Abstract:
Within the Western Australian iron ore industry, various approaches have been attempted to optimise wagon weight in their respective modern train load-out facilities. However, none have reached a reasonable state of optimisation the key issue being the lack of instant measurements of wagon weight and real-time feedback control of the clamshell. Typical track scales are installed at certain distances after the loading chute, leading to a delayed measurement of the wagon weight.
There are large financial gains if wagon weights are loaded closer to their maximum safety weight. In the Western Australian iron ore industry alone, increasing one tonne per wagon is equivalent to an increase of seven million tonnes of production annually, equating to a 700 million US dollar increase in revenue (based on $100USD/ton). It is estimated, there is a potential for three tonnes of additional iron ore that could be added per wagon in train load-out facilities if wagon weights are optimally loaded to safe maximum capacity.
A simple and direct solution to optimise train load-out facilities is to have the capability to instantly measure wagon weight during the loading and have real-time feedback control of the clamshell. Our patent underchute track scale system (AU Patent 2018214111 & 2020223631) has been successfully installed and field-proven. A free and no-obligation trial is on offer for all suitable manufacturing sites.
Background:
The inability to accurately and consistently measure wagon weight whilst loading is one of the major issues troubling modern train load-out facilities. The use of conservative wagon weight setpoints is often required to safeguard against costly reloading efforts or derailment potential. Although these lower setpoints allow for reduced lost-time incidents, it comes at a significant opportunity loss as trains are not loaded to their true safe maximum capacity.
In the Western Australian iron ore industry, it is estimated around up to 3 tonnes of iron ore could be potentially added to the weight of every wagon – achieving just half of that has the potential to add 1.5 billion US dollars annually to the region.
Many attempts have been made to address this, but none of the attempts have addressed the core issue that is hindering wagon weight optimisation.
Some of the common methods that are currently utilised are outlined as follows:
- 3D wagon profile control: This uses profile scanners over the wagon to measure and control the exact volume of the ore loaded to the wagon – this approach indirectly controls the wagon weight and allows even material distribution of the front and the rear wagon (See Figure 1).
However, this approach is vulnerable to quick loading material change, particularly with density changes. Other physical factors such as ore viscosity and moisture could also impact the weight-to-volume ratio. Overall, combined delayed track scale measurement and profile scanning somewhat improve wagon weight control, however, ore density must be constant or slow-changing for successful control of wagon weight while using this method. In reality, this is not the case, as ore density is not often slow-changing, or constant.
Figure 1: 3D wagon profile scanners
- Material tracking: Tracking mass balance using an upstream conveyor belt weigher, the conveyor belt speed to loading bin weight can provide an instant calculated weight loaded to the wagon, and thus alters the amount of ore loaded to wagon based on this measurement. This improves the wagon control to a certain degree, however, any kind of small belt weigher inaccuracy (i.e., uneven conveyor belt surface, conveyor speed) and bin weight inaccuracies (i.e., the ore’s physical impact in the bin when it falls bin at different bin levels) will magnify the deficiency of this approach.
Figure 2: TLO Mass balance calculation system
- Two layer-loading: In this approach, the ore is first loaded into a large silo as a typical TLO facility.
The ore is then loaded to a wagon-size weighing bin(s) with a fine-tuning weight controller. The material in the second weighing bin(s) is then fully emptied to the wagon when the wagon passes through. This approach can control wagon weight closer to the desired weight; however, it limits the train speed as it must allow sufficient time for ore to go through the two layers of material transfer. The typical train speed of two layer-loading is significantly slower than that of direct loading hence loss of production opportunities. A simplified figure is presented below:
Figure 3: Two-Layer of ore weighing process
- Post-loading top-up hopper: This approach is similar to the two-layer loading approach described above. First, it purposely loads the wagon to 90-95% of the desired load in the loading chute that has passed through the track scale. The wagon is then topped up with weighted bins/hopper after the chute. It presents the same issue – the train speed is significantly slower than that of direct loading hence loss of production opportunities.
- Statistical clamshell trim control: this approach applies statistical modelling to upstream collection and final track scales data to model and statistically predict current wagon weight. The clamshell trim control is based on the predicted wagon weight. This approach is based on historical data and assumes ore change follows the historical trend. In reality, this is not the case and ore often change quickly to deviate from historical data.
- Other approaches to improve wagon weight control will not be covered in detail here, but the common approach is to apply mass balance, volume control, and/or a combination of both – all of these methods have the same vulnerabilities as the other approaches that have been mentioned.
All approaches mentioned above have not achieved desired wagon weight optimisation and are especially vulnerable to ore property changes or will sacrifice production rate.
The key issue of inaccuracies in the optimisation of wagon weight management is due to a delayed wagon weight measurement – that is, by the time wagon weight becomes available to the operator or the control system, the operator or the control system does not have a tool to correct wagon weight without stopping and digging out or revering the train to top up the wagon.
After years of research and experiments, in 2018 we successfully patented our track scale technology which allows for an instant and accurate measurement underneath the loading chute area. This technology provides an instant measurement of the real-time wagon weight hence allowing real-time feedback and control of loading the clamshell to optimise wagon weight. The system has been installed on-site with success. Further improvements to the system have been carried out to improve operability and flexibility. We are pleased to offer a free and no-obligation trial to suitable sites. contact us today to arrange a free trial.
Figure 4: Underchute track scale
Figure 5: Patented non-intrusive Load Cells
Figure 6: Underchute track scale loading zones
Figure 7: Underchute track scale wagon weigh value display