RTO electric heating control system based on multistage temperature difference compensation

Abstract

The invention relates to an RTO electric heating control system based on multistage temperature difference compensation, and belongs to the technical field of industrial waste gas treatment. According to the method, data of an LEL sensor, a temperature sensor and a flow sensor are collected in real time through a PLC, the power of an electric heater, the flow of a fan and the opening degree of a proportional air valve are dynamically adjusted, and the operation efficiency of an RTO system is optimized. And when the average temperature of the combustion chamber exceeds 400 DEG C, a multi-stage temperature difference compensation strategy is adopted, and the central temperature target value of the electric heater is set as the average temperature of the combustion chamber plus 110 DEG C and is dynamically updated to the final target value 910 DEG C. Through multi-stage temperature difference compensation adjustment, electric heating output is refined, the temperature of the center is controlled in an interlocking mode, ideal working conditions are maintained, the RTO process requirement is met, electric energy waste is reduced, and the service life of the electric heater is prolonged.

Description

Technical Field

[0001] This invention relates to the field of industrial waste gas treatment technology, and in particular to an electric heating control system for a regenerative thermal oxidizer (RTO) based on multi-stage temperature difference compensation, used to optimize temperature control and energy consumption management in the treatment process of volatile organic compounds (VOCs) waste gas. Background Technology

[0002] Regenerative Thermal Oxidizer (RTO) electric heating technology is mainly used for industrial waste gas treatment, especially the treatment of volatile organic compounds (VOCs). Its application areas include: Chemical industry: treating waste gases containing VOCs, such as benzene, toluene, and xylene; Painting industry: treating organic waste gases generated during painting and drying processes; Pharmaceutical industry: treating organic waste gases generated during production processes; Shipbuilding and repair industry: treating VOCs generated during painting, welding, and other processes.

[0003] The working principle of RTO (Regenerative Thermal Oxidizer) is to heat the exhaust gas to a temperature above the point where the rapid oxidation reaction occurs using an electric heater. This allows the VOCs in the exhaust gas to undergo an oxidation reaction with oxygen at high temperatures, producing carbon dioxide and water. The specific process is as follows:

[0004] The exhaust gas enters the high-temperature regenerator chamber, where it is preheated to a certain temperature by an auxiliary electric heater. The preheated exhaust gas then enters the combustion chamber, where it is further heated above the temperature at which the rapid oxidation reaction occurs. At this high temperature, VOCs react with oxygen to produce carbon dioxide and water. The high-temperature gas after the reaction passes through the regenerator chamber, releasing heat to preheat the next batch of exhaust gas. The purified gas, having released heat through the regenerator chamber, is then discharged through the chimney.

[0005] Existing technologies involve complex adjustment of operating parameters: the composition and concentration of exhaust gases are unstable, and different compositions and concentrations of exhaust gases require different operating parameters, such as temperature and air volume. This necessitates operation and maintenance by specialized technicians, increasing operating costs.

[0006] High energy consumption: Although RTO electric heating technology has high thermal efficiency, when treating low-concentration VOCs waste gas, the gas outlet temperature remains high and the heat energy from waste gas combustion is not fully utilized, requiring electric auxiliary heating, which leads to increased energy consumption.

[0007] Electric heaters have limited lifespan: operating in high-temperature environments, electric heaters are prone to aging and damage. Regular replacement is required, increasing maintenance costs. Patent CN114704843A discloses an RTO exhaust gas treatment system using electric heating, attempting to solve the problem of easily damaged metal thermal resistance wires by using silicon carbide rods for heating. However, while silicon carbide rods have a longer lifespan than thermal resistance wires, they still cannot withstand frequent overheating.

[0008] In order to make fuller use of the heat generated by the oxidation of waste gas, prevent the electric heater from overheating frequently, and reduce manual operation, it is urgent to design a highly automated RTO electric heating control method that meets the current situation of waste gas treatment. Summary of the Invention

[0009] This invention addresses three interconnected problems in RTO electric heating systems: complex adjustment of operating parameters, high energy consumption, and limited heater lifespan. It proposes a multi-stage temperature difference compensation-based RTO electric heating control system. This system uses a PLC controller to automatically adjust the electric heating output, ensuring stable RTO operation under various conditions without manual intervention. Multi-stage temperature difference compensation allows for precise management of the electric heating output, interlocking control of the central temperature to maintain ideal operating conditions. This satisfies RTO process requirements, reduces energy waste, and extends heater lifespan.

