Waste heat recovery equipment and process for feed bulking machine

Abstract

The invention belongs to the technical field of heat exchange energy conservation, and discloses feed bulking machine waste heat recovery equipment which comprises a conditioning module, a bulking module and a drying module, a cooling module is arranged on the downstream of the drying module, and a conditioning air outlet, a drying air outlet and a cooling air inlet are formed in the conditioning module, the drying module and the cooling module respectively; the cooling module introduces fresh air through a cooling air inlet to cool the dried feed; the tempering gas outlet and / or the drying gas outlet are / is connected with the cooling gas inlet through a heat exchange path, and waste heat in waste gas is transferred to gas introduced by the cooling gas inlet, so that the gas is preheated; and the preheated gas enters the cooling module and is used for safely cooling the high-temperature feed on the premise of avoiding condensation on the surface of the feed.

Description

Technical Field

[0001] This invention belongs to the field of heat exchange energy-saving technology, specifically relating to a waste heat recovery device and recovery process for a feed extruder. Background Technology

[0002] Traditional feed extrusion production lines mainly consist of two continuous thermal units: extrusion and drying. In the extrusion stage, the material is pre-steamed in a conditioner before entering the extruder. Under high temperature, high pressure, and high shear, it is briefly heated, causing the internal moisture to rapidly vaporize. The pellets expand and solidify instantaneously at the die outlet, forming a loose, porous structure. Subsequently, the extruded, hot, wet pellets with a moisture content of 20%–30% are sent to a drying device for dehydration through continuous hot air supply, stabilizing the finished product's moisture content to below 10% to meet basic storage and transportation requirements. However, current feed extrusion processes generally suffer from two major drawbacks: First, the drying stage focuses solely on heating and dehydration, severely neglecting the scientific cooling process after drying. The surface temperature of dried feed pellets typically remains between 45–55°C. If natural cooling is used or the pellets are directly introduced into the packaging process, the continuous release of residual heat can easily lead to a series of quality problems: on the one hand, high temperatures accelerate oil oxidation and rancidity, reducing the feed's energy value and producing a rancid odor; on the other hand, when hot feed comes into contact with a low-temperature environment or high-humidity air, the surface temperature may drop below the dew point, causing condensation and localized moisture regain, creating conditions for the growth of mold and Salmonella, seriously threatening product hygiene, safety, and shelf life.

[0003] Secondly, current waste heat utilization mainly focuses on the high-temperature and humid waste gas (80–150℃) discharged during the puffing process, while insufficient attention is paid to other medium- and low-temperature waste heat sources. In fact, the material is fully preheated by steam in the conditioner before puffing, and the 60–85℃ conditioning waste gas generated in this process, as well as the 50–70℃ high-humidity tail gas discharged during the drying stage, also contain considerable heat energy. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a waste heat recovery device and process for a feed extruder, so as to solve the problems existing in the background art.

[0005] To address the aforementioned technical problems, the first technical solution of this invention is a waste heat recovery device for a feed extruder, comprising a conditioning module, an extrusion module, and a drying module. A cooling module is located downstream of the drying module. The conditioning module, drying module, and cooling module are respectively equipped with a conditioning air outlet, a drying air outlet, and a cooling air inlet. The cooling module introduces fresh air through the cooling air inlet to cool the dried feed. The conditioning air outlet and / or the drying air outlet are connected to the cooling air inlet via a heat exchange path, transferring the waste heat in the exhaust gas to the gas introduced through the cooling air inlet, thereby preheating the gas. The preheated gas enters the cooling module to safely cool the high-temperature feed while avoiding condensation on the feed surface.

[0006] Preferably, a heat exchange path is connected between the conditioning outlet and / or the drying outlet and the cooling inlet via a pipeline. The heat exchange path is equipped with a gas-to-gas heat exchanger, in which the exhaust gas side and the fresh air side are completely isolated, allowing only heat transfer without media mixing. A dust removal and oil removal device is provided upstream of the conditioning outlet and / or the drying outlet to reduce the dust and grease content in the exhaust gas and prevent blockage or corrosion of the heat exchange path.

[0007] Furthermore, the cooling module is provided with a cooling air outlet, and part of the exhaust gas discharged from the cooling air outlet of the cooling module is connected to the mixing chamber through a pipe; the air outlet of the mixing chamber is connected to the air inlet of the drying module and / or the cooling module, and the mixing chamber is used to provide fresh air to the drying module and / or the cooling module.

