Akara Mining Limited is the Thai subsidiary of Kingsgate Consolidated Limited. The company owns and operates the Chatree Gold Mine in central Thailand.
The Chatree site had already been running for 11 years using Wonderware's InTouch SCADA system but, due to expansion plans, a revision of these SCADA assets and their operation was on the mine's agenda.
Akara Mining chose engineering company Ausenco for the implementation of the expanded system. According to Ausenco senior electrical/ lead control systems engineer Martyn Hilbers, one of the reasons Akara decided to expand its process plant was due to rising gold prices.
"Since 2008 the world has been experiencing a financial turn down. Investors have been reverting back to the traditional safer commodities such as precious metals, and as result the gold price has gone up," he told PACE. Ausenco partnered with Wonderware Australia as a consultant on the Akara Mining project.
"The effective corporation between Wonderware and Ausenco raised the level of quality of the design and was a great contribution to the success of the project," said Hilbers.
The main emphasis for the project was on the communication failover strategy, intuitive operation and easy maintainability. It was crucial that the upgraded system would be maintainable by local personnel.
"Most of the mine sites are in remote locations and it takes more than 24 hours to travel to the site. The main reason is that when there is a problem resulting in down time, it literally costs gold when the plant stops," said Hilbers.
"It is therefore very important that people working at the mine site are capable of maintaining, trouble shooting and making changes to the system."
Graphics standard
According to Akara Mining maintenance and project manager, Wayne Cole, another important request was the implementation of Wonderware's ArchestrA HMI system, which needed to comply with the existing InTouch HMI graphic's standard, but at the same time use current industry practices and technologies.
"This expansion, revision and updating of our SCADA facilities has given us improved production effectiveness through reliable communications and provision for expansion without the need for repeated and costly engineering efforts in the future," Cole said.
Failover scripting versatility allows for future expansion of the system.
The project took approximately five months in 2011 during which the old and new systems were linked to one another and ran in parallel.
Historical information
The seven InTouch stations are connected to a GE Fanuc-based PLC network via a redundant GigaBit ring topology network, and monitor approximately 2000 I/Os.
All InTouch stations have access to historical information from the Wonderware Historian for analysis and reference purposes.
"ArchestrA's ease of scripting made our job easier and we were able to provide Chatree Mine with more useful functionality in a shorter time than would otherwise be possible," said Ausenco's Hilbers.
Though the project has been completed, the control system has been designed specifically with provisions for future expansion. The control system network backbone design offers the possibility to break the network and insert additional network nodes/cables without taking the system 'down'.
Also, the additional communication load capacity allows for a large number of additional PLCs and HMI stations.
Failover script
Because the legacy system ran on a single communication channel network, Chatree Mining was experiencing some latency as the inter-PLC data exchange and HMI values were not updated rapidly enough. The solution was a redundant GigaBit Ethernet network with redundant I/O servers.
Since the operating rooms are spread out over the site, there are four I/O servers providing communication channels between the PLCs and the HMI stations.
Improved network infrastructure and production monitoring.
The servers are connected via a dual Ethernet channel to the PLCs, allowing the HMI to connect to each PLC in four ways: Lan A via Server 1; Lan B via Server 1; Lan A via Server 2; and Lan B via Server 2.
This means there are four 'access names' or Wonderware communication channels that have to be monitored for the failover mechanism.
"Wonderware has an innate failover functionality, Enable Secondary Source, however this allows failover between two 'access names' where we had four on this project, so this was the challenge," said Hilbers.
"Whenever an access name is active it requires system resources and network bandwidth, so the second challenge was to reduce the amount of access names and the data exchange on these access names. I solved this by actually adding a fifth dynamic access name and making the other four static."
According to Hilbers, the script itself is very short and simple. Every time the failover script activates and changes the access name, or when a heartbeat on one of the communication channels is not detected, the operator is notified by an alarm.
Navigation
Another important feature built into the system is the navigation tabs: "If you read the tabs from the left to the right you will notice that it follows the process flow shown on the overview page [see figure below].
The operator has improved control over the mine's critical processes.
The overview page allows the operator to make a quick assessment of the health of the plant. If there is a fault or an alarm active, the outline (dotted rectangle) of the area with the fault/active alarm, will blink orange on the overview page," explained Hilbers.
"The operator can click on the orange blinking area on the overview page or on the tab to navigate to the process area overview.
"Something that cannot be seen on the screendump is that when the operator 'hovers' the mouse index over the tab, a tab drop-down menu becomes available in which the operator can choose the detail view of that area/tab.
"This make navigating very easy and helps the operator to find the cause of an alarm quick without having to 'drill down' and search through other pages to get to the desired page."
PLC programming
For the Chatree project, object oriented programming (OOP) was applied to the PLC program. According to Hilbers, this was highly efficient for the batch sequences used for the chemical processes involved with leaching gold.
"Batch sequences are more challenging and difficult to program compared to other logic. Batch sequences are designed by a process engineer and are conveyed to the control system engineer in a process control philosophy document.
The quality of this document and the cooperation between process engineer and control system engineer determines the quality of the programming work and subsequently the operational readiness, and commissioning time of the plant.
"As this is a gold process every additional commissioning day is lost revenue," Hilbers said. "The challenge of having a high level of operational readiness made us make the decision to let the process engineer program the batch sequences.
"So the challenge presented to me was to have the most difficult part of the software to be programmed by someone without any programming experience. On top of this challenge, the batch sequencer itself was fairly complex as it needed to have automated fault handling functionality and be able to be run manually as well as automatically.
"I solved this by creating a class for a single batch sequence step by combining step sequence functionality with state machine functionality.
"This piece of software would monitor the current, previous and succeeding step and execute generic functions based on the health, step and conditions of the batch sequence."