- Modular PLC-based system with customer specific configuration and control cabinet with graphic display
- supports local control, from simple constant airflow to complex load-based DO control
- for indoor and outdoor installation
The control cabinet is suitable for indoor and outdoor installation; the operator interface is a 7 inch touch screen display with plant specific screens and menus.
The complete flexibility and intuitive operation of this open system is its outstanding feature. It enables easy adaptation to system requirements - no “black box” that creates uncertainty - but rather standardized modules based on control algorithms that are easy and clear for any control loop and that have been used successfully around the world for many years. All modules are mounted on top hat (DIN) rails and can be changed easily by the operator.
Up to 10 control loops can be implemented in a control cabinet. An unlimited number of control cabinets can be combined so that smaller systems and larger wastewater treatment plants can use the same standardized and thus cost-effective modules. Each control loop has its own processor with software that is configured for the required tasks and works completely independently. This creates maximum operating security and flexibility. Therefore, cost-effective fine-tuning of control parameters for each individual control loop via remote access is also possible.
The operator can change the control parameters on-site or remotely at any time. Up to 40 parameters are available for the fine-tuning of a system. All common interfaces are available. The freely-expandable number of inputs and outputs and data transmission via bus systems open up possibilities for data acquisition and evaluation for more sophisticated process monitoring and optimization. Security updates can be installed remotely. The software modules also offer an automatic mode for the calculation of correction factors for operation, plausibility queries, and thereby offer greatest possible protection against manipulation. The modular structure allows later reprogramming and remote download of customer changes. All parameters can be set via remote access and alarms can be tracked (service). Transmission of standardized reports can be activated in order to rapidly detect process trends in the wastewater treatment system.
The process control system normally only provides a DO set point (which can also be calculated by the flexcontrol based on ammonium concentration). In the event of a DO error signal, the system calculates the new control valve position (stroke), and the valve is accurately repositioned in a single step. This reduces switching frequency compared to conventional step-by-step positioning, reducing premature wear-and-tear of the actuator and valve.
If an airflow meter fails, a substitute value is calculated based on the valve position.
Redundant process parameters such as ammonium or nitrate concentration can be measured and included in the control algorithm, allowing process disturbances or probe failures to be detected immediately. Only functioning probes are used for the aeration demand calculations.
Additional supervisory functions are a standard feature and can be activated at the request of the customer. In the case of an alarm, the control valve automatically moves into a safety position to ensure adequate airflow at all times.
Constant pressure control - variable pressure control - air distribution control
With constant pressure control, the individual valves provide the required aeration air from the constant pressure header to the diffuser grids independently of one another. The blowers are controlled to maintain a constant pressure. In partial load operation, the required air volume and thus the system pressure drop (pipeline and diffuser resistances) are lower, and the excess pressure must be dissipated by the control valves.
More sensible than throttling the air supply via the valves, however, is the variable adjustment of the blower pressure to the specific air requirement. For this purpose, the VACOMASS® econtrol monitors the actual operating conditions of the control valves and determines the required pressure level to ensure that just enough air is supplied for the entire system. By reducing the pressure, the power consumption is also reduced. With VACOMASS® econtrol, efficient system operation is ensured.
Alternatively, air distribution control can be used. In contrast to pressure-based control, where the required pressure in the header must be kept constant and the airflow to the diffusers is controlled by the control valve position, with air distribution control a demand-based air quantity is requested by the blower management.
Detailed timing information about the switching of blowers can be incorporated into the control algorithms so that the air supply is kept as constant as possible during blower transitions and the danger of surging of turbo compressors can largely be avoided.