[0010] The specific technical solution of the present invention is to add monitoring of the center temperature of the electric heater, the combustion chamber temperature, the exhaust gas inlet and outlet temperatures, the exhaust gas concentration, and the exhaust gas flow rate to the RTO system.

[0011] The PLC controller collects data from temperature sensors that monitor the center temperature of the electric heater and the combustion chamber temperature, temperature sensors that monitor the inlet and outlet temperatures of the exhaust gas, LEL sensors that monitor the exhaust gas concentration (volume concentration of combustible gas in the exhaust gas), and flow sensors that monitor the exhaust gas flow rate. It then performs logical judgments and dynamically sets multi-level temperature difference compensation. The controller also adjusts the electric heating power of the electric heater, the fan flow rate, and the opening of the proportional damper.

[0012] The logical judgment is as follows: calculate the input calorific value of the exhaust gas based on the exhaust gas concentration, flow rate, and unit calorific value; calculate the loss calorific value based on the exhaust gas inlet and outlet temperatures, specific heat capacity, and flow rate; calculate the electric heating compensation calorific value based on the difference between the loss calorific value and the input calorific value; and determine the output opening degree of the electric heater.

[0013] The calorific value of the exhaust gas input (kcal) = exhaust gas flow rate (m³ / s). 3 / h) x exhaust gas concentration (volume percentage) x exhaust gas calorific value (kcal / Nm³) 3 );

[0014] The heat loss (kcal) = exhaust gas flow rate (m³ / h) 3 / h)x Specific heat capacity (kcal / m 3 .℃)x(outlet temperature (℃) - inlet temperature (℃));

[0015] The electric heating compensation calorific value (kcal) = loss calorific value (kcal) - input calorific value of waste gas (kcal);

[0016] Electric heater output opening degree (%) = (electric heating compensation heat value (kcal) / electric heating power (kcal / h)) x 100.

[0017] The multi-stage temperature difference compensation involves dynamically setting the target value of the electric heater's center temperature step by step, based on the monitoring results of the electric heater's center temperature and the combustion chamber temperature, in order to achieve stable heating.

[0018] The PLC controller dynamically sets the target value of the electric heater's center temperature based on the temperature difference between the average temperature of the combustion chamber and the center temperature of the electric heater, and adjusts the electric heating power through SCR.

[0019] Fan: The fan sends the exhaust gas into the RTO combustion chamber.

[0020] Proportional air valve: Introduces fresh air from the fresh air inlet. Adjusts the airflow into the system to control exhaust gas concentration and ensure safe combustion.

[0021] LEL (Lower Explosive Limit) sensor: measures the concentration of combustible gases in exhaust gas to ensure it is within a safe range.

[0022] RTO (Regenerative Thermal Oxidizer) is a regenerative thermal oxidizer.

[0023] SCR (Silicon Controlled Rectifier) ​​power regulator: used to control power output and regulate the power of electric heaters.

[0024] PLC (Programmable Logic Controller): A programmable logic controller that monitors and adjusts parameters such as power and temperature of electric heaters, regulates valve opening, and controls the operation of the entire system.

[0025] The temperature sensor is a type K thermocouple: used to measure temperature, including the center temperature of the electric heater (electric heating center temperature) and the average temperature of the combustion chamber, and feeds the data back to the PLC.

[0026] Electric heaters, such as thermal resistance wires, infrared heating tubes, or silicon carbide rods, generate heat in the RTO combustion chamber to heat the exhaust gas to the oxidation temperature.

[0027] RTO combustion chamber: Exhaust gas is heated and oxidized in this chamber to purify the exhaust gas.

[0028] Switching valve: Used to change the direction of exhaust gas flow, so that the heat storage chamber alternately absorbs and releases heat.

[0029] The intake air is monitored by an LEL sensor, and a proportional valve is used to ensure that the exhaust gas concentration is within a safe range.

[0030] The PLC controller controls the output power of the SCR power regulator and adjusts the current output to the electric heater.

[0031] Type K thermocouples measure the center temperature of the electric heater and the average temperature of the combustion chamber.

[0032] The PLC controller adjusts the SCR output power based on the feedback temperature data to maintain an appropriate combustion chamber temperature.

[0033] The PLC controller uses the average temperature of the upper layers of several heat storage chambers as a reference value to identify which heat storage chamber has the highest and lowest upper layer temperature. The cycle of identifying the heat storage chamber with the highest temperature as the intake chamber and the heat storage chamber with the lowest temperature as the exhaust chamber is determined, and this cycle is identified as the adjustment cycle.

