Design of Energy SCADA System for Cigarette Factory

【summary】

This article provides a detailed introduction to the energy monitoring and management system of a cigarette factory, mainly divided into three parts: hardware design, software design, and communication network connection. The system has been put into use in the cigarette factory and is operating well. This system provides users with detailed information on energy and material consumption during the production process, enabling them to promptly identify and resolve problems, thereby maximizing energy and material utilization and achieving comprehensive energy conservation and consumption reduction. Simultaneously, economic efficiency and management level have also been improved.

Keywords: DCS fieldbus energy monitoring Visual Basic

1 Introduction

The tobacco industry has always been a major energy consumer. With the large-scale introduction of advanced foreign technologies and complete sets of equipment, cigarette production has evolved from slow, manual production to high-speed, fully automated production, leading to a significant increase in energy demand. For example, cigarette production requires maintaining constant temperature and humidity in workshops, which directly affects the quality of the tobacco and determines the quality of the finished cigarettes. Therefore, a large amount of air conditioning and dust removal equipment is needed. Combined with the electricity consumption of production equipment, this means the tobacco industry's electricity demand is considerable. Much of the tobacco industry's production equipment relies on gas propulsion. To produce the gas needed for this equipment, coal and oil are consumed to heat water into steam, or air is compressed into compressed air using energy-intensive equipment. It is evident that large-scale cigarette factories consume a large amount of energy daily; therefore, reducing energy consumption and rationally allocating energy will directly improve their production efficiency.

With the deepening of the market economy, the concept of adopting computer-aided management systems is becoming increasingly popular. To reduce the burden on employees, improve work efficiency, and perfect its business management, this cigarette factory decided to establish its own computer-aided management system, primarily for energy monitoring and management. Establishing this monitoring and management system can bring significant benefits to the enterprise. Specifically, it can bring the following advantages:

(1) Using this system enables users to fully understand the energy and material consumption of the production process, discover problems in a timely manner, and solve problems so as to maximize the utilization rate of energy and materials, thereby achieving the goal of comprehensive energy conservation and consumption reduction, and at the same time improving economic efficiency and management level.

(2) It improves the reliability and correctness of data, increases the accuracy of calculation, and reduces losses caused by inaccurate calculations and errors.

(3) It greatly saves manpower and reduces the calculation burden on the actual operators in the statistics office, thus reducing the calculation time.

2. Overall Design of Energy Monitoring and Management System

The prerequisite for the rational use and allocation of energy is a clear understanding of energy usage, which requires the collection and aggregation of real-time energy consumption data from the production site. In a large tobacco production enterprise, the data collection points are distributed throughout the entire factory area, and the number of data points is also large. The challenges of wide distribution and large volume in data collection and transmission need to be addressed. To solve this problem, fieldbus technology was introduced into the traditional DCS system, resulting in a fieldbus-based DCS control system. Fieldbus technology is a hot topic in the field of industrial automation today. It is a fully distributed, fully digital, intelligent, bidirectional, interconnected, multi-point, and multi-station communication system suitable for communication between field instruments, control systems, and control rooms, and is hailed as the computer local area network of the automation field. Fieldbus connects field devices and controllers, distributing control throughout the network, and field devices can also be directly powered via the fieldbus.

The energy management and monitoring system of this cigarette factory is mainly used to collect data from 233 points in various departments of the cigarette factory, summarize and process the data, display energy consumption data in real time, query data for different time periods, print reports, and assess shifts.

The system is built using Siemens' SIMATIC PCS7 series field control equipment, including one S7-400 master station and one S7-300 master station, with nine ET200M substations. It completed the data acquisition of 233 points for steam, compressed air, water, and electricity. This includes data from the second phase project: 15 steam flow rates, 15 steam pressures, 15 steam temperatures, 7 compressed air flow rates, 7 compressed air pressures, 9 water flow rates, and 131 electricity consumption data; and data from the first phase project: 2 steam flow rates, 2 steam pressures, 2 steam temperatures, 1 coal consumption, 2 oil consumption, 19 electricity consumption data, 3 water flow rates, 1 compressed air flow rate, 1 compressed air pressure, and 1 compressed air temperature. The PLC is programmed using Siemens' STEP7 programming software; the program downloaded to the PLC mainly handles data storage and calculation. The upper-level computer configuration also uses Siemens' SIMATIC WINCC, which provides a clear industrial control interface for online monitoring of energy consumption in various departments, enabling time-period queries and printing of detailed energy consumption reports. To better facilitate statistical analysis, cost accounting, and shift performance evaluation, we developed energy monitoring and assessment software using Visual Basic 6.0. This software connects to the OPC program interface integrated within WINCC via a self-developed simple OPC program for data transmission. This software allows for more detailed analysis of recorded field data, yielding cost accounting and shift performance evaluation results, providing a reliable basis for departmental performance evaluations and improving management efficiency. Simultaneously, the various energy consumption curves generated by this software provide a basis for analyzing production energy consumption trends.

