High-temperature heat-conducting oil stepwise recycling and energy-saving system for polyamide fiber

Abstract

The utility model relates to a kind of high-temperature heat transfer oil stepwise recycling energy-saving system for polyamide, the import of variable frequency oil pump is communicated with the oil outlet of oil storage tank, and the export of variable frequency oil pump is communicated with the import of electric heating main body;Electric heating main body is made of five groups of independent controllable heating unit, and its export is connected in proper order with high-temperature pressure-stabilizing buffer chamber and then is connected with the import of three-way switch valve;The first export of three-way switch valve is communicated with the inlet of polyamide heating boiler, and the export of polyamide heating boiler is communicated with the oil return port of oil storage tank by oil return branch pipe, and the second export of three-way switch valve is communicated to the oil return port of oil storage tank;Expansion tank is communicated with oil return branch pipe;PLC control system is connected with the first temperature sensor arranged in the interior of oil storage tank, the second temperature sensor arranged in the export of electric heating main body and the third temperature sensor arranged in the process end of polyamide heating boiler respectively;PLC control system is built-in time-of-use electricity price time period identification module, and temperature impact existing in switching can be avoided.

Description

Technical Field

[0001] This invention relates to an energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon, belonging to the field of nylon spinning heating technology. Background Technology

[0002] Nylon spinning heating boilers require continuous and stable heating for 24 hours. Traditional systems use the boiler's own electric heating throughout the process, without differentiating between peak and off-peak electricity prices, resulting in extremely high electricity costs during peak periods.

[0003] Chinese Patent CN221648770U (authorization announcement date: September 3, 2024) discloses an energy-saving heating system for spinning equipment, including a boiler room, a heat exchanger, an elevated tank, an electric heater, a first valve, a second valve, and a controller. The boiler room indirectly heats the heat transfer oil via steam through the heat exchanger and then sends it to the spinning equipment. The elevated tank also serves as a heat transfer oil return and expansion buffer container. When the first thermometer detects that the temperature of the steam pipeline is lower than a set threshold, the controller determines that the boiler room heating is abnormal, closes the first valve leading to the heat exchanger, opens the second valve leading to the electric heater, and starts the electric heater to directly electrically heat the heat transfer oil to about 320°C to maintain the spinning process without interruption. This system ensures a certain degree of heating continuity by quickly switching to the electric heating backup path when the boiler fails or is under maintenance. However, it is essentially an emergency backup switch triggered by boiler tripping / temperature loss and does not have the ability to actively schedule heat supply and demand according to time-of-use electricity pricing. It does not have a dedicated oil storage tank for storing high-temperature heat transfer oil and a matching dual-loop switching architecture. The switching process also lacks pre-synchronization verification and heat load transition connection mechanisms. Therefore, there is still a risk of temperature shock during switching and it cannot fundamentally reduce the daily operating electricity cost. In particular, it is not designed for the high-temperature heat transfer oil working conditions of nylon, resulting in problems such as large temperature shock during switching, insufficient temperature control accuracy, and inability to meet the stability requirements of the spinning process. Summary of the Invention

[0004] To address the aforementioned problems in the existing technology, this invention provides an energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon, which can avoid temperature shocks during switching.

[0005] The technical solution of the present invention is as follows: A high-temperature heat transfer oil cascade recycling energy-saving system for nylon includes an oil storage tank, a variable frequency oil pump, an electric heating body, a three-way switching valve, a high-temperature pressure stabilizing buffer chamber, an expansion tank, and a PLC control system. The inlet of the variable frequency oil pump is connected to the outlet of the oil storage tank, and the outlet of the variable frequency oil pump is connected to the inlet of the electric heating body. The electric heating body consists of five independently controllable heating units, and its outlet is connected in series with the high-temperature pressure stabilizing buffer chamber and then connected to the inlet of the three-way switching valve. The first outlet of the three-way switching valve is connected to the inlet of the nylon heating boiler, and the outlet of the nylon heating boiler is connected to the return port of the oil storage tank through a return oil branch pipe. The second outlet of the three-way switching valve is connected to the return oil port of the oil storage tank. The expansion tank is connected to the return oil branch pipe. The PLC control system is connected to a first temperature sensor installed inside the oil storage tank, a second temperature sensor installed at the outlet of the electric heating body, and a third temperature sensor installed at the process end of the nylon heating boiler. The PLC control system has a built-in time-of-use electricity price period recognition module.