[0034] Furthermore, the multi-stage temperature difference compensation and adjustment scheme is as follows: during the RTO preheating and heating stage, when the average temperature of the combustion chamber is below 400°C, the normal operation mode is exited, and the PLC controller sets the output power of the electric heater to 70% according to the preset control logic; the electric heater continues to heat at a fixed power until the average temperature of the combustion chamber rises above 400°C.

[0035] When the average temperature of the combustion chamber exceeds 400°C, the target value of the center temperature of the electric heater is set to the average temperature of the combustion chamber plus 110°C. As the temperature of the combustion chamber gradually increases, the target value is dynamically updated, but it is always maintained at a level 110°C above the average temperature of the combustion chamber, until the final target value of 910°C.

[0036] Furthermore, the PLC controller continuously monitors the center temperature of the electric heater, the combustion chamber temperature, and the LEL concentration, and dynamically adjusts them;

[0037] When the LEL sensor detects that the exhaust gas concentration is below 5% LEL, the electric heating power increases by 10%.

[0038] When the flow sensor detects a change in exhaust gas flow exceeding ±10%, the electric heating power decreases by 10% when the flow increases and increases by 10% when the flow decreases.

[0039] The fresh air proportional valve is linked to the average temperature of the combustion chamber, which is between 850-900℃, corresponding to a proportional air valve opening of 0-100%.

[0040] The proportional damper is linked to the LEL concentration. When the LEL concentration is between 15-25%, the corresponding proportional damper opening is 0-100%.

[0041] The proportional valve opening value is calculated based on the two logics mentioned above, and the actual proportional valve opening value is the larger of the calculated opening value.

[0042] Furthermore, the PLC controller adjusts the exhaust gas flow rate by regulating the frequency of the RTO inlet fan and the opening of the proportional damper.

[0043] The variable frequency fan adjusts the fan frequency using PID control based on the comparison between the actual and target values ​​of the inlet flow, so that the inlet flow is stabilized near the target value.

[0044] When the flow sensor detects a change in exhaust gas flow exceeding ±10%;

[0045] When the flow rate increases, the electric heating power decreases by 10%;

[0046] When the flow rate decreases, the electric heating power increases by 10%.

[0047] Furthermore, the PLC presets a temperature threshold of 920°C for the center temperature of the electric heater. Once the center temperature of the electric heater is detected to exceed this threshold, and / or when the electric heater is damaged, the sensor fails, or other equipment malfunctions, the PLC immediately outputs a signal to the SCR to cut off the power supply and issue an audible and visual alarm signal.

[0048] Furthermore, the PLC controller uses the center temperature data to establish a fault prediction model for the equipment and performs data analysis in conjunction with the equipment operating parameters;

[0049] When the center temperature fluctuates abnormally or deviates from the normal range, the PLC will issue a warning signal.

[0050] Through the above control relationships, the entire system can achieve the effect of purifying and treating exhaust gas, improve the utilization rate of electrical energy and heat generated by exhaust gas combustion, and ensure the safety of the combustion process.

[0051] Beneficial effects:

[0052] As can be seen from the above technical solutions, the present invention has the following beneficial effects.

[0053] Precise control: Through PLC controller algorithms and real-time monitoring feedback mechanisms, the compensation calorific value is determined based on the difference between the input calorific value and the loss calorific value, thereby determining the opening degree of the electric heater. This not only precisely controls the combustion chamber temperature, avoiding energy waste due to excessively high temperatures and incomplete oxidation of exhaust gas due to excessively low temperatures, but also allows selection of the optimal regenerator cycle to ensure that it meets the requirements of the exhaust gas treatment process under different operating conditions, thereby improving exhaust gas treatment efficiency and combustion stability.

[0054] Energy-saving and efficient: During the heating process, the electric heating power is dynamically adjusted according to the combustion chamber temperature. Multi-level temperature difference compensation avoids frequent adjustments of gas flow due to excessively high or low temperatures, thus avoiding unnecessary energy waste and reducing operating costs.

[0055] High degree of automation: The entire control process is automatically completed by sensors, PLC, and SCR, which is easy to operate, reduces manual intervention, and improves the system's operating efficiency and reliability.

[0056] Extended lifespan of electric heaters: The use of electric heaters provides faster heating control feedback, and the monitoring of center temperature and interlock protection effectively reduce overheating damage to the electric heaters.

[0057] Safe and reliable: It has a complete interlock protection function, which can quickly cut off the power supply when the temperature rises abnormally, ensuring the safety of equipment and personnel.

