Tubular propels - transporting aggregates
Jonathan Carter and Kevin Troyano-Cuturi, from the Department of Earth Science and Engineering at Imperial College London, UK, show the results of revisiting an old idea for transporting aggregates with modern technology.
The idea of using capsules inside a pipeline to transport freight has been around for 200 years. The earliest proposal was by George Medhurst in 1810, and a practical application was created by Latimer Clark in 1856. The first wheeled capsules appeared in 1861, but the technology was too expensive to operate and the system closed in 1874. The last period of sustained interest in this technology was in the 1970’s, with a number of projects in the quarry/mining industry.
In the USA, Tubexpress Systems Inc built and tested a 1,400ft long, 36-inch diameter pipe with seven foot capsules (see image above). In the USSR, the Lilo-1 system, could transport 25t of aggregate at speeds of 50Km/hr. A later system, Lilo-2, used an eight-kilometre pipe to move eight million tonnes of aggregate per year. Both systems have since closed.
The most successful applications have been in Japan, Sumitomo Metal Industries built a 3.2km pipe, of one metre diameter, in 1980, to transport two million tonnes of limestone each year to a cement plant, it is still in operation today.
Despite the lack of take up by industry, the technology remains attractive for the transport of freight. Research at Imperial College has reviewed how the advances in technology and materials over the last 40 years would allow the design of a system more suited to the requirements.
The design needs to meet several objectives – it must be cost effective, safe, have reduced environmental impact, high reliability and low maintenance. The key issues are –
- Should the basic design be that of a small rail system with rails and trucks, wheeled capsules, or can the technology used in modern rollercoasters be employed?
- What tyre material to use – steel as used in rail systems, rubber compound as used on the Paris Metro, or polyurethane as proposed for a number of light passenger systems?
- What is the best propulsion system? Pneumatic blowers, electric motors attached to each capsule, Linear Synchronous Motors (LSM), or Linear Induction Motors (LIM)?
- What to construct the pipeline from? Steel, concrete or polyethylene?
It is assumed that the system should be applicable to as wide a range of industries and companies as possible, and that it could be applied throughout the world. This means that the pipeline should be capable of being buried. Preliminary calculations have indicated that, to make the system economic, the pipeline needs to have a small diameter. The smallest pipeline that is reasonable for a person to work within for maintenance is 1,250mm.
Rubber compound tyres have a poor wear record. As this did not meet requirements for high reliability and low maintenance, this option was rejected. The rail industry recommended steel tyres be used in a small rail system. However, there is concern about replacing broken rails, given the limited access available. Although rail failure would occur infrequently, it could not be ruled out if steel tyres are used on steel rails. Experience of rollercoasters has shown that polyurethane tyres on steel tracks have good wear characteristics. A polyurethane tyre on either a steel rail or inside a steel pipeline was seen as the most suitable.
Twists and turns
A traditional rail wheel has two bearing surfaces, one that contacts the top of the rail and transmits the weight. The second surface is the wheel flange that guides it round curves. These functions are performed by separate wheels acting on different surfaces within the track in rollercoasters, because a rollercoaster track has to support the vehicle and provide the structural integrity as the vehicle moves at high speed through a complex series of manoeuvres.
For our system the bearing surfaces and the structural elements can be easily formed from strip steel, with the whole assembly resting in the bottom of a pipe. Therefore, it was decided to use rollercoaster technology rather than rail technology for the capsule guidance systems. The idea of using wheeled capsules was rejected because the roller coaster technology was simpler. The picture (below) is a preliminary design for a capsule and the rail system. Each capsule is constructed from two identical parts, each of which has two horizontal wheels and two vertical wheels, which engage with the rail to support and guide the capsule.
The roll of the pipeline has been reduced, keeping the void space open and keeping the water out. All three materials considered are capable of maintaining the void space, although there are concerns that plastic pipes may deform when buried. Concrete pipes will retain their shape, but are difficult to seal completely against water ingress, and steel pipes meet both requirements but are expensive to manufacture. Plastic pipes with a slightly larger diameter to allow for deformation were chosen.
Up and away
The final component is how the capsule will be propelled. The pneumatic approach, used in the Sumitomo Metal Industries system, severely restricts the capacity and as the pipe becomes longer, the problem gets worse. Having an onboard motor would require either a battery or a sliding electrical contact – the motor itself will also add weight and maintenance issues. This option is rejected as it compromises the objectives of high reliability and low maintenance.
The application of either Linear Synch-ronous Motors (LSM) or Linear Induction Motors (LIM) is similar in that both are passive motors with no moving parts. In both cases the electrical supply is fixed to the stationary part of the motor. The main difference is that LSM require an array of powerful permanent magnets to be built into the capsule, while LIM simply require an aluminium plate. Linear Synchronous Motors is the more energy efficient system, however, it requires a sophisticated control system and interruptions to its power supply are not well handled. The biggest problem is that the magnets easily capture steel/iron objects, which can damage the LSM. In an industrial environment it would be difficult to ensure that no steel nuts or bolts got attached to a magnet. Therefore, the chosen propulsion system for the capsules has been LIM.
The proposed system will consist of a 1,350mm plastic pipe with a strip steel track assembly in the base. The capsules will be four metres in length with eight wheels using polyurethane tyres. The drive system will be LIM mounted in the track assembly. All of the components can be prefabricated and bolted together onsite. The system can cope with steep slopes, with being buried or suspended from pylons like a suspension bridge allowing it to operate safely in many environments.
We have compared the economics of the capsule pipeline with those of trucks and conveyors for journeys of two kilometres to 350Km. The capsule pipeline has a 40% lower capital cost and 25% lower operating costs compared to a conveyor. The operating costs of trucks are at least an order of magnitude greater, so, for a transport contract of more than a few years, the capsule pipeline is more economic and has a significantly reduced environmental impact.