[0006] The time-of-use pricing period identification module includes the following steps: S1: Identify whether the current electricity price period is off-peak, peak, or flat. S2: If it is currently a period of off-peak electricity, control the three-way switching valve to switch to the second outlet conduction state, so that the heat transfer oil forms a small circulation loop along the oil storage tank, variable frequency oil pump, electric heating body, high temperature stabilizing buffer chamber, the second outlet of the three-way switching valve, and the oil storage tank. At the same time, control all five heating units to be put into heating, and heat the heat transfer oil to the set temperature to complete heat storage. S3: If it is currently a peak power period, control the three-way switching valve to switch to the first outlet conduction state, so that the heat transfer oil forms a large circulation loop along the oil storage tank, variable frequency oil pump, electric heating body, high temperature stabilizing buffer chamber, first outlet of the three-way switching valve, nylon heating boiler, and oil storage tank. At the same time, all heating units are shut down, and only the heat energy stored in the oil storage tank is used to supply heat to the nylon heating boiler. S4: If the current period is a period of normal power supply, control the three-way switching valve to switch to the first outlet conduction state to form a large circulation loop. At the same time, according to the temperature difference between the oil temperature in the storage tank detected by the first temperature sensor and the target temperature, the heating unit is switched on and off in stages for supplementary heating. S5: When switching between any two operating modes, execute third-order predictive, disturbance-free, and smooth switching control.

[0007] The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 2, wherein the third-order predictive, disturbance-free, and smooth switching control in step S5 includes the following sub-steps: S5.1: Five minutes before switching, read the temperature values ​​of the first temperature sensor, the second temperature sensor, and the third temperature sensor, calculate the maximum temperature difference between the three, and if the maximum temperature difference is ≤0.8℃, the switching is allowed to continue; otherwise, the current mode is locked and the process waits. S5.2: During the switching process, the flow rate of the heat transfer oil is changed by adjusting the speed of the variable frequency oil pump, so that the heat power output by the heat transfer oil system to the nylon heating boiler is matched with the current heat load of the original boiler electric heating in a 1:1 ratio. After the temperature stabilizes, the original boiler electric heating is gradually shut down. S5.3: After the switching is completed, the high-temperature pressure stabilizing buffer chamber absorbs the instantaneous pressure fluctuations and temperature spikes in the pipe section between the outlet of the electric heating body and the inlet of the three-way switching valve. After the temperature stabilizes for 3 minutes, the pressure stabilizing state is exited. At the same time, the following protections are set: when the temperature change rate detected by any temperature sensor is >0.3℃ / min, the switching is immediately terminated and the state before the switching is returned; the switching in the same direction is prohibited from being started again within 15 minutes after the complete switching in the same direction is completed; no switching action is performed within the ±0.5℃ temperature dead zone.

[0008] The electric heating body has five heating units configured with four 20kW and one 16kW power units. Each heating unit is equipped with an independent solid-state relay, which is independently switched on and off by the PLC control system.

[0009] The three-way switching valve is an electric three-way valve with a position feedback signal. The PLC control system only allows the heating unit to start or stop in the corresponding mode after receiving the position feedback signal from the three-way switching valve and confirming that the current actual path is consistent with the set cycle mode.

[0010] The PLC control system is equipped with over-temperature protection and under-temperature protection. Over-temperature protection means that when the second temperature sensor detects a temperature >310℃, all heating units will be immediately cut off and the variable frequency oil pump will be kept at a low speed to circulate and dissipate heat. Under-temperature protection means that when the first temperature sensor detects an oil temperature <280℃ in the oil storage tank, the original boiler electric heating will be prohibited from being turned off and the 16kW heating unit will be automatically put into operation for micro-heating.

[0011] The oil storage tank has a capacity of 2000L and is covered with an insulation layer with a thickness of 300mm. The expansion tank is equipped with a magnetic level gauge and a low level alarm. The variable frequency oil pump has a power of 5.5kW, a flow rate of 35m³ / h, and a head of 25m. The electric heating body has a design temperature of 350℃ and a design pressure of 0.8MPa.

[0012] The method of tiered switching of heating units in step S4 is as follows: when the temperature difference ΔT between the oil temperature in the storage tank and the target temperature is ≤2℃, only a 16kW heating unit is activated; when 2℃<ΔT≤5℃, a 20kW heating unit and a 16kW heating unit are activated; when ΔT>5℃, two sets of 20kW heating units and 16kW heating units are activated.

[0013] In step S2, the off-peak electricity periods include 00:00-08:00 and 12:00-15:00; the peak electricity periods include 10:00-12:00, 15:00-20:00 and 21:00-22:00; and the average electricity periods include 08:00-10:00, 20:00-21:00 and 22:00-24:00.

[0014] In step S5.2, the step-by-step shutdown rate of the original boiler electric heating is a power reduction of 0.5% per second.

[0015] The present invention has the following beneficial effects: This invention utilizes the coordination of an oil storage tank, a variable frequency oil pump, an electric heating body, a three-way switching valve, a high-temperature pressure stabilizing buffer chamber, an expansion tank, and a PLC control system. During off-peak hours, a small circulation loop heats the heat transfer oil and stores it in the oil storage tank. During peak hours, the system switches to a large circulation loop, relying solely on the heat energy stored in the oil storage tank to supply heat to the nylon heating boiler. This achieves the goal of tiered allocation of heat energy by taking advantage of time-of-use electricity price differences, thereby reducing electricity costs during peak hours.

[0016] This invention utilizes a time-of-use pricing period identification module built into the PLC control system to automatically switch between small and large circulation loops based on the current electricity price period. During periods of normal electricity supply, it also switches heating units in stages to provide supplementary heating based on the temperature difference between the oil temperature in the storage tank and the target temperature. This achieves automatic switching of operating modes and precise adjustment of heating power, thereby reducing unnecessary power consumption while ensuring heating quality.

