VOCs pretreatment and oxidation furnace temperature intelligent early warning and cooperative control method

Abstract

The invention discloses a VOCs pretreatment and oxidation furnace temperature intelligent early warning and cooperative control method. An oil washing tower, an acid washing tower, an alkaline washing tower intelligent control module, an activated carbon adsorber intelligent control module, an RTO system waste gas concentration cooperative control module, an RTO hearth safety interlocking control module and an emergency bypass and safe emission control module are included. The intelligent control module of the oil washing tower, the acid washing tower and the alkaline washing tower is used for controlling the liquid level and pH of the oil washing tower, the acid washing tower and the alkaline washing tower; the activated carbon adsorber intelligent control module comprises activated carbon adsorber temperature monitoring and activated carbon adsorber activated carbon saturation prediction; the RTO system waste gas concentration cooperative control module comprises a fresh air pipe with a fresh air valve and a waste gas concentration detector, the fresh air pipe with the fresh air valve is connected to an RTO air inlet main pipe, the opening degree of the fresh air valve is adjusted, air is supplemented to dilute waste gas, and a waste gas fan ensures that suction force of a waste gas main pipe is stabilized within a set range by adjusting frequency.

Description

Technical Field

[0001] This invention relates to the field of coal chemical industry. Background Technology

[0002] In the coal chemical industry, the collection, washing, and adsorption of volatile organic compounds (VOCs) generated on-site cannot meet environmental protection requirements, necessitating the use of combined waste gas incineration technology. VOCs washing and adsorption systems and regenerative thermal oxidizers (RTOs) are widely used in the purification of industrial VOCs. However, in actual operation, the lack of safety linkage with the RTO itself, and the lack of precise control over its own operating status (such as liquid level, pH, and temperature), can lead to abnormal waste gas temperature and concentration. This can cause the RTO furnace temperature to easily exceed safety limits, posing significant safety risks such as equipment damage and explosions.

[0003] Liquid level out of control: If the liquid level in the oil washing tower or scrubbing tower is too high, flooding is likely to occur; if the liquid level is too low, the washing efficiency will be affected. Inaccurate pH control: Large pH fluctuations in the acid / alkali washing tower lead to incomplete neutralization or waste of reagents; Temperature anomaly: Overheating of the pretreatment section adsorber may cause the activated carbon adsorber to catch fire or the RTO inlet to overheat. The management of activated carbon is inefficient: there is a lack of prediction of adsorption saturation, and the carbon is not purged and desorbed in time after adsorption saturation, which leads to VOCs breakthrough and a sudden increase in RTO load. Poor system coordination: There is no state feedback and linkage control between the preprocessing unit and the RTO, making it impossible to intervene in advance of front-end anomalies.

[0004] Lagging response to furnace over-temperature: Most systems rely on a single high-temperature threshold to trigger protection actions, lacking a graded early warning mechanism, and are unable to take intervention measures in the early stages of temperature anomalies; Poor controllability of furnace temperature: When the exhaust gas concentration rises abnormally, the furnace temperature cannot be controlled even if the gas supply is stopped. Emergency emission due to ultra-high temperature and furnace shutdown due to over-temperature interlock will shut off the gas intake, causing the exhaust gas to be directly discharged into the bypass pipe, which poses a pollution risk and does not comply with environmental protection standards such as GB16297-1996. Summary of the Invention

[0005] The objectives of this invention are: to achieve real-time monitoring and automatic control of key parameters such as liquid level, pH, and temperature in oil washing towers, acid washing towers, and alkali washing towers; to calculate the adsorption saturation cycle of activated carbon adsorbers; to provide safe operation control requirements for activated carbon adsorbers to prevent combustion and explosion under high temperature and high concentration conditions; to reduce and stabilize waste gas concentration; to construct a state feedback mechanism between the pretreatment unit and the RTO system to improve the overall system safety and operational stability; to form a complete and replicable pretreatment unit control scheme to improve system reliability; to establish a multi-level intelligent early warning mechanism for furnace temperature to achieve early identification and graded response to abnormal temperature rise; and to provide a fast-responding, logically clear, and engineerable RTO safety control scheme.

