1 Overview

The RTO type regenerative thermal combustion furnace is an efficient, energy-saving, and environmentally friendly device for treating medium to low concentration volatile organic gases; This device mainly utilizes efficient heat storage materials and stores the waste heat from combustion waste gas in the heat storage material through program switching of exhaust gas flow. It is used for preheating the incoming exhaust gas in the next stage, increasing the inlet temperature of the exhaust gas, and recovering the waste heat. The average temperature difference between the inlet and outlet exhaust gases is 30-50 ℃, and the waste heat recovery efficiency can reach over 95%, with low operating energy consumption.

2 Equipment Working Principle

The schematic diagram of RTO combustion furnace is as follows:

The working principle of the regenerative high-temperature purification equipment RTO is to heat the organic waste gas to around 750-800 ℃, causing the VOC in the waste gas to oxidize and decompose into harmless CO2 and H2O; The heat of the high-temperature gas during oxidation is "stored" by the heat storage body for preheating the newly entered organic waste gas, thereby saving fuel consumption required for heating and reducing operating costs.

The organic waste gas to be treated enters the ceramic medium layer of the heat storage chamber 1 through an induced draft fan (which "stores" the heat from the previous cycle). The ceramic releases heat and the temperature decreases, while the organic waste gas absorbs heat and the temperature increases. After leaving the heat storage chamber, the waste gas enters the oxidation chamber at a higher temperature. At this time, the temperature of the waste gas depends on the volume of the ceramic body, the flow rate of the waste gas, and the geometric structure of the ceramic body.

In the oxidation chamber, the organic waste gas is then combusted by a burner and heated to the set oxidation temperature. Decompose the organic matter into carbon dioxide and water. Due to the preheating of the exhaust gas in the heat storage chamber, the fuel consumption of the burner has been greatly reduced. The oxidation chamber has two functions: one is to ensure that the exhaust gas can reach the set oxidation temperature, and the other is to ensure that there is sufficient residence time to fully oxidize the VOC in the exhaust gas. The design residence time of this project is greater than 1.0 second.

The exhaust gas flows through the heat storage chamber A and enters the oxidation chamber for incineration after heating up. It becomes a purified high-temperature gas and leaves the oxidation chamber before entering the heat storage chamber B (which has been cooled in the previous cycle), releasing heat. After cooling down, it is discharged, while the heat storage chamber B absorbs a large amount of heat and then heats up (used for heating the exhaust gas in the next cycle). After treatment, the gas leaves the heat storage chamber B and is discharged into the atmosphere through an induced draft fan.

After the cycle is completed, the inlet and outlet valves undergo a switch to enter the next cycle. The exhaust gas enters from regenerative chamber B and is discharged from regenerative chamber A. Before switching, the purified gas is purged through the reverse blowing chamber to clean the residual organic matter in the pipeline and indoor heat storage chamber A. This can increase the purification rate of the exhaust gas, reaching over 96%,alternating.

On the inlet pipeline of the exhaust gas source, set up a three-way valve and install one pneumatic valve each. When the processing equipment stops or malfunctions, the direct discharge valve is in a normally open state. During work, instructions are issued from the production site or the main control room to start the purification equipment, close the direct discharge valve, and open the air inlet valve.

The processing device is equipped with temperature detection components, fan air pressure detection, furnace pressure control, and other devices to ensure the normal and safe operation of the equipment.

3 Process of regenerative incineration system

Driving phase

Close the exhaust gas inlet valve and the back blowing valve, open the exhaust gas discharge valve in sequence, and the burner will automatically ignite. Heat each of the three heat storage chambers one by one to the operating state.

Normal operation phase

The exhaust gas first enters the regenerative chamber A and is preheated to around 750 ℃. The preheated exhaust gas enters the combustion chamber for combustion. Under the action of combustion supporting fuel, the organic matter contained in the exhaust gas is fully decomposed and burned, maintaining the combustion temperature at around 800 ℃. The generated exhaust gas enters the regenerative chamber C and releases heat. The flue gas after heat release is discharged into the atmosphere through the chimney through the smoke exhaust pipeline. Extract a portion of the flue gas through a reverse blower to the regenerative chamber B for purging, and eliminate residual exhaust gas in the regenerative chamber B. After the switching time is reached, open the exhaust gas valve of regenerative chamber B through the automatic control device, close the exhaust gas inlet valve of regenerative chamber A, open the exhaust gas blowing valve of regenerative chamber A, and after a certain period of time, close the exhaust gas blowing valve of regenerative chamber A.