[0017] This invention employs a three-stage predictive, non-disruptive, and smooth switching control system. Five minutes before switching, the temperatures at three locations—the oil storage tank, the outlet of the electric heating main body, and the process end of the nylon heating boiler—are pre-synchronized and verified. Switching is only permitted when the maximum temperature difference is ≤0.8℃. This eliminates the temperature difference impact between heat sources before switching and reduces temperature fluctuations during the switching process.

[0018] This invention adjusts the variable frequency oil pump speed and changes the heat transfer oil circulation flow rate in the third-order predictive, disturbance-free, and smooth switching control. This allows the heat power output by the heat transfer oil system to the nylon heating boiler to achieve a 1:1 equivalent match with the current heat load of the original boiler's electric heating before gradually withdrawing from the original boiler's electric heating. This achieves a smooth transition between the old and new heat sources and reduces boiler-end temperature fluctuations during the switching process.

[0019] This invention absorbs instantaneous pressure fluctuations and temperature spikes in the pipe section between the outlet of the electric heating body and the inlet of the three-way switching valve through a high-temperature stabilizing buffer chamber. It also sets up protection mechanisms such as terminating the switching and reversing when the temperature change rate exceeds 0.3℃ / min, prohibiting repeated switching in the same direction within 15 minutes, and a ±0.5℃ temperature dead zone. These mechanisms suppress residual disturbances after switching and intervene in abnormal operating conditions in a timely manner, thereby achieving the goal of controlling the temperature fluctuation at the process end of the nylon heating boiler within ±0.5℃. Attached Figure Description

[0020] Figure 1 This is a system diagram of the present invention.

[0021] The reference numerals in the figure are as follows: 1. Oil storage tank; 2. Variable frequency oil pump; 3. Electric heating body; 4. Three-way switching valve; 5. High temperature pressure stabilizing buffer chamber; 6. Expansion tank; 7. Nylon heating boiler. Detailed Implementation

[0022] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0023] Please see Figure 1 The invention provides a technical solution: A high-temperature heat transfer oil cascade recycling energy-saving system for nylon includes an oil storage tank 1, a variable frequency oil pump 2, an electric heating body 3, a three-way switching valve 4, a high-temperature pressure stabilizing buffer chamber 5, an expansion tank 6, and a PLC control system.

[0024] Oil storage tank 1 is a horizontal atmospheric pressure vessel with a capacity of 2000L. The outer wall is covered with a 300mm thick insulation layer to reduce heat loss during nighttime heat storage and improve energy storage efficiency.

[0025] The oil storage tank 1 has an oil outlet at the bottom and an oil return port at the top. When the system is running, the heat transfer oil is drawn out from the bottom and returned from the top, which is beneficial for heat stratification and stable output.

[0026] The inlet of the variable frequency oil pump 2 is connected to the outlet of the oil storage tank 1 through an oil outlet pipeline, and the outlet of the variable frequency oil pump 2 is connected to the inlet of the electric heating body 3 through a pipeline. The variable frequency oil pump 2 has a power of 5.5kW, a rated flow of 35m³ / h, and a head of 25m. Its speed can be adjusted by a PLC control system, thereby changing the circulation flow.

[0027] The electric heating body 3 consists of five independently controllable heating units, with a power configuration of four 20kW groups and one 16kW group, for a total power of 96kW. Each heating unit is equipped with an independent solid-state relay, which is independently switched on and off by the PLC control system. The purpose of this grouping design is to flexibly select the heating power according to the actual temperature difference during the peak power period, avoiding overshoot or undershoot caused by heating with a single power, while also providing sufficient heating capacity for full-power heat storage during off-peak power periods.

[0028] The main reasons for using a combination of four 20kW units and one 16kW unit are as follows: First, the total power of 96kW is sufficient to heat the heat transfer oil in the 2000L oil storage tank from room temperature to about 300℃ during off-peak electricity hours (usually lasting more than 8 hours), meeting the heat storage capacity requirements. Second, the smallest power unit is selected as 16kW, which allows for only a small amount of supplementary heating when the temperature difference is small during normal electricity hours (ΔT≤2℃), avoiding temperature overshoot and energy waste caused by high-power heating. Third, the combination of 20kW and 16kW can be flexibly configured to create various power levels such as 16kW, 20kW, 36kW, 40kW, 56kW, 60kW, 76kW, and 80kW, covering the entire range from fine-tuning to full power. In addition, both 20kW and 16kW are common standard electric heating tube power specifications on the market, which are easy to purchase, replace, and maintain, reducing manufacturing costs and spare parts management difficulties. Each heating unit is equipped with an independent solid-state relay, which is switched independently by the PLC control system. The system can select the optimal power combination in real time according to the actual temperature difference, so as to save electricity to the maximum extent while ensuring the quality of heating.

