CN101329136A - A pulp molding drying line based on frequency conversion speed regulation technology and its production process - Google Patents

Abstract

Translated fromChinese

本发明公开了一种基于变频调速技术的纸浆模塑烘干线及其生产工艺，本发明应用在热风对流带式烘干线上，用于设计一套效能优化自动控制系统，它根据纸浆模塑的干燥特性及不同湿纸坯的尺寸及重量，对复杂对象建模，采用过程控制技术，交流变频调速技术及现代检测技术，根据现场检测的温度，湿度信号，对循环风机，电动风门，抽湿风机，输送链传动电机变频无级调速控制，合理地调整烘道内输送带的运行速度、各分段干燥器中的工作温度、热风风量及水蒸气的排放等，形成合理的干燥曲线，以使产品的变形尽可能小，最大限度地节约电能及热能的损耗，加快烘干速率，加大烘干生产线的产量，实现最优控制。

The invention discloses a pulp molding drying line and its production process based on frequency conversion speed regulation technology. The drying characteristics of molding and the size and weight of different wet paper blanks, modeling of complex objects, using process control technology, AC frequency conversion speed regulation technology and modern detection technology, according to the temperature and humidity signals detected on site, the circulation fan, electric motor Damper, dehumidifying fan, conveyor chain transmission motor frequency conversion stepless speed regulation control, reasonably adjust the running speed of the conveyor belt in the drying tunnel, the working temperature in each segment dryer, the hot air volume and the discharge of water vapor, etc., to form a reasonable Drying curve, so as to make the deformation of the product as small as possible, save the loss of electric energy and heat energy to the greatest extent, speed up the drying rate, increase the output of the drying production line, and achieve optimal control.

Description

Translated fromChinese

一种基于变频调速技术的纸浆模塑烘干线及其生产工艺A pulp molding drying line based on frequency conversion speed regulation technology and its production process

技术领域technical field

本发明涉及一种基于变频调速技术的纸浆模塑烘干线及其生产工艺。The invention relates to a pulp molding drying line based on frequency conversion and speed regulation technology and a production process thereof.

背景技术Background technique

纸浆模塑制品被认为是EPS白色污染包装产品的最佳替代品，被称为“21世纪的绿色包装”。纸浆模塑制品的生产工艺流程是：碎浆，真空成型，烘干，热压整型。首先，把废纸团或原浆板与一定比例的水结合，投入水力碎浆机，利用水力作用高速搅碎分解，从而使纸纤维混合于水中，形成符合一定要求的浆料。再通过真空吸附的方法，使浆料均匀分布在成型模具上，进一步脱水，脱模，此时湿纸坯基本成型。但成型后的湿纸坯含有较高水分，需要干燥除去。为使纸浆模塑制品有更好的防震性能及更整洁光滑的外观，干燥后的制品可放在高温高压的整型机模具上加以定型，至此纸浆模塑制品的生产工序已全部完成。纸浆模塑工业在一些发达国家已有80多年历史，并具一定规模。而我国纸浆模塑工业发展相对缓慢。国外纸浆模塑发展特点是：应用范围广；制品设计标准化；自动化程度高；能源利用率高，节省劳动力。但我国纸浆模塑生产线普遍存在着自动化程度不高，能源浪费大，产品及格率低等制约因素。尤其在纸浆模塑烘干工序上，对上述制约因素表现更为突出。纸浆模塑制品的烘干成本占整个生产成本的30％-40％。而热风对流干燥是国内外普遍采用的干燥方式。目前，国内外的烘干生产线都采用中央供热，分段烘干的构造形式，由燃烧机或其它热源向燃烧室中央供热，主烘道采用烘干区段形式，并通过每段烘道的循环风机把热风从燃烧室输送到烘干区段并持续循环，链式输送带从烘道中间穿过，热风通过气体分布板上的风孔向输送带上的纸浆湿制品吹送，对产品进行分段干燥，烘道内的水分由抽湿风机带走。Pulp molded products are considered to be the best substitute for EPS white pollution packaging products, and are called "green packaging in the 21st century". The production process of pulp molded products is: pulping, vacuum forming, drying, hot pressing and shaping. First, combine waste paper balls or raw pulp boards with a certain proportion of water, put them into a hydropulper, and use hydraulic action to crush and decompose at a high speed, so that paper fibers are mixed in water to form a slurry that meets certain requirements. Then, through the method of vacuum adsorption, the slurry is evenly distributed on the forming mold, further dehydrated, and demoulded, and the wet paper base is basically formed at this time. However, the formed wet paper base contains relatively high moisture, which needs to be dried and removed. In order to make pulp molded products have better anti-shock performance and a more neat and smooth appearance, the dried products can be placed on a high-temperature and high-pressure shaping machine mold for shaping. So far, the production process of pulp molded products has been completed. The pulp molding industry has a history of more than 80 years in some developed countries and has a certain scale. However, the development of my country's pulp molding industry is relatively slow. The characteristics of the development of foreign pulp molding are: wide application range; standardized product design; high degree of automation; high energy utilization rate and labor saving. However, there are generally restrictive factors such as low degree of automation, large waste of energy, and low pass rate of products in pulp molding production lines in my country. Especially in the drying process of pulp molding, the performance of the above restrictive factors is more prominent. The drying cost of pulp molded products accounts for 30%-40% of the entire production cost. Hot air convection drying is a drying method commonly used at home and abroad. At present, the drying production lines at home and abroad all adopt the structure of central heating and segmental drying. The burner or other heat sources supply heat to the center of the combustion chamber. The circulation fan of the tunnel conveys the hot air from the combustion chamber to the drying section and continues to circulate. The chain conveyor belt passes through the middle of the drying tunnel, and the hot air is blown to the wet pulp products on the conveyor belt through the air holes on the gas distribution plate. The product is dried in sections, and the moisture in the drying tunnel is taken away by the dehumidifier.

通常每段烘道的循环风机(抽湿风机)的容量是按照系统需要的最大要求而设计的，然而在实际应用中(根据产品的不同尺寸及质量)，系统大多数时间里在远小于设计容量下工作。当需要减低输送风量的时候，传统的调节方法是在循环风机(抽湿风机)的出口处加装风门，用关小风门加大系统局部阻力即改变管路系统特性曲线的方法来进行调节。这种方法简单有效，但严重影响了系统的效率且浪费了大部分的电能及热能。由流体力学理论可知，风机的输送风量与风机的转速n的一次方成正比，风机的转矩与n的二次方成正比，而其功率则与n的三次方成正比。因此，当风机风量由100％下降到80％时，不采用关小风门的方法而采用改变三相异步电动机的定子供电频率，而改变风机的运行转速的方法，则有效地把风机功耗降到51.2％，从而节约电能49.7％。而且传统烘干线风门开度的调节是人工操作的，它不能及时根据系统参数的变化作出自适应的调节，也没有针对纸浆模塑制品在不同的干燥阶段的干燥特性设置出最优的工作曲线进行分段控制，系统存在严重的随机性及盲目性，导致烘干时间过短或过长，产品变型严重，能源浪费大，烘干效率低，废品率高等制约因素。Usually, the capacity of the circulation fan (humidifier) of each drying tunnel is designed according to the maximum requirement of the system. However, in practical applications (according to the different sizes and qualities of the products), the system is much smaller than the design most of the time. work at capacity. When it is necessary to reduce the conveying air volume, the traditional adjustment method is to install a damper at the outlet of the circulating fan (humidifier), and adjust by closing the damper to increase the local resistance of the system, that is, changing the characteristic curve of the pipeline system. This method is simple and effective, but seriously affects the efficiency of the system and wastes most of the electric energy and heat energy. It can be known from the theory of fluid mechanics that the delivery air volume of the fan is proportional to the first power of the fan speed n, the torque of the fan is proportional to the second power of n, and its power is proportional to the third power of n. Therefore, when the air volume of the fan drops from 100% to 80%, the method of changing the stator power supply frequency of the three-phase asynchronous motor and changing the operating speed of the fan instead of closing the damper can effectively reduce the power consumption of the fan. down to 51.2%, thus saving 49.7% of electric energy. Moreover, the adjustment of the air door opening of the traditional drying line is manually operated, which cannot make adaptive adjustments in time according to changes in system parameters, and does not set the optimal work for the drying characteristics of pulp molded products in different drying stages. The curve is controlled in sections, and the system has serious randomness and blindness, resulting in too short or too long drying time, serious product deformation, large energy waste, low drying efficiency, and high reject rate.