[0058] The key feature of this invention is the real-time monitoring of various parameters of the exhaust gas using multiple sensors (including LEL sensors, temperature sensors, and flow sensors), combined with central temperature monitoring, to achieve precise control of the combustion chamber temperature and optimize exhaust gas treatment. The control logic is implemented by a PLC controller, which is responsible for data acquisition, logic judgment, control output, and fault diagnosis. This project first designed the PLC controller's logic judgment and control output, then adjusted it through experiments, ultimately obtaining the precise control method of this invention.

[0059] Existing RTO waste gas treatment technologies should be known to those skilled in the art, and will not be elaborated upon here, nor should they be considered insufficient disclosure. The specific content of the prior art cited in the background section should also be considered as described in the specification. Attached Figure Description

[0060] The accompanying drawings are not drawn to scale. In the drawings, each identical or nearly identical component shown in the various figures may be denoted by the same reference numeral. For clarity, not every component is labeled in each figure. Embodiments of various aspects of the invention will now be described by way of example and with reference to the accompanying drawings, wherein:

[0061] Figure 1 A schematic diagram of the process flow for a multi-stage temperature difference compensation RTO electric heating system.

[0062] Figure 2 The output operation data curve of the electric heating control for a multi-stage temperature difference compensation RTO electric heating system.

[0063] Explanation of icon numbers:

[0064] Combustion chamber 1, heat storage chamber 2, exhaust gas duct 3, exhaust gas 30, exhaust gas branch pipe 31, fan 32, intake switching valve 33, LEL sensor 34, purge gas duct 4, air 40, proportional air valve 42, purge switching valve 43, exhaust duct 5, chimney 51, exhaust switching valve 53, electric heater 6. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art.

[0066] The terms "first," "second," and similar words used in the specification and claims of this patent application do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, unless the context clearly indicates otherwise, the singular forms of "an," "a," or "the," etc., do not indicate a quantity limitation, but rather indicate the presence of at least one. Terms such as "comprising" or "including" mean that the element or object preceding "comprising" encompasses the features, wholes, steps, operations, elements, and / or components listed following "comprising" or "including," and do not exclude the presence or addition of one or more other features, wholes, steps, operations, elements, components, and / or collections thereof. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0067] Example 1:

[0068] like Figure 1 As shown, in processing 300m 3 In practice, for a waste gas flow rate of / h, the input calorific value of the waste gas is first calculated based on the waste gas concentration, flow rate, and unit calorific value; the loss calorific value is calculated based on the waste gas inlet and outlet temperatures, specific heat capacity, and flow rate; the electric heating compensation calorific value is calculated based on the difference between the loss calorific value and the input calorific value; and the output opening degree of the electric heater 6 is determined.

[0069] 1. Calculation of the input calorific value of exhaust gas under normal operating mode

[0070] The calibration gas for LEL is 1% propane. The input calorific value of the exhaust gas is calculated based on the exhaust gas flow rate, propane concentration (expressed as a percentage of LEL), and the calorific value of propane.

[0071] Formula: Input calorific value of exhaust gas (kcal) = Exhaust gas flow rate (m³ / h) 3 / h) x propane concentration (volume percentage) x propane calorific value (kcal / Nm³) 3 )

[0072] Specific calculations:

[0073] - Exhaust gas flow rate: 300m³ 3 / h

[0074] -LEL explosion lower limit percentage: 20%

[0075] The LEL of propane is 2.1%, therefore, a 20% LEL corresponds to an actual concentration of: 0.20 x 2.1% = 0.42%.

[0076] - Calorific value of propane: 22256 kcal / Nm 3

[0077] The input calorific value of the exhaust gas = 300 x 0.0042 x 22256 = 2837.6 kcal

[0078] 2. Calculate the heat loss value

[0079] The heat loss value is calculated based on the RTO inlet and outlet temperatures, as well as the specific heat capacity of the waste gas.

[0080] Formula: Calorific value lost (kcal) = Waste gas flow rate (m³ / h) 3 / h)x Specific heat capacity (kcal / m 3 .℃)x(Outlet temperature (℃) - Inlet temperature (℃))

[0081] Specific calculations:

[0082] - Exhaust gas flow rate: 300m³ 3 / h

[0083] - Specific heat capacity: 1.005 kcal / m³ 3 .℃

[0084] -RTO inlet temperature: 25℃

[0085] -RTO outlet temperature: 60℃

[0086] Calorific value lost = 300 x 1.005 x (60 - 25) = 10552.5 kcal

[0087] 3. Calculate the compensated calorific value for electric heating.

[0088] The electric heating compensation calorific value is calculated based on the calorific value of the loss and the input calorific value of the exhaust gas.