[0029] The outlet of the electric heating body 3 is connected in series with the high-temperature pressure stabilizing buffer chamber 5 and then connected to the inlet of the three-way switching valve 4. The high-temperature pressure stabilizing buffer chamber 5 is a closed pressure vessel with an elastic diaphragm inside. The diaphragm divides the chamber into a heat-conducting oil chamber and a gas chamber (usually filled with nitrogen). When instantaneous pressure fluctuations or temperature spikes occur in the pipeline due to switching, the oil in the heat-conducting oil chamber pushes the diaphragm to compress the gas chamber, absorbing excess energy, thereby suppressing the sudden pressure rise and temperature shock, and playing the role of pressure stabilization and buffering.

[0030] The three-way switching valve 4 is an electric three-way valve with a position feedback signal. Its first outlet is connected to the inlet of the nylon heating boiler 7, and the outlet of the nylon heating boiler 7 is connected to the return oil port of the oil storage tank 1 through the return oil branch pipe. The second outlet of the three-way switching valve 4 is directly connected to the return oil port of the oil storage tank 1. The position feedback signal ensures that the PLC control system can confirm the actual conduction status of the valve in real time. Only after confirming that the current path is consistent with the set mode is the heating unit allowed to start or stop, so as to prevent the cycle path from being incorrect due to valve jamming or malfunction.

[0031] Expansion tank 6 is a high-level atmospheric pressure vessel installed above oil storage tank 1. Its bottom is connected to the return oil branch pipe via an expansion pipe. The top of the expansion tank is equipped with an exhaust port and an oil filling port, and an overflow port can also be installed if necessary. The main function of expansion tank 6 is to accommodate the volume expansion of heat transfer oil due to temperature rise, and to replenish return oil during system cooling to maintain stable system pressure. In addition, residual air or light components in the system can be discharged through the exhaust port at the top of expansion tank 6 to avoid air resistance affecting circulation.

[0032] The PLC control system is connected to a first temperature sensor located inside the oil storage tank 1, a second temperature sensor located at the outlet of the electric heating body 3, and a third temperature sensor located at the process end of the nylon heating boiler 7. The first temperature sensor is used to monitor the heat storage oil temperature in the oil storage tank 1 and reflect the heat storage status. The second temperature sensor is used to monitor the oil temperature at the outlet of the electric heating body 3 and reflect the output temperature of the heating unit. The third temperature sensor is used to monitor the actual heat consumption temperature at the process end of the boiler and is the direct basis for judging the switching timing and verifying the temperature control accuracy.

[0033] The PLC control system has a built-in time-of-use pricing period identification module, which can automatically switch the operating mode according to the local peak, valley, and flat electricity pricing periods. The specific time period division can be adjusted according to the actual electricity pricing policy. In this embodiment, the following typical time periods are used: valley electricity periods include 00:00-08:00 and 12:00-15:00; peak electricity periods include 10:00-12:00, 15:00-20:00 and 21:00-22:00; and flat electricity periods include 08:00-10:00, 20:00-21:00 and 22:00-24:00.

[0034] The time-of-use pricing period identification module includes the following steps: S1: Identify whether the current electricity price period is during off-peak, peak, or flat periods.

[0035] S2: If it is currently off-peak electricity period, control the three-way switching valve 4 to switch to the second outlet conduction state, so that the heat transfer oil forms a small circulation loop along the oil storage tank 1, variable frequency oil pump 2, electric heating body 3, high temperature stabilizing buffer chamber 5, the second outlet of the three-way switching valve 4, and oil storage tank 1. At this time, the heat transfer oil does not flow through the nylon heating boiler 7, but circulates in a closed loop between oil storage tank 1 and electric heating body 3. At the same time, control all five heating units to be put into heating, and heat the heat transfer oil to the set temperature at full power of 96kW to complete the heat storage. The purpose of this stage is to use low-priced off-peak electricity to convert electrical energy into heat energy and store it in oil storage tank 1 for use during peak electricity periods.

[0036] S3: If it is currently a peak electricity period, control the three-way switching valve 4 to switch to the first outlet conduction state, so that the heat transfer oil forms a large circulation loop along the oil storage tank 1, variable frequency oil pump 2, electric heating body 3, high temperature stabilizing buffer chamber 5, the first outlet of the three-way switching valve 4, nylon heating boiler 7, and oil storage tank 1. At this time, the heat transfer oil flows through the nylon heating boiler 7 and supplies heat to it; at the same time, all heating units are shut down, and only the heat energy stored in the oil storage tank 1 is used to supply heat to the nylon heating boiler 7, realizing zero-electricity heating during peak electricity periods and significantly reducing electricity costs. If the oil temperature in the oil storage tank 1 drops below 280℃ (detected by the first temperature sensor), the PLC control system will automatically activate the 16kW heating unit for micro-heating to prevent the oil temperature from being too low and affecting the boiler heating quality. This is under-temperature protection.