发明内容Contents of the invention

本发明提供的一种基于变频调速技术的纸浆模塑烘干线，包括燃烧机、热风炉、烘箱、循环风机、抽湿风机、输送带，燃烧机连接热风炉；上述烘箱采用框架结构，输送带安装在烘箱内部，烘箱长度及宽度根据生产量决定，烘箱分为若干个烘干区段；每个烘干区段安装有循环风机，每个循环风机连接风机专用型变频器，循环风机除了循环烘箱内的热空气外，循环风机进风口还连接有由热风炉引出的热风管，在热风管与循环风机的进风口之间装有电动风门，电动风门连接有变频器；循环风机出风口与排风管连接，排风管把热风直接送进输送带上；在烘箱内装有抽湿风机，抽湿风机连接风机专用型变频器，在烘干线的每个烘干区段的中央及热风管的出风口处分别安装温度传感器，在抽湿风机的进风口安装湿度传感器，在抽湿风机的出风口安装温度传感器；烘干线的控制由可编程逻辑控制器PLC来完成，PLC通过接收各传感器的数据，并与设定的最优值相比较，得出调节量并向各个变频器发出控制指令；输送带安装有传动电机，传动电机连接变频器，蜗轮蜗杆减速器安在传动电机与输送带之间；烘干线控制台安装有人机界面的触摸屏。A pulp molding drying line based on frequency conversion and speed regulation technology provided by the present invention includes a burner, a hot blast stove, an oven, a circulating fan, a dehumidifying fan, and a conveyor belt, and the burner is connected to the hot blast stove; the above oven adopts a frame structure, The conveyor belt is installed inside the oven. The length and width of the oven are determined according to the production volume. The oven is divided into several drying sections; each drying section is equipped with a circulating fan, and each circulating fan is connected to a special frequency converter for the fan. In addition to circulating the hot air in the oven, the air inlet of the circulating fan is also connected with a hot air pipe drawn from the hot blast stove, and an electric damper is installed between the hot air pipe and the air inlet of the circulating fan, and the electric damper is connected with a frequency converter; The air outlet of the fan is connected to the exhaust pipe, and the exhaust pipe sends the hot air directly to the conveyor belt; a dehumidifying fan is installed in the oven, and the dehumidifying fan is connected to a special frequency converter for the fan, and is placed in each drying section of the drying line Temperature sensors are installed at the center and outlet of the hot air pipe, humidity sensors are installed at the air inlet of the dehumidifier fan, and temperature sensors are installed at the air outlet of the dehumidifier fan; the control of the drying line is controlled by a programmable logic controller PLC. After completion, the PLC receives the data from each sensor and compares it with the set optimal value to obtain the adjustment value and sends a control command to each frequency converter; the conveyor belt is equipped with a transmission motor, the transmission motor is connected to the frequency converter, and the worm gear is decelerated The device is installed between the transmission motor and the conveyor belt; the drying line console is equipped with a touch screen with a man-machine interface.

上述与循环风机连接的变频器是三菱公司生产的风机专用型变频器FR-740-5.5k-CHT(1)，它通过FX2N-485-BD模块与PLC连接，实现对循环风机转速的调节.The frequency converter connected with the circulating fan above is a fan-specific frequency converter FR-740-5.5k-CHT(1) produced by Mitsubishi Corporation. It is connected to the PLC through the FX2N-485-BD module to realize the adjustment of the circulating fan speed.

上述与抽湿风机连接的变频器是三菱公司生产的风机专用型变频器FR-740-3.7k-CHT(1)，它通过FX2N-485-BD模块与PLC连接，实现对抽湿风机转速的PID调节.The frequency converter connected with the dehumidifier above is a fan-specific frequency converter FR-740-3.7k-CHT(1) produced by Mitsubishi Corporation. PID regulation.

上述与风门连接的变频器是三菱公司生产的风机专用型变频器FR-740-1.5k-CHT(1)，它通过FX2N-485-BD模块与PLC连接，实现对风门开度的PID调节.The inverter connected to the damper above is a fan-specific inverter FR-740-1.5k-CHT(1) produced by Mitsubishi, which is connected to the PLC through the FX2N-485-BD module to realize PID adjustment of the damper opening.

上述与输送链传动电机连接的变频器是三菱公司生产的风机专用型变频器FR-740-1.5k-CHT(1)，它通过FX2N-485-BD模块与PLC连接，实现对输送链传输速度的调节.The above-mentioned frequency converter connected with the transmission motor of the conveyor chain is a fan-specific frequency converter FR-740-1.5k-CHT (1) produced by Mitsubishi Corporation. It is connected with PLC through the FX2N-485-BD module to realize the transmission speed of the conveyor chain. adjustment.

上述PLC选用三菱公司生产的FX2N-16MR PLC，PLC通过FX2N-8AD模块从温度传感器和湿度传感器接收实时数据，并与通过纸浆模塑烘干特性分析及其在穿流烘干线的理论模型得出的、通过RS-422连接的HMI设定的最优值相比较，得出调节量并通过FX2N-485-BD模块向各个变频器发出控制指令，从而达到控制风机转速、风门开度以及输送带输送速度的作用.The above-mentioned PLC selects the FX2N-16MR PLC produced by Mitsubishi Corporation. The PLC receives real-time data from the temperature sensor and the humidity sensor through the FX2N-8AD module, and obtains the result from the analysis of the drying characteristics of the pulp molding and the theoretical model of the through-flow drying line. Compared with the optimal value set by the HMI connected by RS-422, the adjustment value is obtained and the control command is sent to each inverter through the FX2N-485-BD module, so as to control the fan speed, damper opening and conveying The effect of belt conveying speed.

上述温度传感器和湿度传感器通过FX2N-8AD模块与PLC连接，将检测到的数据传送到PLCThe above temperature sensor and humidity sensor are connected to PLC through FX2N-8AD module, and the detected data are transmitted to PLC

上述HMI是三菱公司生产的A956WGOT，它通过RS-422与PLC实现无协议通讯。The above-mentioned HMI is A956WGOT produced by Mitsubishi Corporation, which realizes non-protocol communication with PLC through RS-422.

使用上述烘干线的生产工艺步骤如下：The production process steps of using the above drying line are as follows:

1)根据纸浆模塑烘干特性分析及其在穿流烘干线的理论模型，得出关于纸浆模塑烘干线各个烘干段的重要参数的相关公式；1) According to the analysis of the drying characteristics of pulp molding and the theoretical model of the through-flow drying line, the relevant formulas for the important parameters of each drying section of the pulp molding drying line are obtained;

2)根据计划生产产量，计算烘干线长度并分布分段烘箱数目比例，即恒速干燥阶段及降速干燥阶段分段烘箱的数目比例，并得出输送带电机的工作转速及工作频率；2) According to the planned production output, calculate the length of the drying line and distribute the ratio of the number of segmented ovens, that is, the ratio of the number of segmented ovens in the constant-speed drying stage and the reduced-speed drying stage, and obtain the working speed and frequency of the conveyor belt motor;

3)对单个待干燥产品进行干燥实验，得出最优工作参数包括恒速干燥阶段及降速干燥阶段的干燥工艺温度，风量，湿度；3) Carry out a drying experiment on a single product to be dried, and obtain the optimal working parameters including the drying process temperature, air volume, and humidity in the constant-speed drying stage and the decelerating-speed drying stage;

4)将上述步骤1)及2)得出的干燥工艺参数通过触摸屏HMI输入到PLC；4) Input the drying process parameters obtained in the above steps 1) and 2) to the PLC through the touch screen HMI;

5)通过触摸屏启动烘干线自动运行，把待干燥产品投入烘干线，生产开始；5) Start the automatic operation of the drying line through the touch screen, put the product to be dried into the drying line, and start production;

6)烘干区段的温度传感器及湿度传感器实时采集烘干线的生产参数，并通过FX2N-4AD模块把模拟量转变成数字量传给PLC；6) The temperature sensor and humidity sensor in the drying section collect the production parameters of the drying line in real time, and convert the analog quantity into digital quantity and transmit it to the PLC through the FX2N-4AD module;

7)PLC通过RS-485无协议通讯把各数字量对应传给各个烘干区段的电动风门变频器及抽湿风机变频器；7) Through RS-485 non-protocol communication, the PLC transmits each digital value to the electric damper inverter and the dehumidifier fan inverter in each drying section;

8)各电动风门的变频器内部集成的PID整定模块开始工作，它可以根据安装在烘干区段中央的温度传感器采集到的实时温度与预设工艺温度比较，并把他们的误差值作为PID控制器的输入，并把误差乘以比例常数，误差的积分乘以积分常数，误差的微分乘以微分常数，并把他们相加，从而得到PID控制器的输出，然后把结果送给电动风门的变频器，从而调节电动风门的供电频率或正反转运行，达到控制风门开度的目的，从而控制冷暖风的进给比例，实现分段烘箱内热风温度控制的目的；其中比例常数，积分常数，微分常数通过试验确定；8) The PID setting module integrated in the inverter of each electric damper starts to work. It can compare the real-time temperature collected by the temperature sensor installed in the center of the drying section with the preset process temperature, and use their error value as the PID The input of the controller, and the error is multiplied by the proportional constant, the integral of the error is multiplied by the integral constant, the differential of the error is multiplied by the differential constant, and they are added to obtain the output of the PID controller, and then the result is sent to the electric damper Inverter, so as to adjust the power supply frequency of the electric damper or run forward and reverse to achieve the purpose of controlling the opening of the damper, thereby controlling the feed ratio of cold and warm air, and realizing the purpose of controlling the temperature of hot air in the segmented oven; the proportional constant, the integral Constants, differential constants are determined through experiments;

