Using NI LabVIEW and Compact FieldPoint to Improve Efficiency of a Mass-Controlled Train Loading System

Author(s):
Anthony Pruiti BE (Hons) PhD - Meridian Engineers

Industry:
Basic Materials - Steel/ Lumber/ Construction

Products:
Compact FieldPoint, FieldPoint, LabVIEW Datalogging and Supervisory Control Module, PXI/CompactPCI, LabVIEW

The Challenge:
Loading wagons to a specified target accurately at a BHP Billiton iron-ore train loading facility near Newman in Western Australia.

The Solution:
Using Meridian Engineers’ measurement and control system, developed with National Instruments software and hardware, to improve the train loading accuracy substantially.

Reducing Wagon Load Variability to Meet Accuracy Requirements
We at Meridian Engineers were contracted by BHP Billiton. The iron-ore train loading facility at BHP Billiton’s Ore Body 25 (OB25) mine site near Newman in Western Australia had not satisfied its accuracy requirements since commissioning. The OB25 facility was designed to load 10,000-ton iron-ore trains in three hours with a standard deviation in wagon loads of better than 3 tons. Other BHP Billiton train loading sites achieved this specification with very similar hardware. However, at OB25, the wagon load standard deviation was around 6 tons, requiring average wagon loads to be kept down to approximately 110 tons. The problem differentiating OB25 from other train loading sites was that the iron-ore loaded at OB25 had an SG that could vary from 2 to 3 during the loading of a single wagon. At other sites, the iron-ore SG remains relatively constant for the entire trainload. Our solution was to convert the OB25 train loading facility from a volumetric loading system to a mass-loading system.

Converting to a Mass-Controlled Loading System
For volumetric loading, the control system opens and closes the loading chute at set wagon positions and maintains a constant train speed. This provides a reasonably constant volume of ore in each wagon, but can give high variations in wagon load if the product SG varies. The mass-controlled system monitors the weight discharged into the wagon in real time and closes the loading chute when the system achieves the target load. It is independent of product SG changes.

Meridian Engineers System - Key Components
Key inputs to the system include the bin weight monitoring, bin inflow monitoring, wagon ID, incoming wagon weight, wagon position, and outgoing wagon weight.

Bin Weighing System
We developed an accurate "bolt on" weighing system for column-supported bins, consisting of our bolt on modules an NI Compact FieldPoint controller and an embedded LabVIEW Real-Time software control program. Using these products, we created a user interface with specifications to suit our client’s requirements.

Train Weighing System that Easily Interfaces with Other Systems
BHP Billiton preloads the trains entering the OB25 loading facility to about 50 percent capacity. We needed to weigh the wagons prior to final loading to determine the amount of preload in each wagon, and therefore the required finishing load. We installed an in-motion train weighbridge to meet this requirement. Our Meridian in-motion train weighbridge is trade certified to OIML R-106 and includes an NI SCXI strain amplifier system, an NI PXI embedded controller system, and an embedded LabVIEW Real-Time software control program. It provides easy interfacing with other systems

Belt Weighing System
OB25 is typical of train loading facilities in that a feed conveyor continually replenishes the train-loading bin while the train is loaded. We needed continuous knowledge of the loading bin weight, together with the bin feed rate, to determine the mass removed from the bin for each wagon in real-time. Therefore, we required a belt weightometer of accuracy better than 0.5 percent for the performance of the system.

Customized Software Application
We developed a customized software application using NI LabVIEW Datalogging and Supervisory Control Module to process the information from the various system components and control the train loading system. A centralized MasterPC running the control software has inputs from the bin weighing system (networked to the cFP2020 RT module), the in-motion train weighbridges (networked to the PXI-8146RT controllers) and the belt weightometer (networked to the cFP-2020 RT module). We used photocells installed under the loading bin (via digital inputs to the cFP-2020) to determine the wagon number and position of the wagon under the loading chute. We used a vision-based train velocity system to provide continuous train velocity (via Analog input to the cFP 2020).

The system sends outputs to the PLCs through a digital output module connected to the cFP-2020 to request opening and closing of the loading chute. The PLCs return information to the MasterPC through digital inputs to the cFP-2020 on the status of the loading chute such as open, closed, opening, closing. The entire system has access to the Internet through a permanent dial-up connection.

We selected LabVIEW Datalogging and Supervisory Control as the software platform because it provided seamless integration with all the necessary hardware and facilitated the rapid development of customized graphical user interfaces that plant operators could immediately associate with their plant. We developed sophisticated GUIs with LabVIEW to minimize plant operator training on the new system.

Another benefit of the LabVIEW system was the ease of incorporation of complex dependency relationships into the measurement quantities. For example, the in-motion train weighbridges have complex dependencies on rail temperature and train speed for which we must compensate. The bin weighing system also has complex temperature dependencies and vibration sensitivities that we must filter or compensate for. LabVIEW made these tasks considerably easier than other platforms.

With the main operator interface screen, the operator can intuitively determine the:

• Number of the wagon approaching the loading bin
• Number of the wagon under the loading bin
• Amount of preload in the wagon
• Required remaining load
• Instantaneous load in the wagon
• Final wagon load and load eccentricity
• Current contents of the loading bin
• Current feed rate into the loading bin
• Amount loaded into the train so far
  
  

An Increase in Wagon Loads, a Decrease in Expenses
Since the installation in August 2002, BHP Billiton has increased its mean wagon loads by approximately 10 tons, and the standard deviation of wagon loads has reduced by tons. These improvements represent large savings to the BHP Billiton rail operations. The average rake length at OB25 is 104 wagons. The round trip from the mine-site to the port and back is some 800km. On average, BHP Billiton delivers an extra 1,000 tons of iron-ore with each train load.

We successfully demonstrated a cost-effective means of converting an existing volume-based train loading system to a mass-controlled loading system. The improvements have proven substantial, and we quickly offset the system costs for our client by the extra iron-ore they now can deliver.

For Further information, contact:
Anthony Pruiti
Director
Meridian Engineers
L13 251 Adelaide Tce Perth, WA 6000
Tel: 08-9325-2588
Fax: 08-9325-2005
e-mail: tony@meridian-engineers.com.au

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