A negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration

Abstract

This invention relates to the field of hazardous waste incineration technology and discloses a negative-pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration, comprising: a waste heat flue gas heating unit, a negative-pressure closed-loop pyrolysis pretreatment chamber unit, a pyrolysis waste gas return and destruction unit, and a safety control unit. By using medium-temperature flue gas from the downstream section of the waste heat boiler as the heating medium, energy cascade utilization is achieved and high-grade energy consumption is reduced; high-moisture or high-viscosity hazardous waste is dehydrated and pyrolyzed before entering the kiln, significantly reducing the risk of temperature fluctuations and coking / blockage within the kiln; through a closed negative-pressure collection and centralized destruction path in the secondary combustion chamber, front-end control and centralized destruction of pollutants such as volatile organic compounds are achieved; through inerting replacement, flame arrest and backfire prevention, online monitoring, and SIS hard interlocking, the inherent safety level and abnormal operating condition handling capabilities of the system are improved. A systematic solution that can be coupled with existing incineration lines and balances energy utilization, environmental control, and inherent safety is proposed.

Description

Technical Field

[0001] This invention relates to the field of hazardous waste incineration technology, and in particular to a negative pressure closed pyrolysis pretreatment system for rotary kiln hazardous waste incineration. Background Technology

[0002] Rotary kiln-secondary combustion chamber incineration systems are suitable for treating hazardous wastes with complex compositions and diverse forms. However, in actual operation, the differences in the physical properties of hazardous wastes often become significant factors causing fluctuations in kiln conditions and increased energy consumption. For example, when bulk materials, adsorbents, or contaminated materials packaged in ton bags are directly fed into the kiln, the outer packaging and internal materials decompose rapidly due to heat, easily generating large amounts of volatile components and water vapor. This leads to fluctuations in kiln head temperature, oxygen levels, and sudden changes in the load on the secondary combustion chamber. Similarly, when high-moisture sludge or water-containing waste is directly incinerated, the vaporization of water absorbs heat, resulting in a decrease in the effective combustion temperature and an increase in fuel compensation. Furthermore, viscous waste liquids or high-viscosity drummed waste liquids are prone to incomplete combustion, wall adhesion, coking, nozzle blockage, or disruption of continuous feeding during atomization and volatilization. These problems not only increase fuel and combustion air consumption but may also increase the difficulty of flue gas treatment system fluctuations and emission control.

[0003] Meanwhile, the flue gas downstream of the waste heat boiler in rotary kiln systems typically contains a large amount of medium-temperature flue gas. While its thermal energy grade is insufficient to directly undertake high-temperature combustion, it is suitable for material preheating, dehydration, or low-temperature pyrolysis. Existing practices that use steam or electric heating for hazardous waste pretreatment often suffer from drawbacks such as high energy consumption, high operating costs, and poor equipment independence. Furthermore, the lack of a closed negative pressure system and reliable disposal pathway during the volatile organic compound (VOC) release stage can easily lead to fugitive emissions and safety risks.

[0004] Therefore, there is an urgent need for a systematic solution that can be coupled with existing incineration lines and take into account energy utilization, environmental control and intrinsic safety. Summary of the Invention

[0005] This invention provides a negative pressure closed-loop pyrolysis pretreatment system for hazardous waste incineration in rotary kilns, which enables hazardous waste to undergo dehydration, viscosity reduction, or controlled release of volatiles before entering the rotary kiln, thereby reducing disturbance to the main incineration process; at the same time, it makes full use of the waste heat from the medium-temperature flue gas in the downstream section of the waste heat boiler to replace high-grade energy, and sends the waste gas generated by pyrolysis back to the high-temperature zone of the secondary combustion chamber for centralized destruction, achieving an integrated effect of waste heat utilization, front-end control, centralized destruction, and safety interlocking.

[0006] To achieve the above objectives, the present invention provides a negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration, comprising: a waste heat flue gas heating unit, a negative pressure closed-loop pyrolysis pretreatment chamber unit, a pyrolysis waste gas return and destruction unit, and a safety control unit. The gas intake end of the waste heat flue gas heating unit is connected to the flue after the waste heat boiler, so that the extracted medium-temperature flue gas enters the heating channel of the pretreatment chamber after passing through the high-temperature shut-off valve and the variable frequency induced draft fan in sequence, and indirectly heats the hazardous waste in the chamber. The pretreatment chamber unit is equipped with an airtight chamber containing a loading and unloading mechanism and a nitrogen inerting and purging mechanism. The chamber door of the airtight chamber is interlocked with the start and stop sequence and is configured to cause the hazardous waste to undergo pyrolysis and generate pyrolysis waste gas under inerting and negative pressure conditions. The inlet of the return and destruction unit is connected to the exhaust port of the pretreatment chamber, and includes a variable frequency return fan, a flame arrester and a secondary combustion chamber injection assembly. The return variable frequency fan is configured to draw pyrolysis exhaust gas to maintain a slight negative pressure inside the chamber so that the pyrolysis exhaust gas is injected into the high-temperature zone of the secondary combustion chamber for incineration after passing through the flame arrester. The safety control unit includes a PLC and an SIS, and is configured to collect temperature, pressure, oxygen content and combustible gas concentration signals, and interlock to cut off the heating supply and start inerting in case of abnormality.