9)同理步骤7，抽湿风机的变频器内部集成的PID整定模块开始工作，它可以根据烘箱内湿度传感器采集到的实时湿度与预设工艺湿度比较，并把他们的误差值作为PID控制器的输入，并把误差乘以比例常数，误差的积分乘以积分常数，误差的微分乘以微分常数，并把他们相加，从而得到PID控制器的输出，然后把结果送给抽湿风机的变频器，从而调节电机的供电频率，达到抽湿风机的抽风量的无级调节，保证烘箱内湿度在工艺要求范围；其中比例常数，积分常数，微分常数通过试验确定；9) Similarly to step 7, the PID tuning module integrated in the inverter of the dehumidifier starts to work. It can compare the real-time humidity collected by the humidity sensor in the oven with the preset process humidity, and use their error value as PID control The input of the controller, and the error is multiplied by the proportional constant, the integral of the error is multiplied by the integral constant, the differential of the error is multiplied by the differential constant, and they are added to obtain the output of the PID controller, and then the result is sent to the dehumidifier The frequency converter is used to adjust the power supply frequency of the motor to achieve stepless adjustment of the exhaust air volume of the dehumidifier and ensure that the humidity in the oven is within the range of process requirements; the proportional constant, integral constant and differential constant are determined through experiments;

10)根据式(1-23)烘干区段的循环风机通过变频器长期工作在步骤2及3设定的工作频率；10) According to the formula (1-23), the circulating fan in the drying section works for a long time at the operating frequency set insteps 2 and 3 through the frequency converter;

11)重复步骤5)～9)，使烘干线稳定地工作在最优工艺曲线。11) Repeat steps 5) to 9) to make the drying line work stably at the optimal process curve.

本发明根据纸浆模塑制品的干燥机理，分析含湿多孔介质在不同干燥阶段的干燥特性，并根据待烘干产品尺寸及重量，采用交流变频调速技术及现代检测技术，根据现场检测的温度，湿度信号，对循环风机，电动风门，抽湿风机，输送链传动电机无级变频调速控制，自动实现烘干线分段温度控制，风量控制及湿度控制，并自动调整烘干线输送链带的线速度，使烘干生产线工作在最佳工作点，可有效节约电能损耗，提高产品质量及烘干线的生产效率。According to the drying mechanism of pulp molded products, the present invention analyzes the drying characteristics of wet porous media in different drying stages, and according to the size and weight of the product to be dried, adopts AC frequency conversion speed regulation technology and modern detection technology, and according to the temperature detected on site , Humidity signal, for circulating fan, electric damper, dehumidifying fan, conveyor chain transmission motor stepless frequency conversion speed regulation control, automatic realization of drying line segmental temperature control, air volume control and humidity control, and automatic adjustment of drying line conveyor chain The line speed of the belt makes the drying production line work at the best working point, which can effectively save power consumption, improve product quality and production efficiency of the drying line.

本发明将流程生产关键工艺过程的优化控制方法应用于纸浆模塑烘干工艺，以实现优化控制，降低能耗，提高生产效率。研究并开发纸浆模塑行业烘干工序的能源管理和调度技术、重点生产过程节能降耗的优化运行技术，实施节能降耗的技术提升和技术创新，能显著降低流程工业行业的能耗和物耗。The invention applies the optimized control method of the key technological process of process production to the pulp molding and drying process to realize optimized control, reduce energy consumption and improve production efficiency. Research and develop energy management and scheduling technology for drying process in pulp molding industry, optimize operation technology for energy saving and consumption reduction in key production processes, and implement technological upgrading and innovation for energy saving and consumption reduction, which can significantly reduce energy consumption and material consumption in the process industry .

附图说明Description of drawings

图1为烘干线的外形图。Figure 1 is the outline drawing of the drying line.

其中1是循环风机，2是热风炉，3是燃烧机，4是烘箱，5是抽湿风机，6是输送带。Among them, 1 is a circulating fan, 2 is a hot blast stove, 3 is a burner, 4 is an oven, 5 is a dehumidifier, and 6 is a conveyor belt.

图2为干燥流程图。Figure 2 is a drying flow chart.

图3为优化控制过程其中示意图。Figure 3 is a schematic diagram of the optimal control process.

图4为优化控制框图。Figure 4 is a block diagram of the optimized control.

图5为纸浆模塑湿纸坯的干燥曲线图。Fig. 5 is a drying curve diagram of a pulp molded wet paper base.

其中AB表示预热阶段，BC表示恒速阶段，CD表示降速阶段。Among them, AB represents the warm-up stage, BC represents the constant speed stage, and CD represents the deceleration stage.

具体实施方式Detailed ways

纸浆模塑制品在成型后含有较高的水分(70％左右)，需要经过烘干工序除去，干燥后成品的含水量约在10％-15％。水在湿态纸纤维中存在形式有三种：结合水，吸附水和游离水，而纸浆模塑制品的干燥目的就是要除去其中的结合水和吸附水。纸浆模塑产品属于含湿多孔介质，其干燥特性比较复杂，总的干燥过程可以分为三个阶段：预热干燥，恒速干燥，降速干燥。通常预热干燥阶段维持时间比较短，可以忽略。而在恒速干燥阶段，湿纸坯从干燥介质(热空气)吸收热量，使内部水份在压力梯度下向外扩散，而表面水分就蒸发成水蒸气，由干燥介质带走.这时湿纸坯的含水量还是比较多，湿纸坯表面蒸发了多少水分，内部就补充多少水分，干燥速率相等于水在自由表面的蒸发速度，基本上干燥速率是一常数，从湿纸坯抽走的水分与时间成线性关系。当蒸发过程慢慢深入到物料内部，湿纸坯内部水分扩散速度开始小于表面扩散速度，进入降速干燥阶段，物料表面开始有干斑出现，干躁过程在物料内部进行，整个物料可分为干区，蒸发区，和湿区三部分。这时，物料内部水分向外移动速度远少于表面水分向外蒸发速度，纸浆模塑制品的干燥速率不在是一常数，其干燥速率取决于物料内部性质，其干燥曲线的斜率随着时间的递增而逐渐减少，干燥曲线如图5所示。在一般条件下，纸浆模塑制品厚度都在2mm-4mm，相比于长和宽(一般大于10cm)，可视为无限大平板。根据无限大平板在Soret系数＝0时的数学解，得到恒速干燥阶段的干燥速率表达式Pulp molded products contain relatively high moisture (about 70%) after molding, which needs to be removed through a drying process. The moisture content of the finished product after drying is about 10%-15%. There are three forms of water in wet paper fibers: bound water, adsorbed water and free water, and the purpose of drying pulp molded products is to remove bound water and adsorbed water. Pulp molding products are porous media with moisture, and their drying characteristics are relatively complicated. The overall drying process can be divided into three stages: preheating drying, constant speed drying, and reduced speed drying. Usually the duration of the preheating drying stage is relatively short and can be ignored. In the constant-speed drying stage, the wet paper base absorbs heat from the drying medium (hot air), causing the internal moisture to diffuse outward under the pressure gradient, while the surface moisture evaporates into water vapor, which is taken away by the drying medium. At this time, the wet The water content of the paper base is still relatively high. As much water evaporates on the surface of the wet paper base, as much water will be replenished inside. The drying rate is equal to the evaporation rate of water on the free surface. Basically, the drying rate is a constant. The moisture content is linear with time. When the evaporation process slowly penetrates into the interior of the material, the moisture diffusion rate inside the wet paper base begins to be slower than the surface diffusion rate, and enters the deceleration drying stage, and dry spots appear on the surface of the material. The drying process is carried out inside the material, and the whole material can be divided into The dry zone, the evaporative zone, and the wet zone are divided into three parts. At this time, the outward moving speed of the moisture inside the material is much less than the outward evaporation speed of the surface moisture, and the drying rate of the pulp molded product is no longer a constant. The drying rate depends on the internal properties of the material, and the slope of the drying curve changes with time. increasing and gradually decreasing, the drying curve is shown in Figure 5. Under normal conditions, the thickness of pulp molded products is 2mm-4mm, compared to the length and width (generally greater than 10cm), it can be regarded as an infinite flat plate. According to the mathematical solution of the infinite plate when the Soret coefficient = 0, the drying rate expression of the constant drying stage is obtained

$\frac{\mathrm{<span><span>dM</span>D</span>}}{\mathrm{<span><span>d\&tau;</span>d\&tau;</span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>\&alpha;</span>\&alpha;</span>}}{\mathrm{<span><span>\&rho;</span>\&rho;</span>}{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>0</span>0</span>}}\mathrm{<span><span>R</span>R</span>}}<span><span>[</span>[</span>{\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>t</span>t</span>}}}_{\mathrm{<span><span>c</span>c</span>}}<span><span>-</span>-</span>{\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>t</span>t</span>}}}_{<span><span>(</span>(</span>\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span>}<span><span>]</span>]</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>1</span>1</span>}<span><span>)</span>)</span>$

