A combined induced draft fan for waste heat recovery in direct-fired equipment

Abstract

This utility model discloses a combined induced draft device for waste heat recovery in direct-fired equipment. The device includes an induced draft system, an auxiliary induced draft unit, a combined emergency exhaust device, air ducts and connecting components, and an intelligent control system. The induced draft system provides main induced draft force through at least one main induced draft system variable frequency fan. The auxiliary induced draft unit provides auxiliary induced draft through parallel-connected induced draft auxiliary system variable frequency fans. The combined emergency exhaust device is equipped with an automatic exhaust device and a fast exhaust valve. The intelligent control system, based on monitoring the operating status of the direct-fired equipment, can automatically or manually control the operation of each fan and emergency device. This utility model can effectively adapt to rapid load fluctuations, accurately maintain stable negative pressure inside the furnace, and has multiple safety protections, improving operational efficiency, stability, and safety.

Description

Technical Field

[0001] This utility model belongs to the field of flue gas treatment and waste heat recovery technology for direct-fired equipment, specifically relating to a combined induced draft device for a waste heat recovery system of direct-fired equipment, which can adapt to rapid changes in equipment load and maintain stable negative pressure inside the furnace. Background Technology

[0002] In energy-intensive industrial sectors, direct-fired equipment is widely used in process heating, heat supply, and power generation.

[0003] These types of equipment generate a large amount of high-temperature flue gas carrying considerable heat energy during operation. However, companies usually discharge most of this flue gas directly without energy recovery. This not only causes serious energy waste but also leads to local thermal pollution and increases greenhouse gas and pollutant emissions. This is seriously contrary to the current development concept of energy conservation, emission reduction, green and low-carbon. From the perspective of energy utilization efficiency and environmental protection requirements, implementing waste heat recovery for direct-fired equipment is a key path to improve overall energy efficiency.

[0004] In existing technologies, the industry generally integrates heat exchange equipment such as waste heat boilers, economizers or air preheaters, and uses induced draft fans to build a stable flue gas flow channel to achieve basic control of waste heat recovery and flue gas emissions.

[0005] However, these traditional systems are difficult to adapt to the large and rapid load fluctuations of direct-fired equipment. The flue gas flow, temperature and pressure will fluctuate frequently and drastically, making it difficult to maintain a stable negative pressure inside the furnace. The stability of the negative pressure inside the furnace is the core prerequisite for the safe and efficient operation of the equipment. Excessive negative pressure will aggravate air intrusion, which will reduce combustion efficiency and increase fan power consumption. Excessive negative pressure may cause flue gas leakage, thereby damaging equipment components and threatening production safety.

[0006] Currently, most mainstream exhaust systems use baffles or valves for throttling regulation. This method has a slow response speed, low regulation accuracy, and low operating efficiency under non-design conditions, with a large amount of energy being consumed in overcoming regulation resistance.

[0007] Although variable frequency technology has been applied in some induced draft fans, it is still insufficient to cope with sudden load fluctuations. In addition, the system generally lacks a rapid emergency mechanism for abnormal operating conditions such as sudden pressure rise. Once there is a sudden increase in load or an increase in resistance on the waste heat recovery side, the equipment may be damaged due to excessive pressure, or even a safety accident may be caused.

[0008] Some studies have attempted to improve the system from a system-level perspective, such as steam and flue gas co-recovery systems. While these solutions have potential in terms of thermal energy integration and economy, they have not specifically addressed the challenges of airflow and negative pressure control caused by rapid load fluctuations. In fact, their actual operating results further confirm the importance of stable airflow for efficient waste heat recovery.

[0009] In summary, existing waste heat recovery induced draft systems have the following core shortcomings:

[0010] 1. Baffle throttling regulation or single frequency conversion technology is difficult to respond quickly and accurately to drastic changes in load, and cannot stably maintain a constant negative pressure inside the furnace;

[0011] 2. Lack of an auxiliary ventilation backup mechanism in case the main exhaust fan is saturated or malfunctions;

[0012] 3. The system lacks an independent emergency discharge channel in case of abnormal pressure spikes, resulting in weak shock resistance.

