Project Overview

***The existing Phase I project of the water treatment plant has a capacity of 100,000 m³/d, and this Phase II expansion also targets a capacity of 100,000 m³/d. The newly installed automated control system is designed to support an unattended operation mode, ensuring continuous, stable, and reliable production for at least 72 hours without any manual intervention. Moreover, the system guarantees that the treated water quality, pressure, and flow rate meet all specified standards, while maintaining the seamless, safe, energy-efficient, environmentally friendly, and highly automated operation of the plant's equipment. At its core, the automated control system is a sophisticated, integrated solution capable of intelligent production process control as well as advanced production information management and storage functionalities.

System Overview

The control system is integrated from a Programmable Logic Controller (PLC), communication network, human-machine interface, measurement and control instruments, video surveillance, and peripheral devices. The system design adheres to the principles of advanced technology, practicality, reliability, cost-effectiveness, and openness, and is tailored around the guiding vision of "improving water quality, enhancing supply safety and reliability, reducing energy consumption, minimizing leakage losses, and cutting down on chemical usage." At the heart of the control station lies the NA400 PLC.

Process Flow

System Structure and Components

1. Network Structure

The control system consists of a central control room computer, field control stations, field instruments, and actuating devices. The network adopts a multi-layered architecture, divided from top to bottom into the management layer, control layer, and field equipment layer. Given the distributed nature of equipment and the large number of sites in the water treatment plant, the control stations are designed with six substations. Among these, the core control station features a hot-standby redundant processor configuration, while the six substations are interconnected via a redundant ring-shaped industrial Ethernet network. The SCADA system employs a redundant server-plus-client data structure design. For details, please refer to the network architecture diagram.

2. Controller

• Featuring an Intel Pentium M processor with a main frequency of 300MHz, it boasts high-performance redundant CPUs and exceptional reliability.
• Equipped with a built-in Ethernet interface, it supports Modbus TCP and OPC protocols.
• 32MB memory space + 32MB storage space.
• Equipped with a real-time clock to record the current time and enable time-based control of processes.
• Equipped with a Watchdog function, it can automatically reset and restart in case of a failure.
• Supports hot-swapping.
• Data power-loss protection.

Control Function

The system features a human-machine interface, sequential control of the production process, equipment interlock protection, optimized lifecycle management, automatic adjustment, as well as fundamental control functions such as data statistics, accumulation, and analysis—along with video surveillance, security features, and office management capabilities. Below, we will introduce the process control functions of the water treatment plant’s production system in separate sections.

1. Water Pump Control Function

The pumping station units implement a streamlined, step-by-step operation for starting and stopping based on dispatch instructions, including coordinated control of pumps and valves, PID-based frequency conversion motor regulation, optimized pump operation scheduling, automatic operation of drainage pumps according to water levels, as well as control functions such as pump failure protection and alarm systems, and equipment maintenance alerts. Additionally, raw water quality parameters are collected via a fieldbus, enabling real-time monitoring of incoming line current, voltage, power consumption, power factor, pump motor current, active power, and total energy usage.

2. Sedimentation Tank Control Function

The main control functions of the reaction precipitation process include automatic stirring in the sedimentation tank and coagulant dosing, automatic crawling and sludge suction control for the sludge remover, as well as automated periodic sludge discharge via the bottom sludge valves. Additionally, the PLC at the sludge remover substation communicates wirelessly with the main station's AP equipment, enabling seamless coordination among all components.

3. V-Shape Filter Pool Control Function

• The control of V-shaped filter pools is one of the more challenging aspects in the process control of water treatment plants. The effectiveness of the water purification automation process is directly influenced by the quality of the control strategy. The main control functions include:
• V-shaped filter pool water level adjustment control (effluent valve PID regulation);
• V-shaped filter tank sequential control process;
• Coordinate the backwashing of filter cells by managing the flushing queue for filter basins.
• Collection of equipment and electrical parameters, etc.

4. Dosing Room Control Function

Medication control is one of the critical processes in a water treatment plant, directly affecting water quality and operational safety. Generally speaking, its control functions fall into three main areas: automatic alum dosing and adjustment via metering pumps, control of the alum mixing (dilution) process in the alum preparation system, and control of chlorine injection functionality—both before and after filtration.

5. Dewatering Room Control Function

The dewatering system housed in the dewatering room is equipped with a control PLC that independently manages the monitoring of the dewatering machine system and the PAM dosing system within the entire dewatering setup. This PLC communicates with the central control system, which then sends start/stop signals to the dewatering machines. Additionally, the control system handles basic operation of equipment such as the reclaimed water pump, sludge discharge pump, and mixer in the sludge equalization tank.