[0037] S4: If the current power supply is normal, control the three-way switching valve 4 to switch to the first outlet conduction state to form a large circulation loop. Simultaneously, based on the temperature difference ΔT between the oil temperature in the storage tank detected by the first temperature sensor and the target temperature, the heating units are switched on in stages for supplemental heating. The target temperature refers to the ideal operating temperature of the heat transfer oil preset by the system. ΔT is the difference between the actual oil temperature and the target value, reflecting the degree of current heat storage insufficiency. The staged switching is as follows: when ΔT ≤ 2℃, only a 16kW heating unit is activated for fine-tuning; when 2℃ < ΔT ≤ 5℃, a 20kW heating unit and a 16kW heating unit are activated, with a total power of 36kW; when ΔT > 5℃, two sets of 20kW heating units and a 16kW heating unit are activated, with a total power of 56kW. The purpose of this staged strategy is to ensure heating while saving electricity as much as possible, avoiding energy waste and temperature overshoot caused by high-power heating.

[0038] S5: When switching between any two operating modes (such as from off-peak to peak, from peak to off-peak, from off-peak to off-peak, etc.), execute third-order predictive, disturbance-free, and smooth switching control.

[0039] The third-order predictive, disturbance-free, and smooth switching control in step S5 includes the following sub-steps: S5.1: Five minutes before switching, read the temperature values ​​of the first, second, and third temperature sensors, and calculate the maximum temperature difference between them. If the maximum temperature difference is ≤0.8℃, the switching is allowed to continue; otherwise, the current mode is locked and the system waits until the temperature difference shrinks to the allowable range. The purpose of this step is to ensure that the temperatures at the oil storage tank 1, the outlet of the electric heating body 3, and the process end of the nylon heating boiler 7 are basically the same, avoiding thermal shock caused by excessive temperature difference during switching, which could lead to drastic temperature fluctuations at the boiler end.

[0040] It is worth noting that the 0.8℃ threshold was not chosen arbitrarily, but rather based on a comprehensive consideration of the following factors: First, the tolerance limit for temperature fluctuations in nylon spinning is typically within ±1℃. If the thermal shock introduced during switching exceeds this range, it may lead to uneven filament thickness or filament breakage. Therefore, the pre-synchronization deviation before switching must be significantly less than the process tolerance limit, leaving sufficient margin. Second, considering the measurement accuracy of the temperature sensor itself (the typical accuracy of an industrial PT100 platinum resistance thermometer is ±0.3℃) and the unavoidable minute temperature fluctuations during the flow of heat transfer oil, if the threshold is set too low (e.g., 0.3℃), the system may frequently refuse to switch due to normal measurement noise, resulting in a prolonged inability to complete mode conversion and affecting energy-saving benefits. If it is set too high (e.g., 1.5℃), the temperature difference shock during switching may be superimposed on subsequent dynamic adjustment errors, exceeding the process tolerance limit. 0.8℃ falls precisely between these two extremes: on the one hand, it's greater than the sum of the sensor's accuracy and normal pulsation amplitude (approximately 0.5~0.6℃), ensuring the system can successfully pass the pre-synchronization test in most cases; on the other hand, it's less than half the process tolerance limit (half of ±1℃ is 0.5℃, but here we're using the maximum temperature difference between three points, not the deviation from the target value, so we've appropriately relaxed it to 0.8℃), providing ample safety margin for dynamic adjustments during the switching process. Furthermore, 0.8℃, as an integer scale, facilitates comparison calculations and parameter calibration in the PLC program, and also makes it easier for on-site maintenance personnel to understand and debug. Considering all these engineering factors, 0.8℃ was determined as the maximum permissible temperature difference for pre-synchronization before switching.

[0041] S5.2: During the switching process, the flow rate of the heat transfer oil is changed by adjusting the speed of the variable frequency oil pump 2, so that the heat power output by the heat transfer oil system to the nylon heating boiler 7 is matched with the current heat load of the original boiler electric heating in a 1:1 ratio. After the temperature stabilizes, the original boiler electric heating is gradually shut down by reducing the power by 0.5% per second.

[0042] The term "original boiler electric heating" refers to the resistance heating device originally installed or matched with the nylon heating boiler 7. Before this system was put into operation, the boiler relied entirely on this electric heating to maintain the process temperature. After this system was put into operation, the original electric heating serves as a backup or auxiliary heat source, and coordination with it is required during switching. The core function of S5.2 is not simply to gradually increase the new heat source and gradually decrease the old heat source, but rather to first allow the heat transfer oil system to replicate the current output heat power of the old heat source by adjusting the flow rate, so that the boiler does not feel any change in heat, and then smoothly withdraw the old heat source. This equivalent matching strategy is more effective in suppressing temperature fluctuations than the traditional linear gradual increase and decrease method.