[0007] Optionally, the gas intake point of the waste heat flue gas heating unit is configured as the stable flue gas duct area after the waste heat boiler and before dust removal or purification, and the temperature of the extracted flue gas is limited to 250-300℃ and the inlet temperature can be buffered by bypass mixing or adjusting the baffle. The high-temperature shut-off valve adopts a quick-closing structure and is equipped with valve position feedback. The variable frequency induced draft fan is linked with the pretreatment chamber temperature control circuit. It adopts a control strategy based on the chamber temperature and flue gas flow rate, so that the heating rate, steady-state pyrolysis temperature zone and cooling stage can be automatically switched according to the batch process curve, so as to maintain stable heating between batches of hazardous waste with different moisture content and different heat capacity and reduce the impact on the negative pressure of the main flue.

[0008] Optionally, the chamber of the negative pressure closed pyrolysis pretreatment chamber unit is configured as a corrosion-resistant metal shell and equipped with a fire-resistant and heat-insulating lining. The chamber is equipped with rails and material carts or pallets to carry ton bags or viscous waste liquid barrels and realize batch pushing, positioning and pushing out. The hatch adopts a double sealing ring structure and is equipped with door lock status detection, sealing compression detection and door opening permission logic. The door opening interlock is released when the cooling and replacement are completed and the oxygen content, combustible gas concentration and pressure in the cabin meet the preset safety threshold. The chamber is equipped with baffles or heat exchange jackets to isolate the flue gas side from the material side, preventing open flames and oxidation reactions from entering the pyrolysis space.

[0009] Optionally, the nitrogen inerting purging mechanism includes a nitrogen source, a pressure stabilizing component, a switching valve group, a distributed jet pipe, and an oxygen content analyzer; The nitrogen inerting purging mechanism is provided with at least two purging stages: the first stage is to perform a large-flow replacement after the hatch is closed to quickly reduce the oxygen content, and the second stage is to maintain a small flow during the heating and pyrolysis process to inhibit air infiltration. The oxygen content analyzer's measurement is used as the SIS interlock input. When the oxygen content is higher than the threshold or the analyzer fails, a combination of actions is performed, including cutting off the heating supply, maintaining the extraction, and strengthening the nitrogen purging.

[0010] Optionally, the heating channel of the pretreatment chamber is configured as a closed flow channel on the flue gas side, and the material in the chamber is indirectly heated through jacket heat exchange, coil heat exchange or partition radiation heat exchange. The system is equipped with multi-point temperature measuring components for the chamber temperature, flue gas inlet temperature, and flue gas outlet temperature. It uses dual limits of the upper limit of the inlet temperature and the upper limit of the chamber temperature to protect the chamber pyrolysis temperature from 200 to 400°C in order to achieve dehydration and pyrolysis.

[0011] Optionally, the variable frequency return fan and the chamber pressure transmitter are configured to jointly maintain a slight negative pressure inside the chamber, and the slight negative pressure setting value is segmented according to the working conditions: a smaller negative pressure during the loading and unloading stage to reduce air intake, and a larger negative pressure during the pyrolysis stage to enhance exhaust gas capture. The cabin and return pipeline are equipped with pressure relief or flame arrestor combination protection, and the return fan inlet is equipped with anti-condensation measures or heat tracing to prevent water vapor condensation from causing the fan to surge.

[0012] Optionally, the pyrolysis waste gas return and destruction unit is equipped with an LEL combustible gas concentration monitoring point, a temperature monitoring point, and an optional condensation separation or demisting component on the return pipeline. The condensation separation or demisting component is used to separate condensate and mist droplets before return and introduce the condensate into the hazardous waste collection system.

