Author:Michael Chen, Senior Regenerative Thermal Oxidizer Combustion Systems Engineer

A Comprehensive Guide to Regenerative Thermal Oxidizer Combustion Systems: Principles, Operation, and Safety

Table of Contents

1. System Overview

   • 1.1 Introduction to the Regenerative Thermal Oxidizer Combustion System

   • 1.2 Combustion Air Pipeline and Valve Train

   • 1.3 Fuel Gas Pipeline and Valve Train

   • 1.4 Working Principle of the Regenerative Thermal Oxidizer Combustion System

2. Pre-Operation: Verifying Site Conditions

3. Pre-Startup Inspection Checklist

4. Burner Trial Operation

5. Regenerative Thermal Oxidizer Combustion System Shutdown Procedure

6. Post-Operation and Handover

7. Troubleshooting Common Issues During Trial Runs

8. Equipment Inspection, Maintenance, and Precautions

9. Critical Safety Precautions

1. System Overview

In a Regenerative Thermal Oxidizer (RTO) system, the burner is essentially a specialized industrial combustor. It serves as the core heat supply equipment, responsible for igniting the waste gas and maintaining the temperature conditions required for its "auto-ignition." Modern burners are critical execution components for safe, stable, and automated Regenerative Thermal Oxidizer operation, typically integrating functions such as ignition, flame monitoring, and fuel gas/air ratio control.

1.1 Introduction to the Regenerative Thermal Oxidizer Combustion System

The combustion system of this Regenerative Thermal Oxidizer Unit consists of the following main components:

• Combustion air piping and valve train

• Fuel gas piping and valve train

• Burner

• Electrical control panel

1.2 Combustion Air Pipeline and Valve Train

The combustion air fan connects to the air pipe via a flexible connection and a reserved flange. The pipeline is arranged linearly. According to the gas flow direction, the valve train includes the following equipment:

1.3 Fuel Gas Pipeline and Valve Train

The gas pipe inlet connects to the plant's gas network. According to the gas flow direction, the valve train includes the following equipment:

1.4 Working Principle of the Regenerative Thermal Oxidizer Combustion System

1. Pre-Start Checks: The combustion air fan starts. The main gas valve is opened. The system verifies that air pressure and gas pressure are normal.

2. Purge & Safety Check: A pre-ignition purge is completed. Pressure interlocks and safety interlocks are confirmed to be satisfied.

3. Ignition Sequence: The controller executes the ignition program:

   • The spark plug discharges.

   • The pilot gas solenoid valve opens.

   • Upon flame detection by the UV sensor, the main gas solenoid valve opens.

4. Flame Establishment: After successful main flame ignition (typically a 6-second delay), the pilot gas valve closes, and the spark plug stops discharging.

5. Temperature Control: The system receives signals from thermocouples and modulates the opening of the gas and combustion air valves accordingly. This adjusts the burner's firing rate to meet the temperature control requirements.

6. Safety Lockout: If ignition fails, the burner controller automatically locks out. It de-energizes the ignition transformer and gas solenoid valves. The system must be manually reset before attempting another ignition cycle. If ignition fails after five consecutive attempts, the burner must be taken out of service for troubleshooting.

2. Pre-Operation: Verifying Site Conditions

Before commencing any work, ensure the following site conditions are met:

• Gas Pressure: Verify the on-site gas pressure. Generally, this should be between 30 kPa and 80 kPa. If a high-pressure regulator is installed, the inlet pressure can be higher, provided it is within the regulator's pressure rating.

• Combustion Air Fan: Check the fan nameplate parameters. Ensure the flow rate and pressure are compatible with the burner being commissioned.

3. Pre-Startup Inspection Checklist

Before ignition, the commissioning engineer must perform several checks in coordination with the electrical and instrumentation (E&I) technicians.

• Gas Piping Inspection:

  • Visually inspect piping for damage and ensure it is clean.

  • Check that all valves are in the correct open/closed position.

  • Inspect all connections, flanges, and joints for leaks (use leak detection fluid or a gas sniffer; ensure no smell of gas).

  • Ensure no hot work or open flames are present near the furnace; if unavoidable, implement strict isolation measures.

• Gas Supply Verification:

  • Confirm gas pressure is normal (Main burner: 6–9 kPa; Pilot: 4–6 kPa).

  • Slowly open the main shut-off valve upstream of the pressure regulator to prevent pressure shock.

  • Vent air from the line using the vent valve at the end of the gas train for 1-2 minutes to ensure no air-gas mixture remains. Extend this time if the system is new or has been unused for a long period.

• Burner & Electrical Check:

  • Visually inspect the burner for damage. Ensure the burner head is properly installed and adjusted.

  • Verify all external electrical connections. Warning: High-voltage cables for the ignition transformer must not be run inside metal conduit, as this can disrupt the discharge.