[0006] The technical solution adopted in this invention is: a method for intelligent early warning and coordinated control of VOCs pretreatment and oxidation furnace temperature, including intelligent control modules for oil washing tower, acid washing tower, and alkali washing tower; an intelligent control module for activated carbon adsorber; a coordinated control module for RTO system exhaust gas concentration; an RTO furnace safety interlock control module; and an emergency bypass and safe emission control module. The intelligent control modules for oil washing tower, acid washing tower, and alkali washing tower control the liquid level and pH of these towers. The intelligent control module for activated carbon adsorber includes activated carbon adsorber temperature monitoring and activated carbon saturation prediction. The coordinated control module for RTO system exhaust gas concentration includes a fresh air duct with a fresh air valve connected to the RTO inlet main pipe and an exhaust gas concentration detector. Adjusting the opening of the fresh air valve allows for the introduction of air to dilute the exhaust gas. The exhaust gas fan adjusts its frequency to ensure the suction power of the exhaust gas main pipe remains stable within a set range, and the exhaust gas outlet volume concentration is controlled to <10%, ensuring stable RTO operation. A two-level early warning system is set; when the exhaust gas volume concentration... When the concentration is ≥10%, a Level 1 warning is triggered, issuing an audible and visual alarm. When the exhaust gas volume concentration is ≥18%, a Level 2 warning is triggered, issuing an audible and visual alarm and closing the exhaust gas inlet valve while opening the bypass pipeline valve. The RTO furnace safety interlock control module includes thermocouples arranged in multiple areas of the furnace and is equipped with a three-level warning system. When the furnace temperature is ≥820℃, heating is stopped and the gas inlet valve is closed. When the furnace temperature is ≥920℃, the overheat discharge valve opens to release furnace heat. When the furnace temperature is ≥980℃, the overheat discharge valve opens to release furnace heat. When the temperature reaches ℃, an audible and visual alarm is triggered, the exhaust gas inlet is closed, the bypass pipeline valve is opened, and the shutdown procedure is initiated. The emergency bypass and safe emission control module includes a heat exchanger added to the top of the furnace, which is connected to a bypass pipeline. A bypass butterfly valve is installed on the bypass pipeline. When the furnace temperature is ≥920℃, the bypass butterfly valve is opened, and part of the furnace gas is released directly through the bypass pipeline. The heat exchanger on the bypass pipeline cools the high-temperature gas in the bypass pipeline, and the cooled gas in the bypass pipeline is discharged into the main flue gas pipeline.

[0007] Under normal circumstances, the high-temperature gas in the furnace is cooled by the heat storage bricks and then discharged into the main flue gas duct. The gas enters the main flue gas duct at a relatively slow speed and cannot be discharged quickly. This invention uses a bypass pipe to discharge the high-temperature gas in the furnace directly into the main flue gas duct through a heat exchanger. The furnace is supplemented with gas (exhaust gas and air) to cool the furnace.

[0008] The liquid level control includes level gauges installed on the oil washing tower, acid washing tower, and alkali washing tower respectively to monitor the liquid level inside the tower. When the liquid level in each tower is detected to be lower than its set lower limit, the corresponding replenishing pump replenishes the liquid. When the liquid level in each tower is detected to be higher than its set upper limit, the corresponding draining pump discharges the liquid. The pH control includes pH analyzers installed on the oil washing tower, acid washing tower, and alkali washing tower respectively to monitor the pH of the liquid inside the tower. When the pH value of the liquid in each tower is detected to be lower than its set lower limit, the corresponding acid or alkali is replenished. When the pH value of the liquid in each tower is detected to be higher than its set upper limit, water is replenished.

[0009] The activated carbon adsorber temperature monitoring involves installing temperature sensors at the inlet and outlet of the adsorber and in the middle of the bed. When the temperature exceeds the set warning temperature, an automatic alarm is triggered, the inlet and outlet valves of the activated carbon adsorber are closed, and the steam protection system is activated. The activated carbon saturation prediction includes establishing the adsorption saturation prediction formula T = M*C. 吸附 / (Q*C 入口 ), where T is the adsorption saturation time in hours, M is the weight of activated carbon in the activated carbon adsorber in kilograms, and C 吸附 Adsorption capacity, in g / kg, C 入口 The concentration is the imported concentration, expressed in g / m³.