[0089] Formula: Compensated calorific value for electric heating (kcal) = Calorific value lost (kcal) - Calorific value input of waste gas (kcal)

[0090] Specific calculations:

[0091] Compensated calorific value for electric heating = 10552.5 - 2837.6 = 7714.9 kcal

[0092] 4. Calculate the output opening of electric heater 6.

[0093] The electric heating output setting is calculated based on the electric heating compensation heat value and electric heating power.

[0094] Formula: Electric heating output degree (%) = (Electric heating compensation heat value (kcal) / Electric heating power (kcal / h)) x 100

[0095] Specific calculations:

[0096] - Electric heating power: 13kW

[0097] -1kW=860kcal / h

[0098] - Electric heating power (kcal / h) = 13 × 860 = 11180 kcal / h

[0099] Output opening of electric heater 6 = (7714.9 / 11180) x 100 ≈ 69.0%

[0100] Final result

[0101] 1. Input calorific value of exhaust gas: 2837.6 kcal

[0102] 2. Calorific value lost: 10552.5 kcal

[0103] 3. Compensated calorific value for electric heating: 7714.9 kcal

[0104] 4. Electric heating output opening: 69.0%

[0105] Based on the actual exhaust gas flow rate, LEL percentage, RTO inlet and outlet temperatures, and electric heating power, the required output opening of electric heater 6 is calculated to be 69.0%, and the reference output opening of electric heater 6 during the start-up phase is set to 70%.

[0106] like Figure 1 As shown, during the initial startup and heating phase of the RTO equipment, the control strategy involves multiple temperature sensors installed in combustion chamber 1 measuring the temperature at different locations within combustion chamber 1 and calculating the average value. When the average temperature of combustion chamber 1 falls below 400°C, the normal operation phase ends, and electric heater 6 operates at 70% of its output power. The main purpose of this phase is to rapidly increase the temperature of combustion chamber 1 to a certain baseline temperature, creating favorable conditions for the subsequent combustion process.

[0107] The electric heater 6 continues to heat at a fixed power until the average temperature of the combustion chamber 1 rises above 400°C.

[0108] When the average temperature of combustion chamber 1 exceeds 400℃, the system enters the PLC multi-level temperature difference compensation mode.

[0109] In this mode, the PLC, based on preset control logic and combined with multi-level temperature difference compensation, ensures that the temperature of combustion chamber 1 is always maintained within a suitable range.

[0110] Specific PLC control logic:

[0111] Input signals: average temperature of combustion chamber 1, center temperature of electric heater 1, LEL concentration, flow rate.

[0112] Output signal: Power adjustment command for electric heater 6.

[0113] The PLC dynamically calculates the target temperature of the electric heater 6 based on the average temperature and the temperature difference between the center of combustion chamber 1, and adjusts the power of the electric heater according to the deviation.

[0114] When the average temperature of combustion chamber 1 exceeds 400°C, the target temperature value is set to the average temperature of combustion chamber 1 plus 110°C.

[0115] As the temperature of combustion chamber 1 gradually increases, the target temperature value is dynamically updated, but it is always maintained at a level 110°C above the average temperature of combustion chamber 1, until the final target value of 910°C, at which point it enters normal operation mode.

[0116] The refresh frequency of the target value is the sum of the switching cycle times of the six switching valves at the bottom of the heat storage chamber 2, which is approximately 540 seconds (9 minutes).

[0117] Example 2:

[0118] like Figure 1 As shown, the RTO is divided into an interconnected combustion chamber 1 and three parallel regenerator chambers 2. The combustion chamber 1 is located above the regenerator chambers 2. The bottom of the regenerator chambers 2 is provided with an exhaust gas pipe 3, a purge gas pipe 4, and an exhaust pipe 5. Specifically, each regenerator chamber 2 is connected by a branch pipe such as an exhaust gas branch pipe 31.

[0119] Figure 1The diagram shows one cycle in the operation of a three-chamber RTO. The regenerator 2 is divided into a central regenerator and two mirror-symmetrical left and right regenerators. If the upper temperature of the right regenerator is the highest, the bottom air intake switching valve 33 of the right regenerator is opened, and the exhaust gas 30 enters from the right regenerator. If the upper temperature of the central regenerator is the lowest, the bottom exhaust switching valve 53 of the central regenerator is opened, and the oxidized exhaust gas is discharged from the central regenerator. At the same time, the bottom purge switching valve 43 of the left regenerator is opened, and the air 40 is purged through the purge air pipe 4 and regulated by the proportional air valve 42 to purge the residual exhaust gas in the left regenerator. Oxygen-enriched air is then introduced to undergo combustion and oxidation in the combustion chamber 1, and discharged from the central regenerator and then discharged from the chimney 51 through the exhaust pipe 5.

