Air Bio (ABC) Efficient and reliable control of air-supply systems Answers for energy.
Thinking in systems the multiplier effect Siemens has decades of experience in turbocompressor technology and aeration know-how, with more than 6,000 units now in operation worldwide. The three integrated control loops The aeration process consists of three central control loops that when fully integrated and fine-tuned ensure smooth, efficient operation of the aeration system: Dissolved oxygen /ammonium flowcontrol Siemens provides complete air-supply systems for wastewater-treatment plants, thus ensuring effective integration of the aeration process with the other downstream processes in the plant. This makes it possible to achieve full end-to-end control, avoiding bottlenecks and boosting efficiency at every stage. The prime advantages of the system solutions include: Single-source responsibility System integration Greater overall efficiency Better control and smoother operation Avoiding interface issues Start-up and fine tuning Greater system reliability On-line support via modem (wireless or PSTN) Automatic pressure set-point control (based on the most open valve principle) Main-header pressure control Dissolved oxygen/ ammonium flowcontrol Most aeration systems are controlled on the basis of measurements of the dissolved oxygen in the aeration tanks. The settings of the air-flowcontrol valves are based on these measurements. It is possible to achieve considerable additional improvements in control of the aeration system by also including such parameters as ammonium control to determine the oxygen set-point. This results in a lower average air-flow and makes it possible to comply with both current and future environmental requirements worldwide. Automatic pressure set-point control To minimize power consumption, the header pressure is kept as low as possible by monitoring the control-valve positions. During peak loads, the header pressure is increased in order to provide maximum air-flow. Under part-load conditions, it is reduced to keep power consumption to a minimum. This enables continuous adjustment of the total delivered air-flow to match requirements exactly. An unlimited range of different processes can also be linked to the main air header, thus facilitating control of many additional sub-processes. Main-header pressure control The aeration tanks are supplied with airflow through a main-air header. This is kept at a constant pressure by regulating the compressors between 40 100% capacity. The system is designed to match different types of aeration processes to comply with client requirements.
The right choices Increasing demands for quality and tougher legislation on environmental issues create needs for the best possible control of the aeration process. Experience from a large number of wastewater-treatment plants has shown that the right choices for control systems and solutions rapidly give full pay-back in terms of energy savings and ensure full compliance with legal requirements regarding the effluent. With the rapidly accelerating automation of wastewater-treatment plants, choosing the most appropriate technology is no longer sufficient. It is now increasingly important to identify the overall configuration that provides maximum efficiency, via integrated system design. ABC Panel The Siemens ABC Panel is designed to ensure the efficient, reliable control and monitoring of the complete air supply system automatically and/or remotely, if required. The ABC system uses a standard Programmable Logic ler (PLC), running customized, job-specific software, to monitor and control the complete air-supply system for aeration and compressors as one highly efficient, integrated system. A standardized Profibus DP master interface is fitted for communicating with multiple Local Panels (LCPs).
FLOW Where several aeration cells are automated to provide varying air-flow, flowcontrollers can be added to control each air-flow control valve with a fine-tuning sub-loop, enabling set-point adjustment via the dissolved oxygen level. A system that monitors multiple process variables must be designed and implemented to ensure reliable, long-term operation. The most basic solution involves control of the air-flowcontrol valve directly via the oxygen levels, using a controller. This ensures that the biological processes have a constant level of dissolved oxygen. Another option is to add a flowcontroller to the conventional oxygen-control loop. The flowcontroller can also be used to limit the maximum and minimum air-flow. Power consumption 400 300 200 100 Cascade control The graph illustrates the optimized air-flow, with three on-line Siemens compressors. Together, these provide a seamless, consistent air-flow, ranging from one unit at minimum capacity to all three compressors at maximum capacity, meeting needs for a wide variety of plant air-flows and wide-ranging system oxygen demands. The basic oxygen control can be improved by adding an ammonium controller. This increases and decreases the oxygen set-point when needed, reduces the average air-flow (and energy consumption), and ensures optimum nitrogen removal. FLOW The ideal air-supply system features full ammonium and dissolved-oxygen control in order to give precise and stable operation. 0 0 100 200 300 Capacity
Analysis prior to design Each wastewater treatment plant operates differently, with individual characteristics and requirements that result in widely differing operating cycles. Prior to any design work, Siemens experts therefore carefully investigate and analyse the overall operating philosophy behind the hourly, weekly and monthly running of the existing plant. Together with an evaluation of aeration efficiency, this enables Siemens to provide the system designs best suited to system requirements. This covers such parameters as the opening times of flowcontrol valves, and all items that play a crucial role in ensuring minimum downtime and highest efficiency. Experience in action When Siemens deals with your air flow requirements both current and future you benefit from the total sum of our experience from more than 6,000 single-stage turbocompressors throughout the world. We know that it is essential to focus on the correct dimensioning of the aeration system as a whole in order to avoid inefficient operation and unnecessary costs. Siemens is uniquely capable of designing aeration systems that exactly match your present needs, while also taking future requirements into consideration. We spend time with your consultants and plant operators to understand your needs in full and to integrate our know-how with yours in order to find the most effective form of control. The right solution yields considerable savings up front, as well as greater efficiency in all the other processes that interface with aeration. Benefits and features An automated air-supply system assures the lowest system-operating pressure, thereby keeping power consumption to the minimum. Continuous monitoring of process variables such as dissolved oxygen or ammonium ensures the lowest airflow delivery, optimizing the aeration process and minimizing power consumption. Precise, continuous airflowcontrol enables maximization of the more complex nitrification/ denitrification process, as required in the most modern aeration processes. Air-supply system automation eliminates the need for direct operator intervention and optimizes process control, ensuring superior effluent quality.
Published by and copyright 2009: Siemens AG Energy Sector Freyeslebenstrasse 1 91058 Erlangen, Germany Siemens AG Energy Sector Oil & Gas Division Wolfgang-Reuter-Platz 47053 Duisburg, Germany Siemens Energy Inc. 10730 Telge Road Houston, Texas 77095, USA Siemens Turbomachinery Equipment A/S Allégade 2 3000 Helsingør, Denmark Phone +45 49 21 14 00 For more information, please contact our Customer Support Center. Phone: +49 180 524 70 00 Fax: +49 180 524 24 71 (Charges depending on provider) E-mail: support.energy@siemens.com Oil & Gas Division Order No. E50001-G420-A115-X-4A00 Printed in Germany Dispo 34806, c4bs No. 7423 WS 07092. Printed on elementary chlorine-free bleached paper. All rights reserved. Trademarks mentioned in this document are the property of Siemens AG, its affiliates, or their respective owners. Subject to change without prior notice. The information in this document contains general descriptions of the technical options available, which may not apply in all cases. The required technical options should therefore be specified in the contract. www.siemens.dk/turbomachinery