Anyone who owns an aquarium knows how difficult it is to maintain water quality at a consistently high level. The principle “the larger the tank, the more stable the water values,” depends on the number and size of the tank’s inhabitants. When those inhabitants are dolphins, as at the Nuremberg Zoo, located in the Nuremberg Reichswald southeast of Nuremberg, Germany, the water treatment requirements are particularly challenging.
The Nuremberg Zoo’s dolphin lagoon offers large outdoor pools that provide the most space and variety of any dolphinarium in Europe. A new water treatment plant with state-of-the-art pneumatic automation technology is improving the animals’ living conditions.
Cleaner Than a Swimming Pool
“The water in the Nuremberg Zoo dolphin lagoon is cleaner than that of any swimming pool,” said Klaus Held of Sixt, Heiß & Partner, an engineering firm specializing in complex water treatment installations. “Saltwater poses much greater challenges than the chlorinated freshwater used in swimming pools in terms of the durability and corrosion resistance of process valves and actuators.”
The Nuremberg Zoo has its own water treatment plant, which treats 500,000 gal of freshwater every hour. This enormous volume of water is essential for the marine mammals. The plant also processes animal excrement and dead plants. To ensure that temperatures in the outdoor pools never fall below 62°F, even in cold weather, the water is preheated to 86°F. If outdoor air temperatures are below 23°F, an air dome prevents two of the pools from becoming too cold.
Reducing Noise Stress
The pneumatics used in the new system significantly reduce noise pollution for the dolphins. “The electric drives that we used before transmitted noise through the piping to the pools. This meant constant noise stress for the dolphins, which has been virtually eliminated with the pneumatic actuators from Festo,” Held said.
The lagoon water runs through a total of six closed multi-layer filters, which are flushed out at regular intervals. To complete this scrub process, the inlet and outlet are closed and the cleaning air and rinsing water are opened. The contaminants exit the system via a sludge discharge and the water filters then work at full capacity again. Festo pneumatic actuators open and close butterfly valves and fittings. They are controlled using a total of seven ready-to-install control cabinets equipped with sturdy valve terminals, type CPX-VTSA, at the control level.
Pneumatic Control Circuits
Pneumatic control circuits are cost-efficient and thus an effective way of supporting process optimization. To help explain some of the basics of pneumatic systems in water treatment, below are some of the key details of pneumatic position control. As a rule of thumb, five to eight process valves typically are required to control a fixed-bed filter. Of these, up to three are operated in closed-loop control to manage flow rates, while the others are operated in open/close mode.
Level 1: Economical valve positioner for maintaining position. The first level in the automation of water treatment plants is the use of conventional external positioners, such as the Festo CMSX. In closed-loop mode, this positioner continuously compares the set point signal with the actual position of the quarter-turn actuator. Any deviations thus can be immediately detected and corrected. The positioner’s micro-controller continuously displays the current position of the process valve. In the event of a power failure, the process valve can be brought to a previously specified safety position, thus minimizing otherwise incalculable process risks.
Level 2: Decentralized controller with integrated valve terminal and I/O concept. The number of fixed-bed filters can range from two in small, local water treatment plants to 48 or more in large municipal water treatment plants. Any automation concept thus can be decentralized and flexible, and use a combination of pneumatic and electrical components. The Festo CPX decentralized automation platform with integrated pneumatic valve terminal MPA and embedded controller CPX-CEC is one example of a suitable system for these applications.
The CPX-CEC controls the pneumatically actuated process valves locally. It processes the electrical field signals from the end-position switches, sensor boxes and measuring devices; controls the filtration circuit; and establishes the connection to the process management level. Each fixed-bed filter is assigned its own control cabinet in which the decentralized automation platform is integrated with a control panel. A manual control panel enables the system to be operated from the control cabinet even in the event of equipment failure or during a power outage.
The CPX automation platform in the control cabinet with integrated programmable logic controller offers several advantages:
- A decentralized control cabinet and local pneumatic control of process valves lower capital costs and offer faster actuation of process valves.
- Mounting a control cabinet and centralized solenoid valve near the process actuators results in more consistent actuation of the process valves and safer operation.
- Process valves can be adjusted even where there is no electrical power thanks to manual operation via the pneumatic solenoids. Local control is possible even if pneumatic pressure is lost.
- Plant personnel no longer have to physically manipulate the process valves, as changes to the closed-loop control parameters now can be made directly at the local control cabinet.
Level 3: Linear actuator with closed-loop control. Level 3 is defined by integrating the closed-loop control function into the actuator itself. This is because external attachments for closed-loop control frequently cause problems: Lever systems often need to be adjusted, aggressive environmental conditions lead to corrosion, and dust deposits cause wear of moving parts. Furthermore, externally mounted attachments are susceptible to damage during installation and operation.
By contrast, actuators such as Festo’s DFPI Series include features like integration of all system components required for closed-loop control in the housing, which carries up to an IP69k rating. The cylinder, displacement encoder, valve block and positioner are safely accommodated in the housing and offer compact dimensions and robustness for use in outdoor systems.
Another advantage is that compressed air is easy to store. This means that energy reserves are always available in the event of a power failure so that it is still possible to carry out several gate valve operations or advance the gate valve to a defined position.
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