Concept of hydraulic transport 

Hydraulic transport is a transport method where solid particles are suspended in a fluid and transported through a pipeline. The transporting fluid is in most cases water. The most frequently transported solid materials are coal, sand, gravel, ores, slag and various mining, chemical, food and agricultural products or materials (Debreczeni, Tarján, 1989).

Hydraulic transport as a part of hydromechanisation systems is becoming more and more important in different industries. In addition to the economical and technological advantages its application is justified by its environmentally friendly feature. The real benefits of this technology can be achieved if large quantities are transported continuously over long distances. The advantageous features of hydraulic transport in comparison to conventional transport methods are: space requirement is low, no special equipment, roads or other infrastructure are needed, changing the transport direction is easy, difficult terrain can be overcome, the environment is protected in particular from dusting because this is a closed system. Only one station at the starting point and a few pump stations along the transport route are needed even for long distances (several hundreds of kilometres). Weather does not effect the operation and labour requirement is low.

There are however a few disadvantages too: temporal exploitation of the pipe system has strong effect on the economy and performance and wear of equipment and pipes highly depend on the particle size distribution and other properties of the solid particles, unlike other transport methods. There is a high demand for transport water, dewatering of the mixture after transport may prove difficult and expensive, especially when fines content is high and mixing the solids and water before transport may also prove difficult.

Hydraulic transport systems

Hydraulic transport can be performed using slurry pumps or high-pressure feeder systems. In slurry pumps the slurry flows through the pump. Slurry pumps made for handling large solid particles produce low head, therefore these systems are applicable for short transport distances only. High-pressure feeder systems enable direct slurry introduction into the clean water flow under high pressure. This technique requires clean water pumps capable of producing very high head; therefore these systems are suitable for solids transport over medium or long distances.

Special positive displacement pumps and centrifugal pumps have also been developed for slurry transport purposes (Wills et al., 1983). Using erosion-resistant materials, high lifetime can be achieved for both pump types. Since the mixture has to flow through the valves and it gets into contact with the cylinder wall in positive displacement pumps, particle size of the transported material is usually adjusted to 1 mm, and the mixture must not contain particles larger than 3 mm. Development of positive displacement pumps inspired designers to choose solutions where solids are not allowed to get into contact with the cylinder and piston. One option is rinsing the valves by fresh water. For high-concentration slurries it is necessary to use plain slide valves operated by hydraulic actuators instead of valves. The use of positive displacement pumps with stable characteristics is favourable for operation safety reasons to avoid clogging the pipeline. Hydraulic transport systems built for long distances (several hundreds of kilometres) and coal or ore transport use positive displacement pumps without any exception. Centrifugal pumps are applicable for much lower head requirements than positive displacement pumps, but maximum transportable particle size depends on only geometric properties of the impeller of the pump. Centrifugal pumps used in sea dredging are capable of transporting particles as large as 200 - 300 mm while maintaining high flow rates. If coarse material has to be transported over medium or short distances, centrifugal pumps may be the proper option.

Fields of application

Mining, power plants, mineral processing,  water management, agriculture and chemical industry are the main fields where hydromechanisation can be used beneficially. Its advantages become apparent when raw materials or wastes must be transported in a closed system to protect the environment. In the mining industry complex technologies are feasible including hydraulic extraction of minerals followed by mixing the solids with water before transport and dewatering after transportDue to its environmentally friendly feature and safety aspects, hydromechanisation may be even applied in cases when it is not the most economical solution.