[0013] 4. Significant energy waste occurs during the adjustment process, and the induced draft system and the waste heat recovery system do not achieve dynamic coordinated operation.

[0014] Therefore, there is an urgent need to develop a new type of induced draft system. This system should be able to dynamically adapt to rapid and large fluctuations in load, ensure that the negative pressure inside the furnace remains highly stable, and integrate a rapid emergency protection mechanism to further improve the system's energy efficiency and operational reliability. Ultimately, this will promote the development of waste heat recovery from direct-fired equipment towards high efficiency, safety, and large-scale operation. Utility Model Content

[0015] To address the core issues in the aforementioned background technologies, such as slow response, insufficient system resilience, lack of safety redundancy, and low energy efficiency, this utility model aims to provide an innovative combined induced draft device.

[0016] The present invention is entitled "A combined induced draft device for waste heat recovery in direct-fired equipment".

[0017] This solution can dynamically adapt to rapid and significant fluctuations in the load of direct-fired equipment, accurately maintain stable negative pressure inside the furnace, and integrate multiple safety protection mechanisms, thereby providing efficient and reliable airflow organization guarantees for other heat recovery systems.

[0018] To achieve the above objectives, the core of the technical solution adopted by this utility model lies in constructing a composite system in which an exhaust system, an auxiliary exhaust unit, a combined emergency emission device, and an intelligent control system work together.

[0019] The combined induced draft device has the following structure: the induced draft system serves as the core power source, equipped with at least one variable frequency fan for the main induced draft system, which is mainly used to establish the necessary negative pressure environment for the direct combustion equipment and reliably transport the high-temperature flue gas generated by combustion to the waste heat recovery system.

[0020] To cope with complex operating conditions, the device is equipped with an auxiliary induced draft unit connected in parallel with the induced draft system. This unit also includes at least one variable frequency fan for the induced draft auxiliary system. It can provide incremental induced draft force when the main system capacity is close to the limit, and can also serve as a hot standby redundancy for the main system, which greatly improves the overall reliability and adjustment margin of the system.

[0021] The key component of this utility model is a combined emergency exhaust device, which is connected in parallel with the main flue through a bypass flue and integrates an automatic exhaust device and a fast exhaust valve with a faster response speed, forming a graded emergency pressure relief barrier.

[0022] All of the above components, together with the air ducts and connecting parts, form a complete flue gas flow network.

[0023] The intelligent control system consists of a sensor array, a controller, and a human-machine interface.

[0024] The sensor array collects key parameters such as negative pressure inside the furnace, flue gas temperature and flow rate of the direct-fired equipment in real time.

[0025] The controller (such as a PLC) performs closed-loop control of the entire system based on this real-time data and preset algorithms;

[0026] The human-machine interface is used for system status monitoring and parameter setting, and supports switching between automatic and manual control modes.

[0027] In automatic mode, the system operates autonomously according to preset logic;

[0028] In manual mode, operators can directly control the start / stop, speed, and emergency device switches of each fan through the interface, providing a high degree of flexibility and controllability for equipment commissioning, handling special working conditions, and system maintenance.

[0029] This intelligent control system does not simply control individual components, but rather performs independent and coordinated precise control of the variable frequency fan of the main induced draft system, the variable frequency fan of the induced draft auxiliary system, the automatic exhaust device, and the quick exhaust valve, thus forming an intelligent whole that can adapt to changes.

[0030] In summary, this utility model, through its unique modular hardware architecture and intelligent collaborative control, brings significant improvements to the existing waste heat recovery technology of direct-fired equipment.

[0031] Firstly, it achieves precise and stable negative pressure control, directly overcoming the lag and inaccuracy problems of traditional baffle adjustment and single frequency conversion technology, and providing an ideal airflow environment for the combustion and heat exchange process of direct-fired equipment.

[0032] Secondly, it significantly improves the system's energy efficiency. The stepless speed regulation of the variable frequency fan avoids throttling losses, and the coordinated operation strategy of the main and auxiliary fans ensures that the system always operates in the high-efficiency range, thereby reducing overall energy consumption.