Within one operating cycle, the status of each valve is shown in the table below:

 A：Regenerator chamber A         B：Regenerator chamber B      C：Regenerator chamber C

RTO (Regenerative Thermal Oxidizer, abbreviated as RTO), also known as Regenerative incinerator. This technology has been introduced from abroad and has been improved multiple times by our company's scientific and technological innovation personnel on the basis of digestion and absorption, making it more perfect. The basic principle is to oxidize organic waste gas to generate CO2 and H2O at high temperatures (≥ 750 ℃), thereby purifying the waste gas and recovering the heat released during decomposition, in order to achieve the dual purpose of environmental protection and energy conservation. It is an energy-saving and environmentally friendly device used for treating medium to high concentration volatile organic waste gas.

The main structure of RTO consists of a combustion chamber, a ceramic packing bed, and a switching valve. The regenerative ceramic packed bed heat exchanger in this device can maximize the recovery of thermal energy, with a heat recovery rate of over 95%. It does not require or uses very little fuel when processing VOC. If dealing with low concentration waste gas, concentration devices can be installed to reduce combustion consumption. Low operating costs and ultra-low fuel costs. When the concentration of organic waste gas is above 2000PPM, the RTO device basically does not need to add auxiliary fuel. The purification rate is high, usually above 98%. It can achieve fully automated control, with simple operation, stable operation, and high safety and reliability. There is no pulse phenomenon caused by pressure changes.

The temperature in the heat storage room is evenly graded and increased, which strengthens the heat transfer inside the furnace, improves the heat exchange effect, reduces the furnace volume, and reduces the cost of equipment. Adopting staged combustion technology to release heat energy under delayed combustion; The furnace is evenly heated, with low burning loss and good heating effect. There is no local high temperature and high oxygen zone that appears in the traditional combustion process, which inhibits the generation of thermal nitrogen oxides (NOX) and has no secondary pollution. Inert alumina ceramic balls are installed at the exhaust gas inlet to protect, buffer, and filter the thermal storage ceramic, extending its service life.

When the owner stops production, the RTO regenerative chamber combustion system closes the inlet and outlet valves through the PLC control system. The RTO system is in a self insulation state, and the temperature of the RTO itself is controlled at around 750 degrees Celsius through the PLC control combustion system.

4 Equipment Structure Description

（1）Oxidation chamber

The function of the oxidation chamber is to further thoroughly oxidize and decompose the waste gas treated by the regenerative chamber, resulting in an oxidation temperature of around 800 ℃. The oxidation chamber is the highest temperature part of the entire chamber, used for heating and oxidizing decomposition of exhaust gas. The shell material is carbon steel plate, with reinforcing ribs on the outer surface and a refractory insulation layer inside; The shell is well sealed, equipped with inspection doors, temperature detection, and pressure detection. The external temperature of the furnace body is ≤ ambient temperature+30 ℃.

（2）Regenerative chamber

The function of the heat storage chamber is to store most of the heat from the flue gas through the heat storage material, which is used to preheat the exhaust gas and oxidize and decompose it in advance before entering the thermal oxidation chamber, while saving fuel.

The heat storage chamber is composed of three heat storage chambers, which take turns to carry out the three processes of heat storage, heat release, and back blowing. The furnace castor supports the ceramic heat storage body and saddle ring ceramic, and the lower part is hung with a porous air distribution plate to hold the saddle ring ceramic. The furnace body material is carbon steel, and the furnace castor support material is carbon steel. The external temperature of the furnace body is ≤ ambient temperature+25 ℃.

（3）Furnace body insulation

The insulation of the oxidation chamber and heat storage chamber of the furnace body is made of refractory aluminum silicate fiber, with a heat resistance of ≥ 1200 ℃ and a unit weight of 200kg/m3. The thickness of the high-temperature zone of the oxidation chamber and heat storage chamber is 250mm, and the thickness of the low-temperature zone of the heat storage chamber is 200mm. There are three layers of internal insulation, including two layers of aluminum silicate fiber felt and one layer of aluminum silicate fiber module. The aluminum silicate fiber module is equipped with a heat-resistant steel skeleton, which is fixed on the furnace shell with anchors. Apply high-temperature resistant plaster on the outer surface of refractory aluminum silicate fiber.

The furnace body is equipped with a pressure relief device for high-temperature inlet and outlet of some energy.

A collection tray is left at the bottom of the furnace body to collect condensed water.