[0120] The control method based on the temperature balance of RTO heat storage chamber 2 reduces heat loss in the following ways:

[0121] Optimize the temperature distribution in heat storage chamber 2: By automatically calculating the switching timing of the intake, exhaust, and purging valves, the temperature zones of the three heat storage chambers 2 are kept balanced. This avoids the temperature in any one heat storage chamber 2 becoming too high or too low, reducing ineffective heat loss.

[0122] Lowering the outlet exhaust gas temperature: By optimizing the temperature balance, the outlet exhaust gas temperature is lowered, thereby reducing the heat carried away by the exhaust gas.

[0123] Improved heat recovery efficiency: The temperature balance of heat storage chamber 2 allows for a more even distribution of heat between heat storage chambers 2, improving heat recovery efficiency and reducing heat loss.

[0124] Example 3:

[0125] The PLC calculation method and the multi-level temperature difference compensation control method for normal operation mode are the same as in Example 1. The selection of the air intake, exhaust, and purging cycle of the heat storage chamber 2 is the same as in Example 2.

[0126] The PLC has a preset temperature threshold of 920℃. Once the temperature exceeds this threshold, the PLC immediately outputs a signal to the control circuit of the electric heater 6 to cut off the power.

[0127] Temperature sensors collect the temperature signal at the center of the electric heater in real time and transmit it to the PLC. When the temperature value detected by the temperature sensor at the center of the electric heater 6 exceeds 920℃, the system immediately triggers the interlock mechanism, cutting off the power supply to the electric heater 6 through the power regulator SCR, thus stopping the heating process. This measure is to prevent the electric heater 6 from being damaged due to excessive temperature, and to avoid safety hazards caused by local overheating, such as damage to the combustion chamber 1 structure and fire risk.

[0128] Simultaneously, the PLC issues audible and visual alarm signals to remind operators to promptly check and handle any abnormalities. This control strategy has comprehensive interlocking protection functions, capable of quickly cutting off power in the event of an abnormal temperature rise, ensuring the safety of equipment and personnel.

[0129] Example 4:

[0130] The PLC calculation method and the multi-level temperature difference compensation control method for normal operation mode are the same as in Example 1. The selection of the air intake, exhaust, and purging cycle of the heat storage chamber 2 is the same as in Example 2.

[0131] In normal operation mode, multi-level temperature difference compensation control strategy:

[0132] Sudden concentration reduction condition:

[0133] When the LEL sensor 34 detects that the exhaust gas concentration is below 5% LEL, the electric heating output increases by 10%.

[0134] Fluctuating exhaust gas flow rate:

[0135] When the flow sensor detects a change in exhaust gas flow exceeding ±10%, the electric heating power decreases by 10% when the flow increases and increases by 10% when the flow decreases.

[0136] Sudden increase in concentration:

[0137] The proportional air valve is linked to the average temperature of the combustion chamber. When the temperature is between 850-900℃, the opening degree of the proportional air valve is 0-100%.

[0138] The proportional damper is linked to the LEL concentration. When the LEL concentration is between 15-25%, the corresponding proportional damper opening is 0-100%.

[0139] The opening value is calculated based on the two logics mentioned above, and the actual proportional valve opening value is the larger of the calculated opening value.

[0140] Equipment failure conditions:

[0141] When the electric heater is damaged, the sensor malfunctions, or other equipment malfunctions.

[0142] The PLC immediately cuts off the power to the electric heater 6 and issues an audible and visual alarm signal.

[0143] Based on the type and severity of the fault, the PLC adjusts the operating parameters of other equipment to minimize the impact on waste gas treatment.

[0144] The PLC records fault information to remind operators to check and repair in a timely manner.

[0145] Example 5:

[0146] The PLC calculation method and the multi-level temperature difference compensation control method for normal operation mode are the same as in Example 1. The selection of the air intake, exhaust, and purging cycle of the heat storage chamber 2 is the same as in Example 2.

[0147] Predicting equipment failure:

[0148] Function Description: Utilizes core temperature data to establish a fault prediction model for equipment, enabling early detection of potential faults.

[0149] Technical Implementation:

[0150] The PLC records historical data of the center temperature and performs data analysis in conjunction with equipment operating parameters (such as electric heater current and voltage).