及降速干燥阶段的速率表达式：And the rate expression of the drying stage with reduced speed:

$\frac{\mathrm{<span><span>d</span>d</span>}\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>M</span>m</span>}}}{\mathrm{<span><span>d\&tau;</span>d\&tau;</span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>3</span>3</span>}\mathrm{<span><span>\&lambda;</span>\&lambda;</span>}}{\mathrm{<span><span>\&rho;</span>\&rho;</span>}{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>0</span>0</span>}}\mathrm{<span><span>\&epsiv;</span>\&epsiv;</span>}{\mathrm{<span><span>R</span>R</span>}}_{\mathrm{<span><span>2</span>2</span>}}}<span><span>[</span>[</span>{\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>t</span>t</span>}}}_{\mathrm{<span><span>c</span>c</span>}}<span><span>-</span>-</span>{\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>t</span>t</span>}}}_{<span><span>(</span>(</span>\mathrm{<span><span>\&tau;</span>\&tau;</span>}<span><span>)</span>)</span>}<span><span>]</span>]</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>2</span>2</span>}<span><span>)</span>)</span>$

式中M为湿含量；τ为时间；α为对流换热系数；ρ为汽化潜热，kJ/kg；γ₀为物料的重度，kg/m³；R为物料厚度，m；t_(τ)为物料平均温度，℃；t_c为介质平均温度，℃；λ为物料的导热系数，kJ/(m·h·℃)；ε为相变系数；In the formula, M is the moisture content; τ is the time; α is the convective heat transfer coefficient; ρ is the latent heat of vaporization, kJ/kg; γ₀ is the weight of the material, kg/m³ ; R is the thickness of the material, m; t_(τ) is the average temperature of the material, °C; t_c is the average temperature of the medium, °C; λ is the thermal conductivity of the material, kJ/(m h ° °C); ε is the phase change coefficient;

由上式得知，在恒速干燥阶段，介质温度t_c和对流换热系数α是影响干燥速率的两个主要因素，提高介质温度，增大对流换热系数(主要是增大气流流量)，都有利于提高干燥速率。而在降速干燥阶段，干燥速率就取决于物料的导热系数λ和相变系数ε，并且与物料的尺寸的平方成反比，因而提高物料温度改变物料的形状及尺寸，将是提高干燥速率有效的办法。同时，在考虑强制对流干燥时，不仅要考虑到湿纸坯不同阶段的干燥特性，还要考虑到纸浆模塑制品的工艺特性。在干燥过程中，湿纸坯表面水分首先被蒸发，而内部水分较难蒸发，如果干燥介质温度过高，湿纸坯表面干燥得很快，导致表面结面硬化，而此时湿纸坯内部依然很湿润，而且内部水分难以向外扩散，会在很大程度上降低干燥速度。如果工艺参数的温度曲线设置不当，会导致湿纸坯内外向外扩散速度差距拉大，容易出现体积收缩，变形，开裂等现象。因此，本发明将在原有的热风对流带式烘干线上设计一套效能优化自动控制系统，它将根据纸浆模塑的干燥特性及不同湿纸坯的尺寸及重量，采用交流变频调速技术及现代检测技术，根据现场检测的温度，湿度信号，对循环风机，电动风门，抽湿风机，输送链传动电机变频无级调速控制，合理地调整烘道内输送带的运行速度、各分段干燥器中的工作温度、热风风量及水蒸气的排放等，形成合理的干燥曲线，以使产品的变形尽可能小，最大限度地节约电能及热能的损耗，加快烘干速率，加大烘干生产线的产量。It can be seen from the above formula that in the constant-speed drying stage, the medium temperature t_c and the convective heat transfer coefficient α are the two main factors affecting the drying rate. Increasing the medium temperature increases the convective heat transfer coefficient (mainly to increase the airflow rate) , are conducive to improving the drying rate. In the stage of drying at reduced speed, the drying rate depends on the thermal conductivity λ and the phase change coefficient ε of the material, and is inversely proportional to the square of the size of the material. Therefore, increasing the temperature of the material to change the shape and size of the material will be an effective way to increase the drying rate. way. At the same time, when considering forced convection drying, not only the drying characteristics of wet paper blanks at different stages, but also the process characteristics of pulp molded products should be considered. During the drying process, the moisture on the surface of the wet paper base is evaporated first, and the internal moisture is difficult to evaporate. If the temperature of the drying medium is too high, the surface of the wet paper base dries quickly, resulting in hardening of the surface junction, while the inside of the wet paper base It is still very wet, and it is difficult for the internal moisture to diffuse outward, which will greatly reduce the drying speed. If the temperature curve of the process parameters is not set properly, the difference in diffusion speed between the inside and outside of the wet paper blank will widen, and volume shrinkage, deformation, cracking and other phenomena will easily occur. Therefore, the present invention will design a set of performance optimization automatic control system on the original hot air convection belt drying line, which will adopt AC frequency conversion speed regulation technology according to the drying characteristics of pulp molding and the size and weight of different wet paper blanks And modern detection technology, according to the temperature and humidity signals detected on site, control the circulating fan, electric damper, dehumidifying fan, conveyor chain drive motor frequency conversion stepless speed regulation, and reasonably adjust the running speed of the conveyor belt in the drying tunnel, each segment The working temperature, hot air volume and water vapor discharge in the dryer form a reasonable drying curve, so that the deformation of the product is as small as possible, the loss of electric energy and heat energy is saved to the greatest extent, the drying rate is accelerated, and the drying rate is increased. production line output.

为实现上述发明，本烘干线继续采用中央供热方式，中央供热系统由燃烧机(原料：柴油或天然气)与热风炉燃烧室(由优质耐热钢卷制而成)组成；烘箱采用框架结构，烘箱长度及宽度根据生产量决定，烘箱分为若干个干燥区段，每个烘干区段安装一台循环风机及一台风机专用型变频器，循环风机进风口与热风管及烘箱内部连接，并装一电动风门，热风管与燃烧室连接，循环风机出风口与排风管连接，排风管把热风直接送进输送带上。同时在烘箱内装一台抽湿风机，及时把烘干线内的水汽排走，烘干线外形如图1所示。In order to realize the above invention, this drying line continues to adopt the central heating mode, and the central heating system is composed of a burner (raw material: diesel oil or natural gas) and a hot blast stove combustion chamber (coiled from high-quality heat-resistant steel); the oven adopts Frame structure, the length and width of the oven are determined according to the production volume, the oven is divided into several drying sections, each drying section is equipped with a circulating fan and a special frequency converter for the fan, the air inlet of the circulating fan and the hot air pipe and The oven is internally connected, and an electric damper is installed, the hot air pipe is connected to the combustion chamber, the air outlet of the circulating fan is connected to the exhaust pipe, and the exhaust pipe sends the hot air directly to the conveyor belt. At the same time, a dehumidifying fan is installed in the oven to remove the water vapor in the drying line in time. The appearance of the drying line is shown in Figure 1.

为实现本发明，同时在烘干线的每段烘道及热风管安装PT100铂电阻(温度传感器)，实时采集热风管及每段烘干分区的热风温度，在抽湿风机的进风口安装耐高温湿度传感器在出风口安装PT100铂电阻，实时采集烘道内的水蒸气量及排出烘干线的气体温度。每台循环风机(离心通风机5.5kw，2900r/min，6924m³/h)由一台风机专用型变频器控制，抽湿风机(离心通风机3kw，2900r/min，1481m³/h)由一台风机专用型变频器控制，变频器通过改变风机的电机的供电频率，实现风机流量的控制。在循环风机的进风口安装一电动风门(冷暖风比例调节)，由一台经济型通用变频器控制电动风门(1.1kw)无级调速运行，从而自动调节风门开度，控制热风(热风管的热空气)进给量与冷风(分段烘箱内的热空气)进给量的比例，从而调节分段烘箱内工作介质(热空气)温度。输送链传动电机采用通用型变频器控制，并外接蜗轮蜗杆减速器，实现输送链带无级调速控制，干燥流程如图2所示。将采用PLC作为烘干线的控制模块，并扩展12路的A/D转换模块，每段烘箱的PT100铂电阻温度传感器，总热风管的温度传感器及烘箱内的湿度传感器都连接到A/D模块上。PLC外接一触摸屏，方便操作人员输入系统工艺参数(如烘箱工艺温度，工艺湿度，输送链带运行速度，PID的比例参数，积分参数，微分参数等)及湿纸坯的性能参数(如湿含量，尺寸，比表面积等)。PLC通过RS484物理接口实现与每台变频器的无协议通信。其控制流程如图3，图4所示。为实现上述发明，本发明分析了烘干线的干燥数学模型恒速干燥阶段速率v₁In order to realize the present invention, a PT100 platinum resistance (temperature sensor) is installed in each section of the drying tunnel and the hot air pipe of the drying line at the same time, and the hot air temperature of the hot air pipe and each section of the drying partition is collected in real time, and the air inlet of the dehumidifying fan Install a high temperature resistant humidity sensor and install a PT100 platinum resistor at the air outlet to collect the amount of water vapor in the drying tunnel and the temperature of the gas discharged from the drying line in real time. Each circulating fan (5.5kw centrifugal fan, 2900r/min, 6924m³ /h) is controlled by a fan-specific frequency converter, and the dehumidifying fan (3kw centrifugal fan, 2900r/min, 1481m³ /h) is controlled by a It is controlled by a special frequency converter for typhoon fans. The frequency converter realizes the flow control of the fan by changing the power supply frequency of the motor of the fan. Install an electric damper (proportional adjustment of cold and warm air) at the air inlet of the circulating fan, and an economical general-purpose frequency converter controls the electric damper (1.1kw) to run steplessly, thereby automatically adjusting the opening of the damper and controlling the hot air (hot air) The ratio of the feed rate of the hot air) of the tube to the feed rate of the cold air (hot air in the sectional oven), so as to adjust the temperature of the working medium (hot air) in the sectional oven. The transmission motor of the conveyor chain is controlled by a general-purpose frequency converter and connected to a worm gear reducer to realize the stepless speed regulation control of the conveyor chain belt. The drying process is shown in Figure 2. PLC will be used as the control module of the drying line, and the 12-way A/D conversion module will be expanded. The PT100 platinum resistance temperature sensor of each oven, the temperature sensor of the total hot air pipe and the humidity sensor in the oven are all connected to the A/D on the D module. The PLC is connected with a touch screen, which is convenient for the operator to input system process parameters (such as oven process temperature, process humidity, conveyor belt running speed, PID proportional parameters, integral parameters, differential parameters, etc.) and wet paper base performance parameters (such as moisture content , size, specific surface area, etc.). The PLC realizes the non-protocol communication with each inverter through the RS484 physical interface. Its control process is shown in Fig. 3 and Fig. 4 . In order to realize the above-mentioned invention, the present invention has analyzed the dry mathematical model constant speed drying stage velocity_v of drying line