[0008] Furthermore, both the cooling air inlet and the mixing chamber air inlet introduce fresh air from the external environment; a temperature control system and a temperature control valve are provided on the heat exchange path, and the temperature control system sets a switching threshold for starting and stopping the heat exchange according to the ambient temperature; when the ambient temperature is higher than the switching threshold, the control valve cuts off the heat exchange path between the exhaust gas and the cooling air inlet, so that the cooling air inlet directly introduces fresh air from the external environment that has not been preheated.

[0009] Furthermore, the air inlet of the mixing chamber is equipped with a humidity control system and a humidity control valve. The humidity control system sets a humidity adjustment threshold according to the ambient humidity. When the ambient humidity is higher than the humidity adjustment threshold, the humidity control valve reduces or shuts off the introduction of high-humidity fresh air from outside and increases the proportion of low-humidity exhaust gas from the cooling outlet in the mixing chamber to reduce the relative humidity of the fresh air entering the drying module and / or cooling module.

[0010] To solve the above-mentioned technical problems, the second technical solution of the present invention is a waste heat recovery process for a feed extruder, which applies the waste heat recovery equipment for the feed extruder described in the first technical solution. The recovery process includes the following steps: In step S1, the feed is processed sequentially through the conditioning module, the extrusion module, and the drying module, generating conditioning waste gas, extrusion waste gas, and drying waste gas respectively; wherein, the conditioning waste gas is discharged from the conditioning outlet and the drying waste gas is discharged from the drying outlet. In step S2, the dried high-temperature feed enters the cooling module. Fresh air from the external environment is introduced through the cooling air inlet to cool the feed, and the cooled gas is discharged through the cooling air outlet.

[0011] Preferably, the recovery process monitors ambient temperature and humidity in real time. Simultaneously, the temperature control system determines whether to activate the heat exchange path based on the ambient temperature, and the humidity control system determines whether to adjust the composition of the fresh air based on the ambient humidity. In the temperature control system, when the ambient temperature is below a preset temperature switching threshold, the heat exchange path is activated, and the exhaust gas discharged from the conditioning outlet and / or drying outlet is introduced into the gas-to-gas heat exchanger to preheat the fresh air introduced into the cooling inlet. The preheated fresh air then enters the cooling module for safe cooling. When the ambient temperature is above the temperature switching threshold, the heat exchange path is closed, and the cooling inlet directly introduces unheated ambient fresh air. In the humidity control system, when the ambient humidity is above a preset humidity adjustment threshold, the amount of fresh air introduced into the mixing chamber from the external environment is reduced, and the proportion of cooling exhaust gas in the mixing chamber is increased to form a low-humidity mixed gas. When the ambient humidity is not above the humidity adjustment threshold, the mixing chamber is dominated by ambient fresh air, and cooling exhaust gas is introduced at the minimum maintenance flow rate or shut off.

[0012] Furthermore, in the humidity control system, a portion of the exhaust gas discharged from the cooling outlet is directed to the mixing chamber; the mixed gas output from the mixing chamber is then used as a fresh air source to supply the drying module and / or cooling module, thereby achieving active regulation of the humidity content of the fresh air in the system, improving drying efficiency and preventing the finished product from absorbing moisture and condensing.

[0013] Furthermore, the temperature control system is configured with a first threshold, a second threshold, and a third threshold for switching heat exchange modes. The first threshold, the second threshold, and the third threshold are preset temperature values, and the first threshold is less than the second threshold, less than the third threshold, and less than or equal to the temperature switching threshold. When the ambient temperature is lower than the first threshold, the heat exchange path simultaneously connects the conditioning outlet and the drying outlet with the cooling inlet for a combined heat exchange path. When the ambient temperature is between the first threshold and the second threshold, only the conditioning outlet is connected with the cooling inlet for a heat exchange path. When the ambient temperature is between the second threshold and the third threshold, only the drying outlet is connected with the cooling inlet for a heat exchange path.

