SYDNEY Water is the largest water utility in Australia. It supplies water and treats sewage for the four million residents of Sydney, the Illawarra and the Blue Mountains.
One of the facilities that Sydney Water Corporation (SWC) operates is the Malabar Sewage Treatment Plant (STP). Located on the coast in Sydney’s southern suburbs, the plant is responsible for processing nearly half of the city’s sewage.
According to Craig Taylor, asset management specialist at Sydney Water, normal operations at Malabar STP involve sending the primary treated effluent to a deep-water ocean outfall, roughly four kilometres from the shore. Reliable operation of five raw sewage pumps (RSPs) and three centrifuges are critical to the business.
Since protection of the environment is a driving priority, Sydney Water is continuously seeking effective means of minimising the risk of process failure. In 2001, Sydney Water contracted Rockwell Automation to implement an advanced condition-based monitoring solution at Malabar STP. The plant now benefits from real-time feedback of the status of its key machinery systems. Not only does this go a long way to minimising the risk of pollution, but it is also improving the effectiveness of maintenance planning and reliable machine operation.
THE Malabar STP is characterised by its primary treatment process, capable of handling the equivalent waste of 1.8 million people.
Sewage is delivered by the sewer mains to the site, where it is first subjected to screening and grit removal (to filter out sand and solid matter such as paper and plastic). The RSPs then lift the flow into chemically assisted sedimentation tanks, which remove smaller particles by “flocculation”. The final treated wastewater then gravitates to the ocean outfall.
Taylor emphasises that Malabar’s RSPs are integral to the process: “The pumps are what keep the whole of the facility running. They’re large two-storey pumps, with one-megawatt motors, and they drive the sewage through the plant.”
Meanwhile, the “sludge” captured in the sedimentation tanks is further processed in anaerobic digesters. In the digester the solids content of the sludge is reduced and methane is produced.
The methane then fuels co-generation equipment, which produce approximately 65 percent of the total electrical needs of the site. Sludge from the digesters is then dewatered and processed into biosolids that is used to condition soil for agriculture and land rehabilitation.
Taylor states that the centrifuges, which dewater the digested sludge, are also critical to the Malabar plant’s operation.
PREVIOUSLY, condition monitoring of the facility’s rotating plant was carried out manually on a periodic basis.
Once a month, Sydney Water staff would connect accelerometers to the rotating machinery - namely, the pumps and centrifuges - as they were running, and would record vibration data using portable vibration analysers/data collectors. This information was then downloaded onto the Enshare plant asset management system, which is used to track, trend and analyse the health of mechanical and electrical assets.
The monitoring was undertaken monthly. Should problems be identified, the information was used to manually raise requests for maintenance - from greasing a bearing to replacing a pump - using Sydney Water’s computerised maintenance management system (CMMS), Maximo.
Taylor remarks that when heavy rains occur in the Sydney area, the flows into the plant can be almost three times normal capacity, or 1200 ML/day. Where normally two pumps would have sufficed to handle the load, under these extreme circumstances, four of the five pumps are required. It is at this point that Sydney Water becomes very dependent on the quality of its asset health data - failure of an RSP is to be avoided at all costs.
Monitoring against risk
TO provide greater warning of any potential machinery failure, Sydney Water embarked on a project to implement an on-line condition surveillance system at Malabar STP. In 2002, Sydney Water maintenance engineer Nandu Marathe and Rockwell Automation carried out an initial conceptual trial for 45 days.
The trial involved the installation of fixed accelerometers, along with direct connections to the corporation’s Enshare plant asset management system and Maximo. The purpose was to gauge whether Sydney Water could not only take steps to mitigate against the risk of pump failure at Malabar, but also test the concept of on-line condition monitoring as a maintenance tool.
Adem Adil, Rockwell Automation’s solutions consultant, explains that Rockwell Automation has a long history of providing tailor-made asset management systems, and provided the turn-key condition-based monitoring solution, including system design, project management and commissioning.
The core elements of the solution were from Rockwell Automation’s Entek product family, including Enwatch surveillance monitors and the Enshare-Maximo Gateway.