（4）Ceramic heat storage body and rectangular saddle ring

Thermal storage ceramic function:

1. Reduce exhaust heat loss, maximize fuel utilization, and reduce unit energy consumption.

2. Provide theoretical oxidation temperature. Improve oxidation conditions, meet the high temperature requirements of incineration systems, expand the application range of low value fuel, and provide utilization efficiency of fuel calorific value.

3. Reduce the exhaust emissions and harmful gas emissions per unit product of thermal equipment, reduce air pollution, and improve the environment.

Characteristics of thermal storage ceramics:

1. There are various materials available, and products with different materials and specifications can be selected according to the owner and usage environment.

2. The hole wall is large, the capacity is large, the heat storage energy is large, and the space occupied is small.

3. The hole wall is smooth and the back pressure is small.

4. Long service life, less prone to slag corrosion, adhesion and high-temperature deformation.

5. The product has high quality specifications, and during installation, the heat storage bodies are arranged neatly with minimal misalignment.

6. It has the characteristics of low thermal expansion, large specific heat capacity, large specific surface area, small pressure drop, small thermal resistance, good thermal conductivity, and good heat resistance and impact resistance.

Targeted adoption of this medium based on years of customer application experience can maximize the system's thermal storage performance (heat recovery performance) while minimizing the pressure drop of the thermal storage bed as much as possible. Both saddle ring and ceramic honeycomb forms can be used.

Type: honeycomb type; Temperature resistance>1260 ℃; Heat exchange efficiency ≥ 95% at rated air volume.

（5）Valves

●  Main switching valve (wind direction quick switching valve): Due to the crucial performance of the wind direction quick switching valve for the operation of RTO equipment, all wind direction switching valves in the system are of high-quality brand. The selected switching valve has high accuracy, small leakage (≤ 1%), long service life (up to 1 million times), fast opening and closing (1 second), and reliable operation. The valve body material is all carbon steel.

●  Auxiliary damper: adopts pneumatic valve, with small leakage (≤ 1%), quick opening and closing (≤ 1s), and reliable operation.

●  Pneumatic valve actuator

A. The actuator includes cylinder solenoid valves, etc., which are pneumatically operated. The cylinder solenoid valves, pneumatic triplets, etc. are all imported brands. The compressed air pressure of the pneumatic actuator is 0.4-0.6MPa, the swing angle is 90 °, and the torque is 120NM.

B. Pneumatic valves have valve position signal feedback.

（6）Combustion system

●  Burner

Adopting high-quality brand burners and low-pressure head proportional adjustable fuel and gas burners. It can achieve continuous proportional adjustment, with diesel or natural gas as the fuel, high-pressure ignition, and can adapt to various situations. The system includes combustion fan, high-voltage ignition transformer, proportional control valve, flame detector, etc. The proportional control valve can adjust its opening according to the required temperature changes in the furnace, saving fuel; The fuel and combustion air change synchronously, ensuring stable combustion.

The flame detector constantly senses the flame at the burner port, and the flame safety relay monitors the flame status of the burner through the flame detector. The flame detector collects flame signals and displays them on the relay module. When the combustion flame is extinguished, the flame detector does not transmit any signal to the flame safety relay. The fuel pipeline solenoid valve automatically closes to cut off the fuel, ensuring the safety of the burner.

●  Combustion control system

  Schematic diagram of combustion control system

The combustion control system includes a combustion controller, flame detector, high-pressure igniter, and corresponding valve components. The high-temperature sensor in the furnace can provide feedback on the furnace temperature information and control the heating capacity of the burner. The combustion system has functions such as pre blowing before ignition, high-pressure ignition, flameout protection, over temperature alarm, and over temperature cut-off of fuel supply. The temperature of the combustion chamber furnace is stable at around 750 ℃. When the furnace temperature exceeds 825 ℃, the system will automatically alarm. When the temperature exceeds 870 ℃, the system will automatically cut off the fuel supply. When the temperature exceeds 900 ℃, the overtemperature protector will act and also automatically cut off the fuel supply. The negative pressure signal of the filter pressure sensor controls the frequency converter of the supply fan, thereby controlling and regulating the air volume of the supply fan.

The flame detector constantly senses the flame of the burner. During normal combustion, the flame signal is displayed, and when there is no flame, the fuel supply pipeline solenoid valve is closed; When the combustion flame is extinguished, the fuel supply pipeline solenoid valve automatically closes and cuts off the fuel, providing safety protection.