Water Treatment Plant Expansion
A control strategy was developed for the 1.865 MGD trains with constant speed pumps, when raw water wells have different capacities, so that timing of the motorized valves excludes pressure peaks and compensates hydraulic issues.
All control systems communicate via local Ethernet network and are also bridged to the County network for remote data access and control.
During the startup process, a close cooperation with the participants has resulted in a quick troubleshooting and problem solving.
Some original ideas have resulted in the control strategy improvement.
- Design PLC control software and SCADA system for plant operations to enable fully automatic, semi-automatic and full manual control of the system.
- Design PLC control software on Allen Bradley RSLogix 5000 for automated plant start up to include pretreatment systems including sand separation, acid addition, and cartridge filtration; membrane treatment including feedwater pumping, nanofiltration treatment, and associated membrane cleaning facilities; post-treatment including degasification, off gas odor control, blended water clearwell storage, disinfection, chemical addition for water stabilization, carbon dioxide pH regulation and transfer pumping.
- Designed SCADA screens on Wonderware 9.5 platform with DASABCIP communication driver.
- Provided reporting tools with Wonderware's Active Factory reporting tool to periodically generate reports in Excel and PDF format.
- Included in RO Plant control:
- Control for the five raw water wells of a different capacity
- Raw water analysis and pretreatment chemical dosing
- The five two-stage RO trains with dedicated constant speed feed pumps
- Post treatment control - scrubbers, clearwell and transfer pumps
- Post treatment chemical dosing and analysis
Project design completed in 02, 2009
Total Project Cost: $14,000,000.00
In the new RO plant, which was a part of expansion, the RO equipment was new as a part of design, but the wells were old. During the design phase, the hydraulic characteristics of the wells were not taken into the consideration, even though the Owner brought up that issue few times.
During the startup the hydraulic problems from the wells emerged, rising the pressure in the plant supply pipes. Since the piping was old and unreliable, the pressure has been limited to 50 psi, making the plant startup impossible without risk of pipe breaking. Another obstacle was the fact that raw water wells are of the different capacity. It was not possible to auto start without carefully bringing up the wells and keeping pressure below the safe limit.
The ADS Engineering brought up a solution in which operator selects wells, and the matrix that matches capacities of the wells and the motorized valves timing, carefully brings up the pressure in the supply piping, and keeping it below the danger limit.
During the whole design process and at the beginning of the start up, the Owner was not happy with start up progress and design. After the ADS programming, that was not originally part of the control strategy, and implementation of the matrix to provide smooth startup of the plant, the Owner changed his attitude and expressed gratitude during the rest of the startup.