[0010] The beneficial effects of this invention are: significantly improved safety, with a three-level early warning mechanism that can identify abnormal temperature rise 5-10 minutes in advance; over-temperature response time ≤3 seconds, bypass switching time ≤1 second; control accuracy reaches 10±1%, eliminating the risk of explosion; system MTBF (Mean Time Between Failures) >5000 hours. Outstanding energy-saving effect, with the upper limit of fresh air volume controlled within 40% of the total air volume, avoiding excessive dilution leading to increased energy consumption; dynamic optimization of the pretreatment system saves 15-20% of energy. Excellent environmental performance, with stable exhaust gas temperature ≤300℃, meeting regulatory requirements; mixed gas temperature ≤200℃, meeting GB16297-1996 standards; VOCs removal rate ≥99%, and exhaust gas concentration controlled ≤10%. Strong system stability, with multi-point monitoring and redundant control, reducing the failure rate by 70%; supporting automatic recovery algorithms, shortening recovery time after anomalies by 50%; supporting SIL2 safety level certification, meeting the needs of high-risk operating conditions. Detailed Implementation

[0011] A method for intelligent early warning and coordinated control of VOCs pretreatment and oxidation furnace temperature includes intelligent control modules for oil washing tower, acid washing tower, and alkali washing tower, as well as an intelligent control module for activated carbon adsorber. It also includes a coordinated control module for RTO system exhaust gas concentration, an RTO furnace safety interlock control module, and an emergency bypass and safe emission control module.

[0012] The intelligent control module for the oil washing tower, acid washing tower, and alkali washing tower is used for level control and pH control of the oil washing tower, acid washing tower, and alkali washing tower. The level control includes level gauges installed on the oil washing tower, acid washing tower, and alkali washing tower respectively to monitor the liquid level in each tower. When the liquid level in each tower is detected to be lower than its set lower limit, the corresponding replenishing pump replenishes the liquid. When the liquid level in each tower is detected to be higher than its set upper limit, the corresponding draining pump discharges the liquid. The pH control includes pH analyzers installed on the acid washing tower and alkali washing tower respectively to monitor the pH of the liquid in each tower. When the pH value of the liquid in each tower is detected to be lower than its set lower limit, the corresponding acid or alkali is replenished. When the pH value of the liquid in each tower is detected to be higher than its set upper limit, water is replenished.

[0013] In one embodiment, each tower is equipped with a magnetic level gauge (on-site + remote transmission) to monitor the liquid level in real time; the liquid level control range (set normal operating range) is 0.4-1.0m; when the liquid level is below 0.4m, the replenishment pump is automatically turned on to replenish the liquid, and when the liquid level is above 1.0m, the corresponding discharge pump is started to discharge the liquid.

[0014] In one embodiment, the pH control range of the acid washing tower is 0-4, and the pH control range of the alkali washing tower is 9-14. If the pH exceeds the set range, automatic water replenishment or supplementation of sulfuric acid or liquid alkali is implemented to ensure the washing effect.

[0015] During normal production, automatic control is used, with automatic liquid drainage and acid / alkali addition functions for the three towers; when production or equipment malfunctions (beyond the capabilities of automatic control), manual operation is required; this eliminates the inherent unreliability of manual operation, essentially reducing the labor intensity of employees and eliminating operational risks for them.

[0016] The intelligent control module for the activated carbon adsorber includes activated carbon adsorber temperature monitoring and activated carbon saturation prediction. The activated carbon adsorber temperature monitoring involves installing temperature sensors at the inlet and outlet of the activated carbon adsorber and in the middle of the bed. When the temperature exceeds the set warning temperature, an automatic alarm is triggered, the inlet and outlet valves of the activated carbon adsorber are closed, and the steam protection system is activated. The activated carbon saturation prediction includes establishing the adsorption saturation prediction formula T = M*C. 吸附 / (Q*C 入口 ), where T is the adsorption saturation time in hours, M is the weight of activated carbon in the activated carbon adsorber in kilograms, and C 吸附Adsorption capacity, in g / kg, C 入口 The concentration is the imported concentration, expressed in g / m³.

