Research on common safety protection technology of RTO equipment

Abstract: Thermal destruction method is the most commonly used technology for the treatment of industrial organic waste gas (VOCs). Its key equipment is regenerative thermal oxidizer (RTO). After more than ten years of development in China, RTO equipment technology has developed from the early "2-beds RTO" to the second-generation technology "3-beds RTO". In recent years, domestic RTO production plants have successfully achieved technological breakthroughs, and developed a "rotary RTO" with 12 champers and third-generation technology. Due to the linkage work of various systems of RTO equipment, complex control, and high temperature equipment, the safety of RTO equipment has become one of the most concerned issues for users to select and use.

Common safety protection measures for RTO equipment furnace body

（1）The natural gas heating system of RTO equipment adopts internationally famous brand burners and valve groups, and the selected devices must meet international safety standards. Flame detectors are required for flame flameout safety protection, which can quickly turn off the gas when the flame flameout, and the ignition pipeline must adopt double solenoid valves for ignition; The common safety protection of combustion engine system also includes: gas undervoltage protection, gas overpressure protection, gas pressure gauge, counter fire check valve, gas filter, etc; Safety control functions include the following:

1) Fault signal feedback system for successful ignition, ignition failure, etc

2) Natural gas proportion adjustment

3) Natural gas cannot be opened due to insufficient air pressure and high air pressure of combustion supporting fan

4) Automatic alarm for low gas pressure

5) Automatic alarm for high gas pressure

6) Automatic alarm for gas leakage

7) Automatic alarm for flameout of combustion machine.

（2）In the startup procedure of RTO equipment system, a furnace purging process shall be designed before ignition. The furnace purging process is used to clean the residual organic waste gas and fuel in the furnace to avoid explosion during ignition. The furnace purging process shall not be less than 180 seconds;

（3）A high-temperature bypass valve should be set between the furnace and the chimney. The high-temperature bypass valve must be a pneumatic normally open valve with power-off. When the temperature is too high, the high-temperature bypass valve will automatically open to release too much heat, and when the power-off is abnormal, the high-temperature bypass valve will also automatically open to protect the furnace.

（4）A fresh air valve is set at the exhaust gas inlet. When the temperature is too high and over temperature, it will automatically open in linkage with the high-temperature bypass valve to cool down through fresh air.

（5）The system shall be equipped with an emergency discharge valve at the exhaust gas inlet, which can be discharged in case of RTO failure or maintenance shutdown.

（6）A differential pressure transmitter is set at the inlet and outlet of the furnace, which is used to observe the working condition of the heat storage ceramics and detect whether the heat storage ceramics are blocked or damaged. The differential pressure gauge is interlocked with the main fan.

（7）The system is equipped with an audible and visual alarm device, and a DC24V output interface is reserved. The customer can increase the alarm display point according to the actual situation. The main control screen will always display the operation status of the system. If there is a fault, it will automatically record the alarm information in the main control screen, which is convenient for troubleshooting in time.

（8）The system is equipped with a safety emergency stop button. When a dangerous situation occurs in the RTO area, shooting the emergency stop can avoid greater losses.

（9）The RTO system is equipped with an explosion relief port before the exhaust gas enters the furnace, which can release high pressure and reduce losses when the set safety pressure is exceeded.

（10）LEL concentration detector controls the exhaust gas concentration at the inlet of RTO system not to exceed 25% of the lower explosive limit of combustible gas components; LEL concentration detector is installed at a sufficient distance from the front of the system. The detector is linked with the exhaust valve, fresh air valve, emergency discharge valve and high temperature bypass valve to safely treat the waste gas.

（11）Safety design of furnace body: the arrangement of heat storage ceramics is closely staggered; The temperature field is evenly distributed; The insulation structure is tight, and the heat does not leak out; The combustion chamber and regenerator are closely connected without air leakage.

（12）The exhaust gas distribution channel is optimized by hydrodynamic finite element method, with small wind resistance and uniform flow distribution.

（13）Under abnormal conditions, if the RTO or fan is abnormal, resulting in a sharp increase in pressure, the bursting disc will automatically deflate. The pressure relief safety device composed of bursting discs and other assemblies will act immediately to release the pressure when the pressure difference on both sides of the bursting disc reaches the value under the predetermined temperature.

（14）The system platform pedal adopts non-slip galvanized steel grating, and the platform is permanently free of ponding, which can effectively prevent the danger caused by skidding in rainy and snowy days.

Common safety protection measures for RTO electrical system

（1）The system installation has the functions of overload protection, grounding protection, power lightning protection, etc

（2）RTO system adopts PLC automatic control, with overtemperature alarm and pressure interlock protection functions.

（3）Short circuit protection: in case of phase to phase short circuit fault of the stator winding and its outgoing line of the motor, it is equipped with current quick break protection.

（4）Phase failure protection, three-phase AC motors in continuous operation are equipped with phase failure protection devices.

（5）The control interlock control includes: the temperature of thermal oxidation chamber and burner interlock control, the temperature of thermal oxidation chamber and induced draft fan interlock control, valve fault interlock protection, component power-off reset protection, etc

（6）After the exhaust gas is connected, the host automatically realizes PID adjustment according to the negative pressure value (generally negative 100~150pa) set by the front-end wind pressure meter to ensure that it is in a constant micro negative pressure state. The pressure transmitter is interlocked with the main fan to automatically adjust the rating of the main fan.

（7）Two temperature control meters with 485 communication function are also installed on the combustion machine control cabinet to collect the furnace temperature in real time. One of the temperature control meters adjusts the ratio regulating valve of the combustion machine according to the set temperature sent by PLC in real time, so as to realize the control of large and small fires. Another temperature control meter is used for high temperature alarm control and standby temperature detection.

（8）Alarm: when and where the alarm occurs in the system, it will be displayed on the touch screen to facilitate the timely troubleshooting of system faults.

（9）Main fan failure: RTO will be shut down automatically in case of main fan failure.

（10）Temperature control: set double thermocouples in the combustion chamber. Set the three-level alarm point (the alarm value is adjustable). When the temperature in the furnace rises and exceeds the alarm prompt of the first level alarm point, and reaches the set value of the second level alarm point, the high-temperature bypass valve will be opened to discharge the excess temperature; When RTO temperature exceeds the set value of level III alarm point, close the exhaust valve, fully open the emergency discharge valve and fresh air valve, so that RTO equipment can be completely cooled by fresh air.

System safety management measures

In order to ensure the safe operation of RTO processing system, the daily management and maintenance of the system are very important. The main measures are as follows:

1) RTO processing system should be an important part of production equipment, and special personnel are required to be responsible for the operation, patrol, recording, maintenance and other work of the processing system. And implement safety responsibility and responsibility management.

2) Operators must operate according to the operating procedures. New employees must be trained in safety education and operation methods. Those who have not received qualified training in safety technology and operation methods are strictly forbidden to operate alone.

3) Regular safety inspection. Safety inspection is an important way to find dangerous sources and an important method to eliminate hidden dangers of accidents, prevent accident injuries and improve working conditions.

4) Operation standardization. Standardizing the behavior of operators according to scientific operation standards is an effective measure to control people's unsafe behavior and prevent safety accidents.

Therefore, the system is equipped with multiple safety protection measures and safety operation specifications from the aspects of process, equipment, management and control. The operation according to the regulations can fully ensure the safe operation of RTO waste gas incineration treatment system.