[0033] Third, it greatly enhances the safety and reliability of the system. The auxiliary ventilation unit provides valuable operational resilience, while the combined emergency discharge device provides reliable safety redundancy, effectively resisting the impact of abnormal operating conditions and protecting the safety of the equipment itself.

[0034] Fourth, the control mode is flexible. The system supports seamless switching between automatic and manual control, ensuring high efficiency in normal operation while also providing manual intervention capability in special circumstances, with comprehensive control strategies.

[0035] Fifth, it is easy to implement and maintain. The device adopts a modular and standardized design, with a compact structure and unified interfaces, which greatly simplifies the installation and commissioning process. In daily maintenance, the clear system layout and independent component functions make fault location and component replacement easy. With the help of the self-diagnostic function of the control system, maintenance costs and technical thresholds are significantly reduced, making it easy to promote and apply on a large scale in industrial fields. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the system structure of this utility model;

[0037] Figure 2 This is a schematic diagram of the combined emergency discharge device;

[0038] In the diagram, 1. Exhaust fan system, 101. Variable frequency fan of main exhaust fan system, 102. Waste heat recovery system, 2. Auxiliary exhaust fan unit, 201. Variable frequency fan of auxiliary exhaust fan system, 3. Combined emergency exhaust device, 301. Automatic exhaust device, 302. Quick exhaust valve, 4. Direct combustion equipment, 5. Air duct and connecting parts, 6. Schematic diagram of automatic exhaust device and quick exhaust valve opening, 7. Schematic diagram of emergency exhaust device exhaust. Detailed Implementation

[0039] To enhance understanding of this utility model, the present utility model will be further described in detail below with reference to the embodiments and accompanying drawings. These embodiments are only used to explain the present utility model and do not constitute a limitation on the scope of protection of the present utility model.

[0040] It should be noted that the specific equipment models, performance parameters and pressure thresholds mentioned in this embodiment are only to help understand the technical solution of this utility model, and are not intended to limit this utility model. Within the scope of the concept of this utility model, those skilled in the art can make selections and adjustments according to actual working conditions.

[0041] 1. Exhaust system, 101. Variable frequency fan of main exhaust system, 102. Waste heat recovery system, 2. Auxiliary exhaust unit, 201. Variable frequency fan of auxiliary exhaust system, 3. Combined emergency exhaust device, 301. Automatic exhaust device, 302. Quick exhaust valve, 4. Direct combustion equipment, 5. Duct and connecting parts, 6. Schematic diagram of automatic exhaust device and quick exhaust valve opening, 7. Schematic diagram of emergency exhaust device exhaust.

[0042] like Figure 1 As shown, it illustrates the overall system structure of the combined induced draft device of this utility model.

[0043] The device organically connects the direct-fired equipment 4, the induced draft system 1, the waste heat recovery system 102, the auxiliary induced draft unit 2, and the combined emergency emission device 3 into a complete flue gas treatment and energy recovery loop through the air duct and connecting component 5.

[0044] The exhaust system 1 is the core power source for maintaining flue gas flow. Its core equipment is the variable frequency fan 101 of the main exhaust system. This fan is preferably driven by a high-voltage frequency converter, so that its air volume can be continuously and smoothly adjusted within the range of 30% to 110% of the rated air volume.

[0045] Under normal operating conditions, the variable frequency fan 101 of the induced draft main system adjusts its speed according to the control command to establish and maintain a stable micro-negative pressure environment (e.g., -20Pa to -50Pa) in the furnace of the direct combustion equipment 4, while continuously drawing in high-temperature flue gas and transporting it to the waste heat recovery system 102 to realize heat energy recovery.

[0046] The auxiliary induced draft unit 2 is connected in parallel with the induced draft system 1 in the flue. Its core is the variable frequency fan 201 of the induced draft auxiliary system. The design of this unit is one of the key innovations in achieving resilience and wide load adjustment of this system. It is not always running, but serves as a reserve device.

[0047] When the system determines that the main induced draft fan 101 is already operating at full load and still cannot meet the induced draft demand, or when the main fan needs maintenance or malfunctions, the auxiliary induced draft fan 201 will start immediately, operating in parallel with the main fan or independently undertaking the induced draft task. This ensures the continuity and reliability of the system's induced draft capacity under any operating condition and avoids system instability caused by insufficient capacity of a single fan.