[0017] In one embodiment, temperature monitoring is implemented by installing multiple temperature sensors at the inlet and outlet of the activated carbon adsorber and in the middle of the bed. The normal operating temperature is 30-60°C. When the temperature exceeds 60°C, an automatic alarm is triggered, the inlet and outlet valves are shut off, and the steam protection system is activated.

[0018] In one embodiment, the adsorption degree is scientifically predicted, allowing for pre-emptive switching and purging desorption to prevent VOCs from penetrating the activated carbon and causing an increase in the concentration of exhaust gas before the RTO furnace. The saturation time is determined as T = M*C based on the operating conditions. 吸附 / (Q*C 入口 = 3000 * 200 / (5000 * 0.6) = 150 hours ≈ 8.3 days Theoretical calculations show that a single unit can be used for no more than 8 days. There are four adsorbers on site, operating in a three-in-one desorption mode. The cycle for purging / desorption (24 hours) and cooling (24 hours) per unit is 2 days. The four units are used in rotation, with each unit having an online operating time of 6 days. Activated carbon purging / desorption uses steam purging for 24 hours, and cooling must be done with nitrogen purging for 24 hours until the temperature drops below 40°C before operation to prevent spontaneous combustion and flash explosion caused by high temperatures.

[0019] The RTO system exhaust gas concentration collaborative control module includes a fresh air duct with a fresh air valve connected to the RTO intake manifold and an exhaust gas concentration detector. By adjusting the opening of the fresh air valve, air is introduced to dilute the exhaust gas. The exhaust gas fan adjusts its frequency to ensure that the suction power of the exhaust gas main pipe is stable within the set range, and the exhaust gas outlet volume concentration is controlled at <10%, ensuring the stable operation of the RTO. A two-level warning system is set. When the exhaust gas volume concentration is ≥10%, the first-level warning is triggered, and an audible and visual alarm is issued. When the exhaust gas volume concentration is ≥18%, the second-level warning is triggered, and an audible and visual alarm is issued, and the exhaust gas intake valve is closed while the bypass pipeline valve is opened.

[0020] In one embodiment, the RTO intake manifold is equipped with three exhaust gas concentration detectors (multi-point detection to ensure accuracy) to monitor the exhaust gas volume concentration (0-20%) in real time; and a two-level early warning and emergency response are set up. When the exhaust gas volume concentration is ≥10%, the first-level early warning is triggered and an audible and visual alarm is issued. When the exhaust gas volume concentration is ≥18%, the system triggers the second-level early warning and issues an audible and visual alarm. At the same time, the RTO system will automatically interlock and automatically cut off the intake valve within 1 second and open the bypass valve simultaneously.

[0021] Excessive exhaust gas concentration poses an explosion risk and can cause abnormal temperature rise in the RTO furnace, frequently triggering alarms and shutdowns. By adding a fresh air inlet before the pretreatment system to dilute the exhaust gas, and by automatically adjusting the frequency of the exhaust gas fan to ensure that the suction power of the main exhaust gas pipe is stable at -800~-1000pa, and by adjusting the opening of the DN600 fresh air valve to 30-50%, the exhaust gas outlet concentration is stabilized at <10%, ensuring the stable operation of the RTO.

[0022] The RTO furnace safety interlock control module includes thermocouples arranged in multiple areas of the furnace and is equipped with a three-level early warning system. When the furnace temperature is ≥820℃, heating is stopped and the gas inlet valve is closed. When the furnace temperature is ≥920℃, the overheat discharge valve is opened to release the furnace heat. When the furnace temperature is ≥980℃, an audible and visual alarm is triggered, the exhaust gas inlet is closed, the bypass pipeline valve is opened, and the furnace shutdown procedure is triggered.

[0023] In one embodiment, the furnace temperature three-level early warning and control module uses a multi-point arranged thermocouple temperature measuring instrument (range 0-1100℃, accuracy ±1%) to monitor the temperature of key areas of the furnace in real time.

[0024] Level 1 warning (≥820℃): Stop heating and close the gas inlet valve.

[0025] Level 2 warning (≥920℃): The overheat discharge valve opens, releasing some heat from the furnace.

[0026] Level 3 protection (≥980℃): Audible and visual alarm, closes the exhaust gas inlet and switches to the bypass pipeline, triggering the normal shutdown procedure.

