Three tower RTO

Introduction to the principle of VOCs oxidation, combustion and decomposition

The oxidation combustion of VOCs is essentially an exothermic oxidation reaction, and the reaction formula can be expressed as:

C ₙ H ₘ O ₚ+(n+m/4-p/2) O ₂ ¡ú nCO ₂+(m/2) H ₂ O+heat (where C ₙ H ₘ O ₚ represents the chemical formula of VOCs, and n, m, and p are the number of carbon, hydrogen, and oxygen atoms, respectively)

Reaction conditions: Sufficient temperature (usually 300-1200 ¡æ, depending on the type of VOCs), sufficient oxygen (air excess coefficient generally 1.1-1.3), sufficient residence time (to ensure complete reaction), and good mixing (to allow VOCs to fully contact with oxygen) are required.

Key feature: The reaction releases a large amount of heat, and if the concentration of VOCs is high (such as over 2000ppm), self-sustaining combustion can be achieved through heat recovery

Introduction to Process Flow

Three tower RTO workflow (periodic cycle)

The three tower RTO achieves continuous operation through the "intake oxidation exhaust purge" cycle of three towers. During each cycle (about 1-3 minutes), the three towers are in different states. The specific process is as follows:

Phase One:

1. Tower 1 (intake tower): The exhaust gas to be treated enters Tower 1 and is preheated by the heat storage body to a temperature close to the combustion chamber temperature (about 700-800 ¡æ), and then enters the combustion chamber.

2. Combustion chamber: The preheated exhaust gas is oxidized and decomposed at high temperatures (VOCs ¡ú CO ₂+H ₂ O), releasing heat and maintaining the temperature of the combustion chamber.

3. Tower 2 (Exhaust Tower): The oxidized high-temperature purified gas enters Tower 2 and transfers heat to the heat storage body (heat storage) of Tower 2. After cooling to 100-150 ¡æ, it is discharged through the chimney.

4. Tower 3 (Blowing Tower): A small amount of purified gas (or fresh air) is blown back into Tower 3 to push the residual untreated exhaust gas into the combustion chamber for further oxidation, avoiding "escape emissions" during switching.

Second stage (after valve switching):

Tower 2 is converted into an intake tower, Tower 3 is converted into an exhaust tower, and Tower 1 is converted into a purge tower. Repeat the above process.

Phase Three (Switching Again):

Tower 3 is converted into an intake tower, Tower 1 is converted into an exhaust tower, and Tower 2 is converted into a blowing tower.

Through the three tower cycle, the equipment can achieve continuous air intake (without shutdown switching gap), avoiding the problem of direct exhaust gas emissions during single tower/double tower RTO switching.

Characteristics of System Device

Compared to single tower and double tower RTOs, the three tower RTO has significant advantages:

High processing efficiency: The removal rate of VOCs can reach over 99%, far exceeding environmental emission standards (such as China's "Unorganized Emission Control Standards for Volatile Organic Compounds").

Continuous and stable operation: Three tower cycles switch to achieve uninterrupted "intake exhaust", suitable for high air volume exhaust gas (usually processing 10000-100000 m ³/h).

High heat recovery rate: The thermal storage body fully recovers heat, with a heat recovery rate of ¡Ý 95%. Only a small amount of fuel (such as natural gas) needs to be supplemented to maintain the combustion chamber temperature, resulting in low operating costs.

Strong adaptability: It can handle medium to high concentrations (500-5000 mg/m ³) and multi-component VOCs (such as benzene derivatives, esters, ketones, etc.), and has good tolerance to fluctuations in exhaust gas concentration and flow rate.

Economic analysis of operational cases

A pharmaceutical factory in Jiangxi Province emits a large amount of organic waste gas during the production process. The data is as follows:

This device directly uses a three tower RTO for oxidation and decomposition treatment, and the exhaust gas is discharged after reaching the standard.

Operating cost analysis

The operating costs of RTO mainly include three aspects: cold start preheating stage, hot start preheating stage, and normal operation stage. As your company's normal production time is 8hr/day continuous production, which involves hot start preheating, this plan considers cold start, hot start preheating, and normal operation stages, including electricity and natural gas costs;

1. Cold start preheating stage

The cold start preheating stage is the stage when the RTO equipment is shut down and the furnace temperature is ignited from room temperature to working temperature. The electricity and natural gas costs required for one cold start are shown in the table below:

Overall, a cost of 398.8 yuan is required for each cold start.

2. Normal operation phase

After the RTO has been heated to its operating temperature, it requires 280000 kcal/hr of heat to maintain self operation. The specific energy consumption is shown in the table below:

Note: The following data for natural gas is calculated without additional ignition.

3. Annual total operating expenses

On site case presentation