[0043] S5.3: After the switching is completed, the high-temperature pressure stabilizing buffer chamber 5 absorbs the instantaneous pressure fluctuations and temperature spikes in the pipe section between the outlet of the electric heating body 3 and the inlet of the three-way switching valve 4. After the temperature stabilizes for 3 minutes, the pressure stabilizing state is exited. At the same time, the following protections are set: When any temperature sensor detects a temperature change rate > 0.3℃ / min, the switching immediately terminates and reverts to the state before the switching. The selection of this threshold of 0.3℃ / min is based on the following: Nylon spinning is also sensitive to the rate of temperature change. Experiments show that when the temperature change rate exceeds 0.5℃ / min, the uniformity of filament crystallization begins to be significantly affected; while under normal operating conditions, due to the inertia of the heat transfer oil circulation and the buffering effect of the insulation layer, the natural temperature drift rate usually does not exceed 0.1℃ / min. Setting the protection threshold at 0.3℃ / min effectively identifies rapid temperature changes caused by switching anomalies (such as valve jamming, sudden flow changes, heating unit malfunctions, etc.) without mistakenly triggering the revert action due to normal minor fluctuations, thus balancing safety and availability.

[0044] A complete switchover in the same direction is prohibited from being initiated again within 15 minutes after completion. The 15-minute lockout duration is based on the following considerations: A complete switchover operation (including pre-synchronization, equal-value matching, step-by-step exit, and buffer chamber voltage stabilization) typically takes 3-8 minutes. After the switchover, the system needs additional time to allow the temperature field to become sufficiently uniform and to eliminate local hot or cold spots. If the lockout time is too short (e.g., 5 minutes), a switchover may be triggered again before the system is fully stable, leading to repeated oscillations. If the lockout time is too long (e.g., 30 minutes), it will reduce the system's response flexibility, especially near the electricity price period boundary, potentially missing the optimal switchover opportunity. 15 minutes is a compromise value verified through field testing, ensuring both sufficient system stability and timely response to the switchover needs of the next electricity price period.

[0045] No switching actions are performed within the ±0.5℃ temperature dead zone. The temperature dead zone refers to a 1℃ wide interval centered on the target temperature (i.e., target temperature ±0.5℃). Within this interval, the system considers the temperature acceptable and does not trigger any heating or switching actions. The rationale for setting the ±0.5℃ dead zone is as follows: the tolerance limit for temperature fluctuations in the nylon spinning process is ±1℃, therefore the dead zone width must be less than this limit to retain a safety margin. Simultaneously, considering the measurement noise of the temperature sensor (approximately ±0.15℃) and the unavoidable overshoot in PID regulation (approximately 0.3℃), if the dead zone is too narrow (e.g., ±0.2℃), the system will frequently start and stop the heating unit or repeatedly switch modes due to small random fluctuations, increasing equipment wear and potentially exacerbating temperature oscillations. ±0.5℃ is precisely half of the process tolerance limit, avoiding unnecessary frequent actions while ensuring that the process temperature remains within the acceptable range.

[0046] Through the above three-stage predictive control, this system can achieve truly seamless switching between the three modes of off-peak electricity, peak electricity, and flat electricity, and control the temperature fluctuation at the 7th process end of the nylon heating boiler within ±0.5℃, fully meeting the stringent requirements of nylon spinning for temperature stability.

[0047] Through the aforementioned three-stage predictive control, this system can achieve truly seamless switching between off-peak, peak, and flat power modes, controlling the temperature fluctuation at the nylon heating boiler's 7th process end within ±0.5℃, fully meeting the stringent temperature stability requirements of nylon spinning. Simultaneously, by fully utilizing off-peak power periods for heat storage and only releasing heat without heating during peak power periods, overall electricity costs can be reduced.

[0048] If the oil temperature in storage tank 1 drops below 280℃ (detected by the first temperature sensor), the PLC control system will automatically activate the 16kW heating unit for micro-heating to prevent the oil temperature from affecting the boiler's heating quality; this is under-temperature protection. Simultaneously, the system also has over-temperature protection. When the second temperature sensor detects that the outlet oil temperature of the electric heating unit 3 exceeds 310℃, the PLC control system immediately cuts off all heating units and simultaneously keeps the variable frequency oil pump 2 running at low speed, using the flow of heat transfer oil to carry away and disperse heat throughout the pipeline and storage tank 1, preventing localized overheating that could lead to coking of the heat transfer oil or damage to the equipment. Over-temperature and under-temperature protection together constitute the system's temperature safety boundary, ensuring that the electric heating unit 3 operates within the safe window of 280℃ to 310℃ under any operating conditions.

[0049] As a preferred embodiment, before executing S5.1, the PLC control system will pre-fill the gas chamber of the high-temperature pressure-stabilizing buffer chamber 5 with nitrogen at a preset pressure according to the switching direction to be executed, so that the gas chamber pressure With the current heat transfer oil chamber pressure Satisfying the relation ,in The value range is 0.02MPa to 0.05MPa.

[0050] The purpose of this is to establish a certain pressure difference in advance, so that the elastic diaphragm in the buffer chamber is in a properly pre-tightened state near the operating point. When the switching action occurs, the pressure shock wave generated in the pipeline due to sudden changes in flow direction or flow rate acts on the diaphragm, and the diaphragm can immediately move towards the gas chamber, thereby more effectively absorbing and dissipating the impact energy. Conversely, if no pre-pressurization is performed, the diaphragm may be in a relaxed state at the beginning of the impact, and its buffering response sensitivity and effective stroke will be affected, which is not conducive to quickly suppressing pressure fluctuations.

