Rockwell Automation Integrated Architecture™
Through expansion of the installation, the drinking water treatment station (ETAP) at LLobregat has increased its production from 200,000 to 345,000m3/day.
The project, co-financed by the cohesion fund of the European Union, is designed to improve the treatment line, as water from the lower branch of the River Llobregat presents salinity and contamination (Trihalomethanes) problems, which make the purification process difficult. For this reason, ATLL needed to put a desalination plant into operation, based on a reversible electrodialysis system (EDR), which allow improvements to be made to the chemical and organoleptic properties (taste and smell) of the water.
Another challenge was reaching a greater level of plant automation. All the control and site components must be monitored from a central position. The purpose of this is to increase the 100,000 existing signals with 30,000 new signals (distributed over an area of 2,000km2), monitored in real time from the control room which regulates the operation of the regional distribution network. Finally, the high availability of the installation is also a legal issue – it is unacceptable to stop production of drinking water, even for a few hours. This factor implies that the plant process is structured in parallel and that a reliable, flexible, and scalable control solution is found.
Working jointly with ATLL, Rockwell Automation and EBE Associates developed an advanced automation solution for the new plant based on the Rockwell Automation Integrated Architecture solution. The control solution integrates 11 Allen-Bradley ControlLogix® PACs; nine of which are located in the EDR, subdivided into nine totally independent production lines. This allows engineers to only need to stop one-ninth of the plant for any reason. Each of these PACs is connected to an Allen-Bradley PanelView™ Plus 1250 operator panel, allowing the local monitoring and manipulation of each of the nine lines. The I/O is divided into four remote Allen-Bradley ControlLogix frames and the decentralised I/O on site is configured using three frames of FLEX™ I/O cards.
All the controllers, operator panels and decentralised inputs and outputs are connected using a redundant Allen-Bradley ControlNet network, which helps make sure high availability of data in provided in any situation. In order to act on the site valves, there are DeviceNet networks for each of the nine production lines. In summary, the desalination plant includes a total of nine redundant Allen-Bradley ControlNet networks, 18 DeviceNet networks and a total of 10,200 signals, 1,000 of which are analogue for processing.
The other two redundant Allen-Bradley ControlLogix PACs are responsible for managing the pump station, the lime beds, the control of the addition of chemicals and auxiliary components of the installation. The inputs and outputs are distributed on site using Flex I/O cards and joined through a redundant Allen-Bradley ControlNet network. All the controllers are joined together at the central control room using an EtherNet/IP network on fibre optic ring topology, which configures the ideal means for displaying any parameter from any device in real time.
The great versatility of the Integrated Architecture solution combines Logix multidiscipline controllers platform, NetLinx open networks architecture, View display platform and FactoryTalk data and information services. This provides the highest level of reliability, flexibility and scalability necessary for meeting the objectives stated from the start of the project.
On-Line Condition Monitoring
ATLL has experience in the use of predictive maintenance systems based on vibration readings in its machines, through the use of portable data collectors. The advantage in this case, is that with a reduced investment in the acquisition of instrumentation and software, a large number of machines in one plant can be measured. The problem, on the other hand, is the assumed cost of a full team trained in these techniques, and the lack of information in real time of the mechanical condition of equipment considered critical for the process.
One of the most critical installations in the plant is the water intake. This intake, initially made up of four vertical pumps, has now been increased to eight. After an extensive analysis of the different alternatives on the market relating to online monitoring of vibration, temperature and critical parameters, ATLL opted for a solution from Rockwell Automation based on the XM family. The reasons which brought them to this decision are listed below.
In installations where drives are used to regulate motor speed, savings in energy consumption have been achieved of up to 50% when centrifugal loads, such as water, are regulated with pumps working between 100 and 80% of their capacity. This means that the machines used must have a very accurate speed control for regulating the flow, and from a mechanical point of view, certain precautions when operating and maintaining them. Thanks to the tachometer input, which the series Allen-Bradley XM120 vibration control devices have, it is possible to correlate the vibration level and operating speed directly. This allows the vibration value to be controlled permanently as a multiple of the speed of rotation (1x, 2x, 3x, etc.). This data, as well as the phase reading, is key when starting and stopping the pumps, and under normal operating conditions, as they allow the critical and resonance frequencies of the system assembly to be ascertained.