The Ameren Coffeen Power Station in Coffeen, Illinois needed to replace its aging water treatment system, but wanted one that could handle turbidity spikes and total organic carbon (TOC), silica and sodium levels in the lake water. The plant also wanted to minimize the amount of regeneration chemicals discharged to the lake. They needed a treatment system that was not only reliable, with maximum uptime, but one that would produce the required quality and quantity of water while reducing plant costs and maintenance time.
The Ameren Power Station chose a new, innovative, containerized system design from Siemens that used microfiltration (MF) and high-flow-rate reverse osmosis (RO) technology. Since the MF technology is 30 percent smaller than conventional treatment technology, the system could be housed in a container that fit into the power plant's limited space, and eliminated the need to build a separate building to house the equipment. MF was also 40 percent less expensive than conventional technology. The system's skid-mounted design allowed easy installation versus having to construct steel or concrete clarifiers on site, thus reducing the construction time. To meet the power station's need for treated water while the new system was being built, Siemens deployed a temporary mobile water treatment system to the site. This system included a mobile pretreatment trailer consisting of duo-media; two combo RO trailers, which contained multi-media filtration and RO; one mobile deionization (DI) trailer; and two skid-mounted FlexTrex® deionization vessels for polishing the product water after the DI trailer.
The long-term treatment system, which took six months to design and build, was started up in February 2009, replacing both the old treatment system and the temporary mobile system. In this 300-gpm system, lake water is first treated with sodium hypochlorite for disinfection, and then with four MEMCOR® XP pressurized membrane systems. The water is sent to a storage tank. After sodium bisulfite and anti-scalant injection, the water enters the first-pass RO system. The system also has the capability for sodium hydroxide to be injected into the water to convert carbon dioxide to bicarbonate for removal in the RO. A primary set of portable DI exchange vessels polishes the RO water, and a final set of portable DI exchange vessels further polishes the water to an even higher level of purity. Everything is tied together with a single controller via a remote I/O network.
During the six months the system has been operating, it has been reliable and has exceeded the product water specifications. The power plant has saved on operating costs by reducing chemical usage. The amount of chemicals discharged to the lake has been reduced by approximately 35 percent, and plant maintenance has been reduced by approximately 3,000 man-hours per year. The system is owned by Siemens and operated and maintained by personnel from the local Siemens' branch office. The quantity and quality of the water is guaranteed for the life of the contract.