[0051] Specifically, the switching direction includes switching from a small loop to a large loop, or switching from a large loop to a small loop; different switching directions correspond to The values ​​also differ: when switching from a small loop to a large loop, Take a larger value, 0.04MPa to 0.05MPa; when switching from the large circulation loop to the small circulation loop, Take the smaller value, 0.02MPa to 0.03MPa.

[0052] The reason for this distinction is primarily due to the significant differences in pipeline length and flow resistance between the two circulation loops: the smaller circulation loop has a shorter path, passes through fewer devices and pipelines, and has a relatively lower system back pressure; while the larger circulation loop requires flow through the nylon heating boiler 7 and a longer return branch pipe, significantly increasing pipeline resistance and resulting in a higher system back pressure. Therefore, when switching from the smaller to the larger circulation loop, the load on the pump outlet side suddenly increases, and the pipeline pressure tends to rise. Using a larger pre-charge pressure at this time allows the buffer chamber to better absorb this positive pressure shock. Conversely, when switching from the larger to the smaller circulation loop, the load suddenly decreases, and the pipeline pressure tends to fall. Using a smaller pre-charge pressure at this time avoids additional resistance to the pressure drop process due to excessive diaphragm pre-tightening, facilitating a rapid transition of the system to a new steady state.

[0053] also, The range of 0.02MPa to 0.05MPa was determined based on a comprehensive consideration of the rated head of the variable frequency oil pump 2 used in this system (25m, approximately 0.25MPa), the pressure fluctuation range of the heat transfer oil circulation loop under normal operating conditions (measured at approximately 0.01MPa to 0.03MPa), and the allowable deformation of the elastic diaphragm. If the value is too small (e.g., less than 0.02 MPa), the pre-tightening effect will be insignificant, and the active suppression capability of the buffer chamber will be limited; if... If the pressure value is too high (e.g., greater than 0.05 MPa), the diaphragm will be under high stress for a long time, which may affect its fatigue life. Furthermore, it may cause unnecessary pressure disturbances when switching to a low-pressure circuit. In practical applications, a miniature solenoid valve and pressure sensor controlled by a PLC can be installed at the gas chamber's charging port to achieve closed-loop regulation of the gas chamber pressure. This allows for adjustment based on real-time oil circuit pressure before each switch. Automatically calculate the target It also completes inflation, further improving the precision of control and the level of automation.

[0054] The embodiments described above are merely illustrative of specific implementations of the present invention, and while the descriptions are detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A high-temperature heat transfer oil cascade recycling energy-saving system for nylon, characterized in that: The system includes an oil storage tank (1), a variable frequency oil pump (2), an electric heating body (3), a three-way switching valve (4), a high-temperature pressure stabilizing buffer chamber (5), an expansion tank (6), and a PLC control system. The inlet of the variable frequency oil pump (2) is connected to the oil outlet of the oil storage tank (1), and the outlet of the variable frequency oil pump (2) is connected to the inlet of the electric heating body (3). The electric heating body (3) consists of five independently controllable heating units, and its outlet is connected in series with the high-temperature pressure stabilizing buffer chamber (5) and then connected to the inlet of the three-way switching valve (4). The first outlet of the three-way switching valve (4) is connected to the nylon heating pot. The inlet of the furnace (7) is connected, and the outlet of the nylon heating boiler (7) is connected to the return oil port of the oil storage tank (1) through the return oil branch pipe. The second outlet of the three-way switching valve (4) is connected to the return oil port of the oil storage tank (1). The expansion tank (6) is connected to the return oil branch pipe. The PLC control system is connected to the first temperature sensor installed inside the oil storage tank (1), the second temperature sensor installed at the outlet of the electric heating body (3), and the third temperature sensor installed at the process end of the nylon heating boiler (7). The PLC control system has a built-in time-of-use electricity price period identification module.

2. The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 1, characterized in that, The time-of-use pricing period identification module includes the following steps: S1: Identify whether the current electricity price period is off-peak, peak, or flat. S2: If it is currently a period of off-peak electricity, control the three-way switching valve (4) to switch to the second outlet conduction state, so that the heat transfer oil forms a small circulation loop along the oil storage tank (1), the variable frequency oil pump (2), the electric heating body (3), the high temperature stabilizing buffer chamber (5), the second outlet of the three-way switching valve (4), and the oil storage tank (1). At the same time, control all five heating units to be put into heating, and heat the heat transfer oil to the set temperature to complete the heat storage. S3: If it is currently a peak power period, control the three-way switching valve (4) to switch to the first outlet conduction state, so that the heat transfer oil forms a large circulation loop along the oil storage tank (1), the variable frequency oil pump (2), the electric heating body (3), the high temperature stabilizing buffer chamber (5), the first outlet of the three-way switching valve (4), the nylon heating boiler (7), and the oil storage tank (1). At the same time, all heating units are shut down, and only the heat energy stored in the oil storage tank (1) is used to supply heat to the nylon heating boiler (7). S4: If the current period is a period of normal power supply, control the three-way switching valve (4) to switch to the first outlet conduction state to form a large circulation loop. At the same time, according to the temperature difference between the oil temperature of the storage tank and the target temperature detected by the first temperature sensor, the heating unit is switched on and off in stages for supplementary heating. S5: When switching between any two operating modes, execute third-order predictive, disturbance-free, and smooth switching control.