[0013] Optionally, the secondary combustion chamber injection component is configured as a refractory-sheathed spray gun or injector structure, and is arranged in the lower part of the secondary combustion chamber or the high-temperature turbulent zone, so that the pyrolysis exhaust gas is fully mixed with the excess air in the secondary combustion chamber in a high-speed jet and enters the core area with a temperature greater than 1100°C. The secondary combustion chamber injection component is equipped with a check valve or works in conjunction with a flame arrester to form a backfire prevention channel. By matching the injection pressure, nozzle direction and injection position, the pyrolysis exhaust gas is driven to stay in the secondary combustion chamber for more than 2 seconds, so as to completely oxidize and decompose volatile organic compounds.

[0014] Optionally, the safety control unit adopts a dual-layer architecture of PLC process control and SIS hard interlock, and the key measuring points include at least the cabin temperature, cabin pressure, cabin oxygen content and return pipeline LEL; The safety control unit is equipped with an interlock matrix: when any of the following occurs, such as overheating, loss of negative pressure, excessive oxygen content, excessive LEL, abnormal door lock, or failure of critical instruments, it will shut down the high-temperature shut-off valve, close or limit the flow of the induced draft fan, start nitrogen purging, and control the return fan to shut down safely in a preset sequence.

[0015] Optionally, the system is configured to operate automatically in batches and is linked with the main rotary kiln combustion system. The batch process includes at least: charging confirmation, door closure interlock, nitrogen replacement and inerting, introduction of waste heat flue gas for heating and pyrolysis, negative pressure extraction and return of pyrolysis waste gas for destruction in the secondary combustion chamber, cooling and replacement, and release of interlock for material discharge. Flow or pressure coordination control is provided at both the gas intake and return ends to buffer changes in gas intake and maintain a stable negative pressure in the main flue. Based on the coupling of the return amount with the oxygen content, temperature, and load signals in the secondary combustion chamber, combustion instability in the secondary combustion chamber is avoided.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: Firstly, by using medium-temperature flue gas from the downstream section of the waste heat boiler as the heating medium, energy cascade utilization is achieved, and the consumption of high-grade energy such as electricity / steam is reduced. Secondly, by dehydrating and pyrolyzing hazardous waste with high water content or high viscosity before it enters the kiln, the risk of temperature fluctuations and coking blockage within the kiln is significantly reduced. Thirdly, by using a closed negative pressure collection and centralized destruction path in the secondary combustion chamber, the front-end control and centralized destruction of pollutants such as volatile organic compounds are achieved, reducing fugitive emissions. Fourthly, by using a combination of inerting replacement, flame arrest and backfire prevention, online monitoring, and SIS hard interlocking, the inherent safety level of the system and the ability to handle abnormal operating conditions are improved. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the principle of the negative pressure closed pyrolysis pretreatment system for rotary kiln hazardous waste incineration proposed in an embodiment of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] like Figure 1As shown in the figure, this invention proposes a negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration, comprising: a waste heat flue gas heating unit, a negative pressure closed-loop pyrolysis pretreatment chamber unit, a pyrolysis waste gas return and destruction unit, and a safety control unit; wherein, the gas intake end of the waste heat flue gas heating unit is connected to the flue after the waste heat boiler, so that the extracted medium-temperature flue gas passes through a high-temperature shut-off valve and a variable frequency induced draft fan in sequence before entering the heating channel of the pretreatment chamber to indirectly heat the hazardous waste in the chamber; wherein, the pretreatment chamber unit is equipped with an airtight chamber containing a loading and unloading mechanism and a nitrogen inerting purging mechanism, the airtight chamber... The hatch and start / stop sequence are interlocked and configured to cause pyrolysis of hazardous waste and generate pyrolysis waste gas under inerting and negative pressure conditions. The inlet of the return and destruction unit is connected to the exhaust port of the pretreatment chamber and includes a variable frequency return fan, a flame arrester, and a secondary combustion chamber injection assembly. The return variable frequency fan is configured to draw pyrolysis waste gas to maintain a slight negative pressure inside the chamber so that the pyrolysis waste gas is injected into the high-temperature zone of the secondary combustion chamber for incineration after passing through the flame arrester. The safety control unit includes a PLC and an SIS and is configured to collect temperature, pressure, oxygen content, and combustible gas concentration signals and interlock to cut off heating and start inerting in case of abnormality.

[0020] It should be noted that the above unit division is used to understand the functional structure of the present invention. In actual engineering, the equipment can be modularly combined, disassembled or integrated according to the site layout, pipeline conditions and processing scale. As long as it does not deviate from the core concept of waste heat drive, closed negative pressure, inerting pyrolysis and recycling for destruction of the present invention, it should be understood as falling within the protection scope of the present invention.

