Three Major Stages of Energy-Saving Temperature Control in RTO Furnace

Temperature control plays a crucial role throughout the operation of a rotary RTO - Regenerative Thermal Oxidizer, interlocking with other system actuators (such as various fans, proportional regulating valves, and air dampers) to ensure stable and reliable operation. Stable temperature control helps maintain exhaust gas treatment efficiency at over 99%, achieving the goal of reducing energy consumption and delivering economic benefits to enterprises.

Through multiple heating tests on ceramic tiles, the author has summarized an optimized energy-saving temperature control curve for RTO furnace heating. During the heating phase, the heat source primarily comes from the burner located at the top of the furnace. The burner is equipped with an ignition controller, whose primary function is to manage the ignition process. The burner control cabinet also features two temperature controllers with 485 communication functionality, which continuously monitor the furnace temperature in real-time. One controller adjusts the burner's proportional valve in real-time based on the set temperature sent by the PLC, enabling control over both large and small flames. The other serves as a high-temperature alarm and a backup temperature detection system. Users only need to set the heating curve on the touchscreen, and the PLC controller will automatically regulate the temperature in real time.

RTO temperature control can generally be divided into three stages:

1. Heating Phase (No Exhaust Gas Intake)

During heating, once the PLC receives the heating signal, it sequentially:

• Opens the fresh air valve at the main fan inlet.
• Closes the exhaust gas intake valve.
• Closes the emergency exhaust valve and heat exchange valve.
• Activates the rotary valve (40 Hz).
• Starts the combustion air fan, purge fan, and main fan (15 Hz fixed frequency).

After a 3-minute purge, the burner ignites. Upon successful ignition, the system enters the heating phase. The temperature controller continuously receives the real-time set temperature from the PLC, compares it with the current temperature, and performs PID adjustments on the proportional valve to regulate flame size. During this phase, the ceramic regenerative tiles gradually heat up, storing thermal energy.

2. Production Phase (Exhaust Gas Intake)

When the furnace temperature reaches the preset waste gas intake temperature (typically 800°C), the fresh air valve closes, and the waste gas intake valve opens. Once waste gas is introduced, the system automatically adjusts based on the negative pressure value (usually -100 to -150 Pa) set by the front-end pressure gauge, maintaining a stable micro-negative pressure state.

Different exhaust gas concentrations lead to different operational states:

• Non-self-balancing state: The control system automatically adjusts the burner's proportional valve based on furnace temperature, optimizing energy efficiency with a small flame.
• Excess heat generation: If the combustion of organic waste gas produces surplus heat, and the furnace temperature continues to rise even after supplying heat back to the production line, the burner’s proportional valve minimizes the flame before shutting off. The system continuously monitors the furnace temperature, keeping it between 800°C and 820°C. If the temperature exceeds 820°C, the burner shuts off, and the system operates without active heating.

The furnace is divided into 12 sectors, further categorized into four functional zones (see diagram):

1. Purge Zone
2. Heating Zone
3. Cooling Zone
4. Dead Zone

Vertically, the furnace consists of five chambers (see diagram):

1. Combustion Chamber
2. Heat Exchange Chamber
3. Diversion Chamber
4. Inlet/Outlet Chamber
5. Purge Chamber

Waste gas first enters the heating zone, then passes through the diversion chamber, heat exchange chamber, and combustion chamber, where it undergoes high-temperature combustion. The treated gas then moves through the cooling zone, passing again through the heat exchange chamber, diversion chamber, and inlet/outlet chamber before being discharged via the chimney.

During the heating phase, the heat generated by oxidation is stored in the ceramic tiles. When exhaust gas flows upward through the heating zone, its temperature rises sharply. After combustion, the treated gas flows downward through the cooling zone, transferring heat back to the ceramic tiles for the next cycle before being emitted.

High-Temperature Alarm Handling (Typically 880°C):

• The system alerts the user.
• The emergency exhaust valve enters PID adjustment mode.
• The PLC compares the real-time temperature with the set value and adjusts the valve opening via a 4–20 mA signal to maintain normal operating temperature.
• If the temperature drops below 870°C, the PID adjustment stops, and the emergency exhaust valve closes.

Waste Gas Shutdown (Typically 900°C):

If the temperature continues to rise despite the emergency exhaust valve being fully open, reaching 900°C, the system switches to fresh air intake for cooling.

3. Cooling Phase (No Waste Gas Intake)

Upon receiving the shutdown signal, the system:

• Opens the emergency exhaust valve.
• Closes the waste gas intake valve.
• Opens the fresh air valve for cooling.
• Once the temperature drops below the set value, the main fan, purge fan, and combustion air fan are turned off.