  • Power up the burner control panel. Ensure the program controller is securely connected.

  • Check the temperature controller for correct alarm parameter settings. Verify that interlocks (e.g., Furnace Overtemp, Low Air Pressure, Low Gas Pressure, High Gas Pressure) are active.

• Cold Simulation Test:

  • Perform a cold sequence test (requires E&I cooperation).

  • Observe the program logic to ensure the control sequence is correct.

  • Verify the operation of all components, including the flame detector.

  • Note: During this test, the manual gas inlet valve must be closed, and the ignition transformer must be de-energized.

• Control Panel Wiring Check:

  • Verify panel wiring against the electrical schematic.

  • Use a multimeter to check for shorts between L-N and L/N to ground.

  • Confirm correct wiring of remote dry contact signals.

  • Confirm the power supply voltage is 220V.

  • Check local/remote signal communication (without power).

• Valve Train Adjustments:

  • Ignition Electrode: Check the ignition electrode for blockages, install it, and connect the high-voltage cable to the spark plug.

  • Flame Detector: Check the flame detector port for blockages and install the UV sensor.

  • Air Adjustments: Adjust the combustion air ratio valve and verify that the air pressure changes accordingly. Fine-tune the position based on the flame condition after ignition and temperature requirements.

  • Low-Fire Switch Setting: Using a multimeter, adjust the low-fire position of the actuator. Turn the red gear counter-clockwise until the circuit closes (multimeter beeps or relay energizes). Then, turn it back two more clicks to ensure the low-fire signal is reliably engaged and not prone to drifting out of position.

  • Gas Purging: After confirming the gas pressure from the customer's supply, slowly open the main gas ball valve to prevent pressure shock. Completely open it afterwards. Purge air from the installed piping by opening the vent port on the main valve until the smell of gas is detected. Repeat this process for the pilot line.

4. Burner Trial Operation

1. Initial Checks: Start the main (or circulation) fan. Re-confirm gas supply and power. Ensure the burner's modulating butterfly valve is in its initial (closed or low-fire) position.

2. Startup: With the actuator in the initial position, start the burner. In remote mode, initiate the start command. The burner controller will begin its start-up sequence.

3. Post-Ignition: After successful ignition, the burner's output power will be automatically controlled by the PLC's PID loop.

4. Flame Adjustment:

   • Initially, set the burner load to low fire and observe the flame.

   • Manually switch to high fire and observe the flame again.

   • Adjust the manual valves or air shutters as needed to achieve optimal combustion (a stable blue flame). Adjustments must be gradual. Once finalized, these settings should not be altered by unauthorized personnel.                                                           

5. Regenerative Thermal Oxidizer Combustion System Shutdown Procedure

To perform a normal shutdown:

1. Press the stop button on the control panel.

2. The system will enter the stop state, and the gas solenoid valves will close immediately.

6. Post-Operation and Handover

After the entire program sequence has stopped:

1. Close the main manual gas inlet valve.

2. Disconnect the power supply.

3. For long-term shutdowns, close the main gas supply valve and consider depressurizing the line.

7. Troubleshooting Common Issues During Trial Runs

8. Equipment Inspection, Maintenance, and Precautions

• Daily/Shift Inspection:

  • Normal equipment operation, no unusual noise or vibration.

  • Stable burner flame.

  • Electrical component temperature normal (<60°C), no burning smell.

  • Stable temperature, no alarm lights.

  • Stable gas and air pressure, no gas odor in the vicinity of the piping.

• Maintenance Schedule:

  • Clean external surfaces regularly. Ensure the area is well-ventilated.

  • Periodically operate manual valves to ensure they remain functional.

  • Regularly check the piping system for leaks.

  • Periodically inspect electrical equipment and wiring.

9. Critical Safety Precautions

1. If the burner fails to ignite after three consecutive attempts, immediately shut down the system. Troubleshoot the gas supply, electrical connections, and other factors. Only restart after resolving the fault.

2. Strictly prohibit striking the gas pipeline with tools or metal objects to avoid sparks.

3. Strictly prohibit smoking, welding, cutting, or any other hot work on or near the gas valve train or piping.

4. Never perform any open flame tests near the piping, valves, or regulators.

5. Always use a low-pressure gauge to test for the presence of fuel in the line.

6. Even after venting, residual gas or vapor can remain in the pipe walls. Any spark or flame can cause combustion or explosion. Do not perform any hot work without first thoroughly purging and isolating the line.

7. Before disassembling any part of the gas train for repair, always close the main upstream valveand vent the gas from the isolated section.

8. Prohibit the use of non-explosion-proof electrical or pneumatic tools in the hazardous area.

9. Prohibit manually forcing any component or sequence to run outside of the automated control program.