Optimizing Efficient Operation and Dispatch of Osage Plant Turbines
A major part of the new FERC license for Ameren Missouri’s Osage Project at Missouri’s Lake of the Ozarks, received in 2007, included new environmental operating restrictions for such things as increased minimum flows, increased requirements for dissolved oxygen (DO) and Total Dissolved Gas (TDG), and several restrictions on discharge flow rates following flood flows, etc.
The Osage Project successfully utilized several proven technologies along with considerable innovative control techniques to greatly increase generation capability by 20.5% while meeting all new environmental requirements. By the end of 2010, the Plant completed a multi-year project which replaced 4 of its 8 main turbines and both house turbine/generator sets to improve DO/TDG discharge and to improve efficiency. The most significant new accomplishment included the development and implementation of a totally new and innovative generation dispatch algorithm in the Supervisory Control and Data Acquisition (SCADA) system. This SCADA system runs both the air flow and generation dispatch algorithms to optimize the plant environmental discharge parameters while also optimizing plant efficiency by controlling the way each unit is vented and operated.
The Osage Plant was completed in 1931 and was originally equipped with six 25 MW main units and two 2 MW house units. Two additional main units were added to the plant in 1953. All of the original turbines were Allis-Chalmers vertical Francis-type turbines. The licensed capacity of the plant was 176.2 MW. In 2002 two of the original main units were upgraded with new American Hydro runners capable of discharge aeration and 32 MW of generation.
The new minimum flow exceeds the capacity of the 2 old house units and therefore would require operating main units at very inefficient points for a considerable amount of time. The new DO and TDG requirements would necessitate adding a considerable amount of air to the water passage. With the old turbines and venting configurations, this would have a significant impact on unit efficiency.
Ameren Missouri thus embarked on a process of evaluating equipment, processes, and operational parameters to determine the best way to operate under the new rules. The overall goals of the project were to meet environmental compliance parameters required by the new FERC license while optimizing plant efficiency. This was extremely difficult to define in an engineering scope for an automated system because so many variables had to be considered at the same time. The system would be required to quickly respond and change plant operation each time any one of the variables changed.
The most significant challenge was to design a control system that would take any plant load, at any given headwater and tailwater elevation, and select the most efficient way to operate each of the plant’s eight main units and two house units so that the combined overall plant efficiency is maximized while at the same time meeting all of the regulatory environmental requirements.
In order to meet the DO criteria, it was necessary to install some kind of new equipment. Several options were extensively evaluated. All options would be expensive and several were determined to be capable of obtaining the DO criteria. The option selected was to install four new main unit runners that had better capabilities for air mixing with water.
In order to meet the new minimum flow requirements without running large units at inefficient points, it was necessary to upgrade the house units with higher capacity runners.
The most innovative improvement and the one responsible for the most efficiency improvement is the new Supervisory Control and Data Acquisition (SCADA) system. The Advanced Features Control System (AFCS)was also programmed to optimize turbine venting operation to reduce efficiency loss and maximize water quality. The original control system only provided for vents to be fully open or fully closed, but the AFCS uses an algorithm that determines the optimum air flow for each unit and automatically adjusts pneumatically controlled vent valve positioners.
With the installation of the new main and house units, the Osage Plant rating has increased from 176.2 MW to 242 MW. By utilizing all new control technologies to go along with the turbine upgrades that were needed for environmental compliance, Ameren Missouri was able to greatly improve generation capabilities by over 20%, while meeting the new environmental standards.
“Most people who work in the hydro industry have a deep rooted interest in our environment and see the beneficial use of producing power with clean renewable water. I am excited about the efficiency improvements made in the Osage control system and with the new turbines, because it allows us to produce more energy with the same amount of water. Additionally, it helps Ameren Missouri keep rates lower while producing more revenue for the company in the Midwest Independent System Operator (MISO) ancillary service market.”- Philip M. Thompson, Superintendent, Osage Plant, Ameren Missouri