[0027] The emergency bypass and safe emission control module includes a heat exchanger added to the top of the furnace, which is connected to a bypass pipe. A bypass butterfly valve is installed on the bypass pipe. When the furnace temperature is ≥920℃, the bypass butterfly valve is opened to release part of the furnace gas directly through the bypass pipe. The heat exchanger on the bypass pipe cools the high-temperature gas in the bypass pipe, and the cooled gas in the bypass pipe is discharged into the main flue gas pipe.

[0028] In one embodiment, a bypass pipe, heat exchanger, and high-temperature resistant pneumatic bypass butterfly valve (temperature resistance ≥500℃, response time ≤3 seconds) are added to the top of the furnace. This valve automatically opens when a high-temperature warning of 920℃ is triggered, allowing some heat to be released rapidly without being recovered through the heat storage chamber's checker bricks. The bypass path is independently configured and equipped with a shell-and-tube heat exchanger to cool the high-temperature flue gas. The flue gas mixes with the main pipe flue gas before being discharged to the on-site chimney. Simultaneously, the opening of the bypass butterfly valve is automatically adjusted based on feedback from the emitted flue gas temperature to control the emitted flue gas temperature to <300℃.

[0029] In one embodiment, the inlet exhaust gas composition of the VOCs pretreatment system is: benzene series compounds: 2000 mg / m³, NH3: 500 mg / m³, H2S: 300 mg / m³; the outlet exhaust gas composition is: benzene series compounds before the adsorber: 600 mg / m³, benzene series compounds after the adsorber: 50 mg / m³, NH3: 20 mg / m³, H2S: 36 mg / m³.

[0030] Oil washing tower liquid level: 0.85m, benzene series removal rate: 70%; The acid washing tower has a pH of 3.0 and an NH3 removal rate of 96%. The alkaline scrubbing tower has a pH of 13.5 and an H2S removal rate of 88%. Activated carbon penetration rate: 8.3%, VOCs adsorption rate: 91.6%.

[0031] The inlet suction of the VOCs pretreatment system's main exhaust gas pipe is set to -900 Pa. By gradually increasing the opening of the fresh air valve in the VOCs pretreatment system, the frequency of the exhaust gas fan is gradually increased, while maintaining the inlet suction of the main exhaust gas pipe at -900 Pa. When the fresh air valve opening is 0%, the exhaust gas concentration is 14.9%, and the average combustion chamber temperature is 880-930℃, exceeding the normal control requirement (650-920℃). As the fresh air valve opening gradually increases, the exhaust gas concentration and combustion chamber temperature gradually decrease. Controlling the fresh air valve opening to 30-50% can ensure the safe and stable operation of the RTO system, keeping the exhaust gas concentration stable below 8% and the combustion chamber temperature stable at 700-850℃. Note: The exhaust gas concentration mentioned in this invention is a volume percentage concentration. See Appendix Table 1 for specific results.

[0032]

[0033] Appendix 1: Changes in exhaust gas concentration and stable combustion chamber temperature at different fresh air valve openings.

[0034] Heat is released through the emergency exhaust valve (heat exchanger) to reduce the combustion chamber temperature. The initial combustion chamber temperature was 935℃. By adjusting the opening of the emergency exhaust valve, the average combustion chamber temperature gradually decreased, with a temperature drop of 87℃. See Appendix Table 2 for specific results.

[0035]

[0036] Appendix 2: Combustion chamber temperature changes with different opening degrees of the emergency discharge valve.

[0037] Four activated carbon adsorbers are used on site, employing a three-use-one-desorption mode. Based on theoretical calculations and the shift schedule of the operators, the adsorbers that have been purged and cooled are put into use after six days of operation on a single adsorber. On the same day, the cut-out adsorbers are purged, and the following day, after the steam is stopped, nitrogen is used for 24 hours of purging and cooling. The four adsorbers are used in rotation according to their usage time.

[0038] The concentrations of benzene series compounds and the main exhaust gas concentration were measured after a single adsorber was used for 6 days and after it was switched off. The results showed that the benzene series compound concentration after the adsorber was 85 mg / m³ before switching off, indicating that the activated carbon adsorption had reached saturation and had not been penetrated by VOCs. The benzene series compound concentration decreased by 40% after switching off the single adsorber; the main exhaust gas concentration decreased by approximately 6% after switching off the adsorber. See Appendix Table 3 for details.