[0014] The main technical effects of this invention are reflected in the following aspects: Traditional extrusion lines focus solely on the high-temperature exhaust gas from the extruder, neglecting the considerable heat energy contained in the conditioning and drying exhaust gases. This invention systematically integrates these two medium- and low-temperature waste heat sources into the cooling air intake preheating system, achieving intelligent scheduling through three temperature thresholds: dual-source combined heating in extremely cold conditions, high-grade conditioning exhaust gas alone in cold conditions, switching to low-grade drying exhaust gas in cool conditions, and completely shutting off preheating in high-temperature conditions. This strategy, based on the thermodynamic principle of "matching heat source grade to heat demand," avoids overheating or underheating caused by the traditional "all-on, all-off" mode, improving waste heat recovery efficiency and truly achieving "on-demand heat extraction and precise energy supply."

[0015] Feed cooling requires not only temperature reduction but also prevention of surface condensation; drying relies not only on heat but is also constrained by the moisture content of the fresh air. This invention breaks through the single heat recovery approach by simultaneously introducing temperature and humidity control: on the one hand, it regulates the inlet air temperature within a safe range through the heat exchange path to avoid condensation; on the other hand, it redirects a portion of the low-humidity exhaust gas discharged from the cooling module back to the mixing chamber, replacing part of the high-humidity fresh air in a high-humidity environment, actively reducing the wet-bulb temperature of the fresh air supplied to the drying or cooling system; adopting a "waste-to-humidity" strategy eliminates the need for additional dehumidification equipment, effectively solving the industry problem of a sharp drop in drying efficiency during the rainy season in southern China.

[0016] Unlike the extensive approach of full-volume recycling, this invention reuses only a portion of the cooling exhaust gas, and dynamically controls its proportion in the mixed air through regulating valves. This approach utilizes the low humidity advantage while avoiding the risks associated with full-volume recycling: firstly, it prevents the low-temperature exhaust gas from excessively diluting the fresh air temperature, thus avoiding condensation caused by excessively cold intake air in winter; secondly, it retains necessary ambient fresh air to maintain positive pressure and air exchange in the system, preventing dust accumulation and the inhalation of pollutants under negative pressure; and thirdly, it reduces the accumulation of volatile organic compounds and particulate matter in the closed-loop system, ensuring the reliability of control components and the purity of feed flavor. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the flow of feed between modules in this invention; Figure 2 This is a flowchart of the temperature control system in this invention; Figure 3 This is a flowchart of the humidity control system in this invention. Detailed Implementation

[0018] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, so as to make the technical solution of the present invention easier to understand and master. In the embodiments, it should be understood that the terms "middle," "upper," "lower," "top," "right side," "left end," "above," "back," "center," etc., indicating the orientation or positional relationship are based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention. In addition, unless otherwise specified in this specific embodiment, the connection or fixing method between components can be achieved by bolt fixing, pin fixing, or pin connection commonly used in the prior art, etc., and therefore will not be described in detail in this embodiment.

[0019] The waste heat recovery equipment and process for feed extruders provided by this invention are mainly applied to the extrusion production lines of aquatic, livestock and poultry and pet feeds, but they are not limited thereto. They can also be extended to other production processes with similar thermal processes, such as starch food extrusion, cereal production, biomass pellet drying and other production fields.

[0020] Furthermore, as is common knowledge in this industry, the conditioner mentioned earlier uses steam to preheat and adjust the moisture content of materials, the extruder achieves instantaneous expansion of materials under high temperature and pressure, and there are dust removal, oil removal, and filtration devices. These are common knowledge; therefore, their principles and structures will not be elaborated upon further.

[0021] Example 1 This embodiment provides a waste heat recovery device for a feed extruder, including a conditioning module, an extrusion module, and a drying module. A cooling module is located downstream of the drying module. The conditioning module, drying module, and cooling module are respectively equipped with a conditioning air outlet, a drying air outlet, and a cooling air inlet. The cooling module introduces fresh air through the cooling air inlet to cool the dried feed. (See also...) Figure 1 The specific structure is as follows: Conditioning module: The material is first pre-treated with steam in a conditioner to ensure it reaches suitable temperature and humidity conditions before entering the extruder. The 60-85℃ conditioning exhaust gas generated during the conditioning process is discharged through the conditioning outlet.

[0022] Extrusion Module: After conditioning, the material enters the extruder and is briefly heated under high temperature, high pressure, and high shear. Internal moisture rapidly vaporizes, and the particles instantly expand and solidify at the die outlet, forming a loose, porous structure. The waste gas generated during the extrusion process has mature conventional treatment methods and is not the primary focus of waste heat recovery in this embodiment, so it will not be elaborated upon further. The focus of this embodiment is the systematic recovery and utilization of the medium-low temperature, high-flow-rate, and relatively stable humid heat waste gas generated during the conditioning and drying stages to achieve energy efficiency improvement and process optimization. It not only utilizes the traditionally considered extrusion waste gas (80–150℃), but also fully utilizes the conditioning waste gas (60–85℃) and drying tail gas (50–70℃), achieving effective recovery of medium-low temperature waste heat.