This system can be broadly divided into three parts: a host computer, master stations (300 and 400 master stations) and their substations (a total of 9 ET200M substations), as shown in Figure 1. The host computer consists of one server and three client computers. We integrated the server into the enterprise network because Siemens' WINCC host computer configuration software has built-in OPC communication functionality. This makes expanding the client computers extremely easy and simple: just connect the computer to the local area network and perform simple settings to use it as a client computer. To facilitate the work of boiler operators, we added one client computer each in the boiler control room and the oil furnace control room to display real-time data on boiler operation. To allow enterprise management to monitor production energy consumption in real time, we added a third client computer in the same way in the office building equipment management office. The 400 PLC master station and the 300 station are connected to the server via the MPI protocol. MPI can be used at both the unit and field levels, and it can be used to connect a small number of stations very economically. The 400 master station and its substations are connected via PROFIBUS-DP. This networking method can minimize hardware costs while ensuring data acquisition performance requirements. The data acquisition process is roughly as follows: Output signals from field sensors are acquired by signal templates at each station, converted into corresponding digital signals, and then sent to the 400 PLC master station via a communication module. The 400 PLC master station performs various calculations and processes on the data from each station as required, and then transmits it to the server via the MPI network. Data transfer between the client and server is conducted via OPC. The PLC300 station meets the requirements for acquiring sensor signals from nearby locations and high-speed counters.

The PLC programming uses Siemens' STEP7 programming software, and the supervisory control and data acquisition (SCADA) system uses Siemens' SIMATIC WINCC. The energy monitoring and assessment application software for the statistics office is developed using Visual Basic 6.0. STEP7 programming enables the PLC to perform preliminary processing of process data. The SCADA software handles real-time data display, daily and monthly cumulative energy consumption display, daily, monthly, and time-period data querying, and report printing. The statistics office's energy monitoring and assessment program completes various shift performance evaluation tasks, statistically analyzes the input and output of the plant's energy supply department and the energy consumption of energy users, performs cost accounting, etc., providing a reliable basis for improving the plant's energy management and utilization level.

Figure 1 System Overall Structure Diagram

3. Specific Implementation of the Energy Monitoring and Management System

3.1 Software Design

The PLC programming of this system uses Siemens STEP7 programming software, the upper computer monitoring is implemented using Siemens SIMATIC WINCC, and the energy monitoring and evaluation program of the statistics office is written in Visual Basic 6.0.

STEP7 programming enables the PLC to perform preliminary processing of process data. The host software handles real-time data display, daily and monthly cumulative energy consumption display, daily, monthly, and time-period data querying, and report printing. The statistics office's energy monitoring and evaluation program completes the various performance assessment tasks for each shift.

STEP7 is the standard software for creating programmable logic control programs for SIMATIC S7300/400 stations. It can be used to write specific programs in three ways: ladder logic diagram, function block diagram, or statement list.

Before programming according to the actual requirements of the project, the main hardware devices used in the system must first be determined, such as the PLC model, signal acquisition module type, communication module, etc., and the corresponding hardware configurations should be added to the project in the STEP7 SIMATIC Manager window according to the actual situation. Connect the PLC master station to the server through the CP5611 network card, and download the programmed PLC control program to the PLC CPU online through STEP7. The following is an example using an S7-400 PLC program.

The program includes 6 OB blocks, 20 FC blocks, and 15 DB blocks. It processes the data of compressed air, steam, electricity, and water collected on site (including steam flow compensation and steam temperature calculation) and records the cumulative amount of each variable.