[0039]

[0040] Appendix 3: Changes in the concentration of benzene series compounds and the concentration of exhaust gas in the main pipe before and after the activated carbon adsorber is switched off.

Claims

1. A method for intelligent early warning and collaborative control of VOCs pretreatment and oxidation furnace temperature, characterized in that: The system includes intelligent control modules for oil washing tower, acid washing tower, and alkali washing tower; an intelligent control module for activated carbon adsorber; a coordinated control module for RTO system exhaust gas concentration; a safety interlock control module for RTO furnace; and an emergency bypass and safe emission control module. The intelligent control modules for oil washing tower, acid washing tower, and alkali washing tower control the liquid level and pH of these towers. The intelligent control module for activated carbon adsorber includes temperature monitoring and activated carbon saturation prediction. The coordinated control module for RTO system exhaust gas concentration includes a fresh air duct with a fresh air valve connected to the RTO inlet main pipe and an exhaust gas concentration detector. Adjusting the opening of the fresh air valve allows for the introduction of air to dilute the exhaust gas. The exhaust gas fan frequency is adjusted to ensure the suction power of the main exhaust gas pipe remains stable within a set range, and the exhaust gas outlet volume concentration is controlled to <10%, ensuring stable RTO operation. A secondary warning system is set; when the exhaust gas volume concentration is ≥10%, a primary warning is triggered, issuing an audible and visual alarm. The system includes a three-level warning mechanism: when the exhaust gas volume concentration is ≥18%, a level two warning is triggered, issuing an audible and visual alarm and closing the exhaust gas inlet valve while opening the bypass pipeline valve; the RTO furnace safety interlock control module includes thermocouples arranged in multiple areas of the furnace, with a three-level warning system: when the furnace temperature is ≥820℃, heating is stopped and the gas inlet valve is closed; when the furnace temperature is ≥920℃, the overheat discharge valve is opened to release furnace heat; when the furnace temperature is ≥980℃, an audible and visual alarm is triggered, the exhaust gas inlet is closed, the bypass pipeline valve is opened, and the furnace shutdown procedure is triggered; the emergency bypass and safe discharge control module includes a heat exchanger added to the top of the furnace, connected to a bypass pipeline, with a bypass butterfly valve installed on the bypass pipeline. When the furnace temperature is ≥920℃, the bypass butterfly valve is opened, allowing some of the furnace gas to be released directly through the bypass pipeline. The heat exchanger on the bypass pipeline cools the high-temperature gas in the bypass pipeline, and the cooled gas in the bypass pipeline is discharged into the main flue gas pipeline.

2. The method for intelligent early warning and collaborative control of VOCs pretreatment and oxidation furnace temperature according to claim 1, characterized in that: The liquid level control includes level gauges installed on the oil washing tower, acid washing tower, and alkali washing tower respectively to monitor the liquid level inside the tower. When the liquid level in each tower is detected to be lower than its set lower limit, the corresponding replenishing pump replenishes the liquid. When the liquid level in each tower is detected to be higher than its set upper limit, the corresponding draining pump discharges the liquid. The pH control includes pH analyzers installed on the acid washing tower and alkali washing tower respectively to monitor the pH of the liquid inside the tower. When the pH value of the liquid in each tower is detected to be lower than its set lower limit, the corresponding acid or alkali is replenished. When the pH value of the liquid in each tower is detected to be higher than its set upper limit, water is replenished.

3. The method for intelligent early warning and collaborative control of VOCs pretreatment and oxidation furnace temperature according to claim 1, characterized in that: The activated carbon adsorber temperature monitoring involves installing temperature sensors at the inlet and outlet of the adsorber and in the middle of the bed. When the temperature exceeds the set warning temperature, an automatic alarm is triggered, the inlet and outlet valves of the activated carbon adsorber are closed, and the steam protection system is activated. The activated carbon saturation prediction includes establishing the adsorption saturation prediction formula T = M*C. 吸附 / (Q*C 入口 ), where T is the adsorption saturation time in hours, M is the weight of activated carbon in the activated carbon adsorber in kilograms, and C 吸附 Adsorption capacity, in g / kg, C 入口 The concentration is the imported concentration, expressed in g / m³.

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