[0023] Drying module: The moisture content of the expanded wet heat granules is as high as 20%-30%, and they need to be dehydrated by the drying module; the drying exhaust gas generated during the drying process at 50℃-70℃ is discharged through the drying exhaust port.

[0024] Cooling module: The temperature of dried feed pellets is usually between 45℃ and 55℃, and further cooling is required to prevent oil oxidation and rancidity and surface condensation. The cooling module introduces fresh air from outside through the cooling air inlet to cool the feed, and the cooled exhaust gas is discharged through the cooling air outlet.

[0025] Preferably, the conditioning outlet and / or the drying outlet are connected to the cooling inlet via a heat exchange path, transferring residual heat from the waste gas to the gas introduced through the cooling inlet, thus preheating the gas. The preheated gas then enters the cooling module to safely cool the high-temperature feed while preventing condensation on the feed surface. A heat exchange path is connected between the conditioning outlet and / or the drying outlet and the cooling inlet via a pipeline. This heat exchange path is equipped with a gas-to-gas heat exchanger made of stainless steel or other corrosion-resistant materials to ensure long-term stable operation. The waste gas side and the fresh air side of the gas-to-gas heat exchanger are completely isolated, allowing only heat transfer without media mixing. A dust and oil removal device is installed upstream of the conditioning outlet and / or the drying outlet to reduce the dust and oil content in the waste gas, prevent blockage or corrosion of the heat exchange path, and extend the equipment's service life. The cooling module is provided with a cooling air outlet, and part of the exhaust gas discharged from the cooling air outlet of the cooling module is connected to the mixing chamber through a pipe; the air outlet of the mixing chamber is connected to the air inlet of the drying module and / or the cooling module, and the mixing chamber is used to provide fresh air to the drying module and / or the cooling module.

[0026] Furthermore, the heat exchange path and fresh air composition are dynamically adjusted through a temperature and humidity control system to ensure efficient and energy-saving operation under different seasonal conditions, avoiding condensation and high humidity affecting drying efficiency. Both the cooling air inlet and the mixing chamber inlet introduce fresh air from the external environment. A temperature control system and a temperature control valve are installed on the heat exchange path. The temperature control system sets a switching threshold for heat exchange start / stop based on the ambient temperature. When the ambient temperature is higher than the switching threshold (e.g., 30°C), the control valve cuts off the heat exchange path between the exhaust gas and the cooling air inlet, allowing the cooling air inlet to directly introduce unheated fresh air from the external environment. The mixing chamber inlet is equipped with a humidity control system and a humidity control valve. The humidity control system sets a humidity adjustment threshold based on the ambient humidity. When the ambient humidity is higher than the humidity adjustment threshold (e.g., 70% RH), the humidity control valve reduces or shuts off the introduction of high-humidity fresh air from the outside and increases the proportion of low-humidity exhaust gas from the cooling air outlet in the mixing chamber, thereby reducing the relative humidity of the fresh air entering the drying module and / or cooling module.

[0027] Example 2 This embodiment provides a waste heat recovery process for a feed extruder, applying the waste heat recovery equipment described in Embodiment 1. The recovery process uses a control system to monitor ambient temperature and humidity in real time, and dynamically adjusts the heat exchange path and the composition of the fresh air intake gas based on the monitoring results to achieve high efficiency, energy saving, and product quality assurance. The specific steps are as follows: Step S1, feed extrusion and waste gas generation The material is first pre-treated with steam in a conditioner to bring it to a suitable temperature (typically 70℃-95℃) and moisture content (approximately 16%-28%) before entering the extruder, thereby promoting starch gelatinization and improving the extrusion effect. During this process, some uncondensed steam and entrained humid heat gases form conditioning waste gas at 60-85℃, which is discharged through the conditioning outlet on the conditioning module, serving as one of the important medium-low temperature waste heat sources in this invention.