3. The energy-saving system for the cascade recycling of high-temperature heat-conducting oil for nylon as described in claim 2, characterized in that, The third-order predictive, disturbance-free, and smooth switching control in step S5 includes the following sub-steps: S5.1: Five minutes before switching, read the temperature values ​​of the first temperature sensor, the second temperature sensor, and the third temperature sensor, calculate the maximum temperature difference between the three, and if the maximum temperature difference is ≤0.8℃, the switching is allowed to continue; otherwise, the current mode is locked and the process waits. S5.2: During the switching process, the flow rate of the heat transfer oil is changed by adjusting the speed of the variable frequency oil pump (2), so that the heat power output by the heat transfer oil system to the nylon heating boiler (7) is matched with the current heat load of the original boiler electric heating in a 1:1 ratio. After the temperature stabilizes, the original boiler electric heating is gradually withdrawn. S5.3: After the switching is completed, the high-temperature pressure stabilizing buffer chamber (5) is used to absorb the instantaneous pressure fluctuations and temperature spikes in the pipe section between the outlet of the electric heating body (3) and the inlet of the three-way switching valve (4). After the temperature stabilizes for 3 minutes, the pressure stabilizing state is exited. At the same time, the following protections are set: when the temperature change rate detected by any temperature sensor is >0.3℃ / min, the switching is immediately terminated and the state before the switching is returned; the switching in the same direction is prohibited from being started again within 15 minutes after the complete switching in the same direction is completed; no switching action is performed within the ±0.5℃ temperature dead zone.

4. The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 1, characterized in that: The electric heating body (3) has five heating units configured with four groups of 20kW and one group of 16kW. Each heating unit is equipped with an independent solid-state relay, which is independently switched by the PLC control system.

5. The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 1, characterized in that: The three-way switching valve (4) is an electric three-way valve with a position feedback signal. The PLC control system only allows the heating unit to start or stop in the corresponding mode after receiving the position feedback signal of the three-way switching valve (4) and confirming that the current actual passage is consistent with the set cycle mode.

6. The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 1, characterized in that: The PLC control system is equipped with over-temperature protection and under-temperature protection. Over-temperature protection means that when the second temperature sensor detects a temperature > 310°C, all heating units will be immediately cut off and the variable frequency oil pump (2) will be kept at a low speed to circulate heat dissipation. Under-temperature protection means that when the first temperature sensor detects an oil temperature < 280°C in the oil storage tank, the original boiler electric heating will be prohibited from being turned off and the 16kW heating unit will be automatically put into operation for micro-heating.

7. The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 1, characterized in that: The oil storage tank (1) has a capacity of 2000L and is covered with an insulation layer with a thickness of 300mm. The expansion tank (6) is equipped with a magnetic level gauge and a low level alarm. The variable frequency oil pump (2) has a power of 5.5kW, a flow rate of 35m³ / h, and a head of 25m. The electric heating body (3) has a design temperature of 350℃ and a design pressure of 0.8MPa.

8. The energy-saving system for the cascade recycling of high-temperature heat transfer oil for nylon as described in claim 2, characterized in that, The method of tiered switching of heating units in step S4 is as follows: when the temperature difference ΔT between the oil temperature in the oil storage tank (1) and the target temperature is ≤2℃, only a 16kW heating unit is put into operation; when 2℃<ΔT≤5℃, a 20kW heating unit and a 16kW heating unit are put into operation; when ΔT>5℃, two sets of 20kW heating units and 16kW heating units are put into operation.

9. The energy-saving system for the cascade recycling of high-temperature heat-conducting oil for nylon as described in claim 3, characterized in that, In step S5.2, the step-by-step shutdown rate of the original boiler electric heating is a power reduction of 0.5% per second.

10. The energy-saving system for the cascade recycling of high-temperature heat-conducting oil for nylon as described in claim 3, characterized in that, Before the execution of the third-order predictive, disturbance-free, and smooth switching control in step S5, the following steps are also included: S5.0: The PLC control system pre-fills the gas chamber of the high-temperature pressure-stabilizing buffer chamber (5) with nitrogen at a preset pressure according to the switching direction to be executed, so that the gas chamber pressure With the current heat transfer oil chamber pressure Satisfying the relation ,in The value range is 0.02MPa to 0.05MPa; the switching direction includes switching from a small circulation loop to a large circulation loop, or switching from a large circulation loop to a small circulation loop; different switching directions correspond to Different values: when switching from a small loop to a large loop When switching from a large circulation loop to a small circulation loop, take a larger value of 0.04MPa to 0.05MPa. Take the smaller value, 0.02MPa to 0.03MPa.

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