[0151] When the center temperature fluctuates abnormally (such as a temperature change of more than 50°C in a short period of time) or continues to deviate from the normal range, the PLC will issue a warning signal.

[0152] The warning signal reminds operators to check the electric heater, heat storage chamber or other critical components in a timely manner.

[0153] Controlling the quality of exhaust gas emissions:

[0154] Function Description: Based on changes in the core temperature and the combustion characteristics of propane, ensure that exhaust gas emissions meet standards.

[0155] Technical Implementation:

[0156] When the core temperature is maintained within the optimal combustion temperature range of 850℃~900℃, the PLC ensures that propane is fully combusted, and the generated products such as carbon dioxide and water meet environmental emission standards.

[0157] If the center temperature deviates from the optimal range, the PLC automatically adjusts the electric heating power and exhaust gas flow to bring the combustion chamber temperature back to a suitable level.

[0158] like Figure 2 The average temperature and center temperature curves of the combustion chamber are well consistent, the gradient is stable, and the output of electric heater 6 is stable, indicating that the control method of the embodiment is accurate, stable and reliable, and the electric heater is protected.

[0159] Table 1 Energy Saving Effect Assessment - Comparison of Inlet and Outlet Temperatures of Thermal Storage Chamber

[0160]

[0161] 1. Calculation method for heat loss

[0162] Heat loss mainly manifests as the heat carried away by the exhaust gas at the RTO outlet. This portion of heat can be calculated using the following formula:

[0163] Q 显热损失 =mCp .(T 出口 -T 进口 )in:

[0164] m is the exhaust gas flow rate (kg / s).

[0165] C p It is the specific heat capacity of the exhaust gas (J / kg·℃).

[0166] T 出口 It is the RTO outlet temperature (°C).

[0167] T 进口 It is the RTO inlet temperature (°C).

[0168] 2. Specific differences in performance between the two control methods

[0169] Based on the recorded data, the inlet and outlet temperatures of the RTO under traditional operation and control methods based on the temperature balance of the heat storage chamber are as follows: See the table for comparison of inlet and outlet temperatures (heat storage chamber temperature balance regulation).

[0170] The data shows that:

[0171] Under traditional operating conditions, the RTO outlet temperature is approximately 60°C.

[0172] Under the control method based on the temperature balance of the heat storage chamber, the RTO outlet temperature is approximately 45℃.

[0173] 3. Calculation of heat loss

[0174] Assuming the exhaust gas flow rate is 300m³ 3 / h, density is 1.2kg / m³ 3 Its specific heat capacity is 1000 J / kg·℃.

[0175] Traditional operating method

[0176] Temperature difference: 60℃ - 25℃ = 35℃

[0177] Exhaust gas flow rate: 300 m³ 3 / 3600s×1.2kg / m 3 =0.1kg / s

[0178] Heat loss:

[0179] Q 传统 =0.1kg / s×1000J / kg.℃×35K=3500W=3.5kW

[0180] Control method based on heat storage chamber temperature balance

[0181] Temperature difference: 45℃ - 25℃ = 20℃

[0182] Exhaust gas flow rate: 300 m³ 3 / 3600s×1.2kg / m 3 =0.1kg / s

[0183] Heat loss:

[0184] Q 平衡 =0.1kg / s×1000J / kg.℃×20K=2000W=2.0kW

[0185] 4. Reduction in heat loss

[0186] Reduction in heat loss:

[0187] ΔQ=Q 传统 -Q 平衡 =3.5kW - 2.0kW = 1.5kW

[0188] 5. Conclusion

[0189] Based on the data in Table 1, calculations show that the RTO electric heating control system based on multi-stage temperature difference compensation can reduce heat loss by approximately 1.5 kW compared to the traditional operation mode. The multi-stage temperature difference compensation control method significantly improves heat recovery efficiency and effectively reduces heat loss by optimizing the temperature distribution in the heat storage chamber and reducing the outlet exhaust gas temperature.

[0190] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Those skilled in the art can make various modifications and refinements without departing from the spirit and scope of the invention. Therefore, the scope of protection of the present invention shall be determined by the claims. The heat preservation time used in the specification and claims of this patent application should be understood as a roughly contiguous range.

