Triplex plunger pumps play key role in nanoparticle production
06 May 2015
Promethean Particles based in Nottingham is stepping up its nanoparticle manufacturing capabilities from pilot-scale production to a 100 tonne-per-year plant.
The company has already demonstrated the scale-up potential of the technology with a pilot scale reactor system achieving continuous production over a 60-hour period.
A spin-off from the University of Nottingham, Promethean Particles produces nanoparticles using continuous hydrothermal technology. In hydrothermal synthesis the hot, pressurised water is mixed with a metal salt solution, such as iron nitrate, and a reaction occurs (the salt is dehydrated) and nanoparticles are formed.
The company is participating in the EU FP7 funded €10 million SHYMAN (Sustainable Hydrothermal Manufacturing of Nanomaterials) project, which is based on its proprietary technology. The aim of the project is to scale up nanomaterial production whilst maintaining a sustainable, low cost process for producing high quality materials.
The University of Nottingham started research into optimising super-critical water hydrothermal synthesis for nanoparticles about 14 years ago. The result of the University’s work was the development of Promethean Particles’ Nozzle Reactor, a customised design that uses buoyancy induced eddies to produce an ‘ideal’ mixing scenario in a pipe-in-pipe concentric configuration in which the internal pipe has an open-ended nozzle.
The super-critical water is fed downwards through the internal pipe and out the end of the ‘Nozzle’; the aqueous metal salt stream is fed counter-currently upwards through the outer pipe. The reactor has shown a dramatic improvement in process reproducibility and reliability as well as providing the ability to control particle properties, such as size, composition and shape, through the manipulation of process variables.
Research and development commenced with bench scale reactors and later a pilot scale reactor approximately 30 times larger was developed. The reactor now being built is 80 times larger than the pilot plant reactor. Four Cat Pumps Model 3801 high pressure triplex plunger pumps are critical to the process, and will be used for pumping deionised water through a heater that raises the temperature to the super-critical condition of 374ºC at 218bar.
Triplex PD plunger pumps are often considered when high pressure and high operating efficiency is required. These pumps actually increase in efficiency at higher pressures and are most widely used in applications where the pumped liquid is of low to medium viscosity and has little inherent lubricity.
There are two significant advantages of reciprocating positive displacement pumps. Firstly, as they are almost 100 percent positive they will always deliver a predictable volumetric flow irrespective of pressure. This is because on the inlet stroke, the pump takes in a fixed volume of liquid and physically moves it through with virtually no losses or inefficiencies. Secondly, the pump performance is independent of specific gravity so the input power and output flow are unaffected by the liquid density. Cat Pumps UK general manager, Brian Hubbard takes up the story:
“We worked with Promethean from the early stages of the scale-up project, helping the scientists to develop a pump specification and then offering the most elegant solution both technically and commercially. We recommended our Model 3801 as it offers the required combination of flow, pressure, materials compatibility and features, including the facility to flush the pump seals which future-proofs the installation. By pairing up two pumps for the highest capacity duty, and two more solo pumps for the mid-flows, we’ve also given Promethean a high level of commonality and standardisation.”
With the pilot reactor clearly showing that scaling to a much larger commercial reactor was viable, some major decisions had to be made in terms of the pumping capability for the de-ionised water feed. “From our experience with the bench and pilot reactors, we knew that positive displacement pumps were the only viable solution for scaling up the process to commercial viability,” says Lewis Neve, lead chemical engineer on the SHYMAN project. “Originally, the pilot plant used two single head piston-activated diaphragm pumps and these displayed marked signs of pulsation. A further issue was that they were at the edge of their capability range in terms of pressure and flow, so they would not be suitable for the much larger reactor.
“We chose Cat Pumps because they are a well-established international manufacturer and could provide details of similar projects where their pumps had run for many years and this gave us confidence. From the start they were hands-on and came to us on a number of occasions to discuss the technical details and what they could bring to the process and the design of the plant. In terms of design and production output, the pumps were a huge item for us, so we were very impressed that they could do everything that we wanted and even more.”
The step from batch to continuous hydrothermal synthesis had been held back by engineering issues around mixing the heated fluid and the aqueous metal salt flow. It is these issues that have been overcome by Promethean Particles; high pressure triplex plunger pump technology from Cat Pumps will be contributing to the up-scaling of production in the near future.
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