[0021] Specifically, the system provided in this embodiment of the invention serves as an external pretreatment module for a rotary kiln hazardous waste incineration line. Its key feature is the combination of waste heat flue gas heating with closed-loop negative pressure inerting pyrolysis, and the achievement of pollutant feedback control through high-temperature destruction in the secondary combustion chamber. It should be noted that this invention does not require changes to the main structure of the rotary kiln, secondary combustion chamber, or waste heat boiler. Instead, it creates controllable heat and waste gas branches by setting up a gas intake branch in the flue gas duct downstream of the waste heat boiler and a return injection point at a suitable location in the secondary combustion chamber. This results in strong feasibility and compatibility in engineering modifications.

[0022] In a preferred embodiment, the gas intake point of the waste heat flue gas heating unit is configured as the stable flue gas zone downstream of the waste heat boiler and before dust removal or purification. The extracted flue gas temperature is limited to 250-300°C and inlet temperature buffering can be achieved through bypass mixing or adjusting baffles. The high-temperature shut-off valve adopts a quick-closing structure and is equipped with valve position feedback. The variable frequency induced draft fan is linked with the pretreatment chamber temperature control circuit and adopts a control strategy based on the chamber temperature and flue gas flow rate. This allows the heating rate, steady-state pyrolysis temperature zone, and cooling stage to be automatically switched according to the batch process curve, so as to maintain stable heating between hazardous waste batches with different moisture contents and different heat capacities and reduce the impact on the negative pressure of the main flue gas.

[0023] In this embodiment of the invention, the gas intake point of the waste heat flue gas heating unit is selected in a relatively stable section of the flue gas duct downstream of the waste heat boiler. Specifically, the flue gas temperature in this section is typically in the medium temperature range of 250–300°C, which can provide sufficient thermal driving force for the pretreatment chamber to complete dehydration and pyrolysis, while avoiding local overheating of the pretreatment chamber or thermal shock of materials caused by using excessively high-temperature flue gas.

[0024] Furthermore, in one feasible implementation, a mixing bypass or regulating baffle can be installed in the gas intake branch to buffer the temperature fluctuations of the flue gas entering the pretreatment chamber; simultaneously, a high-temperature shut-off valve is installed in conjunction with a variable frequency induced draft fan, enabling the heating unit to possess both rapid shut-off capability and continuous regulation capability. It should be noted that the so-called rapid shut-off is not only used for emergency shutdown, but also to ensure that the heat source is promptly isolated when the pretreatment chamber enters inerting replacement, door opening permission judgment, or abnormal interlock triggering, thereby preventing the continued input of heat into the chamber and the promotion of pyrolysis reactions under dangerous conditions.

[0025] In a preferred embodiment, the negative pressure closed pyrolysis pretreatment chamber unit is configured with a corrosion-resistant metal shell and a fire-resistant and heat-insulating lining. The chamber is equipped with rails and material carts or pallets to carry ton bags or viscous waste liquid barrels and to realize batch pushing, positioning and pushing out. The chamber door adopts a double sealing ring structure and is equipped with door lock status detection, sealing tightness detection and door opening permission logic. The door opening interlock is released when the cooling and replacement are completed and the oxygen content, combustible gas concentration and pressure in the chamber meet the preset safety thresholds. The chamber is equipped with a flow guide baffle or heat exchange jacket to isolate the flue gas side from the material side and prevent open flame and oxidation reaction from entering the pyrolysis space.

[0026] In this embodiment of the invention, the negative pressure closed-loop pyrolysis pretreatment chamber unit is the core for achieving safe pyrolysis. The chamber body adopts a corrosion-resistant metal structure and is equipped with a fire-resistant and heat-insulating lining to ensure long-term stable operation in the pyrolysis temperature range of 200-400℃. It should be noted that this invention emphasizes pyrolysis rather than combustion; therefore, the heating channel preferably adopts a closed flow channel on the flue gas side, transferring heat to the material side through radiation / convection via jackets, coils, or baffles, thus isolating the flue gas from the pyrolysis space and structurally preventing open flames and oxygen-rich flue gas from directly entering the pyrolysis chamber. Furthermore, the chamber is equipped with a track and material cart or pallet support structure, allowing ton bags or drums of viscous waste liquid to be pushed in, positioned, and pushed out in batches, thereby adapting to the intermittent receiving and mixing modes commonly found in incineration lines.

