WO2021109104A1 - Heat treatment furnace having wide turndown ratio and control method - Google Patents

Abstract

Provided are a heat treatment furnace having a wide turndown ratio and a control method. The heat treatment furnace having a wide turndown ratio is provided with multiple temperature control areas, each temperature control area is provided with at least four independent burners (1), and all of the burners (1) are provided with an air-fuel proportional valve. In a practical application, a burner (1) generally employs a medium-high speed burner for gas. According to the loading capacity of the furnace and furnace size requirements, the furnace is generally provided with multiple temperature control areas, and each temperature control area is provided with four or more independent burners (1). By means of pulse control on the switching time of burners (1) and linear adjustment of the power of the burners (1), the controllability of temperature control for the entire heat treatment furnace having a wide turndown ratio is thus greatly improved, and the addition of air-fuel proportional valves enables the output of the burners (1) to be more stable. The inventive combination of the described technical features enables the turndown ratio of the heat treatment furnace having a wide turndown ratio to be greatly improved, so as to satisfy more demanding requirements.

Description

Wide adjustment ratio heat treatment furnace and control method Technical field

The invention relates to the field of metal heat treatment, in particular to a heat treatment furnace with a wide adjustment ratio and a control method.

Background technique

In the metal high-precision heat treatment furnace system, there are generally two basic temperature control requirements. First, in the heating section, the heating speed is required to be fast. In order to meet the higher heating speed, generally according to the installed furnace volume and heating time, high-powered burner. Second, in the heat preservation section, the furnace temperature uniformity is required to be high, the normal requirement is ≤±3℃, and some high-demand items will reach ≤±2.5, or even ≤±2℃. Therefore, in response to these two requirements, an ultra-wide combustion system turndown ratio is required.

Summary of the invention

In order to solve the above technical problems, the present invention discloses a wide turndown ratio heat treatment furnace and a control method, which can improve the turndown ratio of the wide turndown ratio heat treatment furnace. After further optimization, it can finally reach 100:1.

In order to achieve the above objective, the technical solution of the present invention is: a wide-regulation ratio heat treatment furnace, the wide-regulation ratio heat treatment furnace is provided with a plurality of temperature control zones, and each temperature control zone is provided with at least 4 independent burners, all The burner is equipped with an air-fuel proportional valve. In practical applications, the burner generally uses a gas medium and high-speed burner.

According to the furnace load capacity and furnace size requirements, it is generally set into multiple temperature control zones, each temperature control zone has 4 or more independent burners, through the pulse control of the burner switching time, and the burner The linear adjustment of power greatly improves the controllability of the temperature control of the entire wide adjustment ratio heat treatment furnace, and the addition of an air-fuel proportional valve makes the output of the burner more stable. The creative combination of the above technical features makes the adjustment ratio of the wide adjustment ratio heat treatment furnace greatly improved to meet more demanding requirements.

Further, the wide-regulation ratio heat treatment furnace also includes a control system, and the control system includes a PLC pulse logic function program module, and the burners in each temperature control zone are controlled by the PLC pulse logic function program module in the control system. Separate changes to the opening and closing time of the burner, as well as changes to the combination of the opening and closing time of the burner, can realize the control of the burner output. Multiple control factors make the adjustment more flexible. In the prior art, adjustment is made only by changing the opening of the linear valve of the burner or changing the pulse duty ratio, which makes the control flexibility low and affects the adjustment ratio of the entire device.

Further, the starting phases of the burners of all burners in the same temperature control zone are evenly distributed in the control period. During the pulse process of the burner, the opening and closing of the 4 burners are uniformly distributed, which prevents the burner from starting and closing at the same time, causing pressure fluctuations on the upstream air supply system, which will affect the combustion. The stability of the nozzle combustion, such as insufficient combustion, poor ignition, etc.; pressure fluctuations in the furnace pressure in the downstream furnace, and this fluctuation will bring about the instability of the combustion exhaust system. Both of these fluctuations will adversely affect the temperature control.

Further, the wide turndown heat treatment furnace further includes a central controller, a temperature controller, and a temperature sensor arranged in a temperature control zone in the furnace.

The temperature sensor generally can use K-type thermocouple, and the use temperature of nickel-chromium-nickel-silicon thermocouple (K-type thermocouple) is -200～1300℃. The K-type thermocouple has the advantages of good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity, strong oxidation resistance, and low price.

The temperature controller respectively receives the temperature setting value from the central controller and the temperature detection value from the temperature sensor, and undergoes cold junction compensation and linearization processing and PID calculation, and the calculation result is output to the pulse logic function program module to control combustion The device pulses work.