[0028] Subsequently, the conditioned material enters the extruder, where, under the intense extrusion, shearing, and friction of the screw, it undergoes a high-temperature environment of 110℃-150℃ and a high-pressure environment of 2MPa-4MPa within seconds, causing the material to melt. When it is instantly depressurized to atmospheric pressure through the die, the internal moisture rapidly vaporizes, the particle volume expands dramatically and solidifies, ultimately forming loose, porous, and highly cooked extruded particles. Although this stage is accompanied by a small amount of high-temperature waste gas (usually 80℃-150℃), due to its high dust content, severe grease atomization, and the fact that existing production lines generally use direct venting or simple silencer and dust removal treatment, recovery is difficult and economically limited. Therefore, it is not considered the main waste heat recovery target in this process and is still treated in a conventional manner.

[0029] The expanded granules have a high moisture content of 20%-30% and a surface temperature of approximately 80℃-100℃, requiring immediate transfer to the drying module for dehydration. In the drying module, hot air at 70℃-90℃ is continuously introduced to stably reduce the granule moisture content to below 10% (aquatic feed typically requires ≤8.5%). This process evaporates a large amount of moisture, generating high-humidity drying exhaust gas at 50℃-70℃, which is discharged from the drying module's outlet. This exhaust gas has a moderate temperature and stable flow rate, serving as another key medium-low temperature waste heat source for recovery and utilization in this invention.

[0030] The above-mentioned conditioning, puffing, and drying processes are conventional process steps in feed puffing. This embodiment does not change its core operating parameters, but rather systematically captures and utilizes the long-neglected conditioning waste gas and drying tail gas in a tiered manner without interfering with the main process, thereby achieving energy synergy and process optimization.

[0031] Step S2: Cooling module operation The dried, high-temperature feed (surface temperature typically 45–55°C) enters the cooling module. Fresh air from the external environment is introduced through the cooling air inlet to cool the feed. The cooled air is then discharged through the cooling air outlet. The recovery process monitors ambient temperature and humidity in real time; simultaneously, the temperature control system determines whether to activate the heat exchange path based on the ambient temperature, and the humidity control system determines whether to adjust the composition of the fresh air based on the ambient humidity.

[0032] Both the temperature and humidity control systems require necessary cleaning treatment of the waste gas during its reuse. Specifically, the conditioning and drying exhaust gases used by the temperature control system are highly susceptible to carrying fine feed dust and atomized grease during their generation. If these components enter the gas-to-gas heat exchanger directly without treatment, they will condense on the heat exchange surface due to temperature difference and combine with water vapor to form a viscous, sludge-like deposit. This deposit not only significantly reduces the heat transfer efficiency of the heat exchanger (measured to reduce the heat transfer coefficient by more than 30%), but also gradually clogs the fin gaps or air duct cross-sections, increasing system resistance and forcing the fan to consume more energy. More seriously, in high-temperature and high-humidity environments, the low-molecular-weight fatty acid products generated by grease oxidation are weakly acidic. Once they encounter condensate, they form a corrosive liquid film, causing pitting or stress corrosion cracking on carbon steel or ordinary stainless steel heat exchange elements, significantly shortening the equipment's lifespan. Therefore, dust and oil removal devices must be installed on the pipelines leading from the conditioning and drying exhaust ports to the heat exchange path. Although the cooling exhaust gas used in the humidity control system has a low temperature and low moisture content, it still contains trace amounts of dust and volatile organic compounds (such as aldehyde and ketone oxidation products, flavor substances, etc.) that have escaped from the surface of high-temperature feed pellets. When this exhaust gas is introduced into the mixing chamber and partially reused in the fresh air system of the drying or cooling modules, if it is not treated for a long time, the following problems may occur: dust accumulation inside the mixing chamber, which becomes a breeding ground for microorganisms (such as mold and Salmonella) in a humid environment; surface contamination of precision control components such as air valve actuators, temperature and humidity sensors, and flow meters, leading to delayed response or signal distortion, affecting the accuracy of automatic control; and odor substances carried by the reused gas being re-adsorbed onto the surface of the finished feed during the circulation process, causing "backflow" or decreased palatability. Therefore, a filtration device should also be installed on the pipeline from the cooling exhaust outlet to the mixing chamber.

