Mix and MATCH

BHR Group's Nimix IBC 'pipeless plant' technology was last July adopted by Herbert's of Dagenham its first UK customer to mix paint and coatings for vehicles. Completely enclosed batches can be manufactured in the container at volumes up to 1000 litres. Herbert's, which is part of Hoechst, has since taken delivery of 14 vessels, with eight more in the pipeline.

'We have already sold systems to six of the ten largest coatings manufacturers in the world,' says Neil Davies, managing director of Nimix. 'We estimate that this approach significantly cuts wastage in such chemical processes.'

Aside from the development of Nimix (PE June 1996 p35), BHRGroup has its 'impeller' in the R&D of many more mixing environments.

Nimix technology is enabling BHR Group researcher Anne Ball to develop a novel method of remotely assessing extent of mixing. The rising and falling of the diaphragm at the base of a Nimix vessel causes a liquid 'dome' to form inside the closed vessel. Scanning a laser beam over the dome and collecting the reflected light in a CCD camera allows the profile of the dome to be assessed.

Ball (pictured top with a screen presentation of the liquid's profile) says: 'The dome can be analysed by our vision rheometer.' She is conducting experiments with honey, a Newtonian fluid. Its viscosity changes with temperature. 'I expect that the vision rheometer will become a permanent feature of a customer's system, possibly in paint and food manufacture. Considering the colour matching of paints, the degree of mixing is critical. We think we could save 16 per cent of the cost of making paint.'

Gul Ozkan Tascin heads the Fluid Mixing Process division of BHR Group; a consortium of 45 member companies. 'We believe it is particularly important to research the scale up of mixing processes, particularly for immiscible liquids. With some projects, we are working at a relatively large scale. FMP has vessels up to 3m diameter for research, which suits some of the consortium members because the scale is closer to operational.'

In one project (above, centre), another optical technique is employed to analyse the behaviour of such mixtures. The closed (red) vessel avoids the entrainment of gas.

'In this situation, a fibre optic source illuminates the liquid and the signal is picked up by a camera on the end of a dip probe,' she says.

Caroline Leguay (above, bottom), a PhD student from the University of Cambridge, is investigating a mixing process designed by Praxair, a member company of FMP. 'They have a design for gas-liquid contacting,' she says, 'and they want us to find any possible improvements.'

A combination of a helical impeller in the vessel and special baffles causes downdraft; gas above the liquid is sucked in. The technique is appropriate where sparging of gas is not a viable alternative and it allows a relatively expensive gas to be recycled until it reacts, such as in oxygenation and hydrogenation reactions.

'At the moment we are doing a generic research project, the final aim of which is to model oxygen transfer.'

A further key area of research is liquid blending, involving the addition of a highly viscous liquid to a less viscous solution. The progress of the added liquid in the bulk liquid as mixing occurs is monitored by electronic probes at different positions in the vessel. Test liquids are sugar solutions at different concentrations.

Research involves the simulation of the modification of the viscosity of a product, such as is needed in shampoo blending. Techniques derived can also be applied in paint manufacture and and wastewater processing industries.

Other work involves jet mixing, where metal impellers are not permissible, such as in the nuclear industries.

BHR Group's capabilities: a client's view

Peter Veenstra (below) of Shell Research and Technology Centre, Amsterdam, visits BHR Group to take advantage of its laser doppler anemometry research facilities.

Gul Ozkan Tascin explains: 'We make measurements of liquid velocity at different positions in the tank and gain quantitative information about turbulence.

'We have used tanks from 12cm to 1.9m diameter to see how the measurements scale up.'

Shell is a member of the FMP consortium at BHR Group. The particular aim of the project is confidential, but Veenstra tells PE: 'A major interest of ours is scale-up based on 1-2l up to 40kl and bigger. What we are aiming to do is to get better liquid-liquid dispersion and to determine droplet size distribution in processes.

'We have some ideas about scaling rules in liquid-liquid dispersions. We have done experiments in Amsterdam but we have found that there are some differences with the literature and wondered why they are there. We have also performed some CFD type modelling and we are comparing experimental results with that.'