${\mathrm{<span><span>v</span><figure-callout\; label="v"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">v</figure-callout></span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>\&rho;H</span>\&rho;H</span>}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>x</span>x</span>}}<span><span>)</span>)</span>}{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>1</span>1</span>}}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>3</span>3</span>}<span><span>)</span>)</span>$

式中，v₁为恒速干燥阶段的干燥速率，kg/(m²·h)；ρ为被干燥物料表观密度，kg/m³；t₁为恒速干燥阶段时间，h；H为料层高度，mIn the formula, v₁ is the drying rate of the constant-speed drying stage, kg/(m² h); ρ is the apparent density of the material to be dried, kg/m³ ; t₁ is the time of the constant-speed drying stage, h; H is Layer height, m

恒速干燥阶段时间t₁Constant drying stage time t₁

${\mathrm{<span><span>t</span><figure-callout\; label="t"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">t</figure-callout></span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>=</span>=</span>\frac{<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>)</span>)</span>\mathrm{<span><span>\&rho;</span>\&rho;</span>}{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>w</span>w</span>}}}{\mathrm{<span><span>3.6</span>3.6</span>}{\mathrm{<span><span>K</span>K</span>}}_{\mathrm{<span><span>V</span>V</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>W</span>W</span>}}<span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>4</span>4</span>}<span><span>)</span>)</span>$

式中，x₀为物料湿含量，kg/kg；x_cr为物料临界湿含量，kg/kg；γ_w为湿球温度时水的汽化潜热，kJ/kg；K_V为体积总传热系数，W/(m³·K)；T₁为料层顶部热空气温度，℃；T_w为空气湿球温度，℃。In the formula, x₀ is the moisture content of the material, kg/kg; x_cr is the critical moisture content of the material, kg/kg; γ_w is the latent heat of vaporization of water at the wet bulb temperature, kJ/kg; K_V is the total heat transfer coefficient of the volume , W/(m³ ·K); T₁ is the hot air temperature at the top of the material bed, °C; T_w is the air wet bulb temperature, °C.

其中，体积总传热系数Among them, the total volumetric heat transfer coefficient

K_V＝ρaK_a    (1-5)K_V = ρaK_a (1-5)

式中，a为物料比表面积，m²/kg；K_a为总传热系数，W/(m²·K)。In the formula, a is the specific surface area of the material, m² /kg; K_a is the overall heat transfer coefficient, W/(m² ·K).

总传热系数K_a可由下式求得The overall heat transfer coefficient K_a can be obtained by the following formula

K_a＝1.175(G)^0.37_Ka = 1.175(G)^0.37

(1-6)(1-6)

式中，G为空气的质量速度，kg/(m²·h)。In the formula, G is the mass velocity of air, kg/(m² ·h).

把式(1-6)代入式(1-5)得，Substitute formula (1-6) into formula (1-5) to get,

K_V＝ρa1.175(G)^0.37             (1-7)_KV = ρa1.175(G)^0.37 (1-7)

把式(1-7)代入(1-4)得Substitute formula (1-7) into (1-4) to get

${\mathrm{<span><span>t</span><figure-callout\; label="t"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">t</figure-callout></span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>=</span>=</span>\frac{<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>)</span>)</span>{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>w</span>w</span>}}}{\mathrm{<span><span>4.23</span>4.23</span>}\mathrm{<span><span>a</span>a</span>}{<span><span>(</span>(</span>\mathrm{<span><span>G</span>G</span>}<span><span>)</span>)</span>}^{\mathrm{<span><span>0.37</span>0.37</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>W</span>W</span>}}<span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>8</span>8</span>}<span><span>)</span>)</span>$

恒速干燥阶段输送带长度L₁Conveyor belt length L₁ in constant speed drying stage

${\mathrm{<span><span>L</span><figure-callout\; label="L"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>=</span>=</span>\frac{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>1</span>1</span>}}{\mathrm{<span><span>m</span>m</span>}}_{\mathrm{<span><span>s</span>the\; s</span>}}}{\mathrm{<span><span>\&omega;H\&rho;</span>\&omega;H\&rho;</span>}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>9</span>9</span>}<span><span>)</span>)</span>$

式中，L₁为恒速干燥阶段输送带长度，m；m_s为被干燥物料投料量，kg/h；ω为输送带有效宽度，m。其他符号意义同前。In the formula, L₁ is the length of the conveyor belt in the constant-speed drying stage, m; m_s is the feeding amount of the material to be dried, kg/h; ω is the effective width of the conveyor belt, m. The meanings of other symbols are the same as before.

把式(1-8)代入式(1-9)得Substitute formula (1-8) into formula (1-9) to get

${\mathrm{<span><span>L</span><figure-callout\; label="L"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>=</span>=</span>\frac{<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>)</span>)</span>{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>w</span>w</span>}}{\mathrm{<span><span>m</span>m</span>}}_{\mathrm{<span><span>s</span>the\; s</span>}}}{\mathrm{<span><span>4.23</span>4.23</span>}\mathrm{<span><span>a\&omega;H\&rho;</span>a\&omega;H\&rho;</span>}{\mathrm{<span><span>G</span>G</span>}}^{\mathrm{<span><span>0.37</span>0.37</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>W</span>W</span>}}<span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>10</span>10</span>}<span><span>)</span>)</span>$

降速干燥阶段时间t₂Deceleration drying stage time t₂

${\mathrm{<span><span>t</span><figure-callout\; label="t"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">t</figure-callout></span>}}_{\mathrm{<span><span>2</span>2</span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>\&rho;H</span>\&rho;H</span>}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}{{\mathrm{<span><span>v</span><figure-callout\; label="v"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">v</figure-callout></span>}}_{\mathrm{<span><span>1</span>1</span>}}}\mathrm{<span><span>ln</span>ln</span>}\frac{<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}{<span><span>(</span>(</span>\mathrm{<span><span>x</span>x</span>}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>11</span>11</span>}<span><span>)</span>)</span>$

式中，t₂为降速干燥阶段干燥时间，h；v₁为恒速干燥阶段的干燥速率，kg/(m²·h)；x为湿纸坯湿含量，kg/kg；x_cr为湿纸坯临界湿含量，kg/kg；x_eq为湿纸坯的最终湿含量，kg/kg；把式(1-3)及(1-8)代入式(1-11)得In the formula, t₂ is the drying time in the falling speed drying stage, h; v₁ is the drying rate in the constant speed drying stage, kg/(m² ·h); x is the moisture content of the wet paper base, kg/kg; x_cr is The critical moisture content of the wet paper base, kg/kg; x_eq is the final moisture content of the wet paper base, kg/kg; substitute formulas (1-3) and (1-8) into formula (1-11) to get

${\mathrm{<span><span>t</span><figure-callout\; label="t"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">t</figure-callout></span>}}_{\mathrm{<span><span>2</span>2</span>}}<span><span>=</span>=</span>\frac{{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>w</span>w</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>)</span>)</span><span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}{\mathrm{<span><span>4.23</span>4.23</span>}\mathrm{<span><span>a</span>a</span>}{\mathrm{<span><span>G</span>G</span>}}^{\mathrm{<span><span>0.37</span>0.37</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>x</span>x</span>}}<span><span>)</span>)</span><span><span>(</span>(</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>W</span>W</span>}}<span><span>)</span>)</span>}\mathrm{<span><span>ln</span>ln</span>}\frac{<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}{<span><span>(</span>(</span>\mathrm{<span><span>x</span>x</span>}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>12</span>12</span>}<span><span>)</span>)</span>$