[0027] In one implementation, the hatch employs a double-sealing structure and is equipped with door lock status detection, seal tightness detection, and door opening permission logic. It is important to emphasize that the hatch interlock is not merely a mechanical closure, but rather a component of process safety conditions: the system is only allowed to enter the inerting and replacement phase after the hatch is confirmed to be airtight; the system is only allowed to enter the pyrolysis phase after the inerting and replacement reaches the target oxygen content; and the door opening interlock is only allowed to be released after pyrolysis is completed and cooling and replacement are finished, and the oxygen content, combustible gas concentration, and pressure inside the hatch meet the threshold values. Through these sequential constraints, the pyrolysis reaction is always conducted within the triple boundaries of airtightness, inerting, and negative pressure.

[0028] In a preferred embodiment, the nitrogen inerting purging mechanism includes a nitrogen source, a pressure stabilizing component, a switching valve group, a distributed spray pipe, and an oxygen content analyzer. The nitrogen inerting purging mechanism has at least two purging stages: the first stage involves high-flow-rate replacement after the hatch is closed to rapidly reduce the oxygen content; the second stage involves maintaining a low-flow-rate operation during the pyrolysis process to suppress air infiltration. The oxygen content analyzer's measurement serves as the SIS interlock input; when the oxygen content exceeds a threshold or the analyzer fails, a combined action of cutting off heating, maintaining extraction, and intensifying nitrogen purging is executed.

[0029] In this embodiment of the invention, a nitrogen inerting purging mechanism is used to establish and maintain a low-oxygen environment. Specifically, nitrogen gas enters the switching valve group via a pressure stabilizing component, and is then uniformly injected into the chamber through distributed spray pipes, causing the air inside the chamber to be displaced and discharged. It should be noted that inerting replacement must consider both replacement efficiency and its synergistic relationship with negative pressure extraction: if negative pressure is formed solely by extraction without inerting, the infiltration of outside air may lead to an increase in oxygen content; if inerting is relied upon solely without negative pressure extraction, pyrolysis waste gas may accumulate in local spaces, increasing the risk of leakage.

[0030] Therefore, in one feasible implementation, the system employs a two-stage purging strategy: a high-flow-rate rapid purging after loading to quickly reduce the oxygen content to, for example, below 5%; and a low-flow-rate maintenance during the pyrolysis phase to counteract the rising oxygen trend caused by micro-leakage. Furthermore, the oxygen analyzer serves not only as a process display but also as a SIS interlock input, triggering a heating cutoff and enhanced inerting when the oxygen content exceeds the limit or the analyzer fails, ensuring that any anomaly prioritizes a return to the low-oxygen safety boundary.

[0031] In a preferred embodiment, the heating channel of the pretreatment chamber is configured as a closed flow channel on the flue gas side, and the material inside the chamber is indirectly heated through jacket heat exchange, coil heat exchange or partition radiation heat exchange; wherein, the system is equipped with a multi-point temperature measuring component for the chamber temperature, flue gas inlet temperature and flue gas outlet temperature, and the chamber pyrolysis temperature is limited to 200-400°C by the dual limit values ​​of the upper limit of the inlet temperature and the upper limit of the chamber temperature to achieve dehydration and pyrolysis.

[0032] In a preferred embodiment, the variable frequency return fan and the in-cabin pressure transmitter are configured to jointly maintain a slight negative pressure in the cabin, and the slight negative pressure setpoint is segmented according to the operating conditions: a smaller negative pressure during the loading and unloading stage to reduce air intake, and a larger negative pressure during the pyrolysis stage to enhance exhaust gas capture; wherein, the cabin and return pipeline are equipped with pressure relief or flame arrestor combination protection, and the return fan inlet is equipped with anti-condensation measures or heat tracing to avoid water vapor condensation causing fan surge.

[0033] In a preferred embodiment, the pyrolysis waste gas return and destruction unit is equipped with an LEL combustible gas concentration monitoring point, a temperature monitoring point, and an optional condensation separation or demisting component on the return pipeline. The condensation separation or demisting component is used to separate condensate and mist droplets before return and to introduce the condensate into the hazardous waste collection system.

[0034] In this embodiment of the invention, the pyrolysis waste gas recovery and destruction unit is used to reliably capture the water vapor and volatile components generated during pyrolysis and introduce them into the secondary combustion chamber for destruction. Specifically, the return fan and the chamber pressure transmitter form a feedback regulation to maintain a slight negative pressure inside the chamber. It should be noted that the slight negative pressure is not a single fixed value, but can be set in stages according to the operating conditions: a smaller negative pressure is used during the loading and unloading stage to reduce the inerting burden caused by a large amount of air intake, and a larger negative pressure is used during the pyrolysis stage to enhance waste gas capture and reduce the risk of fugitive emissions.

