Queensland Rail has just commissioned an innovative system for getting cement from Townsville to Mount Isa using low investment shipping containers and efficient pneumatic transfer.
The new system confirms the effectiveness of using shipping containers for the long distance haulage of fine powders.
How do you provide a transport system with capability of delivering 6000 tonnes of dry cement in a 14 day period whilst sourcing cement product from 1000 km’s away. This was the challenge presented to Queensland rail by MIM some two years ago.
A change in the delivery system was necessary due to an ageing and outdated system that no longer met the increasing demand from the customer.
MIM had just commissioned the new George Fisher mine and cement usage was growing rapidly. Queensland Rail confronted this challenge by implementing a transport system and handling system centred on purpose built 20ft freight containers, a discharge system and an efficient rail line-haul operation. The new system provides MIM with guaranteed capacity to supply the amount of cement required, taking into account variable demand and the inconsistencies associated with traversing 1000 kilometres of harsh North West Queensland country.
Transport costs have been reduced and tonnage per vessel has been increased by 30 percent.
The Containers are filled with cement product in Townsville and transported by rail to Mt Isa where they are loaded on to a tipping skel trailers are tipped and discharged pneumatically at 60 tonne per hour into the silo nest. Queensland Rail performed trials in the year 2000 at the Mt Isa site, to demonstrate the concept of unloading a modified freight container in prototype form to its customer Kockums Bulk Systems Pty Ltd in Melbourne were awarded the contract for the unloading system, silo pipelines and control system.
For a fine and dense powder material like cement this is understood to be the highest rate discharge system operating in Australasia from non-pressurised shipping containers being directly discharged into silos. The rate is equal to that of pressure discharge road tankers. Because of the high work load for the application Queensland Rail invested in two identical systems, complete with compressors and vacuum pumps, to ensure a 100 percent standby, based on the consistency of supply required by their client.
Queensland Rail's purpose built low maintenance containers each has the capacity to carry 28 tonne of cement powder. Each container is fitted with a discharge valve that can be pneumatically or manually operated. Following the container discharge operation only a few kilograms of product are retained in the container.
Queensland Rail's non-pressurised purpose built containers coupled with their outstanding performance has proven to be an efficient and effective means of transporting cement powder.
Connecting to the system
When the skel trailer arrives at the site, the vacuum hose is coupled to the container along with the control hoses for the aeration airlines and the container is tipped. Then the system is started. Cement transfer is automatically controlled by the re-loader system, which also controls the operation of the aeration and discharge valve on the containers.
To achieve the high transfer rate required, cement is simultaneously vacuumed from the shipping containers to the Reloader, and discharged from the PCV (Pneumatic Conveying Vessel) to the silos. Kockums in-house tailored control system also has significant read-out for warnings and reasons for shut down, should the need arise. At the completion of the vacuum and pressure cycles, the collected product is dumped from the suction chamber directly into the PCV below utilising Kockum's Sonoforce Pulsed Aeration system. As the cement powder is completely de-aerated after the vacuum cycle, it is very densely packed, so high quality aeration is required to quickly dump the product.
A roots type vacuum blower is used to suck the cement into the Reloader from the container. The dust entrained in the air passes through a heavy duty primary filter then to a secondary and finally a tertiary filter to ensure it is well cleaned before reaching the blower. One of the many inbuilt safety features is the use of dual level probes to confirm that high level has been achieved in the Reloader, to protect the air filters. A purpose built, reverse pulse jet cleaning system is used for the filter elements.
The vacuum pump is put into standby mode during the PCV filling stage, and the Reloader is vented down through the Sonoforce panels
The 2 cubic metre capacity PCV receives conveying air from a Bulk-Air compressor and conveys to the silo at 200 kPa by dense phase in a 150 mm line. The instantaneous vacuum rate and pressure conveying rate of the cement is actually designed for 90 tonne per hour. This allows for the change over and dump time in the cycle. An air-to-air after cooler was fitted to cool the air from the compressor. Kockums diverter valves are used on the silo and are automatically controlled by level probes to fill the silos in a preset sequence.
The conveying method Kockums employ is called low velocity "dense phase" and is very well suited to the conveying of cement because of the abrasive nature of the product. The significant gains using dense phase are in efficiency of conveying (lower power required) and dramatically lower wear on pipes, bends and valves. Consequently the expected life of conveying pipe systems in heavy duty dense phase applications is in excess of 5 years.
The system was successfully commissioned in June this 2003, and confirms the choice of utilising low investment shipping containers for long distance hauling of fine powders. This system also demonstrated the low energy use for a combined vacuum/pressure system of only 1.5 kW per tonne.
Queensland Rail once again proved its ability to implement and manage cutting edge purpose built systems for complex transport tasks. The Kockums design team have accumulated many decades of powder handling experience to ensure such successful applications.