Optimisation and integration of membrane processes for the fruit juice industry

IntroductionMembrane processes can be either used in direct competition with conventional separation processes or in combination with these to cover a wider separation range. The focus of this work is on the applications in an apple juice plant using membrane processes in combination with conventional separation processes, i.e. separators and evaporators.Traditional Apple Juice Plant The traditional apple juice production process is shown. This process involves settling tank(s) and/or kieselguhr filtration for the clarification of apple juice. Both processes are normally regarded as costly and difficult. Additionally, the traditional process includes an evaporation step for the concentration of apple juice above 75 Brix.Apple Juice ClarificationRecently ultrafiltration has established itself as a unit operation to clarify apple juice by removing suspended solids or other high molecular solids such as proteins and starch. So far the industrial standard has been the use of either tubular or Plate&Frame ultrafiltration modules. However, both module configurations are commonly associated with low packing density and high membrane replacement costs. Furthermore, this process is commonly run in batch mode and diafiltration water has to be added in the final stage of the clarification to maximise the process yield. A new concept developed by Alfa Laval combines a high-speed separator with spiral wound ultrafiltration modules to overcome these limitations. The key advantages of new concept are:•High quality juice with respect to colour, taste and clarity.•Elimination of bentonite, gelatine, and kieselguhr. •Lower membrane replacement costs compared to tubular and Plate&Frame modules.•Elimination of diafiltration water. •Continuous operation with long running cycles at stable fluxes. Even though the new clarification concept has slightly higher initial investment costs and an increased number of unit operations this is quickly offset by the advantages. After only two years the lower operating and membrane replacement costs make the investment more profitable.Apple Juice ConcentrationFor the concentration of apple juice, the combination of reverse osmosis and evaporation can provide an interesting process combination. Reverse osmosis, as initial step can remove more than 50% of the water content prior to evaporation, making it possible to significantly reduce overall costs. By applying reverse osmosis concentration levels of 20–25 Brix can be achieved, while the subsequent evaporation can boost these levels to above 75 Brix. The key advantages of new concept are:•Combination of reverse osmosis and evaporation saves up to 25 to 40% energy compared with direct evaporation. •Concentration of 20 to 25 Brix with only 7-9 kWh/m3. •98–99% rejection of sugar and acid. •80–90% rejection of volatile flavours. •Recycling of permeate as process water.Conclusions & OutlookThis case study on apple juice production demonstrates that integration and optimisation of membrane-based separation processes with conventional separation processes such as high-speed separators and evaporators can lead to improved process designs. The two concepts discussed offer both technical and economical advantages compared with stand-alone units. Furthermore, the concepts discussed in this study are not only applicable to apple juice but also suitable for other fruit juices. Overall, this study indicates that the future of membrane processes will rarely be as stand alone process units, but rather it will be as an integrated and optimised part of a process package achieving a predefined separation. Hence, optimisation and integration will play an important role in the future of membrane processes.

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