability to operating conditions, and high thermal energy recovery efficiency. For the complex organic waste gas generated during the drying process of PVC paste resin, Regenerative Thermal Oxidizer technology can effectively compensate for the shortcomings of traditional processes in terms of treatment efficiency and emission compliance, and has become a key development direction in this industry.
PVC paste resin, with its excellent paste-forming and dispersion properties, is mainly used in the field of flexible PVC materials. It is suitable for coating, dipping, spraying, foaming, and other processing techniques. It is widely used in artificial leather, decorative materials, flooring, wallpaper, industrial conveyor belts, sports flooring, coatings, toys, disposable medical gloves, daily decorative items, electrical instruments, and electrical tools.
During the production process of PVC paste resin products, the drying and heating process generates waste gas. The main components of the waste gas include DOP, DOTP, and D60/D70 solvent oil. This portion of waste gas must be treated by environmental protection equipment to achieve compliant emissions in accordance with national or local environmental regulations. Under such conditions, the introduction of a Regenerative Thermal Oxidizer System can effectively improve the overall waste gas treatment efficiency and ensure stable compliance with emission standards.
I. Overall Technical Scheme for Waste Gas Treatment in PVC Paste Resin Drying (Combined with Regenerative Thermal Oxidizer Process);
1. Existing Waste Gas Treatment Process;
Existing waste gas treatment flow diagram
Currently, waste gas from PVC paste resin drying is treated using electrostatic recovery technology: the waste gas is first cooled, and then DOP, DOTP, and other plasticizers are captured and converted into liquid oil through electrostatic capture for recovery. Although this process can recover DOP, DOTP, and other plasticizers, it has the following disadvantages:
1) The electrostatic recovery device has low efficiency in treating DOP and DOTP. The waste gas contains D60/D70 solvent oil components, and electrostatic recovery cannot effectively capture these low-boiling, small-molecule solvent oils, resulting in non-compliant emissions. In this case, adding an RTO unit downstream can perform deep oxidation of uncaptured VOCs to ensure compliance.
2) The electrostatic recovery device cannot effectively remove odors, whereas RTO can significantly reduce odor through high-temperature decomposition of organic compounds.
3) The electrostatic recovery device requires periodic cleaning of the electric field cylinders. Wastewater is generated during the cleaning process, leading to secondary pollution and requiring further treatment. In contrast, the RTO system does not produce wastewater during operation, effectively avoiding secondary pollution.
2. Technical Route for Waste Gas Treatment in PVC Paste Resin Drying
In response to the problems existing in the current waste gas treatment process, the following technical routes are adopted: “electrostatic recovery + RTO deep treatment” or “pre-treatment + RTO main treatment” to achieve stable compliance and low energy consumption. The RTO system utilizes regenerative beds to recover heat, significantly reducing fuel consumption and improving overall system efficiency.
1) According to the actual concentration of waste gas from PVC paste resin drying, and considering the actual benefits of electrostatic recovery, it can be determined whether electrostatic recovery equipment is necessary.
2) Install a flame arrester at the RTO inlet to prevent flashback.
3) The waste gas enters the RTO and is oxidized and decomposed at a high temperature of about 800°C, converting DOP, DOTP, and solvent oils into carbon dioxide and water. At the same time, heat is released to sustain the RTO operation. The emissions are stable and compliant, and odors are effectively removed.
4) Considering that DOP and DOTP may exist in the form of fine suspended oil droplets in the waste gas, long-term operation of the RTO may cause these droplets to adhere to the bottom layer of the regenerative ceramic beds. A mixing chamber is installed at the RTO inlet, and high-temperature air from the combustion chamber is periodically used to preheat the waste gas. The preheated gas passes through the bottom regenerative beds, removing adhered oil and carrying it into the oxidation chamber for decomposition, effectively solving the problem of oil adhesion.
5) Since the waste gas contains oil mist, there is a risk of clogging the regenerative media in the RTO, which can lead to poor exhaust flow and reduced heat storage efficiency. The following measures are adopted: using large-pore ceramic regenerative media at the bottom of the RTO, optimizing the arrangement of regenerative media, and properly designing maintenance access ports.