(1) Main program (organization block OB1)

Main program flowchart:

A brief introduction to the main FCs used:

①FC1 Data Acquisition: The digital data collected on-site is placed into the corresponding data blocks of each substation and awaits processing.

②FC10 Global Data Allocation: Used to allocate some global data for easy future access and modification, reducing the chance of errors. The M storage area defined in the program is shown in Table 1:

Table 1. Main M-memory areas defined in the program

③FC100 Accumulation Clear: Used to clear the data block storage unit that stores the accumulation amount.

④FC106 Power Linearization: Call FC107 to convert the power signal acquired on site according to the range.

⑤ FC107 Power Linearization: Power in kilowatts = (Field digital value / 27648) × Power meter range

(2) 1-second cycle (tissue block OB32)

Program flowchart (as shown in Figure 3)

A brief introduction to the main FCs used:

(1) FC3 Compressed Air Flow Compensation: The pressure range of compressed air is 3-8 kg/cm². FC104 is called, Tf=MW20, Tn=273.15, Pf and Qf are data collected from the field and placed in the DB block, Pn=MD16. For special handling of compressed air flow at the air compressor station, FC105 is called.

(2) FC4 Compressed Air Accumulation: Calls FC102 to accumulate the amount of compressed air.

(3) FC5 steam flow compensation: The steam pressure range is 3-13 kg/cm2. Call FC104.

(4) FC6 steam temperature calculation: Call FC101 to calculate the steam temperature using the steam pressure.

(5) FC7 Water vapor accumulation: Call FC102 to accumulate water vapor flow.

⑹FC8 Power Accumulation: Calls FC103 to accumulate power.

(7) FC9 Water Accumulation: Calls FC103 to simply accumulate the data.

(8) FC101 Steam Temperature Calculation: The steam temperature value is obtained by referring to the table based on the steam pressure value. Where: Steam pressure = (Field digital signal / 27648) × Pressure gauge range / 0.098. The temperature value is obtained by referring to the table using the steam condition diagram.

(9) FC102 Gas Accumulation: Accumulated Amount = Accumulated Amount + Gas Flow Rate / MD34 (MD34 is 3600.0, a floating-point number. Considering that the flow rate unit is based on hours, and since the accumulation cycle of this system is 1 second, the time unit of hours is converted to seconds).

(10) FC103 Hydropower Accumulation: Accumulated Amount = Accumulated Amount + Hydropower Current / MD34 (MD34 is 3600.0, a floating-point number. Considering that the flow rate unit is based on hours, and since the accumulation cycle of this system is 1 second, the unit is converted to seconds).

(11) FC104 gas flow compensation:

Gas pressure = (Field data signal / 27648) × Pressure gauge range + MPa value corresponding to 1 atmosphere

Absolute temperature of a gas = Celsius temperature of the gas + 273

Gas flow rate after compensation = Gas flow rate before compensation (on-site digital value) × (Gas pressure / Required gas pressure) × (Required gas temperature / Absolute gas temperature)

12. Compressed air flow compensation for FC105 air compressor station:

Compressed air pressure = (on-site digital value / 27648) × pressure gauge range + MPa value corresponding to 1 atmosphere

Compressed air flow rate = Uncompensated flow rate signal from the field before compensation × Compressed air pressure × [273.15 / (0.10135 × absolute temperature of compressed air)]

(3) 500ms loop (OB33)

The FC42 is used to accumulate pulsed energy signals. The FC42 is primarily used to control the counters. Two counters are used for each variable, each with a maximum count of 999. Using two counters increases the total count. Energy consumption (kWh) = number of pulses / 1000 × transformation ratio. To improve counting accuracy, four DBWs are used to store the collected energy. The storage locations for each energy value are listed in Tables 2 and 3.

Table 2 Comparison Table of Electricity Storage Areas in Air Compressor Stations

Table 3 Comparison of Electricity Storage Areas in the Thin Film Workshop

3.2 Specific Structure of the System Communication Network

The general structure of the communication system is as follows: the master station connects to each substation via PROFIBUS-DP to complete data transmission. The 300 and 400 master stations connect to the data acquisition card of the host computer via the MPI protocol, and the server is integrated into the enterprise network. This makes client expansion extremely simple; simply connect the computer to the local area network and share data using the OPC read/write protocol built into WINCC. To monitor production in real time, we connected three operator stations in the boiler room, oil furnace room, and equipment management office using the plant's local area network. To better complete assessment and statistical work, an operator station was connected in the statistics office using the same method—connecting it to the existing plant local area network and the OPC integrated into WINCC. Communication between this operator station and the energy monitoring and evaluation system developed in VB6.0 is achieved through WINCC.Client, as shown in Figure 4, via an OPC client application developed in VB.