Claims

1. A multi-stage temperature difference compensation-based RTO electric heating control system, characterized in that, This includes monitoring the center temperature of the electric heater, the combustion chamber temperature, the inlet and outlet temperatures of the exhaust gas, the exhaust gas concentration, and the exhaust gas flow rate; The PLC controller collects data from temperature sensors that monitor the center temperature of the electric heater and the temperature of the combustion chamber, temperature sensors that monitor the temperature of the exhaust gas inlet and outlet, LEL sensors that monitor the exhaust gas concentration, and flow sensors that monitor the exhaust gas flow rate. It then performs logical judgments and dynamically sets multi-level temperature difference compensation. Adjust the electric heating power of the electric heater, the flow rate of the fan, and the opening of the proportional damper; The logical judgment is as follows: calculate the input calorific value of the exhaust gas based on the exhaust gas concentration, flow rate, and unit calorific value; calculate the loss calorific value based on the exhaust gas inlet and outlet temperatures, specific heat capacity, and flow rate; calculate the electric heating compensation calorific value based on the difference between the loss calorific value and the input calorific value; and determine the output opening degree of the electric heater. The multi-stage temperature difference compensation involves dynamically setting the target value of the electric heater's center temperature step by step, based on the monitoring results of the electric heater's center temperature and the combustion chamber temperature, in order to achieve stable heating.

2. The control system according to claim 1, characterized in that, In normal RTO operation mode, The calorific value of the waste gas input = waste gas flow rate x waste gas concentration (volume percentage) x waste gas calorific value; The heat loss value = exhaust gas flow rate x specific heat capacity x (outlet temperature - inlet temperature); The electric heating compensation calorific value = loss calorific value - input calorific value of waste gas; Electric heater output opening = (electric heating compensation heat value / electric heating power) x 100.

3. The control system according to claim 1, characterized in that, The PLC controller uses the average temperature of the upper layer of the RTO heat storage chamber as a reference value to compare the heat storage chambers with the highest and lowest upper layer temperatures. The heat storage chamber with the highest upper layer temperature is the air intake chamber, and the air intake switching valve is opened. The heat storage chamber with the lowest upper layer temperature is the exhaust chamber, and the exhaust switching valve is opened. The purge switching valves of the remaining heat storage chambers are opened.

4. The control system according to claim 2, characterized in that, The multi-stage temperature difference compensation and adjustment scheme is as follows: during the RTO preheating and heating stage, when the average temperature of the combustion chamber is below 400°C, the RTO normal operation mode is exited, and the PLC controller sets the output power of the electric heater to 70% according to the preset control logic; the electric heater continues to heat at a fixed power until the average temperature of the combustion chamber rises above 400°C.

5. The control system according to claim 2, characterized in that, When the average temperature of the combustion chamber exceeds 400°C, the target value of the center temperature of the electric heater is set to the average temperature of the combustion chamber plus 110°C. As the temperature of the combustion chamber gradually increases, the target value is dynamically updated, but it is always maintained at a level 110°C above the average temperature of the combustion chamber, until the final target value of 910°C.

6. The control system according to claim 2, characterized in that, The PLC controller continuously monitors the center temperature of the electric heater, the combustion chamber temperature, and the LEL concentration, and dynamically adjusts them. When the LEL sensor detects that the exhaust gas concentration is below 5% LEL, the electric heating power increases by 10%.

7. The control system according to claim 1, characterized in that, The proportional air valve is linked to the average temperature of the combustion chamber, which is between 850-900℃, corresponding to a proportional air valve opening of 0-100%. The proportional damper is linked to the LEL concentration. When the LEL concentration is between 15-25%, the corresponding proportional damper opening is 0-100%. Based on the two logics above, the opening value of the proportional damper is calculated respectively, and the actual opening value of the proportional damper is the larger of the calculated opening value.

8. The control system according to claim 1, characterized in that, The PLC controller adjusts the exhaust gas flow rate by regulating the frequency of the RTO inlet fan and the opening of the proportional damper. The variable frequency fan adjusts the fan frequency using PID control based on the comparison between the actual and target values ​​of the inlet flow, so that the inlet flow is stabilized near the target value. When the flow sensor detects a change in exhaust gas flow exceeding ±10%; When the flow rate increases, the electric heating power decreases by 10%; When the flow rate decreases, the electric heating power increases by 10%.

9. The control system according to claim 1, characterized in that, The PLC presets a temperature threshold of 920°C for the center temperature of the electric heater. Once the center temperature of the electric heater is detected to exceed this threshold, and / or when the electric heater is damaged, the sensor fails, or other equipment malfunctions, the PLC controller immediately outputs a signal to cut off the power supply and issues an audible and visual alarm signal.

10. The control system according to claim 1, characterized in that, The PLC controller uses the center temperature data to establish a fault prediction model for the equipment and performs data analysis in conjunction with the equipment operating parameters; when the center temperature fluctuates abnormally or deviates from the normal range, the PLC issues an early warning signal.

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