[0048] like Figure 2 As shown, the combined emergency emission device 3 is also connected in parallel with the main system via a bypass flue.

[0049] It integrates two exhaust components with different response speeds and functions: an automatic exhaust device 301 and a quick exhaust valve 302.

[0050] This combined design constitutes the core safety innovation of this utility model, as shown by markings 6 and 7 in the figure, which together form a staged pressure relief safety valve.

[0051] The automatic venting device 301, as the first line of defense, typically opens slowly according to the controller command when the system pressure exceeds a lower first preset threshold (e.g., +50Pa) to release pressure in order to deal with slow pressure buildup.

[0052] The quick exhaust valve 302 serves as the ultimate safety barrier. When the system pressure instantly exceeds a higher second preset threshold (e.g., +150Pa) due to some drastic change, it receives an emergency signal from the controller and fully opens within seconds, forming a powerful exhaust flow as shown in the emergency exhaust device diagram 7, quickly releasing the dangerous pressure and protecting the equipment.

[0053] The core of the entire system's intelligence lies in the intelligent control system.

[0054] The system collects operating parameters in real time through sensor groups (including pressure sensors, thermocouples, flow meters, etc.) deployed in key locations such as the furnace and flue of the direct-fired equipment.

[0055] These data are transmitted to the controller. The PLC stores a preset control algorithm, which can calculate and judge the load status of the direct-fired equipment 4 in real time, and then independently and accurately send control commands to the main induced draft system variable frequency fan 101, the auxiliary induced draft system variable frequency fan 201, the automatic exhaust device 301 and the fast exhaust valve 302.

[0056] Operators can monitor the operating status of the entire system in real time through the human-machine interface, and can manually set key parameters such as target negative pressure and pressure threshold.

[0057] Furthermore, the system has an independent manual control mode. When switched to this mode, the operator can bypass the automatic control logic and directly and independently start, stop and adjust the speed of the variable frequency fan of the main induced draft system and the variable frequency fan of the induced draft auxiliary system. The operator can also manually trigger the opening and closing of the automatic exhaust device or the quick exhaust valve.

[0058] This feature is crucial in the early stages of system commissioning, during maintenance of automated components, or when dealing with specific complex operating conditions, ensuring ultimate flexibility in system control.

[0059] The design of this utility model also takes into full consideration maintainability.

[0060] The air duct and connecting components 5 adopt a standardized design and are made of high-temperature and corrosion-resistant stainless steel or lined with steel, ensuring long-term reliability and uniformity of connection interfaces.

[0061] The induced draft system 1 and the auxiliary induced draft unit 2 are independent of each other. When the main fan needs to be repaired, the auxiliary unit can be started to maintain the basic operation of the system and achieve maintenance without stopping the machine.

[0062] The self-diagnostic function of the intelligent control system can report fault information in real time, further guiding maintenance personnel to quickly locate and troubleshoot faults, significantly shortening maintenance time and reducing operation and maintenance difficulty and cost.

[0063] To make the technical solution and advantages of this utility model clearer, a specific application example is given below.

[0064] A textile printing and dyeing company uses a direct-fired hot air furnace with a rated thermal power of 10MW to provide hot air for the drying process.

[0065] This process requires the hot blast stove load to be frequently and rapidly adjusted between 60% and 100% within a short period of time (e.g., 5-10 minutes).

[0066] Existing problem: The company originally used a single industrial frequency induced draft fan in conjunction with a baffle plate for throttling regulation. When the load increased rapidly, the flue gas volume increased sharply, and the induced draft volume could not keep up in time. This caused the negative pressure in the furnace to frequently turn into positive pressure, resulting in flue gas escaping. This not only posed a safety hazard but also worsened the workshop environment. At the same time, the baffle plate throttling caused huge energy waste, and the equipment was extremely unstable when the load fluctuated.

[0067] After applying the solution of this utility model:

[0068] Equipment configuration:

[0069] Variable frequency fan 101 for the main exhaust system: Select a variable frequency fan with an air volume of 50,000 m³ / h and a total pressure of 2500 Pa.