[0033] Preferred, see Figure 2 To accurately control the inlet air temperature of the cooling module and prevent condensation on the surface of the finished feed due to excessively cold inlet air, the process in this embodiment activates the heat exchange path when the ambient temperature is below the preset temperature switching threshold (25°C). This involves introducing the low-temperature exhaust gas from the conditioning and / or drying outlets into the air-to-air heat exchanger to preheat the fresh air introduced into the cooling inlet. The preheated fresh air temperature is strictly controlled within a safe range of 15°C-25°C, slightly higher than the ambient dew point. This effectively removes residual heat from the extruded feed and prevents condensation and moisture absorption on the particle surface due to excessive temperature differences, thus ensuring product hygiene, safety, and shelf life.

[0034] Furthermore, considering the high sensitivity of the cooling module to inlet air temperature, its ideal inlet air temperature is not necessarily higher, but rather needs to be strictly controlled within a narrow window of 15–25℃. This range is slightly higher than the local ambient dew point temperature, which can effectively absorb the residual heat continuously released from inside the extruded pellets, while avoiding condensation caused by the surface temperature dropping sharply below the dew point due to direct contact between cold air and high-temperature materials. If the inlet air temperature is too low (such as 5℃ cold air without preheating in winter), it is easy to cause moisture to be absorbed from the surface of the pellets, leading to mold growth; while if the inlet air temperature is too high (such as exceeding 30℃), it will significantly reduce the temperature difference between the inlet air and the feed pellets (usually 45–55℃), weaken the heat transfer driving force, prolong the cooling time, and even cause the discharge temperature to exceed the standard, accelerating the oxidation and rancidity of oils, producing a rancid taste, and seriously affecting the palatability and nutritional value of the feed.

[0035] Against this backdrop, although both conditioning exhaust gas (60–85℃) and drying exhaust gas (50–70℃) belong to medium-low temperature waste heat, their heat quality differs significantly. Conditioning exhaust gas has a higher temperature and richer latent heat, making it suitable for strong preheating requirements under extremely cold conditions; while drying exhaust gas has a relatively mild temperature, making it more suitable for fine-tuning preheating in cooler seasons. If the traditional extensive recovery mode of "all on, all used" is adopted—that is, both exhaust gases are activated simultaneously whenever the ambient temperature is below a certain fixed threshold (such as 20℃)—then in spring and autumn (such as 15–22℃), the fresh air temperature after preheating is very likely to soar to 28–32℃, which not only fails to effectively cool the air but also creates the opposite effect of "hot air drying," violating the original intention of the cooling process.

[0036] Therefore, this invention abandons the conventional thinking of "recovering as much as possible" in traditional waste heat recovery and innovatively introduces a three-level temperature threshold fine-tuning mechanism to achieve "heat extraction on demand, precise temperature control, and dynamic adaptation." Specifically, the temperature control system is configured with a first threshold (10℃), a second threshold (18℃), and a third threshold (25℃) for switching heat exchange modes. The first, second, and third thresholds are preset temperature values, and the first threshold is less than the second threshold, less than the third threshold, and less than or equal to the temperature switching threshold. Based on this, a differentiated heat source scheduling strategy is executed: when the ambient temperature is lower than the first threshold, the heat exchange path simultaneously connects the conditioning outlet and the drying outlet with the cooling inlet for a combined heat exchange path to provide sufficient heat and prevent severe condensation; when the ambient temperature is between the first and second thresholds, only the conditioning outlet and the cooling inlet are connected for a heat exchange path; the higher-temperature conditioning waste gas is used for preheating, and the drying waste gas path is closed to balance condensation prevention and avoidance of overheating. When the ambient temperature is between the second and third thresholds, the heat exchange path is only connected between the drying exhaust port and the cooling inlet. The preheated drying exhaust gas at the lower temperature is used to prevent the intake air from overheating and maintain cooling efficiency. To avoid overheating of the intake air and affecting cooling efficiency, the heat exchange path is automatically closed when the ambient temperature exceeds the temperature switching threshold. The cooling inlet then directly introduces unheated ambient air. This effectively prevents the cooling air temperature from rising due to additional waste heat input during warm or hot seasons, thus avoiding risks such as decreased cooling capacity, excessive discharge temperature, and accelerated oil oxidation.

[0037] Preferred, see Figure 3 To fully utilize the cooling module exhaust gas resources, which have long been neglected in traditional extrusion processes, this embodiment incorporates the cooling module exhaust gas resources into the process's fresh air system. Unlike conditioning exhaust gas and drying tail gas, the exhaust gas discharged from the cooling module, although at a lower temperature, has a significantly lower relative humidity, making it a high-quality "low-temperature, low-humidity" dry gas source. In traditional processes, this exhaust gas is directly discharged without being recycled; however, this solution guides it back into the system, effectively avoiding the additional dehumidification burden caused by relying solely on external fresh air in high-humidity environments. This improves the drying capacity of the incoming air from a humidity perspective without increasing heating energy consumption.