3. Selection Factors for Treatment Equipment;
1. Selection of electrostatic recovery equipment;
Based on the actual concentration of waste gas from PVC paste resin drying and the economic benefits of electrostatic recovery, it can be determined whether electrostatic recovery equipment is required.
a) If the waste gas concentration is high, and after electrostatic recovery, the concentration can still meet the self-sustaining operation condition of the RTO (i.e., no natural gas consumption), or if the economic benefit of electrostatic recovery exceeds the natural gas consumption of the RTO, it is recommended to retain (or add) electrostatic recovery equipment;
b) If the waste gas concentration is low, the waste gas can be directly treated by the RTO to achieve compliant emissions.
1. Selection of downstream treatment equipment;
The mainstream downstream treatment technologies are RCO and RTO. Since the composition of PVC paste resin is not a single solvent and includes complex components such as fast-drying agents, leveling agents, viscosity reducers, and defoamers, catalyst poisoning and deactivation are likely to occur. In addition, the investment cost of large-air-volume RCO is high, and the catalyst lifespan is generally only 8,000–100,000 hours, making replacement costs high. Therefore, RTO is selected as the downstream treatment method.
4. Emission Control Targets:
Post-treatment VOCs concentration: ≤30 mg/m³, meeting local environmental standards;
Odor removal efficiency: 99%;
| Pollutant | Emission Limit (mg/m³) | Rate Limit (kg/h) | Target Rate (kg/h) |
|---|---|---|---|
| VOCs (national standard) | ≤120 | - | - |
| After rotary RTO treatment | ≤50 | - | - |
II. Energy Consumption Analysis
1. Self-sustaining Operation Heat of Rotary RTO
Self-sustaining operation of RTO means that all the heat required for operation is provided by the heat released from waste gas decomposition, without consuming natural gas.
Rotary RTO self-sustaining heat table
| RTO Air Volume | Heat Required for Self-operation |
|---|---|
| 10000 m³/h | 120,000 kcal |
| 20000 m³/h | 240,000 kcal |
| 30000 m³/h | 360,000 kcal |
| 40000 m³/h | 480,000 kcal |
| 50000 m³/h | 600,000 kcal |
| 60000 m³/h | 720,000 kcal |
| 70000 m³/h | 840,000 kcal |
2. Energy Consumption Analysis
The comprehensive calorific value of DOP, DOTP, and D80 in PVC paste resin drying waste gas is similar to that of kerosene. Based on a calorific value of 10,000 kcal/m³, when the waste gas concentration reaches 1200 mg/m³, the RTO can operate in a self-sustaining mode without consuming natural gas.
Solvent mass required for RTO self-operation
| RTO Air Volume (m³/h) | 10000 | 20000 | 30000 | 40000 | 50000 | 60000 | 70000 |
|---|---|---|---|---|---|---|---|
| Solvent Mass (kg/h) | ≥12 | ≥24 | ≥36 | ≥48 | ≥60 | ≥72 | ≥84 |
From the above analysis, when the waste gas concentration reaches 1200 mg/m³, the RTO can operate in a self-sustaining mode; when the concentration is lower than 1200 mg/m³, a small amount of natural gas is required. The recovery efficiency of the electrostatic recovery device can be adjusted according to the actual waste gas concentration to achieve optimal energy-saving operation.
For example, if the waste gas concentration generated from the PVC paste resin drying process is 2000 mg/m³, the recovery efficiency of the electrostatic recovery device can be adjusted so that the outlet concentration becomes 1200 mg/m³. In this case, the RTO can operate without natural gas consumption, while the front-end can recover solvents for economic benefits, achieving optimal system performance.
III. Social Benefits
Using a rotary RTO system to treat waste gas generated during PVC paste resin production can achieve the following:
1. Non-methane total hydrocarbons emission ≤30 mg/m³, meeting national and local standards;
2. Odor in the waste gas can be completely removed.
3. For processes without electrostatic recovery and using only RTO, no wastewater or solid waste is generated during treatment, avoiding secondary pollution.