July 2010, Vol. 22, No.7

Problem Solvers

Treatment Plant Implements New Control System To Increase Capacity While Maintaining Staff Levels

Problem: A need to increase flow capacity and meet regulatory environmental standards.
Solution: Installing a process automation system that integrates controls for process operations and motors into a single system.

 

In November 2006, the City of Plano, Ill., completed a $13.6 million improvement project at its water reclamation facility that increased maximum flow capacity from 6.32 million L/d (1.67 mgd) to 9.24 million L/d (2.44 mgd) and helped ensure that the facility meets its regulatory environmental standards.

As part of the project, the city expanded its plant process control to an integrated supervisory control and data acquisition (SCADA) system with intelligent motor control and networking. The expansion has contributed to improved system diagnostics, process control, data collection, and remote monitoring that all help reduce employee workload.

Motor starters and variable-frequency drives on the plant’s process motors helped save energy for long-term return on investment. The existing plant had very little instrumentation for process control, which resulted in restricted data collection, historical trending, and monitoring capabilities.

“Getting this kind of information manually was really time-consuming,” said Darrin Boyer, plant superintendent at the city’s water reclamation facility. “EPA [U.S. Environmental Protection Agency] reporting took 2 full days, and it took three field operators to constantly monitor the equipment.”

 

Control System Solution

To control processes at the new facility, the city implemented the Plant-wide Process Automation Excellence (PlantPAx) process automation system from Rockwell Automation (Milwaukee). The system integrates all process-operations controls and motor controls into one system with access from remote telemetry–terminal units (RTUs) at each of the seven main process buildings.

At the heart of each RTU is an Allen–Bradley® ControlLogix® programmable automation controller (PAC) with redundant power supply. The RTUs enable operators to access plantwide production information in real time, including water quality monitoring, load trending, water levels, clarity, detailed alarming, data collection, and automated reporting.

Wireless transmission through a high-speed dual fiber-optic network enables control of any process from any location offsite or in the plant. The main work station in the facility’s office runs a component-based human–machine interface (HMI) with touch screen operation.

The facility now composes EPA reports electronically through PAC inputs and submits them to the state automatically. “The regular EPA reporting has been cut from a 2-day operation each month to little more than a click of a button,” Boyer said. “The daily flow data automatically populate the EPA discharge-monitoring reporting form, which then automatically uploads to the EPA site.”

 

Intelligent Motor Control Reduces Energy Use

The city also incorporated intelligent motor control at the plant to help reduce energy use and manage the motor speeds of its many pumps, fans, and blowers. Soft starters with IntelliCENTER® provide soft start and stop of the continuous-run motors and provide the ability to connect to the rest of the process automation system.

For motors that require varied speed, the city installed PowerFlex® 700 variable-frequency AC drives that also have integrated intelligence for additional monitoring, safety, and easy configuration and installation. Advanced motor control performance helps gather process information at the drive level and disperse it automatically to any part of the plant.

The new control system helps save energy by enabling operators to run equipment on a demand schedule instead of a time schedule. Operators can program systems to run enough only to meet demand even when no one is physically present at the plant.

 

Remote Operation Saves Time and Costs

Remote monitoring and control gives operators access to information about any process in the plant from any of the HMI locations or the main office. Boyer estimates that the flexibility of remote monitoring replaces the surveillance work of three operators in the field. These operators can now anticipate and detect a potential problem earlier, which allows time for a quick adjustment or small repair that could prevent catastrophic failure. This has contributed to a significant reduction in equipment downtime, Boyer said.

Remote monitoring from home at night or on weekends enables Boyer to determine if an alarm is critical or can be dealt with the following day. This saves the cost and inconvenience of unnecessary callouts.

Manufacturer “dial-in” functions also have saved downtime and expenses. The city can rely on quick, inexpensive troubleshooting, as each major equipment manufacturer can access the city’s system from its factory and assess the situation without visiting. Often, a solution can be implemented without any follow-up from a service technician, Boyer said.

The process automation system provides the right information in real time to help Plano meet its environmental and capacity goals. The city reports that there have been no effluent violations since the new plant was brought on-line, and it has maintained plant staff levels while more than doubling its wastewater treatment capacity.

“The plant effectively handles more flow through the equalization basin,” Boyer said. “There is precise control of the biomass in the aeration tanks, accurate flow splitting to each final clarifier is achieved, and we have a controlled wasting schedule from the [return activated sludge] pumps.”

Boyer describes the new SCADA as “the eyes and ears” of the plant and a valuable tool to help reduce the risk of compliance issues. The accuracy of automatic “smart” control improves performance of the process equipment and enables precise monitoring of information.

 

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