The cold-junction compensation is to eliminate the influence of the temperature change of the free-end, and the number of thermocouple graduations is based on the condition that the temperature of the free-end is 0°C, and the electromotive force that is reduced due to the increase of the temperature of the free-end must be compensated during use. The compensation method generally includes a zero-degree thermostat or a cold-junction compensation module. This solution uses a cold-junction compensation module to connect the cold junctions of all temperature sensors to the cold-junction compensation module. This module is equipped with a high-precision thermal resistance. Measure the ambient temperature of the access terminal and automatically convert it through the system to eliminate the influence of temperature changes at the free terminal.

The PID adjustment adopts a classic algorithm, first calculates the deviation between the system set value and the actual value, and then performs proportional calculation, integral accumulation, and differential calculation of the rate of change of the deviation. The three calculation results are calculated according to different weights. And get the output value to control the system output.

Further, the conventional heat treatment furnace with wide regulation ratio is generally divided into 3 temperature control zones, a total of 12 burners are configured, and each temperature control zone is equipped with 4 independent burners, and each burner is equipped with an air-fuel proportional valve. , Stable control of the proper ratio of fuel to air. The burners are arranged on one side wall, and each temperature zone has 2 burners on the upper and lower sides. Through the circulation of the hot air circulation fan in the middle, the furnace gas is forced to circulate in the required direction for heat exchange. This arrangement helps the furnace to reduce the upper and lower floors. The temperature difference makes the temperature uniformity better.

Further, the width adjustment ratio heat treatment furnace is also provided with an air supply device for the burner and an air pressure adjustment device for adjusting the air supply pressure, and the air pressure adjustment device adjusts the air supply pressure according to the following criteria: The regulation ratio reduces the production demand power in the heat treatment furnace and reduces the air supply pressure.

Further, the adjustment ratio of the wide adjustment ratio heat treatment furnace is 100:1. Generally, through pulse adjustment, the adjustment ratio of not less than 20:1 is satisfied, and the adjustment ratio of 5:1 is satisfied through the wind pressure condition, and the adjustment ratio of the entire system is not less than 100:1.

Further, the air pressure adjusting device performs closed-loop control on the air supply pressure of the wide adjustment ratio heat treatment furnace.

A method for controlling a wide adjustment ratio heat treatment furnace includes the following steps:

S1, the heating section, the burners of all burners are burnt and heated at full load to meet the requirements of rapid heating;

In S2, the heat preservation section, the heat demand of the load is reduced, and the combustion load of the burner is adjusted according to the PID to perform the pulse combustion mode.

Further, in the process of S1 and S2, the air supply pressure of the burner is adjusted, the width adjustment ratio is lower than the production demand power in the heat treatment furnace, and the air supply pressure is reduced.

Description of the drawings

Figure 1 is a schematic diagram of the phase diagram of the present invention and the relationship between the burner and the pulse control;

Figure 2 is a schematic diagram of the temperature control dynamic response process of the present invention;

Figure 3 is a cross-sectional view of a single temperature control zone of the present invention;

Figure 4 is a schematic diagram of the burner side of a single temperature control zone of the present invention;

Figure 5 is a schematic diagram of the air supply device and the air pressure adjusting device of the present invention;

Figure 6 is a schematic diagram of the present invention achieving a 100:1 adjustment ratio;

Fig. 7 is a circuit diagram of the temperature control system of the present invention.

Detailed ways

The technical solutions of the present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to these embodiments.

In order to achieve the objective of the present invention, the present invention provides a heat treatment furnace with a wide regulation ratio, which is provided with a plurality of temperature control zones, and each temperature control zone is provided with at least 4 independent burners, all burners Equipped with an air-fuel proportional valve. In practical applications, the burner generally uses a gas medium and high-speed burner.

According to the furnace load capacity and furnace size requirements, it is generally set into multiple temperature control zones, each temperature control zone has 4 or more independent burners, through the pulse control of the burner switching time, and the burner The linear adjustment of power greatly improves the controllability of the temperature control of the entire wide adjustment ratio heat treatment furnace, and the addition of an air-fuel proportional valve makes the output of the burner more stable. The creative combination of the above technical features makes the adjustment ratio of the wide adjustment ratio heat treatment furnace greatly improved to meet more demanding requirements.

