Annual electricity savings exceed 900,000; sharing the practice of intelligent transformation of the printing process cooling water system!

The traditional process water cooling system of the printing factory of the author's group is mainly responsible for cooling the electric cabinet and main motor of the two German MANN COLORMAN wide format machine production lines, which has been in operation for nearly 20 years, and there are several outstanding pain points: Trane refrigeration host, water pump and other equipment operate at fixed power, and the energy air consumption is serious; The temperature control error is large, and condensation is easy to occur in summer, which affects the printing quality and equipment life, and will cause many running and dripping problems; Summer cooling in office and production areas relies on independent Carrier host systems, and overall energy consumption remains high.

To this end, based on the actual production, our factory launched the transformation of PLC-based process water cooling system, achieved precise temperature control and intelligent energy saving through PID control algorithm, and innovatively expanded the function of "winter printing cooling energy saving + summer office cooling". After the transformation, the temperature control error of the system is ≤ 0.5°C, and the comprehensive energy saving rate is as high as 30%, which not only provides solid support for enterprises to reduce costs and increase efficiency, but also provides replicable practical experience for the upgrading of green energy-saving technology of printing enterprises.

Analyze the current situation and clarify the core needs of cooling system transformation

In the process of high-speed operation of printing equipment, electronic control equipment such as frequency converters in the electrical cabinet will generate a large amount of heat energy, which directly affects the life of the equipment, and even causes equipment failure and shutdown, which is also the core problem to be solved by the process water cooling system.

The original process water cooling system of our factory adopts the traditional configuration mode of "refrigeration host + cooling tower + water pump", and the core equipment includes two water-cooled Trane hosts, two cross-flow cooling towers, multiple circulation pumps, as well as ordinary solenoid valves, control valves and plate heat exchangers. The cooling of the office and production areas is provided separately by a set of independent large centrifugal Carrier central air conditioners. After years of operation practice, the process water cooling system has exposed three outstanding problems.

(1) Insufficient temperature control accuracy. Relying on the direct cooling of cold water from central air conditioning, the temperature cannot be flexibly adjusted according to production demand, and the temperature error of the outlet water is large, making it difficult to meet the requirements of the equipment for process water temperature.

(2) Energy consumption remains high. On the one hand, the central air conditioner for printing cooling runs at full capacity all year round, and the supporting water pump and fan lack an intelligent speed regulation mechanism. On the other hand, the cooling of the office area relies on the original independent carrier air conditioning host of the plant, and the actual cooling demand has decreased significantly due to the reduction of the scale of the plant in the later stage, but the cooling capacity of the original host has not been matched and adjusted, resulting in a large amount of energy waste and further pushing up operating costs.

(3) Low degree of automation. Lack of perfect real-time monitoring and fault alarm functions, key parameters such as temperature and pressure need to be manually inspected and recorded, and equipment fault response lags behind, which not only increases labor costs, but may also lead to production interruption due to untimely disposal.

Combined with the actual production and the requirements of the national energy-saving policy, this transformation clarifies five core needs.

(1) Precise temperature control. The adjustable range of cooling water temperature is set to 13~22°C, and the temperature error of the outlet water is strictly controlled at ≤0.5°C, which fundamentally solves the problem of condensate generation.

(2) Energy conservation and consumption reduction. Optimize the operation mode of equipment through intelligent control, greatly reduce the energy consumption of central air conditioners, water pumps, and fans.

(3) Intelligent monitoring. It has real-time display functions of key parameters such as temperature and pressure, and also has automatic fault detection and alarm prompt functions, which is convenient for operators to grasp the operating status of the system in time.

(4) Stable and reliable. It supports automatic and manual dual-mode switching, which can ensure production continuity through manual operation when the system fails, and avoid production line downtime due to equipment failure.

(5) Economic adaptation. There is no need to add new large-scale equipment, and upgrade based on the original system to control the transformation cost to the greatest extent and ensure that the project achieves a win-win situation of economic and social benefits.

Hardware upgrade to build a hardware support system for precise temperature control

The core idea of this transformation is based on PLC as the core, PID control as the algorithm support, intelligent perception as the basis, through hardware optimization and software upgrade, to build a new cooling system of "precise temperature control + energy-saving operation + intelligent monitoring", the core idea is around hardware upgrade, control upgrade, algorithm optimization and mode innovation, hardware selection adheres to the principle of adaptability and diversification to ensure the coordinated and efficient operation of each component.