[0035] A flame arrester is installed at the outlet of the return fan to suppress backfire and detonation propagation. In a more advanced implementation, LEL monitoring points, temperature monitoring points, and differential pressure monitoring points can be installed in the return pipeline, and condensate separation or demisting components can be optionally installed to separate condensate and mist droplets, preventing pipeline corrosion, fan scaling, or surge. It should be understood that condensate separation does not change the core path of return and disposal, but rather is an optimized configuration for engineering reliability and maintainability.

[0036] In a preferred embodiment, the secondary combustion chamber injection component is configured as a refractory-sheathed spray gun or injector structure, arranged in the lower part of the secondary combustion chamber or the high-temperature turbulent zone, so that the pyrolysis waste gas is fully mixed with the excess air in the secondary combustion chamber at high speed and enters the core area with a temperature greater than 1100°C; wherein, the secondary combustion chamber injection component is equipped with a check valve structure or works with a flame arrester to form a backfire prevention channel, and by matching the injection pressure, nozzle direction and injection position, the pyrolysis waste gas is driven to stay in the secondary combustion chamber for more than 2 seconds to completely oxidize and decompose volatile organic compounds.

[0037] In this embodiment of the invention, the secondary combustion chamber injection component is used to deliver pyrolysis waste gas into the high-temperature turbulent zone of the secondary combustion chamber. Specifically, the injection component can be a refractory-sheathed spray gun or an injector structure, arranged in the lower part of the secondary combustion chamber or near the high-temperature core zone, so that the pyrolysis waste gas enters in the form of a high-speed jet, quickly mixes with excess air, and achieves complete oxidation and decomposition under conditions of a temperature greater than 1100°C and a residence time greater than 2 seconds.

[0038] It should be noted that the composition of pyrolysis exhaust gas may vary with different batches of materials. Improper control of the injection rate may affect the temperature and combustion stability of the secondary combustion chamber. Therefore, in one feasible implementation, the return rate is coupled and adjusted with the oxygen content, temperature, or load signal of the secondary combustion chamber to make the injection process "gradually changeable and followable," thereby avoiding sudden temperature drops or combustion fluctuations. Furthermore, the injection assembly can be equipped with a check valve structure and work in conjunction with a flame arrester to form a backfire prevention channel, ensuring that it still has backfire suppression capability during transient fluctuations in the secondary combustion chamber.

[0039] In a preferred embodiment, the safety control unit adopts a dual-layer architecture of PLC process control and SIS hard interlock. The key measuring points include at least the cabin temperature, cabin pressure, cabin oxygen content, and return pipeline LEL. The safety control unit is equipped with an interlock matrix: when any of the following occurs, such as over-temperature, loss of negative pressure, oxygen content exceeding the limit, LEL exceeding the limit, door lock malfunction, or key instrument failure, the unit will shut down the high-temperature shut-off valve, close or limit the flow of the induced draft fan, start nitrogen purging, and control the return fan to shut down safely in a preset sequence.

[0040] In this embodiment of the invention, the safety control unit adopts a dual-layer architecture of PLC process control and SIS hard interlocking. The PLC side is used to realize batch sequential control, temperature regulation, pressure regulation, and automatic switching of valves / fans; the SIS side is used to realize independent protection for critical hazardous conditions.

[0041] It's important to note that the design philosophy of SIS (Safety Information System) is to directly execute verifiable safety actions without relying on complex calculations when a hazard occurs. Therefore, SIS receives at least critical inputs such as cabin temperature, cabin pressure, cabin oxygen content, return pipeline LEL (Leadership Level), and door lock status, and establishes an interlock matrix: when any of the following occurs—overheating, loss of negative pressure, oxygen content or LEL exceeding limits, door lock malfunction, or critical instrument failure—it immediately executes a combination of actions: shutting off the high-temperature shut-off valve, closing or limiting the flow of the induced draft fan, initiating nitrogen purging, and controlling the safe shutdown of the return draft fan according to a preset sequence. Furthermore, the system sets interlock reset conditions, operating permissions, and event logging to prevent accidental resets that could lead to the recurrence of hazardous conditions when safety boundaries are not met, while also providing a data foundation for operational optimization and accident tracing.