[0070] Variable frequency fan 201 for induced draft auxiliary system: A variable frequency fan with an air volume of 20,000 m³ / h and a total pressure of 2500 Pa is selected as an auxiliary.

[0071] Combined emergency discharge device 3: Automatic exhaust device 301 is set to open proportionally when the furnace pressure exceeds +50Pa; quick exhaust valve 302 is set to fully open within 2 seconds when the pressure exceeds +150Pa.

[0072] Intelligent control system: A PLC is used as the controller, and a pressure sensor is installed in the furnace of the hot blast stove to monitor the negative pressure in real time.

[0073] Running result:

[0074] When the hot blast furnace load steadily increases from 70% to 85%, the PLC detects a tendency for the negative pressure to become positive through the pressure sensor, and immediately increases the operating frequency of the variable frequency fan 101 of the main induced draft system to increase the induced draft volume, stabilizing the negative pressure back to -30Pa within 3 seconds.

[0075] When the production process requires the hot blast furnace to rapidly reach 100% full load in a short period of time, the flue gas volume surges. The frequency of the main induced draft fan 101 rises to its highest frequency, but it still struggles. The negative pressure value continues to drop to -10Pa. At this time, the PLC quickly makes a judgment and starts the auxiliary induced draft fan 201. The two fans work together, and the induced draft volume increases significantly. It successfully restores the negative pressure to a stable range within 5 seconds, completely eliminating the phenomenon of flue gas leakage.

[0076] In an extreme case, the waste heat recovery system 102 experienced a temporary blockage, causing a sudden increase in flue gas resistance and an instantaneous increase in furnace pressure above +50Pa. The automatic exhaust device 301 automatically opened to release pressure, but due to severe blockage, the pressure continued to climb to +120Pa. Before reaching the critical point of +150Pa, the rapid exhaust valve 302 opened rapidly according to the command, and a large amount of flue gas was directly discharged through the bypass. The furnace pressure quickly dropped, effectively avoiding a potential equipment damage accident caused by overpressure.

[0077] In summary, this embodiment fully demonstrates that the combined induced draft device of this utility model can effectively solve the problem of negative pressure control caused by rapid load fluctuations in the waste heat recovery process of direct-fired equipment, significantly improve the stability, safety and energy efficiency of the system operation, and has extremely high practical value and promotion prospects.

[0078] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A combined induced draft fan device for waste heat recovery in direct-fired equipment, characterized in that, include: Exhaust ventilation system, auxiliary exhaust ventilation unit, combined emergency exhaust device, air duct and connecting components, and intelligent control system; The exhaust system includes at least one main exhaust system variable frequency fan, which provides the main exhaust force for the direct-fired equipment and guides the flue gas to the waste heat recovery system. The auxiliary air-expelling unit includes at least one variable frequency fan for the auxiliary air-expelling system, which is connected in parallel with the air-expelling system to provide auxiliary air-expelling force. The combined emergency discharge device is connected in parallel with the exhaust system and the waste heat recovery system. The combined emergency discharge device includes an automatic exhaust device and a fast exhaust valve, which is set to perform emergency discharge when the system pressure exceeds a preset value. The air duct and connecting components connect the direct-fired equipment, the induced draft system, the auxiliary induced draft unit, the combined emergency exhaust device, and the waste heat recovery system. The intelligent control system receives monitoring signals of the operating status of the direct-fired equipment and independently controls the operation of the variable frequency fan of the main induced draft system, the variable frequency fan of the induced draft auxiliary system, and the combined emergency emission device based on the monitoring signals.

2. A combined induced draft fan device for waste heat recovery in direct-fired equipment according to claim 1, characterized in that, The intelligent control system includes: a sensor group, a controller, and a human-machine interface; The sensor group is configured to monitor at least one of the following parameters of the direct-fired equipment: furnace negative pressure, flue gas temperature, and flue gas flow rate. The controller is signal-connected to the sensor group; The human-machine interface is connected to the controller to display the current status and parameter settings.

3. A combined induced draft fan device for waste heat recovery in direct-fired equipment according to claim 1, characterized in that, The rapid exhaust valve is either a pneumatically controlled valve or an electrically controlled valve.

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