(1) The core control unit selects the mainstream mid-range PLC products in the market, and can choose multiple brands such as Siemens, Mitsubishi, Inovance and other brands according to actual needs, with corresponding analog input modules, output modules and input/output integrated modules to fully meet the needs of system signal acquisition and control. This transformation uses Siemens S7-1200 series PLC as the control core, equipped with 1214CDC/DC/DC model CPU, and supports 8 external expansion modules to meet complex control needs. Combined with SM1231 AI 8×13BIT analog input module, SM1232 AO 4×14BIT analog output module, and SM1234 AI/AO 4×13BIT/2×14BIT analog input/output module, it is responsible for receiving sensor signals, outputting control signals, and improving signal processing flexibility, respectively.

(2) The human-computer interaction interface adopts an 8~10-inch mainstream touch screen, which supports multi-device communication and real-time monitoring functions, which is convenient for operators to intuitively grasp the system operating status and parameter adjustment. The HMI HMI uses Siemens TP900 Comfort 9-inch display, which supports multi-PLC communication and real-time monitoring functions, making it easy for operators to intuitively grasp the operating status of the system and adjust parameters.

(3) The selection of sensing and execution equipment focuses on stability and accuracy, the temperature sensor selects products with a range covering the temperature range of the production environment and stable signal output, the pressure sensor accurately adapts to the pressure conditions of the pipeline, and the length of the probe rod is reasonably set according to the actual size of the pipeline in the factory area (Note: the length of the probe rod is half the diameter of the pipeline) to ensure the accuracy of the detection data.

(4) The valve and actuator are equipped with electric three-way valves with fast response speed and high control accuracy and adapted actuators to accurately adjust the water flow rate and ensure the temperature control effect. The frequency converter selects products with power adapted to water pumps and fans, and supports precise frequency adjustment, which can not only ensure the smooth start and stop of the equipment, but also achieve energy-saving operation. This renovation adopts Siemens SVB series actuators, with a maximum torque of 1600N; The selection of electric actuator needs to be determined in combination with the valve body, pipe and pipe pressure, that is, to meet the "actuator torque≥ the maximum starting torque of the valve× safety factor (1.3~1.5)".

(5) Implement linkage control for the original coil heater of the cooling tower to prevent the water temperature from freezing in winter and affecting the system circulation; The relay components use switching power supplies, transformers and relays with voltage and power matching to provide a solid guarantee for the stable operation of the entire circuit system.

The same brand should be selected as much as possible for equipment selection, and the unity and coordination of different brand component combinations are poor, which is prone to errors, which ultimately leads to an increase in the difficulty of debugging and an increase in the number of maintenance. The following are three key measures for hardware transformation.

01/ Optimize pipe connections

(1) The cooling tower inlet and outlet pipes are renovated in parallel with the central air conditioning chilled water pipes (as shown in Figure 1), and solenoid valves are installed to control the on/off, and when the outdoor temperature is low in winter, the cooling tower cooling water can be directly used to replace the central air conditioning chilled water, which greatly reduces the running time of the air conditioning host and realizes energy saving.

Figure 1 Renovation roadmap

(2) Renovate and optimize the air conditioning and cooling pipes in the original factory office area, and add valves to cut off the connection pipeline between the office area and the original Carrier central air conditioner, so that the original central air conditioner can maintain independent operation and only serve the original adaptation scenarios such as newspaper production workshops; The cooling pipeline in the office area is accurately connected to the central air conditioning chilled water pipeline of the printing cooling system of the existing plant, which can directly use the surplus cooling capacity of the printing cooling system to cool the office area without consuming additional energy to generate a cold source, thereby greatly reducing the operating time of Carrier's centrifugal central air conditioner, effectively reducing equipment energy consumption, realizing efficient energy recycling, and achieving significant energy conservation and consumption reduction goals.

02/ Added external manual circuit

In the event of system failure or maintenance, operators can manually control the operation of valves and pumps to ensure that production is not affected and improve the reliability of system operation.

03/ Improve the perception monitoring network

Temperature and pressure sensors are installed in the four key positions of refrigeration inlet, frozen outlet, cooling inlet and cooling outlet to realize the data collection of the whole process of the cooling system, provide comprehensive and accurate data support for PLC precise control, and ensure the realization of temperature control and energy-saving goals.

Software optimization to create intelligent control core programs

In this transformation, the software design selects a mainstream equipment control software development platform with integrated functions and convenient operation, which needs to support a variety of programming languages, which can simplify the program writing and debugging process, effectively shorten the project cycle, and provide technical support for the stable operation of the system. The design uses Siemens Botu V17 (TIA PORTAL V17), considering that the design software needs to be compatible with hardware PLCs and touch screens, so the same brand products are preferred.