[0042] In a preferred embodiment, the system is configured to operate automatically in batches and is linked to the main rotary kiln incineration system. The batch process includes at least: charging confirmation, door closure interlocking, nitrogen replacement and inerting, introduction of waste heat flue gas for heating and pyrolysis, negative pressure extraction and return of pyrolysis waste gas for destruction in the secondary combustion chamber, cooling and replacement, and release of material after interlocking. Flow or pressure coordination control is provided at both the gas intake and return ends to buffer changes in gas intake and maintain a stable negative pressure in the main flue. Based on the coupling of the return amount with the oxygen content, temperature, and load signals in the secondary combustion chamber, combustion instability in the secondary combustion chamber is avoided.

[0043] Finally, the system operation process needs further explanation. In a typical batch operation mode, the system first completes the loading confirmation and door closure interlock, then enters the nitrogen replacement and inerting stage. After reaching the target oxygen content, waste heat flue gas is introduced to raise the temperature, bringing the chamber into the pyrolysis temperature zone of 200-400℃ and maintaining this temperature for a certain period. The waste gas generated during pyrolysis is returned under negative pressure extraction and, after flame arrestor protection, is sprayed into the high-temperature zone of the secondary combustion chamber for centralized destruction. When the batch endpoint criteria are reached, the cooling and replacement stage begins. After meeting the door opening permission conditions, the interlock is released and the material is discharged. It should be understood that the batch endpoint criteria are not limited to time, but can also be comprehensively judged by combining information such as temperature plateau changes, returned gas composition trends, LEL changes, or energy balance. This invention does not limit the selection of endpoint criteria, as long as a safe, controllable, and traceable pretreatment effect can be achieved.

[0044] Meanwhile, considering the coordination between the system and the rotary kiln main system, this invention employs flow / pressure coordinated control at both the gas intake and return ends to minimize disturbances to the negative pressure in the main flue and the combustion stability of the secondary combustion chamber. Furthermore, the system can output batch reports, recording temperature curves, oxygen content curves, LEL curves, and interlock events, providing a basis for hazardous waste type parameterization, process curve optimization, and equipment maintenance.

[0045] It is understood that in the description of this specification, references to the terms "one embodiment," "another embodiment," "other embodiments," or "first embodiment to Nth embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0046] It should be noted that, in this document, the terms include, encompass, or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or system that includes a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or system. Without further limitations, an element defined by the statement "including a…" does not exclude the presence of other identical elements in the process, method, article, or system that includes that element.

[0047] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration, characterized in that, include: Waste heat flue gas heating unit, negative pressure closed pyrolysis pretreatment chamber unit, pyrolysis waste gas return and destruction unit and safety control unit; The gas intake end of the waste heat flue gas heating unit is connected to the flue after the waste heat boiler, so that the extracted medium-temperature flue gas enters the heating channel of the pretreatment chamber after passing through the high-temperature shut-off valve and the variable frequency induced draft fan in sequence, and indirectly heats the hazardous waste in the chamber. The pretreatment chamber unit is equipped with an airtight chamber containing a loading and unloading mechanism and a nitrogen inerting and purging mechanism. The chamber door of the airtight chamber is interlocked with the start and stop sequence and is configured to cause the hazardous waste to undergo pyrolysis and generate pyrolysis waste gas under inerting and negative pressure conditions. The inlet of the return and destruction unit is connected to the exhaust port of the pretreatment chamber, and includes a variable frequency return fan, a flame arrester and a secondary combustion chamber injection assembly. The return variable frequency fan is configured to draw pyrolysis exhaust gas to maintain a slight negative pressure inside the chamber so that the pyrolysis exhaust gas is injected into the high-temperature zone of the secondary combustion chamber for incineration after passing through the flame arrester. The safety control unit includes a PLC and an SIS, and is configured to collect temperature, pressure, oxygen content and combustible gas concentration signals, and interlock to cut off the heating supply and start inerting in case of abnormality.

2. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The gas intake point of the waste heat flue gas heating unit is configured as the stable flue zone after the waste heat boiler and before dust removal or purification. The temperature of the extracted flue gas is limited to 250-300℃ and the inlet temperature can be buffered by bypass mixing or adjusting the baffle. The high-temperature shut-off valve adopts a quick-closing structure and is equipped with valve position feedback. The variable frequency induced draft fan is linked with the pretreatment chamber temperature control circuit. It adopts a control strategy based on the chamber temperature and flue gas flow rate, so that the heating rate, steady-state pyrolysis temperature zone and cooling stage can be automatically switched according to the batch process curve, so as to maintain stable heating between batches of hazardous waste with different moisture content and different heat capacity and reduce the impact on the negative pressure of the main flue.

3. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The negative pressure closed pyrolysis pretreatment chamber unit is configured with a corrosion-resistant metal shell and a fire-resistant and heat-insulating lining. The chamber is equipped with rails and material carts or pallets to carry ton bags or viscous waste liquid barrels and realize batch pushing, positioning and pushing out. The hatch adopts a double sealing ring structure and is equipped with door lock status detection, sealing compression detection and door opening permission logic. The door opening interlock is released when the cooling and replacement are completed and the oxygen content, combustible gas concentration and pressure in the cabin meet the preset safety threshold. The chamber is equipped with baffles or heat exchange jackets to isolate the flue gas side from the material side, preventing open flames and oxidation reactions from entering the pyrolysis space.

4. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The nitrogen inerting purging mechanism includes a nitrogen source, a pressure stabilizing component, a switching valve group, a distributed spray pipe, and an oxygen content analyzer. The nitrogen inerting purging mechanism is provided with at least two purging stages: the first stage is to perform a large-flow replacement after the hatch is closed to quickly reduce the oxygen content, and the second stage is to maintain a small flow during the heating and pyrolysis process to inhibit air infiltration. The oxygen content analyzer's measurement is used as the SIS interlock input. When the oxygen content is higher than the threshold or the analyzer fails, a combination of actions is performed, including cutting off the heating supply, maintaining the extraction, and strengthening the nitrogen purging.

5. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The heating channel of the pretreatment chamber is configured as a closed flow channel on the flue gas side, and the material in the chamber is indirectly heated through jacket heat exchange, coil heat exchange or partition radiation heat exchange. The system is equipped with multi-point temperature measuring components for the chamber temperature, flue gas inlet temperature, and flue gas outlet temperature. It uses dual limits of the upper limit of the inlet temperature and the upper limit of the chamber temperature to protect the chamber pyrolysis temperature from 200 to 400°C in order to achieve dehydration and pyrolysis.

6. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The variable frequency return fan and the in-chamber pressure transmitter are configured to jointly maintain a slight negative pressure in the chamber, and the slight negative pressure setpoint is segmented according to the working conditions: a smaller negative pressure during the loading and unloading stage to reduce air intake, and a larger negative pressure during the pyrolysis stage to enhance exhaust gas capture. The cabin and return pipeline are equipped with pressure relief or flame arrestor combination protection, and the return fan inlet is equipped with anti-condensation measures or heat tracing to prevent water vapor condensation from causing the fan to surge.

7. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The pyrolysis waste gas return and destruction unit is equipped with LEL combustible gas concentration monitoring points, temperature monitoring points, and optional condensation separation or demisting components on the return pipeline. The condensation separation or demisting components are used to separate condensate and mist droplets before return and introduce the condensate into the hazardous waste collection system.

8. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The secondary combustion chamber injection component is configured as a refractory-sheathed spray gun or injector structure and is arranged in the lower part of the secondary combustion chamber or the high-temperature turbulent zone, so that the pyrolysis waste gas is fully mixed with the excess air in the secondary combustion chamber in a high-speed jet and enters the core area with a temperature greater than 1100°C. The secondary combustion chamber injection component is equipped with a check valve or works in conjunction with a flame arrester to form a backfire prevention channel. By matching the injection pressure, nozzle direction and injection position, the pyrolysis exhaust gas is driven to stay in the secondary combustion chamber for more than 2 seconds, so as to completely oxidize and decompose volatile organic compounds.

9. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The safety control unit adopts a dual-layer architecture of PLC process control and SIS hard interlock. The key measuring points include at least the cabin temperature, cabin pressure, cabin oxygen content and return pipeline LEL. The safety control unit is equipped with an interlock matrix: when any of the following occurs, such as overheating, loss of negative pressure, excessive oxygen content, excessive LEL, abnormal door lock, or failure of critical instruments, it will shut down the high-temperature shut-off valve, close or limit the flow of the induced draft fan, start nitrogen purging, and control the return fan to shut down safely in a preset sequence.

10. The negative pressure closed-loop pyrolysis pretreatment system for rotary kiln hazardous waste incineration as described in claim 1, characterized in that, The system is configured for automatic batch operation and is linked to the main rotary kiln incineration system. The batch process includes at least: charging confirmation, door closure interlock, nitrogen replacement and inerting, introduction of waste heat flue gas for heating and pyrolysis, negative pressure extraction and return of pyrolysis waste gas for destruction in the secondary combustion chamber, cooling and replacement, and release of interlock for material discharge. Among them, flow or pressure coordination control is set at both ends of gas intake and return to buffer changes in gas intake and maintain a stable negative pressure in the main flue. Based on the coupling of return amount with oxygen content, temperature and load signals in the secondary combustion chamber, combustion instability in the secondary combustion chamber is avoided.

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