降速干燥阶段输送带长度L₂Speed-down drying stage conveyor belt length L₂

${\mathrm{<span><span>L</span><figure-callout\; label="L"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span><span>2</span>2</span>}}<span><span>=</span>=</span>\frac{{\mathrm{<span><span>t</span>t</span>}}_{\mathrm{<span><span>2</span>2</span>}}{\mathrm{<span><span>m</span>m</span>}}_{\mathrm{<span><span>s</span>the\; s</span>}}}{\mathrm{<span><span>\&omega;H\&rho;</span>\&omega;H\&rho;</span>}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>13</span>13</span>}<span><span>)</span>)</span>$

把式(1-12)代入式(1-13)得Substitute formula (1-12) into formula (1-13) to get

${\mathrm{<span><span>L</span><figure-callout\; label="L"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">L</figure-callout></span>}}_{\mathrm{<span><span>2</span>2</span>}}<span><span>=</span>=</span>\frac{{\mathrm{<span><span>\&gamma;</span>\&gamma;</span>}}_{\mathrm{<span><span>w</span>w</span>}}{\mathrm{<span><span>m</span>m</span>}}_{\mathrm{<span><span>s</span>the\; s</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>)</span>)</span><span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}{\mathrm{<span><span>4.23</span>4.23</span>}\mathrm{<span><span>a\&omega;H\&rho;</span>a\&omega;H\&rho;</span>}{\mathrm{<span><span>G</span>G</span>}}^{\mathrm{<span><span>0.37</span>0.37</span>}}<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>0</span>0</span>}}<span><span>-</span>-</span>\stackrel{<span><span>\&OverBar;</span>\&OverBar;</span>}{\mathrm{<span><span>x</span>x</span>}}<span><span>)</span>)</span><span><span>(</span>(</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>1</span>1</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>T</span>T</span>}}_{\mathrm{<span><span>W</span>W</span>}}<span><span>)</span>)</span>}\mathrm{<span><span>ln</span>ln</span>}\frac{<span><span>(</span>(</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>cr</span>cr</span>}}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}{<span><span>(</span>(</span>\mathrm{<span><span>x</span>x</span>}<span><span>-</span>-</span>{\mathrm{<span><span>x</span>x</span>}}_{\mathrm{<span><span>eq</span>eq</span>}}<span><span>)</span>)</span>}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>14</span>14</span>}<span><span>)</span>)</span>$

对烘干线作总体热量恒算得，Calculate the total heat of the drying line,

q₁-q₂＝s(q₃-q₄)       (1-15)q₁ -q₂ ＝s(q₃ -q₄ ) (1-15)

式中，q₁为物料带入热量，kJ/h；q₂为物料带出热量，kJ/h；q₃热空气带出热量，kJ/h；q₄为热空气带入热量，kJ/h；s为热量无用功损耗百分比，％。In the formula, q₁ is the heat brought in by the material, kJ/h; q₂ is the heat taken out by the material, kJ/h; q₃ is the heat taken out by the hot air, kJ/h; q₄ is the heat brought in by the hot air, kJ/h h; s is the percentage of heat and idle power loss, %.

其中q₁＝m_s(c_s+4.187x₁)T₁        (1-16)where q₁ =m_s (c_s +4.187x₁ )T₁ (1-16)

q₂＝m_s(c_s+4.187x₂)T₂            (1-17)q₂ =m_s (c_s +4.187x₂ )T₂ (1-17)

式中，m_s为被干燥物料投料量，kg/h；c_s为物料定压比热容，kJ/(kg·K)；T₁为物料进干燥箱前温度，℃；T₂为物料出干燥箱后温度，℃；T₃为尾气温度，℃；T₄为干燥箱内工艺温度，℃；x₁为物料进干燥箱前湿含量，kg/kg；x₂为物料出干燥箱后湿含量，kg/kg；m_g1为循环风机流量，kg/h；y₁为进循环风机前热空气中水量，kg/h；y₂干燥箱内热空气中水量，kg/h；三相交流异步电机为风机的动力源，其同步转速n为In the formula, m_s is the feeding amount of the material to be dried, kg/h; c_s is the specific heat capacity of the material at constant pressure, kJ/(kg K); T₁ is the temperature before the material enters the drying oven, °C; T₂ is the drying temperature of the material Temperature after the oven, °C; T₃ is the exhaust gas temperature, °C; T₄ is the process temperature in the drying oven, °C; x₁ is the moisture content before the material enters the drying oven, kg/kg; x₂ is the moisture content after the material leaves the drying oven , kg/kg; m_g1 is the circulation fan flow rate, kg/h; y₁ is the water volume in the hot air before entering the circulation fan, kg/h; y₂ is the water volume in the hot air in the drying box, kg/h; three-phase AC asynchronous motor is the power source of the fan, and its synchronous speed n is

$\mathrm{<span><span>n</span>no</span>}<span><span>=</span>=</span>\frac{\mathrm{<span><span>60</span>60</span>}\mathrm{<span><span>f</span>f</span>}}{\mathrm{<span><span>p</span>p</span>}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>20</span>20</span>}<span><span>)</span>)</span>$

式中，n为电机的同步转速，r/min；f为电机供电频率，Hz；p为极对数。In the formula, n is the synchronous speed of the motor, r/min; f is the power supply frequency of the motor, Hz; p is the number of pole pairs.

电动机转速n与风机流量Q有以下关系The motor speed n has the following relationship with the fan flow Q

$\frac{{\mathrm{<span><span>Q</span>Q</span>}}_{\mathrm{<span><span>1</span>1</span>}}}{{\mathrm{<span><span>Q</span><figure-callout\; label="Q"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">Q</figure-callout></span>}}_{\mathrm{<span><span>2</span>2</span>}}}<span><span>=</span>=</span>\frac{{\mathrm{<span><span>n</span>no</span>}}_{\mathrm{<span><span>1</span>1</span>}}}{{\mathrm{<span><span>n</span>no</span>}}_{\mathrm{<span><span>2</span>2</span>}}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>21</span>twenty\; one</span>}<span><span>)</span>)</span>$

因此，式(1-17)的m_g1为Therefore, m_g1 of formula (1-17) is

$\frac{{\mathrm{<span><span>m</span>m</span>}}_{\mathrm{<span><span>g</span>g</span>}\mathrm{<span><span>1</span>1</span>}}}{{\mathrm{<span><span>Q</span>Q</span>}}_{\mathrm{<span><span>n</span>no</span>}}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>60</span>60</span>}{\mathrm{<span><span>f</span>f</span>}}_{\mathrm{<span><span>1</span>1</span>}}}{\mathrm{<span><span>p</span>p</span>}{\mathrm{<span><span>n</span>no</span>}}_{\mathrm{<span><span>n</span>no</span>}}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>22</span>twenty\; two</span>}<span><span>)</span>)</span>$

${\mathrm{<span><span>m</span><figure-callout\; label="m\; g"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">m</figure-callout></span><figure-callout\; label="m\; g"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}"></figure-callout>}}_{\mathrm{<span><span></span></span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>60</span>60</span>}{\mathrm{<span><span>f</span>f</span>}}_{\mathrm{<span><span>1</span>1</span>}}{\mathrm{<span><span>Q</span>Q</span>}}_{\mathrm{<span><span>n</span>no</span>}}}{\mathrm{<span><span>p</span>p</span>}{\mathrm{<span><span>n</span>no</span>}}_{\mathrm{<span><span>n</span>no</span>}}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>23</span>twenty\; three</span>}<span><span>)</span>)</span>$

式中，Q_n为循环风机额定风量，kg/h；n_n为电机的额定转速，r/min；f₁为循环风机供电频率，Hz。In the formula, Q_n is the rated air volume of the circulating fan, kg/h; n_n is the rated speed of the motor, r/min; f₁ is the power supply frequency of the circulating fan, Hz.

输送链带电动机运行速率n与物料在烘箱内输送速率的关系为The relationship between the running speed n of the conveyor chain belt motor and the conveying speed of the material in the oven is

${\mathrm{<span><span>nN</span>n</span>}}_{\mathrm{<span><span>A</span>A</span>}}<span><span>=</span>=</span>\frac{{\mathrm{<span><span>m</span>m</span>}}_{\mathrm{<span><span>s</span>the\; s</span>}}}{\mathrm{<span><span>\&rho;\&omega;H</span>\&rho;\&omega;H</span>}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>24</span>twenty\; four</span>}<span><span>)</span>)</span>$

式中，N_A为输送链带减速箱的减速比。In the formula, N_A is the reduction ratio of the conveyor chain belt gearbox.