Figure 4 System Data Network Structure Diagram

4. Design of the Energy Monitoring and Assessment Procedure of the Statistical Office

4.1 Communication connection with the server

Because the statistics office needs to conduct monthly performance evaluations of various departments and assess bonuses accordingly, its requirements are more complex. It needs to record changes in over 70 quantities from the boiler room, air compressor station, sheet metal workshop, and main power distribution room, and perform corresponding data processing to evaluate workers in each department and shift. It also needs to calculate production costs and print detailed monthly reports. Using the WINCC supervisory control software to meet so many detailed requirements would be extremely labor-intensive, and due to many of WINCC's inherent limitations, it would be difficult to meet the factory's requirements. Therefore, considering the powerful data manipulation capabilities of Visual Basic 6.0 in statistical reporting and database access, the system was developed using VB6.0 combined with an Access database. For communication, the client and server communicate via Wincc.Client on the server and the OPC integrated within WINCC on Wincc.Server. Communication between Visual Basic 6.0 on the client and Wincc.Client on the local machine is achieved through an OPC client program developed in VB.

The specific structure is shown in Figure 5. The role of Wincc.Client shown in Figure 5 is quite special; it acts as the client for Wincc.Server shown in the figure, but as the server for this energy management software. This is done to better utilize the OPC integrated within WinCC for more complex communications, while using the VB OPC client application only for simpler parts.

4.2 Basic Functions of Energy Monitoring and Assessment Procedures

The system needs to perform monitoring and management functions for three major departments (as shown in Figure 6). The monitoring section needs to perform real-time monitoring and accumulation of more than 70 quantities and display the real-time curves of each instantaneous quantity; the management section needs to perform several major functions such as statistical calculation, statistical reports, cost accounting, data analysis, error list, data backup, parameter setting, and importing Excel spreadsheets. It needs to have comprehensive data aggregation functions, as well as robust query functions and database maintenance capabilities. Based on this, extensive data analysis and network database querying will be designed.

Figure 6 Monitoring and Management Function Diagram

The system performs the following functions: It communicates with the local WinCC client via an OPC client program. Whenever the data on the server changes, the data on the WinCC client also changes, and the data on the corresponding management software also changes, thus enabling real-time monitoring. Every four minutes, all instantaneous quantities are read into a 4-minute database to plot real-time curves. Every half hour, all quantities (including instantaneous and cumulative quantities) are read into a half-hour database, generating an 8-hour database and a daily database through statistical calculations. These two intermediate databases are necessary for performance evaluation of each shift and to meet future daily query requirements. The cigarette factory's production workshop is divided into three shifts (A, B, and C), each working 8 hours, hence the 8-hour database. Since future queries are based on daily queries, a 24-hour database was also created. Through these two intermediate databases, reports can be displayed for data from each department as required, costs or consumption for each department can be calculated, and data calculations can be performed based on selected conditions. This allows users to analyze and compare the production status of each department, and the data can be displayed visually in bar charts and pie charts. During data collection, errors exceeding limits for various monitored quantities are recorded in real time and written to an error list, which can be queried based on selected criteria. At the start of the new year, a backup function can be executed to back up data that no longer needs analysis to a backup database. To facilitate further data processing and analysis, data from various departments can be linked to Excel spreadsheets as required, generating Excel files.

5. Conclusion

The Energy Monitoring and Management System is a complete monitoring system, including field signal acquisition and transmission, communication between PLC substations and the main station, communication between the main station and the host computer, client expansion and host communication, data processing, report printing, production cost accounting, and shift performance evaluation. It achieves real-time monitoring, data statistics, cost accounting, and report printing functions. The implementation of this system provides users with detailed information on energy and material consumption during the production process, enabling them to promptly identify and resolve problems, thereby maximizing energy and material utilization and achieving comprehensive energy conservation and consumption reduction.

About the author:

Hu Xiaofeng, male, is a master's student. His main research area is mechatronics.