| Abstract | A study has been carried out to develop a generic simulation tool for food processes, particularly aseptic and thermal processing of canned foods. A literature review of the requirement for food process simulation has been undertaken together with a review of the process simulation packages available in both the chemical and food industries. It was concluded that a general-purpose simulator already in use in the chemical industry, capable of representing subregions within units, could be adapted by providing it with facilities appropriate to the food industry. The chosen simulation environment was Flowpack III. The adaptations included the installation of the simulation package onto a readily available relatively cheap desk-top personal computer, enhanced with transputers and running under the Helios operating system, and creating a new physical property harness. To validate the installation, a simulation of an aseptic process was undertaken where lethality was computed. The results are presented. It was concluded that all the modules which make up Flowpack III interacted in the correct manner.
Food products are not uniformly treated during processing yet the treatment must be adequate to ensure that potentially harmful organisms are destroyed effectively at the centre of each item whilst not processing them so vigorously that vitamins and taste are destroyed near the outside. Such spatial effects, whereby the properties are distributed in 3-dimensions for each item, is important and forms a central part of the modelling of food operations. The approach taken was based on zone and hierarchical modelling.
• Zone models provide a limited finite element facility that enables unit operations modelled by partial differential equations to be solved as part of a larger solution incorporating many distinct units.
• Hierarchical modelling employs the recursive decomposition of a unit operation into assemblies of sub-units. Thus, whole unit operations are built from models of smaller sections of the operation.
Flowpack III's network analysis flowsheeting language, BASYS, and its dynamic facilities (ability to store time delayed values) coupled with zone and hierarchical modelling have been instrumental in achieving the goal of modelling of spatial effects encountered in food operations. The dynamic facilities of Flowpack III have been extended to handle efficiently streams of discrete objects (e.g., cans) and to model continuous unsteady processes. The capabilities of the resulting package are illustrated by modelling hydrostatic retort units, operating in steady-state and dynamic modes. Cans with pure conduction, mixed particulates and well mixed materials were modelled in steady-state retorts. The novel dynamic pure conduction retort models enabled the simulation of variations in belt speed and belt stoppages, thus allowing predictions of product quality in terms of lethality and cooked values. The package has also been employed to model successfully a continuous cyclic process, namely, a battery of coffee extraction beds. Where possible models have been compared with experimental data. The results obtained illustrate the stability and reliability of the models. However, it was concluded that better results could have been obtained at the start of simulation had the physical property data of the raw materials been used and not those of the products. Additionally, work was undertaken to create an interface to a graphical front-end package (Procede) which would replace all the input and output functions of the simulator. Procede is a commercially available computer program which allows the engineer to create diagrams and databases of chemical process plants. The interface program was written in Turbo Pascal operating under DOS. The interface program successfully converts Procede output to Flowpack III input. However, it was concluded that Procede cannot easily be adopted as a front-end package to Flowpack III because communication from Flowpack III to Procede was extremely difficult (e.g., diagnostic messages could not be relayed on to the user). For this particular application, additional difficulties were encountered because Procede and Flowpack III did not operate under the same operating system. The achievements of this research programme include the installation of Flowpack onto its new transputer enhanced platform, the provision of an alternative property harness and the increased portability of Flowpack III. Moreover, the incorporation of zone models into Flowpack III has enhanced the dynamic performance of the simulator and has enabled modelling of spatial effects. An environment has been created that enables the simulation of individual operations and complete food process plants. It is concluded that the package developed is suitable for simulating a wide range of food processes and that the hierarchical and zone modelling techniques could be applied to adapt other chemical process simulators for food process applications. |
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