把式(1-20)代入式(1-24)得输送链带电动机供电频率f₂与物料在烘箱内输送速率的关系为Substituting the formula (1-20) into the formula (1-24), the relationship between the power supply frequency_f2 of the conveyor belt motor and the conveying rate of the material in the oven is as follows:

$\frac{\mathrm{<span><span>60</span>60</span>}{\mathrm{<span><span>f</span>f</span>}}_{\mathrm{<span><span>2</span>2</span>}}{\mathrm{<span><span>N</span>N</span>}}_{\mathrm{<span><span>A</span>A</span>}}}{\mathrm{<span><span>p</span>p</span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>ms</span>ms</span>}}{\mathrm{<span><span>\&rho;\&omega;H</span>\&rho;\&omega;H</span>}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>25</span>25</span>}<span><span>)</span>)</span>$

式中，f₂为输送链电机的供电频率，Hz。In the formula,_f2 is the power supply frequency of the conveyor chain motor, Hz.

假设热风管温度足够高，则Assuming that the temperature of the hot air pipe is high enough, then

T₄＝f₃N_B                (1-26)T₄ =f₃ N_B (1-26)

式中，f₃为循环风机供电频率，Hz；N_B为风门开度比例系数。In the formula, f₃ is the power supply frequency of the circulating fan, Hz; N_B is the proportional coefficient of the damper opening.

同理，参考式(1-23)得，Similarly, referring to formula (1-23), we get,

${\mathrm{<span><span>m</span><figure-callout\; label="m\; g"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}">m</figure-callout></span><figure-callout\; label="m\; g"\; filenames="A20081002965200171.png"\; state="\{\{state\}\}"></figure-callout>}}_{\mathrm{<span><span></span></span>}}<span><span>=</span>=</span>\frac{\mathrm{<span><span>60</span>60</span>}{\mathrm{<span><span>f</span>f</span>}}_{\mathrm{<span><span>4</span>4</span>}}{\mathrm{<span><span>Q</span>Q</span>}}_{\mathrm{<span><span>m</span>m</span>}}}{\mathrm{<span><span>p</span>p</span>}{\mathrm{<span><span>n</span>no</span>}}_{\mathrm{<span><span>m</span>m</span>}}}<span><span>-</span>-</span><span><span>-</span>-</span><span><span>-</span>-</span><span><span>(</span>(</span>\mathrm{<span><span>1</span>1</span>}<span><span>-</span>-</span>\mathrm{<span><span>27</span>27</span>}<span><span>)</span>)</span>$

式中，m_g2为抽湿风机风量，kg/h；f₄为抽湿风机供电频率，Hz；Q_m为抽湿风机额定流量，kg/h；n_m为抽湿风机额定转速，r/min。In the formula, m_g2 is the air volume of the dehumidifier, kg/h;_f4 is the power supply frequency of the dehumidifier, Hz; Q_m is the rated flow of the dehumidifier, kg/h; n_m is the rated speed of the dehumidifier, r/ min.

为实现上述发明，其烘干生产工艺步骤如下：In order to realize the above invention, its drying production process steps are as follows:

步骤1)根据计划生产产量参照式(1-10)及(1-14)计算烘干线长度并分布分段烘箱数目比例(恒速干燥阶段及降速干燥阶段分段烘箱的数目比例)，并按照式(1-24)及(1-25)得出输送带电机的工作转速及工作频率。Step 1) Calculate the length of the drying line according to the planned production output with reference to formulas (1-10) and (1-14) and distribute the ratio of the number of segmented ovens (the ratio of the number of segmented ovens in the constant-speed drying stage and the reduced-speed drying stage), And according to the formula (1-24) and (1-25), the working speed and working frequency of the conveyor belt motor are obtained.

步骤2)对单个待干燥产品进行干燥实验，得出最优工作参数(包括恒速干燥阶段及降速干燥阶段的干燥工艺温度，风量，湿度)。Step 2) Carry out a drying experiment on a single product to be dried, and obtain the optimal working parameters (including the drying process temperature, air volume, and humidity in the constant-speed drying stage and the decelerating-speed drying stage).

步骤3)将上述步骤1及2得出的干燥工艺参数通过触摸屏人机界面输入到PLC，触摸屏及PLC通过RS422无协议通讯。Step 3) Input the drying process parameters obtained in theabove steps 1 and 2 into the PLC through the touch screen man-machine interface, and the touch screen and PLC communicate through RS422 without protocol.

步骤4)通过触摸屏启动烘干线自动运行，把待干燥产品投入烘干线，生产开始。Step 4) Start the automatic operation of the drying line through the touch screen, put the product to be dried into the drying line, and start the production.

步骤5)烘干区段的PT100铂电阻温度传感器及湿度传感器实时采集烘干线的生产参数，并通过A/D模块把模拟量转变成数字量传给PLC。Step 5) The PT100 platinum resistance temperature sensor and humidity sensor in the drying section collect the production parameters of the drying line in real time, and convert the analog quantity into digital quantity and transmit it to the PLC through the A/D module.

步骤6)PLC通过RS-485无协议通讯把各数字量对应传给各电动风门变频器及抽湿风机变频器。Step 6) The PLC transmits each digital quantity correspondingly to each electric damper inverter and dehumidifier fan inverter through RS-485 non-protocol communication.

步骤7)各烘干区段电动风门的变频器内部集成的PID整定模块开始工作，它可以根据烘箱内PT100铂电阻采集到的实时温度与预设工艺温度比较，并把他们的误差值作为PID控制器的输入，并把误差乘以比例常数，误差的积分乘以积分常数，误差的微分乘以微分常数，并把他们相加，从而得到PID控制器的输出，然后把结果送给电动风门变频器，从而调节电机的供电频率或正反转运行，达到控制风门开度的目的，从而控制冷暖风的进给比例，实现分段烘箱内热风温度控制的目的。其中比例常数，积分常熟，微分常数通过试验确定。Step 7) The PID tuning module integrated in the frequency converter of the electric damper in each drying section starts to work. It can compare the real-time temperature collected by the PT100 platinum resistor in the oven with the preset process temperature, and use their error value as the PID The input of the controller, and the error is multiplied by the proportional constant, the integral of the error is multiplied by the integral constant, the differential of the error is multiplied by the differential constant, and they are added to obtain the output of the PID controller, and then the result is sent to the electric damper Inverter, so as to adjust the power supply frequency of the motor or run forward and reverse to achieve the purpose of controlling the opening of the damper, thereby controlling the feeding ratio of cold and warm air, and realizing the purpose of controlling the temperature of hot air in the segmented oven. Among them, the constant of proportionality, integral constant and differential constant are determined through experiments.

步骤8)同理步骤7，抽湿风机的变频器内部集成的PID整定模块开始工作，它可以根据烘箱内湿度传感器采集到的实时湿度与预设工艺湿度比较，并把他们的误差值作为PID控制器的输入，并把误差乘以比例常数，误差的积分乘以积分常数，误差的微分乘以微分常数，并把他们相加，从而得到PID控制器的输出，然后把结果送给抽湿风机变频器，从而调节电机的供电频率，达到抽湿风机的抽风量的无级调节，保证烘箱内湿度在工艺要求范围。其中比例常数，积分常熟，微分常数通过试验确定。Step 8) In the same way as step 7, the PID tuning module integrated in the inverter of the dehumidifier starts to work. It can compare the real-time humidity collected by the humidity sensor in the oven with the preset process humidity, and use their error value as the PID The input of the controller, and the error is multiplied by the proportional constant, the integral of the error is multiplied by the integral constant, the differential of the error is multiplied by the differential constant, and they are added to obtain the output of the PID controller, and then the result is sent to the dehumidifier Fan frequency converter, so as to adjust the power supply frequency of the motor, to achieve stepless adjustment of the exhaust air volume of the dehumidifier, to ensure that the humidity in the oven is within the range of process requirements. Among them, the proportional constant, the integral constant and the differential constant are determined through experiments.

步骤9)根据式(1-23)烘干区段的循环风机通过变频器长期工作在步骤2及3设定的工作频率。Step 9) According to the formula (1-23), the circulation fan in the drying section works for a long time at the working frequency set insteps 2 and 3 through the frequency converter.

步骤10)重复步骤5-9，使烘干线稳定地工作在最优工艺曲线。Step 10) Repeat steps 5-9 to make the drying line work stably at the optimal process curve.

步骤1-10的控制流程如图4，图5所示。The control flow of steps 1-10 is shown in Fig. 4 and Fig. 5 .

