Twisted pipes give heart to energy saving

By sending fluids up (or down) helically twisted pipes as opposed to straight pipes, it is possible to improve the transport of entrained gases and solids, reduce risk of separation, save energy and improve mixing. The idea came from a long running study of why human arteries are not straight but follow what at first sight might seem to be unnecessarily tortuous paths. One of the consequent developments, therefore has been the development of improved grafts made of expanded polytetrafluorethylene (ePTFE) to restore arterial blood flow, but there are also many important applications already being demonstrated in studies being undertaken for the water, oil and gas and process industries, some slashing energy consumptions by as much as a half. The idea comes from studies of arterial blood flow undertaken by Professor Colin Caro, emeritus professor of Physiological Mechanics in the Department of Bioengineering in Imperial College, London. He was convinced there must be some good reason why arteries tended to branch and bend in a three-dimensional rather than a two dimensional way and came to the conclusion that such configurations had evolved to reduce the development of vascular diseases such as atherosclerosis, the cause of heart attack and stroke. Having ascertained the facts, Professor Caro and his colleagues have now set up two spinoff companies: Veryan Medical, to produce the grafts and other medical devices, and HeliSwirl Technologies, to exploit the process plant and other industrial applications. The medical studies of the effect began 15 to 20 years ago, but the commercial applications have only begun to be tackled in the last two to three years. One of the first applications expected to reach the commercial arena is currently being developed in conjunction with Thames Water, who have a problem with entrained gas in water which then tracks through filter beds, dragging dirt particles with it. This requires de-aerating the water before it goes through the beds. If the water is instead passed along a helical pipe, it is centrifuged, leaving the gas in the centre, requiring that it only needs to be removed from that small proportion of the water passing down the centre of the pipe. The crucial parameters are the helix angle, the relative amplitude - the lateral deviation from the overall axis of the spiral and the relative pitch - the repeat distance between helix turns. The developments depend heavily on computational fluid dynamics (CFD) to optimise the designs, and a set of software design tools is currently being developed by Intelligent Fluid Solutions in Greenwich, a specialist modelling company run by Dr Jim Shaikh, who was originally a student at Imperial College but went off to undertake his doctorate in the Engineering Department in Cambridge. The other main area of practical development work, according to HeliSwirl Chief Executive Officer Dr Ross Waring, is the undertaking of large pilot scale design trials, mostly relating to the needs of the oil and gas industries, using the £4.5 million EPSRC backed multiphase flow rig at Cranfield University in collaboration with Wellstream International. As easy-to-access wells run dry, oil companies are increasingly turning to deeper wells in deeper waters producing multi-phase mixtures of oil, water, gas and sand. This work, under contract to Dr Hoi Yeung, has included studies of catenary risers, comparing the performance of straight and helical pipes. Experiments have also been conducted on lengths of helical pipe to prevent the formation of and avoid the need for slug catchers. The work is focussing on the reduction of pressure losses in flexible and fixed risers, suppressing the formation of gas slugs, and ways of improving the separation of oil, gas and water sub-sea. It has been found that the helical tubes destroy stratified flows in slightly downward, inclined pipelines and reduce the region of severe slugging in risers, which means that the amount of gas required to 'stabilise' risers is much lower, reducing the requirement for gas compression and consequent energy costs. The work with Thames Water is at their Kempton facility, and as well as entrained air removal includes studies of uses of helical sections of pipe to keep sediments in suspension to scour pipe bores and avoid deposition in stub ends such as those ending in water hydrants. At the present time, these are frequently found to be clogged when they are urgently needed. It as also been found in the studies at Thames Water that passing fluids down helical pipes is a very good way of mixing in necessary chemicals, requiring the input of no additional energy from impellers and with only about one quarter the pressure drop of conventional systems. "The thing I most like about this technique is that it is completely passive", explained Dr Waring, "Requiring no gas re-injection or other complicated equipment. Oil and gas is the big win if long to market but water offers the prospect of early sales." While the team is currently focussed on water and oil and gas, there are also a great many other potential practical applications that have been identified. One of the identified chemical applications is in ethylene reactors that pass naptha feedstock through pipes in a furnace at temperatures of 800 to 900 deg C. The naptha is broken down by heat after which the free radicals re-join to make ethylene, among other compounds. The reactors tend to coke up but it is anticipated that by improving mixing and heat transfer, the working temperature can be reduced, saving on energy, and carbon deposition can be cut, reducing repair and maintenance costs. Retro fit costs of helical as opposed to straight pipes in most applications are expected to be almost trivial. The business strategy is for HeliSwirl to become a "Flow assurance company" in Dr Waring's words, offering design tools and advice and licensing technology but not necessarily going into large scale manufacturing. The technology is well patented, and perhaps surprisingly, there has been no prior art found that comes anywhere close. Financial backing is from the founders, some angel investors, Imperial College Innovations, the Esmée Fairbairn Foundation and the Carbon Trust, which has invested £700,000 in total plus and experimental grants of £100,000 for the studies at Cranfield and Thames Water. HeliSwirl Technologies Eureka says: An amazingly simple basic idea with enormous consequences. Just think what the Victorian steam engineers could have done with it if they had thought of it Pointers * By using helical instead of straight pipes it is possible to keep entrained gas bubbles in the centres of flows instead of their forming slugs * Deposition of solids is also prevented * Mixing and heat transfer are greatly improved * No mechanics are required and cost is trivial