As shown in Figure 3 and Figure 4, in practical applications, for example, a wide adjustment ratio heat treatment furnace uses 3 temperature control zones, and a total of 12 independent burners 1 are configured, and each temperature control zone is equipped with 4 independent burners. Each burner 1 is equipped with an air-fuel proportional valve to stably control the proper ratio of fuel to air. The burner 1 is arranged on the same side wall of the heat treatment furnace with a wide regulation ratio, and each temperature zone has two burners 1 on the upper and lower sides. The air in the furnace is circulated through the middle hot air circulation fan 2 to force the furnace gas to circulate in the required direction. For heat exchange, this arrangement helps the furnace to reduce the temperature difference between the upper and lower layers and make the temperature uniformity better.

As shown in FIG. 10, in some embodiments, four or more burners 1 may be arranged in a staggered arrangement on the two side walls of the width adjustment ratio heat treatment furnace, for example, two are arranged above one side wall. Burner 1, two burners 1 are arranged at the lower position on the opposite side wall, so that the burners of some burners are located above one side wall in the furnace, and the burners of some burners are located below the opposite side wall in the furnace , The flame is sprayed in opposite directions, and the heat flow naturally forms convection in the furnace, which accelerates the flow and heat exchange of the heat flow in the furnace. At the same time, coupled with the circulation of the air in the furnace by the intermediate hot air circulation fan 2 arranged on the side wall, the furnace gas is forced to circulate in the required direction for heat exchange. This arrangement helps the furnace to reduce the temperature difference between the upper and lower layers, so that The temperature uniformity is better. The position of the intermediate hot air circulation fan 2 can be set at the same height of the burner on the same side wall, and located in the middle position to enhance the convection effect. At the same time, in some embodiments, in order to ensure the consistency of the temperature in the furnace, especially to ensure the temperature and heat exchange efficiency of the central area (the area where the processed product is placed), a plurality of guides are provided above and below the furnace. Flow fins 21. These guide fins 21 are bent and extended from the inner wall of the furnace along the flow direction of the hot air, thereby guiding a part of the heat flow from the upper and lower middle area of the furnace to the lower and upper central area, forming a vortex and guiding the flow The slices can be arranged in multiple rows, as shown in Figure 10. The windward surface of the baffle 21 can be set as a concave curved surface, similar to a curved baffle from top to bottom, to strengthen the guidance of the hot air. On the windward side of the guide vane 21 at one end away from the furnace inner wall, guide fins that gradually increase from the furnace inner wall direction to the furnace center direction are also provided, and the lateral width of the guide vane 21 is also from the furnace inner wall direction to the furnace center direction Gradually increase, the distance between the multiple guide fins gradually increases from the direction of the inner wall of the furnace to the direction of the center of the furnace, guiding the hot air to diverge and blow to the central area, and improve the uniformity of temperature. In some examples, the length of the baffle 21 is between 5-30 cm and the width is more than 5 cm, which can also be determined according to needs. The guide vane 21 can also use the same refractory material on the inner wall of the furnace to directly process similarly shaped protrusions to achieve the above-mentioned functions. The convex windward surface has the same structure as the windward surface of the guide vane 21.

In some embodiments, the wide turndown heat treatment furnace further includes a control system, and the control system includes a PLC pulse logic function program module, and the burners in each temperature control zone are controlled by the PLC pulse logic function program module in the control system. Separate changes to the opening and closing time of the burner, as well as changes to the combination of opening and closing time of the burner, can realize the control of the burner output, and multiple control factors make the adjustment more flexible. In the prior art, adjustment is made only by changing the opening of the linear valve of the burner or changing the pulse duty ratio, which makes the control flexibility low and affects the adjustment ratio of the entire device.

In some examples, as shown in Figure 1, the starting phases of the burners of all burners in the same temperature control zone are evenly distributed during the control period. During the pulse process of the burner, the opening and closing of the 4 burners are uniformly distributed, which prevents the burner from starting and closing at the same time, causing pressure fluctuations on the upstream air supply system, which will affect the combustion. The stability of the nozzle combustion, such as insufficient combustion, poor ignition, etc.; pressure fluctuations in the furnace pressure in the downstream furnace, and this fluctuation will bring about the instability of the combustion exhaust system. Both of these fluctuations will adversely affect the temperature control.

In some embodiments, the wide turndown heat treatment furnace further includes a central controller, a temperature controller, and a temperature sensor arranged in a temperature control zone in the furnace.

The temperature sensor generally can use K-type thermocouple, and the use temperature of nickel-chromium-nickel-silicon thermocouple (K-type thermocouple) is -200～1300℃. The K-type thermocouple has the advantages of good linearity, large thermoelectromotive force, high sensitivity, good stability and uniformity, strong oxidation resistance, and low price.

