Steam implosions power novel pump

An ejector pump, which uses steam to achieve high flow rates – even when the fluid contains large amounts of solids – can offer flow rates of up to 45,000 litres/hr and pressures of more than 9m water gauge. Overall system efficiencies are claimed to be more than 30%, compared with 6 to 15% for conventional pumping systems. The pump, which is suitable for pumping any liquid-based mixture, is also being seriously considered for powering marine craft. Steam ejection pumps are an old idea, taking momentum from expanding steam to pull fluid through a tube. However, Pursuit Dynamics, a small company based in Royston, has developed a new spin on the idea, by injecting the steam through the tubular walls of the unit instead of down the centre. In addition, by introducing a second fluid through a ring of ports behind the steam injection annulus, it is possible to use the device to mix a second fluid into the pumped flow. Chief technical officer Mike Todman informs us that as well as transferring momentum, the new design uses the implosion of condensing steam as an additional source of energy. The PDX pump, as it has been christened, uses a parallel-sided working tube, unlike traditional steam ejectors, which tend to use a Venturi shape. The basic design was originally patented by Alan Burns in Australia in 1999. He sold his intellectual property to Pursuit Dynamics which has subsequently improved the efficiency of the basic design with the help of CFX computational fluid dynamics software. The pump can, for example, be configured so that a standing supersonic shockwave macerates fluid borne solids. The company has been pursuing three main market areas with the technology. One uses it as the basis of a marine propulsion systems, while the other two use it as a pump for chemical or physical processing. Chemical processes include the entrainment of hydrocarbons, dyes, powders, chemical dosing and bio gas. Entraining air can reduce frictional effects, reduce density, change viscosity and oxygenate water. Physical processing includes the ability to macerate or soak solid matter passing through the pump by way of the shockwave effect. The device currently exists as two prototypes, one under test and investigation as a pump, and the other as a digester unit. Steam is supplied by a commercially available steam generator. The prototype pump, with a flow capacity is 45,000 litres per hour, has a 47mm bore and is mounted in a 30m long, 63mm diameter pipe system. It has shown itself capable of passing rope, wallpaper waste, vegetable matter, cloth, sand, gravel, wood chips and latex gloves. The pump pressure depends on the applied steam pressure, but at 4.5 bar steam pressure, water head is over 9m at 40% maximum flow. The argument about relative efficiency is based on overall system energy efficiency. For example, while an electric motor driving a pump may have 95% efficiency, the energy efficiency of a typical power station is about 35%, with a further 10% loss in transmission, reducing overall efficiency at the pump shaft to about 30%. If this is coupled to a conventional high-solids capability pump, with an efficiency of 20 to 50%, overall system efficiency is reduced to 6 to 15%. On the other hand, using a steam raising system, basic Rankine Cycle efficiency of 35%, a steam generator whose efficiency is 85% and a PDX solids pump at 40% efficiency, the final overall efficiency is 12%. But if heat is recovered from the downstream flow in a combined cycle configuration, overall efficiency is more than 30% and can approach 100%. Other advantages of the pump include its simple design, with no moving parts, bearings or seals. These advantages also apply to its original conception, which was to replace two-stroke outboard engines on marine craft, which have an overall efficiency of not much above 12%. In-water propulsion efficiency of the PDX pump appears similar, but it still offers the advantages of being very much quieter while being immune to fouling. Commercial markets for the pump are seen in sewage pumping, aeration, agitation, heating, slurry transport, mining, mixing, food and confectionery manufacture and the chemical, pharmaceutical, petroleum, pulp and paper industries. Fluidic pumps powered by high-pressure fluids other than steam are also possible. Pneumatic fluidic pumps are commercially available, with the range of products made by Meech Air-Tec probably being the best known in the UK. Steam, however, is very widely available. It has, for example, been estimated that 45% of all fuel burnt by US manufacturers is used to generate it. In addition, process operations in many industries produce low level waste heat which could be usefully converted into steam for pumping applications. Pursuit Dynamics CFX computational fluid dynamics software and services Meech Air-Tec Pointers The pumps have no moving parts and can transport liquids containing a range of solid objects, including pieces of rope, latex gloves and gravel They can be used to mix fluids and macerate solid matter suspended in the flow stream Powered by steam, overall system energy efficiencies compare favourably with conventional technologies, and are very much better if used as part of combined cycle heating systems