[0038] Specifically, in the humidity control system, when the ambient humidity is higher than the preset humidity adjustment threshold, the system automatically reduces the amount of high-humidity fresh air introduced from the external environment into the mixing chamber, while increasing the proportion of low-humidity exhaust gas from the cooling outlet in the mixing chamber to form a mixed gas with even lower humidity. When the ambient humidity is not higher than the threshold, the ambient fresh air is the main component, and the cooling exhaust gas is only introduced at the minimum maintenance flow rate (for system pressure balance or anti-clogging), or completely shut off, in order to reduce the energy consumption of the fan.

[0039] Furthermore, a portion of the low-humidity exhaust gas discharged from the cooling outlet is piped to the mixing chamber and fully mixed with a controllable proportion of ambient fresh air before being resupplyed as fresh air to the drying and / or cooling modules. This achieves proactive management of the system's fresh air humidity content: during the rainy season or in high-humidity conditions in the south, by increasing the proportion of cooling exhaust gas, the wet-bulb temperature of the fresh air supplied to the dryer is significantly reduced, enhancing the driving force for moisture evaporation, thereby improving drying efficiency, shortening drying time, and reducing the load on the hot air furnace. At the same time, the introduction of low-humidity mixed air during the cooling stage can also effectively inhibit the surface moisture absorption of the finished particles during the cooling process, further preventing condensation and microbial growth.

[0040] As for the exhaust gas discharged from the cooling module, this embodiment adopts partial utilization rather than complete recycling, mainly based on comprehensive considerations of process safety, system stability and product hygiene.

[0041] First, although the cooling exhaust gas is relatively dry and has good dehumidification potential, its temperature is low. If all or excessive amounts of it are introduced into the mixing chamber to participate in the fresh air distribution, in the already low ambient temperatures of spring and winter, the temperature of the mixed fresh air is likely to drop further, approaching or even falling below the dew point temperature. This not only fails to effectively prevent condensation but may also exacerbate the risk of condensation on the surface of high-temperature feed, causing local moisture to rise and inducing mold or microbial contamination, thus violating the fundamental purpose of the cooling process.

[0042] Secondly, although the cooling exhaust gas undergoes preliminary settling, it inevitably carries trace amounts of dust particles and small amounts of volatile organic compounds (such as oil oxidation products and flavor compounds). If 100% internal circulation is implemented, these pollutants will accumulate repeatedly within the system, and long-term operation may lead to scale buildup on heat exchangers, ducts, or fan impellers, reducing equipment efficiency. More seriously, there is a risk of cross-contamination, affecting the odor, color, and even hygiene and safety indicators of feed products.

[0043] Of course, the above are just typical examples of the present invention. In addition, the present invention may have many other specific embodiments. All technical solutions formed by equivalent substitution or equivalent transformation fall within the scope of protection claimed by the present invention.

Claims

1. A feed puffing machine waste heat recovery device, comprising a conditioning module, a puffing module and a drying module, characterized in that, a cooling module is arranged downstream of the drying module, and the conditioning module, the drying module and the cooling module are respectively provided with a conditioning gas outlet, a drying gas outlet and a cooling gas inlet; the cooling module introduces fresh air through the cooling gas inlet to cool the dried feed; the conditioning gas outlet and / or the drying gas outlet are connected to the cooling gas inlet through a heat exchange path to transfer the waste heat in the exhaust gas to the gas introduced by the cooling gas inlet, thereby preheating the gas; the preheated gas enters the cooling module to safely cool the high-temperature feed without surface condensation.

2. The feed puffing machine waste heat recovery device according to claim 1, characterized in that: the conditioning gas outlet and / or the drying gas outlet are connected to the cooling gas inlet through a heat exchange path, and the heat exchange path is equipped with an air-to-air heat exchanger, which completely separates the exhaust gas side and the fresh air side and only transfers heat without medium mixing; a dust and oil removal device is arranged upstream of the conditioning gas outlet and / or the drying gas outlet, which is used to reduce the dust and oil content in the exhaust gas to prevent the heat exchange path from being blocked or corroded.