The temperature controller respectively receives the temperature setting value from the central controller and the temperature detection value from the temperature sensor, and undergoes cold junction compensation and linearization processing and PID calculation, and the calculation result is output to the pulse controller to control the burner pulse jobs.

The cold-junction compensation is to eliminate the influence of the temperature change of the free-end, and the number of thermocouple graduations is based on the condition that the temperature of the free-end is 0°C, and the electromotive force that is reduced due to the increase of the temperature of the free-end must be compensated during use. The compensation method generally includes a zero-degree thermostat or a cold-junction compensation module. This solution uses a cold-junction compensation module to connect the cold junctions of all temperature sensors to the cold-junction compensation module. This module is equipped with a high-precision thermal resistance. Measure the ambient temperature of the access terminal, and eliminate the influence of temperature changes at the free terminal through conversion.

As shown in Figure 2, the PID adjustment adopts a classic algorithm, first calculates the deviation between the system set value and the actual value, and then performs proportional calculation, integral accumulation, and differential calculation of the rate of change of the deviation. The three calculation results , According to different weights to get the output value, to control the system output.

As shown in Figure 5, the wide adjustment ratio heat treatment furnace is also provided with an air supply device for the burner and an air pressure adjustment device for adjusting the air supply pressure, and the air pressure adjustment device adjusts the air supply pressure according to the following criteria: With the reduction of the production demand power in the heat treatment furnace with the wide turndown ratio, the air supply pressure is reduced. In the example of FIG. 5, the air supply device includes a fan 31, a frequency converter that controls the speed of the fan 31, and a wind pressure sensor 32. The wind pressure sensor 32 detects the wind pressure in the air supply pipeline in real time and transmits the data to the control device. (Or central controller), the control device sends out control commands to the frequency converter according to the real-time air pressure requirements of the entire heat treatment furnace. By adjusting the fan speed, the air pressure value meets the system requirements, so as to achieve the air pressure Real-time control.

In order to meet the requirements of certain production processes, the adjustment ratio of the wide adjustment ratio heat treatment furnace is 100:1. Generally, through pulse regulation, the regulation ratio of not less than 20:1 is satisfied, and the regulation ratio of 5:1 is satisfied through the wind pressure condition, so that the regulation ratio of the entire system is equal to or even greater than 100:1. As shown in Figure 6, the pulse adjustment and the air supply pressure adjustment are superimposed at the same time, so that an ultra-wide adjustment ratio can be achieved, reaching or even exceeding 100:1.

Further, the air pressure adjusting device performs closed-loop control on the air supply pressure of the wide adjustment ratio heat treatment furnace.

As shown in Figures 8 and 9, in practical applications, the system is equipped with a combustion-supporting fan 5, a smoke exhaust fan 6, and a plate heat exchanger. The combustion-supporting fan 5 uses a centrifugal blower to provide sufficient air volume and sufficient air for the combustion of the burner. Compressed combustion air. The exhaust fan 6 adopts a high-temperature centrifugal exhaust fan, which is used to discharge the combusted flue gas out of the factory building through the exhaust duct, and provide sufficient air volume and air pressure to overcome the duct resistance of the exhaust duct and the plate heat exchanger. The combustion-supporting air duct connected to the flame-retardant fan 5 and the exhaust duct connected to the exhaust fan are all connected to the plate heat exchanger. Through the plate heat exchanger, the high-temperature flue gas in the exhaust duct and the air in the combustion-supporting air duct (combustion-supporting air) ) The heat exchange is carried out through the plate heat exchanger to preheat the combustion air to reduce the exhaust gas temperature, effectively improve the thermal efficiency of the system, and save energy and reduce emissions.

A cooling device can also be added. The cooling device includes a cooling fan 4 and a cooling pipeline. The cooling pipeline includes a furnace door frame cooling system for cooling the furnace door frame, and a burner cooling system for cooling the burner of each burner. The fan sends the cooling air to the furnace door frame and burner through the pipeline system, and cools it when needed. In the examples in Figures 8 and 9, a pipeline can also be drawn from the combustion-supporting air pipeline between the combustion-supporting fan and the plate heat exchanger to communicate with the cooling pipeline, and an electronic or manual control valve is installed in the middle. Normally closed, only when the cooling fan 4 is damaged or additional wind pressure is needed for efficient cooling, this valve is opened, and the combustion-supporting fan 5 is used as a backup or auxiliary for the cooling fan 4.