The core of intelligent control program design includes three modules: data conversion, dual-mode control and alarm. The data conversion module accurately converts the 4~20mA analog signal collected by the sensor into the temperature and pressure values that can be recognized by the control unit by NORM_X standardized instructions and SCALE_X scaling instructions. The data width of each channel of Siemens analog is 16 bits, and the fixed operating range is adjusted to -27648~27648, corresponding to the input and output voltage ±10V, of which 5533~27648 corresponds to the input and output current of 4~20mA, and the floating point data of 0.0~1.0 is obtained by the standardized operation "OUT=(VALUE–MIN)/(MAX–MIN)", and then the scaled operation "OUT=[VALUE×(MAX–MIN)]+MIN" Establish a correspondence with actual physical quantities to ensure the accuracy of data conversion.

Dual-mode control is the core innovation of this software design, which can automatically switch the operating mode according to the outdoor temperature to maximize energy utilization (Figure 2). In daily mode, when the outdoor temperature is high (more than 12°C), the system starts the central air conditioning, adjusts the valve opening and frequency converter frequency in real time through the PID control algorithm, accurately controls the amount of cold water and the speed of the pump, and maintains the constant pressure and temperature of the system. In addition, the PID control algorithm automatically optimizes the adjustment parameters by comparing the set temperature, pressure difference and actual detection value, ensuring that the valve opening and pump speed are always in the optimal state, which not only ensures the cooling effect, but also avoids energy waste.

Figure 2 Dual-Mode Control Interface

In winter mode, when the outdoor temperature is low (≤12℃), the system automatically shuts down the air conditioning unit, opens the cooling tower and the central air conditioning pipeline communication valve, and directly uses the cooling tower water for cooling. At this time, the fan speed and heater on/off are adjusted through a PID control algorithm to prevent the water temperature from dropping too low and causing freezing that affects system circulation, while minimizing energy consumption to achieve efficient operation of the winter cooling system.

The alarm program design fully considers the safety and reliability of system operation. By setting thresholds for key parameters such as temperature and pressure, when the detected data exceeds the normal range or a device fault occurs, the system immediately triggers an alarm signal and clearly displays it on the HMI interface, while also feeding back to the PLC input module. This allows operators to promptly identify problems and respond quickly. The HMI human-machine interface is designed with multiple functional screens (Figure 3), supporting one-click switching, and can display key information in real time, including the system operation mode, temperatures and pressures of various pipelines, and the valve opening degree. It also supports temperature setting and alarm acknowledgment operations, enabling operators to comprehensively and intuitively understand the system operation status, greatly reducing operational difficulty and risk of misuse, and improving overall production efficiency.

Figure 3 HMI interface

Energy consumption accounting highlights the effectiveness of energy conservation and emission reduction transformation

The energy consumption accounting is based on the actual production conditions of the printing plant, the process water cooling system runs 24 hours a day, 365 days a year, and the winter mode operation period is concentrated from December to February of the following year, a total of 90 days; The price of industrial electricity is calculated at 0.7 yuan/kWh.

The process water refrigeration host is the core energy-saving link of this transformation. Before the transformation, the annual power consumption of the refrigeration host reached 1,822,100 kWh, and after the transformation, the refrigeration host was stopped for 90 days in winter, and the annual power consumption dropped to 1,479,300 kWh, saving 342,800 kWh of electricity per year.

In terms of office area cooling transformation, the office area cooling is incorporated into the printing process water cooling system through pipeline docking, and the original Carrier central air conditioning system is only open in the early morning production time of the workshop, and the start-up time is reduced to one-third of the original, which greatly improves the utilization efficiency of the air conditioning host of the printing process water cooling system, and can save 16 hours of operating energy consumption of the Carrier central air conditioning system (one Carrier host, two circulation pumps, and one cooling tower fan) every day. The air conditioner in the office area is mainly used for 4 months (120 days in total) in spring and summer, saving 857,000 kWh of energy consumption per year after the renovation.

The total annual power consumption of the three 18.5kW circulation pumps before the transformation was 486,200 kWh, and after the transformation, the average operating frequency was reduced to 40Hz, the energy consumption was reduced by 20%, and the total annual power consumption of the three pumps was reduced to 388,900 kWh, saving 97,200 kWh of electricity per year.

After comprehensive accounting, it was found that the company saved 1.297 million kWh of electricity and about 907,900 yuan in electricity bills per year. At the same time, the temperature control error of the system after the transformation ≤ 0.5°C, which completely solves the problem of condensate and greatly reduces the failure rate of printing equipment. The whole process is automatically monitored, and the fault response time is shortened to less than 5 minutes, taking into account the technical effectiveness, economic benefits and management benefits.