具体操作说明现需设计一条日产1.5吨的鸡蛋托盘烘干生产线。成品鸡蛋托盘的重量是65g左右，外形尺寸是310mm*310mm*50mm。成型后烘干前的鸡蛋托盘湿纸坯干湿比为1∶3.4，即烘干前湿含量为70％，重量为0.221kg，厚度为3mm，投料量为221kg/h，为方便实现烘干后的热压整型工序，现要求湿纸坯出烘干线后的含水率降到10％。即在烘干前湿纸坯的比表面积为0.435m²/kg，对单个鸡蛋托盘进行烘干试验，得恒速干燥阶段的最优工作温度为160℃，风量为5700m³/h，降速干燥阶段最优工作温度为120℃，风量为5400m³/h，鸡蛋托盘湿纸坯临界湿含量为0.846。并设输送带有效宽度为1.2m，把上述已知参数代入数学模型公式，得恒速干燥阶段输送带长度约为10m，降速干燥阶段输送带长度为15m。设烘干区段长2.2m，即恒速干燥阶段占4个烘干区段，降速干燥阶段占7个烘干区段。每个烘干区段配置一台循环风机(离心通风机5.5kw，2900r/min，6924m³/h)由上述参数也可解得恒速干燥阶段循环风机工作频率为39.7Hz，降速干燥阶段的循环风机工作频率为37.6Hz。输送链带电机(2.2kw)工作频率为45Hz。因此，把风机，电机的运行频率39.7Hz，37.6Hz，45Hz，及恒速干燥阶段工艺温度160℃及降速干燥阶段工艺温度120℃，烘箱内相对湿度90％(抽湿风机工作湿度)，通过触摸屏输入到PLC，烘干线便能在指定的最优工艺曲线下工作。经生产实践证明，鸡蛋托盘湿纸坯在经过烘干线烘干后，产品变形少，并基本达到工艺要求的10％最终含水率。Specific operation instructions Now it is necessary to design an egg tray drying production line with a daily output of 1.5 tons. The weight of the finished egg tray is about 65g, and the overall size is 310mm*310mm*50mm. The dry-wet ratio of the egg tray wet paper base before drying after molding is 1:3.4, that is, the moisture content before drying is 70%, the weight is 0.221kg, the thickness is 3mm, and the feeding amount is 221kg/h. For the convenience of drying In the final hot pressing and shaping process, it is now required that the moisture content of the wet paper base be reduced to 10% after it leaves the drying line. That is, the specific surface area of the wet paper blank before drying is 0.435m² /kg. A drying test was carried out on a single egg tray, and the optimum working temperature in the constant-speed drying stage was 160°C, and the air volume was 5700m³ /h. The optimal working temperature in the drying stage is 120°C, the air volume is 5400m³ /h, and the critical moisture content of the egg tray wet paper base is 0.846. Also assume that the effective width of the conveyor belt is 1.2m. Substituting the above known parameters into the mathematical model formula, the length of the conveyor belt in the constant-speed drying stage is about 10m, and the length of the conveyor belt in the slow-speed drying stage is 15m. Assume that the drying section is 2.2m long, that is, the constant-speed drying stage occupies 4 drying sections, and the reduced-speed drying stage occupies 7 drying sections. Each drying section is equipped with a circulating fan (centrifugal fan 5.5kw, 2900r/min, 6924m³ /h). From the above parameters, the operating frequency of the circulating fan in the constant-speed drying stage is 39.7Hz, and the circulating fan in the slow-speed drying stage The working frequency of the fan is 37.6Hz. The operating frequency of the conveyor chain belt motor (2.2kw) is 45Hz. Therefore, the operating frequency of the fan and motor is 39.7Hz, 37.6Hz, 45Hz, and the process temperature in the constant-speed drying stage is 160°C and the process temperature in the slow-down drying stage is 120°C, and the relative humidity in the oven is 90% (the working humidity of the dehumidifier), Input to the PLC through the touch screen, the drying line can work under the specified optimal process curve. The production practice has proved that after the egg tray wet paper base is dried by the drying line, the product has less deformation and basically reaches the final moisture content of 10% required by the process.

Claims (9)

1, a kind of paper pulp molding drying line based on variable-frequency control technique comprises combustor, hot-blast stove, baking oven, circulating fan, dehumidifier blower fan, conveyer belt, and combustor connects hot-blast stove; Above-mentioned baking oven adopts frame structure, and conveyer belt is installed in oven interior, and baking oven length and width determine that according to output baking oven is divided into several drying sections; It is characterized in that: each drying section is equipped with circulating fan, each circulating fan connects blower fan tailored version frequency converter, the hot-air of circulating fan in the circulation baking oven, the circulating fan air inlet also is connected with the warm-air pipe of being drawn by hot-blast stove, between the air inlet of warm-air pipe and circulating fan MOD is housed, MOD is connected with frequency converter; The circulating fan air outlet is connected with exhaust duct, and exhaust duct is directly sent to hot blast on the conveyer belt; The dehumidifier blower fan is housed in baking oven, the dehumidifier blower fan connects blower fan tailored version frequency converter, the mounting temperature sensor respectively at the air outlet place of the central authorities of each drying section of drying line and warm-air pipe, air inlet at the dehumidifier blower fan is installed humidity sensor, at the air outlet mounting temperature sensor of dehumidifier blower fan; The control of drying line is finished by programmable logic controller (PLC) PLC, and PLC passes through to receive the data of each sensor, and compares with the optimal value of setting, and draws regulated quantity and sends control instruction to each frequency converter; Conveyer belt is equipped with driving motor, and driving motor connects frequency converter, and worm type of reduction gearing is installed between driving motor and the conveyer belt; The drying line console is equipped with touch-screen.

2, drying line according to claim 1 is characterized in that: the blower fan tailored version frequency converter that above-mentioned circulating fan connects is to be connected with PLC by the FX2N-485-BD module.

3, drying line according to claim 1 is characterized in that: the blower fan tailored version frequency converter that above-mentioned dehumidifier blower fan connects is to be connected with PLC by the FX2N-485-BD module.

4, drying line according to claim 1 is characterized in that: the frequency converter that above-mentioned MOD connects is to be connected with PLC by the FX2N-485-BD module.

5, drying line according to claim 1 is characterized in that: the frequency converter that the said conveyer belt driving motor connects is to be connected with PLC by the FX2N-485-BD module.

6, drying line according to claim 1, it is characterized in that: above-mentioned programmable logic controller (PLC) PLC passes through the FX2N-8AD module from temperature sensor and humidity sensor receiving real-time data, and compare with the optimal value of setting by paper pulp molding drying specificity analysis and the touch-screen HMI that draws at the theoretical model of percolation drying line, be connected by RS-422 thereof, draw regulated quantity and send control instruction to each frequency converter by the FX2N-485-BD module.

7, drying line according to claim 1 is characterized in that: the said temperature sensor is connected with PLC by the FX2N-8AD module with humidity sensor.

8, drying line according to claim 1 is characterized in that: above-mentioned touch-screen is to realize the no-protocol communication by RS-422 and PLC.

9, use the production craft step of above-mentioned drying line as follows:

1), draws correlation formula about the important parameter of each oven dry section of paper pulp molding drying line according to the paper pulp molding drying specificity analysis and at the theoretical model of percolation drying line;

2) according to planned production output, calculate the drying line length and the segmentation baking oven number ratio that distributes, i.e. the number ratio of constant rate drying period and falling rate drying period segmentation baking oven, and draw the working speed and the operating frequency of conveyer belt motor;

3) single product to be dried is carried out drying experiment, draw the drying process temperature that optimum running parameter comprises constant rate drying period and falling rate drying period, air quantity, humidity;

4) with above-mentioned steps 1) and 2) the drying process parameter that draws is input to PLC by touch-screen HMI;

5) start drying line by touch-screen and move automatically, product to be dried is dropped into drying line, produce beginning;

6) temperature sensor of drying section and humidity sensor are gathered the manufacturing parameter of drying line in real time, and by the FX2N-4AD module analog quantity are transformed into digital quantity and pass to PLC;

7) PLC passes to each digital quantity correspondence by the communication of RS-485 no-protocol the MOD frequency converter and the dehumidifier fan frequency converter of each drying section;

8) the inner integrated PID of the frequency converter of each MOD module of adjusting is started working, it can compare according to real time temperature and the default technological temperature that the temperature sensor that is installed in drying section central authorities collects, and of the input of their error amount as the PID controller, and error be multiply by proportionality constant, the integration of error multiply by integral constant, the differential of error multiply by derivative constant, and their addition, thereby obtain the output of PID controller, then the result is given the frequency converter of MOD, thereby regulate the frequency of supply or the rotating operation of MOD, reach the purpose of control throttle opening, thereby the feeding ratio of control changes in temperature wind realizes the purpose that hot blast temperature is controlled in the segmentation baking oven; Proportionality constant wherein, integral constant, derivative constant is determined by test;

9) step 7 in like manner, the inner integrated PID of the frequency converter of the dehumidifier blower fan module of adjusting is started working, real-time humidity that it can collect according to humidity sensor in the baking oven and default technology humidity ratio are, and of the input of their error amount as the PID controller, and error be multiply by proportionality constant, the integration of error multiply by integral constant, the differential of error multiply by derivative constant, and their addition, thereby obtain the output of PID controller, then the result is given the frequency converter of dehumidifier blower fan, thereby regulate the frequency of supply of motor, reach the step-less adjustment of the exhausting amount of dehumidifier blower fan, guarantee that humidity is in the technological requirement scope in the baking oven; Proportionality constant wherein, integral constant, derivative constant is determined by test;

10) repeating step 5)～9), make drying line stably be operated in the optimum process curve.

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