According to Adil, the reason for using the Entek-based software solution was to keep implementation costs to a minimum. “The key differentiator with the Enwatch was the ability to gather vibration data and store this into the same Enshare software that Sydney Water know, and have been using, for years,” he said.
Commenced in April 2003, the project was carried out over four months and in two stages: software installation and configuration, and electrical hardware installation at the site. Accelerometers were connected to all five RSPs and all three centrifuges at Malabar. Enwatch surveillance monitors were then provided to automate data collection.
Links between the central Malabar control room network server and the running equipment was achieved through the use of Ethernet hubs and fibre-optic cable for the pumps, and a wireless link to the more distant centrifuges.
“When we put together the proposal, we looked at the costs of running 250 metres of fibre optic over to the centrifuges,” said Adil, who was responsible for developing the project scope for Sydney Water. “The wireless system proved to be more cost-effective and a simpler option - it amounted to a substantial cost-saving.”
To pass the monitoring information from the Malabar control room to Sydney Water’s Enshare asset management database server (located 40 minutes drive away in the city), Rockwell Automation installed software on the “unload PC” transfer station in Malabar’s operations support office. Responsible for storing the collected vibration data, the unload PC was configured to send vibration data, via the corporate WAN, to the live Enshare database every ten minutes.
“Instead of taking data once a month under the previous regime, we now have the data coming into the Enshare system on a 10 minute rotation. If there’s an alarm, then we’ll store that data, otherwise we’ll keep one reading every six hours,” said Adil.
Gateway to maintenance
BRINGING the information to the plant operators, Rockwell Automation implemented a user-friendly interface, known as the Entek “PlantLink”.
Essentially the interface provides a graphical representation of the health of all machinery being monitored online. Where equipment is running properly, a green visual indicator is used; by contrast, the first and second alarm levels are represented by orange and red respectively.
“We can actually set it up as a screen saver in the production offices,” said Taylor. “If they see green dots, they know everything is fine. If they see a different colour, then they know something is up and they can investigate further.”
The final step, Adil explains, was to create a direct link between the Enshare system and Sydney Water’s Maximo maintenance management system, by installing an Enshare-Maximo Gateway. While the gateway is offered as a standard software product, Rockwell Automation provided a significant amount of site engineering to ensure that the solution was suitably customised to meet Sydney Water’s needs.
Adil reveals the advantage offered by the gateway: “It’s a true bi-directional linkage between Enshare and Maximo. The linkage allows the people who are analysing the health of the machine to streamline any requests with the Maximo system. It also allows the guys who are analysing the machine to look at the asset’s maintenance history. For example, if a pump item was replaced with a spare unit, it is possible to determine quickly whether there is a problem with the spare now in service.”
A CERTIFICATE of practical completion of the project was granted to Rockwell Automation on August 2003.
The most obvious advantage is the greater visibility of the health of the rotating machines - both RSPs and centrifuges - and now, regular analysis is performed on-line. “It’s providing the more selective data we were expecting,” said Taylor, referring especially to the readings now taken automatically during the peak periods each evening.
Taylor also suggests that the greatly reduced time loop is very significant. “By having the online monitoring 24 hours a day, 365 days a year, we are able to detect changes that may be a trigger for a potential failure.” In this way, Sydney Water has far greater confidence that its Malabar plant will operate as required, without major failure or subsequent downtime for monitored equipment.
The new online system also has important implications for the way maintenance is conducted. “The Maximo-Entek gateway is the final link in the chain. It lets us create a reactive work order in our Maximo based on the online monitoring,” commented Taylor. “Basically, we are able to do more of our reactive maintenance on a planned basis.”
Such maintenance issues are far from trivial. Over a 12 month period, Taylor estimates that the greater effectiveness in maintenance planning may translate into a 10 to 15 percent overall saving in maintenance costs for these units.
Taylor points out that the Malabar trial also has wider ramifications for Sydney Water. In the long term, it will prove the viability of the online condition-based monitoring concept. By reducing the risk to the environment and public health through cleaner waterways, the beneficiaries will be the vast majority of the corporation’s owners: the four million residents of Australia’s “Emerald City”.