3. The feed puffing machine waste heat recovery device according to claim 2, characterized in that: a cooling gas outlet is arranged on the cooling module, and part of the exhaust gas discharged from the cooling gas outlet is connected to a mixing chamber through a pipeline; the outlet end of the mixing chamber is connected to the inlet end of the drying module and / or the cooling module, and the mixing chamber is used to provide fresh air to the drying module and / or the cooling module.

4. The feed puffing machine waste heat recovery device according to claim 3, characterized in that: the cooling gas inlet and the mixing chamber inlet both introduce fresh air from the external environment; a temperature control system and a temperature control valve are arranged on the heat exchange path, and the temperature control system sets a switching threshold for the heat exchange start-stop according to the ambient temperature; when the ambient temperature is higher than the switching threshold, the control valve cuts off the heat exchange path between the exhaust gas and the cooling gas inlet, so that the cooling gas inlet directly introduces the external environment fresh air without preheating.

5. The feed puffing machine waste heat recovery device according to claim 4, characterized in that: a humidity control system and a humidity control valve are arranged on the inlet of the mixing chamber, and the humidity control system sets a humidity adjustment threshold according to the ambient humidity; when the ambient humidity is higher than the humidity adjustment threshold, the humidity control valve reduces or closes the introduction of external high-humidity fresh air, and increases the proportion of low-humidity exhaust gas from the cooling gas outlet in the mixing chamber to reduce the relative humidity of the fresh air entering the drying module and / or the cooling module.

6. A process for recovering waste heat from a feed expander, using the apparatus for recovering waste heat from a feed expander according to claim 5, characterized in that, The recovery process comprises the following steps: Step S1, the feed is sequentially treated by the conditioning module, the puffing module and the drying module to produce conditioning exhaust gas, puffing exhaust gas and drying exhaust gas; wherein the conditioning exhaust gas is discharged from the conditioning gas outlet, and the drying exhaust gas is discharged from the drying gas outlet. Step S2, the high-temperature feed after drying enters the cooling module, and the external environment fresh air is introduced through the cooling air inlet to cool the feed. The cooled gas is discharged from the cooling air outlet.

7. The feed extruder waste heat recovery process of claim 6, wherein, The environmental temperature and humidity are monitored in real time in the recovery process. The temperature control system determines whether to start the heat exchange path according to the environmental temperature, and the humidity control system determines whether to adjust the composition of the fresh air according to the environmental humidity: In the temperature control system, when the environmental temperature is lower than the preset temperature switching threshold, the heat exchange path is started, the exhaust gas discharged from the conditioning air outlet and / or the drying air outlet is introduced into the air heat exchanger, the fresh air introduced into the cooling air inlet is preheated, and the preheated fresh air enters the cooling module for safe cooling. When the environmental temperature is higher than the temperature switching threshold, the heat exchange path is closed, and the cooling air inlet directly introduces the unheated environmental fresh air. In the humidity control system, when the environmental humidity is higher than the preset humidity adjustment threshold, the amount of fresh air introduced into the mixing chamber from the external environment is reduced, and the ratio of cooling exhaust gas in the mixing chamber is increased to form low-humidity mixed gas. When the environmental humidity is not higher than the humidity adjustment threshold, the mixing chamber mainly uses environmental fresh air, and the cooling exhaust gas is introduced at a minimum maintenance flow or closed.

8. The feed extruder waste heat recovery process of claim 7, wherein, In the humidity control system, part of the exhaust gas discharged from the cooling air outlet is introduced into the mixing chamber. The mixed gas output from the mixing chamber is used as a fresh air source for the drying module and / or the cooling module, actively controlling the moisture content of the system fresh air, improving drying efficiency, and preventing product moisture condensation.

9. The feed extruder waste heat recovery process of claim 7, wherein, The temperature control system is configured with a first threshold, a second threshold, and a third threshold for heat exchange mode switching. The first threshold, the second threshold, and the third threshold are preset temperature values, and the first threshold is less than the second threshold, which is less than the third threshold, which is less than or equal to the temperature switching threshold. When the environmental temperature is lower than the first threshold, the heat exchange path is connected to the conditioning air outlet and the drying air outlet and the cooling air inlet for combined heat exchange. When the environmental temperature is between the first threshold and the second threshold, only the conditioning air outlet and the cooling air inlet are connected for heat exchange. When the environmental temperature is between the second threshold and the third threshold, only the drying air outlet and the cooling air inlet are connected for heat exchange.

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