The present invention also provides a method for controlling a wide adjustment ratio heat treatment furnace, which includes the following steps:

S1, the heating section, the burners of all burners are burnt and heated at full load to meet the requirements of rapid heating;

In S2, the heat preservation section, the heat demand of the load is reduced, and the combustion load of the burner is adjusted according to the PID to perform the pulse combustion mode.

In actual control, the starting phases of the burners of all burners in the same temperature control zone are evenly distributed in the control cycle. For example, during the pulse process of the burner, the opening and closing moments of all burners (for example, 4 burners) in the same temperature control zone are uniformly distributed, which prevents the burner from starting and closing at the same time, which brings about the upstream supply. The pressure fluctuations of the air supply system will affect the stability of the burner combustion, causing insufficient combustion, poor ignition, etc.; for the pressure fluctuations in the furnace pressure in the downstream furnace, this fluctuation will cause the combustion exhaust system to fail. stable. Both of these fluctuations will adversely affect the temperature control.

In a further optimization scheme, in the process of S1 and S2, the air supply pressure of the burner is adjusted, the width adjustment ratio of the heat treatment furnace is reduced, and the air supply pressure is reduced. Generally, through pulse regulation, the regulation ratio of not less than 20:1 is satisfied, and the regulation ratio of 5:1 is satisfied through the wind pressure condition, so that the regulation ratio of the entire system is equal to or even greater than 100:1. As shown in Figure 6, the pulse adjustment and the air supply pressure adjustment are superimposed at the same time, so that an ultra-wide adjustment ratio can be achieved, reaching or even exceeding 100:1.

Further, the air pressure adjusting device performs closed-loop control on the air supply pressure of the wide adjustment ratio heat treatment furnace.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, without departing from the inventive concept of the present invention, a number of modifications and improvements can be made, all of which belong to the present invention. The scope of protection of the invention.

Claims (10)

A wide-regulation ratio heat treatment furnace, characterized in that the wide-regulation ratio heat treatment furnace is provided with multiple temperature control zones, each temperature control zone is provided with at least 4 independent burners, and all burners are provided with air-fuel proportional valves , Each burner can work independently. The wide turndown heat treatment furnace of claim 1, further comprising a control system, the control system includes a PLC pulse logic function program module, each burner in the temperature control zone is controlled by the PLC pulse logic function in the control system Program module control. The heat treatment furnace with wide turndown ratio according to claim 2, characterized in that the starting phases of the burners of all burners in the same temperature control zone are evenly distributed in the control period to reduce load fluctuations when the burners are started. The wide turndown heat treatment furnace according to any one of claim 3, wherein the wide turndown heat treatment furnace further comprises a central controller, a temperature controller, and a temperature sensor arranged in a temperature control zone in the furnace, and The temperature controller respectively receives the temperature setting value from the central controller and the temperature detection value from the temperature sensor, after cold junction compensation and linearization processing and PID calculation, the calculation result is output to the pulse controller to control the pulse operation of the burner. The wide adjustment ratio heat treatment furnace according to any one of claims 1 to 4, characterized in that there are 3 temperature control zones, and a total of 12 burners are configured in the wide adjustment ratio heat treatment furnace, and each temperature control zone is equipped with 12 burners. There are 4 independent burners, and each burner is equipped with an air-fuel proportional valve to stably control the proper ratio of fuel to air. The wide adjustment ratio heat treatment furnace of claim 5, wherein the wide adjustment ratio heat treatment furnace is further provided with an air supply device for the burner and an air pressure adjustment device for adjusting the supply air pressure. The pressure adjustment device adjusts the air supply pressure according to the following criteria: as the heat absorption of the material in the wide adjustment ratio heat treatment furnace reaches saturation, the production demand power decreases and the air supply pressure is reduced. 8. The wide turndown heat treatment furnace according to claim 6, wherein the turndown ratio of the wide turndown heat treatment furnace is 100:1. 7. The wide turndown heat treatment furnace according to claim 7, wherein the air pressure adjusting device performs closed-loop control on the supply air pressure of the wide turndown heat treatment furnace. A method for controlling a heat treatment furnace with a wide turndown ratio is characterized in that it comprises the following steps: S1, the heating section, the burners of all burners are burnt and heated at full load to meet the requirements of rapid heating; In S2, the heat preservation section, the heat demand of the load is reduced, and the combustion load of the burner is adjusted according to the PID to perform the pulse combustion mode. The method for controlling a wide turn-down ratio heat treatment furnace according to claim 9, characterized in that, in the process of S1 and S2, the air supply pressure of the burner is adjusted, and the wide turn-down ratio heat treatment furnace reduces the required power for production. Supply air pressure.

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