6. Secondary Pump Room Control Function

The secondary pump house machinery control system is similar to that of the water intake pump house, primarily handling the start-up and shutdown of equipment in a streamlined manner based on dispatch instructions programmed into the system. This includes coordinated operation of pumps, valves, and vacuum-generation units, as well as functions like variable-frequency PID control for maintaining set pressure during water supply. Additionally, the system integrates with factory-produced water quality parameter collection and communication interfaces linked to the Environmental Protection Bureau, along with signals gathered by comprehensive protection units installed on high- and low-voltage switchgear.

7. Key Highlighted Features

The control system is a custom-built automated product tailored specifically to the processes of a water treatment plant, enabling fully automated management and control of the entire water purification process. The system features the following outstanding capabilities:

(1) The Realization of Comprehensive Coordination

With improvements in equipment and advancements in automation technology, the water treatment plant has already achieved "small-scale integration"—enabling fully automated operations for localized systems such as automatic chemical dosing, automatic sludge removal, automatic filtration, automatic start-and-stop control of drainage pumps, and constant-pressure automatic frequency modulation. However, to realize fully automated operation across the entire plant, all these individual processes must be seamlessly interconnected, creating a comprehensive "large-scale integration." Achieving this "large-scale integration," in turn, hinges on resolving the dynamic balance between the water intake pump's supply capacity and the overall water demand—once this critical issue is addressed, the "large-scale integration" will naturally fall into place. Through meticulous analysis and research of the water treatment plant's operational processes, we have successfully tackled this challenge by calculating the output of the intake pump based on the outflow rate from the booster pump and the liquid level in the collection well, thereby enabling the plant to achieve fully automated, plant-wide operations.

(2) Motor Maintenance Reminder

According to the operating instructions for motor equipment such as water pumps and blowers, by analyzing accumulated motor usage time, abnormal motor temperatures, and electrical three-phase imbalances—among other unusual conditions—we aim to proactively notify maintenance personnel to perform inspections and maintenance before equipment failure or during scheduled repair periods, thereby reducing both repair costs and overall maintenance expenses.

(3) Operational Parameter Memoryability

The water plant often needs to set the outlet pressure according to the operators' experience and time periods, with the booster pumps adjusting the water output at a constant pressure based on the scheduled pressure levels. The control system features a memory function that analyzes and refines the operational parameters provided by the staff. Based on process requirements, it can automatically determine the target outlet pressure values for different time periods, eliminating the need for the long, tedious, and repetitive task of manual pressure adjustments.

Human-Machine Interface Function

1. Process flow diagram displayed

The system accurately reflects the production process flow, featuring a concise and smooth visual presentation that brings the workflow to life in a vivid and engaging manner. It consists of an overview screen and multiple detailed views, each equipped with navigation keys linking seamlessly to related screens, enabling convenient browsing and control of the equipment.

2. Report Display and Printing Function

System historical data is stored in standard database formats, supporting dBASE VI, ACCESS, ODBC, and other formats. The reporting feature enables advanced data processing and calculations, offering not only basic capabilities like mean, maximum, minimum, and cumulative values, but also allowing time-based calculations for individual devices. Additionally, the reports are highly flexible, enabling users to generate daily, monthly, quarterly, or annual reports according to their specific requirements.

3. Alarm Function

The alarm function enables operators to instantly understand the operational status of equipment related to alarm parameters and take necessary actions when required, serving as a critical measure to ensure continuous and stable production. Operators can check the alarm overview at any time and conveniently confirm individual alarms, view full-screen alarms, or acknowledge all alarms collectively.

4. Real-time Trend Chart and Historical Trend Chart

Real-time trends can be accessed directly with a right-click, and the unified interface also supports displaying multiple trends simultaneously. The historical trend chart is collected at 10-second intervals, allowing up to N data points to be shown on the same table for easy comparison and analysis. Additionally, the historical trend charts can be filtered by system and time period. By default, the historical database retains data for up to 2 years, but users can easily save or back up the database files. The system also features powerful automatic historical data retrieval and robust query capabilities for historical events.

5. Operation Permission Management and Operation Logging Function

Provides differentiated operation and login permissions for visitors/browsers, operators, maintenance engineers, and more. Features include operation logs and runtime event records, as well as robust data query capabilities—supporting partitioned and site-specific queries by time periods.

Product Features

• The system utilizes domestically produced PLC products under our own brand.
• The control unit features a hot-standby redundancy configuration and a high-performance processor.
• For environments such as dosing rooms and filter pools, hardware equipment undergoes three-proof treatment.
• The product features a versatile, standardized communication interface, supporting commonly used fieldbuses such as PROFIBUS, HART, MODBUS, and OPEN CAN, offering excellent scalability and openness.
• Adopting an Ethernet architecture for high-speed communication with reserved bandwidth;
• Fiber-optic 100M industrial Ethernet self-healing ring network connection, using standard TCP/IP protocol;
• Good versatility, human-centered design;
• Tailor-make products and control programs that meet customers' process requirements based on their specific needs;
• Rapid after-sales service and a strong technical team.